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Thursday, December 16, 2010

handy answer book for kids

Gina Misiroglu began noting dozens of questions and answers for the second edition
of The Handy Answer Book for Children (and Parents) while fielding life’s
questions from her two children, who are now 6 and 16. When she’s not busy parenting,
she spends her time writing books, specializing in the authorship and editing
of pop culture, biography, American history, and general interest titles.
Misiroglu has developed dozens of titles for publishers as varied as Warner Bros.
Worldwide Publishing, Price Stern Sloan, New World Library, Macmillan Reference
USA, and Sharpe Reference. She is the editor of American Countercultures: An
Encyclopedia of Nonconformists, Alternative Lifestyles, and Radical Ideas in U.S.
History (2008); Girls Like Us: 40 Extraordinary Women Celebrate Girlhood in
Story, Poetry, and Song (2000)—winner of the New York Public Library’s “Best
Book for Teens” Award—and Imagine: The Spirit of Twentieth-Century American
Heroes (2001). Her books for Visible Ink Press include The Handy Politics Answer
Book (2002), The Superhero Book: The Encyclopedia of Comic-Book Icons and
Hollywood Heroes (2004), and The Handy Presidents Answer Book (2005). She lives
in Los Angeles.
About the Author
Also from Visible Ink Press
Please visit us at visibleink.com.
The Handy Anatomy Answer Book
by James Bobick and Naomi Balaban
ISBN: 978-1-57859-190-9
The Handy Astronomy Answer Book
by Charles Liu
ISBN: 978-1-57859-193-0
The Handy Biology Answer Book
by James Bobick, Naomi Balaban,
Sandra Bobick, and Laurel Roberts
ISBN: 978-1-57859-150-3
The Handy Dinosaur Answer Book
2nd edition
by Patricia Barnes-Svarney
and Thomas E Svarney
ISBN: 978-1-57859-218-0
The Handy Geography Answer Book
2nd edition
by Paul A. Tucci
and Matthew T. Rosenberg
ISBN: 978-1-57859-215-9
The Handy Geology Answer Book
by Patricia Barnes-Svarney
and Thomas E Svarney
ISBN: 978-1-57859-156-5
The Handy History Answer Book
2nd Edition
by Rebecca Nelson Ferguson
ISBN: 978-1-57859-170-1
The Handy Math Answer Book
by Patricia Barnes-Svarney
and Thomas E Svarney
ISBN: 978-1-57859-171-8
The Handy Ocean Answer Book
by Patricia Barnes-Svarney
and Thomas E Svarney
ISBN: 978-1-57859-063-6
The Handy Philosophy Answer Book
by Naomi Zack
ISBN: 978-1-57859-226-5
The Handy Physics Answer Book
by P. Erik Gundersen
ISBN: 978-1-57859-058-2
The Handy Politics Answer Book
by Gina Misiroglu
ISBN: 978-1-57859-139-8
The Handy Religion Answer Book
by John Renard
ISBN: 978-1-57859-125-1
The Handy Science Answer Book™
Centennial Edition
by The Science and Technology Department,
Carnegie Library of Pittsburgh
ISBN: 978-1-57859-140-4
The Handy Sports Answer Book
by Kevin Hillstrom, Laurie Hillstrom,
and Roger Matuz
ISBN: 978-1-57859-075-9
The Handy Supreme Court Answer Book
by David L Hudson, Jr.
ISBN: 978-1-57859-196-1
The Handy Weather Answer Book
by Kevin Hile
ISBN: 978-1-57859-221-0
THE
HANDY
ANSWER
BOOK for
KIDS
(and Parents)

THE
HANDY
ANSWER
BOOK for
KIDS
(and Parents)
Copyright © 2010 by Visible Ink Press®
This publication is a creative work fully protected by all applicable copyright
laws, as well as by misappropriation, trade secret, unfair competition, and other
applicable laws.
No part of this book may be reproduced in any form without permission in writing
from the publisher, except by a reviewer who wishes to quote brief passages
in connection with a review written for inclusion in a magazine, newspaper, or
web site.
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Visible Ink Press®
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Canton, MI 48187-2075
Visible Ink Press is a registered trademark of Visible Ink Press LLC.
Most Visible Ink Press books are available at special quantity discounts when
purchased in bulk by corporations, organizations, or groups. Customized printings,
special imprints, messages, and excerpts can be produced to meet your
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Press, www.visibleink.com, or 734-667-3211.
Managing Editor: Kevin S. Hile
Art Director: Mary Claire Krzewinski
Typesetting: Marco Di Vita
Indexing: Lawrence W. Baker
Proofreader: Sharon R. Gunton
ISBN 978-1-57859-219-7
Cover images: iStock.com.
Library of Congress Cataloging-in-Publication Data
Misiroglu, Gina Renée.
The handy answer book for kids (and parents) / by Gina Misiroglu. — 2nd ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-57859-219-7
1. Children's questions and answers. I. Title.
AG195.G25 2009
031'.02—dc22
2009020191
Printed in Thailand by Imago.
10 9 8 7 6 5 4 3 2 1
OUTER SPACE … 1
Mysteries of the Universe … Planets and
the Solar System … Our Sun and the Stars
… Comets, Meteors, and Asteroids …
Exploring Space
PLANET EARTH
AND OUR MOON … 21
The Blue Planet … The Moon … Up in the
Sky … Clouds and Storms … Hot and Cold
Days … Big Mountains, Deep Holes …
Water, Water Everywhere … Volcanoes and
Earthquakes … Going Green
CREATURES BIG
AND SMALL … 49
Dinosaurs and Ancient Life … Amazing
Animals … Bug Zoo … Fish and Sea
Creatures … Reptiles and Amphibians …
Birds
PLANT LIFE … 79
Plant Basics … Seeds and Growth …
Fragrant Flowers, Beautiful Blooms …
Poisonous, Meat-eating, and Other Extreme
Plants … Ferns, Mosses, and Mushrooms
… Trees … Plants that Help and Heal
PEOPLE AROUND
THE WORLD … 105
Lots of People! … Languages and Cultures
… City Life … Farm Life
POLITICS AND
GOVERNMENT … 125
Countries … Wars … Governments …
American Government … U.S. State Facts
and Trivia
HOW THINGS
WORK … 143
Nuts and Bolts … Buildings … Moving on
the Ground … Flying High … The Water
Highway … Communications and
Electronic Devices … Pictures, Lights, and
Lasers … Handy Things around the House vii
Contents
INTRODUCTION ix
FOR MORE INFORMATION 277
INDEX 281
MATH, MEASUREMENT,
AND TIME … 179
Numbers and Counting … Weights and
Measures … Calendars and Telling Time
ALL ABOUT
MY BODY … 197
Bones and Joints … Muscle Power … My
Building Blocks … Blood … Organs …
Hair, Skin, and Nails … My Senses …
Eating and Drinking … Sickness and
Health … Disabilities and Substance Abuse
DAILY LIFE … 231
Home Life … Families … Pets … Going to
School … Serving My Community …
Internet Safety … Bicycle Tips … Other
Safety Tips … Tough Questions: Divorce,
Death, God
viii
When Visible Ink’s publisher, Roger Jänecke, approached me about updating the
first edition of The Handy Answer Book for Kids (and Parents), I was a bit skeptical.
Why, one might ask, update a great reference book that contains just about
every question kids from ages 4 to 12? Well, the answer is simple: Because kids ask
the darndest things … and they keep asking … and asking.…
Anyone who has ever been a kid, or had a kid, or hung out with a kid, knows
that asking questions is what kids do. It happens to be a great way to find out about
the world around you. Kids have an insatiable hunger for information and a curiosity
that winds its way down every road. And it’s an adult’s job to satisfy that yearning
for learning—by answering the questions you know, or by pointing kids in the
direction of a good reference book when you don’t.
Written with a child’s imagination in mind, this revised edition of The Handy
Answer Book for Kids (and Parents) is bursting with nearly 800 questions and answers
on just about every topic in a kid’s world. After collecting many new questions from
moms and dads across the country, we were able supplement the book’s already popular
edition with intriguing information on dozens of different topics, helping parents
provide answers that go beyond “because” and “it just is” and “I don’t know.” Consider
The Handy Answer Book as a starting point—or for those who own the first edition,
a punctuation mark—a launching pad that will send an inquisitive mind in many different
directions. Or think of it as a fun way to spend a few hours, flipping from page
to page and absorbing new nuggets of trivia to introduce to your friends.
The expanded second edition focuses on subjects that are front-and-center in a
child’s world, things that are part of kids’ daily lives or spark their imaginations—
from the stars twinkling overhead to earthworms burrowing into the earth. By the
way, do you know why stars seem to twinkle? Or how big Earth is? Can you name
our plants and pull a quick definition of a dwarf star out of your hat? Can you
answer the ever-popular question, “Why is the sky blue?” The expanded “Outer
Space” and “Planet Earth and Our Moon” chapters provide answers to these questions,
explore the mysteries of the universe, and investigate weather-related phenomena
(“What is a hurricane? An avalanche? Lightning? Thunder?”) and various
features of our planet, including rainforests, deserts, oceans, and volcanoes. ix
Introduction
“People around the World” takes you on a journey around the globe, delivering
answers to intriguing questions like which country is the smallest (Vatican City)
and which country is the largest (Russia). This chapter also provides details about
different cultures throughout the world, explaining why we have different religions,
why people speak different languages, and which language is spoken by the most
people in the world (Mandarin Chinese). You can also compare the starkly different
lifestyles of those who live amid the bustle of a city and those who work the land.
Speaking of farm life, do you know why so many barns are painted red? Or why
horses sleep standing up? “Politics and Government ” supplements this chapter
with explanations about different types of government and the troubling question
of why countries fight wars. Included here are also fascinating answers about state
trivia. Is the District of Columbia a state? Which U.S. state was once its own kingdom?
You’ll find out in this section.
Perhaps the most interesting subject for kids (and adults, too) is the sometimes
mysterious workings of their own bodies, particularly as they navigate their way
through the minefield of burgeoning adolescence. “All about My Body” addresses
the many changes a kid’s body goes through and covers the body’s basic functions,
from how muscles work to why knuckles crack. And we don’t shy away from the less
appealing (or more appealing, depending upon your age and point of view) aspects
of the human body, answering questions about sweat, pimples, warts, scabs, vomit,
burps, and hiccups.
From a very young age, children become aware of and are fascinated by animals,
and for many of us that fascination continues throughout our lives. “Creatures
Big and Small” answers scores of questions about animals of all kinds, from
the ancient dinosaurs to the tiniest insects and bee-sized bats to the slowest mammal
(the sloth) and the biggest animal that has ever lived (the blue whale). Sometimes
learning one small fact—like why each zebra has unique black-and-white
stripes—can inspire us to look around and see things a bit differently.
In “Plant Life,” curious minds will learn that plants are more than just attractive
ways to decorate a yard; the Earth’s unique ecosystem depends on plants, and
their life systems are complex and amazing. Looking for a concise explanation of
photosynthesis? Look no further. Do you wonder about the differences between the
plants in your own backyard and those that survive in the Arctic tundra? Wonder
no more. Have you always wanted to know if there’s a flower big enough to float in?
In the Amazon jungle, the Giant Water Platter grows leaves that reach six to eight
feet across and can support the weight of small child.
All of us—young and not so old—use numerous high-tech tools and gadgets
everyday. It’s hard to imagine life without cellular phones and e-mail, not to mention
elevators, airplanes, televisions, and light bulbs. But what miracles of technology
make these items function? The chapter “How Things Work” explains it all. Did
you know that a television relies on photo cells, electrical signals, and a microphone
to function? And how do those things work together, anyway? Ever wonder how an
X-ray takes pictures or how a submarine can submerge and rise in the water? What
are barcodes, anyway? And why do stores—and consumers—rely on them? And
x what about numbers, counting, weights and measures, and telling time? The new
chapter on “Math, Measurement, and Time” complements the “How Things Work”
chapter and supports topics that kids encounter in school.
The chapter “Daily Life” addresses such critical questions as “How can I get a
bigger allowance?” “Why do I need to get along with my brother and sister?” “Why
do I have to go to school?” “Why do dogs wag their tails and bark?” “And why do I
have to do homework, anyway (assuming the dog didn’t eat it)?” This chapter also
helps kids define the roles of various family members and explains the value of things
like telling the truth, behaving politely, and being a good sport. It also anticipates
some of the more difficult questions kids ask about divorce, growing old, and dying.
It’s been said that children are like sponges, soaking up an amazing array and
depth of information at a mind-spinning rate. Part of this rapid learning rate can be
explained by physiological developments, but little knowledge would be possible
without a sense of wonder and interest. And while those qualities can be found in
abundance in most children, they are by no means the exclusive province of the
young. If we’re lucky, we continue to feel the excitement of learning new things and
deepening our understanding our entire lives.
—Gina Misiroglu
xi
For Oliver and Luke—
who always keep the questions coming!
MYSTERI E S OF
THE UNIVERS E
How did the universe begin?
Humankind has always puzzled over the origins of the universe. Scientists believe
that the universe began with the Big Bang, a cosmic explosion that occurred
between 10 and 20 billion years ago and threw matter in all directions. The universe
began as a dense, hot fireball, a scrambling of space and time. Within the first second
after the bang, gravity came into being. The universe expanded rapidly and
became flooded with subatomic particles that slammed into one another, forming
protons and neutrons. Three minutes later, when the temperature was 500 billion
degrees Fahrenheit (280 billion degrees Celsius), protons and neutrons formed the
simplest elements, including hydrogen, helium, and lithium.
According to the Big Bang theory, it took another 500,000 years for atoms to
form and 300 million more years for stars and galaxies to begin to appear. Countless
stars evolved and died before our own Sun and its planets came into being in
our galaxy, called the Milky Way. And it was only 4.5 billion years ago that our solar
system was formed from a cloud of dust and gas.
How big is the universe?
No one really knows just how big the universe is. The universe is everything that
exists: the planets, moons, stars, and galaxies. There are over 100 billion galaxies—
or massive star systems—in the visible universe. The number of stars in
each galaxy varies, but each galaxy probably contains billions of stars. Now that’s
a big universe! 1
OUTER
SPACE
How does the universe stay together?
Gravity, the same force that keeps your two feet on the ground, holds the entire universe
together. Gravity is the force of attraction that exists between any two particles
of matter, or any two objects. It holds planets in their orbits around the Sun,
and the Moon in its orbit around Earth. Gravity is also the force that holds any
object to Earth—or to any other heavenly body—instead of allowing it to fly into
space. The larger an object, the greater its gravitational pull.
What is a light year?
A light year is a way of measuring distance, and astronomers use light years to
measure the distances between stars. It is the distance that light travels in one year,
and is equal to almost 5.9 trillion miles (9.5 trillion kilometers). To think about how
long a light year is, consider this: The Sun is about 93 million miles (149 million
kilometers) from Earth, and a person would have to travel 31,620 round trips from
Earth to the Sun to travel the distance of a light year. Scientists can see things in
the universe more than 15 billion light years away.
Is the universe expanding?
In the 1990s, Australian and British astronomers compiled the largest map of the
universe by plotting the positions of more than 30,000 galaxies. Most of these galaxies
are moving away from us here on Earth. Most astronomers believe that the universe
is expanding—that all points in the universe are getting farther apart all the
time. It’s not that stars and galaxies are getting bigger, but rather the space between
all objects is expanding with time.
We never notice the expansion on planet Earth because it happens over such a
large scale. In fact, it was only in 1929 that the expansion of the universe was discovered,
when American astronomer Edwin Hubble brought together many scientists’
work. He studied the sky and created “Hubble’s diagram,” which showed that
the redness of a galaxy’s light, and thus the speed with which the galaxy moved away
from Earth, increased with its distance from Earth, and that the increase graphed
into a straight line. The farther away a galaxy is, the faster it moves away from us.
Is it possible for the universe to collapse instead?
According to the Big Crunch theory, at some point all matter will reverse direction
and crunch back into the single point from which it began. Another theory, called
the Plateau theory, says that the expansion of the universe will slow to the point
where it will nearly cease, at which time the universe will reach a plateau and
remain essentially the same.
Is Earth at the center of the universe?
The Greek philosopher Aristotle proposed that the heavens were composed of 55
2 concentric, crystalline spheres to which the celestial objects were attached and
Scientists figured out that the universe began with a Big Bang. Background microwave radiation and infrared light gives clues
as to how the universe was formed and how it is still expanding today. (NASA/JPL-Caltech/A. Kashlinsky)
which rotated at different velocities, with the Earth at the center. People believed
this for almost 2000 years, until Polish astronomer Nicolai Copernicus proposed
that the Sun, not Earth, was the center of the solar system. His model, called a
heliocentric system, said that Earth is just another planet (the third outward from
the Sun), and the Moon is in orbit around Earth, not the Sun. While this might be
true of our solar system, astronomers cannot see the whole universe through their
telescopes, so no one knows where the true “center” of it lies.
What is outer space?
Outer space, sometimes simply called “space,” are the areas between Earth and the
Moon, between the planets of the solar system, and between the stars. Space is not
completely empty. It does not contain any air, but it does contain a few specks of
dust and atoms of gases.
Which galaxy is closest to ours?
The nearest big spiral galaxy to our galaxy, the Milky Way, is the Andromeda galaxy.
Appearing as a smudge of light in the constellation Andromeda, this galaxy is about
twice as big as the Milky Way. It is about 2.3 million light years away from us,
although its vast size and luminosity make it visible to the naked eye. In fact, it is
the most distant object that can been seen from Earth without a telescope. 3
OUTER SPACE
PLANETS AND THE SOLAR SYSTEM
What is the solar system?
The solar system is made up of the Sun and all things orbiting around it, including
the nine major planets, several dozen satellites like our Moon, and all the asteroids
and comets. Each one moves in a unique path around the Sun, and the Sun’s force
of gravity holds all the celestial bodies together. Our solar system is part of the Milky
Way galaxy, a group of some hundred billion stars that are arranged in a vast disklike
shape held together by gravitational forces. Our solar system is located about
halfway between one edge of the Milky Way and its center, so all the stars that we
can see from Earth belong to our galaxy. But with giant telescopes, scientists have
been able to observe many other galaxies in our universe; they believe there are 100
billion other galaxies.
How old is the solar system?
Scientists believe that the solar system in about 4.6 billion years old. Earth and the
rest of the solar system formed from a giant cloud of gas and dust. Gravity and rotational
forces caused the cloud to flatten into a disc and much of the cloud’s mass to
drift into the center. This material became the Sun. The leftover parts of the cloud
formed small bodies called planetesimals. These planetesimals collided with each
other, gradually forming larger and larger bodies, some of which became the planets.
This process took approximately 25 million years, according to scientific estimates.
What is an orbit?
An orbit is the circular or oval path that something follows as it moves through
space. For example, the planets move in orbits around the Sun and the moons travel
in orbits around the planets. To get into orbit around Earth, a spacecraft must fly
out into space at a speed of at least 17,500 miles (28,163 kilometers) per hour. If a
4 spacecraft does not reach this speed, it will fall back to Earth.
Why is the Andromeda galaxy so special?
Andromeda has a bright disk that scientists believe spans as much as
260,000 light years—almost twice the size of the bright disk seen in photographs.
The outer disk emits nearly 10 percent of the galaxy’s total light and
may be made up of stars stripped from smaller galaxies that strayed too close.
In 2007, a team of astronomers announced the discovery of low-metallic, red
giant stars up to some 500,000 light years from Andromeda’s core. This discovery
suggests that the galaxy is much larger than scientists originally
thought, and that Andromeda’s glowing halo may actually overlap with that
of the Milky Way.
What is a planet?
The word “planet” comes from the Greek word for “wanderer.” Ancient astronomers
defined planets as objects that moved in the night sky against a background of fixed
stars. Today, astronomers define a planet as an object in orbit around the Sun that is
large enough (massive enough) to have its self-gravity pull itself into a round, or nearly
round, shape. In addition, a planet orbits in a clear path around the Sun—there are
no other bodies in its path that it must “sweep up” (or clear) as it moves around the Sun.
How many planets are there?
Scientists do not know how many planets there are in the universe. However, eight
planets orbit the Sun. They are Mercury (which is closest to the Sun), Venus, Earth,
Mars, Jupiter, Saturn, Uranus, and Neptune.
Which planets are the rocky planets?
Planets come in different sizes, compositions, and colors. Mercury, Venus, Earth,
and Mars, the four planets closest to the Sun, are called “rocky” or “terrestrial”
planets. Mars, Mercury, and Venus are similar to Earth in composition. Heat from
the Sun evaporated lightweight elements like hydrogen and helium into interplanetary
space. Mostly rock and metal were left in this zone and clumped together to
form the inner rocky planets. These planets have no rings and only two of them—
Earth and Mars—have moons. 5
For many years, the solar system included Pluto, for a total of nine planets. Pluto is now considered a planetoid and not a
true planet. This drawing shows the arrangement of the planets, as well as how far each planet tilts on its axis.
OUTER SPACE
Which planets are called the gas giants?
The four outer planets—Jupiter, Saturn, Uranus, and Neptune—are called the gas
giant planets. Much larger than the rocky planets, they all have rings and many
moons. They are made up mostly of hydrogen, helium, frozen water, ammonia,
methane, and carbon monoxide. Jupiter and Saturn contain the largest percentages
of hydrogen and helium, while Uranus and Neptune contain the largest amounts of
ices (frozen water, ammonia, methane, and carbon dioxide).
What is Planet X?
In the 1930s, when American mathematician and astronomer Percival Lowell
decided to search for a planet beyond Neptune, he called the hypothetical planet
“Planet X.” This search led to the discovery of Pluto, but for many years some
astronomers believed that another world larger than Pluto must exist undiscovered
beyond Neptune. They thought this because Neptune’s orbit seemed to be influenced
by the gravity of an unseen planet. More recent studies indicate that a large
Planet X most likely does not exist, but the term Planet X is still used in pop culture
for an undiscovered planet in our solar system.
Who named our planets?
Except for the name Earth, our planets’ names come from Roman and Greek
mythology. The five planets easily visible to the naked eye—Mercury, Venus, Mars,
Jupiter, and Saturn—were called different things by different cultures. The Romans
6 named these planets, meaning “wanderers,” according to their movements and
Why isn’t Pluto a planet anymore?
Pluto was once included in the list of planets, but is now considered a
“dwarf” planet—an object in orbit around the Sun that is massive enough
to have its own gravity to pull itself into a round (or nearly round) shape.
Dwarf planets are generally smaller than Mercury. Pluto’s composition is similar
to that of comets, and its orbit is quite different from that of the other
planets. Pluto also has one moon, Charon. It is located within a part of our
solar system called the Kuiper Belt.
Scientists have discovered many objects in our solar system recently, but
none of them have been classified as planets. Most are called either asteroids
or minor planets, also called small solar system bodies. Some are called trans-
Neptunian objects (TNO), because they are objects located past Neptune. One
of the most recent discoveries of a TNO was in October 2000, when
astronomers discovered a TNO and called it 2000 EB 173. It is between 186 and
435 miles (300 and 700 kilometers) in size and, as far as non-planets go in the
solar system, it is second in size to the asteroid Ceres.
appearance. For example, they
named Jupiter after the king of the
gods; they named Venus, the planet
that appears the brightest, after
the Roman goddess of beauty; they
named the reddish Mars after the
god of war. Saturn is named after
the god of agriculture. These
Roman names were adopted by
European languages and culture
and became standard in science.
Is a day the same on all
planets?
No, it varies from planet to planet.
A day is the period of time it takes
for a planet to make one complete
turn on its axis. Venus and Uranus
display retrograde motion, which
means they rotate in the opposite
direction from other planets. There
are 24 hours in a day on planet
Earth and 10.5 hours on Saturn.
Which planets have rings?
Jupiter, Saturn, Uranus, and Neptune
have rings—or thin belts of
rocks—around them. Jupiter’s
ring is thin and dark, and cannot be seen from Earth. Saturn’s rings are bright,
wide, and colorful. Uranus has nine dark rings around it, and Neptune’s rings are
also dark, but contain a few bright arcs. At one time all of the planets, Earth included,
had rings. These rings were unstable and the material was either lost in space
or collected into the satellites of these planets.
Is there a red planet?
Yes. Mars, the fourth planet from the Sun, is called the Red Planet. It looks red
because the rocks on the surface contain rusted iron. It has an atmosphere with
clouds, winds, and dust storms—its red dust floats in the atmosphere and gives the
planet a red sky. Mars, which has two moons, orbits the Sun every 687 days and
rotates on its axis once every 24 hours and 37 minutes.
Which planet might float on water?
Saturn, the second largest planet in the solar system, is the least dense. Water has
a density of 1.0 grams per centimeter cubed. Saturn, which is made mostly of gas 7
Saturn’s rings are the most noticeable in the solar system, but other
planets, including Jupiter, Uranus, and Neptune, have rings, too. (NASA)
OUTER SPACE
The greenhouse effect refers to the way in which gases in our planet’s atmosphere can keep heat from escaping into space.
and liquid, has a density of 0.69 grams per centimeter cubed. This means that if you
could somehow take a chunk of the planet and haul it back to Earth, it would float
in your swimming pool.
Which planet could melt metal?
Most people think that Mercury is the hottest planet because it is nearest to the
Sun. However, Venus, the second nearest planet, is the hottest because it has an
atmosphere. Its atmosphere is primarily composed of carbon dioxide, which acts
like a greenhouse. The solar heat enters Venus’s atmosphere, but it cannot leave,
heating the planet’s surface to about 900 degrees Fahrenheit (482 degrees Celsius).
This temperature is hot enough to melt several metals, including lead, tin,
and zinc.
Where in space could you ice skate?
On Europa, one of Jupiter’s moons, it is possible to ice skate, as long as you wore a
space suit. A little smaller than Earth’s moon, Europa is covered in smooth ice. Its
gravity is only about one-eighth of planet Earth’s, which makes for great leaps.
However, Europa temperatures reach about –328 degrees Fahrenheit (–200 degrees
Celsius), which means you would be frozen stiff in a nanosecond. The only colder
object in the solar system is Neptune’s moon, Triton, which has unique “ice volcanoes”
and a surface temperature of –391 degrees Fahrenheit (–235 degrees Celsius).
Which is the windiest planet?
Although there are other windy planets (like Uranus), Neptune’s winds are the
fastest in the solar system, reaching 1,600 miles (2,575 kilometers) per hour. Nep-
8 tune’s large, sweeping wind storms could consume the entire planet Earth!
Which planets experience the greenhouse effect?
The greenhouse effect describes a warming phenomenon. (In a greenhouse, closed glass
windows cause heat to become trapped inside.) The greenhouse effect occurs when a
planet’s atmosphere allows heat from the Sun to enter, but refuses to let it leave. A good
example of the greenhouse effect can be found on Venus. There, solar radiation penetrates
the atmosphere, reaches the surface, and is reflected back into the atmosphere.
The re-radiated heat is trapped by carbon dioxide, which is abundant in Venus’s atmosphere.
The result is that Venus has a scorching surface temperature of 900 degrees
Fahrenheit (482 degrees Celsius). The greenhouse effect can also be found on Earth and
in the upper atmospheres of the giant planets: Jupiter, Saturn, Uranus, and Neptune.
How does the greenhouse effect work on Earth?
On Earth, solar radiation passes through the atmosphere and strikes the surface. As
it is reflected back up, some solar radiation is trapped by gases in the atmosphere,
including carbon dioxide, methane, chlorofluorocarbons (CFCs), and water vapor,
resulting in the gradual increase of Earth’s temperature. The rest of the radiation
escapes back into space.
Human activity is largely responsible for the buildup of greenhouse gases in
Earth’s atmosphere, and hence Earth’s gradual warming. For instance, the burning of
fossil fuels (such as coal, oil, and natural gas) and forest fires add carbon dioxide to the
atmosphere. Methane buildup comes from the use of pesticides and fertilizers in agriculture.
Large amounts of water vapor are released from various industries. And CFCs
are released by some aerosol cans and coolants in refrigerators and air conditioners.
How is Mars different from Earth?
Mars is smaller, about half the size of Earth, with a radius of 2,108 miles (3,393 kilometers)
compared to 3,963 miles (6,378 kilometers) for Earth. Because of its small 9
OUTER SPACE
Could the greenhouse gas buildup
ever make Earth as hot as Venus?
With a slow but steady increase in Earth’s temperature, it could—far off in
the future—become scorching hot like Venus. Earth’s temperature
increase has caused more water to evaporate from the oceans and some ice to
melt in the Arctic, which increases the clouds in the atmosphere. The greater
cloud covering blocks some solar heat from entering Earth’s atmosphere, but it
also worsens the greenhouse effect by trapping more of the heat that does make
it down to the surface. Prolonged heating of the atmosphere could shut down
Earth’s tectonic plates—free-floating sections of crust—and cause the planet’s
crust to become locked in place, making it more like Venus’s bone-dry surface.
size, Mars’ interior cooled more quickly than Earth’s, and thus it has less volcanic
activity than Earth. The red planet also has no plate tectonics. Its crust is rigid,
unlike the constantly moving crust of Earth. Therefore, Mars does not have extensive
mountain chains, oceans, or lines of volcanoes, such as those found on Earth.
Is there life on Mars?
Earth is the only place that scientists know for certain supports life. The United States
and other countries have been sending spacecraft to orbit or land on Mars since the
1960s, and each mission teaches scientists more about this fascinating planet.
Although Mars is more similar to Earth than other planets in the solar system, it is
still different from Earth in many ways. In 1976, NASA landed robotic spacecraft
named Viking 1 and Viking 2 on Mars. Viking 1 scooped up samples of Martian soil
and tested it for signs of life, but none were found. In the future, NASA will be looking
for live bacteria and searching for tiny fossils that might indicate life may have
existed early in Mars’s history but—unlike on Earth—did not survive and evolve into
larger life forms. In 2008, NASA’s Phoenix Mars Lander landed on the planet to search
for complex organic molecules in the ice-rich soil of the arctic region.
Is there life on planets in other solar systems?
Because of great distances, it has been impossible for scientists to determine
whether or not planets in other solar systems contain life. If we were able to gather
data about the extrasolar planets, we might be able to tell if there is life on another
planet. In particular, the presence of carbon dioxide could tell us that the planets
have an atmosphere; a significant amount of water vapor—which is unique to
Earth’s atmosphere in our solar system—would tell us that a planet has an ocean;
and ozone, the layer of gas that protects life on Earth from the ultraviolet radiation
from the Sun, may tell us if a planet has life.
What is the difference between a planet and a moon?
There is a very basic difference between the two: A planet revolves around the Sun and
a moon orbits a planet. Technically, the moon also orbits the Sun as it spins around
its planet, but because it has its own suborbit of a planet scientists define it as a moon.
All planets have moons, except for Mercury and Venus. Earth and Pluto have one
moon, and Jupiter has 16. Saturn has the most known moons—more than 22.
OUR SUN AND THE STARS
What is the difference between a planet and a star?
A star is a huge ball of hot glowing gas, like the Sun, and a planet is a world, like
Earth. Stars produce their own light; they undergo nuclear reactions that burn
10 hydrogen in their cores. But planets are lit by light from the Sun. When you look
up into the night sky, it is hard to tell planets and stars apart. However, early
astronomers were able to tell the difference because planets in our solar system
appear to move in complicated paths across the sky, but stars don’t. There are also
other observational differences: planets almost never twinkle, but stars do.
What is the Sun made out of?
The Sun is a star, made up of hot gases that contain elements such as hydrogen,
helium, calcium, sodium, magnesium, and iron. Its temperature is so high that it
glows white, emitting both light and heat rays. It is also very large: if the Sun were
the size of a basketball, Earth would only be the size of the head of a pin.
How hot is the Sun?
The Sun is extremely hot. The surface of the Sun (or its outer visible layer, called
the photosphere) is about 10,000 degrees Fahrenheit (5,537 degrees Celsius)—
about 50 times the temperature required to boil water. The core of the Sun, where
solar energy is created, reaches 27 million degrees Fahrenheit (15 million degrees
Celsius). It is so intense that nuclear reactions take place there.
What would happen if there wasn’t a Sun?
Without the Sun, life on Earth would not exist. The planet would be a frozen dark
ball, drifting in space. The Sun provides light, heat, and energy, which stirs up the
atmosphere to create winds and rain. With it, plants grow, and animals and humans
eat. However, the Sun’s heat output changes over time, which affects our daily lives,
the climate, and our satellite communications.
What happens during an eclipse of the Sun?
Once in a while the Moon passes directly in front of the Sun as it makes its way
around Earth. It temporarily blocks out the Sun, casting a shadow on a portion of
Earth that is experiencing day. When this total eclipse of the Sun—a solar eclipse— 11
Why do stars twinkle?
On a clear, dark night in your backyard, you can see about 2,000 or so stars
in the sky, a small fraction of the 100,000 or so stars that make up our
galaxy. They seem to twinkle, or change their brightness. In reality, most of the
stars are shining with a steady light. The movement of air (sometimes called
turbulence) in the atmosphere of Earth causes the starlight to get slightly bent
as it travels from the distant star through the atmosphere down to the ground.
This means that some of the light reaches us directly and some gets bent
slightly away. To the human eye, this makes the star seem to twinkle.
OUTER SPACE
occurs, the part of Earth affected becomes dark and cold until the Moon passes by.
Surrounding areas experience a partial eclipse, when just part of the Sun is temporarily
covered by the Moon.
Where does the Sun shine the most?
In the United States, Yuma, Arizona has a yearly average of 90 percent of sunny
days, or more than 4,000 sunny hours per year. St. Petersburg, Florida, is a close
second; that city had 768 consecutive sunny days from February 9, 1967 to March
17, 1969. If you were to travel, you would find the eastern end of the Sahara Desert
in North Africa the sunniest—the Sun shines there 97 percent of the time.
Is there a place on Earth where the Sun does not rise?
In the Arctic and Antarctic circles there is at least one day a year when the Sun does
not rise and one day when the Sun does not set. This is because of their close location
to Earth’s poles. The Sun does not set on the summer solstice (June 21 in the
north and December 21 in the south) and does not rise on the winter solstice
(December 21 for the north and June 21 for the south). For this reason, the Arctic
and Antarctic are called the “lands of midnight Sun” in the summer and “lands of
noon darkness” 12 in the winter.
When shown next to the Earth (the little dot on the right) you can really get a sense of how huge our Sun is! (NASA/JPLCaltech/
R. Hurt)
What is a supernova?
A supernova is the explosion caused when a massive star, at least eight times the
Sun’s mass, exhausts its fuel (or dies) and then collapses. If the original star is less
than 20 solar masses, the supernova will leave behind a neutron star, or remnant.
Heavier stars will collapse into black holes. Supernova explosions are among the
most energetic events in the universe, and are a rare sight. The last supernova seen
in our galaxy, the Milky Way, was in 1604.
What is a black hole?
A black hole is an invisible region of space that is thought to have such intense
gravity that not even light can escape. Scientists believe that a black hole is created
when a giant star collapses in upon itself as it dies. A star lives as long as it
can burn fuel. The burning of fuel acts as a counterforce against gravity; without
that counterforce, a star’s gravity would cause it to collapse in on itself. So when
that fuel runs out, gravity takes over and crushes the star. If the star is large
enough and has a strong enough force of gravity, it will become a black hole when
it collapses. Scientists have discovered evidence of several black holes in our
galaxy, and they believe there may be millions more that have not been identified.
What is a quasar?
In 1960, astronomers discovered some mysterious space objects and called them
quasars because they were discovered to be a strong source of radio waves. In fact,
the term “quasar” comes from the words “quasi-stellar radio source.” Quasars are
sources of light or radio waves, just like galaxies, that emit enormous amounts of
energy. They are the most distant objects scientists have discovered. They are very
bright (as bright as hundreds of galaxies, burning with the energy of 1 trillion Suns)
and much smaller than most galaxies. Today, many astronomers refer to these
objects as quasi-stellar objects, or QSOs.
What are the patterns of stars called?
Fixed groups of stars that seem to form a particular shape, such as that of a person,
animal, or object, are called constellations. Astronomers have identified 88 constellations
and many of them represent characters from Greek and Roman mythology.
For example, the name Hydra, the largest constellation, comes from the water snake
monster killed by Hercules in ancient mythology. Some of the constellation names
are in Latin; for example, Cygnus means Swan and Scorpius means Scorpion.
COMETS, METEORS, AND ASTEROIDS
What are comets?
Comets are solar system bodies that orbit the Sun, just as planets do, except a comet
usually has a very elongated orbit. Part of its orbit is very, very far from the Sun and 13
OUTER SPACE
This is an image of Comet 73P, also called the Schwassman-Wachmann 3 comet. In 1995 it broke into pieces, two of which
are seen here. This particular comet orbits our Sun every 5.5 years. (NASA/JPL-Caltech/W. Reach)
part is quite close to the Sun. They are sometimes nicknamed dirty “cosmic snowballs,”
because they are small, irregularly shaped chunks of rock, various ices, and
dust. As the comet gets closer to the Sun, some of the ice starts to melt and boil off,
along with particles of dust. These particles and gases make a cloud around the
nucleus, called a coma. The coma is lit by the Sun. The sunlight also pushes this
material into the brightly lit “tail” of the comet.
What is an asteroid?
Asteroids are rocky objects that orbit around the Sun; most of them are located in
a belt between Mars and Jupiter. Scientists believe there may be more than 50,000
asteroids in that belt, and perhaps millions more elsewhere in space. They range in
size from nearly 20 feet (6 meters) in diameter to some as large as 600 miles (965
kilometers) across. (While 20 feet seems small compared to 600 miles, the smallest
asteroids would still have a strong impact if they hit Earth.) Slight changes in asteroids’
orbits occasionally cause them to collide with each other, resulting in small
fragments breaking off from the whole. Sometimes these small fragments leave
their orbit and fall through Earth’s atmosphere as meteors. Some scientists have
suggested that it was a huge asteroid’s collision with Earth 65 million years ago that
caused the massive damage that led to the extinction of dinosaurs.
What is the difference between a meteor and a shooting star?
None, but the terms can sometimes be confusing. A meteoroid is a rock in space—it
can be any size, from microscopic to many meters across. A meteor is the same rock
falling through Earth’s atmosphere, creating a streak of light, sometimes also called
a “shooting star” after the white-hot glow produced by the heat 14 of friction between
the meteor and the air. Fragments of meteors that survive the trip through the atmosphere
and land on Earth’s surface are called meteorites. Some of Earth’s craters were
caused by meteorites, but eventually Earth’s wind and rain erode the evidence of most
craters. Because the Moon has no air to rub against, meteors do not burn up before
hitting the Moon’s surface, which is one reason why the Moon has lots of craters.
How many meteorites reach Earth in one year?
In any given year, approximately 26,000 meteorites, each weighing more than 3.5
ounces (99.2 grams) land on Earth. About 3,000 of these meteorites weigh more than
2.2 pounds (1 kilogram), according to the number of fireballs actually seen by scientists.
Only a handful of these are witnessed or cause property damage; the majority of
them fall into the oceans, which cover about 70 percent of Earth’s surface.
EXPLORING S PACE
Who invented the telescope?
In 1608, Hans Lippershey, a Dutch eyeglass maker, invented the telescope, a device
used by an astronomer to magnify images of distant objects. He noticed that objects
appeared nearer when seen through two eyeglass lenses, so he mounted the lenses
in a tube, making the first telescope. Crude telescopes and spyglasses may have been
created much earlier, but Lippershey is believed to be the first to apply for a patent
for his design (called the “Dutch perspective glass”), thus making it available for general
use in 1608. A year later, the Italian astronomer Galileo Galilei built a telescope
and was the first to use it to study the solar system systematically. He built about 30
telescopes but used only 10 to observe the sky. Through his careful observations, he
found support for the Copernican, or Sun-centered, view of the solar system.
How powerful are
astronomers’ telescopes?
Before Lippershey and Galileo, magnification
instruments had not been used to
investigate objects beyond Earth. Since
their time, far more powerful visiblelight
telescopes have been developed
along with other types of telescopes
capable of “seeing” invisible forms of
radiation, such as infrared, ultraviolet,
radio, X-ray, and gamma-ray. Today’s
optical telescopes (made from glass,
lenses, or mirrors) are 100 million times
more sensitive than Galileo’s telescope.
For example, Hawaii’s twin Keck Tele- 15
The Hubble Space Telescope is seen here as it is being
serviced by a space shuttle. (NASA)
OUTER SPACE
scopes are the world’s largest optical and infrared telescopes. Each stands eight stories
tall and weighs 300 tons. The Hubble Space Telescope, named after astronomer
Edwin Hubble and launched into space in 1990, orbits Earth at a speed of 5 miles (8
kilometers) per second, and beams images back to Earth. Because its position is
above the atmosphere (which distorts and blocks the light that reaches Earth) it is
able to view the universe more thoroughly and clearly than ground-based telescopes.
How does a rocket blast off?
Explosive chemical reactions are what send spacecraft into space. A rocket burns
fuel to produce a jet of hot, expanding gas. What fuel is used varies, but whatever
the mixture, it causes the explosive chemical reaction. Because a rocket needs
thrust to escape Earth’s gravity, the explosive chemical reaction takes place in a
confined chamber and releases gases into a cone-shaped nozzle out the back end of
the rocket. The cone shape accelerates the gases and they blast out of the engine at
up to 9,941 miles (15,998 kilometers) per hour.
When did the first spacecraft go up into space?
The Soviet satellite Sputnik 1, which was launched into space on October 4, 1957, was
the first spacecraft to go into orbit around Earth. It had no crew members or animals
aboard, but instead contained machines that sent information back to Earth via radio.
The former Soviet Union’s (now Russia) launch of Sputnik prompted the United
States to get its first satellite, Explorer 1, into orbit quickly, igniting the so-called
space race. This was the two countries’ rivalry over being the “first” in many areas of
space exploration. Explorer 1’s test run in December 1957 burned on the ground, but
the satellite was successfully launched into orbit around Earth on January 31, 1958.
What is a space shuttle?
NASA’s space shuttle, also called the Space Transportation System (STS), takes off
from Earth like a rocket but lands like an aircraft. It cannot fly to the Moon, but is
used to orbit Earth, where the crew can do scientific work, place satellites in orbit,
and visit orbiting space stations. Usually five to seven crew members ride the space
shuttles, which have all been launched from Kennedy Space Center in Florida. Six
shuttles have been built: the first orbiter, Enterprise, was built in 1974 for testing
purposes. Five others have gone into space: Columbia, Challenger, Discovery,
Atlantis, and Endeavour. The space shuttle Challenger disintegrated 73 seconds
after launch in 1986, and Endeavour was built as a replacement. Columbia broke
apart during re-entry in 2003. NASA announced that the space shuttle would no
longer be used after 2010, and from 2014 on would be replaced by the Orion, a new
space vehicle that is designed to take humans to the Moon and beyond.
What do the astronauts wear in space?
Crew members of the space shuttle are required to wear their space suits for launch
16 and landing. Soviet cosmonauts are required to wear them during takeoff, landing,
What has the Hubble Space Telescope discovered?
According to the National Aeronautics and Space Administration (NASA),
which is in charge of space exploration and scientific discovery for the
United States, the Hubble transmits about 120 gigabytes of science data every
week. That’s equal to about 3,600 feet (1,097 meters) of books on a shelf. The
growing collection of pictures and data is stored on magneto-optical disks.
Among its many discoveries, Hubble has revealed the age of the universe to
be about 13 to 14 billion years, which is a more accurate estimate than the
Big Bang range of between 10 to 20 billion years. Hubble also played a key role
in the discovery of dark energy, a mysterious force that causes the expansion
of the universe to accelerate. Hubble has shown scientists galaxies in “toddler”
stages of growth, helping them understand how galaxies form. It found
protoplanetary disks, clumps of gas and dust around young stars that likely
function as birthing grounds for new planets. It discovered that gamma-ray
bursts—strange, incredibly powerful explosions of energy—occur in far-distant
galaxies when massive stars collapse.
and docking—a big difference from when they originally used to fly in only their
underwear.
Space suits come in different sizes, and the various body parts, such as the arms
and legs, attach together for a customized fit. The inner suit is made of a layer of
tubing, which is filled with a cool liquid; the outer suit is made of multiple layers of
materials such as Dacron, nylon, and aluminum (Mylar). The boots come attached
to the pants, and the middle part of the spacesuit, which covers the torso, is made
of inflexible fiberglass. In all, the modern space suit is like a modern-day suit of
arms, which is put over the head. Built-in backpacks hold life-support systems, a
camera, and other useful items for space exploration.
What are space probes?
A space probe is an unmanned spacecraft that flies into outer space. It may land on
the Moon or other planets, go into orbit around them, or fly past them. Its purpose
is to conduct research: It contains cameras and other advanced equipment so that
it can send pictures back to Earth by radio. The first successful space probe took
place in 1959 with the Soviet Luna 1, which passed within 3,725 miles (5,995 kilometers)
of the Moon’s surface after 83 hours of flight. It then went into orbit
around the Sun, between the orbits of Earth and Mars. In 1977, the United States
launched Voyager 1 and Voyager 2 from rockets. These space probes explored all
the giant planets of our outer solar system (Jupiter, Saturn, Uranus, and Neptune),
48 of their moons, and the unique system of rings and magnetic fields for each of
those planets. 17
OUTER SPACE
What does a satellite do?
A satellite is any body or object that moves around another; for example, the Moon
is a satellite of Earth. But when most scientists use the word “satellite” they are
referring to a man-made object that orbits Earth and collects and returns data. A
single satellite may serve many purposes. Satellites can be used for weather forecasts
by measuring clouds, winds, and the temperature of the atmosphere from
space. They are also used in military contexts to track battle zones, watch for missile
launches and nuclear testing, spy on countries, and track incoming objects like
meteoroids. Satellites also send television programs and telephone calls from one
continent to another. The first Global Positioning Satellite (GPS) was launched on
November 22, 1978, and today GPS is the standard navigation tool used by the military,
scientists, and industry. Space satellites are used for learning about the universe,
including how the Sun and Earth interact and details about planets.
Who was the first man in space?
The Soviet cosmonaut Yuri Gagarin became the first man in space when he made
a full orbit of Earth in Vostok I on April 12, 1961. Although he was in space less
than two hours, he became an international hero. The United States launched
the first American into orbit on February 20, 1962: Astronaut John Glenn completed
three orbits of Earth in Friendship 7, traveling about 81,000 miles
(130,329 kilometers).
Who was the first woman in space?
Valentina V. Tereshkova-Nikolaeva, a Soviet cosmonaut, was the first woman in
space. She spent three days circling Earth, completing 48 orbits aboard Vostok 6,
which launched on June 16, 1963. Although she had little cosmonaut training, she
was an expert parachutist. The United States put a woman in space twenty years
later, on June 18, 1983, when astronaut
Sally K. Ride flew aboard the space shuttle
Challenger mission STS-7.
Who was the first African
American in space?
Guion S. Bluford Jr. became the first
African American to fly in space during
the space shuttle Challenger mission
STS-8, which took place from August 30
to September 5, 1983. He returned to
space again in 1985 aboard Challenger
mission STA-61-A/Spacelab D1. Mae C.
Jemison became the first African American
woman in space on September 12,
1992, when she flew aboard the space
18 shuttle Endeavour mission Spacelab-J.
The Soviet cosmonaut Yuri Gagarin was the first man in
outer space. He rode aboard the Vostok I in 1961. (NASA)
How many U.S. astronauts have walked on the Moon?
Twelve astronauts have walked on the Moon, all via Apollo lunar aircrafts. Each of
the six Apollo flights, which took place between 1969 and 1972, had a crew of three.
However, since one crew member remained in orbit in the command service module
(CSM), the other two actually stepped onto the Moon. When Neil Armstrong
became the first astronaut in history to walk on the Moon on July 20, 1969, he said,
“That’s one small step for a man, one giant leap for mankind.”
When were animals sent up in space?
In 1957, the first animal, a small female dog named Laika, was launched aboard the
Soviet Sputnik 2. Laika was placed in a pressurized compartment within a capsule
that weighed 1,103 pounds (500 kilograms), and died after a few days in orbit. The
United States send a squirrel monkey named Old Reliable into space aboard the
December 12, 1958, Jupiter flight, but it drowned during recovery. The next year,
on another Jupiter flight, NASA sent two female monkeys into space and both were
recovered alive.
What is the space station Skylab?
A space station is an orbiting satellite that allows astronauts to live in space for
weeks or months at a time. The first U.S. space station, called Skylab, was launched
unmanned on May 14, 1973. In 1973 and 1974, three more manned missions followed
with Skylab, during which astronauts observed Earth, solar flares, and the
comet Kohoutek. Skylab included a solar observatory, a laboratory for studying the
effects of microgravity, and a refrigerator that held prime rib, German potato salad,
and ice cream. Skylab orbited Earth 2,476 times during the 171 days and 13 hours
of its three manned missions.
What was the Challenger disaster?
Seven astronauts were aboard Challenger flight STS-51L when it exploded during
liftoff on January 28, 1986. Christa McAuliffe was a Concord, New Hampshire, high
school social studies teacher. She and the other six crew members were killed when 19
OUTER SPACE
Can astronauts drink soda in space?
Yes! U.S. astronauts aboard Challenger’s 1985 flight drank Coke and Pepsi
from special cans. Other astronauts have enjoyed corned beef sandwiches,
hot dogs, graham crackers, and Life Savers. At Mir station in 1988, French
cosmonaut Jean-Loup Chretien treated fellow cosmonauts to 23 gourmet
foods from a French chef, including compote of pigeon with dates and dried
raisins, duck with artichokes, oxtail fondue with tomatoes and pickles, and
beef bourguignon. Now that’s fine dining!
a solid-fuel booster rocket leak led to a massive fuel tank explosion during liftoff
from its launch pad. NASA’s next flight was Discovery, which was launched on September
28, 1988. After the Challenger disaster, NASA’s three remaining shuttles—
Atlantis, Discovery, and Columbia—were rebuilt, each with more than 250 modifications
improving safety and performance.
Will people live in space one day?
Many films and science-fiction books have shown colonies of humans living on the
Moon or Mars, but at this time it is still a distant possibility. Since the 1960s, NASA
has been planning lunar bases to use for scientific study or for training astronauts to
go to Mars. Space stations have been designed to keep astronauts as comfortable as
possible, with a 70 degrees Fahrenheit (21 degrees Celsius) constant temperature
and all of the freeze-dried food, exercise equipment, and other amenities necessary
for short-term life in space. However, only some people can actually adapt to a life in
space, which includes a weightless environment, living in close quarters, and using
technology necessary for carrying out routine daily activities. While it is possible for
a scientific community to be functioning in space by the year 2020, it is less likely
that the average citizen will be able to permanently relocate there anytime soon.
20
Astronauts Kathryn Sullivan (left) and Sally Ride use Velcro and bungee cords to keep from floating too much in the shuttle.
Life in space can be difficult, but exciting! (NASA)
THE BLUE PLANET
How old is Earth?
Scientists estimate that Earth—born out of a swirling cloud of gas and dust—is
about 4.6 billion years old. They have reached this conclusion by studying Moon
rocks and meteorites (rocks that have fallen from space to Earth) that they believe
were formed at the same time as our planet.
How big is Earth?
Earth, which is almost round in shape, measures 24,901 miles (39,842 kilometers)
around at its widest part, the equator. (The equator is the imaginary line that crosses
the planet midway between the North and South Poles.) A measurement through
Earth at the equator—in other words, the planet’s diameter—reveals that it is 7,926
miles (about 12,700 kilometers) across. Earth’s weight, or mass (the amount of
matter it is made of), is around 6 sextillion tons. That is 6 with 21 zeros after it!
Because Earth cannot be put on an enormous scale to find its weight, scientists use
the laws of gravity and mathematical equations to figure this out.
Is the Earth round?
The Earth is not round, but slightly squashed; it’s diameter at the equator (the
imaginary line on Earth’s surface that divides Earth into a Northern and a Southern
Hemisphere) is about 24 miles (38 kilometers) greater than its diameter at the
poles. Why? Because the planet is constantly spinning, forcing material out toward
the equator. The Earth’s surface is both smooth and bumpy, with vast oceans, tall
mountains, rolling plains, canyons, swamps, and deserts. The tallest mountain on
our planet, Mount Everest in the Himalayas, stands at an altitude of 29,108 feet 21
PLANET EARTH
AND OUR MOON
(8,872 meters), while Africa’s Sahara, the largest desert on Earth, spans over 2.1
million square miles (500,000 square kilometers) of land.
How many continents are there?
A continent is one of several major land masses on the Earth. Most people say that
there are seven continents: Africa, Antarctica, Asia, Australia, Europe, North America,
and South America. However, in Europe and other parts of the world, many students
are taught there are six continents, because teachers consider North and
South America to be one single continent: America. Many scientists also agree that
there are six continents, but for different reasons: they combine Europe and Asia,
since they’re one solid geologic landmass. Thus, these six continents are Africa,
Antarctica, Australia, Eurasia, North America, and South America.
Is there a place where two continents almost touch?
There are several places in the world where the continents almost touch. Asia and
North America are only 56 miles (90 kilometers) apart at the Bering Straight
between the Pacific and Arctic Oceans. Africa and Europe are only 8 miles (12.8
kilometers) apart at the Straight of Gibraltar, the strait that connects the Atlantic
Ocean to the Mediterranean Sea and separates Spain from Morocco. Europe and
Asia are separated by about half a mile (0.80 kilometers) at the Bosporus Straight
in Turkey, where Istanbul’s Bosporus Bridge joins the two continents. In May 2005
tennis star Venus Williams played a show game on the bridge, making it the only
game of tennis to be played on two continents.
Did the continents always look like they do now?
No. About 200 million years ago, the continents started out as a single land mass, a
22 gigantic supercontinent called Pangaea (meaning “all the land” in Greek). The land
How is Earth like an onion?
Scientists often compare Earth to an onion because the planet is made up
of many layers of rocks of different densities. On the outside, there is a
think crust of hard, cold rock, which is about 4 miles (7 kilometers) thick
under the oceans and 22 miles (35 kilometers) thick under the continents. The
crust—the layer we live on—surrounds a hard, rocky surface that marks the
top of the mantle, called the lithosphere. Most of Earth is made of its mantle,
which goes almost halfway down to Earth’s center. At the very center is Earth’s
core, which has a center of solid iron and nickel about the size of the Moon
(called the inner core) and a molten exterior (called the outer core). The temperature
of Earth increases about 36 degrees Fahrenheit (2.2 degrees Celsius)
for every 0.62 miles (1 kilometer) down you go, reaching temperatures as high
as 11,000 degrees Fahrenheit (6,093 degrees Celsius) at its center.
tore apart from itself and formed two smaller supercontinents, called Laurasia and
Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the
continents were separating into landmasses that look like our modern-day continents.
These continents split because hot areas in Earth’s mantle below them
caused the crust to get thin, and start moving away from the hot areas. (This phenomenon
creates a new spreading ridge, and the continent becomes two smaller
continents.) Because the continents are constantly moving, in a billion years they
will look a lot different than they do today. For example, Australia is moving northward
toward Asia at a rate of about 5 centimeters per year—which is about the same
rate at which your fingernails grow!
Why does Earth look blue from outer space?
Earth looks blue from outer space because about two-thirds of the planet is covered
with water. In fact, Earth is called the “Blue Planet” for this reason. (In reality, the
oceans aren’t blue; they only appear that way because the water reflects the color of
the sky overhead—which also appears to us as blue, due to refraction of light.)
Is it true that parts of Earth are always covered in ice?
About one-tenth of Earth’s surface is always under the cover of ice. And almost 90
percent of that ice is found in the continent of Antarctica. The remaining 10 percent
is found on the mountains in the form of glaciers. The ice sheet that covers
Antarctica is almost one-and-a-half times the size of the United States.
Why did life develop on Earth and not on the other planets?
Earth is the only planet on which water can exist in liquid form on the surface.
Earth had the right temperature to allow water to circulate in all three states— 23
Our planet has seven continents: 1) North America, 2) South America, 3) Europe, 4) Asia, 5) Africa, 6) Australia, and 7)
Antarctica (not shown).
PLANET EARTH AND OUR MOON
solids, liquid, and water vapor—conditions that helped produce life. Scientists
believe that early life was primitive single-celled organisms that lived in the oceans.
The reason is simple: life needed a filter to protect it from the incoming ultraviolet
energy from the Sun, and the deep ocean waters gave life that protection.
Why do deserts have special plants and animals?
Deserts cover about one-fifth of Earth’s surface and occur where rainfall is less than
10 inches (25 centimeters) per year. Most deserts—such as the Sahara of North
Africa and the deserts of the southwestern U.S., Mexico, and Australia—occur at low
latitudes. Another kind of desert, cold deserts, formed in the basin area of Utah and
Nevada and in parts of western Asia. Most deserts grow a large amount of specialized
vegetation. Soils are rich in nutrients because they need only water to become
very productive and have little or no organic matter. Deserts often have the most
“weird weather,” such as occasional fires, cold weather, and sudden, intense rains
that cause flooding. There are relatively few large mammals in deserts because most
are not able to store sufficient water and withstand the heat, which often reaches
113 degrees Fahrenheit (45 degrees Celsius) in the summer months. Deserts provide
little shelter from the Sun for large animals. Mammals are usually small, like
the kangaroo rats of North American deserts. Other life that can be seen in the
desert includes insects and spiders, such as stinkbugs, ticks, and tarantulas; reptiles
such as snakes and lizards; and birds, such as hawks, owls, roadrunners, and woodpeckers,
who make their homes in cactuses.
Where are the world’s rain forests?
The name “rain forest” comes from the fact that these lush areas of land receive a
lot of rain—between 160 and 400 inches per year. They are located near the equator,
which means that their climate is warm. Rain forests cover only a small part of
Earth’s surface, about 6 percent, yet they are home to over half the species of plants
and animals in the world. For example, the jungles and mangrove swamps of Central
America contain many plants and animals found nowhere else, including many
types of parrots. The Amazon jungle in South America is the world’s largest tropical
rain forest, and is home to one-fifth of the world’s plants and animals. The forest
covers the basin of the Amazon, the world’s second longest river. Central Africa
has the world’s second largest rain forest. To the southeast, the large island of Madagascar
is home to many unique animals. The rain forests of Asia stretch from India
and Burma in the west to Malaysia and the islands of Java and Borneo in the east.
Bangladesh has the largest area of mangrove forests in the world. Australia, too, has
rain forests: undergrowth in this county’s tropical forests is dense and lush.
What is the Arctic tundra?
Known for its cold, desert-like conditions, Arctic tundra is located in the Northern
Hemisphere, encircling the North Pole. The stark landscape is frozen for most of
the year, and water is unavailable. Temperatures during the arctic winter can dip to
24 –60 Fahrenheit (–51 Celsius). In the summer the ground thaws for just a few weeks,
and the region’s plants and animals—which include geese, sea birds, polar bears,
caribou, and shrews—fight for survival. Because the tundra is not usually exposed
to human activity it is most susceptible to change and damage from human use or
pollution. Oil spills damage the plants, land, and animals that live along the coast.
THE MOON
What is the Moon?
The planets of our solar system orbit the Sun, held in their paths by the Sun’s gravitational
force. Other heavenly bodies in our solar system—called natural satellites
or moons—orbit the planets in a similar way. Some planets have many moons (Saturn
has 18!), but Earth has just one. Our Moon is an almost-round natural satellite
that consists of layers of different rock, similar in structure to Earth. It is believed
that both were created at the same time, when our solar system was formed. (Some
scientists think that the Moon broke off from Earth after our planet collided with
another.) Unlike Earth, however, the Moon has no water or atmosphere, so nothing
can live or grow on it. Without an atmosphere, nights (where the Moon is turned
away from the Sun) are fiercely cold, and days (where the Moon receives the Sun’s
full rays) are very hot.
The Moon is located about 240,000 miles (386,400 kilometers) from Earth,
close enough for astronauts to make a visit. The Moon’s diameter is about 2,160
miles (3,478 kilometers), roughly one-quarter that of Earth, and Earth has about 80
times more mass, or weight. The Moon does not shine on its own: the moonlight
that we see is simply sunlight reflected off its surface.
Is there a Man in the Moon?
There is no real Man in the Moon, but the
expression comes from the dark patches
on the Moon’s surfaces (the lunar maria,
or “seas”), which some people think look
like two eyes and a big smile. In the early
evening, when the Moon is nearly full,
you can most easily see the face. Some
cultures perceive different shapes, such
as the silhouette of a woman, a moose, a
buffalo, a hare, a frog, or a dragon in the
full Moon.
What are moonquakes?
Moonquakes are quakes that happen on
the Moon. Moonquakes are much less 25
Our Moon causes tides in our oceans and is the only place
outside of Earth that humans have actually visited. (NASA)
PLANET EARTH AND OUR MOON
common and weaker than earthquakes, but certain types can register up to 5.5 on
the Richter scale—which would damage buildings if they occurred on Earth. Vibration
from shallow moonquakes usually continues for more than ten minutes compared
to earthquakes which last around one or two minutes on Earth.
Does the Moon really have volcanoes?
Yes, the Moon has some volcanoes, but scientists classify them as “dead” volcanoes
because they have not erupted for millions, perhaps billions, of years. In fact, studies
based on rocks collected from the Moon’s surface during the Apollo missions
between 1969 and 1972 suggest that the bulk of the Moon’s volcanic activity
occurred around 3.9 billion years ago. Most of the deep craters on the Moon are
from the surface being hit by asteroids and comets at that time.
How does the Moon affect the ocean tides?
Without the Moon, Earth would have no ocean tides, or periodic rises and falls
in the level of the sea. Tides occur because the Moon exerts pull (or gravity) on
the ocean water, causing it to rise and fall on a regular schedule. The gravitational
pull of the Moon tugs on the surface of the ocean until its surface mounds
up and outward in the direction of the Moon. When the mound of water has
reached its highest point it is called high tide. On the side of the Earth opposite
the Moon, the centrifugal force caused by Earth’s rotation produces another
mound of water and high tide on the opposite side of the globe. Somewhere in
between these two high tides are two flat areas on the surface of the ocean,
which are low tides.
Why does the Moon follow us when we’re driving?
According to astronomers, the reason why the Moon seems to be following us is
because it is so far away. The Moon is about 240,000 miles (386,400 kilometers)
away from Earth. Because of this distance, the angle you view it from changes very
little as you drive down the highway. So mile after mile, the Moon remains in
roughly the same spot of sky. No matter how fast you drive, you just can’t “pass” it.
And just as you can’t pass the Moon, neither can you dodge the presence of the Sun,
26 planets, or stars.
How high could you jump on the Moon?
You could jump higher on the Moon than on Earth because your body
would weigh less. The Moon’s gravity is one-sixth of the gravity on Earth,
but you probably could not jump six times as high as you could on Earth
because you would be wearing a heavy, bulky spacesuit!
Why is Earth mostly crater-free compared to the pockmarked Moon?
Earth is more active, in terms of both geology and weather, which makes it hard for
craters to remain. Even those craters scientists can see on the surface—which may
be millions of years old—have been overgrown by vegetation, weathered by wind and
rain, and changed by earthquakes and landslides. The Moon, meanwhile, is geologically
quiet and has almost no weather, so its hundreds of thousands of craters are easy
to see. The craters are the result of both meteorites and volcanic activity. Interestingly,
some of the oldest Earth rocks might be awaiting discovery on the Moon, having
been blasted there billions of years ago by asteroid impacts that shook both worlds.
UP IN THE SKY
What is air made of?
Air is a mixture of gases that circle Earth, kept in place by gravity. Air makes up
Earth’s atmosphere. The air we breathe is 78 percent nitrogen gas, 21 percent oxygen,
0.9 percent argon, and 0.03 percent carbon dioxide, along with water vapor
(floating molecules of water). Also present are traces of other gases and tiny bits of
dust, pollen grains from plants, and other solid particles. As our atmosphere
extends higher and higher above Earth, toward outer space, air becomes thinner
and the combination of gases in the air changes.
Why is the ozone layer important to Earth?
Ozone, or three molecules of oxygen (03, compared with the O2 that humans breathe)
is a blanket in the atmosphere that covers Earth. The ozone layer is located between 9
and 25 miles (15 and 40 kilometers) up in the atmosphere, and it is produced by the
interaction of the Sun’s radiation with
certain air molecules. While this bluetinged
gas benefits the atmosphere, ozone
forms a layer of chemical smog at ground
level. The smog is a secondary pollutant
produced by the photochemical reactions
of certain air pollutants, which usually
come from cars and industrial activities.
The ozone layer is important to all
life on planet Earth because it protects all
living things from the effects of Sun’s
damaging ultraviolet radiation. Scientists
believe that, about 2 billion years ago,
oxygen was being produced by shallowwater
marine animals. This outgoing oxygen
helped produced the ozone layer. As
the oxygen levels increased, ocean ani- 27
This image taken by satellite shows the hole in the ozone
over Antarctica. The redder colors indicate low levels of
ozone. (National Oceanic and Atmospheric Administration)
PLANET EARTH AND OUR MOON
mals evolved. Once the protective layer was in place in the atmosphere, marine plants
and animals were able to safely spread onto land. The loss of ozone means some sensitive
organisms—necessary to Earth’s food chain—may be killed by exposure to intense
ultraviolet radiation from the Sun.
Is it true that at one time there was no oxygen?
Oxygen is necessary for all humans, animals, and plant life to survive. When Earth
was first formed, its atmosphere had no oxygen—the colorless, odorless and tasteless
gas that makes up about 20 percent of the air we breathe. It had only a deadly
combination of hydrogen, methane, ammonia, and hydrogen cyanide. The hydrogen
escaped into space and ultraviolet radiation from the Sun broke down the mixture,
leaving only nitrogen and carbon dioxide. Only when life began and photosynthesis
(the conversion of light energy into chemical energy by living organisms)
occurred did oxygen first appear—about 3.4 billion years ago.
Why is the sky blue?
The white light of the Sun consists of many wavelengths. When seen separately,
each wavelength corresponds with a different color. The air molecules and particles
of matter that make up our atmosphere scatter some of the Sun’s light as it travels
to Earth, especially the shorter wavelengths that give us the color blue. Coming to
us from all angles in the sky, these light waves make the sky appear blue.
How do we see the wind?
A big layer of air called the atmosphere surrounds Earth. The air within this layer
moves from place to place when it warms up or cools down. This moving air is called
wind. Winds move moisture and heat around the world and also produce much of
our weather. You can see wind—which sometimes moves slowly and is barely noticeable—
blowing through the trees. You can also sometimes feel wind as a gentle
breeze in your face and in your hair. At other times, the air can move very quickly
and become a hurricane, blowing down trees and damaging cars and buildings.
Where is the windiest place on Earth?
Antarctica is the coldest, highest, windiest, driest, and iciest continent on Earth.
Winds can reach up to 200 miles (322 kilometers) per hour for five hours per day!
CLOUDS AND STORMS
What are clouds made of?
Clouds are formed from billions of minute water droplets and tiny ice crystals that
float together in the air. Each of the droplets in a cloud is about 100 times smaller
28 than a raindrop. In general, low-level clouds, or those that are lower than 6,000 feet
(1,828 meters) above the ground, are mostly made of water droplets. However in
cold weather, they can also contain small snow and ice crystals. Mid-level clouds, or
those between 6,000 and 20,000 feet (1,828 and 6,096 meters), are composed of
water droplets during the summer months but have a high concentration of ice
crystals during winter. High-level clouds above 20,000 feet are largely made of ice
crystals. In addition to carrying water and ice crystals, many clouds contain small
quantities of solid particles such as smoke and dust.
How do clouds float?
Although the water and ice in clouds may typically weigh tons, the weight of a cloud
is spread out over a very large area. The cloud’s droplets are also very small—about
one-hundred-thousandth of an inch across. A cloud’s individual particles are so
small, in fact, that warm air rising from Earth’s surface is able to keep them floating
in the air.
Why do jet airplanes leave white trails in the sky?
Jets leave white trails, called contrails, in their paths for the same reason you can
sometimes see your breath on a cold winter morning. The hot, humid exhaust from jet
engines mixes with the atmosphere, which at a high altitude is of much lower vapor
pressure and temperature than the exhaust gas. The water vapor contained in the jet
exhaust condenses and may freeze, and this mixing process forms a cloud. Depending
how high the plane is flying, and the temperature and humidity of the atmosphere,
contrails may be thick or thin, long or short. The different types of jet contrails can be
used to predict the weather. For example, a thin, short-lived contrail indicates lowhumidity
air at high altitude, a sign of fair weather, whereas a thick, long-lasting contrail
reveals humid air at high altitudes and can be an early indicator of a storm.
Why are rain clouds gray?
Rain clouds are generally dark gray because light cannot penetrate them due to the
deep and densely packed water droplets and ice inside the cloud. Generally, the 29
Can it rain cats and dogs?
Although there are no records of cats and dogs falling from the sky, rain can
sometimes bring other things with it besides water, such as fish, snakes,
snails, worms, and frogs. The strong updrafts that bring heavy rain, called
waterspouts, suck up water along with creatures from ponds and lakes and
whirl them up into the air. Sometimes the waterspout will move over dry land;
when it starts to die out, the fish or amphibians fall to the ground. Some of the
early instances include a 10-minute shower of toads in Jout-en-Jous, near Versailles,
France, in June 1833, and a shower of jellyfish in Bath, England, in 1894.
PLANET EARTH AND OUR MOON
color of a cloud depends on the cloud’s relationship to the sunlight: Clouds appear
gray when they block sunlight. The thicker the cloud, the more light it blocks.
When a cloud is about 3,000 feet (914 meters) thick, hardly any sunlight will make
its way through the cloud.
What causes a rainbow?
A rainbow is an arc that shows all the colors, with their different wavelengths,
that make up visible light. Seven colors make up a rainbow, and they always
appear in the same order: red, with the longest wavelength, is on the top, followed
by orange, yellow, green, blue, indigo (a deep reddish-blue that is often difficult
to see), and violet, which has the shortest wavelength. A good way to remember
the order of those colors is by taking the first letter of each to spell “ROYGBIV,”
pronounced “roy-jee-biv.”
A rainbow occurs when sunlight passes through water droplets and is
refracted or bent by their rounded shape into separate wavelengths. Rainbows
can sometimes be spotted in the spray of lawn sprinklers, in the mist of waterfalls,
and—most spectacularly—in the sky during a rain shower when the Sun is
still shining. A rainbow appears in the part of the sky opposite the Sun. Because
the Sun must also be low in the sky, near the horizon, late afternoon is the best
time to look for a rainbow if the day has been sunny with a few short rain showers
or thunderstorms.
How thick is a lighting bolt?
In a large rain cloud, as water droplets bump into each other and increase in size,
they become electrically charged. This activity causes electric charges on the
ground, too. Sometimes the charges increase until they become so strong (up to
200 million volts!) that electricity runs through the air between the cloud and
the ground in the form of a giant spark or lightning bolt. The diameter of a lightning
bolt is about a 0.5 to 1 inch (1.3 to 2.5 centimeters) wide, but can be up to
5 inches (12.7 centimeters) wide. The average length of a lightning bolt from a
cloud to the ground is 3 to 4 miles (4.8 to 6.4 kilometers) long. Lightning can
occur not only in thunderstorms, but also in snowstorms, sand storms, and
above erupting volcanoes.
How far away is thunder and lightning?
As lightning flashes in the sky, it causes a thunderclap. Light from the flash travels
almost instantly to your eyes, but the sound of the thunder arrives a few seconds later.
If you count the seconds between the flash and the thunder, you can estimate the distance
of the flash of lightning: Every five seconds equals 1 mile (1.6 kilometers).
Where is the wettest place in the world?
Lloro, Colombia, in South America receives the most rain in any given year, about
30 523.6 inches (1,330 centimeters).
Where is the driest place in the world?
The driest place on Earth is the 15-million-year-old Atacama Desert in Northern
Chile. Made up of salt basins, sand, and lava flows, it is 50 times more arid than California’s
Death Valley. The average rainfall is just 1 millimeter per year!
Which snowstorm was the worst in U.S. history?
Called the “Storm of the Century,” the worst snowstorm in U.S. history occurred in
March 1993, when heavy snow blanketed most areas of the East Coast, with several
states seeing record snow falls. Every airport on the East Coast closed at some
point during the storm. At its height, the stormy blizzard stretched from Canada to
Central America, but its main impact was on the eastern United States and Cuba.
As much as 50 inches of snow fell in North Carolina and Tennessee, and $2 billion
in damages were attributed to the storm, and over 300 people died as a result. The
storm also spawned tornadoes, heavy wind gusts, and other severe weather. The
Great Blizzard of 1899, which occurred in the northeastern United States in February
of that year, is also considered among the worst. And the greatest snowfall in
one day happened between April 14 and 15, 1921, at Silver Lake, Colorado, where
more than 75 inches fell.
Why are hurricanes called monster storms?
A hurricane—from the Arawak Indian word huracán—is a massive storm in which
a vast system of dark clouds, heavy rains, and strong winds circle around a calm 31
Lightning can be beautiful, but also dangerous! Thousands of lightning bolts shoot through our atmosphere every day.
PLANET EARTH AND OUR MOON
center. It originates in the warm waters of the tropics, then lumbers slowly across
the world’s oceans (such as the Atlantic, the Gulf of Mexico, the Caribbean, and the
Western Pacific Ocean, where they are called typhoons), at speeds of 5 to 20 miles
(8 to 32 kilometers) per hour, spinning around a core of low atmospheric pressure.
Although the whole storm moves slowly, the circling winds in the storm blow at
speeds ranging from 75 miles per hour up to nearly 150 miles (121 to 241 kilometers)
per hour. During these “monster storms,” houses fly apart, leaves and branches
are ripped off of strong trees, plants are torn out of the ground, and flash floods
carry away anything not firmly rooted to the ground, including houses, animals,
and people. The central core of the storm—in some cases almost 15 miles (24 kilometers)
in diameter—is called the eye of the hurricane. In the North Atlantic, hurricane
season is from June 1 to November 3; in the East Pacific they are mostly just
tropical storms. Today, space satellites track the course of hurricanes so that early
warning can be given to those cities in the path of the storm.
Why are tornadoes so dangerous?
Tornadoes—violent, funnel-like storms of strong winds that usually form during thunderstorms—
present danger to anyone nearby. These “twisters” can demolish anything
in their path, including homes, people, cars, trees, animals, and even entire communities.
Sometimes lightweight mobile homes are flipped over. A strong tornado that
swept into Xenia, Ohio, on April 3, 1974, leveled a farmhouse and broke everything
inside, leaving only three fragile items totally intact: a mirror, a case of eggs, and a box
of Christmas ornaments! Occasionally, tornadoes do other strange things—like lifting
a 386-ton railway train off its tracks and dropping it 16 feet (5 meters) away!
In the United States, an average of 1,000 tornadoes spin up beneath thunderstorms
each year. A downward flow of cold air from clouds meets a rising flow of
warm air from the ground; if atmospheric conditions are just right, a tornado starts.
32 They occur mainly in a 10-state area known as Tornado Alley, stretching from Texas
Is it true that no two snowflakes are the same?
Yes. Snowflakes fall from the sky in an infinite variety of shapes, but no two
are exactly the same. Snowflakes are made of clusters of ice crystals and
most are six-sided (hexagonal). Rarer varieties with needle-like crystals (formed
at particularly low temperatures) and columns (formed at temperatures close to
freezing) are also found, but you would need a microscope to tell the difference.
More than 100 years ago, Wilson A. Bentley, an American farmer from the small
town of Jericho, Vermont, photographed snowflakes through a microscope. By
adapting a microscope to a bellows camera, he became the first person to photograph
a single snowflake in 1885. In his lifetime he photographed more than
5,000 snowflakes, earning him the moniker “The Snowflake Man.”
to Nebraska that also includes Colorado, Iowa, Illinois, Indiana, Missouri, and
Arkansas. Most weak tornadoes last less than 10 minutes and travel short distances.
Powerful tornadoes have been known to last for hours and a few have traveled more
than 100 miles (161 kilometers).
How far can a tornado lift and carry items?
The furthest distance a one-pound object can be carried is about 100 miles (161 kilometers).
In the Great Bend, Kansas, tornado of November 10, 1915, debris from the town
was carried 80 miles (128 kilometers). This included receipts, checks, photographs,
money, clothing, shingles, and pages of books, which fell on almost every farm north
and west of Glasco, 80 miles to the northeast. After passing through the town, the tornado
went through Cheyenne Bottoms, and 45,000 migrating ducks fell from the sky
25 miles (40 kilometers) northeast of the end of the tornado path. And after the Worcester,
Massachusetts tornado of 1953, chunks of soggy, frozen mattress fell into Boston
Harbor, 50 miles (80 kilometers) to the east of where the mattress was picked up.
HOT AND COLD DAYS
When were the hottest and coldest days of the year?
In the United States, the hottest day that we know of was July 10, 1913. On that day,
Death Valley, California, reached 134 degrees Fahrenheit (56 degrees Celsius). The 33
The United States is hit with more tornadoes than any other country. They are particularly bad in the Central Plains states,
such as Oklahoma and Kansas. (NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory)
PLANET EARTH AND OUR MOON
highest temperature in the world was recorded on September 13, 1922 in Al
Aziziyah, Libya, where it reached 136.4 degrees Fahrenheit (58 degrees Celsius).
The coldest temperature ever measured was –129 Fahrenheit (–89 Celsius) at Vostok,
Antarctica, on July 21, 1983. The world’s most extreme temperatures take place
in Verhoyansk, northeast Siberia, where temperatures fall as low as –90 degrees
Fahrenheit (–68 degrees Celsius) in winter and rise as high as 98 degrees Fahrenheit
(37 degrees Celsius) in summer.
What are “dog days”?
“Dog days” are the hot, humid days of summer that usually take place in the Northern
Hemisphere in July and August—typically between July 3 and August 11. The
days get their name from the dog star Sirius of the constellation Canis Major. At this
time of year, Sirius, the brightest visible star, rises in the east at the same time as
the Sun in the northern hemisphere. Ancient Egyptians believed that the heat of
this brilliant star added to the Sun’s heat to create this hot weather—and they
blamed the star for everything from withering droughts to sickness.
If I don’t have a thermometer handy, can I count cricket chirps to
calculate the temperature outside?
Yes! The current temperature can be estimated by using a simple mathematical calculation
involving counting the number of times a cricket chirps over a period of
time. Male crickets chirp (usually at night when it’s cooler) to attract female crickets
and to scare other males away from their territory. The chirping sound is made
by the male cricket rubbing together little teeth on its wings. The frequency of
chirping varies according to temperature. When the temperature rises, so does the
frequency of the cricket’s chirp. To get a rough estimate of the temperature in
degrees Fahrenheit, count the number of chirps in 15 seconds and then add 37. The
number you get will be an approximation of the outside temperature.
Who were Gabriel Fahrenheit and Anders Celsius?
Today’s thermometers are calibrated in standard temperature units of Fahrenheit or
34 Celsius, both named for early researchers. In the early 1700s, the German scientist
Was pond ice used as the first refrigerator?
In a way, yes. Before the invention of refrigeration machines in 1805, people
cut ice from ponds in winter and stored it in an icehouse. These icehouses
were pits dug into the ground and lined with wood or straw and packed with
snow and ice. They were covered with an insulated roof. Because cold air
sinks, the pit remained very cold, keeping foodstuffs cold and unspoiled until
the early summer months.
and engineer Gabriel Fahrenheit developed the alcohol and mercury thermometers
and in 1724 invented the first temperature scale. The zero-degrees point was based
on the lowest point to which the mercury fell during Germany’s cold winters. The
freezing point of water was 32 degrees Fahrenheit, the boiling point of water was
212 degrees Fahrenheit, and the human body temperature was defined as 96
degrees Fahrenheit. The Fahrenheit scale was widely used in the Europe, until
Alders Celsius, a Swedish astronomer, developed the Celsius temperature scale in
1742. His thermometer labeled 0 degrees for the freezing point of water, and 100
degrees for water’s boiling point. The Celsius temperature scale is also called the
“centigrade” scale; centigrade means “consisting of or divided into 100 degrees.”
How has the world’s climate changed over the years?
Over the past few million years, Earth’s climate has changed many times. In the last
million years, there have been four ice ages, or glacials, which occurred about every
100,000 years and were interspersed with shorter, warmer interglacials. During the
ice ages there was severe cold and large sections of ice spread across the land. The
average temperature of Earth was six to eight degrees Fahrenheit below today’s
averages. As the ice moved, it made hollows in the land, pushing soil and rocks
ahead of it. The sea level dropped and much of the water froze. After the ice ages,
the interglacial period brought warmer weather. The ice melted and the huge hollows
filled with water and became lakes. About 7,000 years ago the North American
and Scandinavian ice sheets melted, and as sea levels rose the coastlines of the continents
slowly took on their present shape. Scientists gather evidence about these
past climates by studying sediment samples from the beds of the oceans or ice samples
taken from Antarctica.
What was the Little Ice Age?
For about six hundred years, from 1250 to 1850, most parts of the world experienced
colder and harsher climates than usual. The cooler temperatures were caused by a
combination of less solar activity and large volcanic eruptions. Northern Europe’s
Little Ice Age took place between 1430 and 1850. When the climate became colder,
crops died, and there was widespread famine and disease. Although it was not a true
ice age because it did not get cold enough for long enough to cause ice sheets to
grow larger, England experienced some of the coldest winters in its history during
the 1820s. Its longest river, the River Thames, froze over regularly and townspeople
held Frost Fairs, during which they played games and danced on its icy surface.
BIG MOUNTAINS, DE E P HOLE S
How many kinds of rock does Earth have?
There are three different kinds of rock: sedimentary, igneous, and metamorphic,
and each type tells how the rock formed. Sedimentary rocks formed long ago in lay- 35
PLANET EARTH AND OUR MOON
ers, often along the bottom of the sea. They include conglomerate, sandstone, and
limestone. Igneous rocks formed from liquid rock like volcano lava, which cooled
and became solid. Basalt, granite, and obsidian are all igneous rocks. Metamorphic
rocks, such as marble and slate, formed from sedimentary or igneous rocks that
were changed by heat, friction, or other natural causes.
Can mountains grow and shrink?
Yes. Mount Everest, Earth’s highest summit, continues to rise. The 29,035-foothigh
(8,850-meter-high) mountain grows about 0.16 inch (0.41 centimeters) per
year. That’s because the Himalayas, the mountain range that includes Mount Everest,
was formed 50 million years ago when the Eurasian and Indian plates collided.
Today, the plates continue to press against each other, causing the mountains in the
range to rise. Other mountains shrink. For example, Mount St. Helens, a volcano in
Washington State, erupted on May 18, 1980. The mountaintop was blasted into volcanic
ash, shrinking the summit height from 9,677 feet (2,950 meters) to 8,364 feet
(2,550 meters).
What is an avalanche?
An avalanche is a huge mass of ice and snow that breaks away from the side of a
mountain and slides downward at great speed. Most avalanches result from weather
conditions, such as heavy winds and earth tremors, that cause snow on a moun-
36 tain slope to become unstable. A large avalanche in North America might release
U.S. presidents George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln are carved out of a mountain
in South Dakota’s impressive Mt. Rushmore.
300,000 cubic yards of snow—the equivalent of 20 football fields filled 10 feet (3.3
meters) deep with snow. Wintertime, particularly from December to April, is when
most avalanches occur.
Why is the Grand Canyon unique?
Located in Arizona and stretching to Colorado, the Grand Canyon is 18 miles (29
kilometers) wide, 227 miles (365 kilometers) long, and 6,000 feet (1,828 meters)
deep in its deepest section. It takes about two days by foot or mule to travel from
the top to the bottom. Although it is not the biggest canyon in the world—Barranca
de Cabre in northern Mexico and Hell’s Canyon in Idaho are deeper—it is known
for its amazing landscape. The canyon’s walls are made up of rocks, cliffs, hills, and
valleys formed millions of years ago, and it is home to hundreds of species of mammals,
reptiles, and birds. Although people lived in the canyon some 4,000 years ago,
today it is a national park and national landmark.
How are caves formed?
Water erosion creates most caves found along coastal areas. Waves crashing against
the rock over years and years wear down part of the rock, creating a cave. Inland
caves are also created by water erosion; groundwater erodes limestone, creating
underground passageways and caverns. Lechuguilla Cave, in Carlsbad Caverns
National Park, New Mexico, is the deepest cave in the United States. Unlike most
caves in which carbon dioxide mixes with rainwater to produce carbonic acid, these
caverns were shaped by sulfuric acid. The sulfuric acid was the result of a reaction
between oxygen that was dissolved in groundwater and hydrogen sulfide that came
from far below the cave’s surface. Since 1984, explorers have mapped 120-plus miles
(193-plus kilometers) of passages and recorded the depth of the cave as 1,604 feet
(489 meters), ranking Lechuguilla the fifth longest cave in the world. (The longest
cave in the world is Kentucky’s Mammoth Cave, which is almost 350 miles [560
kilometers] long!) 37
What is Mount Rushmore?
Carved into the southeast face of a mountain in South Dakota are the faces
of four presidents: George Washington, Thomas Jefferson, Theodore Roosevelt,
and Abraham Lincoln. Known as Mount Rushmore, these 68-feet (20.7
meters) high granite sculptures were the brainchild of South Dakota state historian
Doane Robinson. In 1923, he conceived the project to attract more people
to the Black Hills of South Dakota. Congress passed legislation that authorized
the carving in what is today known as Black Hills National Forest. In 1927,
the sculptor Gutzon Borglum and 400 workers began the project, using dynamite
to remove unwanted rock. Mount Rushmore was completed in 1941.
PLANET EARTH AND OUR MOON
Where is the deepest hole?
The deepest hole ever made by humans is in Kola Peninsula in Russia, where in
1989 geologists dug a hole 7.6 miles (12.2 kilometers) deep. The Kola Superdeep
Borehole began in the 1970s. Russian teams used special drilling techniques to dig
into the Baltic continental crust, presumed to be about 22 miles (35 kilometers)
thick, exposing rocks 2.7 billion years old at the bottom.
WATER, WATER EVERYWHERE
How much of Earth is covered with land and water?
Only 30 percent of Earth is covered by land, which includes all types of environment,
such as the desert, rain forest, and Arctic tundra. Far more of Earth, about
70 percent, is covered with water. Of this, more than 97 percent is salty seawater
from our oceans. All of Earth’s freshwater makes up the remaining 3 percent.
Freshwater includes water from the polar icecaps, lakes, rivers, and groundwater
(water from wells and aquifers).
Why is the ocean salty?
Today, about 3.5 percent of ocean water is salt. When planet Earth was still young,
its atmosphere contained a mix of hydrogen chloride, hydrogen bromide, and other
gasses from volcanoes. Oceanographers (scientists who study the ocean) believe
that some of these gases dissolved in the early ocean, making it salty. Today, however,
most of the salt in the oceans comes from rain. Rain falling on the land dissolves
the salts in eroding rocks, and these salts are carried down the rivers and out
to sea. The salts accumulate in the ocean as water evaporates to form clouds. The
oceans are getting saltier every day, but the rate of increase is so slow that it hard
to measure. If the oceans suddenly dried up, there would be enough salt to build a
180-mile- (290-kilometer) tall wall around the equator.
What is the difference between an ocean, a sea, a gulf, and a bay?
All four bodies of water are different in size and location. Oceans, rich in seawater,
are the largest bodies of water. There are four oceans: the Pacific, the Atlantic, the
Indian, and the Arctic. At the edges of the oceans are seas, a part of the ocean that
is partially enclosed by land. For example, the North Sea borders the Atlantic Ocean.
(Not every body of water with the word “sea” in it is a sea: the Caspian Sea, Dead
Sea, and Aral Sea are actually saltwater lakes because they lack an outlet to the
ocean.) Gulfs and bays are bodies of water that jut into the land; a gulf is larger,
sometimes has a narrow mouth, and is almost completely surrounded by land. The
world’s largest gulf is the Gulf of Mexico, with a total surface area of about 600,000
square miles (1.5 million square kilometers). It is surrounded by Mexico, the south-
38 ern coast of the United States, and Cuba, and contains many bays, such as Matagorhandy
da Bay in Texas and Mobile Bay in Alabama. The San Francisco Bay, off the coast of
northern California, is a well-known bay in the United States.
What is an iceberg?
An iceberg is a large block of floating ice. A majority of the icebergs in the North
Atlantic come from about 100 iceberg-producing glaciers along the Greenland
coast, and a few originate in the Eastern Canadian Arctic Islands. The glaciers of
western Greenland—where 90 percent of Newfoundland’s icebergs originate—are
among the fastest moving in the world, drifting up to 4.3 miles (7 kilometers) per
year. Although some Antarctic icebergs are more than 60 miles (100 kilometers)
long, they look a lot smaller because most of the iceberg floats underwater. This can
be dangerous to ships, whose navigators may underestimate the length or depth of
the iceberg.
What are coral reefs?
Tropical coral reefs are ridgelike or moundlike structures composed of corals and
other aquatic organisms. They border the shorelines of more than 100 countries.
Although coral reefs comprise less than 0.5 percent of the ocean floor, it is estimated
that more than 90 percent of marine species are directly or indirectly dependent
on them—they are home to approximately 4,000 species of fish alone. Reefs protect
human populations along coastlines from wave and storm damage by serving as
buffers between oceans and near-shore communities. The Great Barrier Reef, locat- 39
A diver watches butterfly fish swim in a coral reef. Coral reefs are like the rain forests of the oceans—beautiful and filled
with wildlife.
PLANET EARTH AND OUR MOON
ed in northeast Australia’s Coral Sea, measures 1,616 miles (2,000 kilometers) in
length. It the largest living structure on Earth, and can be seen from the Moon.
Do rivers ever dry up?
Some rivers have a lifetime of many thousands of years, but they eventually dry up.
As a river flows over land, the water wears away, or erodes, the rock of the riverbed.
Over time, the river levels out the land until it is flat, and then it stops flowing.
Rivers also need a steady source of water, such as from a mountain’s rainwater or
snowmelt, or from rainfall. Without it, they will dry up.
What is an estuary?
Estuaries are bodies of water along the beaches that are formed when freshwater
from rivers flows into and mixes with saltwater from the ocean. Tides may rise and
fall in the estuary, making this area a unique ecosystem rich in nutrients. Only certain
types of plants, such as saltwort, eelgrass, and saltgrass can grow there, and few
animals can live their entire lives there. However, mud shrimp, certain types of
mussels, and the Western sandpiper all call estuaries home.
VOLCANOE S AND EARTHQUAKE S
How do volcanoes erupt?
A volcano is a natural opening in Earth’s crust through which lava (hot molten, or
melted, rock), gases, steam, and ash escape, often in a big, noisy eruption or explosion.
These eruptions are thought to act like safety valves, relieving the enormous
heat and pressure that exist deep in Earth’s interior. A volcano is usually a coneshaped
mountain (its sides built up from solidified lava and ash) that has a hole or
crater in its center through which it vents. There are several different 40 kinds or stages
Why do planes disappear in the Bermuda Triangle?
The Bermuda Triangle is an area in the Atlantic Ocean bounded by imaginary
lines in the shape of a triangle that run from Bermuda down to Puerto Rico,
over to southeast Florida, and back up to Bermuda. Over the past century, hundreds
of ships and aircraft have either disappeared or crashed in this region. Scientists
believe there are many reasons why planes and ships disappear, including
strong and unpredictable tropical storms, hurricanes, compass or equipment
failure, lack of radios on board, and the structural weakness of the aircraft.
Other people believe that ships disappear because of other less scientific reasons—
such as unidentified flying objects (UFOs) that may have interfered.
of eruptions, many causing no damage
to the places or people located near the
volcano. But a few eruptions are huge
and destructive. During these, lava can
pour out and run down the volcano into
surrounding areas, and enormous suffocating
clouds of steam, ash, hot gases,
and shooting rock can travel downhill at
great speeds, covering many miles.
What is the Ring of Fire?
Many volcanoes occur near the area
where two ridges or plates of Earth’s
crust meet. Circling the Pacific
Ocean—where crust plates meet—is a
group of volcanoes known as the Ring of
Fire. Plate movement in such regions
may allow liquid rock, called magma
(it’s called “lava” only after it rises to the surface), that is located in chambers in
Earth’s interior to rise, resulting in volcanic activity. (Such conditions often result
in earthquakes as well.) Volcanic activity can take place under the ocean as well as
on land, and when this happens the formation of islands sometimes results.
How do earthquakes happen?
An earthquake is a great shaking of Earth’s surface. It is caused by the cracking and
shifting of the plates of rock that make up the planet’s layered crust. As shifting
plates suddenly slide past one another, vibrations in the form of waves are released.
These shock waves travel through Earth, gradually weakening as they move farther
from the spot (or spots) where the quake began, which is called the epicenter.
Regions located near faults (places where cracks in Earth’s crust are known to
exist), are particularly vulnerable to earthquakes. Earthquakes vary in size and
intensity. They may last a few seconds or continue for a few minutes. They may
cause no damage, or they can result in widespread destruction and the deaths of
thousands of people. Earthquake vibrations can be so violent that they collapse
bridges and buildings, destroy highways, cause landslides, and lead to flooding if
they occur in shallow water near a coast.
What are earthquake zones?
Scientists have learned that earthquakes occur in a number of definite zones,
mainly where there are deep trenches in the ocean bed with groups of islands nearby,
such as around the Pacific. In these zones, seismologists (people who study
earthquakes) try to guess whether stress is building up underneath the surface. If
the area has been dormant (quiet) for a long time, it may be that an earthquake is
about to happen. They also use seismometers to detect the tiny shock waves that 41
Volcanoes usually form in places where the Earth’s crust is
weakened, such as the places where plates of crust meet
along the Ring of Fire.
PLANET EARTH AND OUR MOON
occur right before an earthquake. It is estimated that there are 500,000 detectable
earthquakes in the world each year. Of these, 100,000 can be felt, and 100 of them
cause damage.
When is earthquake season?
There is no such thing as “earthquake season.” Earthquakes happen in cold weather,
hot weather, dry weather, and rainy weather. Weather, which takes place above
Earth’s surface, does not affect the forces several miles beneath the surface, where
earthquakes originate. The changes in air pressure that are related to the weather
are very small compared to the forces in Earth’s crust, and the effect of air pressure
does not reach beneath the soil.
What are icequakes?
The interior of Antarctica has icequakes which, although they are much smaller, are
more frequent than earthquakes in Antarctica. The icequakes are similar to earthquakes,
but occur within the ice sheet itself instead of the land underneath the ice.
Polar observers detect icequakes using South Pole seismometers, located 1,000 feet
(304 meters) beneath the surface of the 10,000-foot-tall (3,048-meter-tall) ice cap.
These seismometers measure and record the quietest vibrations of Earth.
What is a tsunami?
The Japanese word tsunami (pronounced soo-NAH-mee) means “harbor wave.” It is
a huge volume of moving seawater—kind of like a giant wave—that can travel for
thousands of miles across the sea and then approach the shoreline with the
strength to destroy buildings, trees, wildlife, and people. Tsunamis can be triggered
by an undersea earthquake, landslide, or volcanic eruption. The most frequent
tsunami-maker is an undersea earthquake, which buckles the seafloor and displaces
large volumes of seawater, creating a tsunami. This unique ocean event is not related
to tides, although it is sometimes mistakenly called a tidal wave.
GOING GRE EN
What is smog?
The word “smog” was first used in London during the early 1900s to describe the
combination of smoke and fog. Today, the term “smog” is used to describe a mixture
of pollutants, primarily made up of ground-level ozone. Ozone can be beneficial
or harmful depending on its location. The ozone located high above the surface
in the stratosphere protects human health and the environment, but ground-level
ozone is responsible for the choking, coughing, and stinging eyes associated with
smog. Smog-forming pollutants come from many sources, such as automobile
42 exhaust, power plants, factories, and many consumer products, including paints,
hair spray, charcoal starter fluid, solvents, and even plastic popcorn packaging. In
many American cities, at least half of the pollutants come from cars, buses, trucks,
and boats. Scientists estimate that about 90 million Americans live in areas with
ozone levels above the standards for health safety.
What is climate change, and how does it differ from global warming?
Climate change refers to any significant change in measures of climate (such as
temperature, precipitation, or wind) lasting for an extended period (decades or
longer). Global warming is an average increase in the temperature of the atmosphere
near Earth’s surface and in the troposphere, which can contribute to changes
in global climate patterns. Global warming and climate change can be caused by a
variety of factors, both natural and human-induced.
What is the greenhouse effect?
The greenhouse effect is a natural phenomenon that helps regulate Earth’s temperature.
Greenhouse gases—carbon dioxide, methane, nitrous oxide, chlorofluorocarbons—
act like an insulating blanket, trapping solar energy that would otherwise
escape into space. Without this natural “greenhouse effect,” temperatures would be
about 60 degrees Fahrenheit (15.5 degrees Celsius) lower than they are now, and
life as we know it today would not be possible. However, human activities, primarily
the burning of fossil fuels and clearing of forests, have enhanced the natural
greenhouse effect, causing Earth’s average temperature to rise.
When was the greenhouse effect discovered?
The greenhouse effect was first described in theoretical terms by a Swedish
researcher, Svante Arrhenius, in the late 1800s. However it wasn’t until the following
century that Arrhenius’s theory was observed. In the 1930s, scientists
realized that parts of the globe had warmed during the previous half-century.
Then in the early 1960s scientists discovered that the level of carbon dioxide in
the atmosphere was rising. Researchers began to take an interest and found a
strong relationship between the increasing levels of carbon dioxide and average
global temperature. 43
Why is smog bad for us?
Smog causes health problems such as difficulty breathing, asthma, reduced
resistance to lung infections and colds, and eye irritation. The ozone in
smog also inhibits plant growth and can cause widespread damage to crops and
forests, and the haze reduces visibility. The smog or haze is particularly noticeable
from mountains and other beautiful vistas, such those in national parks.
PLANET EARTH AND OUR MOON
Are human activities responsible for the warming climate?
Yes. Careful measurements have confirmed that greenhouse gas emissions are
increasing and that human activities (for example, the burning of fossil fuels and
changes in land use, such as cutting down forests) are the primary cause. Scientists
have confirmed that the recent increase in atmospheric greenhouse gas concentrations
is primarily due to human activity. Human activities have caused the atmospheric
concentrations of carbon dioxide and methane to be higher today than at any
point during the last 650,000 years. Scientists agree it is very likely that most of the
global average warming since the mid-twentieth century is due to human-induced
increases in greenhouse gases, rather than to natural causes.
When do I send greenhouse gases in the air, and how can I make
a difference?
You send greenhouse gases in the air during everyday activities, like every time you
watch television, use the air conditioner, play a video game, listen to a stereo, turn on
a light, use a hair dryer, wash or dry clothes, turn on the dishwasher, or microwave a
meal. The trash that we send to landfills produces a greenhouse gas called methane.
Methane is also produced by the animals we raise for dairy and meat products and
when we take coal out of the ground. And when factories make the things that we buy
and use everyday, they too are sending greenhouse gases into the air.
Whenever we use electricity, we help put greenhouse gases into the air. By turning
off lights, the television, and the computer when you are through with them,
you can help a lot. You can save energy by sometimes taking the bus, riding a bike,
or walking. Planting trees is a great way to reduce greenhouse gases. Trees absorb
carbon dioxide, a greenhouse gas, from the air. And you can recycle cans, bottles,
plastic bags, and newspapers. When you recycle, you send less trash to the landfill
and you help save natural resources, like trees, oil, and elements such as aluminum.
What is a carbon footprint?
A carbon footprint is a measure of the impact our activities have on the environment,
and in particular climate change. It relates to the amount of greenhouse
gases produced in our day-to-day lives through the burning of fossil fuels for elec-
44 tricity, heating, and transportation. The carbon footprint is a measurement of all
How much oil is there left in the world?
The world uses about 80 million barrels of oil per day to keep itself running.
Based on this figure, scientists estimate that there may only be enough oil
for another 100 years or so. Almost all of the world’s oil is found in the Middle
East, with Russia, Saudi Arabia, and Iran contributing the most oil to the world.
greenhouse gases we individually produce and has units of kilograms of the carbon
dioxide equivalent.
Do people still mine for gold in America?
Yes. Yet unlike a few centuries ago, gold panning today is primarily a recreational
activity. Gold nuggets are found in areas where lode deposits and erosion have
occurred—for example, in streams, rivers, ravines, and lake areas. All you need is a
gold pan, a shovel, and a lot of patience. Both gold mines and gold prospecting sites
exist in national parks from near Montgomery, Alabama to Washington, D.C. In
addition, North Carolina, South Carolina, Georgia, Virginia, and Alabama have
many gold mines and prospecting sites. These states were America’s main source of
gold for 45 years before the California Gold Rush of 1838, when gold was discovered
at Sutter’s Mill in Coloma, California. Its news spread like wildfire, resulting in
some 300,000 people coming to California to pan for gold. In California, the five
counties of Mariposa, Tuolumne, Calaveras, Amador, and El Dorado—nicknamed
the “Mother Lode”—still have gold for discovery. In 1837, the U.S. government
established gold coin mints in Georgia and North Carolina to avoid transporting the
raw gold to the U.S. Mint in Philadelphia, where coins are made.
How much garbage do we throw away every year?
Each year, Americans create nearly 210 million tons of solid waste. According to the
Environmental Protection Agency, the average American produces about 4.4 pounds
(2 kilograms) of garbage per day, or a total of 29 pounds (13 kilograms) per week and
1,600 pounds (726 kilograms) per year. With the garbage produced in America alone,
you could form a line of filled-up garbage trucks and reach the moon!
What does the slogan “Reduce, Reuse, and Recycle” mean?
You may have heard this expression
used in school, in television commercials,
or on a sign at your local parks
and recreation. Basically, the slogan
means that there are three key ways to
produce less waste:
1. Reduce the amount of trash (and
toxicity) you throw away.
2. Reuse containers and products
whenever possible.
3. Recycle as much as possible and buy
products with recycled content.
As much as 84 percent of all household
waste can be recycled—so it
makes sense to be conscious of what
we use and how we can reuse it. 45
People make lots and lots of garbage. Americans make more
garbage per person than anyone else. It all has to be put
somewhere, and most of it ends up in huge landfills.
PLANET EARTH AND OUR MOON
Why is it important to recycle?
Recycling turns materials that would otherwise become waste into valuable
resources. Collecting used bottles, cans, and newspapers and taking them to the
curb or to a collection facility is the first step in recycling. Recyclables are sent to a
materials recovery facility to be sorted and turned into other items for manufacturing.
Recyclables are bought and sold just like any other product. Besides reducing
greenhouse gases by sending less garbage to the landfill, recycling helps you actively
contribute the environment and your community.
You can help the environment if you buy recyclable products instead of nonrecyclable
ones. Look for the recycle mark—three arrows that make a circle—on
the package. Recyclable products are usually made out of things that already have
been used. It usually takes less energy to make recycled products than to make new
ones. In addition, many consumer products—like computers, TVs, stereos, and
VCRs—have special labels on them. The label says “Energy” and has a picture of a
star. Products with the ENERGY STAR® label are made to save energy and ultimately
help protect the environment. And, if you have the yard space, you can practice
composting by using microorganisms (mainly bacteria and fungi) to decompose
organic waste, such as food scraps and yard trimmings.
Why is it important to conserve water?
Water is vital to the survival of everything on the planet and is limited in supply.
Earth might seem like it has abundant water, but in fact only 1 percent is available
for human use. While the population and the demand on freshwater resources are
increasing (each person uses about 12,000 gallons of water every year), supply
remains the same. Water is constantly being cleaned and recycled through Earth’s
water cycle, yet we still need to conserve it because people use up Earth’s freshwater
faster than it can naturally be replenished. When you use water wisely, you help
the environment. You save water for fish and animals, help preserve drinking water
supplies, and ease the job of wastewater treatment plants—the less water you send
down the drain, the less work these plants have to do to make water clean again.
When you use water wisely, you also save the energy that your water supplier uses
to treat and move water to you, and the energy your family uses to heat your water.
Your family pays for the water you use, so if you use less water, you’ll have more
money left to spend on other things.
What is acid rain?
Acid rain is a problem that affects us all—whether it is damaging the family car,
defacing historical statues, harming trees in a once-beautiful mountainous forest,
or destroying the fish population in a lake. Acid rain is rain, fog, or snow from the
atmosphere that contains higher than normal amounts of nitric and sulfuric acids.
Acid rain comes from both natural sources, such as volcanoes and decaying vegetation,
and human-made sources, such as emissions of sulfur dioxide and nitrogen
46 oxides, which come from fossil fuel combustion. In the United States, most of these
emissions come from electric-power generation that relies on burning fossil fuels,
like coal. Acid rain occurs when these gases react in the atmosphere with water,
oxygen, and other chemicals to form acidic compounds. The result is a mild solution
of sulfuric acid and nitric acid. When sulfur dioxide and nitrogen oxides are
released from power plants and other sources, the wind blows these compounds
across state and national borders, sometimes over hundreds of miles.
Which country pollutes Earth the most?
The United States is the worst air polluter in the world, contributing about 25 percent
of the world’s carbon dioxide emissions (which result from burning gasoline,
oil, and coal). China is second in line, followed by Russia, Japan, Indonesia, and
India. Most of these country’s emissions result from industrial waste and automobile
emissions. Within the United States, Los Angeles is the most polluted city.
47
What is Earth Day?
Earth Day is a national holiday that was first celebrated on April 22, 1970. It
was created by Senator Gaylord Nelson, a Democrat from Wisconsin who
was elected to the U.S. Senate in 1962. Senator Nelson decided to set aside one
day aside for the entire nation to focus on environmental issues, learn about
ways to improve the environment, and protest against the federal government’s
unwillingness to help solve problems such as air pollution and the
widespread destruction of forests. After lots of hard work and publicity, on the
first Earth Day 20 million Americans gathered at different places from the East
to West coasts to hear speeches, participate in community-wide cleanup
efforts, and demonstrate to the government that the environment is a major
national issue. Ever since then, April 22 has been the date for celebrating Earth
Day—a time when the United States (and now many countries all over the
world) could participate in educational activities that celebrate Earth and
think of new ways to preserve our natural resources. On Earth Day 2008, over
100 million people joined in the effort to celebrate and protect our planet.
PLANET EARTH AND OUR MOON

DINOSAURS AND ANCI ENT LI FE
What are fossils?
A fossil is the hardened remains or an imprint of a plant or animal that lived a very
long time ago. Some fossils are thousands of years old, others are several hundred
million years old. Most plants and animals died and then decayed without ever leaving
a trace. But some were buried under mud, rocks, ice, or other heavy coverings
before decaying. The pressure of these layers over thousands of years turned animal
and plant remains into rock. Usually fossils preserve the organism’s hard parts: the
bones or shells of an animal and the seeds, stems, and leaf veins of plants.
Sometimes the fossil is the actual animal part, like a bone or tooth, that has
hardened into rock. Some fossils, called trace fossils, show the imprint of parts of
the animal or plant. Occasionally these imprints act as a mold, and the sediment
that fills the imprint hardens and becomes a cast of, for example, a dinosaur footprint.
Sometimes bones or trees are preserved by minerals that seep into the part’s
pores and then harden, or petrify, that part. Arizona’s Petrified Forest contains
numerous examples of giant trees that were petrified millions of years ago.
What were the first primitive plants to appear on land?
The first primitive plants appeared on land about 470 million years ago. But these
plants did not look like the lush greenery we see in the world today. Rather, they
were rootless patches of thin, leaflike plants called liverwarts, so named because
some species look like green livers. Liverwarts used a specialized filament (called a
rhizoid) to absorb water and stick to rocks. Fossils reveal that the first true plants
to colonize land appeared about 420 million years ago. These plants included flowerless
mosses, horsetails, and ferns. They reproduced by throwing out spores, or 49
CREATURES BIG
AND SMALL
minute organisms that carried the genetic blueprint for the plant. The ferns eventually
bore seeds, but not until about 345 million years ago. Plants with roots,
stems, and leaves (called vascular plants) evolved about 408 million years ago.
What were the first animals to appear in water and on land?
Fossils reveal that the first soft-bodied animals appeared about 600 million years
ago in the oceans, and included a form of jellyfish and segmented worms. The first
land animals to conquer the land may have been the arthropods, such as scorpions
and spiders. Many of these creatures have been found in the old rock layers, usually
with fossils of the oldest known vascular land plants. The first land animals
evolved around 440 million years ago and the dinosaurs evolved around 250 million
years ago. So, it took about 190 million years for dinosaurs to appear after the first
land animals. These numbers change as scientists discover new fossils.
Have scientists ever discovered an entire animal fossil?
Yes, in some cases, an entire animal is preserved in ice, hardened tree sap (called
amber), or in dry, desert areas. In these instances, as with woolly mammoths found in
Alaska, Siberia, and elsewhere, the whole animal—hair, skin, bones, internal organs—
is preserved much as it was when it died thousands of years earlier. During the last Ice
Age, there were many large mammals, including mammoths, saber-toothed cats, giant
ground sloths, woolly rhinos, and mastodons. These animals, which are now extinct,
are known mostly from fossils and frozen, mummified 50 carcasses.
Fossils aren’t actually bones, they are stones that formed out of the bones of dead animals or from plants. This is good news
for scientists who can learn a lot from uncovering fossils.
When did the woolly mammoths live?
Woolly mammoths lived from about 2 million years ago to 9,000 years ago, during
the last Ice Age (called the Pleistocene Epoch), and are now extinct. The Ice Age
took place millions of years after the dinosaurs became extinct. Mammoths were
elephant-like animals that were herbivores, or plant eaters. They ranged in size
from about 9 feet (2.7 meters) tall to more than 15 feet (4.5 meters) tall, and had
long, dense hair and underfur, large ears, a long nose, and long tusks. Both the
males and the females had tusks, which were really incisor teeth. Some species had
tusks that were straight, and others had tusks that were curved. Sometimes reaching
17 feet (5.2 meters) in length, the tusks were used in mating rituals, for protection
and self-defense, and for digging in the snow for food. Modern-day Indian elephants
are related to woolly mammoths.
When did the dinosaurs live?
Dinosaurs first appeared about 230 to 250 million years ago, during the Triassic
Period. Their large size and vast numbers meant that they dominated animal life on
Earth for millions of years. Dinosaurs became extinct around 65 million years ago,
at the end of the Cretaceous Period. Earth was much different when dinosaurs
roamed the planet. Several hundred million years ago, instead of there being seven
continents, or large land masses, there was just one giant mass of land that was surrounded
by ocean. This land mass gradually broke apart into separate continents.
Areas that are now covered with tall buildings or mountain ranges were once
beneath the sea, and scientists believe the climate was fairly warm throughout the
year. By the end of the era in which dinosaurs lived, temperatures had cooled and
distinct seasons had developed.
Which was the biggest dinosaur?
Information about dinosaurs changes all the time as new bones are found and new
evidence about their surroundings becomes available. The largest complete
dinosaur fossil found by paleontologists (scientists that study dinosaurs) was Bra- 51
Will animals and plants that die today become fossils?
Yes, if the conditions are right. Many organisms will decay quickly, as sunlight,
water, or air interacts with them. This is especially true if the
organisms do not have hard parts. If the organisms do have hard parts, those
that are quickly buried have the best chance of becoming fossils, as soil stops
much of the decay. Most of Earth’s future fossils will be from oceans, lakes,
and rivers because these are areas in which quick burial and fossilization will
most likely happen because dirt and other sediments quickly pile up over dead
plants and animals in such places.
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chiosaurus (meaning “arm lizard”), a huge dinosaur that lived during the Jurassic
Period. It weighed about 80 tons (72,640 kilograms) and reached 75.5 feet (23
meters) in length and 39 feet (12 meters) in height—about the length of two large
school buses and the height of a four-story building. Parts of leg bones and vertebrae
of even larger dinosaur species have been discovered, and scientists have studied
these parts to try and determine their exact size. Several of these—such as
Argentinosaurus and Amphicoelias—might have been one and a half to two times
larger than Brachiosaurus. The Argentinosaurus, thought to weigh as much as 100
tons (90,800 kilograms), was uncovered in the late 1990s in Argentina, which was
home to many of the world’s largest dinosaurs.
These gentle giants were once thought to live in watery, swampy regions, but
recent evidence suggests that most of them were forest dwellers that ate leaves from
the tops of trees. They had enormous bodies, very long necks, relatively small heads,
and thick, tree-trunk-like legs, much like an elephant’s legs. They moved very slowly
and did not have many ways to defend themselves, but their tremendous size kept
most predators away.
Which was the smallest dinosaur?
The smallest dinosaurs were just slightly larger than a chicken. Compsognathus
(meaning “pretty jaw”) was 3 feet (1 meter) long and probably weighed about 6.5
pounds (2.5 kilograms). At one time, scientists thought that Mussaurus (meaning
“mouse lizard”) was the smallest dinosaur, but it is now known to be the hatchling
of a dinosaur type that was much larger than Compsognathus when fully grown. If
birds are advanced dinosaurs, as some scientists believe, then the smallest dinosaur
would be the hummingbird!
What did dinosaurs eat?
Dinosaurs came in many different shapes and sizes, and they also had a variety of
diets. Most dinosaurs ate plants, with the very large dinosaurs eating leaves from
52 the tops of trees and smaller ones eating plants and bushes growing close to the
What does the word dinosaur mean?
The word dinosaur comes from the term dinosauria, which is a combination
of the Greek words deinos and sauros. Deinos means “terrible” and
sauros means “lizard” or reptile. Thus, dinosaur means “terrible lizard.” As
dinosaurs are discovered, scientists generally name them after a unique body
feature, after the place where the fossils of the dinosaur were found, or after
a person involved in the discovery. Usually the name is made up of two Greek
or Latin words, or combinations of the two. For example, the Greek and Latin
combination Tyrannosaurus rex means “king of the tyrant lizards.”
ground. Rocks that contain dinosaur bones also contain fossil pollen and spores
that indicate hundreds to thousands of types of plants existed during the Mesozoic
Era (70 million to 220 million years ago). Many of these plants had edible leaves,
including evergreen conifers (pine trees, redwoods, and their relatives), ferns,
mosses, horsetail rushes, cycads, ginkos, and—in the latter part of the dinosaur
age—flowering (fruiting) plants. Some dinosaurs were meat eaters, with most
hunting other animals for food and some being scavengers who ate the flesh of dead
animals they encountered. The hunters preyed on plant-eating dinosaurs and even
on each other. Smaller meat-eating dinosaurs fed on other animals, like insects,
lizards, and mammals. Evidence suggests that some dinosaurs hunted in packs,
while others lived solitary lives.
Would it hurt if a plant-eating dinosaur bit you?
Absolutely. Being bitten by a plant-eating dinosaur such as Brachiosaurus, with its
52 chisel-like teeth, would certainly hurt! The bite of a Parasaurolophus, with its
interlocking rows of teeth, might take off your fingers. In the Iguanodon, numerous
sharp teeth were set in rows in the upper and lower jaws, and at steep angles to each
other. When the teeth were pressed together, the upper jaw was forced outward, creating
a grinding motion between the teeth and its meal of crushed plant tissue.
What did dinosaurs use their teeth for?
Dinosaur teeth were used for chewing, cutting or slicing plants, or, in meat eaters,
tearing apart flesh. Dinosaurs had more teeth than humans do, and they would shed
their teeth throughout their life, much like sharks do today. For example, duckbilled
hadrosaurs (meaning “bulky lizards”) had hundreds of teeth waiting to
replace their worn-out teeth. Other dinosaurs, such as the ornithomimosaurs
(meaning “bird mimic”), had no teeth at all, but a beak similar to a bird. Some
dinosaurs also had a combination of a
beak and teeth.
Did all dinosaurs lay eggs?
As far as scientists can tell, all dinosaurs
nested and laid eggs. From these eggs,
their babies hatched. Hundreds of sites
with fossil eggs of different dinosaurs
have been found all over the world,
including in the United States, France,
Mongolia, China, Argentina, and India.
The largest dinosaur egg fossil found is
about 12 inches (30 centimeters) long
and 10 inches (25 centimeters) wide,
and may have weighed 15.5 pounds (7.0
kilograms). Scientists think the egg
came from a giant, 100-million-year-old 53
Dinosaurs were egg-laying animals, and they left behind
many fossilized eggs to prove it.
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dinosaur called a Hypselosaurus. This is more than twice the size of the eggs of the
modern African ostrich, which can lay eggs up to 6 inches (15 centimeters) long
and 5 inches (13 centimeters) wide. The smallest fossilized egg found so far came
from a Mussaurus; it measures about 1 inch (2.5 centimeters) long.
Did dinosaurs communicate?
Dinosaurs probably communicated both vocally and visually. Large meat eaters like
Tyrannosaurus rex, with its loud roar, or a Triceratops shaking his head, would have
made its intentions very clear. The chambered head crests on some dinosaurs such as
Corythosaurus and Parasaurolophus might have been used to amplify grunts or bellows.
Mating and courtship behavior and territory fights probably involved both vocal
and visual communication. Scientists believe that the sounds created by dinosaurs
like Parasaurolophus were so individual that each had a slightly different tone. They
also believe that these dinosaurs had different calls, ranging from low rumbles to
high-pitched notes, which they used for different situations.
Were dinosaurs warm-blooded?
Scientists have conflicting opinions about whether dinosaurs were warm-blooded
or cold-blooded. Some paleontologists think that all dinosaurs were “warm-blooded”
in the same way that modern birds and mammals are, with a high rate of metabolism
(body chemistry). Some scientists think they were “cold-blooded,” much like
modern reptiles. Some scientists think that very big dinosaurs could have had warm
bodies because of their large body size, just as some sea turtles do today. It may be
that some dinosaurs were warm-blooded—the problem is that it is hard to find evidence
that shows with certainty what dinosaur metabolisms were like.
An understanding of dinosaur metabolism helps paleontologists understand the
behavior of dinosaurs. If they were cold-blooded, they were most probably sluggish,
with only occasional bursts of quickness. In addition, they probably would not have
been very smart creatures. Like modern crocodiles, they probably spent most of
their time basking in the sun, moving only to get more food. On the other hand, if
dinosaurs were warm-blooded, then they were probably active, social animals. They
would have been quick, alert, and intelligent. They would have spent much of their
54 time actively grazing, like the modern antelope, or hunting in packs, like the lion.
Did dinosaurs get sunburned?
It was very hot and humid during the time of the dinosaurs, especially during
the Mesozoic Era, so there may have been a lot of sunshine. But it’s
doubtful that a dinosaur would get sunburned. Fossils show that most
dinosaur skin was thick, tough, and scaly—similar to that of modern reptiles
like turtles and crocodiles.
Which dinosaur was the fastest?
Based on the trackways (stride lengths)
found, it is difficult to name the fastest
dinosaur. But scientists guess that the
speediest dinosaurs were probably the
small, two-legged, meat eaters, especially
those with long, slim hindquarters
and light bodies. These swift dinosaurs
probably didn’t run any faster than the
fastest modern land animals. One carnivorous
dinosaur called Ornithomimus
is thought to have run about 43 miles
(70 kilometer) per hour—about the
speed of a modern African ostrich.
What other types of animals lived
at the time of the dinosaurs?
During the Triassic Period, a lot of
plants and animals existed along with
the dinosaurs. There were all types of
animals (except birds)—crocodiles, turtles,
lizard relatives, giant amphibians,
and the first mammals. In the oceans,
there were many types of reptiles,
sharks, and fish, including ichthyosaurs, predatory sea reptiles that ate shellfish,
fish, and other marine reptiles. They looked similar to, and probably had some of
the same habits of modern dolphins, whales, and sharks. Some animals were closely
related to the land-dwelling dinosaurs, like the flying pterosaurs. These creatures
were all different sizes—some skimmed the surface of the water while others flew
like birds. At the beginning of the Jurassic period, dinosaurs began to dominate the
land. But there were still plenty of salamanders, frogs, turtles, lizards, small mammals,
and ancient crocodiles, the crocodilians. During the Cretaceous period, many
crocodiles became massive, including the Deinosuchus, a large land creature that
reached 50 feet (15 meters) in length. By this time there were also snakes, birds,
winged insects, and mammals.
Why did dinosaurs become extinct?
Scientists do not know for sure why dinosaurs became extinct. They have many
different theories, some of which explain the extinction as something that happened
gradually over a long period of time. Other theories suggest that a single
catastrophe, such as fallen asteroid from outer space, caused the dinosaur population
to die off rather suddenly. And some scientists believe the dinosaur population
had been gradually getting smaller and then was finished off by some dramatic
event. 55
What if dinosaurs had never become extinct and lived with
us today? Extinction can actually provide an opportunity for
other types of animals to evolve.
CREATURES BIG AND SMALL
Those who believe gradual changes brought about the dinosaurs’ end suggest
that, as more and more mammals appeared, the dinosaurs had trouble competing
with them for food sources. And these mammals may have eaten dinosaur eggs in
such large numbers that fewer and fewer baby dinosaurs were born. Some experts
believe that widespread disease killed off dinosaurs. Many suggest that gradual climate
changes—from continuously warm, mild weather to seasonal variations with
hot summers and cold winters—affected the dinosaurs. Scientists are not sure
whether dinosaurs were warm-blooded or cold-blooded (and there may have been
some of each). If they were cold-blooded, meaning that their body temperature
changed depending on the temperature of their surroundings, it would have been
difficult for such large animals to survive extreme temperatures. Smaller coldblooded
creatures can burrow under the ground, for example, to escape both heat
and cold. But most dinosaurs were simply too large to do that.
The scientists who believe that dinosaurs became extinct after a major catastrophe
point to evidence that suggests a huge asteroid, perhaps several miles wide, hit
Earth. The impact of such an object would have created enormous clouds of dust
and other debris. The heat of impact would have started fires over a great area.
Between the dust clouds and the smoke from the fires, sunlight would have been
blocked, maybe for several months. A lack of sunlight would have caused a dramatic
drop in temperature, and much plant life would have died. Without plants, the
plant-eating dinosaurs and many other animals would have died; without the planteating
dinosaurs and those other animals, the meat-eating dinosaurs would eventually
die as well.
Will the dinosaurs ever come back?
When the dinosaurs became extinct, the world’s environment was already changing.
It was stressed by natural events, such as falling sea levels and volcanic eruptions,
leading to the decline and disappearance of many plants and animals. Our
modern world has continued to create many environmental changes and stresses—
most man-made, including pollution and global warming—and our fragile ecosystem
could not support the return of dinosaurs. (Imagine a large dinosaur roaming
New York City!) However, some scientists argue that not all dinosaurs became
extinct. The striking similarities between modern birds and some kinds of
dinosaurs have led some people to believe that birds are living descendants of
dinosaurs. Although not all dinosaurs were similar to modern birds, some did have
features such as bony tails, claws on the fingers, beaks, and feathers.
AMAZING ANIMALS
How many different kinds of animals are there?
Experts estimate that more than 100 million different kinds of animals have been
56 identified in the world. There may be millions more, particularly insect species, that
have not yet been identified or discovered by scientists. Hundreds of years ago scientists
began dividing the animal kingdom into categories based on certain characteristics
like body type, ways of reproducing, and what the animals can do (fly, swim,
walk on two legs, and so on). The animal kingdom, and every other kingdom as well,
is divided and subdivided into numerous other categories.
What is a mammal?
Mammals are a class of animal. They have certain traits that distinguish them from
animals in other classes, such as fish, reptiles, and amphibians. All mammals share
two characteristics: they all feed their young with mammary gland milk, and they all
have hair. Almost all of them are warm-blooded, which means they try to keep the
inside of their bodies at a constant temperature. They do this by generating their own
heat when they are in a cooler environment, and by cooling themselves when they are
in a hotter environment. Unlike reptiles, who sit in the hot sun to regulate their body
temperature, mammals wake up and are ready to go! In general, mammals spend
much more time raising and training their young than other animals do. Some examples
of mammals include apes, bats, lions, mice, moose, aardvarks, beavers, elephants,
gorillas, pandas, hamsters, dogs, cats, horses, whales, and dolphins.
There are three types of mammals: placental mammals, monotremes, and marsupials.
Placental mammals are those whose young are born live and at a relatively
advanced stage. Before birth, the young are nourished through a placenta. Like the
human placenta, it is a specialized embryonic organ that is attached to the mother’s
uterus and delivers oxygen and nutrients to growing young. Most mammals are
placental mammals, including cats, dogs, and horses. The monotremes are egg-laying
mammals. These include the echidnas (spiny anteaters) and the duck-billed
platypus. Marsupials give birth to their young in an immature state, and most
female marsupials have pouches in which to carry and nurse their young. Some
marsupials include the koala, kangaroo, and the numbat. Some mammals, such as
cows, horses, and pandas, are plant
eaters—called herbivores. Others,
including tigers, lions, and whales, are
meat eaters—called carnivores. Other
mammals, including bears, eat a combination
of plants and meat.
Which mammals fly?
There is only one mammal that flies: the
bat. Most bats are nocturnal, which
means they sleep during the day and are
most active at dawn, dusk, or nighttime.
During the day, they sleep by hanging
upside down in groups called roots.
Most bats, called microbats, eat flying
insects, such as moths and flies, but A fruit bat, like all bats, is a large flying mammal, not a bird. 57
CREATURES BIG AND SMALL
others eat small mammals, like mice. Some insect-eating bats can land on the
ground and chase insects that live in leaf litter or dirt. One of these bats, the pallid
bat, feeds on scorpions and large centipedes. Others eat fish or live on cow’s blood.
The largest bats are megabats, which feed mostly on fruit.
How are bats able to see in the dark?
Bats, which are most active at night, have eyesight that ranges from very good to
very poor. However, they rely primarily on echolocation to “see” in the dark.
Echolocation is the transmission of sound waves to locate objects, including food,
and to detect obstacles in an animal’s path. These sound waves travel out away from
the bat and then bounce off objects and surfaces in the bat’s path, creating an echo.
The echo returns to the bat, giving it a sense about the object’s size, shape, direction,
and distance. This high-frequency ultrasound is higher than the range of
human hearing and usually comes from the bat’s mouth. A few species emit sounds
from their noses, freeing their mouths for eating at the same time.
Are there any poisonous mammals?
Venomous mammals produce venom, a poisonous chemical in their saliva. They use
their venom to kill prey or to defend themselves against predators. They include the
male duck-billed platypus, several species of shrews, and the solenodon, a nocturnal,
burrowing animal that looks like a large shrew. Venomous mammals are rare:
There are many more species of venomous reptiles such as snakes and amphibians.
There are no species of venomous birds, however some birds are poisonous to eat
or touch, such as the brightly colored pitohui and the ifrita. Both birds live in the
rain forests of New Guinea.
Which mammal is the fastest?
The cheetah can run as fast as 70 miles (110 kilometers) per hour, making it the
58 fastest mammal in the world. They accelerate from 0 to 45 miles (72 kilometers) per
What is special about the Galapagos Islands?
The Galapagos Islands are a group of 19 islands located in the Pacific Ocean
more than 620 miles (1,000 kilometers) off the coast of South America.
Located at the confluence of three ocean currents, they are home to thousands
of marine species. Ongoing seismic and volcanic activity reflects the
processes that formed the islands. These processes, along with the islands’
extreme isolation, led to the development of unique animal life, such as the
land iguana, the giant tortoise, and the many types of finch. The British naturalist
Charles Darwin was one of the first geologists to visit the islands in
1835. His research led to his theory of evolution by natural selection.
hour in just two seconds, reaching top speeds of about 70 miles per hour for up to
300 yards. Its body parts are built for speed: Large nostrils, lungs, liver, heart, and
adrenals give the cheetah an ability to respond to its environment and hunt down
prey. Its long, slender body is flexible and curls like a whip when it needs to make
huge bursts of acceleration—usually to hunt down a small antelope or escape the
jaws of a pack of hungry hyenas. Special paw pads and nonretractible claws provide
traction for sprinting.
The cheetah (which comes from the Indian name for “spotted one”) lives in the
open savannas of southwestern Asia and Africa, where it has lots of room to run,
roam, and hunt down its prey. Cheetah mothers spend much time teaching their
young how to hunt game. The mothers bring small, live antelopes—such as
gazelles or impalas—to the cubs and release them, so they can chase and catch
them. The cheetah usually hunts during daylight, preferring early morning or early
evening, but is also active on moonlit nights. They communicate by purring, hissing,
whining, and growling.
Which mammal is the slowest?
The sloth is the slowest mammal on Earth. It spends most of its time alone hanging
upside down from tree branches, where it eats shoots and leaves, sleeps (up to
15 hours per day!), mates, and gives birth. The sloth holds onto tree branches with
strong, curved claws that are on each of its four feet. It is a nocturnal creature that
moves about slowly, sometimes foraging for insects. Sloths have a short, flat head,
big eyes, a short snout, a short tail, long legs, and tiny ears. They live in Central and
South America.
Which animal is both the biggest mammal and the largest living creature
on Earth?
The blue whale, who swims all of the world’s oceans, in the largest mammal. The
largest blue whale cited was at least 110 feet (33.5 meters) long and weighed 209
tons (189,604 kilograms). The average length is about 82 feet (25 meters) for the
males, and 85 feet (26 meters) for the females. A newborn blue whale can weigh
anywhere from 2.5 to 4 tons (2,268 to 3,628 kilograms), and can reach 100 to 120
tons in adulthood. Whale calves drink 50 to 150 gallons of its mother’s milk per day,
adding about 8 pounds (3.6 kilograms) of weight per hour, or 200 pounds (90.7 kilograms)
per day. At about eight months of age, when the calf is weaned, it measures
close to 50 feet (15.2 meters) long and weighs about 25 tons (22,679 kilograms).
Blue whales do not have teeth. Instead, in their upper jaw they have rows of
hundreds of baleen plates—flat, flexible plates with frayed edges, arranged in two
parallel rows that look like combs of thick hair. The blue whale feeds on a small
shrimp-like animal called krill. Scientists believe that large marine mammals, like
whales and dolphins, have brains much like those of humans. They are able to communicate,
follow instructions, and adapt to new environments. Throughout history,
these gentle giants have been hunted for their baleen and blubber (fat), and are 59
CREATURES BIG AND SMALL
today considered an endangered species. Scientists believe there are about 4,000 or
so of them left in the world.
What is an endangered species?
There are many organizations in the United States and all over the world that study
and research plant and animal species, determining which ones may be headed for
extinction (when a species of plant or animal dies out completely). Any species in such
danger is described as “endangered.” Once a species is endangered, it becomes illegal
to hunt that animal or destroy its habitat. In 2008 the U.S. Fish and Wildlife Service,
the organization that maintains the nation’s list of endangered and threatened plants
and animals, listed more than 1,000 animals worldwide (“threatened” species are
those that might soon become endangered). The goal of such organizations is to help
a species recover to the point that it no longer needs to be listed as endangered.
Which mammal spends the most time sleeping?
The western European hedgehog—which likes to live in hedges—spends most of its
life asleep. It builds a nest of grass and leaves among tree roots or under a bush, and
spends about 18 hours a day there during summer months. It wakes up at night to
eat, sniffing out worms, insects, snails, and snakes for its evening meal. During the
winter months, it hibernates (sleeps all the time). When it sleeps or senses danger,
the hedgehog rolls into a tight, spiny ball for protection. Related creatures, including
sloths, armadillos, and opossums, sleep almost as long as the hedgehog—accumulating
up to 17 hours each day! Other animals that sleep a lot are the dormouse
(about 17 hours), koalas (about 15 hours), and all kinds of felines, including pet cats.
Which mammal is the smelliest?
If you have ever been to the zoo, you might think that some of the large animals,
like the elephant, are the smelliest. But this title goes to one of the smaller mammals,
the striped skunk. This black and white-striped creature sprays a foulsmelling,
musky fluid as a defense against predators. Most wild skunks spray only
when injured or attacked, as a defense mechanism. Their scent is composed of a
chemical composition that can be released from one or both of their anal glands,
located on both sides of their rectum. They can aim their glands at a target up to
15 feet (4.5 meters) away with great accuracy, but fortunately they tend to give a little
bit of advanced warning: to signal being angry or scared, they often stamp their
front feet, knead the ground like a cat, and hold their tail erect.
Why do camels have humps?
Camels are the only animals with humps. A camel’s hump is a giant mound of fat,
which can weigh as much as 80 pounds (35 kilograms). The hump allows a camel
to survive up to two weeks without food. Because camels typically live in the deserts
of Africa and the Middle East, where food can be scarce for long stretches, their
60 hump is key to their survival. When camels are born their humps are empty pockhandy
ets of flexible skin. As a camel grows and begins to form its fatty tissue reserves, the
humps begin to fill out and take shape.
The humps also come in handy for humans who have domesticated the camel.
For thousands of years, people have used these strong, resilient creatures for transportation
and for hauling goods. The two-hump, or Bactrian, camel was domesticated
sometime before 2500 B.C.E., probably in northern Iran, northeastern Afghan -
istan, and northern Pakistan. The one-hump, or Dromedary, camel was domesticated
sometime between 4000 and 2000 B.C.E. in Arabia.
Why do zebras have stripes?
Researchers believe a zebra’s stripes help camouflage the animal and protect it from
predators. The wavy black-and-white stripes of a zebra blend in with the wavy lines
of tall grass in its savanna surroundings. Although the zebra’s stripes are black and
white and the lines of the grass are yellow, brown, or green, the zebra is still able to
roam undetected. Why? Because the zebra’s main predator, the lion, is colorblind.
In fact, if a zebra is standing still among tall grass, a lion may overlook it completely.
Zebra stripes work even more efficiently in a herd. When individual zebras band
together, the pattern of each zebra’s stripes blends in with the stripes of the zebras
around it. This is confusing to the lion, who sees a large, moving, striped mass
instead of many individual zebras. The lion’s inability to distinguish zebras makes
it difficult for the lion to target and track its meal.
But while zebra stripes act as a defense mechanism for predators, individual
striping helps zebras recognize one another. Stripe patterns are like zebra finger- 61
When zebras are together in herds, their striped fur is very confusing to predatory lions.
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prints: Every zebra has a slightly different look, helping each member of the herd
distinguish one another. This helps human researchers and animal preservationists,
too, because unique stripe patterns help them track individual zebras in the wild.
Which African animal can eat up to half a ton of plants each day?
The wild African elephant, the biggest animal on land, can easily consume more
than 770 pounds (349 kilograms) of food each day. While that’s not technically half
a ton, or 1,000 pounds (453 kilograms), it’s pretty close to it! The average male
weighs 12,000 pounds (5443 kilograms), is 11 feet (3.3 meters) tall, and spends 16
hours of every day foraging for food in herds with up to 1,000 members. To find
food, these vegetarians must roam large areas of the forest and jungle, where grass,
shrubs, leaves, roots, bark, branches, fruit, and water plants are plentiful. Wild elephants
often devour bamboo, berries, coconuts, plums, and sugarcane. An elephant
uses its strong tusks (long, curved teeth) to tear bark off trees and to dig up roots
and shrubs. It then relies on its trunk—a combined nose and upper lip—as a “hand”
for picking up the food and passing it to its mouth.
Do bears really sleep through an entire winter?
No. Denning bears, such as brown and black bears, often retire to their caves for the
winter months, but they sleep lightly, and are often active, with females giving birth
to cubs during the winter. They don’t technically hibernate during these months.
Hibernation is when a species passes the winter in an inactive state, conserving
their resources and energy until winter passes. Bears are not true hibernators
because their body temperature drops only a few degrees and they show only a moderate
drop in their metabolism. Small animals with high metabolic rates such as
rodents, hummingbirds, and bats are true hibernators: their body temperature
drops almost to the level of the surroundings and they show little response to
nature’s sights and sounds. These animals collect and eat a lot of high-calorie foods
62 (such as nuts) to store calories to make it through the hibernation period.
Why don’t polar bears freeze in the icy Arctic waters?
In a polar bear’s Arctic home, winter temperatures can drop as low as –50
degrees Fahrenheit (–45 degrees Celsius). A polar bear spends the winter
living on sea ice, but the bear is so well insulated that it doesn’t freeze in these
extreme temperatures. A layer of fat more than four inches thick, a thick fur
coat, and special white hairs that absorb the heat of the Sun keep the polar
bear warm. During ice storms—when wind and blowing snow make travel
and hunting too difficult—the polar bear curls up and lets the snow cover it
completely. Although this stunt sounds chilling, it is warmer under the snow
than aboveground, where the animal is exposed to the freezing air.
Why are polar bears white?
The polar bear lives in the Arctic, the region of the North Pole. Most of its environment
is barren, covered year-round with ice and snow and not much else. A polar
bear might eat what few plants it can find, but it feeds mostly on water animals like
seals and small walruses, which share its frozen home. The polar bear’s yellowishwhite
coat helps it blend into its snowy surroundings as it hunts its prey. After all,
there is not much in the Arctic to hide behind! The fur of a polar bear is also
extremely thick, allowing it to withstand polar temperatures and swim in Arctic
waters, where its prey is often found. Polar bears are excellent swimmers, and their
unique paws—with hairy soles—allow them to run very quickly over ice and snow
without slipping.
Do bighorn sheep break their horns when they charge?
No. The wild bighorn sheep, which make their home in the Rocky Mountains from
southern Canada to Colorado, are known by the large heavy horns (weighing as
much as 31 pounds [14 kilograms]) that the males grow for sparring, or territorial
fighting. In the breeding season, they compete for females. Although the males
charge at one another with a series of running head-butts that can last several
hours, their skull is double-layered and designed to withstand these hard blows.
These sheep also have a broad, massive tendon that connects its skull and spine,
which helps the head pivot and recoil from blows.
Why is the walrus nicknamed “tooth walker”?
The walrus’s two tusks—which are really two long, sharp teeth—aid the cold-water
creature in battling polar bears, fending off other walruses, and walking around the
bottom of the ocean while searching for its favorite food, clams. The “tooth walker”
temporarily anchors itself to the bottom of the ocean by pushing its tusks into the
muddy sand, where it can look for food.
It then pulls its tusks out, moves on,
and repeats the process.
Is it true that a shark can smell a
drop of blood from a mile away?
No, but they can detect blood from very
far away. Sharks are carnivores (meat
eaters) known for their keen sense of
smell. Sharks have two nostrils through
which some species can detect odors up
to almost 300 feet (91 meters) away,
which is about the length of a football
field. Fourteen percent of the Great
White shark’s brain matter, for example,
is devoted to smell. Sharks zig-zag along 63
Walruses have huge tusks, long teeth that are useful for
defending their territory against polar bears and other
walruses.
CREATURES BIG AND SMALL
ocean currents, using their highly sensitive nostrils to find sources of odors and
food. Some species can smell one molecule of blood in over one million molecules
of water—which is equal to one drop of blood in 25 gallons (94 liters) of water. A
shark can also detect vibrations of passing prey with its “lateral line,” a row of sensors
along the side of its body.
How long is the giant anteater’s tongue?
Anteaters are slow-moving mammals with long snouts and claws and no teeth. If you
can image it, a giant anteater can grow a tongue up to 2 feet (0.60 meters) long! The
anteater uses its long tongue to investigate anthills in South America’s tropical dry
forests, rain forests, and savannas. It sticks its long, sticky tongue down the anthill,
twirls it around, and scoops up a mouthful of ants. Anteaters can eat mouthful after
mouthful of ants—up to 30,000 per day! It also eats termites and other insects.
BUG ZOO
How many different kinds of insects are there?
Insects are small creatures with three pairs of legs, a body with three main parts (a
head, thorax, and abdomen), and a tough shell-like outer covering, called an
exoskeleton. Insects are arthropods, which means they do not have a backbone.
Most have one or two pairs of wings and a pair of antennae. There are 900,000
known species of insects in the world, and entomologists (scientists who study
bugs) estimate that there are millions (perhaps up to 10 million!) more yet to be
discovered. Insects are everywhere—there are more bugs in 1 square mile (2.59
square kilometers) of rural land than there are human beings on the entire globe.
Insects are divided into 32 orders, or groups. The largest insect order is the beetles
(Coleoptera) with 125 different families and approximately 500,000 different
species. In fact, one out of every four animals on Earth is some type of beetle. In the
United States, there are some 73,000 species of insects: approximately 24,000 beetles,
19,500 flies, 17,500 ants, bees, and wasps, and 11,500 moths and butterflies.
64
Why are there so many insects?
Entomologists believe that there are so many insects for a few reasons.
Their exoskeleton provides protection, they are small, and most of them
can fly. These traits help them escape from enemies and travel to new environments.
Because they are so small they only need small amounts of food to
survive and can live in very small cracks and crevices. Insects have lived on
Earth a very long time. The oldest group of insects on Earth are the cockroaches,
which first appeared some 300 million years ago.
How do insects grow?
Insects grow through the process of metamorphosis, meaning that they undergo
change. Insect groups that undergo a complete metamorphosis include beetles,
moths, butterflies, sawflies, wasps, ants, bees, and flies. All these groups begin their
life cycle as an egg. The egg hatches into a larva—such as a caterpillar, grub, or
maggot—that feeds, molts (sheds its skin), and grows larger. The larva goes
through an inactive pupa stage—for example, it is wrapped up in a cocoon—and
emerges as an adult insect, such as a butterfly or beetle, that looks very different
from the larva it once was. Other insect groups do not go through a complete metamorphosis,
but rather experience gradual changes as they turn into adults. These
include scales, aphids, cicadas, leafhoppers, true bugs, grasshoppers, crickets, praying
mantises, cockroaches, earwigs, and dragonflies. Immature forms of these
insects are called nymphs. The nymphs grow and gradually change size, shedding
their skin along the way. After a final molt, the full adult form emerges.
Why do butterflies and other insects fly from flower to flower?
Butterflies and other insects fly from one plant to the next to feed on the sweet nectar—
and sometimes the pollen—located in the interior of flowers. The sugar in nectar
supplies insects with the energy they need, and pollen contains protein, fat, vitamins,
and minerals. In the process of feeding, many insects transfer pollen—which
sticks to their bodies—from one plant’s flower to another. Pollen, which is a fine
powdery grain from a flower’s male reproductive organ, must be transferred to the
female reproductive organ of a flower for fertilization to take place and seeds to form.
Why do insects have eyes with thousands of lenses?
Most adult insects, including bees and dragonflies, have two large compound eyes,
made up of separate, sometimes thousands, of lenses. They all point in different directions
to give the insect a very wide field
of vision. The lenses also help the insect
see movement, enabling it to react
quickly to seize its prey or escape danger.
You can witness this yourself as you try
to swat a fly in your home—it’s almost
impossible to catch a flying insect!
What do the spots on the wings of
butterflies and moths do?
The large round spots on the wings of
butterflies and moths, which look like
big round eyes, are a defense mechanism.
When a bird or other animal tries
to eat the insect, it opens its wings and
flies off. The wing movement reveals the 65
Flies and many other types of insects have compound eyes
with thousands of lenses, unlike human eyes, which only
have one lens.
CREATURES BIG AND SMALL
moth’s “eyes,” confusing the insect’s enemy by making it think it has attacked something
much bigger with eyes. The predator hesitates, and the insect is able to escape.
Do some insects use slaves to survive?
Yes. Ants are social insects that live in colonies, or underground chambers, which
may house as many as 500,000 individuals. Ant chambers are connected to each
other and to the surface of the earth by small tunnels. There are rooms for food
storage, rooms for mating, and nurseries for the young. A queen produces eggs to
supply new ants for the colony. The colony is built and maintained by legions of
worker ants, who carry tiny bits of dirt in their mandibles (a pair of appendages near
the insect’s mouth) and deposit them near the exit of the colony, forming an ant
hill. While most ant colonies are self-sufficient, Amazon ants, aggressive red ants
found in the western U.S., steal the larvae of other ants to keep as slaves. The slave
ants build homes for and feed the Amazon ants, who cannot do anything but fight.
They depend completely on their slaves for survival.
What is the largest insect on Earth?
That depends on what you mean by “large.” The longest insect is Pharnacia serritypes,
which lives in western Malaysia. These insects get to be 22 inches (56 centimeters)
long! They are related to the group of insects called walking sticks. Walking
sticks get their name from the fact that they do, indeed, look like sticks with
legs. The largest walking sticks can grow to up to 13 inches (33 centimeters) in
66 length. There are approximately 3,000 tropical species of walking sticks, and 10
There are over 3,000 kinds of tropical walking stick insects, some of which are among the largest insects on the planet.
species that live in North America. One species, Megaphasma dentricus, is the
longest insect in the United States, reaching 7 inches (17.7 centimeters) in length.
If you are talking about the heaviest insect, then take a look at the giant weta
(scientific name Deinacrida heteracantha), an endangered insect that can weigh up
to two and a half ounces (71 grams). These insects may look ferocious and scary
because of their size, but they are actually harmless. Another insect that is often
considered the biggest is the acteon beetle (Megasoma acteon) because it is very
bulky looking and can be as big as 3.5 inches (9 centimeters) long by 2 inches (5
centimeters) wide and 1.5 inches (4 centimeters) thick
Which insect is sometimes called a “vicious predator”?
The praying mantis, also called a praying mantid, is a large flesh-eating insect that
lives in warm areas of the world. Mantis species from Europe and China were introduced
to the northeastern United States about 75 years ago for use as pest exterminators
on farms and in gardens. These carnivorous insects—sometimes called
“vicious predators”—are among the few insects that can rotate their heads to look
over their shoulders, making them extremely effective hunters. They pose in a deceptively
humble posture when searching for food, as if their front legs are folded in
prayer. Mantises grab their victims with their raptorial front legs, which quickly
shoot out from their bodies. Mantises almost always start eating their catch while it
is alive, and they often start eating their victim’s neck to quickly end the struggle.
Praying mantises eat a variety of insects—other mantises, beetles, butterflies, crickets,
grasshoppers—and spiders. They also eat small tree frogs, lizards, mice, hummingbirds,
and other nesting birds. Because they keep down the populations of “bad
bugs” that threaten farms, they are highly useful to agricultural workers.
What’s the difference between an insect and a spider?
Many people think of spiders as insects, but actually they are classified in a separate
category. Spiders are part of a group called arachnids, which also includes mites,
ticks, and scorpions. Arachnids share many features with their arthropod cousins,
but they differ in that they do not have antennae. Also, spiders have eight legs
(insects have six), and their bodies are segmented into two parts (insects’ bodies
have three parts).
How long does it take a spider to spin its web?
Spiders spin their webs at different speeds, and no two spider webs are the same. It
takes about one hour for the average spider to construct an elaborate web of silk
thread, called an orb web. An orb web is a series of wheel-shaped, concentric outlines,
with spokes extending from a center. Many species of spiders weave orb webs,
which are most noticeable in the morning dew.
Like other webs, spiders use orb webs to capture insects for food. The orb web
is the most efficient type of spider web, since it covers the greatest area with the
least amount of silk. Pound for pound, spider silk is about five times stronger than 67
CREATURES BIG AND SMALL
steel and twice as strong as Kevlar. Spider silk also has the ability to stretch about
30 percent longer than its original length without breaking, making its threads very
resilient. Still, a spider usually spins a new orb web every day to help it keep its
stickiness and insect-trapping capability. Throughout the day, the spider makes frequent
repairs to damaged threads.
What do spiders do with their victims?
All spiders are predators. They do not eat plants, but only other living things, such
as insects, other spiders, and invertebrates (animals without backbones). When a
spider catches a bug in its web, it doesn’t chew it. Instead, the spider bites the insect
and injects its venom, which either paralyzes or kills its prey. Then the venom turns
the bug’s insides into liquid. While the venom is working, the spider wraps the bug
in silk. At that time, the spider may drink the liquid, or tie the little silk bundle to
its web to snack on later.
Do doctors ever use bugs for medical reasons?
As strange it may sound, both leeches and blowfly maggots are used occasionally in
the field of medicine. The U.S. federal government’s Food and Drug Administration
considers both bugs “approved medical devices,” the first live animals to be called
that name. Maggots are used to eat dead tissue, thus helping to kill bacteria, clean
open wounds, and stimulate healing. Leeches suck out excess blood from the body,
and their saliva contains a powerful blood thinner. About 5,000 clean, laboratorygrown
maggots are delivered to hospitals across the United States every week.
F I SH AND S EA CREATURE S
How can fish breathe underwater?
Living creatures need oxygen to survive, and fish are no exception. Human beings
68 use their lungs to take in oxygen, and fish breathe using their gills. A fish’s gills are
What is “ballooning”?
Spiders do not have wings and cannot, technically, fly. Several types of spiders,
however, can travel long distances through the air by a process called
ballooning. The spiders spin long strands of silk that are caught by the wind,
carrying the spiders along the currents. Spiders can travel far by this method
(as far as hundreds of miles), and in some cases they can “fly” as high as 2,600
feet (800 meters). One spider was even recorded at an altitude of 15,000 feet
(4,572 meters).
full of blood vessels that absorb the tiny particles of oxygen from the water. The fish
sucks the water in through its mouth and squirts it out through its gills; during this
process, the gills take the oxygen from the water into the blood vessels. A fish’s gills
are not constructed to take oxygen from the air, so they cannot breathe on dry land.
Are there certain fish that can live without water?
Yes, for a period of time. The mangrove killfish spends several months of every year
out of the water, living inside rotting branches and tree trunks. The 2-inch- (5-centimeter-)
long fish normally lives in muddy pools and the flooded burrows of crabs
in the mangrove swamps of Florida, Latin America, and the Caribbean. When their
pools of water dry up, they temporarily alter their gills to retain water and nutrients,
while they excrete nitrogen waste through their skin. These changes are
reversed as soon as they return to the water. The mangrove killfish is not the only
fish able to temporarily survive out of water. The walking catfish of Southeast Asia
has gills that allow it to breathe in air and in water. The giant mudskippers of
Southeast Asia breathe through their gills underwater and breathe air on land by
absorbing oxygen through their skin and the back of the mouth and throat.
Can a fish fly?
Flying fish, who live in the warm waters of the Atlantic and Pacific Oceans, can
spread and stiffen their large fins like wings and propel themselves into the air for
short distances. A flying fish can glide through the air for at least 30 seconds and
can reach a top speed of at least 40 miles (64 kilometers) per hour, produced by the
quick movement and vibration of its tail fin. The fish extends its “flight” by plunging
its vibrating tail into the water, thus adding momentum. Flying fish can be seen
gliding over waves when they are trying to escape their predators, such as albacore
or blue fish, or to escape collision with a boat.
Which undersea creatures are
known for making electricity?
Certain fish produce electricity to kill
their prey or to defend themselves. The
electric eel, a South American fish with
a long, wormlike body, can grow to a
length of 9 feet (2.75 meters) and weigh
nearly 50 pounds (22.7 kilograms). The
electric eel floats through slow-moving
water, searching for fish to eat. It
breathes air, which means it must come
to the surface every few minutes. The
electric eel has organs made up of electric
plates that run the length of its tail,
which makes up most of its body length.
This eel, which has no teeth, uses elec- 69
The unusual flying fish uses its long fins to actually soar out
of the water for hundreds of feet at a time!
CREATURES BIG AND SMALL
tric shocks to stun its prey, probably to protect its mouth from the struggling, spiny
fish it is trying to eat. The eel shocks the fish with several brief electrical charges,
temporarily paralyzing it so the eel can suck it into its stomach. The electrical charge
can be anywhere from 300 to 600 volts, enough of a shock to jolt a human being.
Electric rays have two special kidney-shaped organs that generate and store electricity
like a battery. A large Atlantic torpedo ray can produce a shock of about 220
volts, which it uses to stun its prey before eating it. In addition to stunning potential
prey and discouraging possible predators, the electric organs of electric rays may
be used to communicate with each other. Like the rays, the electric catfish of Africa
produces an electric shock of up to 400 volts, which it uses for self-defense and prey
capture. Mormyrids, which live in very muddy waters in West Africa, use electrical
signals as a form of radar, allowing them to travel safely and to find food.
Which fishes blow themselves up like balloons?
Porcupine fish and puffer fish look like normal fish most of the time. When they are
threatened by another fish or perceive danger, they swallow water and inflate their
bodies into a ball shape—up to five times their normal size. Predators see this and
are scared away, and the enlarged size makes it difficult for larger predators to eat
them. When the fish senses that there is no longer any danger, it slowly deflates.
Which fish makes a nursery out of bubbles?
Siamese fighting fish, which live in the muddy waters of Thailand and Cambodia in
Southeast Asia, have a special way of caring for their eggs. The males of the species
build a nest of bubbles among the plant leaves. To make the bubbles, the fish swims
to the surface of the water, takes air in its mouth, coats it with saliva, and spits out
the bubbles, which stick together on the surface of the water. After the female hatches
her eggs, the male catches them in his mouth and spits them into the bubble nest.
The male also guards the nest and protects the eggs from being eaten by other fish.
Is it true that a salmon will always return to its birthplace?
Yes, the salmon is most famous for its life cycle. It is born in tiny streams far from the
sea, where it spends the first part of its life in freshwater. In the springtime, it
migrates down streams to rivers, sometimes traveling hundreds of miles, until it ends
up in the open ocean, where it spends much of its adult life. Then, when it’s time to
lay its eggs, the salmon makes the journey back to its birthplace to spawn and die. The
salmon’s body is rich in oils that are picked up during its life in the ocean. The oil
helps give the salmon the energy it needs to navigate the journey upriver.
Which animals live inside empty seashells?
Unlike other crabs, hermit crabs have soft exoskeletons (outer coverings). Their delicate
bodies need protection from the harsh elements of undersea life, as well as a
place to hide from predators. In order to survive, they crawl into abandoned
70 seashells. The crab’s flexible body allows it to twist and turn into a curved shell,
leaving only its claws exposed. A hermit
crab will carry the shell on its back as it
moves along the ocean floor. When it
outgrows its home, it moves on to a
larger shell.
Is coral a plant or an animal?
Both. Coral is made up of two living
organisms, an animal and a plant that
lives inside of the animal. The animal
portion is a simple creature called a
polyp, a miniature sea anemone that
looks a little like a flower. Single cells of
algae live inside the cells of the polyp.
The polyp needs the algae to provide
energy and recycle nutrients. Like most
animals, coral has a skeleton, but unlike
mammals and fish, its skeleton is formed
by the outer skin and is external to the
polyp. This “exoskeleton” is made up of
limestone, a hard, white chalky material
that acts as the animal’s protective covering
and gives coral its unique shape. The
polyps build massive, intricate structures
called coral reefs, which can be found in
warm waters of more than 100 countries.
Which male sea creature keeps its young in a pouch?
The male seahorse takes care of the female’s fertilized eggs in a pouch on the front
of his abdomen, which works much like the womb of a female mammal. The female
seahorse deposits 100 or more eggs into the male’s pouch. The male releases sperm
into the pouch, fertilizing the eggs. The fertilized eggs grow in the wall of the pouch
and are coated in a fluid that provides nutrients and oxygen. After two to six weeks
(depending upon the species), the eggs hatch and the male seahorse gives birth to
live offspring as tiny as 0.04 inches (1 centimeter) long—the only male in the animal
kingdom to do so.
What is the difference between a porpoise and a dolphin?
At first glance, it’s hard to tell a porpoise and a dolphin apart from one another.
Both are fascinating undersea creatures, both are carnivores, and both belong to
the same scientific group: Cetacea. However, there are slight physical differences
between the two: Porpoises tend to be smaller than dolphins and do not have pronounced
beaks. Dolphins have cone-shaped teeth, while porpoises have spadeshaped
teeth. Dolphins usually have a hooked or curved dorsal fin, and porpoises 71
Seahorses are fish that really do look like horses! They are
also unique because the male seahorse raises its babies in a
pouch until they are ready to swim free.
CREATURES BIG AND SMALL
usually have a triangle-shaped dorsal fin. (Some have no dorsal fin at all.) There are
over 30 species of true dolphins, including familiar species like the bottlenose, spinner,
and spotted dolphins.
RE PTI LE S AND AMPHIBIANS
Why does a lizard need to lie in the sunshine to get energy?
The lizard is a reptile, a cold-blooded animal that is unable to internally control its own
body temperature. In order to warm up or cool down, lizards and other reptiles—such
as snakes, turtles, and crocodiles—move to different areas of their environment. They
also use certain other behavioral traits to keep their body temperatures constant. For
instance, if a lizard is starting to feel the intensity of the tropical sun, it might head
into the shade or take a dip in a pool of water. The same lizard might also bask in the
sun to warm up. Frilled dragons and collared lizards run on their hind legs in the heat
of the day, making an artificial breeze to help cool themselves off. And another reptile,
the crocodile, holds its jaws open to cool down on hot days. The blood vessels in its
mouth are close to the skin surface, and help transfer heat. Lying quietly is another
technique the crocodile uses to warm its body and help digest its food. Because they
are cold-blooded, reptiles can survive on much less food, compared to warm-blooded
small mammals and birds, which burn much of their food to keep warm.
How do lizards and snakes smell?
Lizards and snakes smell by licking the air with their tongues. The tongue picks up
scents in the form of airborne molecules that the animal then draws back into its
mouth. The forked tips of the tongue are inserted into two openings of a special
organ, called Jacobson’s organ, which identifies the molecules and passes it on to
the brain. Thanks to this unique organ, both lizards and snakes have a sharp sense
of smell, which they use to track prey and find potential mates.
Which snake builds a nest to care for its young?
Generally, snakes show little or no parental care. But a male and female King Cobra—
the world’s largest venomous snake—often cooperate to find a safe nesting spot for
their young. In April, the female builds her nest of dead leaves by scooping them up
with her large body. She then lays approximately 20 to 50 eggs, with an incubation
period ranging from 60 to 80 days. The female lies on her nest until just before the
eggs hatch, at which point instinct causes her to leave the young so she does not eat
them. The male king cobra guards the nesting area until the young hatch.
Why do snakes have scaly skin?
Snake bodies are covered with plates and scales, which help them move over hot
72 surfaces like tree bark, rocks, and desert sand. Rough belly scales help the snake
keep its grip on rough branches and push off of surfaces when it needs to move. The
scales are also waterproof, helping keep water away from the snake’s body. The
scales are made up of many layers of cells. The outer cells are dead and protect the
living ones underneath them. Several times each year a snake sheds a layer of its
dead skin, allowing a new layer to emerge. Before the skin peels, the snake is sluggish,
its colors become dull, and its eyes turn cloudy. When a snake is ready to shed
its old skin it rubs up against a rough surface, like a rock, to rip its skin. Then it
glides out. Snakes shed their skin so they can grow, as well as to remove parasites
along with their old skin.
Are crocodiles living dinosaurs?
Crocodilians—scaly, carnivorous reptiles that include crocodiles, alligators,
caimans, and gharials—are descendents of the archosaurs who lived on Earth with
the dinosaurs 200 years ago. Today’s modern crocodiles are semi-aquatic predators
that have remained relatively unchanged since the Triassic period. Besides birds,
they are the dinosaurs’ closest living relatives.
What is the difference between an alligator and a crocodile?
Alligators are slightly larger and more bulky than crocodiles. A wild alligator can
reach up to 13 feet (3.9 meters) in length, and weigh up to 600 pounds (272 kilograms).
Besides the two animals’ size difference, the easiest way to tell them apart 73
This is an American alligator. Alligators are different from crocodiles in several ways, but the easiest way to tell them apart is
their snouts. Alligators have wider snouts compared to a crocodile’s narrower, V-shaped snout.
CREATURES BIG AND SMALL
is by their snout. A crocodile has a very long, narrow, V-shaped snout, while the alligator
has a wider, U-shaped snout. The alligator’s wide snout delivers more crushing
power to eat prey like turtles, which make up a large part of the animal’s diet.
The crocodile’s upper and lower jaws are nearly the same width, so its teeth are
exposed all along the jaw line in an interlocking pattern, even when its mouth is
closed. An alligator, on the other hand, has a wider upper jaw, so when its mouth is
closed the teeth in the lower jaw fit into sockets of the upper jaw, hidden from view.
South Florida is the only known place in the world where crocodiles and alligators
live together in the same area.
What’s the difference between a lizard and a salamander?
Lizards and salamanders may look alike, but they are very different from one another.
Lizards are reptiles, and salamanders are amphibians. Both are cold-blooded animals
that use the environment to help regulate their body temperature. And both animals
are vertebrates, which means they have a backbone. An amphibian needs moist
conditions in which to live, has smooth and moist skin without scales, and stumpy
toes. Salamanders can be found under leaves in the forest, or under rocks in a stream.
Lizards have dry and scaly skin, have longer toes that can be used for climbing, and
live in a dry, hot environment. They can go long periods of time without water. Salamanders
lay eggs without shells, and must lay them in a moist environment. Many
salamander eggs need to be laid completely underwater, because when the larvae
hatch they soon develop gills and are dependent on water. These aquatic salamanders
go through metamorphosis—from tadpole to adult—just as frogs do. Lizard eggs
have shells and their nests are typically in the sand. Upon hatching, young lizards are
small versions of their parents and do not change or morph.
How do frogs make their loud croaking sound?
Frogs are able to make their croaking noises because they have simple vocal cords
that have two slits in the bottom of the mouth. These slits open into what is called
a vocal pouch. When air passes from the lungs through the vocal cords, a sound is
produced. The inflating and deflating vocal pouch makes the sound louder or quieter.
That sound changes depending on the kind of frog—there are as many different
kinds of croaks as there are frogs! Frogs croak for the same reasons that many
animals make noises: to track down and then select a mate, and to protect their territory
from other male frogs.
BIRDS
How do birds fly?
Birds have one major feature that distinguishes them from all other animals: feathers.
These strong but lightweight feathers, in combination with the structure of their
bodies, allow birds to fly with amazing skill and speed. Many birds 74 have hollow bones,
making their bodies very lightweight,
and the muscles that move their wings
are extremely powerful. Birds fly, basically,
by flapping their wings and using
their tails to steer. A bird’s wing is a very
complicated instrument that can be
adjusted in many different ways to control
the flight’s speed, angle, height, and
direction. The wider base of the wing
(the part closer to the bird’s body), gives
it support, while the tip of the wing propels
the bird forward. The way the bird’s
body is built, particularly the shape and
structure of the wing, determines the
way the bird flies. Some fly at high altitudes,
while others stay low to the
ground. Some fly quickly with small,
rapid wing movements, others flap their
wings slowly but powerfully.
Can all birds fly?
Most birds fly. They are only incapable
of flight during short periods while they
molt, or naturally shed their old feathers
for new ones. There are, however, several birds that do not fly, including the
African ostrich, the South American rhea, and the emu, kiwi, and cassowary of Australia.
The penguins of the Southern Hemisphere are also incapable of air flight.
They have feathers and insulation for breeding purposes, but use a different form of
motion: their sleek bodies “fly” through the ocean using flipper-like wings. All of
these flightless birds have wings, but over millions of years of evolution they have
lost the ability to fly, even though they probably descended from flying birds. These
species may have lost their ability to fly through the gradual disuse of their wings.
Perhaps they became isolated on oceanic islands and had no predators; therefore,
they had no need to fly and escape danger. Another possibility is that food became
plentiful, eliminating the need to fly long distances in search of food.
Why do birds fly south for the winter?
Birds migrate—or move regularly from one place to another—for several reasons,
including warmth and the availability of food and water. Many species of birds mate
and nest in specific areas of the world. Most of these areas are only comfortable during
the warmer months of the year, so when the cold weather arrives birds migrate
to warmer climates. These trips can be as long as thousands of miles. For example,
the American golden plover breeds north of Canada and Alaska during the Northern
Hemisphere’s spring and summer. In the Northern Hemisphere’s fall, the 75
Ostriches are the biggest bird on the planet. While they can
run very fast with their powerful legs, they cannot fly.
CREATURES BIG AND SMALL
plovers travel to southeastern South America to spend the “winter”—which is the
summer season in the Southern Hemisphere—allowing the birds to find plenty of
food. When spring arrives again in the Northern Hemisphere, the trip is reversed,
and the plovers migrate back to the northern nesting grounds to breed.
Why is a bird’s beak important?
Bird beaks, which vary greatly in size, form, and color, are important to the animal’s
survival. The beak is the “instrument” that a bird uses to gather and break apart
food. They also use their beak to clean themselves, itch, collect material for nesting,
and protect their territory. A strong, cone-shaped bill, used for cracking seeds,
is found in many birds such as finches and grosbeaks. Thin, slender, pointed beaks
are found mainly in insect eaters, such as the warbler. Woodpeckers have strong
beaks that form a chisel at the tip, which is used for pecking holes in trees for food
or nests. Hummingbirds have long, tubular bills that look like drinking straws,
which they use to sip nectar from flowers. Although these birds are all different,
they have one thing in common: without their beaks, they would not survive long.
How do birds replace their feathers?
Birds replace their feathers by molting, the periodic shedding of old feathers and
the growing of new ones. They do this one to three times each year, although different
birds molt at different times of the year. Male goldfinches, for example, molt
from a dull greenish yellow to bright yellow during spring. The periodic shedding
of feathers and their replacement with new ones makes perfect sense in the animal
kingdom. Feathers are incapable of further growth, and may get worn down, broken,
and faded over the year from normal wear-and-tear. Molting replaces these
damaged feathers and helps the males look attractive to females, which is why many
76 molts take place during the mating season.
The bald eagle’s head is covered with white feathers.
So why is it called the bald eagle?
Because one meaning of the word “bald” that is not commonly used anymore
refers to white markings. “Bald” used to refer to people with white
hair. Due to excessive hunting, environmental pollution, and loss of habitat,
the bald eagle population became dangerously low at one point, prompting
the U.S. Congress to pass a law protecting it. Bald eagles were once listed by
the U.S. Fish and Wildlife Service as an endangered species, meaning they
were close to being extinct. Thanks to the laws protecting it, these birds have
rebounded a bit. They are now listed as threatened, which means they are not
as close to being extinct as they once were, but their numbers are still few
(only about 50,000 in the United States), and it is illegal to hunt them.
Why do birds often crash into windows?
Birds don’t see the way mammals do, and a reflection in a window might look like
another bird. Most birds that are active during the day have eyes on either side of
their heads, which gives them a wide field of view but little depth perception. In the
springtime, many birds are territorial and when they establish territories they
become aggressive and chase off intruders. Unfortunately, they don’t distinguish
between their own reflection in a window (or car mirror) and they try to chase that
reflection off. People sometimes add awnings and window screens to eliminate the
reflection and stop birds from colliding into their homes or office buildings.
Although a bird can crash into glass at any time, the behavior is seen less often
when nesting season begins.
What do worms eat?
While some birds eat mostly insects, others, like penguins, eat seafood. Beach birds,
like seagulls, eat shellfish as well, but they are also scavengers that will eat discarded
people food. Some birds, such as ducks and geese, float on the water, dipping or
diving to nibble on plants from oceans, lakes, and rivers. Others, such as raptors,
swoop out of the sky to capture and eat small mammals, such as mice or rabbits.
Some birds also prey on each other, such as large predatory birds like eagles and
hawks. Many birds, like crows, jays, and magpies, eat the eggs and young of others.
Individual bird species eat the foods from their local environment, but they have also
developed physical characteristics that help them harvest food. Specific birds have
adapted to feasting on plants as well, including algae, lichen, grass, herbs, flower
nectar, leaves and buds of trees, ferns, acorns, nuts, corn, rice, and seeds of all kinds.
Which birds are called “birds of prey”?
Birds of prey, also known as raptors, are meat eaters that use their feet, instead of
their beak, to capture prey. They have exceptionally good vision, a sharp, hooked
beak, and powerful feet with curved, sharp talons. Birds of prey include falcons,
hawks, eagles, kites, osprey, and vultures. Most of these birds capture live prey,
including reptiles, insects, fish, birds, mammals, mollusks, and carrion (the dead
and decaying remains of an animal). In general, birds of prey feed on game that
average 12 to 50 percent of their own body weight; however, larger species will
catch prey their own weight or larger. For example, bald eagles have been seen carrying
mule deer fawns, which can weigh 15 to 20 pounds (6.8 to 9 kilograms).
Can an eagle see a mouse from two miles away?
Yes! The expression “eagle eyes” is taken from the golden eagle, whose incredible
eyesight allows it to see a rabbit or mouse from 2 miles (3.2 kilometers) away. For
comparison purposes, a human being could not see the same rabbit from one-quarter
of a mile (0.40 kilometers) away. As a bird of prey, an eagle has eyes that are
designed for clear vision in daylight, from early morning light to early evening. Its
pupil is not big enough for night vision. The bony ridge above the eagle’s eyes helps 77
CREATURES BIG AND SMALL
protect them from sunlight and assist in
effective hunting.
Why does a peacock spread
its tail?
The peacock is a male Indian peafowl.
An adult peacock has an average of 200
tail feathers, which are shed and
regrown each year. When it spreads its
long feathers above its tail, it makes a
large fan of glossy, bluish-green plumes
that have large eyespots. They are iridescent
and contain many intricate patterns.
This site attracts the female peahen,
and may encourage her to breed
with him. The decorative feathers are
also called display feathers, because the
male “displays” them as part of its mating
ritual.
How fast can a hummingbird fly?
Hummingbirds are very tiny birds,
about 4 inches (10 centimeters) long,
with long bills and tongues to sip nectar from tubular flowers. Because they are
light—they only weigh about one-tenth of an ounce—they are skilled air acrobats.
They can fly in every direction, even upside down, reaching speeds of up to 60 miles
(96.5 kilometers) per hour. To keep up its energy level, a hummingbird eats every
15 to 20 minutes and may visit up to 1,000 flowers per day.
78
Golden eagles are a type of bird of prey, also known as a
raptor, a word that means “hunting with the claw.”
PLANT BAS ICS
How are plants different from animals?
Plants and animals make up almost all of the living things in the world. They are
alike in a lot of ways. Both are made up of cells, tiny building blocks of life that produce
chemicals that control growth and activity. Often these cells become specialized
in a plant or animal, with different types of cells doing particular jobs. In addition,
both plants and animals use gases, water, and minerals to carry on life processes.
Both experience life cycles in which they are created, grow, reproduce, and die.
But plants are very different from animals in one big way: most do not move
around and thus cannot go and get food. Instead, plants are able to perform a special
process called photosynthesis. For this remarkable process, plants use energy
from sunlight, a gas in the air called carbon dioxide, and water and minerals from
soil to produce their own food. Animals cannot do this. They must look for food,
eating plants or other animals in order to get the energy they need to live.
How are plants and animals related?
The waste product produced by photosynthesis is oxygen, the gas that all animals
need to breathe. So without plant life, there would be no animal life on Earth. And
without plants around to absorb carbon dioxide, an excess amount of this gas would
linger in our atmosphere, trapping the Sun’s heat and causing an unwanted
increase in the planet’s average temperatures. Plants, then, are essential not only
because they provide so much of the food people eat (and provide nourishment for
many of the animals we eat), but because they make the air healthier, using up carbon
dioxide and releasing oxygen. In addition, we depend on plants to provide us 79
PLANT LIFE
with other things we need, like wood for building, fibers for making clothes, and
medicines to improve our health.
How do plants get their nutrients?
Green plants get nourishment through a chemical process called photosynthesis,
which uses sunlight, carbon dioxide, and water to make simple sugars. Those simple
sugars are then changed into starches, proteins, or fats, which give a plant all
the energy it needs to perform life processes and to grow.
Generally, sunlight (along with carbon dioxide) enters through the surface of a
plant’s leaves. The sunlight and carbon dioxide travel to special food-making cells
(palisade) deeper in the leaves. Each of these cells contain a green substance called
chlorophyll. Chlorophyll gives plants their green color and traps light energy, allowing
food making to take place. Also located in the middle layer of leaves are special
cells that make up a plant’s “transportation” systems. Tubelike bundles of cells called
xylem tissue carry water and minerals throughout a plant, from its roots to its outermost
leaves. Phloem cells, on the other hand, transport the plant’s food supply—
sugar dissolved in water—from its manufacturing site in leaves to all other cells.
How do plants grow?
Special cells in plants produce hormones, chemical messengers that tell different
plant cells to perform certain activities. Plant hormones are responsible for things
like fruit development, the death of flower petals and leaves, and, most importantly,
for growth. Cells in stem tips, new leaves, and buds, for instance, produce various
growth hormones that tell plant cells to multiply by division or to become larger.
The pattern of growth in plants is an important example of how they differ from animals.
While animals eventually become fully grown (and live for a long time after
that point), plants never stop growing throughout their life cycles. In other words,
there is no such thing as an adult plant that no longer grows but continues to live.
How many different types of plants are there?
Scientists have found and described more than 275,000 kinds of plants, but they
80 believe that many more are yet to be discovered. Plants vary greatly in size and
What is plant food from the nursery made of?
The plant food that we buy in garden stores and nurseries is simply a mixture
of minerals that plants need to grow well. These include nitrogen,
phosphorus, and potassium. Usually a plant is able to get these things from
the soil in which it grows, drawing them up with water through its roots. But
gardeners, farmers, and other plant growers add to this natural mineral supply
so plants can thrive.
appearance. Some, like single-celled algae, are so small that you can only see them
with the help of a microscope. Others, like giant sequoia trees, are so big that you
cannot even see the tops of them. Plants are very different from one another
because they have developed features—over millions of years—to help them live in
the world’s many different environments.
Who is called the “father of botany”?
Botany is the scientific study of plants. The ancient Greek Theophrastus (371–286
B.C.E.) is known as the father, or founder, of botany. He wrote two large books, On
the History of Plants and On the Causes of Plants. These books contained so much
information about plants that 1,800 years went by before any new discovery in
botany was made. Theophrastus was the first person to include the practice of agriculture
(growing plants for food) into botany. He also developed a theory of plant
growth and wrote about how plants were structured. He identified and described
550 different plants. Theophrastus spent most of his time in Athens, Greece, where
he was in charge of the first existing botanical garden.
Do all plants have leaves?
Most plants have leaves, even if they do not look like leaves. For example, blades of
grass are really leaves. Mushrooms and other fungi do not have leaves, and seaweeds
and lichens do not have leaves. Seaweed, a type of algae, also does not have flowers
or roots. As an underwater plant, it usually clings to stones, shells, and rocks with
its holdfast, a part of the plant that looks like roots. Unlike other plants that feed
through their roots, seaweed takes its nutrients from the water in which it grows.
How are a water lily’s leaves different?
A water lily is a floating aquatic plant with large, fragrant, white or pink flowers and
flat, round, floating leaves. The leaves have long stems and are bright green above
and reddish or purplish underneath.
The underside of the leaf contains air
spaces; the air that traps beneath the
leaf makes it float on water. The leaves’
strong stems help them grow and stay
upright in the water—which allows the
leaves to absorb sunlight and stay alive.
Do all plants have flowers?
No. Although most of the world’s plants
are flowering plants called angiosperms
(from the Greek words for “vessel” and
“seed”), there are hundreds of plants that
do not make flowers. Seed plants that do
not have flowers—such as cycads, ginkgo,
and conifers—are called gym- 81
Water lilies have specialized leaves that allow them to easily
float on water.
PLANT LIFE
nosperms. Conifers, for example, are common gymnosperms; instead of flowers,
conifers have cones that produce pollen or eggs. Well-known examples are cedars,
cypresses, Douglas firs, junipers, pines, redwoods, and spruces. Male cones are small
and soft, and female cones are large and hard. Wind carries pollen from the male cone
to the female cone. As the eggs are pollinated and seeds develop, the scales of the cone
open up to release the seeds. Once the seeds take root, a new plant grows. Other plants
that do not have flowers are mosses; although they sometimes look like they are
blooming, the flower-like part is a little capsule full of spores at the end of a small stem.
S E EDS AND GROWTH
What is a seed?
A seed contains all that is needed to create a new plant. It holds the embryo, from
which the seedling develops. It also holds enough food to help the plant through its
first stages of growth—either packed around the embryo or stored in special internal
leaves called cotyledons. When conditions are right—for example, when it has
been exposed to water for a period of time—the seed germinates. As the young plant
develops, stems and roots grow. The plant reaches maturity when it is able to reproduce
by creating new seeds.
How do seeds become plants?
Once seeds are fully developed, they need a good place to grow. If they just fell to the
ground beneath their parent plant, they would struggle, competing against each
other for sunlight, water, and minerals. Most seeds need to travel—by wind, water, or
with the help of insects and other animals—to better places to germinate, or start to
grow into new plants. Some seeds, like those from conifer and maple trees, have
wings attached. Others, like those of dandelions, have parachutes made of tiny hairs.
Both features allow the seeds to be carried great distances by the wind, and they sometimes
land in spots that are good for germination. Water carries other seeds to good
growing places; the hard, watertight shell of a coconut, for instance, allows it to travel
many miles at sea before finding a beach where conditions are suitable for growth.
Seeds sometimes have to wait a long time before they find good places to grow,
places where the sun, moisture, and temperature are right. Most seeds are designed
for the wait, protected by a hard outer pod (except those of conifers). Some seeds
wait years to germinate, and some just never do. But inside each seed pod is a baby
plant, or embryo, and endosperm, a supply of starchy food that will be used for early
growth if germination takes place. Then a tiny root will reach down into the soil,
and a tiny green shoot will reach up, toward the light.
Do animals ever carry seeds?
Yes, animals are great seed carriers. They take them from one place to another in
82 their mouths (as does a squirrel preparing for winter), or sometimes seeds stick on
their fur or feathers. But most often seeds travel in animals’ digestive systems.
Some plants grow colorful and tasty fruits, which are really just fleshy seed coverings
meant to attract hungry animals. When creatures like birds, bats, raccoons, or
bears eat berries and other fruits they usually swallow the seeds whole. Safe inside
a hard coating, the seeds pass through unaffected by digestive juices, appearing
many hours later in animal waste. The seeds sometimes emerge in places far from
their parent plants, in locations better for germination.
Which plant spreads its seeds with the help of children at play?
The dandelion, of course! A dandelion is really many tiny flowers bunched together
in one plant. After a dandelion blooms yellow, each of its tiny flowers produces a
seed. Each seed is attached to a stem with white fluffy threads. Children who pick
up and blow dandelions—even if they do not make a wish—are spreading their
seeds. Dandelion seeds are carried away by the wind and travel like tiny parachutes—
often miles away from the parent plant—eventually landing and taking
root. The dandelion seeds are also a tasty treat for many small birds, and its pollen
is an important food source for bees.
How do flowering plants make their seeds?
Most flowers contain both male and female sex cells. The typical flower has four
main parts: an outer cup of leaflike sepals, a ring of petals within the sepals, and 83
Dandelions are considered weeds, but they have a clever strategy for survival. Kids—and even a lot of adults—find it very
irresistible to blow their seeds off their stems, helping them to populate lawns everywhere.
PLANT LIFE
inside, male reproductive organs surrounding female parts. Male cells develop in
structures called stamens and travel enclosed in the hard shell of pollen grains.
Female cells, or ovules, develop deep in a flower’s ovary, enclosed in a structure
called a pistil. The top of the pistil—known as the stigma—is long and sticky and a
good target for pollen. After it reaches the stigma, a small tube grows out of the
pollen grain. The male cells travel down the pollen tube, eventually reaching female
ovules. Then fertilization occurs and seeds start to grow.
What is the difference between self-pollination and cross-pollination?
Since flowers possess both male and female parts, some flowers can fertilize themselves—
or fertilize another flower on the same plant—which is called self-pollination.
Or the ovules of one flower may be fertilized by the pollen of a different flowering
plant of the same species, a method called cross-pollination. The wind, water,
insects, and other animals help to carry pollen from one flower to another. Crosspollination
usually produces a better plant: the offspring of cross-pollination possesses
the genetic traits of two parents, which may give it new characteristics that
will help it survive in an always-changing environment. Cross-pollination is so desirable,
in fact, that many flowering plants have developed different ways to keep selfpollination
from happening. In the flowers of a spiderwort plant, for example, the
stamens are ready to release pollen grains before the pistils are ready to accept them,
so the pollen has to travel to other spiderwort plants in search of a ripe pistil.
Are there plants that do not grow from seeds?
Yes. Not all plants are seed plants. Some plants, such as ferns and mosses, reproduce
with spores instead of seeds. Spores, like seeds, can survive harsh conditions
and develop into new plants. However, unlike seeds, spores are produced without
84 fertilization and contain neither a plant embryo nor endosperm. Some plants can
Does the expression “Open sesame!”
have anything to do with sesame seeds?
Sesame seeds burst open when they ripen, so the phrase may be related to
that fact. The English word sesame traces back to the Arabic word simsim.
Sesame seeds are believed to be one of the first condiments as well as one of the
first plants to be used for edible oil, and its usage dates to 3000 B.C.E. The earliest
recorded use of the sesame seed comes from an Assyrian myth that claims
that the gods drank sesame wine the night before they created the earth. More
than 5,000 years ago, the Chinese burned sesame oil as a light source and also
to make soot for their ink blocks. Today, sesame seeds are a source of food and
oil in different parts of the world, including the United States. Sesame seed oil
is still the main source of fat used in cooking in the Near East.
reproduce without spores or seeds through vegetative reproduction, in which a part
of the stem or root gives rise to a new plant.
What is the difference between a bulb, a corm, and a tuber?
Bulbs, corms, and tubers are all parts of a plant that grow underground. They are
each a storage unit for food that gives the plant the energy it needs to grow, bloom,
and complete its life cycle each year. A bulb is an underground stem and leaf. It
grows in protective layers, much like an onion. At the very center of the bulb is a
small version of the flower itself. The bulb’s basil plate—a round and flat hairy mass
(the beginnings of roots) on the bottom of the bulb—helps the bulb stay together.
Examples of bulbs include tulips, daffodils, lilies, narcissus, and amaryllis. A corm
is an underground stem. It has the same type of protective covering and basal plate
as the bulb, but it does not grow in layers. Instead, the corm is the base for the
flower stem and has a solid texture. Crocuses and gladiolus are both corms. The
tuber is an underground stem or root. Just like a potato, it has leathery skin, lots of
“eyes,” and no basal plate. The eyes are the growing points where the plants eventually
emerge. Dahlias, begonias, and anemones are all tubers.
FRAGRANT FLOWERS,
BEAUTI FUL BLOOMS
When did the first flowers bloom?
Mosses and fungi probably appeared about 400 million years ago. By about 200 million
years ago, the earth sprouted sweeping forests of giant cycads, conifer trees,
huge horsetails, and ferns. But the first flowering plants did not appear until the
dinosaurs, sometime in the middle of the Cretaceous period, about 100 million
years ago. Before this, most of the trees had been gymnosperms, or plants with
cones. Magnolias are among the oldest of all flowering plants, appearing about this
time, along with orchids. With flowers came many insects, including butterflies,
ants, termites, and bees. The flowering plants provided food for these insects, who
spread the pollen from flower to flower to produce the seeds that would keep the
flowers reproducing.
What is the difference between annual, perennial, and biennial flowers?
An annual grows from seed, blooms, sets seed, and dies in just one growing season.
Petunias, marigolds, and poppies are examples of flowers widely grown as annuals.
Most annuals bloom continuously from spring through fall, and need to be replanted
every spring. A perennial flower is a “permanent” one, as it lives for three or
more seasons. Perennials need to be fed plant food and/or replaced about every
three to five years. Most perennials, such as roses and tulips, offer a burst of color
for only a few weeks once a year. A biennial grows its first year, lives over the win- 85
PLANT LIFE
ter, and then blooms in the second season,
before dying. Foxgloves and hollyhocks
are examples of biennials.
Why are so many flowers
brightly colored?
Flowers are brightly colored to attract
insects and other animals to them,
which help the plant’s fertilization by
carrying pollen from one plant to
another. Butterflies, bees, and hummingbirds
are attracted to bright colors
like reds, oranges, pinks, yellows, blues,
and purples. A flower’s fragrance is
another method of attracting pollinating
visitors, especially at night when
moths are out. The way in which a
flower is shaped also attracts pollinators. For instance, butterflies prefer flowers
with flat petals that act like a landing strip for them to sit on. Long, tubular flowers,
such as honeysuckle, daylilies, and salvia are just a few of the flowers that
attract hummingbirds because their long beaks can easily fit into the flower when
gathering nectar.
What makes a plant bloom at the right time of year?
All flowering plants have a mechanism to make sure that their blooms develop at
just the right time of year, whether in the springtime or autumn. Most respond to
the amount of sunlight, and can distinguish between 16 hours of light and 8 hours
of light. Some flower only when days are long and nights are short, such as radishes,
asters, petunias, and beets. Others, such as chrysanthemums, goldenrods, and
poinsettias, flower only when nights are long and days are short.
Do all flowers close up at night?
Although many flowers close up at night, not all of them do. Those that open their
petals during the day and then close them at night are reacting to light or temperature
changes. Some flowers, such as tudaylilies, remain open for twenty-four
hours. Other flowers have unusual opening and closing habits. Crocuses, poppies,
and morning glories, for example, open as the temperature increases during the day
and close as the day gets cooler in the late afternoon. The flower called the fouro’clock
closes in the morning and opens again late in the afternoon, right around
four o’clock. Moonflower, night-blooming jasmine, evening primrose, angel’s trumpet,
night phlox, and night-blooming cereus open only at dusk or at night. Some
plants also react to touch and close up their leaves and “play dead” if a hand or twig
brushes against them. For example, if you touch a mimosa plant, it will fold its
86 leaves and the stalk will droop.
Some flowers we have to plant every year in our gardens
because they are annuals and only survive until the next
winter.
Flowers close their petals at night because they are protecting the pollen and
other reproductive parts of the plant that are inside from the cold and rain. Also,
many flowers are pollinated by insects and birds that are active during the day, so
there is no reason to be open at night. However, some types of flowers—such as
some types of tropical fruit plants and varieties of cactus flowers and related
plants—are pollinated by bats at night, and these flowers will be open at night and
closed during the daytime.
Can you eat flowers?
Yes, flowers can be eaten or used to garnish a dish. Cooking with flowers dates to
Roman times, and to Chinese, Middle Eastern, and Indian cultures. Edible flowers
were especially popular in the Victorian era during Queen Victoria’s reign. Today,
many restaurant chefs decorate their entrees with flower blossoms, such as pansies
and violets. Dandelions, arugula, watercress, lilac, nasturtiums, and garlic blossoms
are often used in salads. In fact, you are probably eating flowers for dinner tonight.
Broccoli, cauliflower, and artichokes are all flowers. The spice saffron, often used to
flavor rice dishes, is the stamen from the crocus flower. And capers are the
unopened flower buds from a bush that grows in the Mediterranean.
What it the largest flower in the world?
The flower with the world’s largest bloom is the rafflesia, which grows in the rain
forests of Indonesia. It can grow to be 3 feet (0.91 meters) across and weigh up to
15 pounds (6.8 kilograms). It is a parasitic plant, with no visible leaves, roots, or
stem. It attaches itself to a host plant to obtain water and nutrients. When in
bloom, the rafflesia gives off a repulsive odor, similar to that of rotting meat.
Although people do not want to come near it, the strange odor attracts insects that
pollinate the plant.
Which is the smallest flower in
the world?
The smallest individual flowering plant
is watermeal, a member of the duckweed
family. The plant itself is 1/32 of an inch
in width, or about the size of a pinhead.
The light green free-floating, rootless
plant grows in lakes and ponds, and
weighs about 1/190,000 of an ounce,
equivalent to two grains of table salt.
They are very hard to see; in fact, you
would need about 5,000 plants to fill up
one thimble. However, because they
grow in colonies, these plants look like
algae spreading across the water. Their 87
The rafflesia, which is found in Indonesia, is the world’s
biggest flower, though certainly not the prettiest.
PLANT LIFE
capacity to reproduce very quickly can cause a pond to be completely covered in the
green plants in just a few weeks.
Are all flowers fragrant?
Unlike the fragrant blossoms that attract bees, carrion flowers simulate the odor of
a rotting animal carcass and attract carrion beetles and different types of flies,
including blowflies, flesh flies, and midges. The stapelia flower, which is shaped like
a starfish and grows in Africa, has fine hairs around its petals, perhaps to imitate the
appearance of a small dead animal. When the bloom opens it gives off a rotting
smell, imitating dead animal meat. The smell attracts flies, which collect pollen
before they fly away. Some carrion flowers, such as the European and Brazilian
Dutchman’s pipe, lure insects into dark openings that lead to the foul-smelling
interior where they become trapped. When the flower “releases” the insect, it is
coated with fresh pollen to be taken to a different plant. The lantern stinkhorn, a
fungus that releases a feces-like odor, attracts green bottle flies to spread its spores.
POI SONOUS, MEAT-EATING,
AND OTHER EXTREME PLANTS
What are carnivorous plants?
Carnivorous plants are plants that receive some or most of their nutrients from
trapping and eating insects, other arthropods, and sometimes small frogs and mammals.
(They are sometimes called insectivorous plants because insects are the most
88 common prey.) Like other plants, carnivorous plants need sunlight, soil, and water
Which flowering plant can you float on?
Known as the “Giant Water Platter,” South America’s giant Amazon water
lily has strong leaves that reach 6 to 8 feet (1.8 to 2.4 meters) across and
can support the weight of a child. The water lilies produce flowers that open
at night and are the size of a dinner plate. The first night they are white female
flowers; on the second night they turn to pink male flowers. Beetles and
sphinx moths that live in the Amazon River region pollinate the flowers and
the seedpods—that are the size of a baby’s head—sink beneath the water,
where they lay dormant in the mud for up to four years before germinating.
The plant lays dormant for a period every year before producing more leaves
that increase in size before it flowers again. However, the giant water lily’s
leaves are not the biggest on Earth. Palm trees can grow leaves up to 65 feet
(20 meters) long!
to grow. Carnivorous plants generally
grow in places where the soil is thin or
poor in nutrients, especially nitrogen,
such as bogs. Today, there are more
than 600 plant species around the world
that attract and trap prey, produce
digestive enzymes, and absorb parts of
the insect as its nutrients.
How do carnivorous plants digest
their prey?
Carnivorous plants use enzymes to
digest their prey. Most of them, including
Venus flytraps, butterworts, sundews,
and many types of pitcher plants,
all make their own digestive enzymes.
These enzymes help them digest their
prey. After their insects have been
digested, all that remains is a mass of
dead insect parts. Other carnivorous
plants do not make their own digestive
juices. Instead, they rely on bacteria to
produce their enzymes. Once captured,
the insect rots, and the carnivorous
plants absorb the decomposed molecules.
Many plants, such as sarracenia, use both their own enzymes and bacteriagenerated
enzymes. This is called a symbiotic relationship because both organisms
benefit from this unique feature: The plant enjoys the bug-soup digested by the bacteria,
while the bacteria get a comfortable place to grow. Bacterial digestion is no
stranger to the animal kingdom: termites have bacteria inside them that help them
digest wood, for example; and humans have Escherichia coli (E. coli) in their intestines
to help them digest food.
Which plants drown bugs?
The pitcher plant drowns small insects, who are attracted to the colorful leaf
rosettes that resemble flowers. At the ends of the leaves are traps shaped like
small pitchers, with a leafy “lid” to keep the rain out. Insects love the sweat nectar
the plant produces around its slippery rim. When an insect lands on the rim,
it slips inside, and drowns in the fluid at the bottom—a mixture of rain, dew,
and a digestive enzyme that soon dissolves the insect. The pitcher plant’s meals
include not only insects but also mites, spiders, and, occasionally, a small frog.
The pitcher plant grows in bogs, savannas, and wooded areas of the South—
from Florida to Mississippi, and north to Virginia and Maryland—where insects
are plentiful! 89
Some plants, like this Venus flytrap, have turned into meat
eaters because they live in soil that does not have enough
nutrients to sustain them otherwise.
PLANT LIFE
Does a Venus flytrap really snap up live flies?
Indeed, it does. A Venus flytrap is a carnivorous plant that attracts, captures, and
kills insects and digests and absorbs their nutrients. The leaves of the Venus flytrap,
which can open wide, have short, stiff hairs called trigger hairs. When anything
touches these hairs enough to bend them, the two lobes of the leaves snap shut,
trapping whatever is inside. The “trap” will shut in less than a second, capturing
flies and other insects. When the trap closes over its prey, finger-like projections
called cilia keep larger insects inside. In a few minutes the trap shuts tightly and
forms an air-tight seal in order to keep its digestive fluids inside. These fluids help
the plant digest prey. At the end of the digestive process, which takes from 5 to 12
days, the trap reabsorbs the digestive fluid and reopens. The leftover parts of the
insect blow away in the wind or are washed away by rain.
How do plants defend themselves?
Because plants cannot move to escape danger, many have developed defense mechanisms.
Most plants today have one or more defenses that include poisons, physical
structures (tough branches; sharp, pointy leaves; spikes; or thorns), irritants (such
as hairs, prickles, or oils that annoy the skin), and bad flavors (that can cause stomach
pain and diarrhea). These defenses ward off predators (animals that want to eat
them) and some defenses protect them from invading diseases. For example, waxy
or tough leaves make it hard for bacteria or fungi to get into the plant. In addition,
many bacteria and fungi rely on water to live, move, and reproduce. If the plant’s
leaves shed water quickly, it is less likely that a disease-causing pathogen will be
able to make its way into the plant.
How many poisonous plants are there in the world?
Thousands of plants around the world contain varying amounts of poison, or those
properties that can injure animals or people. Plants may be poisonous to the touch
(such as poison ivy and poison sumac) or toxic if swallowed (such 90 as deadly amanita
Is the Amazing Flynapping Arum of Sardinia a circus performer?
No, it is a fly-trapping flower that grows in the rocky Mediterranean island
soil of Sardinia and Corsica. It is sometimes called the “dead-horse arum”
because it smells like a horse carcass. Blowflies are lured into the funnel-like
flower, then force their way into the neck and its pitch-dark chamber. Carrying
pollen from another plant, they unknowingly pollinate the female flowers
at the base of the chamber. Unable to escape from the chamber because it is
filled with stiff hairs, the flies remain prisoners until the male flowers above
the stiff hairs start to release pollen. Then the hairs wilt and the flies are able
to escape, getting dusted with pollen as they fly away.
or poison hemlock). Sometimes the
entire plant is poisonous, and other
times a certain part of the plant—such
as the seeds, leaves, berries, and flowers—
is poisonous. For example, the leaf
blades of rhubarb are poisonous, but not
the stalks. Many times, there is not
enough poison to affect humans, and
sometimes cooking the plant destroys
its poisonous substance. Some plants
have substances that are dangerous to
some animals, but not others. For example,
onions occasionally poison horses or
cattle, but are widely used for human
food. Poison ivy or poison oak can affect
some people’s skin, but not others, and
goats eat it regularly without any side
effects. Some of the more common poisonous
plants found in the United States and Canada are belladonna, daffodil, foxglove,
holly, iris, lily-of-the-valley, mistletoe, morning glory, and rhubarb.
Is poison ivy really poisonous?
A popular summer-camp rhyme is “Leaves of three, let it be.” Poison ivy, the threeleaved
plant that grows wild in all regions of the United States, is aggravating to the
skin, though not lethal if swallowed unless you are very allergic. After brushing up
against the poison ivy plant, a red rash usually develops. Rubbing the rash will not
spread poison ivy to other parts of the body (or to another person) unless urushiol
oil—the sticky, resin-like substance that causes the rash—has been left on your
hands. Other plants that usually irritate the skin upon contact include cowhage,
poison oak, poison sumac, rengas tree, and trumpet vine.
How was hemlock used to poison in ancient times?
In ancient times, small doses of the plant were used to relieve pain, with a great risk
of poisoning. One species, Conium maculatum, was used to carry out the death sentence
in ancient times. The Greek philosopher Socrates was condemned to death in
329 B.C.E.; he killed himself by drinking a potion made from hemlock. The hemlock
plant was introduced to North America from Europe, and has often been mistaken
for a pretty garden plant. All parts of the weedy hemlock plant are poisonous, especially
leaves and seeds. Hemlock is a member of the wild carrot family, and it grows
along roadsides and waterways in North America.
How do nettles sting?
Certain kinds of nettles have tiny, sharp hairs on them that stick into your skin if
you touch them. As they stick, they inject a stinging liquid called formic acid, 91
“Leaves of three, let it be,” is an easy rhyme to remember to
identify poison ivy.
PLANT LIFE
which produces a stinging pain, followed by redness and skin irritation. Despite
its unique defense mechanism, which stops animals from eating the plant, stinging
nettle has a long history of use in both European and North American communities.
The tough fibers from the plant stem have been used to make cloth, and
cooked nettle leaves were eaten as vegetables. Since ancient Greek times, stinging
nettle has been used to treat coughs, tuberculosis, and arthritis, and to stimulate
hair growth.
Why do cacti and desert plants have spines, and not leaves?
Most cacti do not have leaves because they grow in a hot, dry environment, with little
water. They are able to survive by storing water for long periods of time; they do
this through their extensive root system, which absorbs water from the soil when
it rains. In a typical leaf, there is a large amount of water loss through small openings
at the leaf surface (called the stomatas). This water loss, called transpiration,
is speeded up with warm temperatures. Cacti have adapted by being leafless, storing
water in their stems, developing waxy skin to seal in moisture, and growing
spines, a form of leaf modification. Spines help shade the rounded or ribbed stems
from the blazing sun of their desert habitat. They also protect desert animal species
by providing them with shelter.
Why do tropical rain forests grow so many plants?
Rain forests—thick forests of trees and other plants found in the lowland areas of
the Tropics around the world—exist in parts of Australia, Indochina, India, the
Malay Peninsula, the East Indies, in central and western Africa, and in Central and
South America. Unlike forests in many other parts of the world, which have been
affected by global climate changes like the Ice Age, tropical rain forests have been
growing uninterrupted in some places for millions of years. During that time an
unimaginable number of different types of plants and animals have evolved to use
every food source and live in every spot there.
Tropical rain forests have more plant and animal species than the rest of the
world combined, and scientists continue to discover new species. Because tropical
rain forests are located near the equator, their climate is warm. The name
“rain forest” comes from the fact that they receive a lot of rain—between 160 and
400 inches (4 and 10 meters)—throughout the year. Plants grow very quickly
under such ideal conditions. In order to get the sunlight that they need for photosynthesis
(the process by which they and other green plants make their own
food), rain forest trees grow very tall, up to 130 feet (40 meters) high. Their tops
form a huge canopy that shades most of the ground, protecting plants on the
ground from excessive sunshine as well as wind. Rain forest trees have very shallow
roots, for the soil in which they grow is poor, having long been depleted of
nutrients by the needs of thick plant life over millions of years. But the abundant
life all around contributes organic matter (the decomposed remains of plants and
animals) to the surface of the soil, which is enough to nourish these grand,
92 ancient forests.
Which plants grow in the rain forests?
More than two-thirds of the world’s plant species are found in the tropical rain forests
of the world. In this environment—where there is abundant plant growth with little
ground space for roots and plenty of moisture—some plants grow high up in trees.
These epiphytes, or air plants, have fibrous, spongy, aerial roots that get moisture
from the frequent rains and take minerals from the surface of the tree on which they
grow, or from the plant debris that gathers around their roots. Many orchids and
bromeliads are epiphytic plants. Other plants that grow in this unique environment
include bamboo, which is one of the fastest growing plants in the world. Found in
Asian rain forests, the plant can grow 6 to 15 inches (15 and 38 centimeters) a day,
reaching as tall as 120 feet (36.5 meters). The hearty grass, which is hard like wood,
is used in the tropics to build houses, rafts, and bridges, and to make mats, hats, fish
traps, chopsticks, and musical instruments. Other unique plants, many of which provide
food and products for local populations, include Brazil nut trees, cacao trees,
palm trees, kapok trees, rubber tree plants, and climbing plants called lianas.
Can a plant grow in ice and snow?
It is difficult for plants to survive in the coldest regions of the world, where snow
covers the ground for most of the year. In the Arctic tundra that circles the North
Pole, once the snow melts in the spring the growing season is short (50 to 60 days),
and flowers have little time to make their seeds. Even in the summer it is cold and
windy, with just a few months of sunshine. Yet, many different types of plants have
adapted to this cold area, where winter temperatures dip below –30 degrees Fahrenheit
(–34 degrees Celsius) and the average summer temperature is 37 to 54 degrees
Fahrenheit (3 to 12 degrees Celsius). In fact, there are about 1,700 kinds of plants
in the arctic and subarctic, including low shrubs, sedges, reindeer mosses, liverworts,
and grasses; more than 400 types of flowering plants; and lichen.
Most plants, such as purple saxifrage, are small, and grow close together and
close to the ground. This protects them from the cold temperatures and the strong
winds, which can soar up to 100 miles (161 kilometers) per hour. Others, such as
the arctic crocus, have fuzzy coverings on the stems, leaves, and buds to protect
them from the wind. Plants like the arctic poppy have cup-shaped flowers that face
up to the Sun, so the Sun’s rays can easily reach the flower’s center. These plants
stay warmer than the air around them. The Alpine soldanella uses its food stores to
keep warm, producing enough “heat” to melt the snow near its roots. Other plants
are dark-colored so they can absorb more solar heat. Often, small leaves help the
plants retain moisture. Certain plants, such as edelweiss, have a thick coat of hair
on them, which traps heat and cuts down water loss. And lichen is super-hardy. It
can grow on bare rock and survive long droughts and extremely cold temperatures.
What is lichen?
Thought to be among the oldest living things on Earth, lichen is a unique growth
that is made up of a fungus and either green algae or bacteria called cyanobacteria. 93
PLANT LIFE
The algae or bacteria live underneath the sheltering fungus, and provide it with
sugars (food) from photosynthesis. In return, they receive protection from the sunlight
and are able to live without drying out. In this way, lichen represents one of
the most unique living “partnerships” on Earth. Lichen is a hardy plant that grows
on all kinds of bare surfaces in extreme environments, such as rocks, tree trunks,
desert sand, cleared soil, and living bark. Most kinds grow very slowly—often less
than 1 millimeter per year.
FERNS, MOSS E S, AND MUSHROOMS
What are ferns?
Ferns are an ancient group of plants that first appeared on Earth about 325 million
years ago. They are most closely related to mosses and liverworts. There are more
than 12,000 species of ferns that grow around the world, and many live in moist,
shady, tropical regions such as rain forests. Ferns are called vascular plants because
they have internal vein structures that help spread water and nutrients throughout
the plant. Ferns do not have flowers or fruit. They reproduce by spores, microscopic
dustlike particles that are released by the hundreds and spread by wind and water.
They are typically produced on the lower side of the fronds or “leaves.” When
released, each spore grows into a tiny heart-shaped structure called the thallus,
which makes male sperm cells at the pointed end and female cells in the notch.
After a heavy rainfall, the sperm burst free from the thallus and swim to the female
cells, where they are fertilized.
Are fiddleheads and ferns related?
Yes. Fiddleheads are young fern fronds that have not yet opened up. Fiddleheads are
named for their appearance, which resembles the scroll at the head or top of a fiddle.
They often appear on menus in the
eastern United States during springtime.
Many fern species produce these
edible shoots, which have a unique texture
but taste a bit like asparagus. They
include the ostrich fern, the bracken
fern, the royal fern, and cinnamon and
flowering ferns.
What is moss?
Moss is a type of plant that does not
have traditional roots, stems, or leaves.
Because they have no true roots, mosses
use delicate growths called rhizoids
to anchor them to soil, 94 rocks, or tree
A Boletus mushroom (a type of fungus) grows in a patch of
dense, green moss.
bark. Moss grows along the ground where it is moist, absorbing water and nutrients
from the air. Like their cousins the ferns and liverworts (leafy mosses), mosses
reproduce from spores, not seeds, and need to be moist in order to reproduce.
They grow in soft cushions or small clumps, and can spread out like a blanket
along the ground.
What is fungi?
Fungi are neither plants nor animals, and include mushrooms, toadstools, molds,
and yeast. Fungi do not have chlorophyll (the green food-making compound found
in plants), so they cannot make their own food. To survive, they release enzymes
that break down living or dead plants, animals, or other fungi, and live off of their
nutrients. All fungi reproduce by spores. In many mushrooms, spores are located
on the underside of the mushroom cap and released from vertical plates or flaps
called gills. The stinkhorn is a tall fungus that shoots up out of the ground, and
produces a foul, stinking smell as it ripens. Its slimy body is covered with spores,
and its foul smell attracts flies, which help deliver the stinkhorn’s spores to new
locations in the forest.
Why are some mushrooms called toadstools?
The word “toadstool” dates to the Middle Ages when it was associated with the toad,
which was thought to be poisonous. Toadstools, with their stool-like shape, are really
mushrooms that are poisonous or inedible. For example, the bright red “fly agaric”
toadstool’s juice was once used to make a remedy for killing bugs. It is a very
poisonous mushroom that still lives today and should be avoided.
What is a giant puffball?
The giant puffball is an edible mushroom that grows in meadows, forests, and
fields all over the world. Big and white, the giant puffballs look like a large ball of
thick whipped cream that has been dropped on the ground. The giant puffball is
one of the biggest mushrooms—it can grow as large as a basketball and weigh up
to 40 pounds (20 kilograms). When it reaches its full size, the giant puffball starts
to crack slightly, revealing a white interior. Within days, the spores in the interior
mature and are released through a hole in the top of the puffball’s cap. The
mushroom then begins to rot, and touching it will cause it to—puff!—burst into
a cloud of dust.
What is bracket fungus?
Bracket fungus is a type of fungus that grows on both living and dead trees. It looks
a lot like a hard mushroom, and is called bracket fungus (or sometimes shelf fungus)
because it grows like a bracket or shelf in horizontal rows. Some forms grow
so thick they may speed up the death of the tree, and then feed off the wood for
years afterwards. 95
PLANT LIFE
TRE E S
What are the longest-living trees in the United States?
Of the 850 different species of trees in the United States, the oldest is the bristlecone
pine, which grows in the deserts of Nevada and southern California. Scientists
think that some of these trees are more than 4,600 years old. They believe they can
live as long as 5,500 years. Although this seems old, it is actually very young when
compared to the oldest surviving species in the world, the maiden-hair tree, or
Ginkgo biloba, of China. This tree first appeared during the Jurassic era some 100
million years ago. Also called icho, or ginkgo, meaning “silver apricot,” this species
has been grown in Japan since 1100 B.C.E..
How can you tell how old a tree is?
Scientists can tell the age of a tree by examining it. Researchers call this area of
study dendrochronology, which is a combination of several Greek root words:
dendro, meaning “tree”; chrono, meaning “time”; and ology, meaning “the study
of.” Scientists have several ways to tell how old a tree is. First, they count the
whorls around it. A whorl is the circular growth of branches in the same spot
around the tree trunk. As the tree gets older, it will loose its whorls and markings
will be left behind. They count from the bottom whorl up to tell how old it is.
Sometimes, they will use a boring tool to drill into the core of the tree to tell its
age. (A boring tool is a T-shaped tool with a long, thin hollow plug that drills into
the tree to take a sample of the core.) Scientists count the rings on the sample to
determine the age of the tree and then cover the hole to keep the tree alive. If a
tree is cut down, they look inside the core for circles, called annual circles. The
circles start off very small in circumference and get larger with each ring. Each
ring represents one year of life for the tree—researchers begin with the innermost
part of the core (called the pith) and count outward toward the bark until
they determine the age.
What else do the tree rings tell us?
Scientists also use a tree’s annual rings to tell what the climate was like and what
happened in the area where the tree grew. Every year the tree produces an annual
layer of cells that appear as one wide, light ring (during spring and early summer)
and one narrow, dark ring (during the winter). Very thick rings mean it was a good
growing season with plenty of rainfall. Darker areas mean that the tree was not
growing much because of lack of nutrients, less water, and less sunlight. Other
markings reveal information about fires, floods, deforestation, and insect damage.
Which tree is the biggest and tallest?
Living species of sequoias are some of the biggest and widest trees in the world. The
tallest trees are the coastal redwoods of California, while the widest ones are the
96 giant sequoias, which have much larger trunks and branches. These trees grow in
the Sierra Nevada mountains of Central
California at elevations of about 6,500
feet (1,981 meters). The trees have survived
for 2,000 or 3,000 years. Some of
the largest sequoia trees measure 35
feet (10.6 meters) in diameter and up to
300 feet (91 meters) in height. Their
bark can be 4 feet (1.2 meters) thick!
Many are found in California’s Sequoia
National Park. The General Sherman,
for example, is one of the tallest giant
sequoias in the world, with a height of
about 275 feet (85 meters).
Which tree can have more than
2,000 trunks?
The banyan tree, which grows in tropical
Asia, is a member of the ficus or
fig family. As the massive limbs spread
horizontally, the tree sends down roots
that develop into secondary, pillar-like
supporting trunks. Over many years a
single tree may spread to take over an
entire area. The Great Banyan Tree, in
the Botanical Gardens in Calcutta,
India, has more than 2,000 trunks. It became diseased after it was struck by
lightning, so in 1925 the middle of the tree was removed to keep the remainder
of the tree healthy. But still it kept growing, thanks to its elaborate root system.
The Great Banyan is about 250 years old and is spread over an area of 3.7 acres
(1.5 hectares).
What is the Joshua tree?
The Joshua tree is a desert tree that grows in southwestern North America, in California,
Arizona, Utah, and Nevada. A native of the Mojave Desert, these droughttolerant
trees thrive in the open grasslands of California’s Joshua Tree National
Park. The Mormon pioneers named this tree after the prophet Joshua, because its
extended branches resembled the outstretched arm of Joshua as he pointed with
his spear to the ancient city of Ai. The trees are twisted and spiky, with tough
leaves, and look a little bit like a tree from a Dr. Seuss book. Joshua trees can grow
from seed or from an underground rhizome of another Joshua tree. They grow
very slowly, sometimes 3.9 to 7.8 inches (10 to 20 centimeters) in their first few
years. The tallest trees reach about 49 feet (15 meters) tall. The trunk of a Joshua
tree is made of thousands of small fibers and does not have yearly growth rings,
which makes it hard for scientists to tell the tree’s age. Although the fragile tree 97
A redwood forest can make you dizzy just by looking up.
Redwoods are among the tallest trees on the planet and can
live for thousands of years.
PLANT LIFE
has shallow roots, if it survives the harsh desert environment, it can live hundreds—
even thousands—of years.
Why do leaves change color in the autumn?
Tree leaves change color as autumn approaches because the days are shorter and
the temperatures are cooler. As the length of the days shortens, the leaves stop their
production of chlorophyll, a pigment that provides the leaves’ green color. Other
pigments in the leaves, mostly yellow, are then able to show through. The yellow
color is mostly seen in aspen, birch, hickory, willow, and yellow poplar trees. Sugars
that are trapped in the leaves as the trees prepare for winter form red pigments,
also called anthocyanins. Some trees with red leaves are the dogwood, red and silver
maple, oak, sumac, and sassafras.
Why are these trees called deciduous?
After turning shades of yellow, orange, and red, deciduous trees shed their leaves.
Trees such as birch, oak, and maple lose water quickly from their wide, flat leaves.
In wintertime, it is hard for them to absorb water from the cold, often frozen
ground, so their leaves die and fall off. In the springtime, leaf and flower bud return,
burst open, and come into full foliage by summer.
Is it true that hundreds of wild things live in oak trees?
Oak trees—with their broad leaves that provide shelter and shade—provide a home
for more than 300 species of insects, birds, and mammals. Their bark is crawling
with a wide variety of insects, including ants, ladybugs, weevils, wasps, oakworms,
caterpillars, and moths. Blue jays, hummingbirds, magpies, finches, sparrows,
wrens, and woodpeckers feed off of the insect life and make their nests in the
branches. The oak’s acorns are an important food source for mice, squirrels, chip-
98 munks, deer, bears, foxes, quails, blue jays, crows, and turkeys. Oaks can live more
Which tree grows on stilts?
Mangrove trees live in estuaries near the ocean’s edge where freshwater
and saltwater mix. Most mangrove estuaries are found in tropical and
subtropical climates near the equator, including coastal Florida, Central
America, the Caribbean, South America, and parts of Africa. These trees have
waxy leaves and an elaborate root system that branches from the stem and
helps prop up the tree, which appears to be growing on stilts. The protected
waters between the mangrove roots are a breeding ground for fish, crabs, and
birds. The tree’s decaying leaves fall into the water and provide nutrients for
animals and plants. Mangroves help protect coastlines by trapping soil and
sediment and reducing erosion caused by waves and tides.
than 200 years; by the time they are 70
years old they produce thousands of
acorns per year.
What do fir and pine trees tell us
about the weather?
Firs and pines are coniferous trees, which
have tall, straight trunks and either flat
narrow leaves or sharply tipped needles.
Conifers bear their seeds inside dry,
woody, female cones. In cool or damp
weather the scales of the cones close up
tightly, protecting the seeds inside with a
waterproof layer of waxy resin. When the
weather is warm and dry, the resin softens,
and the cone’s scales open to release
their seeds. Some species, like the lodgepole
pine, need the heat of a forest fire to
melt the wax that seals their cones.
What is bonsai?
Bonsai means “tree in a pot” in Chinese
and is pronounced BONE-sigh. It is a
special method for growing trees or
shrubs in a pot, tray, or dish, which results in an artificially dwarfed plant. Bonsais
are regular trees or shrubs, such as juniper or cypress, that are stunted by pruning
their roots and tying their branches with wire. The art originated in China around
200 C.E., and was adapted by the Japanese early in the sixth and seventh centuries.
What is a fruit?
A fruit is the part of the plant that nourishes and protects new seeds as they grow.
The plant’s ovaries develop into fruit once the eggs inside have been fertilized by
pollen. Some plants produce juicy fruit, such as peaches, pears, apples, lemons, and
oranges. Others produce dry fruit, such as nuts and pea pods. If an animal doesn’t
eat the fruit, or a human doesn’t pick it off, it falls to the ground and decays and fertilizes
the soil where a new seed will grow.
Which fruit tree makes the heaviest fruit?
The jackfruit tree, which grows in southern Asia, produces the largest fruit in the
world. The fruit, which grows directly from the trunk, may reach nearly 3 feet (0.9
meters) in length and weigh up to 75 pounds (34 kilograms). Jackfruit and its close
relative, breadfruit, belong to the mulberry family. Asians eat the fruit raw or preserved
in syrup, and they eat the seeds after boiling or roasting them. 99
Some people think that bonsai trees are dwarf trees, but they
actually are regular trees and bushes that have been specially
pruned to look like miniature versions of themselves.
PLANT LIFE
Which tree produces the largest nut?
The coco de mer tree, a palm that only grows today on two islands in the Seychelles,
produces both the largest seed (each weighs about 44 pounds [20 kilograms]) and
the largest nut in the world. The nut, which takes six to seven years to mature and
another two years to germinate, is sometimes called the sea coconut or Seychelles
nut. When early explorers first discovered the nut, they thought it came from a
mythical tree at the bottom of the sea. Sixteenth-century European nobles decorated
the nut with jewels as collectibles for their private galleries. Today, the coco de
mer is a rare protected species.
How do coconuts swim?
The coconut palm, or coconut tree, grows in many tropical areas of the world,
including the coastal regions of Indonesia, the Philippines, India, Brazil, and Sri
Lanka. When the tree is four or five years old, it begins to produce male and female
flowers, followed by nuts. The coconuts reach full size in about six months and, as
they mature, drop from trees. The fallen coconuts, which are light and able to float,
get scooped up by waves. The ocean currents carry the “sea-beans” across oceans,
until they land on another shore, ready to sprout new trees. Scientists believe this
why coconut trees appear in so many faraway regions of the world.
PLANTS THAT HE LP AND HEAL
Which tree was used in the fledgling shipbuilding industry?
During colonial times the U.S. Navy used the oak tree’s hard wood to build its ships.
The U.S.S. Constitution received its nickname, “Old Ironsides,” during the War of
1812 because its live oak hull was so tough that British war ships’ cannonballs lit-
100 erally bounced off it. Because the Constitution was built before shipbuilders learned
Did Johnny Appleseed really plant apple trees?
Yes. John Chapman, a pioneer nurseryman who lived in the 1800s, was
also called Johnny Appleseed because he planted orchards in the Midwest
United States. He also encouraged the development of fruit-tree orchards farther
west by giving away free seedlings to pioneers. In drawings, he is often
shown as a barefoot tramp roaming the countryside scattering seeds from a
bag slung over his shoulder. The real Appleseed, however, was a curious figure
who often preached from the Bible and from religious texts to passersby.
At the time of his death in 1845, he was a successful businessman who owned
thousands of acres of orchards and nurseries.
to bend or steam wood into shape, the live oak’s long, arching branches were used
as braces to connect the ship’s hull to its deck floors. Throughout the years, oak
wood has been used as lumber, railroad ties, fenceposts, veneer, and fuel wood.
Today it is manufactured into flooring, furniture, and crates.
Which plant is used to make linen?
Linen, one of the oldest human fabrics, is woven from fibers of the flax plant. The
fibers are located in the stalk, which is picked by hand. After the fibers have been
separated from the stalk and processed, they are spun into yarns and woven or
knit into linen textiles. However, many years ago linen was used for sheets and is
still used for household items such as tablecloths and personal items such as
handkerchiefs. Slacks, dresses, suits, and blazers are all common clothing items
made from linen today.
How is cotton harvested?
Cotton, which comes from flowering Gossypium plants, is a key vegetable fiber used
for making clothes, and oil from its seeds can be used in cooking or for making
soap. The cotton plant grows in 17 states that make up the U.S. “Cotton Belt”: California,
Arizona, New Mexico, Texas, Oklahoma, Arkansas, Missouri, Mississippi,
Alabama, Louisiana, Florida, Tennessee, North Carolina, South Carolina, Virginia,
Georgia, and Kansas.
In the United States, where cotton is no longer picked by hand, machines called
pickers or strippers harvest the crops. Cotton-picking machines have spindles that
pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers—
a series of circular rubber pads—then remove the seed cotton from the spindles
and knock the seed cotton into a conveying system. Conventional cotton stripping
machines use rollers equipped with alternating bats and brushes to knock the
fluffy white bolls, which contain seeds and hairs, from the plants into a conveyor.
After harvest, most of the cotton is pressed into large blocks for storage. These cotton
bundles are then transported to the cotton gin, a machine that pulls out the
seeds from the cotton bolls.
What is paper made of?
Around the world, people have made paper from a wide variety of plant materials,
such as wood pulp, rice, water plants, bamboo, cotton, and linen clothing. The
ancient Egyptians made paper from papyrus reeds that grew abundantly along the
Nile River. Today’s paper fiber comes mainly from two sources: pulpwood logs and
recycled paper products. In fact, much of the paper today is a blend of new and recycled
fiber. To make paper commercially, companies mash up these wood fibers and
mix them with water. This mixture is mashed into a thin sheet. The sheet is dried
and pressed flat into large rolls, cut into different sizes, and converted into paper
products. Recycling paper and paper products helps save trees and support the
paper-making process. According to the American Forest and Paper Association 101
PLANT LIFE
more than half—53.4 percent—of the
paper used in the United States was
recovered for recycling in 2006.
What is aloe vera?
A cactus-like plant of the lily family, aloe
vera grows wild in Madagascar and on
the African continent. It also is cultivated
in Japan, the Caribbean, the Mediterranean,
and the United States. People
around the world have used its gooey,
jelly-like sap for healing and cosmetic
purposes. Aloe extracts can be used to
treat digestive problems, including constipation,
and aloe oils are used in cosmetic
creams to help keep skin soft and
to treat minor skin irritations.
Are marine plants used in toothpaste?
Yes, and lots of other products, too. Substances from marine plants and animals are
used in many home products, including ice cream, toothpaste, fertilizers, gasoline,
and cosmetics. If you read the labels of some of these products, you may find the
words carrageenan and alginate. Carrageenans are compounds extracted from red
algae that are used to stabilize and jell foods. Brown algae contain alginates that
make foods thicker and creamier and add to shelf life. They are used to prevent ice
crystals from forming in ice cream, for example. Alginates and carrageenans are
often used in puddings, milkshakes, and ice cream. The remains of diatoms (algae
with hard shells) are used to make pet litter, cosmetics, and pool filters. The kelp
plant is often used in lipstick, toothpaste, and clothing dye.
Why do people plant marram grass on sand dunes?
Marram is a tough perennial grass that is often planted in shifting sand dunes to
help stabilize them. Between the edge of the water and the beginning of the dunes,
dry sand is constantly shifting and floating. One of the few plants that can take root
in this windy environment is marram grass. It spreads its tuberous roots just under
the surface of the sand, and forms an underground web that helps hold the sand in
place. This allows the soil to stabilize and the dune to grow higher.
What were ancient spices used for?
Spices are dried and ground up plant seeds, fruits, root, or bark. Grown for centuries
in the Middle and Far East, spices have been used for their antibacterial properties,
to flavor foods, and to aid in digestion. In ancient times, spices were used as
102 a way to mask the unpleasant tastes and odors of food, and later to keep food fresh.
The sap from the aloe vera plant has long been known to
have healing properties.
They were very important commodities. As early as 1000 B.C.E., a handful of cardamom
was worth as much as a poor man’s yearly wages, and many slaves were
bought and sold for a few cups of peppercorns. During the time of the Ancient
Greeks, the spice trade flourished between the Mediterranean region and the Far
East. Arab merchants brought spices such as cinnamon, cassia, black pepper, and
ginger by camel caravan to Europe. During this time, spices were used for cooking,
in medicine, and in luxury items such as perfumes, bath oils, and lotions. During
the fifteenth and sixteenth centuries, European explorers introduced spices to the
New World. During the days of American colonization the most popular cooking
spices were pepper, cinnamon, vanilla, nutmeg, ginger, cloves, and allspice. Colonial
families experimented with exotic spices to flavor dishes, including chili peppers,
cardamom, cumin, saffron, and turmeric (which was also used as a food preservative).
Today, most spices are grown on large plantations in China, India, the
Middle East, South America, and North Africa, where they are often picked by hand.
Are there plant species that are endangered?
Yes. According to scientists, at least 34,000 of the world’s 275,000 fern, conifer, and
flowering plant species—or about one in eight—is endangered with extinction.
Researchers think that the true number of these plants is actually much higher
because many plants species have not yet been identified. In the United States, 29
percent of its 16,000 plant species are considered endangered. Throughout the
world, the main threats to plants are habitat destruction, the spreading of towns,
and modern farming techniques that use pesticides. Some plants, such as rare
orchids and cacti, are threatened because they have been overcollected. In addition,
climate changes, disease, and plant-eating animals, such as goats, have destroyed
many rare pants.
Why are rain forests so important to the health of our planet?
In 1800 there were 7.1 billion acres of rain forest in the world. Now—a little more
than 200 years later—less than half, or 3.5 billion acres, remain. Over 100,000 acres
of the world’s rain forests are destroyed each day, with trees cut down for their valuable
wood and land cleared for farming. While covering just two percent of Earth’s
surface, the dense vegetation of these forests plays an important role in the health
of our planet. The destruction of rain forests threatens the health of our planet by
reducing the amount of oxygen in our air and increasing carbon dioxide. Too much
carbon dioxide in our atmosphere keeps the Sun’s heat from radiating back into
space, increasing global temperatures (called the greenhouse effect). Global warming,
in turn, could bring about major climate changes. Melting glaciers and rising
sea levels, for example, could cause the flooding of coastal regions.
The plants in rain forests produce natural chemicals that fight off destruction
by insects, and scientists have learned how to make plant-based insecticides from
rain forest plants (without destroying the rain forests) to spray on crops. These natural
insecticides are far less toxic than synthetic, or human-made, chemicals.
Numerous medicines, as much as one-quarter of all prescription drugs, have been 103
PLANT LIFE
made from materials gathered in rain forests, and many more life-saving medicines
may await discovery there. Many products, like natural rubber, essential oils used in
cosmetics and perfumes, and rattan, a material weaved together to make furniture,
can be taken from rain forests without causing widespread destruction. In addition,
rain forests can absorb huge amounts of water. When rain forests are destroyed, the
vast amounts of rainfall in those regions cannot be absorbed, resulting in widespread
flooding. International efforts have begun trying to save what remains of the
rain forests by helping the people who destroy them find other ways to earn a living.
Still, the destruction of these important forests continues at a rapid pace.
104
LOTS OF PEOPLE!
How many people are there in the world?
The world’s population, or the total number of humans on Earth, reached 6.6 billion
in 2008. Different regions have different rates of population growth, but in the
twentieth century, the world saw the biggest increase ever in its population due to
medical advances and increasing agricultural productivity. In 2000, the United
Nations estimated that the world’s population was growing at the rate of 1.14 percent
(or about 75 million people) per year, and by the year 2050 there may be as
many as 9.2 billion people in the world!
Why did people begin exploring?
For many hundreds of years, adventurous travelers have explored the far reaches
of the earth. They traveled for many reasons: some were looking for new areas to
trade with; others were looking for new areas to conquer, settle, and farm; some
desired to spread their religion; and others hoped to achieve fame and become
wealthy. Some of the earliest oceanic voyages were made by the Polynesians of New
Guinea more than 3,500 years ago. They traveled the Pacific Ocean in small boats
the size of canoes. Around this time, Egyptians sent their large trading ships to the
land of Punt, south of Egypt at the tip of the Red Sea. Hanno the Navigator was
one of the first known explorers. A Carthaginian explorer who lived about 450
B.C.E., Hanno was best well known for his naval exploration of the African coast.
Around 1000 C.E. Leif Eriksson and his Viking explorers became the first Europeans
to sail across the Atlantic Ocean to North America. These early explorers
used ancient maps and the stars’ position at night to guide them—but they would
often get lost or shipwrecked. It would take hundreds of years of trial and error 105
PEOPLE
AROUND
THE WORLD
before Italian-born explorer Christopher Columbus set sail from Spain in 1492,
hoping to find a western sea route to China. Like other Europeans of his time,
Columbus did not know that North and South America, and the islands of the West
Indies, lay between Europe and China. When he landed in the West Indies, he
believed it was part of China.
What is the U.S. Census?
The U.S. Census is a survey that the United States government takes every ten years,
according to Article 1 of the U.S. Constitution. The survey asks questions about you,
your family, your friends and their families, and all the other families or individuals
who live in the 105 million households that are in the United States. The survey
gathers information about how many people live in your house, how old you are, if
you are male or female, and what race you are—white, black, American Indian,
Asian, or Hispanic. In 1790 the first census counted 4 million people living in the
United States. Today, there are more than 281 million.
The census count tells a state how many people it can send to represent it in
the U.S. Congress, which includes both the Senate and the House of Representatives.
Every state sends two people to the Senate. But the House of Representatives
is different—the number of people a state sends to the House is based on that state’s
population. According to the 2000 Census, the state with the smallest population is
Wyoming, while the state with the largest population is California. Wyoming can
send only one person to the House, but California can send 53 people to the House
of Representatives.
The census also gives information about everyday things, so that the government
can tell which states and regions of the country need improvements. If a town
has more children living in it than it had ten years ago (when the last census count
was taken), this would be a good place to build another school. Or, if workers in a
city are spending too much time getting to work, this would be a good place to build
more roads or increase public transportation like subways and buses.
Which parts of the world have the fastest growing populations?
From the three billion people that will be added to the world population between
now and 2050, Asia will contribute some two billion, mainly because of the already
massive size of its population and high fertility rates. Most of Asia’s growth will occur
in the next three decades. The 10 countries which will contribute 106 most to the world’s
How many kids are there in the world?
In 2000, one out of every three people was under the age of 15; which means
there were about 1.8 billion kids in the world. About 70 million of these
children lived in the United States.
population growth over the next 30 years are India, China, Pakistan, Nigeria,
Ethiopia, Indonesia, the United States, Bangladesh, Zaire, and Iran—in that order.
Where in the world do people live the longest?
The Japanese have the longest lifespan in the world. Japanese men live to be 78
years old on average while Japanese women live to be about 85. Okinawa, Japan, has
a population of one million and of those 900 are centenarians, or people who are at
least 100 years old. Scientists believe this is because the Okinawans eat more soy
products than any other population in the world, as well as a wide range of different
vegetables and fruit all rich in antioxidants. After Okinawa, the Sardinian
mountain town of Ovodda has the most centenarians, on average 5 out of its small
population of 1,700. For hundreds of years families in Ovodda have lived in isolation
from the rest of the world, marrying into each others’ families, which may
result in few genetic diseases.
Where are people suffering from disease and poverty?
Disease and poverty exist all over the world. The areas with the most disease and
poverty are countries in sub-Saharan Africa and the Asia-Pacific region. In these
areas, people do not have enough food to eat, water to drink, or money to live. They
have diseases like AIDS, which weakens the immune system, and cholera, an intestinal
infection. In the United States, about 33 million people live in poverty, according
to government statistics. Almost 12 million of these people are children, and
about 3.5 million were age 65 or older. 107
The world’s population is soaring, and some cities, such as New Delhi, India, are crowded with millions of people. China and
India are home to over a third of our planet’s 6.6 billion people.
PEOPLE AROUND THE WORLD
LANGUAGE S AND CULTURE S
What is a country’s culture?
A culture is made up of many complex parts of the country—its traditions, beliefs,
art, music, clothing, food, holidays, languages, family and marriage rules or laws,
games, folktales, and mythology. Culture is “the way of life” of a country or society,
and these ways of living together—including value systems, traditions, and
beliefs—are passed down from generation to generation. While all cultures have
universal traits, different cultures have developed their own specific ways of
expressing them. For example, people around the world are similar in that we communicate
with each other, live by eating food and drinking water, and dream when
we sleep. Yet we speak different languages, eat different foods, and dream different
dreams. Anthropologists (people that research different cultures and how they
develop) say that culture is made up of at least three parts: what people think, what
they do, and the products they produce. In complex cultures such as the United
States, culture is what knits us together as human beings living in one country, but
also separates us into our different ethnic communities.
Why do people speak different languages?
While some animals have demonstrated the ability to communicate with other animals
and with humans, people are the only creatures on Earth who communicate
through language, which is a system of vocal symbols. Scientists don’t know exactly
when humans first spoke, though they know that it happened a very long time ago,
in prehistoric times. Different languages arose when groups of people—separated by
things like deserts, mountains, or great oceans—developed their own systems of
communicating that reflected their unique ways of life. These new languages were
passed on when children learned to speak the same way the people around them did.
As groups of people spread out to settle different parts of the world, they took
their languages with them. They began to pronounce some words differently as
time passed and had to add words to describe the new things and situations they
found in distant lands. Languages gradually changed from their parent languages,
though they still shared some characteristics. Today, English and French are languages
that seem very different from one another, but they came from the same
parent language (Indo-European) a long time ago. All languages that share a parent
language belong to the same “family.” There are 13 large language families in
the world today, from which most languages have descended.
Which language is most widely spoken?
There are more than 6,000 languages spoken in the world today. In some large countries,
several languages are spoken. (India has more than 800!) In other large countries,
different versions or dialects of the same language are spoken in different areas.
In both cases, an “official” language is usually chosen for the country. That language
is used in schools, by the mass media (like television), and by the 108 government. It is
not surprising that Chinese—the language spoken in the world’s most populous
country—is the world’s most widely spoken language. Although many different versions
or dialects of Chinese are spoken in the country, the standard or official language,
Mandarin Chinese, is spoken in its northern and central regions. It is the
native language of nearly 900 million people. Spanish is the second most widely spoken
language, and English is the third. English is the most common international
language, which means it is spoken in more places around the world than any other.
How does a person’s clothing tell where he or she comes from?
In all countries, climate, usefulness, and customs (including religion) all influence
the way people dress. When people immigrate or move to another country, they
sometimes keep their style of national dress as a marker of their ethnicity and culture.
In Saudi Arabia, which has a hot, desert-like climate, men and boys wear the
thawb, an ankle length piece of clothing, sometimes made of cotton, which is long
and fits loosely. Men also wear a ghutra an iqal on their heads—a square head cloth
with a double circle of black rope or cord to hold it on the head, which keeps them
cool. Women wear a long dress with long sleeves, called a jallabia, which covers
every part of their body because their religion (Islam) does not permit them to show
any body parts. Women in Japan sometimes wear kimonos, a traditional, full-length
garment that wraps around the body like a robe, and is secured by a wide belt called
an obi, usually tied in the back. In Japan, professional sumo wrestlers are often seen
in kimonos because they are required to wear traditional Japanese dress whenever
they appear in public. Nigerians often wear traditional Nigerian clothing, both in
Africa and when they travel, which is made from lace, jacquard, and ankara, and
sometimes tie-dyed. It usually consists of a shirt, long, flowing skirt (that can be
tied in different ways), and a headpiece for women and cap for men. And Americanmade
Levi’s Jeans are worn across the globe by everyone from Americans to Europeans
and South Americans, so it might
be hard to tell where a person wearing
jeans really comes from!
Why do women in some countries
wear veils?
A veil is a piece of cloth that is usually
worn to hide a person’s hair or face.
Women have worn veils since ancient
times—mostly in Middle Eastern countries—
primarily to keep men from looking
at them. Many women of the Muslim
faith still wear veils of some type
when they are out in public. In some
Muslim countries, only a woman’s eyes
are allowed to show. Although Westerners
(people from North America and 109
Wearing veils is an important tradition in many cultures,
especially among Muslim women, who wear them as a sign
of modesty and obedience to their faith.
PEOPLE AROUND THE WORLD
Western Europe) may find these veils symbolic of women’s restricted freedoms in
many Muslim societies, Muslim women wear them to honor long-held traditions of
modesty and to show respect for their religion and the men in their lives.
Why are there different religions and how did they spread?
From our earliest days, many people have believed in a power or powers greater
than themselves. This belief is known as religion. In ancient times, it was a way to
make sense of the mysteries of the natural world; evil spirits were thought to be
responsible for bad weather and disease, for instance. Ancient peoples felt that they
had a measure of control over their lives when they made offerings and prayed to
friendly spirits, whom they believed could help them win battles or grow better
crops. Even today, when people know the scientific explanations for such things as
thunder or the eruption of volcanoes, many look to religion to explain some of the
other hard-to-understand things that we experience as humans—things like the
purpose of life or the reasons for tragedies.
While most religions spring from the same basic human need to believe in a
great power or powers, the ideas, practices, and traditions that religions involve can
be very different. Long ago, groups of people—separated by things like deserts,
mountains, or great oceans—developed special religious beliefs and forms of worship
that fit their unique ways of life. Some, like the ancient Greeks, built their religions
around the belief in several gods (a practice called polytheism), while others,
like the Jews, believed in a single god (monotheism). Great temples, shrines, and
churches were built to honor these gods, and believers showed their faith through
ceremonies, sacred writings, prayers, and other forms of worship. As civilizations
developed and ways of traveling long distances improved, explorers, traders, settlers,
and missionaries spread different religions to other parts of the world. As religions
spread, they were often changed into different forms that better fit the conditions
and people of various lands. All the major religions of the world began in Asia
before they gradually spread to other parts of the world—Judaism, Christianity, and
Islam in the Middle East; Buddhism, Hinduism, and Sikhism in India; Taoism and
Confucianism in China; and Shinto in Japan.
Which religions are the most widely practiced around the world?
Today there are some 4,300 religions in the world. Nearly 75 percent of the world’s
population practices one of the five most influential religions of the world: Christianity,
Buddhism, Hinduism, Islam, and Judaism. Christianity, which is based on the
teachings of Jesus Christ, who preached in Palestine about 2,000 years ago, is the
most widely practiced religion in the world today, with 2.1 billion followers. The
second most practiced religion is Islam, with 1.3 billion followers.
Why is America called a “melting pot”?
Except for Native Americans and slaves from Africa, the United States is a nation of
110 people who left their home country looking for a better life (called immigrants). As
a result, the population of the United States is made up of a mixture of people from
different countries, such as France, Ireland, China, Brazil, and Mexico. For this reason,
the United States is sometimes called the “melting pot.” The next time you are
in class, look around. Everyone around you is different. Although your classmate
may have been born in the United States, at some point, that person’s family left
their home country and came to the United States.
CITY LI FE
What is the difference between a metropolitan area, a city, and a
megalopolis?
A metropolitan area includes a core city as well as nearby communities, making it a
larger settlement of people than just a city. A city is any urban settlement that is larger
than a town (which generally has between 2,500 and 20,000 residents), and that
is able to function on its own, with a government and other public services. A megalopolis
is any multicity area with more than 10 million people. For example, in the
United States, the third largest metropolitan area is the Chicago-Gary-Kenosha area,
with 8.8 million residents, which also houses the third largest U.S. city, Chicago.
Which city is the largest?
There are many cities around the world that are “big,” meaning they have more
than 10 million people living in them. Tokyo, Japan, ranks the largest, since it has
33.2 million people living in the city, according to 2005 estimates. The next biggest
cities in order of size are São Paulo, Brazil (17.7 million), Seoul-Incheon, South
Korea (17.5 million), Mexico City, Mexico (17.4 million), Osaka-Kobe-Kyoto, Japan
(16.4 million), and New York City (about 8 million people). Most of these cities are
located in different places around the globe. In the United States, after New York,
Los Angeles is the biggest city (with almost 4 million people), and then Chicago
(with almost three million people). Populations of cities are constantly changing as
people move in and out of them, according to the U.S. Census Bureau, a government
organization that estimates how big or small cities are based on their populations,
or the number of people living in them.
Which city is the smallest?
Ferdania, in Saudi Arabia, is probably the world’s smallest city: it has one police station,
one school, one market, one gas station, one health center, and about 10 houses.
According to the Guinness Book of World Records, Hum, Croatia, is the smallest
town in the world, with a population of only 23 citizens. The tiny town, which
rose during the Middle Ages, is closed off on one side by high towers and a system
of walls; the other side is closed off by the outer walls of houses. The smallest city
in the United States is Maza, located in Towner County, North Dakota. Established
in 1893, the city had a population of 5 when the 2000 Census was taken. 111
PEOPLE AROUND THE WORLD
Which U.S. city has the most public landmarks?
New York City has the most landmarks in the United States. Landmarks are permanent
structures, such as trees, bridges, buildings, and statues that contribute
to the historic, cultural, or architectural heritage of a city. In New York, there
are 1,116 designated landmarks, 104 interior landmarks, 9 scenic landmarks,
and 84 historic districts, resulting in the largest number of designated landmarks
and the most valuable real estate in any city in the United States. Some
of the most famous landmarks include the Empire State Building, which is
1,250 feet (381 meters) high from the ground to its tip. There is an observatory
on the 86th floor of the building that overlooks the city, but you have to
either take the elevator or climb more than 1,000 steps to reach it. Another
famous New York City landmark is the Statue of Liberty, which was built by
French sculptor Auguste Bartholdi, with the help of many laborers working ten
hour days, seven days a week for nine years! The statue was finally finished in
July 1884, and shipped to America in 350 individual pieces that were finally
assembled many months later.
Where are the largest factories located?
Factories, also called manufacturing plants, are large buildings where workers
create and assemble all types of useful things, or supervise machines to make
them, including airplanes, cars, shoes, clothing, household appliances—even
chocolate. Today’s factories usually have large warehouses that hold heavy
equipment used for assembly-line production. Most industrial cities—like
Shanghai, China; Seoul, South Korea; St. Louis, Missouri; and Detroit, Michigan—
have factories. Hershey, Pennsylvania, has the largest chocolate factory in
the world, where it makes one billion pounds of chocolate products each year.
Other areas—such as the Garment Districts in New York and Los Angeles—
make many of the clothes we wear. Recycling plants, found in every major city,
take millions of old aluminum cans, plastic bottles, and glass containers and
make new ones. The world’s largest plastic bottle recycling plant is in Spartenburg,
South Carolina.
Which city has the most elaborate subway system?
London, England’s underground subway system, called the Underground, is the
world’s largest metro subway system and the world’s oldest underground system (it
was inaugurated in 1863). Its 253 miles (407 kilometers) of track and its 11 lines
transport more than three million people around the city each day. Londoners
beware: If the Chinese capital is successful with its plans to expand its Beijing subway
system to 348 miles (561 kilometers) by 2020, it will surpass London as the city
with the world’s most extensive underground subway system. After London, the
most substantial system is New York City’s rapid transit system. Built in 1904, its
229 miles (369 kilometers) of routes carries 4.9 million people around the city every
day, making it one of the ten busiest systems in the world, with more boardings
112 than systems in London, Paris, Tokyo, Moscow, and Mexico City.
Other extensive subway systems include the Paris subway system which is the
second oldest in the world (the initial system was completed in 1900), with more
than 133 miles (214 kilometers) of track and 380 stations; and the Moscow subway
system, which boasts the largest ridership of all metro systems throughout the
world, with about 8.2 million passengers per day. While most of the Moscow trains
run underground, some lines cross bridges and provide scenic views of the Moskva
River and the Yauza River.
Which airport is the busiest in the world?
The biggest airport is not necessarily the busiest one. If you were to measure all the
airports around the world, the King Khalid International Airport in Riyadh, Saudi
Arabia, would be the largest: It takes up some 81 square miles (209 square kilometers),
an area larger than many cities! But the Hartsfield-Jackson Atlanta International
Airport is the busiest airport in the world, handling about 1,121,000,000 passengers
annually. Atlanta overtook Chicago’s O’Hare International Airport in 1998,
which handled 66.6 million passengers in 2002. London’s Heathrow Airport accommodates
the most international passengers, but ranks third behind Atlanta and
Chicago in total number of passengers.
Why do cities have dams?
Dams, which are structures that hold back water, have been built since ancient times.
They are usually made of earth, rock, brick, or concrete—or a combination of these
things. They are constructed to control the flow of water in a river, and they are built 113
The London subway system—commonly called the Underground—has over 250 miles (400 kilometers) of track and services
three million people daily.
PEOPLE AROUND THE WORLD
for a number of reasons. One reason is to prevent flooding. Heavy rains in high country
may cause water levels in a river to rise. As the river flows downhill, it may overflow
its banks, flooding communities located downstream. A dam can prevent this by
stopping or slowing rushing water, allowing it to be released at a controlled rate.
Dams are also frequently used to store water for general use and farming. When a
river’s flow is restricted by a dam, water often spreads out behind the dam to form a
lake or reservoir in the river valley. That water can then be used as needed, preventing
water shortages and crop damage during long periods of dry weather.
A great number of dams today are used to make electricity. Such hydroelectric
dams are built very tall, to create a great difference in the height of the water level
behind and in front of it. High water behind a dam passes through gates in the dam
wall that allow it to fall to the river far below. As the water falls, it flows past huge blades
called turbines; the turbines run generators that make electricity. One of the world’s
largest and most productive hydroelectric dams is the Hoover Dam, located on the Colorado
River between Nevada and Arizona. Built in the 1930s, it is 726 feet (221 meters)
high and 1,244 feet (379 meters) long. Its reservoir (Lake Mead)—the world’s largest—
supplies water to several states, allowing huge regions of naturally dry terrain in southern
California, Arizona, and Mexico to flourish. Many modern dams are used for all
three purposes: flood control, water storage, and hydroelectric power.
How does nuclear energy work to make a city run?
We usually make heat energy by burning fuels—oil, gas, coal, or wood. In large
quantities, such energy can be used to heat water, and the resulting steam can be
used to run generators that make electricity for a city. Burning fuel (combustion)
is a chemical reaction that converts one form of energy into another: it recombines
elements from the fuel and the oxygen in the air into things like ash, smoke, and
waste gases, as well as heat.
A fission-generated nuclear reaction produces heat in a different way: it breaks
apart elements themselves, turning them into waste products with less mass, which
creates a great amount of energy. The tiniest particles of matter—atoms—of heavy
elements like uranium or plutonium provide the fuel for nuclear reactors. At the
center of each atom is a nucleus, which is made up of even tinier particles called
protons and neutrons. A nucleus is held together by a powerful force, and breaking
up the nucleus releases that force. A nuclear reaction starts when fast-moving neutrons
strike the nuclei of fuel atoms, causing them to break into smaller nuclei.
These in turn release neutrons that break up more fuel nuclei. All this movement
produces great heat, which can be used to make steam to run electric generators.
Why is nuclear power dangerous?
The good thing about fission-generated nuclear energy is that very little fuel is needed
to produce huge amounts of energy. (Two pounds of nuclear fuel could produce
as much energy as 6.5 million pounds of coal, for instance!) The challenging part is
that the process must be very carefully controlled. (In a nuclear reactor, 114 control rods
that absorb neutrons are moved in and
out of the core to control the process.) If
it isn’t controlled, the result could be a
build up of pressure within the reactor.
If this continues, radioactive gases
might be released along with steam. It
was a situation like this that happened at
the Chernobyl plant in the Soviet Union
in 1986, resulting in radioactive pollution
that still exists today.
An uncontrolled nuclear reaction
can cause harmful radioactive materials
(such as iodine isotopes that can cause
thyroid cancer) to be released into the
environment. This by-product of nuclear
fission is a problem connected with
nuclear power. Nuclear reactors are
encased in thick layers of steel and concrete
to keep radiation from escaping. And because leftover nuclear fuel is highly
radioactive, it must be carefully stored far away from people for decades or even centuries
before it is safe again. Transporting and disposing of dangerous waste is another
challenge presented by nuclear power; at present, used fuel is sealed in safety containers
and buried deep underground.
The nuclear process that we get our power from is called fission, where atomic
nuclei that break apart produce great energy and heat. But nuclear power can also
be created by a process called fusion, where atomic nuclei join together. Scientists
are still working on creating a satisfactory fusion reactor. The Sun produces its
great energy and heat through the nuclear fusion of its hydrogen gases.
FARM LI FE
Where does our food come from?
People in industrialized nations like the United States eat food that comes from all
over the world. Such countries have the wealth to buy food products that are
brought by plane or ship from far away. A wide variety of canned and packaged foods
are available from every corner of the globe. And even fresh foods like fruits, vegetables,
fish, and meats can now be sped across oceans in refrigerated boats. So
foods that were once rare treats are now available at nearly every time of the year,
arriving from places with different climates and seasons. That means that the
asparagus and strawberries you eat may be grown nearby—or halfway across the
world! Today, when you look in your cupboards, it can be like taking a trip around
the world: you will see tea from India, coffee from Brazil, olive oil from Italy, and
much more. In the past, people ate only the food that they could produce on their 115
Nuclear energy currently provides about 15 percent of the
world’s energy needs. As of 2009, there were 104 operating
nuclear power plants in the United States.
PEOPLE AROUND THE WORLD
farms or find at their local markets. That is still true of many people who live in
developing nations.
How has farming changed in the United States?
In the 1700s, English farmers settled in New England villages; Dutch, German,
Swedish, Scotch-Irish, and English farmers settled on Middle Colony farmsteads;
English and French farmers settled on plantations in tidewater and on isolated
Southern Colony farmsteads in Piedmont; Spanish immigrants, mostly indentured
servants, settled the Southwest and California. Farmers endured a rough pioneer
life while adapting to their new environments, and by the 1800s small family farms
grew and sold crops such as wheat, cotton, corn, and rice. But the work was hard
and slow going: In 1830, it took 250 to 300 hours of labor using very basic tools to
produce 100 bushels (5 acres) of wheat. The growth of farming brought many laborsaving
devices to nineteenth- and early-twentieth-century farm life, including reaping
and threshing machines, which replaced work done by hand. Today, with modern
methods of agriculture that include complex machinery, scientific breeding,
and chemical pesticides, farms require far fewer workers.
Before the Industrial Revolution (which began in the 1800s in the United
States), most people lived and worked on farms. In 1935, there were 6.8 million
farms in the United States, and the average farmer produced enough food each year
to feed about 20 people. In 2002, the number of farms dropped to about 2.1 million,
yet the average U.S. farmer produced enough food to feed almost 130 people. Average
farm size in 1935 was smaller than it is today, about 155 acres (63 hectares)
compared to about 467 acres (189 hectares) today.
Which states are the biggest farm states?
California produces the most agriculture (animal and plant foods) for the United
States, contributing about two-thirds of the nation’s fruits, nuts, berries, and melons.
Almost one-quarter of the state’s land—about 27.7 million acres (11.2 million
hectares)—is dedicated to farming. Other states that grow a large percent of the
nation’s agriculture include Texas, Iowa, Kansas, Nebraska, North Dakota, and
Arkansas. Texas, for example, produces the most cattle; Iowa raises the most hogs
and grows the most corn; and North Dakota grows the most wheat, followed by
Kansas. Arkansas tops the list as the state with the largest poultry production.
How does the combine harvester help farmers?
The combine harvester saves the farmers time and labor. Before modern machinery,
harvesting crops was a painstaking process. Gathering and removing mature plants
from the field had to be done by hand. Farm workers used sharp-bladed, long-handled
scythes and curved sickles to cut down cereal crops like wheat. Even the fastest
reaper could only clear about a third of an acre a day. Because rain could ruin harvested
wheat, workers called sheaf-makers quickly tied it into bundles, so that it
could be safely stored if the weather turned stormy. During the 116 long winter months
farm workers used jointed wooden tools
called flails to thresh or beat the dried
wheat in order to separate its edible
grain seeds from its stalks. But in 1786 a
machine that threshed wheat by rubbing
it between rollers was invented, replacing
human threshers. And around 1840
a reaping machine—whose revolving
wheel pressed grain stalks against a
sharp blade that cut them down—
replaced human harvesters. Today, farm
machines called combine harvesters do
this work in much the same way. These
machines are very efficient and combine
all three jobs of cutting, collecting, and
threshing a crop. A single combine harvester
can process five acres of wheat in
less than an hour!
Who invented the earliest
milking machines?
There are reports that primitive milking
machines were used around 300
B.C.E. by the ancient Egyptians, who
used hollow wheat stems inserted in the teats to milk cows. But hand milking was
popular in the United States until about the 1860s, when American inventors
began finding more efficient ways to milk cows. In 1860, Lee Colvin invented the
first hand-held pump device. In 1879, Anna Baldwin patented a milking machine
that used a large rubber cup connected to the cow’s udder and to a pump lever and
bucket. Working the pump lever pulled the milk out of the udder and into the
bucket. Baldwin’s was one of the earliest American patents, but it was not successful.
Her invention, like others of the time, created a continuous suction on the
udder, damaging the cow’s fragile mammary tissue and causing the cow to kick.
These ideas laid the groundwork for the successful milking machines that started
to appear in later decades, and today modern milking machines use a computerized
vacuum suction to gather milk.
What is a seed drill?
A seed drill was a device that allowed farmers to plant seeds in the soil and then cover
them up. The instrument, created in 1701 by the English farmer Jethro Tull, allowed
farmers to sow seeds in well-spaced rows at specific depths at a specific rate. Before
this, farmers cast seeds to the ground in a haphazard fashion by hand, allowing them
to grow where they landed (called “broadcasting”). The seed drill allowed farmers
more control over their crops and less waste, and was one of Tull’s several inventions, 117
Farmers used to milk cows by hand, but now most dairy
farms use milking machines like this one.
PEOPLE AROUND THE WORLD
which included the horse-drawn hoe and an improved plough. Seed drills are still in
use today, although they are more sophisticated mechanisms that allow farmers to
cultivate many more acres of land than the machines of yesterday.
What are windmills used for?
Windmills, mechanisms that look like giant pinwheels, have been used to generate
power and grind wheat since ancient times. American colonists used windmills to
power machinery that could then grind wheat into flour and corn into cornmeal.
Windmills also powered tools to saw wood and make typical household items, such
as oil, paper, spices, chalk, and pottery. Through the 1920s, Americans used small
windmills to generate electricity in rural areas. When power lines began to transport
electricity to these areas in the 1930s, local windmills were used less and less,
although they can still be seen in some parts of the western United States. When
the oil shortages of the 1970s created an interest in alternative energy sources,
windmills became fashionable again, especially in states like California whose governments
encouraged renewable energy sources.
Today, clusters of giant windmills—with blades up to 200 feet (61 meters)
long—sit atop windy hillsides in great numbers to make electricity. The force of the
wind pushes the slanted blades, which causes them to rotate because they are bound
by a shaft. This spinning shaft runs an electrical generator, which creates power.
They are sometimes called wind power plants or wind farms. The world’s largest
wind farm, the Horse Hollow Wind Energy Center in Texas, has 421 wind machines
that generate enough electricity to power 230,000 homes per year. The states with
the most wind production are California, Texas, Iowa, Minnesota, and Oklahoma.
What are barns used for?
Today, the huge, airy farm structures we
know as barns are used mostly to store
modern farm machinery and house
farm animals. But before modern farming,
they had a greater number of
important uses. Before the invention of
threshing machines (which separate
cereal grains like wheat from their
stalks), the grain harvest had to be
stored in barns, where it would await
threshing or pounding by hand during
winter months. The structures had to
be large and drafty for the process of
winnowing, which separated straw dust
from the grains after threshing.
Before farmers began to raise spe-
118 cial crops to feed their livestock during
The tradition of painting barns red in America began for no
other reason than because the chemical used to make paint
red was inexpensive.
the winter, they used hay, which is dried grass (grown wild or taken from the stalks
of cereal crops). Huge amounts—enough to last several months—had to be stored
away. Hay was usually kept in barn lofts located above the main floor, where farm
animals spent the winter. This high storage place allowed air to circulate around the
hay, keeping it from rotting. It was convenient, too, because hay could be pulled
down as needed to feed the livestock.
Because farmers had to store their harvest crops in barns, they wisely cut
entrance holes near their roofs, inviting barn owls to make nests there. The birds
would hunt the rats and mice that liked to feed on the grain.
What is a silo?
The tall, cylinder-shaped farm structures known as silos are used to store silage,
which is animal feed. Silage is moist feed made from green crops that ferment when
stored in an airtight place. This fermentation process preserves the feed, which is
used along with or instead of hay (dried grasses) to feed livestock like horses, cattle,
and sheep during the winter when they cannot feed in green pastures. Silage gives
farm animals needed nutrients. Before farmers started to raise food crops to feed
their livestock (during the eighteenth century), they had to kill most of their animals
when winter approached, because grass in pasturelands stopped growing and the
creatures faced starvation. But herds of livestock could be kept year-round once
farmers began to grow crops for winter feed. Root crops like turnips, as well as leafy
crops, were sometimes used. Today, corn is the crop most often used for silage. 119
Why are barns usually painted red?
Paint coats wood, protecting it from sunlight and rain damage and making
it last longer. When early farmers had enough money to paint their
barns, they usually used inexpensive paint because the structures were so
large. Ferrous oxide, a chemical powder that gives paint its red color, was
readily available and cost little. Thrifty farmers in New England, New York,
and the upper Midwest region painted their barns red. In those places, red
barns remain a tradition.
But there are plenty of barns in other parts of the country that are not red.
Early farmers that were poor—especially in regions like Appalachia and the
South—left their barns unpainted because they did not have the money to do
the job. Unpainted wood usually weathers to a soft gray color. And in places like
Pennsylvania, Maryland, and some southern Midwestern states, the most frequently
seen barn color is white. Some people think that white barns grew
popular when dairy farming became more important after the Civil War; white
suggests cleanliness and purity, desirable qualities to be associated with milk
production. Special farms where fancy horses or prize livestock were raised
sometimes had barns painted unusual colors, like yellow, green, or black.
PEOPLE AROUND THE WORLD
Why are crops sprayed with pesticides?
Farmers and state governments use chemical pesticides to protect their crops from
insect pests, weeds, and fungal diseases while they are growing. They also spray
their crops with pesticides to prevent rats, mice, and insects from contaminating
foods while they are being stored. While these actions are meant to benefit human
health and bring a wide variety of fruits and vegetables to the supermarket, they can
also harm people, wildlife, and the environment. This is why there are strict controls
in place over their sale and use.
What is organic farming?
While most large farms today use chemicals to control weeds and insects and to
produce increased amounts of vegetables, milk, or eggs, some farmers have chosen
to run their farms without chemicals. Organic farmers believe that the chemicals
many farmers use can be damaging to the environment and to the people that eat
the food grown on such farms. They feel that natural fertilizers and pest-control
methods are just as effective and far healthier.
A British farmer and scientist named Albert Howard began the practice of
organic farming as an alternative to modern chemical-based methods in the
1930s. His ideas have spread all over the world, taking hold in the United States
in the late 1940s. A basic principle of organic farming is to focus on keeping the
soil rich with nutrients by feeding it natural fertilizers like cow manure. Such fertile
soil can help create stronger plants that are better able to resist disease and
insects. Organic farmers also prevent insect damage by putting up insect traps or
by bringing in beneficial insects that feed on the harmful ones that are causing
the problem. In extreme cases, they need to use pesticides, but to continue being
certified as organic farmers in the United States, such farmers need to use botanical
pesticides (those that are made from plants) rather than synthetic, or manmade,
chemicals.
Does organic farming contribute to less pollution?
Yes. Organic farmers also try to do more tasks using human power rather than
gas-powered vehicles, thereby using less fuel and cutting down on pollution.
Organic farms that raise livestock like dairy cows or chickens feed the animals
with natural food, avoiding pollution-causing chemicals and growth hormones
that make cows produce more milk and chickens produce more eggs. Some
organic farmers also allow their animals to roam in a large area (such animals are
described as “free range”) rather than keeping them in small, climate-controlled
pens for their entire lives.
What is a fish farm?
Fish farms are businesses that produce a limited number of fish for sale in restaurants
and supermarkets. The business is called aquaculture, which includes the
120 farming of fish, shrimp, shellfish, and seaweed. Fish can be grown in natural
waters—such as ponds, lakes, rivers, and streams—or artificial environments, like
tanks, pools, and special cages. Fish species such as salmon, catfish, rainbow trout,
tilapia, and cod grow in fish farms. Fish farms around the world supply almost half
of the world’s total food fish supply. The United States has fish farms in California,
Idaho, Alabama, Arkansas, Louisiana, Mississippi, and along the southeastern U.S.
coast. However, it imports about 80 percent of its seafood—and half of these
imports come from fish farms in Asia and Latin America.
Can farm animals be cloned?
Yes. In 1997 a team of scientists at the Roslin Institute in Edinburgh, Scotland,
announced the birth of Dolly the sheep, the first clone (identical copy) of an adult
mammal. The process used to create Dolly, called somatic cell nuclear transfer,
began with an egg cell from one sheep. The scientists destroyed that egg cell’s
nucleus and then injected the nucleus from the cell of another sheep into the egg
cell. With a little encouragement from electronic stimulation, the donated nucleus
fused with the egg cell, and the new cell began to divide. The cluster of cells was
then implanted into the uterus of the sheep that had provided the egg cell, and five
months later Dolly was born—an exact replica not of the sheep that had carried her
in the womb but of the sheep that had supplied the nucleus. While cloning mammals
is very controversial, some scientists argue that cloning farm animals has
advantages to livestock farmers, who could use the technology to breed only highquality
animals that produce the most milk or the finest wool.
How can cows make so much milk?
A cow, like all mammals, produces milk to feed its young. If its calf nurses regularly,
the mother cow’s mammary glands will produce enough milk to give the baby
animal all the food it needs. Gradually a calf will nurse less as grass and other feed
makes up more of its diet. A mother cow, in turn, will produce less milk until it is
no longer needed. 121
Why does a rooster crow when the Sun comes up?
Afarm rooster is an adult male chicken. Long ago, when chickens had not
yet been tamed or domesticated by people and lived in the wild, roosters
crowed to call female chickens to mate. This loud crowing caused problems
for roosters, though, because it attracted predators as well as female chickens.
So to avoid being eaten, roosters began to do most of their crowing when they
couldn’t be easily seen, like at dawn or at nightfall, when light was dim.
Today’s roosters continue the habit, crowing mostly in the early morning or
early evening. But it is usually most noticeable at dawn because there aren’t
a lot of other activities and noises to distract your attention.
PEOPLE AROUND THE WORLD
But by milking the cows regularly—two or three times a day—dairy farmers
can cause the cows to continue producing milk. Certain breeds of cows are particularly
good at milk-making, producing 18–27 pints (around 2–3 gallons, or 10–15
liters) each day. A cow’s large, round udder, located on its underside, has four nipples,
or teats, that are squeezed to release stored milk. While once done by hand,
milking is done on modern dairy farms by machines with suction hoses, which do
the job more quickly and cheaply. Tank trucks collect milk from farms daily and
take it to processing plants where it is pasteurized (made germ-free) and used to
make dairy products like cheese, butter, and ice cream.
Why do cows stand around in fields eating all day?
In order to produce four or more gallons of milk each day, dairy cows have to eat a
lot. Producing milk requires additional calories in the form of extra food. A large
dairy cow may eat up to 150 pounds (about 68 kilograms) of grass each day, and all
that munching takes time!
Cows have special stomachs, too, that make eating a slow process. Instead of
having one chamber like a human’s, a cow’s stomach has four chambers. When a cow
takes a bite of grass it swallows it right away without chewing it. The food goes into
the first chamber of its stomach, called the rumen (animals that have such stomachs
are called ruminants), where it mixes with fluid to form a soft mass. The mushy grass
is regurgitated or brought back up again later, when the cow is resting. This “cud”
is thoroughly chewed, swallowed, and digested as it passes through all the other
chambers of the stomach. A cow spends nearly nine hours each day chewing its cud.
Scientists think that when animals like cows lived in the wild they had to snatch
grass in a hurry before predators attacked them. Their special stomachs allowed
them to store food for later chewing and digestion once they were hidden and out of
danger. Goats, sheep, camels, and antelope are other examples of ruminants.
Why do horses sleep standing up?
Horses sleep standing up for a number of reasons. Their legs can lock in place,
enabling them to fall asleep without falling over. Because they are 122 prey animals, hors-
Why do flies like cow poop?
Flies like animal feces—such as dog, cat, cow, or horse poop—because
these warm, moist areas are the ideal spots for laying eggs and give the
larvae something to eat while they develop into pupa. Flies land on the piles
of excretion looking for mouth-watering bacteria, which provides them with
a meal. Although it sounds disgusting, it’s the fly’s job to take the diseasecausing
bacteria and eat it up. However, because of their habits of being
attracted to feces and decaying meat, flies often carry diseases such as dysentery,
typhoid fever, and cholera.
es often do not feel comfortable sleeping
on the ground, and most of their sleeping
is done during the day rather than at
night when the predators are out hunting.
Horses have straight backs, so they
cannot get up quickly. If a predator were
to come while a horse was on the ground,
it might not be able to get up fast enough
to escape. However, horses do occasionally
take short naps laying down during the
day, which helps them rest their legs.
When horses are in groups, they will
often take turns guarding each other as
they rest, with one horse standing up
near the sleeping horse.
Why are pigs so dirty?
Because pigs will eat almost anything, they have traditionally been fed farm leftovers
and waste. This unappealing diet—commonly known as slop—may contain
food waste from a farm household or the unusable by-products of the manufacturing
processes for things like butter and cheese and even beer brewing. Pigs are natural
foragers, frequently using their snouts to dig up roots or grubs for food when
they are in the wild. On farms they are fed from low troughs, but their big snouts
and foraging habits still make them very messy eaters. Adding to the dirty reputation
of pigs is the fact that they have usually been kept in pens, or sties, close to
farm buildings to make their feeding quick and easy. They—and their messes—
have been confined to small spaces, unlike cows and sheep, which are free to roam
pastureland. Because pigs are raised mainly for their meat and fat, they are given a
lot of food and spend most of their time eating. Piglets that weigh only a few pounds
at birth can reach more than 200 pounds (90 kilograms) in less than half a year.
123
Pigs like to roll in the mud to protect their skin from the sun
and from insects, not because they are filthy animals.
PEOPLE AROUND THE WORLD

COUNTRI E S
How many countries are there?
There are about 195 countries in the world today. But because the political world is
constantly changing, that number never stays the same for very long. The number
195 includes Taiwan. Although Taiwan operates as an independent country, many
countries (including the United States) do not officially recognize it as one. Of these
countries, 192 belong to the United Nations (UN), an international organization
that aims to get countries to cooperate with one another. The exceptions are Taiwan
(in 1971, the UN disqualified Taiwan and replaced it with the People’s Republic of
China), Vatican City, and Kosovo. The newest UN members are Switzerland (2002)
and Montenegro (2006).
What are the world’s newest countries?
The world’s newest country is Kosovo, which declared independence from Serbia in
February 2008. Before that, the newest country was Montenegro, which became a
country in June 2006, after splitting off from Serbia. Since 1990, 28 new nations
have come into being. Many of these emerged from the collapse of the Soviet Union
(14 countries) and the breakup of the former Yugoslavia (7 countries).
Which country is the biggest?
Russia is the largest country in the world, with 6,592,812 square miles (17,075,383
square kilometers) of area. It stretches across two continents, Europe and Asia. It is
far bigger than the next largest country in the world, Canada, which has 3,851,809
square miles (9,976,185 square kilometers) of area. 125
POLITICS AND
GOVERNMENT
Which country is the smallest?
The smallest country in the world is Vatican City. It is located on 108.7 acres (44
hectares) in the city of Rome, Italy. Vatican City is where the central government of the
Roman Catholic Church is located. The home of the pope, who is leader of the Church,
is also located there. About 850 people are citizens of Vatican City, which is ruled by
the pope, though a governor and a council actually run it. Vatican City has its own
money, postage stamps, flag, and diplomatic corps. Monaco, which is less than 1 square
mile (around 2 square kilometers) in area, is the second smallest country in the world.
How does the United States’s size compare with that of other countries?
The United States has an area of 3.79 million square miles (9.83 million kilometers)
and a population of more than 303 million people, making it the third or fourth
largest country by total area, and third largest by land area and by population. The
United States is one of the world’s most ethnically diverse nations.
How are countries formed?
Often it is a group of people with something in common, whose members identify
with one another, that makes up a country. It may be a shared race, religion, language,
history, or culture that makes people feel that they belong together as a
nation. Because of its uniqueness, the group feels that it should govern itself as an
independent country. This feeling of shared identity and loyalty to the group is frequently
behind the rise of nations. Some countries are so large and have such complicated
histories of war and conquest that they are home to many different groups
of people who have their own separate beliefs, languages, and customs. The differences
between these groups sometimes make it difficult for them to get along. A
nation is weakened by such groups if they put their own interests ahead of those of
their country. But a population of many different groups can also enrich a country
with diverse ideas and cultures if a spirit of acceptance and cooperation exists.
Which countries have the most neighbors?
Except for island nations, every country in the world touches at least one neighbor,
and most touch three or four. China has the most neighbors, 13 in all: Afghanistan,
Bhutan, Burma, Hong Kong, India, Laos, Macao, Mongolia, Nepal, North Korea,
Pakistan, Russia, and Vietnam. Russia is next in line, with 12 neighbors: Afghan -
istan, Czechoslovakia, China, Finland, Hungary, Iran, Mongolia, North Korea, Norway,
Poland, Romania, and Turkey. Five countries—Austria, Mali, Niger, Yugoslavia,
and Zambia—share borders with 7 neighbors.
What is a “landlocked” country?
A landlocked country is one that has no coastline, meaning it has no direct access
to a sea or ocean. As of 2007, there are 43 landlocked countries. Africa includes a
total of 15 landlocked countries; Asia has 12; Europe has 15; and South America has
126 2. The largest landlocked country is Kazakhstan, the ninth largest country in the
world covering just over 1 million square miles (2.65 million square kilometers).
Two countries in the world are double landlocked, which means that they are surrounded
only by other landlocked countries: Lichtenstein and Uzbekistan.
Does every country have its own flag?
Every country has a national flag, including the United States. Flags date back to
around 1000 B.C.E., when the Egyptians used primitive versions of flags—some were
even made out of wood or metal—to identify themselves and to signal to others.
Ships started using flags at sea to signal to each other and to harbors, often to let
them know they had a diseased crew aboard. Flags are still used today to let sailors
know what weather conditions await at sea. The military also made use of flags to
rally its troops. During the ancient wars, capturing an enemy’s flag was considered
an honorable seizure. Today, the most popular use of flags is to identify and symbolize
the world’s countries, which became commonplace in the 1700s. When new
lands are discovered—and, for example when Mount Everest and the Moon were
conquered—explorers raise their country’s flag as a sign of their being the first to
set foot on these unchartered lands.
WARS
Why are there wars?
Wars have taken place since the beginning of recorded history, and they surely
occurred before that as well. A war begins when one group of people (the aggressors)
tries to force its will on another group of people, and those people fight back.
War frequently springs from the differences between people, or from the desire of 127
Is there really a place called Atlantis?
Historians are still debating that question. Atlantis is the name of an island
that supposedly sank long ago, and on which was a great civilization. The
city of Atlantis has been mentioned in many stories and religions, and the
great philosopher Plato wrote about a great, technologically advanced sunken
continent in his book Critias in 360 B.C.E. Plato believed that Atlantis was
approximately the size of Libya and Asia put together, had a vast army with
chariots, and was located somewhere in the Atlantic Ocean. Although historians
agree there was no island like this in the Atlantic, in the Aegean Sea in
Greece, a volcanic island exploded in about 1645 B.C.E. The center of the
island, today called Santorini or Thera, sank. Excavations of this island show
an advanced civilization that may have been Atlantis. Archaeologists have
found sophisticated multistory buildings with wall paintings, furniture, and
stone and bronze pottery and an elaborate drainage system for the city.
POLITICS AND GOVERNMENT
one group to increase its power or wealth by taking control of another group’s land.
Often the aggressors feel that they are superior to the group they want to dominate:
they believe that their religion, culture, or even race is better than that of the people
they wish to defeat. This sense of superiority makes them feel that it is acceptable
to fight to take the land, possessions, and even lives of the “inferior” group, or
to force their ways on the dominated people.
Because countries can be very different from one another in government, religion,
customs, and ideology (ways of thinking), it is not surprising that nations disagree
on many things. But great efforts are usually made to settle the disagreements
through discussion and negotiation—a process called diplomacy—before
they result in anything as destructive as a war. War usually occurs when diplomacy
fails. Because science and technology have allowed us to create such powerful and
destructive weapons that can result in such devastating wars, we now have international
organizations that work all the time to try to keep peace among nations.
Which wars has the United States been involved in?
America has been involved in war since its beginnings, and American colonists or
U.S. citizens officially participated in more than 25 major conflicts. When Europeans
settled North America, for example, the Native Americans who lived there fought a
series of wars with them for the next 250 years, trying to keep their land and preserve
their way of life. They eventually lost the battle and were forced to either live
like their European conquerors or relocate to parcels of land set aside for them called
reservations. The Americans also fought in the Revolutionary War from 1775 to
1783, which the 13 early colonies fought with Great Britain in order to overthrow
Britain’s royal rule and declare their independence as a new nation, the United States
of America. Civil wars take place between groups of people within a single country.
The U.S. Civil War, which took place between 1861 and 1865 was a war between the
Northern states (called the “Union”) and the slave-holding Southern States (the
“Confederacy”) over the expansion of slavery into Northern territories. In the twentieth
century, the United States was involved in several major international wars—
wars occur between nations—including World War I (1914–1918), World War II
(1939–1945), the Vietnam War (1959–1975), and the Persian Gulf War (1990–1991).
Why did soldiers once wear armor?
Since ancient times, soldiers have worn special clothing or armor to protect themselves
during warfare. Hard materials like leather, wood, shells, and even woven
reeds were used to give soldiers extra protection against enemy arrows. Metal started
to be used for armor about 3,500 years ago, by warriors in the Middle East. By
the time of the ancient Greeks, about 1,000 years later, soldiers were well protected,
wearing large pieces of metal on their chests and backs, shin guards, and metal
helmets, and they carried metal shields.
Soon armored clothing, garments with metal strips and plates attached, began to
be made for soldiers. Then chain mail, a type of metal cloth, was 128 developed. Made of
small metal rings linked together, chain mail was much more flexible than metal
plates, but could not withstand the force of larger weapons, like lances. So full suits
of armor made of steel plates, hinged at the knees and the elbows, came into use
around the fourteenth century. Soldiers were covered with steel from head to toe,
with heavy metal helmets covering their faces, heads, and necks. A warrior could see
and breathe through small slits or openings in the helmet’s visor, a movable metal
flap that could be lifted up. (Only important or wealthy warriors could afford this kind
of elaborate armor.) Suits of armor weighed so much that the soldiers or knights who
wore them usually could not move around in them very well; they wore such armor
mostly when they fought on horseback. Even the horses sometimes wore armor.
As the methods and weapons of warfare changed, clumsy personal armor was
no longer useful. It became far more important for soldiers to be able to move
quickly and easily. Today’s soldiers usually wear cloth uniforms, body armor, and
steel helmets. But armor is used on war vehicles like tanks, naval vessels, and aircraft.
The bulletproof vests that police officers use are also a type of armor.
GOVERNMENTS
Why does government exist?
Governments exist for many reasons, but most importantly they exist to provide a
sense of order in the land. All governments tax, penalize, restrict, and regulate their 129
Suits of armor were often worn by soldiers centuries ago when fighting was done with swords and arrows. Such metal armor
would not deflect today’s bullets, however.
POLITICS AND GOVERNMENT
people. A democracy exists to give voice to the people and to protect their basic
human rights. In contrast, a totalitarian government exists to benefit the state or
those in charge, and this type of government empowers its leaders to rule in any
way they see fit. In this type of government, the people’s personal freedom is not
recognized. In the United States, the purpose of the government is outlined in the
Constitution: to form a more perfect union, to establish justice, to insure tranquility;
to provide for the common defense, to promote the general welfare, and to
secure the blessings of liberty. As a whole, our government provides us with an
organized system by which we can live as a nation in peace.
What types of government are there in the world?
There are three general forms of government, based upon who rules: (1) those governments
in which the authority is placed in one single person, (2) those dominated
by several people, and (3) those controlled by many. In some nations, governing
is done by a single individual, such as a king, queen, or dictator. This form of government
is known as an autocracy. An autocratic government is called an oligarchy
if a small group, such as landowners, military officers, or wealthy merchants, make
up the government. If the country’s people make up the government and contribute
to its decision-making process, that nation’s government is known as a democracy.
There are also several ways in which governments do their governing. Limited
governments, such as the United States and most countries in Western Europe, are
known as constitutional governments, since these governments are limited as to
what they are permitted to control. In other words, they have limited power, and this
limited power is enforced by a separation of powers. Most of these nations have constitutions
that define the scope of governmental power. In contrast to a constitutional
government, a government is called authoritarian when it has no formal limits;
the government is limited by other political and social institutions in the land—such
as churches, labor unions, and political parties. While these governments are sometimes
responsive to these sources of limitation, there is no formal obligation for the
government to represent its citizens. Examples of recent authoritarian governments
include Spain from 1936 to 1975 under General Francisco Franco.
Totalitarian governments attempt to control every area of political, economic,
and social life and are usually associated with dictators who seek to end other social
institutions that might challenge the government’s complete, or total, power. Some
examples of totalitarian governments include Nazi Germany from 1933 to 1945
under dictator Adolf Hitler, the Soviet Union from 1928 to 1953 under dictator
Joseph Stalin, and Cuba from 1959 to 2008 under Fidel Castro.
What is a democracy?
The word democracy comes from the ancient Greek word demokratia. Demo means
“the people” and kratia means “to rule.” A democracy, then, is a form of government
in which the people rule. The power lies in the hands of the people, who may either
govern directly or govern indirectly by electing representatives. 130 The American govhandy
ernment is a democracy, and the Constitution of the United States ensures this.
Under this “social contract” the people of the United States established a government,
gave it its powers, placed upon it certain limitations, set up its structure, and
provided the means of control over it. At the heart of democracy lies the concept of
“popular sovereignty”—the idea that the people are the supreme authority, or sovereignty,
and that authority rests in the body of citizens, not one supreme ruler.
AMERICAN GOVERNMENT
What does the U.S. government do?
The government is the institution that enforces our public policies. Public policies
are all the things that the government decides to do, such as impose an income tax,
service its armed forces, protect the environment, and hold businesses to certain
standards. In the democratic United States, the people elect representatives to the
government to carry out the popular will. The people who exercise the powers of
the government include legislators, who make the law; executives and administrators,
who administer and enforce those laws; and judges, who interpret the law.
Each year, Congress enacts about 500
laws and the state legislators enact
about 25,000 laws. Local governments
enact countless ordinances, or city laws.
What is the federal government?
The federal government is the national
government of the United States of
America. It includes the executive, legislative,
and judicial branches. The executive
branch is responsible for enforcing
the laws of the United States. Its main
components include the president, the
vice president, government departments,
and independent agencies. The
president is the leader of the country
and commander in chief of the armed
forces; the vice president is the president
of the Senate and the first in line for the
presidency should the president be
unable to serve; the departments and
their heads (called Cabinet members)
advise the president on decisions that
affect the country; and independent
agencies help carry out the president’s 131
A U.S. president is not all powerful, but as head of state he
has great influence on the country. Some presidents, such as
Abraham Lincoln, have been credited with changing the
course of American history.
POLITICS AND GOVERNMENT
policies and provide special services. The legislative branch is the lawmaking branch
of the federal government. It is made up of a bicameral (or two-chamber) Congress:
the Senate and the House of Representatives. The judicial branch, made up of the
Supreme Court and other federal courts, is responsible for interpreting the meaning
of laws, how they are applied, and whether or not they violate the Constitution.
What is the president’s job?
The president’s chief duty is to protect the Constitution and enforce the laws made by
Congress. However, he also has a host of other responsibilities tied to his job description.
They include: recommending legislation (laws) to Congress, calling special sessions
of Congress, delivering messages to Congress, signing or vetoing legislation,
appointing federal judges, appointing heads of federal departments and agencies and
other principal federal officials, appointing representatives to foreign countries, carrying
on official business with foreign nations, acting as commander in chief of the
armed forces, and granting pardons for offenses against the United States.
What is the difference between a senator and a representative?
The U.S. Congress consists of the Senate and the House of Representatives. Both
senators and representatives are responsible for representing the people of the
states they serve. This involves voting on and writing bills in the U.S. Congress.
There are, however, some major differences between a U.S. senator and a representative.
While both senators and representatives are permitted to introduce bills,
senators are restricted from introducing bills that raise revenue, such as tax bills.
There are 100 senators in Congress; two senators are allotted for each state. This
number is independent of each state’s population. However, the number of U.S. representatives
a state has is determined by the population of that particular state.
There are 435 representatives in Congress and each state has at least one represen-
132 tative. Another difference involves the length of time a senator and a representative
How can the average person get involved in the government?
The average person can get involved in the government by first educating
him- or herself about current issues. This can be done through reading
the paper daily, reading a weekly newsmagazine, or watching the evening
news. In order to make a difference, a person needs to have a working understanding
of the U.S. government—indeed, a democratic system of government
assumes there is a knowledgeable, interested public body of citizens.
Next to education, other very practical methods of involvement include
attending a city council meeting, volunteering at a local politician’s office,
working with voter registration drives, or registering to vote. Often, people
call or write legislators to voice their opinion on a certain topic, or participate
in nonviolent protest demonstrations or marches.
are permitted to serve. A senator represents his or her state for a six-year term. A
representative, on the other hand, serves for a two-year term.
How is state government organized?
Like the national government, state governments have three branches: the executive,
legislative, and judicial. Each branch functions and works a lot like its national
branch. The chief executive of the state is a governor, who is elected by popular
vote, typically for a four-year term (New Hampshire and Vermont have two-year
terms). Except for Nebraska, which has a single legislative body, all states have a
bicameral (two-house) legislature, with the upper house usually called the Senate
and the lower house called the House of Representatives, the House of Delegates, or
the General Assembly. The sizes of these two legislatures vary. Typically, the upper
house is made up of between 30 and 50 members; the lower house is made up of
between 100 and 150 members.
What is a governor’s job?
The governor is responsible for the well-being of his or her state. The details of this
job include many hands-on tasks and leadership duties. The governor’s executive
powers include the appointment and removal of state officials, the supervision of
thousands of executive branch staff, the formulation of the state budget, and the
leadership of the state militia as its commander in chief. Law-making powers
include the power to recommend legislation, to call special sessions of the legislature,
and to veto measures passed by the legislature. In 43 states, governors have
the power to veto (or reject) several parts of a bill without rejecting it altogether.
The governor can also pardon (excuse) a criminal or reduce a criminal’s sentence.
What does a mayor do?
The mayor-council is the oldest form of city government in the United States. Its
structure is similar to that of the state and national governments, with an elected
mayor as chief of the executive branch and an elected council that represents the
various neighborhoods, forming the legislative branch. The mayor appoints heads
of city departments and other officials. The mayor also has the power to veto the
laws of the city (called ordinances), and prepares the city’s budget. The council passes
city laws, sets the tax rate on property, and decides how the city departments
spend their money to make the city a better place.
What is a town meeting?
The town meeting is one aspect of local government that still exists today, although
it was created in the early years of the republic. At least once a year the registered voters
of the town meet in open session to elect officers, debate local issues, and pass laws
for operating a government. As a group, or body, they decide on road construction and
repair, construction of public buildings and facilities (such as libraries and parks), tax
rates, and the town budget. Having existed for more than two centuries, the town 133
POLITICS AND GOVERNMENT
meeting is often called the purest form of direct democracy because governmental
power is not delegated, but rather exercised directly by the people. However, town
meetings cannot be found in every area of the United States. They are mostly conducted
in the small towns of New England, where the first colonies were established.
What is the Bill of Rights?
The Bill of Rights is made up of the first 10 amendments to the U.S. Constitution.
The Bill of Rights guarantees rights and liberties to the American people. These
amendments were proposed by Congress in 1789, and ratified (approved) by threefourths
of the states on December 15, 1791, thereby officially becoming part of the
Constitution. The first eight amendments outline many individual rights guaranteed
to all people of this nation, while the Ninth and Tenth Amendments are general
rules of interpretation of the relationship among the people, the state governments,
and the federal government.
How does the Bill of Rights protect individual liberties?
The Bill of Rights limits the ability of the government to intrude upon certain individual
liberties, guaranteeing freedom of speech, press, assembly, and religion to all
people. Nearly two-thirds of the Bill of Rights was written to safeguard the rights of
those suspected or accused of a crime, providing for due process of law, fair trials,
freedom from self-incrimination and from cruel and unusual punishment, and protection
against being tried twice in court for the same crime. Since the adoption of
the Bill of Rights, only 17 additional amendments have been added to the Constitution.
While a number of these amendments revised how the federal government is
structured and operates, many expanded individual rights and freedoms.
What happens when a person breaks the law?
Laws are enforced by the courts and the judicial system. If an adult breaks a law in
the community or a business or organization does something illegal, they go to the
judicial branch of government for review of their actions. The judicial branch is
made up of different courts. The court leader, or judge, interprets the meaning of
laws, how they are applied, and whether they break the rules of the Constitution. If
a person or group is found guilty of breaking a law, the judicial system decides how
they should be punished.
In the United States, several laws have been written to protect the rights of someone
accused of committing a crime. He or she is considered innocent until proven
guilty in a court of law. Someone suspected of a crime is usually arrested and taken
into custody by a police officer. Sometimes, the case is presented before a grand jury
(a group of citizens who examines the accusations made). The grand jury files an
indictment, or a formal charge, if there appears to be enough evidence for a trial. In
many criminal cases, however, there is no grand jury. While awaiting trial, the
accused may be temporarily released on bail (which is the amount of money meant
to guarantee that the person will return for trial instead of leaving 134 the country) or
kept in a local jail. Trials are usually held before a judge and a jury of 12 citizens. The
government presents its case against an accused person, or defendant, through a district
attorney, and another attorney defends the accused. If the defendant is judged
innocent, he or she is released. If he or she is found guilty of committing a crime, the
judge decides the punishment or sentence, using established guidelines. The lawbreaker
may be forced to pay a fine, pay damages, or go to prison.
What is a citizen?
Citizens of the United States enjoy all of the freedoms, protections, and legal rights
that the Constitution promises. However, living in the United States doesn’t automatically
make a person an American citizen. Only those people born in the United States
or born to U.S. citizens in foreign countries are citizens of the United States. Persons
born in other countries who want to become citizens must apply for and pass a citizenship
test. Those who become citizens in this way are called naturalized citizens.
Why is it important to vote?
Republics such as the United States are based upon a voting population. If the citizens
of the country do not vote, then politicians do not necessarily need to heed
their interests. It is necessary for the people of a democratic country to constitutionally
voice their opinions, and they do this by voting for state propositions and
for their city, state, and country’s leaders.
Why is the Statue of Liberty such an important symbol of the United States?
The Statue of Liberty stands for many of the nation’s most cherished ideals: freedom,
equality, and democracy. Perhaps most importantly to the millions of immigrants
for whom the statue was one of their first sights of the United States, it
stands for the ideal of opportunity—the chance to begin a new life, in a new land.
While their lives in the United States were frequently difficult, for millions of immi- 135
Why do we need to follow the law?
Almost everything we do is governed by some set of rules. There are rules
for games, for sports, and for adults in the workplace. There are also rules
imposed by morality (or ethics) that play an important role in telling us what
we should and should not do. However, some rules—those made by the state
or the courts—are called “laws.” Laws are designed to control or alter our
behavior, and to help make society a more ordered place. If people were allowed
to choose at random what to do and how to behave, our country would be dangerous
and chaotic. Laws that govern business affairs help businesses to operate
properly, and laws against criminal behavior help to protect personal property
and human life.
POLITICS AND GOVERNMENT
grants America offered the chance to
escape from grinding poverty and abusive
governments in other lands.
Standing in the midst of New York
Harbor, the point of entry into the United
States for so many immigrants arriving
on ships from other countries, the
Statue of Liberty has been a powerful
symbol of opportunity for more than
100 years. A poem called “The New
Colossus,” written by Emma Lazarus,
was mounted on the statue’s pedestal in
the early 1900s. Its famous lines include
these words that Lazarus imagined Lady
Liberty to be saying:
Give me your tired, your poor,
Your huddled masses yearning to
breathe free,
The wretched refuse of your teeming
shore;
Send these, the homeless, tempest-tost
to me,
I lift my lamp beside the golden door!
Why is the bald eagle the official national symbol of the United States?
In 1782, six years after the end of the Revolutionary War, leaders of the newly independent
United States were designing a national seal, an image that would appear on
official documents and elsewhere. Eventually these men settled on the bald eagle for
the Great Seal of the United States. The bald eagle was chosen in part because it was
believed to be found only in North America. The bald eagle was also admired for its
strength, its noble appearance, and the freedom of its life spent soaring through the
sky. While the eagle became an important American symbol when it was adopted for
the U.S. seal in 1782, it wasn’t until 1787 that it officially became the national emblem.
The bald eagle has been used for the official seals of many states, and it has appeared
on stamps, currency (or paper money), and several coins, including the quarter.
What do the stars and stripes on the United States flag mean?
When the first United States flag was adopted in 1777, it had 13 alternating red-andwhite
stripes (seven red, six white) and, in the upper left portion, 13 white stars on
a blue background. The number 13 was chosen because that was the number of
original states that formed the United States. For several years after that design was
136 adopted, a new stripe and a new star were added each time a new state joined the
The Statue of Liberty, which has stood as a symbol of
American freedom since 1886, was a gift from France. The
statue was designed by sculptor Frederic Auguste Bartholdi.
Union, but in 1818 Congress decided to keep the number of stripes at 13 and simply
add a new star for each new state. The U.S. flag has several nicknames: the Stars
and Stripes, the Star-Spangled Banner, and Old Glory.
At the time the U.S. flag was designed, the stars and stripes (and the colors of
each) were given no specific meaning. The ideas for the design most likely were based
on other countries’ flags. In 1782, when the national seal was designed and the flag
was incorporated into it, national leaders decided that each color and symbol should
have a meaning. As reported in the book Our Flag, published by the U.S. House of
Representatives in 1989, it was decided that red symbolized “hardiness [strength] and
valour [bravery]”; white symbolized “purity and innocence”; and blue represented
“vigilance, perseverance, and justice.” It has also been said that the stars are symbols
of the heavens, and the stripes represent rays of light coming from the Sun.
How did we get the United States national anthem?
In September 1814, the United States and Great Britain were in the midst of fighting
what is known as the War of 1812. The British had taken over Washington, D.C.,
and planned to attack Baltimore, Maryland. A few American citizens, including a
lawyer and poet named Francis Scott Key, approached the British fleet, which was
anchored in Chesapeake Bay, to request the release of an American who had been
taken prisoner. The British agreed to let the prisoner and the others return to
American shores, but only after the British were done attacking Fort McHenry,
which was defending Baltimore.
Throughout the night of September 13–14, Key heard the explosions of the battle,
anxiously awaiting morning to see whether the Americans had won the battle. In the
early morning light, Key could see that Fort McHenry’s enormous American flag was
still waving, indicating that the Americans had been triumphant. Relieved and inspired
by the sight, Key composed a poem called “Defence of Fort M’Henry.” Its opening lines
recalled his first glimpse of the flag that morning: “Oh, say can you see, by the dawn’s
early light / What so proudly we hailed at the twilight’s last gleaming?” Key may have
had a popular tune in mind when writing the poem. That tune, called “To Anacreon in
Heaven,” had been an English drinking song, but it soon became linked with Key’s
poem, and the title of the new song became “The Star-Spangled Banner.”
“The Star-Spangled Banner” (which actually has four verses, though usually
only the first is sung) spread quickly throughout the country and became extremely
popular. It was played at important ceremonies and military functions for many
years before being officially declared the national anthem by Congress in 1931.
U.S. STATE FACTS AND TRIVIA
How did the United States begin?
The United States of America (USA), or United States for short, is a country that
takes its name from the fact that it is made up of states that are joined together, or 137
POLITICS AND GOVERNMENT
united, by the U.S. Constitution to form one nation. The country began as 13
colonies of England, which were spread out along the central Atlantic Coast of
North America. The original 13 colonies were Connecticut, Delaware, Georgia,
Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina,
South Carolina, Pennsylvania, Rhode Island, and Virginia. The first colony, Virginia,
was founded in 1607, and the thirteenth colony, Georgia, was founded in 1733.
More than 40 years passed before the colonies joined together, rebelled against England,
and declared themselves free, independent states on July 4, 1776, in the
famous Declaration of Independence.
To gain freedom, the colonies fought the Revolutionary War against the British.
The set of peace treaties that ended the war, called the Peace of Paris, was signed in
1783. With this treaty, England gave up its claim to the 13 colonies, along with all
land east of the Mississippi River from Canada to Florida. The original 13 colonies
became the first U.S. states, with additional states added into the Union over time.
Today there are 50 states, and one district, the District of Columbia.
The U.S. Constitution provided that new states can be admitted into the Union
by the U.S. Congress. Before they gained statehood, most of the other 37 states
passed through a period of time when they were known as territories, organized by
Congress. When the people of a territory felt they were ready to form a state gov-
138 ernment, they elected delegates, prepared a state constitution, and then voted to
A 1795 map made in England of the United States shows the original 13 colonies.
decide whether they would accept the constitution and ask Congress to approve
their admission into the Union. The dates that these territories were admitted into
the Union as states are their official birthdays.
Is the District of Columbia a state?
No, it is not a state or a part of any state. The District of Columbia, or D.C. for short,
is a district in the national capital, Washington, D.C. The district, named after
explorer Christopher Columbus, sits on the Potomac River on land that once
belonged to the state of Maryland. Because the city of Washington—which was
named after the nation’s first president, George Washington—covers the entire
area, the names “Washington, D.C.” and “District of Columbia” have the same
meaning. The area is 69 square miles (178 square kilometers) and a federal district,
meaning it is an area reserved as the seat of the U.S. government. So, Washington,
D.C. is almost like two cities in one—a federal city with government monuments,
buildings, and parks (including the White House, the Capitol, and the Supreme
Court), and an everyday city more than half a million people call home.
Why do states have names and nicknames?
When people initially founded the states of the nation, the first thing they did was
choose a name for their area of land. The name helps establishes the identity of the
state. Almost half of the states have names of that come from Native American languages;
for example, Arizona probably came from the Indian word arizonac, meaning
“small springs” and Connecticut came from the Indian quinnitukq-ut, meaning
“at the long river.” Other states were named for people or places—the Spanish
explorer Juan Ponce de León named Florida after the Spanish words Pascua florida,
meaning “flowery Easter.” He discovered Florida during the Easter season, in
March 1513, when his ships landed on Florida’s east coast near present-day St. 139
Which states were not organized as territories first?
Afew U.S. states outside of the original 13 have been admitted that were
never organized territories of the federal government. The most notable
are Vermont, an unrecognized, independent republic until its admission in
1791; Kentucky, a part of Virginia until its admission in 1792; Maine, a part of
Massachusetts until its admission in 1820 following the Missouri Compromise,
an agreement that regulated slavery in the Western territories; Texas, a
recognized independent republic until its admission in 1845; California, created
as a state out of the unorganized territory of the Mexican Cession in 1850
without ever having been a separate organized territory; and West Virginia,
created from areas of Virginia that rejoined the Union in 1863, after the 1861
secession of Virginia during the Civil War era.
POLITICS AND GOVERNMENT
Augustine. “La Florida” had a lavish landscape, abundant flowers, and beautiful
beaches, so the state name embodies both aspect of de León’s discovery.
Similarly, the people give nicknames to their states to further establish their identities.
Alaska is called “Land of the Midnight Sun,” because the Sun shines almost all
night long during Alaskan summers; Colorado is nicknamed the “Centennial State”
because it became a state in the year 1876, 100 years after the signing of our nation’s
Declaration of Independence; Georgia is called the “Peach State” because of the growers’
reputation for producing delicious peaches; and Wyoming is known as the “Equality
State” because of the civil rights women have traditionally enjoyed there.
In addition to naming their states, founders design a flag, using colors and symbols
that have special meaning. They also choose mottoes (words or phrases), often
in Latin, that help express the state’s character. For example, New York’s motto is
Excelsior, Latin for “Ever upward!” Oklahoma’s motto, Labor omnia vincit, means
“Labor conquers all things.” Another important emblem is the state seal, which is
placed on all official documents and usually bears the state motto.
Which is the largest state (in area), and which is the smallest?
Alaska, the northernmost and westernmost state of the United States, is the largest
state of the Union, covering 571,951 square miles (more than 1.4 million square kilometers).
It makes up the extreme northwestern region of the North American continent
and is separated from Asia by the 51-mile- (82-kilometer-) wide Bering Strait.
Alaska has been a part of the United States since 1867, when it was bought from Russia
by Secretary of State William H. Seward for $7.2 million. The smallest state is
Rhode Island, which covers just 1,045 square miles (2,706 square kilometers). Rhode
Island—officially named the State of Rhode Island and Providence Plantations—was
the first of the 13 original colonies to declare independence from British rule (on May
4, 1776) and the last to ratify the United States Constitution (on May 29, 1790).
Which state has the most people?
California, a state on the West Coast of the United States, along the Pacific Ocean,
140 is the third largest state by area and the most populous U.S. state. By 2007, Califor-
How can you travel across Alaska’s miles of snow?
By dog sled, of course! The native people of Alaska’s icy terrain have been
traveling by dog sled for hundreds of years. Dog racing is such a part of the
state’s history that Alaskans hold an annual event, the Iditarod (dubbed “The
Last Great Race on Earth”), a competitive dog-sled race over 1,150 miles (1,850
kilometers) of sub-zero terrain. From Anchorage, in south central Alaska, to
Nome on the western Bering Sea coast, each team of 12 to 16 dogs and their
musher cover over more than 1,000 miles (1,609 kilometers) in 10 to 17 days.
nia’s population reached about 37.7 million people, making it the most populated
state, and the thirteenth fastest-growing state in the nation. Almost 12 percent of
all American citizens live in California.
Where can you stand in four states at the same time?
The Four Corners, located 40 miles (64 kilometers) southwest of Cortez, Colorado,
is the only place in the United States where four states come together at one place.
Arizona, New Mexico, Utah, and Colorado meet at the Four Corners. Here, a person
can put each of his or her hands and feet in four states at the same time. The unique
landmark is on Navajo Nation land and is open for visits from the public. The area
surrounding the monument is also Indian land, which includes part of New Mexico,
Utah, and Arizona and covers 25,000 square miles (64,750 square kilometers).
The Four Corners Monument was originally established by the U.S. Government
Surveyors and Astronomers in 1868 with the survey of Colorado’s southern
boundary. Surveys followed of New Mexico’s west boundary and Utah’s east boundary
in 1878. The northern boundary of Arizona was surveyed in 1901. A small permanent
marker was made in 1912 to
show where the boundaries of the four
states intersect. The Monument was
refurbished in 1992 with a bronze disk
embedded in granite. The disk shows
the state boundaries and each state’s
seal rests within that state’s boundary.
Which state was once an
independent kingdom?
Hawaii is the only U.S. state that was
once a kingdom with its own monarchy.
From 1810 to 1893, Hawaii was an independent
kingdom, ruled by King Kamehameha
I and his successors, including
David Kalakaua, the last king of Hawaii.
It was formally annexed by the United
States in 1898, became a territory in
1900, and was admitted to the Union as
a state in 1959. The state of Hawaii is
made up of eight main islands—Niihau,
Kauai, Oahu, Maui, Molokai, Lanai,
Kahoolawe, and the Big Island of
Hawaii—and is America’s 50th state.
141
A statue of King Kamehameha stands in front of Honolulu’s
Judiciary Building. Hawaii was an independent kingdom
before it became America’s fiftieth state.
POLITICS AND GOVERNMENT

NUTS AND BOLTS
What is the difference between an invention and a discovery?
An invention is something that is made by human beings and that did not exist in
the world before. Inventions include items, devices, processes, materials, machines,
and toys—from AstroTurf® to zippers. A discovery is something that existed before,
but was not yet known or “discovered”; for example, the concept of black holes in
outer space. Inventions and discoveries usually come about by bringing together
existing technologies in a new way, and they may take centuries to take shape. They
usually are created in response to a specific human need, such as a medicine to heal
sickness; as a result of the creator’s desire to complete a task more efficiently or
effectively, such as a tool or machine; or even by accident, such as the Slinky. Sometimes
just one person makes the discovery or invention; other times the end result
is the product of a team effort. Sometimes different people have made the same
invention independently at the same time. In very rare cases different people have
made the same invention on the same day.
What is a patent?
According to the United States Patent and Trademark Office, a patent for an invention
is the grant of a property right to the inventor. A patent gives the inventor the right
to exclude others from making, using, offering for sale, or selling his or her invention
in the United States or importing the invention into the United States. According to
the Patent and Trademark Office, any person who invents or discovers any new and
useful process, machine, manufacture, or composition of matter may obtain a patent.
The American inventor Thomas Edison filed more than 1,000 patents in his lifetime,
including 141 patents for batteries and 389 for electric light and power. 143
HOW THINGS
WORK
What was the Industrial Revolution?
The Industrial Revolution was an era of sweeping change, as the focus in different
societies changed from agricultural to mass-producing and industrial. It began in
Great Britain in the 1700s. By the early 1800s it had spread to western Europe and
the United States. It was brought about by the introduction of steam-power-driven
machinery to manufacturing. As inventors made new machines that could take over
manual labor, sweeping changes in agriculture, textile and metal manufacture,
transportation, economic policies, and social structures took place. By the end of
the eighteenth century, most finished goods—which had once been made by hand
or by simple machines—were produced in quantity by technologically advanced
machinery. Factories were built to house the new machines, causing a population
shift from rural areas to urban ones.
What is the Nobel Prize?
The Nobel Prize is the most famous international science award. Three science
prizes, for chemistry, physics, and physiology or medicine, are awarded every year
to people who have made significant contributions to these fields. The prize was
created by the Swedish chemist and industrialist Alfred Nobel, who made a fortune
from his invention of dynamite and left much of his money to fund the prize. Since
1901, the Nobel Prize has been honoring men and women from all parts of the
world for their discoveries and inventions in these areas, as well as in the fields of
literature and peace. Some famous scientists and inventors who have been awarded
the prize include Ivan Pavlov (in 1904), Albert Einstein (1921), and Linus Pauling
(1954). Eleven women, from a total of 500 scientists, have been awarded a Nobel
Prize in the sciences from 1901 to 2008. Among them, Marie Curie is the only person
ever to have twice received a Nobel Prize in the sciences, each time in a different
field of specialization: in Physics, in 1903, and in Chemistry, in 1911.
BUI LDINGS
How is steel used in skyscrapers?
Tall, multistory structures called skyscrapers are made of steel, which is sturdier
and lighter in weight than other building materials, such as brick and stone. In the
late 1800s, when steel production became common, architects experimented with
steel, forming it into long, thin pieces called girders. The first skyscrapers, built in
the United States in the 1880s, were constructed using vertical columns and horizontal
beams made from steel girders. This supporting skeleton allowed buildings
to rise to 10 or more stories. Skyscrapers grew taller when designers began using
bundled steel tubes instead of heavy girders. Tube buildings, like Chicago’s Sears
Tower, get most of their support from a stiff grid of steel columns and beams in
their outer walls. The lighter weight pieces need less support, and so architects can
144 add more height. Additional beams can be placed diagonally for additional support
while adding little extra weight.
The girders and beams are bolted
together and welded on all sides so
that the building will not sway
from side to side as a unit when
there is wind.
What is the tallest building in
the world?
When its construction is completed,
the Burj Dubai skyscraper in
the United Arab Emirates will be
the world’s tallest skyscraper at
2,064 feet (629 meters) high. As of
early 2009, the world’s tallest
completed skyscraper was still the
Taipei 101, located in the Hsinyi
district of Taipei, Taiwan. With 101
stories, it reaches 1,671 feet (509
meters) high. Taipei 101 became
the world’s tallest building when it
was finished in 2003, surpassing the
Petronas Towers in Kuala Lumpur,
Malaysia, the world’s tallest twin
towers. The Sears Tower in Chicago,
Illinois, is the world’s third
tallest building that people can
live and work in. Built from 1970
to 1974 for Sears, Roebuck &
Company, it rises 110 stories to a height of 1,450 feet (442 meters). (If you count
the tower’s antenna, it actually reaches 1,730 feet [527 meters]) high. Another very
tall structure (though it is not a skyscraper building where people can live and
work) is the CN Tower in Toronto, Canada. This transmission tower is 1,815 feet
(553 meters) tall and was built in 1976.
How do elevators work?
An elevator moves things or people from one level to another, and is important to
tall structures like skyscrapers. The car of an elevator, in which people ride, is
attached to guard rails inside a tall, empty space called a shaft. It is moved by a steel
cable that is attached to a large weight that counterbalances it. An electric motor
raises and lowers the cable, changing the positions of the car and weight as the elevator
moves from floor to floor. (Usually posted inside an elevator are numbers that
indicate the car’s weight limit; an elevator motor cannot do its job if a car is a lot
heavier than the weight that balances it.) 145
The Burj Dubai skyscraper, located in the United Arab Emirates, will
be the world’s tallest skyscraper when it is completed.
HOW THINGS WORK
The first elevators in use were not especially safe because once in a while a
cable would break, and a car, pulled by gravity, would come crashing down. Safety
devices were soon added, though, to keep such disasters from occurring.
(American inventor Elisha Otis invented the first “safety” elevator in 1853.) Additional
ropes attached to cars and powerful metal “jaws” that grip guard rails keep
elevators from falling if their main cables break. Other safety devices keep elevators
from moving when their doors are still open and from traveling too fast.
Automatic switches in the shaft allow an elevator to hurry past unwanted floors,
or to slow and stop when a chosen floor is reached, unlocking its doors to admit
and release passengers. Very long elevators are not always practical, so some
buildings use one set of elevators to take passengers part way up the building and
another set to service the upper floors.
How does an escalator work?
The escalator is a set of moving stairs that transports people from one floor to
another in a department store, airport, or other public place. Underneath the stairs
is a continuous belt that moves around wheels. The stairs are attached to two side
belts or to one central belt, which is driven by electricity. The moving handrails on
both sides of the escalator work the same way and are timed at the same speed as
the steps. At the top and bottom of the escalator, the steps fold flat so they can move
underneath the floor, and after traveling around the belt they open up and start
again. The same set of steps can be used to run up or down, depending on the direc-
146 tion in which the belt is driven.
Why are they called skyscrapers?
Some buildings are called skyscrapers because they are of great height and
have an iron or steel frame inside that supports its floors and walls. Before
builders figured out how to make such frames, stone or brick walls had to
bear the weight of structures, which could not stand up if they were made too
high. And tall stone or brick buildings had to have very thick walls on lower
floors to bear the weight of the walls and floors above them. These thick walls
wasted a lot of useful space. Because cities have limited land, builders experimented
with materials and construction methods in an effort to construct
taller buildings that were more practical. Finally, in 1885, William Le Baron
Jenny built the first modern skyscraper in Chicago. While just 10 stories high,
which seems short by today’s standards, the Home Insurance Company Building
was the first structure to have an internal steel skeleton bear all of its
weight. From that point on, tall buildings began to soar into the air, scraping
the sky. Just 30 years after the first skyscraper was built, buildings were erected
that reached 60 stories high.
MOVING ON THE GROUND
How does a cable car stop and go?
Also called an “endless ropeway,” the cable car was invented by Andrew S. Hallidie,
who first operated his system in San Francisco, California, in 1873. A cable car
moves because of its cable, which runs continuously in a channel, between the
tracks located just below the street. The cable is controlled from a central station,
and usually moves about 9 miles (14.5 kilometers) per hour. Each cable car has an
attachment, on the underside of the car, called a grip. When the car operator pulls
the lever, the grip latches onto the moving cable and is pulled along by the moving
cable. When the operator releases the lever, the grip disconnects from the cable and
comes to a halt when the operator applies the brakes.
Who invented the automobile?
The history of the automobile is complex and dates back to the fifteenth century
when the Italian inventor and engineer Leonardo da Vinci was creating designs and
models for transport vehicles. However, two men, Karl Benz and Gottleib Daimler,
are both credited with the invention of the gasoline-powered automobile, because
they were the first to make their automotive machines practical to people. Both
German engineers living in the nineteenth century, Benz and Daimler worked independently,
unaware of each other’s efforts. Both built compact, internal-combustion
engines to power their vehicles. Benz built his three-wheeler in 1885; it was
steered by a tiller (a farming tool used to prepare the soil for planting). Daimler’s
four-wheeled vehicle was produced in 1887.
What were some of the earliest steam- and gasoline-driven vehicles?
Before Benz and Daimler, there were earlier, self-propelled road vehicles, including
a steam-driven contraption invented by Nicolas-Joseph Cugnot. The French inventor
rode the Paris streets at 2.5 miles (4 kilometers) per hour in 1769. Richard Trevithick,
a British inventor and mining engineer, also produced a steam-driven vehicle
that could carry eight passengers. It first ran in 1801, in Camborne, England.
Londoner Samuel Brown built the first practical four-horsepower gasoline-powered
vehicle in 1826. And the Belgian engineer J.J. Etienne Lenoire built a vehicle with
an internal combustion engine that ran on liquid hydrocarbon fuel in 1862, but he
did not test it on the road until September 1863, when it traveled a distance of 12
miles (19.3 kilometers) in three hours.
How does an electric car work?
On the outside, most electric cars look exactly like gas-powered cars. An electric
car does not have a tailpipe or a gas tank, but the overall structure is basically the
same. Instead of a huge engine, an electric car uses an electric motor to convert
electric energy stored in batteries into mechanical energy. Different combinations
of generating mechanisms—solar panels, generative braking, internal combustion 147
HOW THINGS WORK
engines driving a generator, fuel cells—
and storage mechanisms are used in
electric vehicles.
When did people first use
electric cars?
During the last decade of the nineteenth
century, the electric vehicle became
especially popular in cities across America.
People had grown familiar with
electric trolleys and railways, and technology
had produced motors and batteries
in a wide variety of sizes. The Edison
Cell, a nickel-iron battery, became the
leader in electric vehicle use. By 1900,
electric vehicles were the most popular
car. In that year, 4,200 automobiles
were sold in the United States. Of these,
38 percent were powered by electricity,
22 percent by gasoline, and 40 percent
by steam. By 1911, the automobile
starter motor did away with handcranking
gasoline cars, and Henry Ford
had just begun to mass-produce his
Model T’s. By 1924, not a single electric vehicle was exhibited at the National Automobile
Show, and the Stanley Steamer was scrapped that year.
Because of “Clean Air” legislation, the energy crises of the 1970s, and concern for
the well-being of the environment, car manufacturers have again marketed several
all-electric cars and “hybrid” vehicles. Hybrid cars use two or more different power
sources to propel them, such as a gasoline engine and an electric motor. General
Motors sold the Impact, an electric vehicle. And Honda offered people two hybrids, the
Insight and a Civic sedan. The Toyota Prius is a hybrid that first went on sale in Japan
in 1997, making it the first mass-produced hybrid vehicle. According to the United
States Environmental Protection Agency, the 2008 Prius is the most fuel-efficient car
sold in the United States. Because of this, electric cars and hybrid vehicles may be the
new cars of the future, eventually replacing all-gasoline-powered cars.
What are the types of bridges, and how do they work?
There are more than half a million bridges in the United States. They transport people
across valleys, streams, and railroads, and they are constructed as one of four
basic types: a beam bridge, an arch bridge, a suspension bridge, and a cantilever
bridge. The simplest and most common form of bridging, the beam bridge has
straight slabs or girders carrying the roadbed. Its span is relatively short (often not
148 more than 250 feet [76 meters]) and its load rests on its supports or piers. The arch
Many people hope that electric cars will help reduce pollution,
as well as America’s dependence on oil from other countries.
bridge, usually made of steel or concrete, looks like an arch, and thrusts outward
on its bearings at each end. They can span up to 800 feet (244 meters). In the suspension
bridge, the roadway hangs on steel cables, with the bulk of the load carried
on cables anchored to the banks. Suspension bridges can span great distances—
2,000 to 7,000 feet (610 to 2134 meters)—without intermediate piers. A cantilever
bridge is a bridge built using cantilevers—structures that are built horizontally into
space, supported on only one end. The cantilevers may be simple beams; however,
large cantilever bridges made to handle road or rail traffic use trusses, an interconnected
framework of beams, built from structural steel.
Where is the longest bridge?
The longest bridge in the United States—and the world, for that matter—consists
of two parallel bridges called the Lake Pontchartrain Causeway, near New Orleans,
Louisiana. The Causeway runs over water, is 23.87 miles (38.42 kilometers) long,
and is supported by more than 9,000 concrete pilings. The south end of the Causeway
is in Metairie, Louisiana, a suburb of New Orleans, and the north end is in Mandeville,
Louisiana. 149
What is the importance of America’s interstate highways?
Today, two million trucks travel the interstates and move more than 10 billion
tons of goods across the United States. It is possible for them to drive
more than 2,400 miles (4,000 kilometers) from the East Coast to the West
Coast, or more than 1,200 miles (2,000 kilometers) from the Canadian border
to the Mexican border—all thanks to the interstate (“between states”) highways.
People in passenger cars can also drive these distances, making it possible
for them to travel easily and quickly from one part of the country to
another. The highways, which have no traffic signals or stop signs, cross more
than 55,000 bridges and can be found in 49 of America’s 50 states. (Only Alaska
has no interstate highways, although Hawaii’s “interstate” highways don’t
cross state lines either). The Interstate Highway system is usually two roads,
one in each direction, separated by an area that is planted with grass and
trees. Each road holds two lines of cars that can travel at speeds between 65
and 75 miles per hour (104 to 120 kilometers per hour).
The Interstate Highway system—signed into law in 1956 by President
Dwight Eisenhower—set off a highway-building boom that produced nearly
47,000 miles (75,639 kilometers) of interstate highways as of 2004. It has been
an important part of the nation’s economic growth since the 1950s, as trucks
using the system carry about 75 percent of all products that are sold in the country.
Jobs and new businesses have been created near the busy interstate highways,
including hotels, motels, diners and fast-food restaurants, gas stations, and
shopping centers. At the end of the twentieth century, the U.S. government
renamed the Interstate Highway system to the Eisenhower Interstate System.
HOW THINGS WORK
New York City houses the Verrazano-Narrows Bridge, the longest suspension
bridge (a type of bridge where the main load-bearing elements are hung from suspension
cables) in the United States. Its total length is 4,260 feet (1,298 meters).
The ends of the bridge are at historic Fort Hamilton in Brooklyn and Fort
Wadsworth in Staten Island, both of which guarded New York Harbor at the Narrows
for over a century. The bridge was named after Giovanni da Verrazano, who,
in 1524, was the first European explorer to sail into New York Harbor. Next in line
is San Francisco’s Golden Gate Bridge, which is 4,200 feet (1,219 meters) long. The
third longest suspension bridge in the United States is Michigan’s Mackinac Straits
suspension bridge, which connects the upper and lower peninsulas of the state.
Nicknamed “Big Mac,” the bridge spans 3,800 feet (1,158 meters).
Other cities around the world with long suspension bridges include Japan, Denmark,
China, and England: The Akashi Kaikyo Bridge, for example, also known in
Japan as the Pearl Bridge, is the longest suspension bridge in the world with a main
span of 6,532 feet (1,991 meters). By comparison, the bridge is almost one-quarter
mile longer than the previous record holder, the East Bridge (StoreBaelt) in Denmark,
which opened the same year, in 1998.
Who built the Brooklyn Bridge?
John A. Roebling, a German-born American engineer, constructed the first truly
modern suspension bridge in 1855. Its characteristics included towers supporting
150 massive cables and a roadway suspended from main cables. In 1867, Roebling was
The historic Brooklyn Bridge in New York was completed in 1883 and is still heavily used by traffic today.
given the ambitious task of constructing the Brooklyn Bridge. In his design he proposed
the revolutionary idea of using steel wire for cables rather than the lessresilient
iron. Just as construction began, Roebling died of tetanus when his foot
was crushed in an accident, and his son, Washington A. Roebling, took over the
bridge’s construction. Fourteen years later, in 1883, the bridge was completed. At
that time, it was the longest suspension bridge in the world, spanning the East
River and connecting New York’s Manhattan with Brooklyn. The bridge has a central
span of 1,595 feet (486 meters), with its masonry towers rising 276 feet (841
meters) above high water. Today, the Brooklyn Bridge is among the best-known of
all American civil engineering accomplishments.
How are tunnels built?
Bored through mountains or burrowed beneath oceans, tunnels provide spaces for
cars and trains, water and sewage, and power and communication lines. Although
tunnels have existed for thousands of years—Roman engineers created the most
extensive network of tunnels in the ancient world—they have been perfected by
today’s technology. To build a stable tunnel, engineers dig through the earth, or
excavate, using special tools and equipment. If the ground is unstable, engineers
must support the ground around them while they dig. For the support work, they
often use a tunnel shield, a cylinder pushed ahead of tunneling equipment to provide
advance support for the tunnel roof. For harder, mountainous rock, engineers
use humungous rock-breaking devises called tunnel-boring machines. Once the
tunnel is structurally sound, engineers line tunnels with final touches, like the
roadway and lights. If builders are working underwater, pre-made tunnel segments
are often floated into position, sunk, and then attached to other sections.
How does a roller coaster work?
A roller coaster works the same way as a bicycle coasting down a hill. When you ride
your bike to the top of a hill, you pedal to get there. Then, to coast down the hill, you
take your feet off the pedals and glide down the other side. If the slope is steep enough,
you can go very fast. Similarly, a roller coaster is only powered at the beginning of the 151
What is a “kissing bridge”?
“Kissing bridges” are covered bridges with roofs and wooden sides. They
are called kissing bridges because people inside the bridge cannot be
seen from the outside, making them good places to kiss discreetly. They were
first built in the nineteenth century by engineers who designed coverings to
protect the structures from the effects of the weather. More than 10,000 covered
bridges were built across the United States between 1805 and the early
twentieth century. As of January 1980, only 893 of these covered bridges
remained—231 in Pennsylvania alone, where the first one was erected.
HOW THINGS WORK
ride, when the coaster, or train, is pulled up the first hill. When it goes over the top
of the hill, the weight of the train itself, pulled downward by gravity, is what keeps the
entire unit moving. There are no cables that pull the train around the track. This conversion
of potential energy (stored energy) to kinetic energy (the energy of motion) is
what drives the roller coaster, which often reaches 60 miles (96.5 kilometers) per
hour. Running wheels guide the train on the track, and friction wheels control the
train’s movement to either side of the track. A final set of wheels keeps the train on
the track even if it is upside down. Air brakes stop the car as the ride ends.
FLYING HIGH
How do airplanes fly?
Airplanes function according to a complex mix of aerodynamic principles—theories
that explain the motion of air and the actions of bodies moving through that air.
Airplanes get their power from engines. Small planes generally use piston engines,
which turn propellers that push aircraft through the air in the same way that boat
propellers push vessels through water. But bigger planes use jet engines, powered
by burning fuel. These engines expel great amounts of air that thrust a plane forward
and up. An airplane must be in constant motion—its wings slicing through
rushing air to create lift—in order to stay up; moving air is also required to steer
it. In order to get enough lift to rise into the air on takeoff, an airplane has to travel
along the ground first at great speed.
Airplanes are able to lift into the air and stay there because of the shape of their
wings. An airplane wing is flat on the bottom and curved on the top. When a plane’s
engines push it forward, air divides to travel around its wings. The air that passes
over the larger curved top moves faster than the air that passes under the flat bottom.
The faster-moving air on top becomes thinner and has lower pressure than the
air below, which pushes the wing up. Uneven air pressure caused by the shape of an
airplane’s wings, then, creates a force called lift, which allows an aircraft to fly.
How do pilots steer an airplane?
The force of moving air steers an airplane. Steering is done through a system of
moveable flaps—working much like boat rudders—that are located on the plane’s
wings and tail. When set at an angle, they push at flowing air that pushes back,
turning or tilting an airplane. To descend, for instance, a pilot lowers a plane’s tail
flaps, causing airflow to direct its nose downward. Turning requires changing the
direction of wing flaps and the tail rudder.
Who were the Wright brothers?
The Americans Wilbur and Orville Wright, known as the Wright brothers, were the
152 first people to successfully build and fly an airplane. The owners of a bicycle shop in
their hometown of Dayton, Ohio, Wilber
and Orville were interested in mechanics
from early ages. After attending high
school, the brothers went into business
together and, interested in aviation,
began experimenting with gliders in
their spare time. The brothers consulted
national weather reports to figure
out the best place to conduct flying
experiments. They determined that the
ideal location was Kitty Hawk, North
Carolina. So in 1900 and 1901, on a narrow
strip of sand called Kill Devil Hills,
they tested their first gliders. Back in
their bicycle shop in Ohio, they built a
small wind tunnel in which they ran
experiments using wing models to
determine air pressure.
The Wright brothers use their
research to design and build an airplane,
which they tested in Kitty Hawk in 1903.
On December 17 of that year, they made
the world’s first flight in a power-driven,
heavier-than-air machine. Orville piloted
the craft a distance of 120 feet (36.5
meters) and stayed in the air 12 seconds. The brothers made a total of four flights
that day, and Wilbur made the longest: 59 seconds of flight time that covered just
more than 850 feet (259 meters). They received little media attention for their
efforts, until 1908, when they signed a contract with the Department of War to build
the first military airplane. A year later, they set up the American Wright Company
to manufacture airplanes.
What is a supersonic airplane?
A supersonic airplane is shaped quite differently than a regular, “subsonic” plane, or
commercial plane. It is usually shaped like a dart, with a long pointed nose and wings
that swing back and hug the plane body. This slim shape causes less friction as it races
through the air. The close-set wings also stay within the shock waves the plane creates,
which is necessary to maintain control of the aircraft. While the special wings of
supersonic planes don’t provide as much lift as those of regular planes, the aircraft get
the lift they need for takeoffs and landings by traveling at very high speeds.
How do helicopters fly?
Although a helicopter doesn’t have wings like an airplane, it uses the same principle
of lift to rise and maneuver in the air. The blades of a helicopter’s propeller-like 153
A 60-foot-tall memorial to Orville and Wilbur Wright’s
historic airplane flight was dedicated at Kill Devil Hills, North
Carolina, in 1932.
HOW THINGS WORK
top rotor are shaped just like a plane’s wings—flat on the bottom and rounded on
the top—and are likewise adjustable. Instead of rushing forward through the air
like a plane does to gather enough lift to fly, a helicopter moves only its (three to
six) rotor blades, which are attached to a central shaft driven by an engine. The
rotor blades slice through enough air—creating the changes in surrounding air
pressure that produce lift—to achieve flight. Adjusting the angle at which the rotor
blades are set helps control a helicopter’s lift and manner of flight. Because the
angle of the rotor is adjustable, too, a helicopter has far greater maneuverability
than an airplane: besides moving up, down, and forward, it can fly backward and
hover in the air.
THE WATER HIGHWAY
How do boats float?
The weight of an object pulls it down into water. It displaces or pushes water aside.
But if the object’s density (its weight in relation to its size) is less than the density
of the water it displaces, it will float. That principle explains why a heavy wooden
raft can float in water, while a small stone will sink to the bottom: the raft spreads
its weight over a large area, while the stone’s weight is concentrated.
Boats, which are hollow, float because of this principle. The air inside them
makes them less dense than they appear. Large ships that transport heavy material,
though, have less air inside when they are carrying a big load. Such ships must be
careful about weight limits and have load lines on their hulls that show how low
they can ride in the water and still maneuver safely. Weight limits vary with the kind
of water the boats are traveling through: they can carry more weight when in saltwater
seas, which are denser than freshwater, and in cold water, which is denser
than warm water.
How are boats powered to move through the water?
Boats need a power source to move them forward in the water. In small vessels this
power can be provided by people, who use oars to paddle along. Muscle power cannot
move boats very fast or very far, though. The wind can be used, too, to move
boats equipped with sails. But for a large boat that needs to go a long distance, the
most reliable source of power is a motor-driven engine.
Depending on the size of the boat, a gasoline engine, diesel engine, or steam
engine does the job. Nuclear power is even used to run some boat engines, like
those found in submarines. Motors rotate boat propellers, which have large twisting
blades that radiate around a central hub. These blades push water backward,
and the boat moves forward as the disturbed water pushes back. Rotating propellers
also create lower water pressure in the space in front of them, which sucks them
154 forward, along with the vessel to which they are attached. (Using these same prinhandy
ciples of movement, propellers can also power aircraft.) A boat is steered by a rudder,
which is a flat, upright, movable piece of wood or metal that is attached to its
stern, or rear. When turned, the rudder changes the direction of the water around
it, which pushes back, forcing the stern, and gradually the rest of the boat, to
change direction, too.
How do submarines sink below the water and then rise?
The body of a submarine is uniquely constructed. Under its strong outer hull are
huge ballast tanks that surround its working core. The tanks can be filled with and
emptied of seawater and air, which allows the submarine to sink or rise in the water.
When a submarine travels on the surface, its ballast tanks are filled with air,
which makes it less dense than the seawater it displaces, and it floats. But when a
submarine needs to submerge or dive below the surface, its ballast tanks are flooded
with seawater. This action makes the submarine sink; now equal in density to the
water that surrounds it, it can move about below the surface. Motor-driven propellers
are used to move the vessel along (its streamlined shape creates as little
water resistance as possible), and swiveling fins (called hydroplanes) located on its
sides direct it up and down. When a submarine needs to return to the surface, compressed
air stored in tanks is blown into the ballast tanks. This air forces out the
seawater, and the vessel begins to rise, aided by the hydroplanes. Once again lighter
than the seawater it displaces, the submarine is able to float on the surface.
How do submarine pilots know where they are going when they are
underwater?
Submarine pilots use a periscope to navigate their direction if they are not too far
below the water’s surface. This tall, rotating, tube-shaped instrument can be raised
above the water’s surface to view surroundings, using a series of mirrors and lenses
inside to relay images. Beyond that, submarines use sonar (sound waves) to make 155
Submarines fill or empty their ballast tanks with water in order to float or sink under water.
HOW THINGS WORK
echo soundings of their surroundings. Transmitted sound waves are reflected off
objects or the ocean floor; the time it takes for these sound waves to be reflected
back indicates how far away things are located. The echoes are then converted into
electrical signals that appear on a display screen, which gives a picture—similar to
that of an airport’s radar screen—of surrounding waters.
COMMUNICATIONS AND
E LECTRONIC DEVICE S
How are newspapers made?
People usually read newspapers to get information about current events, things that
are happening at the present time or have just occurred. When a good news story
breaks, reporters are immediately sent out to gather as much information about the
situation as possible and photographers take pictures that add visual information.
When they return to the newspaper office, the reporters type their story into a computer,
and camera film is developed into photos in a darkroom.
The photographs are put into the computer with a device called a scanner.
Increasing numbers of photographers use digital cameras, which means their photos
do not have to be first developed on paper. They are automatically in digital, or
computer-ready, format and can be transmitted over phone lines or via satellites
just like e-mail or other electronic files. Once the photos are in digital format, the
printed story and the pictures that illustrate it are arranged together. The story
may take up part of a newspaper page or may extend for a few pages. Designers
arrange all the stories and photos that make up a newspaper into visually appealing,
easy-to-read pages on the computer screen. They are then printed out on
pieces of clear film.
Next, the film print of each newspaper page is laid on a light-sensitive metal
plate. When it is exposed to a flash of bright light, shadows of the film’s letters and
pictures are left on the plate. The shadows are permanently etched or marked into
the plate when it is soaked in acid, which eats some of the metal away. What is left
is a perfect copy of the film print of the newspaper page, with its words and pictures
appearing as grooves in the metal.
The newspaper page is now ready to be printed on paper. The metal plate is first
wrapped around a roller on a motor-driven printing press and coated with ink. After
being wiped clean, ink still stays in the grooves. When paper (in big rolls) is passed
under the roller, it is pressed into the grooves, and perfectly printed pages appear.
This process is repeated for each newspaper page. As you can imagine, printing
plants are enormous, with some presses standing three stories tall. These expensive
machines (costing tens of millions of dollars) can print and sort up to 70,000 copies
of a newspaper per hour. Once the press is done printing and sorting, the newspa-
156 pers are bundled for delivery the next day to homes and newsstands.
How was printing done before computers and motor-driven presses?
Long before computers and motor-driven presses, printing was done by hand with
wooden blocks of letters and figures dipped in ink and pressed onto paper. Historians
believe that this method of printing was invented in China around the year 700.
A hand-operated printing press—with moveable type or letters—was first used in
Europe in the mid-fifteenth century. Johannes Gutenberg printed the first book, a
Bible, in what is now Germany, in 1455. Until that time all books and other manuscripts
were written out by hand.
Why do newspapers fade and yellow within a few months?
Most commercial cellulose paper manufactured in the last century, including
newsprint, is acidic. The acid makes paper brittle and eventually causes it to crumble
with only minor use. The problem comes from two features of modern paper:
the paper manufacturing process results in cellulose fibers that are very short and
acid is introduced (or not removed by purification) during manufacture. Acid in the
presence of moisture degrades the fibers, and the acidic reaction splits the cellulose
chains into small fragments. The reaction itself produces acid, accelerating the
degradation. Ironically, the older the paper the longer it lasts. Paper manufactured
up until about the mid-nineteenth century was made from cotton and linen. These
early papers had very long fibers, the key to their longevity. Today’s newspaper print
is the weakest paper; it is unpurified and has the shortest fibers. Consequently,
newspapers generally fade and yellow within a few months.
What is the Morse code?
In 1835, the American painter-turned-scientist Samuel F.B. Morse devised a code
composed of dots and dashes to represent letters, numbers, and punctuation. Telegraphy—
the long-distance transmission of a message—uses an electromagnet, a
device that becomes magnetic when activated and raps against a metal contact. A
series of short electrical impulses repeatedly can make and break this magnetism,
resulting in a tapped-out message. 157
What is a hornbook?
Ahornbook is a flat, wooden board with a handle that students used in
English and American classrooms from the fifteenth to the eighteenth
centuries. A sheet of paper was pasted on the board. It contained the alphabet,
the Benediction (a special prayer from the Book of Numbers), the Lord’s
Prayer, and the Roman numerals. A thin, flat piece of clear animal horn covered
the whole board to protect the paper, which was scarce and expensive at
the time. Hornbooks were used as early as 1442 in England and became standard
equipment in English schools by the 1500s. They were discontinued
around 1800, when books became cheaper to produce.
HOW THINGS WORK
Morse secured his patent on the code in 1837, and several years later established
a communications company with machinist and inventor Alfred Vail. In
1844, the first long-distance telegraphed message was sent by Morse in Washington,
D.C., to Vail in Baltimore, Maryland. This was the same year that Morse took out a
patent on the telegraphy, although he did not acknowledge the unpatented contributions
of Joseph Henry, who invented the first electric motor and working electromagnet
in 1829 and the electric telegraph in 1831. Still in use today by the military,
the maritime service, and by amateur radio operators, the International Morse Code
now uses sound or a flashing light to send messages.
Who invented radio?
Guglielmo Marconi, of Bologna, Italy, was the first to prove that radio signals could
be sent over long distances. Radio is the radiation and detection of signals spread
through space as electromagnetic waves to convey information. It was first called
wireless telegraphy because it duplicated the effect of telegraphy without using
wires. On December 21, 1901, Marconi successfully sent Morse code signals from
Newfoundland to England.
What was “the Audion”?
In 1906, the American inventor Lee de Forest build what he called “the Audion,”
which became the basis for the radio amplifying vacuum tube. This devise made
158 voice radio practical, because it magnified the weak signals without distorting
Morse code messages used to be transmitted to and from telegraph offices like this one. In larger cities, big telegraph
exchange rooms were filled with telegraph machines manned by large staffs.
them. The next year, de Forest began regular radio broadcasts from Manhattan, New
York. As there were still no home radio receivers, de Forest’s only audience was ship
wireless operators in New York City Harbor.
How does television work?
Television works through a series of complicated processes. It starts with a television
camera, which takes pictures of scenes. Photo cells inside the camera change
the pictures to electrical signals. At the same time, a microphone records sounds
that are occurring during the scenes. A vibrating magnet in the microphone
changes these sounds into electrical signals, too. Some television shows, like news
reports, are recorded live, which means that they are broadcast to homes as they
occur. But most of the television programs that we watch are recorded, which
means that they are put on videotape and sent out later. The electrical signals of
sound and pictures are stored as magnetic signals on videotape, which are converted
back to electrical signals when played.
Before a program is broadcast, its electrical picture and sound signals are run
through a device called a television transmitter. With the help of strong magnets,
the transformer turns the electrical signals into invisible bands of energy called
radio waves (similar to visible light waves), which can travel great distances
through the air. They can travel directly to outdoor television antennae, which
catch the waves and send them to television sets that change them into pictures and
sounds again. Cable companies send electrical picture and sound signals through
cables directly to homes. When broadcasting to distant places, communication
satellites that orbit Earth are used to bounce or return the waves back to Earth,
extending their travel distance. Satellites are necessary because radio waves move
in straight lines and cannot bend around the world.
When an antenna or satellite dish receives radio waves, it changes them back
into electrical signals. A speaker in a television set changes some of the signals
back into sound. The pictures are reproduced by special guns at the back of a television
set that shoot electron beams at the screen, causing it to glow with tiny
dots of different colors. Viewed together, the dots look like a regular picture. The
individual pictures that make up a scene are broadcast and received, one after
another, at a pace so quick that it looks like continuous action is occurring on the
screen. The entire process happens very fast because television stations and broadcast
towers are all around and because radio waves travel very quickly, at the speed
of light. Radio programs broadcast talk and music across the airwaves using the
same technology.
What is high-definition television?
High-definition television (HDTV) is a digital television broadcasting system with
higher resolution than traditional television systems. The amount of detail shown
in a television picture is limited by the number of lines that make it up and by the
number of picture elements on each line. The latter is mostly determined by the 159
HOW THINGS WORK
width of the electron beam. To obtain
pictures closer to the quality of 35-millimeter
photography, HDTV has more
than twice the number of scan lines
with a much smaller picture element.
American and Japanese HDTVs have 525
scanning lines, and Europe has 625
scanning lines.
How does a telephone work?
All sound is made by the back and forth
movement, or vibration, of objects.
When an object vibrates, it makes the
molecules around it vibrate too, causing
a ripple of motion known as a sound
wave, which can travel through air,
water, and solid materials. A telephone
has vibrating parts—a disc in the mouthpiece and one in the earpiece—that turn
voice sounds into electrical signals that can travel along telephone wires and then
turn back into sound again.
Phones are usually connected to wires because they run on electricity. When
you pick up a phone, a low electrical current allows you to dial the series of numbers
that will connect you to the phone of a friend, for example. Each number on
the phone has its own special electrical signal, and when the right numbers are
combined, they can exactly identify your friend’s phone line. A local telephone office
receives this information when you dial and sends your call in the right direction.
Call signals to places close by travel along wires or cables buried underground or
strung high in the air between supports. But when the person you call is very far
away, the electrical signals sent from your phone are changed into invisible waves
of energy called microwaves, which can travel long distances through the air. These
waves are sent through space to communication satellites that orbit the world,
which bounce them back to Earth, extending the waves’ travel distance. An antenna
at a receiving station near the home of your friend picks up the waves and
changes them to electrical signals once more. They travel by cable to the telephone
office that services your friend’s neighborhood, where his or her number is identified.
A signal is then sent to your friend’s phone to make it ring. The entire process
from dialing to ringing takes just a few seconds!
When your friend answers the phone, a microphone in its mouthpiece contains
a plastic disc that vibrates, turning his or her message into electrical signals that
travel along the same path as before. A speaker in the earpiece of your phone
receives the electrical signals, which vibrate another plastic disc that changes them
back into sound. Two circuits—from microphone to speaker—are created, and you
can talk back and forth with your friend. The next time you use the phone, think of
160 the remarkable process that makes it possible!
Kids today really take telephones for granted. Phones are an
everyday part of our lives, but do you know how they work?
How does a fax machine work?
A fax machine, also called a telefacsimile, transmits (carries) graphic and textual
information from one location to another through telephone lines. A transmitting
machine uses either a digital or analog scanner to convert the black-and-white representations
of the image into electrical signals that are transmitted through the
telephone lines to a receiving machine. The receiving unit converts the transmission
back to an image of the original and prints it. In its broadest definition, a fax
terminal is simply a copier that can transmit and receive images. Although the fax
was invented by Alexander Bain of Scotland in 1842, it wasn’t until 1924 that it was
first used to transmit wire photos from Cleveland to New York as part of the newspaper
industry.
How does a cellular phone work?
Cellular, or cell, phones first became available to consumers in the early 1980s, but
the technology that made them small and truly portable evolved gradually over the
next 10 years or so. By the beginning of the twenty-first century, millions and millions
of people in countries all over the world were using cell phones on a daily
basis. And it isn’t just adults who enjoy the benefits of completely mobile phone
capabilities: in the United States alone, more than 20 percent of teenagers have a
cell phone. That translates to at least one in five American teens.
The cellular system divides each city into many small cells (a large city can have
hundreds). Each cell has its own tower (which contains an antenna as well as transmitters
and receivers that send and receive signals). Each tower can handle numerous
callers at a given time, and their small size and weaker signal (compared to the
radio antennae) means that their signals don’t interfere with those of nearby towers.
When you call someone using a cellular phone, your phone is sending and
receiving signals via radio waves, invisible bands of energy that work like light rays. 161
How did people communicate
from their cars before cellular phones?
Before portable cellular phones, people like police officers or taxi drivers
communicated from their cars using two-way radios. All of the radios in
one city transmitted signals via a large, central antenna located on top of a tall
building. With all callers sharing one antenna, the number of calls that could
be made at any one time was very limited. Consumers, like you and me, had
an old type of cell phone that was permanently attached to the car and powered
by its battery. The first transportable cellular phones had their own battery
packs that allowed owners to detach them from the car and carry them
in a pouch. However, most weighed about 5 pounds (2.25 kilograms) and were
not very practical when used this way.
HOW THINGS WORK
In other words, your cell phone is a fancy, high-tech radio. After you dial a friend’s
number, your phone must find the closest tower by searching for the strongest signal.
Once that signal is located, your phone transmits certain information—like
your cell phone number and serial number—that help your service provider make
sure you are one of their customers. Then the mobile telephone switching office
(MTSO) finds an available channel where your conversation can take place. The
MTSO then completes the connection (all of this happening in a few short seconds)
and you are chatting with your friend, without wires or cords to hold you down. If
you are sitting in the back seat of the car while talking, and your mom is driving
you from one end of town to the other, your call will be switched automatically from
one cell tower to the next without any pause in your conversation.
What is a “smartphone”?
A smartphone is a mobile, or cellular, phone that offers advanced capabilities
beyond a typical mobile phone, such as e-mail or Internet capabilities, and/or a
complete keyboard. The BlackBerry®, Trio®, and iPhone™ are all called smartphones.
For example, the iPhone™, which was introduced by Macintosh in 2007,
blends five devices—a mobile phone, an iPod® portable media player, a camera, a
personal organizer, and a widescreen mobile Internet device—into one.
How does a computer work?
Like all digital machines, a computer changes writing, images, and sound into a
special numerical language. It is a binary (or two-part) language that has just two
numbers: 0 and 1. These numbers are called “binary digits,” or bits for short. In a
digital machine, the numbers take the form of electric signals. With a 1 the electricity
is switched on and with a 0 it is switched off. Information of all kinds, then,
is turned into electrical on-off signals arranged in countless individual patterns.
These patterns can be stored, sent along
digital pathways, or converted back into
forms that we can use and understand
with extraordinary speed and accuracy.
Bits enter a personal computer from the
keypad, mouse, microphone, and scanner.
They are received and sent out by
cable or broadband modem technology,
as well as stored in various memory
devices. The computer screen, printer,
and speakers convert the bits into forms
of information that we can use.
What is a silicon chip?
Today’s computers contain millions of
transistors placed in a tiny piece of sili-
162 con, some so tiny that they can fit in an
Far smaller than the vacuum tubes that were used decades
ago, modern silicon chips allow us to have computers small
enough to rest on our laps or fit in our hands.
ant’s mouth. The transistors (devices that control the flow of electric current) are
packed and interconnected in layers beneath the surface of the chip, which is used
to make electrical connections to other devices. There is a grid of thin metallic
wires on the surface of the chip. This silicon chip was independently co-invented by
two American electrical engineers, Jack Kilby and Robert Noyce, in 1958–1959. The
chip, along with the invention of the microprocessor, allowed computers to get
smaller and more efficient. Silicon chips are also used in calculators, microwave
ovens, automobile radios, and video cassette recorders (VCRs).
Who invented the first computer?
In 1823, the English mathematician Charles Babbage originated the concept of
a programmable computer. At this time, he persuaded the British government to
finance what he called an “analytical engine.” This would have been a machine
that could undertake any kind of calculation. It would have been driven by
steam, but the most important innovation was that the entire program of operations
was stored on a punched tape (a long strip of paper in which holes are
punched to store data). Babbage’s machine was not completed in his lifetime
because the technology available to him was not sufficient to support his design.
However, in 1991 a team lead by Doron Swade at London’s Science Museum built
the analytical engine (sometimes called a “difference engine”) based on Babbage’s
work. Measuring 10 feet (3 meters) wide by 6.5 feet (2 meters) tall, it
weighed three tons and could calculate equations down to 31 digits. The feat
proved that Babbage was way ahead of his time, even though the device was
impractical because one had to a turn a crank hundreds of times in order to generate
a single calculation. Modern computers use electrons, which travel at the
speed of light.
Which types of computers predated Babbage’s “analytical engine”?
Computers developed from calculating machines. One of the earliest mechanical
devices for calculating, which is still widely used today, is the abacus—a
frame for carrying parallel rods on which beads or counters are strung. The abacus
originated in Egypt in 2000 B.C.E. It reached the Orient about a thousand 163
How many computers are there in the world?
According to statistics from technology research companies such as Gartner
Inc., in April 2002 the billionth personal computer (PC) was shipped.
The second billion mark (some being ordered as replacements for older PCs)
was reportedly reached in 2007. With personal computers becoming more popular
around the world, research companies estimate that there will be more
than two billion PCs in active use by 2015. In the United States, more than half
of the people who use a computer are also connected to the Internet.
HOW THINGS WORK
years later, and arrived in Europe in about the year 300 C.E. In 1617, the Scottish
scholar John Napier invented “Napier’s Bones”—marked pieces of ivory for
multiples of numbers. In the middle of the same century, the French mathematician
Blaise Pascal produced a simple mechanism for adding and subtracting.
Multiplication by repeated addition was a feature of the stepped drum or
wheel machine of 1694, invented by the German mathematician Gottfried Wilhelm
Leibniz.
When was the earliest programmable computer built?
In 1943 and 1944, the British government developed two Colossus computers.
These huge machines were electronic computing devices used by British code
breakers to read encrypted German messages during World War II. Dubbed
“Colossus Mark 1” and “Colossus Mark 2” these devises were the world’s first
programmable, digital, electronic, computing machines. Based on concepts of
the British mathematician Alan M. Turing, the mathematician Max Newman
and engineer Tommy Flowers designed and built the machines, which used
vacuum tubes (thermionic valves) to perform the calculations. The Colossus
hardware and blueprints were destroyed as part of an effort to keep the project
secret. However, based on notes in engineers’ logs and other information, in
2007 a functional replica of a Colossus computer was completed. The computer
is on display at the Bletchley Park Museum in Milton Keynes, Buckinghamshire,
England.
What is the Internet?
The Internet is the world’s largest computer network. It links computer terminals
together via wires or telephone lines in a web of networks and shared software. With
the proper equipment, an individual can access vast amounts of information and
search databases on various computers connected to the Internet, or communicate
with someone located anywhere in the world as long as he or she has the proper
equipment. According to various sources, including the International Telecommunications
Union, in 2008 approximately 1.4 billion people around the world were in
some way using the Internet. About 578 million are in Asia, 384 million are in
Europe, and 248 million are in North America.
How does the Internet work?
Just as telephones are connected by a worldwide phone system, home and work
computers can connect with a global computer communications network known as
the Internet. Each computer that is linked to the system has its own Internet
address, as individual as a phone number. Home computer users buy the services of
an Internet provider, which is an organization with powerful computers that link
all its subscribers to the Internet. Many large organizations and companies have
computers that link them directly to the network. Internet users can visit the World
Wide Web, which is a global network of Web sites providing information, entertain-
164 ment, products, and other services.
How does a search engine work?
Internet search engines are like computerized card catalogs at libraries. Viewed
through a Web browser with an Internet connection, they provide a hyperlinked
listing of locations on the World Wide Web according to the requested keyword or
pattern of words submitted by the searcher. Search engines use computer software
called “spiders” or “bots” to search out, inventory, and index Web pages automatically.
The spiders scan each Web page’s content for words and the frequency of
words, then stores that information in a database. When the user submits words or
terms, the search engine returns a list of sites from the database and ranks them
according to the relevancy of the search terms.
How is an MP3 player related to a computer?
An MP3 player—an electronic device that weighs less than one ounce (28 grams)—
allows music to be copied from the Internet, organized, and stored into a computer’s
memory. An MP3 player plays MP3 files, a compressed digital audio file. With
an MP3 player, like Apple’s iPod®, a consumer can create personalized music lists
and carry thousands of songs wherever he or she goes.
What is e-mail?
People can use the Internet to send electronic mail, known as e-mail, to one another
in just a few seconds. Once you type a message into your computer to send to
your cousin, let’s say, who lives miles from you across the country, it travels
through the wires of your phone line as a series of electrical signals (or, for some
people, the signals travel through the same cables that bring them cable television). 165
Tiny MP3 players allow us to carry thousands of songs with us everywhere we may go.
HOW THINGS WORK
These signals travel to a station run by your service provider, where a big computer
sends them to an Internet routing center. Located all over the world, routing
centers, which are linked to organizations and Internet providers, send the countless
computer communications that come to them each second along the quickest
possible routes to their destinations. A giant computer there reads the address on
your e-mail and sends it farther: depending on the distance it must travel, it may
continue along phone lines, be changed into light signals that can travel with great
speed along thin glass strands called fiber-optic cables, or be converted into equally
speedy invisible bands of energy known as radio waves and transmitted to a communications
satellite that will bounce it back to Earth, to a ground station located
close to where your cousin lives. Once your message reaches the routing center
nearest your cousin, it will be sent to the station of his or her service provider. From
there it will be sent along regular phone lines to his or her computer. And all of this
happens in a matter of moments.
What is “snail mail” and how does it travel?
The term “snail mail” is used for regular mail that is sent through the United States
Postal Service. Once you address a letter, affix postage stamps, and drop it in the
mailbox, a complex process begins that requires the efforts of many people and
machines—sometimes located in different parts of the world. Mail carriers visit
mailboxes in your town or city a few times each day to pick up their contents. The
mail collected by carriers is taken to a local postal sorting office, where it joins all
the other letters that have been mailed in the area that day. High-speed machines
take over then, preparing your letter to reach its destination.
Mail is dumped onto a moving conveyor belt that brings it to a machine that
separates it by size. Another machine checks to make sure that all the mail is properly
stamped, and then it cancels, or prints over, the stamps so that they cannot be
used again. A postmark is also printed on each envelope, which tells the time, date,
166 and place where it was processed.
How was mail delivered before there were mail carriers?
In early colonial times, correspondents depended on friends, merchants, and
Native Americans to carry messages among the colonies, either by foot or on
horseback. However, most correspondence ran between the colonists and England,
the Netherlands, or Sweden—their mother countries. These letters were
carried overseas on ships. It was largely to handle this mail that, in 1639, the
first official notice of mail service in the colonies appeared. The General Court
of Massachusetts designated Richard Fairbanks’s tavern in Boston as the official
repository of mail brought from or sent overseas, and people gathered there to
collect letters from loved ones and business associates from faraway places.
A machine reads the zip codes written in the addresses of letters, which tell
exactly to which part of the country, or the world, they are headed. (Postal services
around the globe work together to distribute mail and most have similar code systems.)
Postal workers process by hand the letters that have missing or unreadable
zip codes. The zip code machine prints a bar code (a machine-readable series of
lines, more reliable than written numerals) on each letter, and a second sorting
machine reads and separates them by destination. Mail is grouped by city and country.
Local mail is prepared for delivery the next day. Other mail travels by truck,
express train, or plane, depending on where it is going. Each delivery day, the Postal
Service sorts and delivers more than 700 million pieces of mail. Because of this
complex process, and that it takes longer to reach its destination than email, it is
referred to as snail, or slow, mail.
What happens to the mail when it gets close to its destination?
Once mail travels close to its destination, it is unloaded at another postal sorting
office. A bar code–reading machine scans the letters again, separating them further
for delivery to districts, neighborhoods, and streets. The letters are sent to local post
offices, where carriers are given the mail for their delivery areas. Routes may include
homes, shops, and office buildings. Carriers who work in farm country, where people
live very far apart, may have to travel many miles to deliver the mail each day.
When was the first post office in the United States established and how did
the system grow?
Governor William Penn established Pennsylvania’s first post office in 1683. Central
postal organization came to the colonies after 1692, when Thomas Neale received a
21-year grant from the British Crown, whose settlements dominated the Atlantic
seaboard, for a North American postal system. It wasn’t until 1774, however, that
William Goddard, a newspaper publisher and former postmaster, set up the Constitutional
Post for intercolonial mail service. Colonies funded it by subscription, and
net revenues were used to improve mail service rather than to pay back to the subscribers.
By 1775, when the Continental Congress met in Philadelphia, Goddard’s
post was flourishing, and thirty post offices operated between Williamsburg, Virginia,
and Portsmouth, New Hampshire. The Constitutional Post provided security
for colonial messages and created a communication line that played a vital role in
bringing about American independence during the Revolutionary War.
PICTURE S, LIGHTS, AND LAS ERS
Why do I see my shadow on the sidewalk on a sunny day?
Whenever light hits an object, it casts a shadow. A shadow forms when an object
blocks light from its light source, creating an area behind the object that the light
cannot reach. A screen placed behind the object will be dark where it lies in the 167
HOW THINGS WORK
shadow. When you stand on the sidewalk, the screen is the cement surface on which
you are standing. The Sun is your light source. As the Sun moves in the sky, the
shadow—since it is the part of space “behind” you as viewed from the Sun—will
move as well.
Because the sidewalk touches your feet, the shadow will always form an image
connected to your feet. It will extend from there in a direction opposite to the direction
to the Sun. When the Sun is in the East, in the morning, the shadow will
extend to the West, and when the Sun is in the West, in the evening, the shadow
will extend to the East.
How does a light bulb work?
An incandescent light bulb, like the ones on your desk lamp, use heat caused by an
electrical current. When electrical current passes through a wire, it causes the wire
to heat. The wire, or filament, gets so hot that it glows and gives off light. Light
bulbs for everyday usage have a filament made of tungsten. Since the hot tungsten
would quickly burn away if it were exposed to oxygen, it must be placed in a sealed
glass bulb, which is either evacuated or filled with a gas that won’t let it burn.
Thomas Edison, the creator of the light bulb, thought that it would take him six
weeks to develop it, but instead it took more than one year. Of this experience, he
famously said, “I have not failed … I have just found 10,000 ways that will not
work.” When he finally got it right, in 1879, it was due to two important factors:
First he put the filament in a glass bulb and then he removed the air (including oxygen)
from inside the bulb. Edison tested more than 1,500 materials to find the right
filament, including coconut fibers, fishing line, and facial hair.
How does an ear thermometer read body temperature?
An ear thermometer reads the spectrum of thermal radiation given off by the inner
surfaces of a person’s ear. All objects give off thermal radiation (including the light
emitted by a glowing incandescent light
bulb) and that radiation is characteristic
of their temperatures. The hotter an
object is, the brighter its thermal radiation
and the more that radiation shifts
toward shorter wavelengths. The thermal
radiation from a person’s ear is in
the invisible infrared portion of the
light spectrum, which is why you can’t
see people glow. But the ear thermometer
can see this infrared light and it uses
the light to determine the ear’s temperature.
The thermometer’s thermal radiation
sensor is very fast, so it can measure
a person’s body temperature in just
168 a few minutes.
Ear thermometers, unlike other thermometers, read body
temperature by detecting invisible infrared light.
Why do certain items glow-in-the-dark?
Glow-in-the-dark stickers, stars, toys, and clothes, all work by absorbing light and
emitting it later. These items contain phosphors, substances such as zinc sulfide
that radiate visible light after being energized by natural light. Phosphorescent
materials continue to glow after the energizing light is removed. They have electrons
that are easily excited to higher energy levels when they absorb light energy.
In phosphorescent materials—such as glow-in-the-dark objects—the excited electrons
drop to a lower, but still excited intermediate level and stay there for a period
of time before returning to their ground state (original energy level) and emitting
the excess energy as visible light.
How does a camera take pictures?
When you press the picture-taking button on a camera, you open the shutter and
let light inside for a fraction of a second. The light passes through a lens that focuses
it on film, leaving a record there of what the camera “saw” during that buttonpressing
instant. The film is coated with light-sensitive chemicals that save the
impression, but it usually has to be placed into a bath of other chemicals to make
an image appear and remain permanently. The film is developed into negatives, on
which appear images that look very different than those that were photographed:
dark shades appear light, light shades appear dark, and colors are the opposite of
what they should be. But when light passes through these negatives onto special
photo paper, which is also developed using chemicals, the images that appear are
normal again—exact copies of the photographed scenes. With “instant” cameras,
developing chemicals are contained inside, treating the film right away. A picture
pops out on photo paper, its image forming while you wait. Digital cameras work
the same way that television cameras do: Instead of using film, they make electronic
pictures. The pictures are loaded onto a computer, where they can be altered in
size, shape, and color, and printed out.
What was the daguerreotype?
The daguerreotype was the first successful type of photograph. It was named after
the French chemist Louis Daguerre, who announced his invention to the public at
a meeting of the French Academy of Sciences in Paris in 1839. His photographic
process created a highly detailed image on a sheet of copper, plated with a thin coat
of silver, without the use of a negative. The process was complex. First, the silverplated
copper plate had to be cleaned and polished until the surface looked like a
mirror. Next, the plate was sensitized in a closed box over iodine until it took on a
yellow-rose appearance. The plate, held in a lightproof holder, was then transferred
to a simple camera. After exposure to light, the plate was developed over hot mercury
until an image appeared. To fix the image, the plate was immersed in a special
chemical and then toned with gold chloride. Exposure times for the earliest
daguerreotypes ranged from 3 to 15 minutes. American photographers quickly capitalized
on this new invention, and portraits based upon daguerreotypes, such as
those of President Abraham Lincoln, appeared in popular periodicals and books. 169
HOW THINGS WORK
The popularity of the daguerreotype declined in the late 1850s when the ambrotype,
a faster and less expensive photographic process, became available.
How does an X-ray take pictures of bones?
X-rays are similar to visible light in that both are forms of electromagnetic energy,
which travels in waves. But X-rays have much shorter wavelengths than light, so
they are invisible. Just as light can pass through some things, like glass, X-rays can
pass through certain materials. They can pass through your skin, muscles, and
organs, for example, but not through dense things like your bones (which contain
heavier atoms). When you have an X-ray taken, the waves are projected through you
onto a film or plate that is coated with special chemicals. Most X-rays are stopped
when they hit a bone but pass through other body parts, which appear dark on the
X-ray after it is developed. Bones stand out light and clear. When organs like the
stomach or intestines need to be X-rayed, the patient drinks a special liquid that
stops the rays. That liquid coats the organ, and a picture can be taken.
What are lasers?
First built in 1960 by American physicist Theodore Maiman, lasers are machines
that produce intense beams of high-energy light. Laser light is more powerful than
ordinary light because all its rays have the same wavelength and move together in
exactly the same direction, allowing them to be focused in a narrow beam with
great precision. Laser light beams vary in strength, depending on the materials and
amount of energy used to make them. Lasers can melt, burn, or cut through a variety
of different surfaces, from hard metal to the delicate human body, which is why
they are often used in surgery today. Lasers can be used to make precise measurements,
to reshape corneas to correct poor vision, to transmit telephone signals, to
guide weapons, and to read supermarket bar codes.
What are bar codes?
Bar codes are numerical product codes that appear on the labels of merchandise. A
full-length bar code has 12 digits. Each digit is coded by two black and two white
stripes that range in width. Each digit represents something different; for example,
the first digit indicates the type of product it is; other digits form the manufacturer’s
identification number and price. Bar codes were originally created to help grocery
stores speed up the checkout process and keep better track of inventory, but
the system quickly spread to all other retail products because it was so successful.
Barcodes are read by laser scanners called bar code readers or scanned from an
image by special software.
How does a laser make musical sound off of a CD?
Music is stored on a compact disk (CD) as digital data. On the bottom side of a CD is a
thin metal sheet. Tiny round depressions called pits, which represent sound, fill its spiral
track. A beam of laser light is used to change a CD’s pitted track 170 back into sound.
Unlike ordinary light, which spreads out in all directions once it leaves its source, laser
light can be focused with great accuracy. It moves along the track of a CD, and sensors
detect the pattern of shiny flat parts (which reflect light back) and pits (which do not).
These on-and-off flashes of reflected light turn into electrical signals. A computer in a
compact disc player, which has an enormous memory that stores every possible combination
of on-and-off patterns, converts the signals to musical notes with different
pitches and volumes in the player’s speakers. And then the music plays!
How do mirrors use light to create a reflection?
We see objects in a mirror, because a mirror, when hit by particles of light called
photons, reflects the photons back to us and some reach, and enter, our eyes. Photons
that hit a rough surface will bounce off of the surface in a haphazard manner,
while those that hit a smooth surface, such as a mirror, only bounce off of the surface
at the same angle at which they hit the object. The scientific term for this phenomenon
is reflection. Photons that bounce off of any part of our bodies and hit the
mirror reflect back to our eyes from only one place on the mirror, and at only one
angle. Therefore, each point on our bodies that reflects back to our eyes from one
point on the mirror produces an image in the mirror. All of the images together
make up our body’s reflection.
How does a magnifying
glass work?
A magnifying glass is a convex lens,
which means that it is curved outward,
much thicker in the middle than
around its edges. This shape bends the
light waves of objects viewed through it,
causing us to see them in unusual ways.
When you hold a magnifying glass close
to an object, its light waves are widened
before they are focused on your eyes,
causing the object to appear very large.
But when you hold a magnifying glass
out and view a distant object with it, the
item appears smaller and upside down.
This effect is due to the image being
beyond the focus of the lens. The more
curved a convex lens is, the greater its
ability to bend light and magnify. Microscopes
(which allow us to look at things
that are too small to be seen with our
eyes), binoculars, and telescopes (which
make far away things look bigger and
nearer to us) also use convex lenses. 171
Because light waves change speed when they pass through
material like glass, we can bend light and even magnify
objects through a lens.
HOW THINGS WORK
HANDY THINGS
AROUND THE HOUS E
Who invented the zipper?
Like many inventions, the development of the modern zipper can be traced to a
series of events. In 1893, Whitcomb Judson patented and marketed a “clasp locker,”
a complicated hook-and-eye shoe fastener. Together with businessman Colonel
Lewis Walker, Whitcomb launched the Universal Fastener Company to manufacture
the new device. He did not use the word “zipper,” although many people often
credit him as the zipper’s creator. Instead, it was Swedish-born Gideon Sundback,
an electrical engineer who was hired to work for the Universal Fastener Company,
who gets the credit. He was responsible for improving Judson’s fastener, and by
December 1913, he had designed the modern zipper. Sundback increased the number
of fastening elements from four per inch to ten or eleven, had two facing-rows
of teeth that pulled into a single piece by a slider, and increased the opening for
the teeth guided by the slider. Sundback also created a machine that was able to
manufacture the zipper.
What do many household appliances have in common?
Despite their varied uses and different systems of wires, pipes, and vents, household
appliances use electricity to run. They also rely on a transformer, a nineteenth-
century invention that made it possible to transmit power for home use.
In the early 1900s two major engineering innovations—resistance heating and
small, efficient motors—led to electric stoves and irons, vacuum cleaners, washers,
dryers, and dishwashers. In the second half of the twentieth century
advances in electronics made the way for appliances that could be set on timers
and even programmed, further reducing the workload necessary to complete
simple tasks.
How does a vacuum cleaner pick up dirt?
James Spangler, a janitor at an Ohio department store who suffered from asthma,
invented his “electric suction-sweeper,” in 1907 as way of picking up the dust and
debris that triggered his health condition. His invention was the first practical
domestic vacuum cleaner. It used an electric fan to generate suction, rotating
brushes to loosen dirt, a pillowcase for a filter, and a broomstick for a handle.
Because it was heavy and hard to handle, Spangler sold the rights of his invention
to his relative, William Hoover, whose redesign of the appliance coincided with the
development of the small, high-speed universal motor, in which the same current
(either AC or DC) passes through the appliance’s rotor and stator. This gave the vacuum
cleaner more horsepower, higher airflow and suction, better engine cooling,
and more portability than was possible with the larger, heavier induction motor.
Hoover’s model has since been refined, but the mechanics of his vacuum cleaner
172 are still used in vacuum cleaners today.
How does a washing machine clean our clothes?
All washing machines work by using a mix of mechanical energy, thermal energy,
and chemical action. Mechanical energy is employed by the rotation of an agitator
(a simple device that moves back and forth) in top loaders, or by the tumbling
action of a drum in front loaders. Thermal energy is used in the temperature of the
water. Chemical action involves the detergent and water mix that works to remove
dirt. Once you load your clothes, add laundry detergent, and push the buttons or
dials to select a temperature, agitation strength, rinse cycle, and time duration, the
machine does the rest of the job. It stirs (or washes) clothes with its agitator or
drum, drains the dirty water, and follows it with a spin of clothes to remove the
remaining water. In order to do its job, a washing machine has an inner and outer
tub. The inner tub, which contains the agitator, holds the clothes and helps in the
removal of water. It is attached to a gearbox, which in turn is attached to a black
metal frame, which holds the machine’s motor as well. The outer tub is bolted to
the washer’s body. The back of the machine has hook-ups for a hot and cold water
line. After the machine has performed the washing, rinsing, and spinning processes,
the clean clothes are ready for the dryer.
How does a refrigerator work?
In the 1870s the German engineer Carl von Linde invented a continuous process
of liquefying gases in large quantities, which led to his invention of the first efficient
compressed-ammonia refrigerator. His revolutionary machine paved the way
for the modern technology of refrigeration. Modern refrigerators run on ammonia
gas, which liquefies when it is under high pressure using thermodynamics—a scientific
law that says when two different temperatures of things touch or are near
each other, the hotter surface cools and the colder surface warms up. Through the
use of a compressor, small valves, and a coil, the liquid ammonia hits a low pressure,
boils, and changes to a vaporizing gas. The coils go through the coldest part
of the fridge, the freezer, as well as the main body of the refrigerator. The colder
ammonia in the coil absorbs the heat out of the freezer and fridge, keeping the
whole appliance cold. The compressor then takes back the ammonia gas and recycles
it continuously. The thermometer inside the fridge regulates the temperature
to make sure it is always the same.
How does a thermos keep cold things cold and hot things hot?
A thermos is also called a vacuum bottle because it uses a vacuum—a space that has
no air in it—to keep heat from escaping from hot things inside; it also keeps heat
from getting inside to make cold things warmer. The vacuum is located in a thin
space between the thermos liner and its outer wall, where it stops the movement of
heat to and from the outside air. A vacuum works in a thermos because it is empty
of air (and molecules) and therefore has no conductivity. (Heat is caused by the
motion of molecules.) Because the opening of a thermos is also tightly sealed with
a stopper or lid made of a nonconductive material, no heat can escape or enter
there, either. Hot food stored in a thermos can keep its heat for many hours; in the 173
HOW THINGS WORK
same way, cold food can remain cold
because the vacuum insulates it from
the warm air surrounding the thermos.
The linings of thermoses used to be
made of glass, which is a good insulator.
The linings were also coated with silver,
which made them shiny and reflective.
Such mirrored liners worked very
well—they were able to efficiently
bounce back the invisible rays of heat
energy (radiation) given off by all hot
things. But there was one problem: glass
thermos bottles broke easily. Today,
most thermos containers are made of
metal or plastic, which don’t break easily
but also generally don’t work quite as
well. Also, because vacuums in thermoses
aren’t perfect—they contain
some air—and because their lids don’t
seal perfectly, they cannot keep cold
things cold and hot things hot forever.
How does a coffeemaker cook up
the morning’s brew?
With the most common coffeemaker, the drip coffee machine, hot water drips down
freely onto ground coffee beans to make coffee. The water inside the machine’s water
bucket is heated as it passes along a heat-resistant tube. The tube goes into the drip area
and releases heated water, just below boiling temperature (212 degrees Fahrenheit [100
degrees Celsius]). The water is heated by a heating element (a resistive heating coil that
gives out heat when electricity is passed through it). The heating element has direct
contact with the water inside the water bucket, and also heats the heating pad on which
the glass coffee container is rested. Today, most models of coffee machines are either
semi-automatic or automatic. Buttons and switches have replaced the manual coffee
straining and lever-pushing of espresso machines. And some machines now have special
features, such as built-in coffee bean grinders and froth makers.
How does a toaster work?
Inside a toaster are thick wires arranged in panels that heat up and toast your food.
When you push down the lever that lowers your bread, it catches on a hook inside,
turning on the heater. While your bread turns brown and crispy, a special metal
switch inside the toaster gets hot, too, and bends. After a certain amount of time it
bends so much that it pushes on a bar that releases the lever from the hook, and
the toasting stops. This action also releases a spring, which pushes the lever up
174 again—and your toast pops up.
Thermoses keep hot things hot and cold things cold because
they use insulation and store things within a vacuum.
How can a microwave oven cook food so fast?
Unlike other ovens, which cook food with heat waves made from burning gas or electric
currents, microwave ovens use special bands of electromagnetic energy called
microwaves (similar to light waves) to cook food. While heat waves gradually work
their way inside food to cook it, microwaves can travel right through food in an
instant. In a microwave oven a device called a magnetron produces a beam of
microwaves that pass through a spinning fan, which sends the waves bouncing in all
directions. As they travel through food their energy is absorbed by molecules of
water. The water molecules vibrate at the same high speed as the microwaves (2.45
billion times per second!) and rub against other molecules. All this movement and
friction causes a great deal of heat, cooking the food inside and out. Microwaved food
is cooked through a process similar to steaming, which explains why it doesn’t turn
brown. But some microwave ovens have traditional heating elements to make food
look more appealing—giving it the outer color that we expect in cooked food.
Certain materials allow microwaves to pass through (meaning they are not
heated by the waves) while other materials absorb the waves and still others reflect
them, or bounce them back. For this reason it is important to be careful about the
containers and coverings we use in microwave ovens. Microwaves pass through
glass and plastic wrap, for example, which are safe to use, as are paper products and
most sturdy plastics. But metal containers and coverings like aluminum foil are
reflective. Such surfaces keep food from absorbing microwaves, allowing the waves
to bounce around so much inside an oven that it may break.
Why do burning things make smoke?
During a fire, the air around the fire becomes heated. The heated air sweeps up
water vapor (molecules of water that float in the air) and tiny specks of the fuel (the
material being burned) into a dark cloud of smoke. The more incompletely something
burns, the more smoke it produces, because more particles are left to be
swept up into the air. Smoke gradually spreads out and drifts away, with gravity
pulling the heaviest bits back to the ground. When a fire first starts to burn, there 175
How does the metal switch in a toaster bend?
It bends because it is made of two metals that are joined together, something
called a bimetal switch. One metal (usually brass) expands quickly when
heated, while the other expands much more slowly. This difference causes the
switch to bend toward the low-expansion metal. Bimetal switches are used in
other appliances that switch electricity on and off to keep their temperatures
even, like irons and refrigerators. The thermostat that regulates the temperature
of your home by turning your furnace and air conditioner on and off
also uses a bimetal switch.
HOW THINGS WORK
is usually a lot of smoke, which decreases as more of the fuel is burned completely.
Smoke detectors take advantage of the fact that fires cause a lot of smoke in their
early stages. The detectors sense the small particles in smoke before a fire really
starts to burn. An optical smoke detector uses a light beam and light sensor that
sounds an alarm when smoke particles get in the way of the beam. An ionizing
smoke detector can sense even smaller particles; they disturb a low electric current
inside, which sets off an alarm.
How does a fire extinguisher work?
In order for something to burn, high heat and oxygen are needed. All fuels have
their own particular temperatures at which they begin to burn when exposed to
high heat (called their flash points). Removing heat or oxygen from fuel will put out
a fire. Water is frequently used to extinguish fires. Large supplies of water can be
found almost anywhere, an important condition when dealing with large fires, like
those in burning buildings. Water works in two ways to put out a fire. First, it
sharply reduces the temperature of the burning material. Second, it covers the
material, keeping oxygen-filled air from reaching the material.
But water cannot put out oil fires. Because oil floats on the surface of water, an
oil fire’s oxygen supply can’t be cut off by water. Other substances—liquids, gases, or
powders that don’t burn—must be used to smother the fire and remove its oxygen
supply. Most fire extinguishers are filled with carbon dioxide, a heavy gas that prevents
burning. When released, the gas forms a type of snowy foam that both covers
and cools a fire. Powdered sodium bicarbonate (what we know as baking soda) is also
used in extinguishers, usually for use on oily chemical fires. It quickly melts in heat,
forming a crust that keeps oxygen out. (If you do not have a fire extinguisher on
hand you should always throw baking soda on a cooking fire that 176 involves grease;
Fire extinguishers should only be used by adults or under adult supervision—and only during a fire emergency!
water will only spread the fire by causing splattering.) Because the substance in a fire
extinguisher must cover a large area very quickly, it needs to be released in a powerful
spray. The extinguishing substance is stored inside the tank under high pressure,
which drives it out of a nozzle with great force once it is released.
Has a robot been invented to help with housework?
Yes! Robots already do a lot of the jobs that humans cannot or do not want to do.
In 1986, the Honda Motor Company introduced ASIMO, which stands for Advanced
Step in Innovative Mobility, the most advanced humanoid robot in the world. At 4
feet 3 inches (1.3 meters) high and weighing 119 pounds (54 kilograms), ASIMO is
the first humanoid robot in the world that can walk independently and climb stairs.
In addition to ASIMO’s ability to walk like humans, it can also understand preprogrammed
gestures and spoken commands, recognize voices and faces, and interface
with communication cards. ASIMO has arms and hands so it can do things like turn
on light switches, open doors, carry objects, and push carts. Rather than building a
robot that would be another toy, Honda wanted to create a robot that would be a
helper for people—a robot to help around the house, assist the elderly, or help
someone confined to a wheelchair or bed. In 2008, researchers at the Korea Institute
of Science and Technology unveiled Mahru, a humanoid robot that can dance
and do household chores. In some countries, robots have already replaced jobs, like
at help desks in a few Japanese businesses.
How do robots like ASIMO and Mahru work?
Robots like ASIMO and Mahru are sophisticated, expensive, highly technologically
advanced machines that are built upon major components found in humans. Robot
technicians use the inner workings of the human body as the model for the robots
that they make. This modeling ensures that their robots are as lifelike as possible.
First, the robot technician designs the five major components he or she will put
into the robot: a body structure, a muscle system, a sensory environment, a power
source, and a brain system. Next, they build an intricate machine made up of electrical
circuits, electrical valves, piston cylinders, electric motors, solenoids,
hydraulic systems, and more—each plays a specific role in getting the robot to
work. Every robot has a computer that controls everything else within its body.
Many robots can talk and some can even smell, taste, and hear. To get the body of a
robot moving, the computer must “tell” the specific part to move. If the technician
wants the robot to do something new once it has been made, he or she writes a new
computer program. In some cases, if the task is too big for the robot’s wiring system,
new parts need to be installed.
177
HOW THINGS WORK

NUMBERS AND COUNTING
Where and when did numbers originate?
Thousands of years ago there were no numbers to represent one, two, or three.
Instead, people used fingers, rocks, sticks, or eyes to represent numbers. There were
neither clocks nor calendars to help keep track of time. The Sun and the Moon were
used to distinguish between 1:00 P.M. and 4:00 P.M. Most civilizations did not have
words for numbers larger than two so they used terminology familiar to them such
as flocks of sheep, heaps of grain, piles of sticks or stones, or groups of people. People
had little need for a numeric system until they formed clans, villages, and settlements
and began a system of bartering and trade that in turn created a demand
for currency.
The Babylonians, who lived in Mesopotamia, between the Tigris and Euphrates
rivers, began a numbering system about 5,000 years ago. It is one of the oldest
numbering systems in the world. The ancient Egyptians used special symbols,
known as pictographs, to write down numbers more than 3,000 years ago. The
Babylonians and the Egyptians were the first to complete a system for arithmetic
based on whole numbers and positive rational numbers. About 500 B.C.E. the
Romans developed a system of numerals that used letters from their alphabet rather
than special symbols (for example, III represented three). Roman Numerals was the
standard numbering system and method of arithmetic in ancient Rome and Europe
until about 900 C.E., when the Arabic numbering system, which was originated by
the Hindus, came into use. Today, we use numbers based on the Hindu-Arabic system.
We can write down any number using combinations of up to 10 different symbols
(0, 1, 2, 3, 4, 5, 6, 7, 8, and 9).
179
MATH,
MEASUREMENT,
AND TIME
180
Who was Pythagoras?
Pythagoras was one of the first Greek mathematical thinkers. He is known for proving
and teaching the Pythagorean Theorem, which says that in a right triangle, the
sum of the squares of the two right-angle sides will always be the same as the square
of the hypotenuse (the long side). He lived in the 500s B.C.E., and spent most of his
life in the Greek colonies in Sicily and southern Italy. He had a group of followers
who studied with him and taught other people what he had taught them. The
Pythagoreans were known for their pure lives (they did not eat beans, for example,
because they believed that beans were not a pure food). They wore their hair long,
wore only simple clothing, and went barefoot. Both men and women Pythagoreans
were interested in philosophy, but especially in music and mathematics, which they
believed were two ways of making order out of chaos. Nichomachus of Gerasa was
a Pythagorean of the first and second centuries. His ideas about arithmetic built
upon Pythagoras’s ideas of the harmonic sounds of the motions of the planets and
the proportional relationships of numbers.
What is Euclid’s Elements?
Euclid’s Elements is a series of 13 geometry and mathematics books written by the
Greek mathematician Euclid in Alexandria about 300 B.C.E. It is a collection of definitions,
postulates (axioms), theorems, and mathematical proofs of the propositions.
The 13 books cover Euclidean geometry and the ancient Greek version of elementary
number theory. Along with the Greek mathematician Autolycus’s On the Moving
Sphere, the Elements is one of the oldest Greek mathematical treatises to have survived,
and is the world’s oldest continuously used math textbook. Historians do not
know a lot about Euclid’s life, but his work has proven important to the development
of logic and modern science. Most of the theorems in the Elements were not discovered
by Euclid himself, but were the work of earlier Greek mathematicians such as
Pythagoras, Hippocrates of Chios, Theaetetus of Athens, and Eudoxus of Cnidos. However,
Euclid is credited with arranging these theorems in a logical manner.
What is a “perfect” number?
Approximately 2,500 years ago the Pythagoreans defined a “perfect” number as one
for whom the sum of its divisors, excluding itself, equals the number itself. For
example, 6 can be divided by 1, 2, 3, and 6. If you add these numbers together,
excluding 6 itself, the total is 6. Therefore 6 is a perfect number. Over the centuries,
many mathematicians from all over the world have contributed to finding and
defining perfect numbers.
Why is the number 10 important?
One reason is that the metric system is based on the number 10. The metric system
emerged in the late eighteenth century out of a need to bring standardization to
measurement. But 10 was important before the metric system. For example,
Nichomachus of Gerasa, a second-century mathematician from Judea, considered
10 a perfect number, the figure of divinity present in creation with humankind’s fingers
and toes. Pythagoreans believed 10 to be “the first-born of the numbers, the
mother of them all, the one that never wavers and gives the key to all things.” And
shepherds of West Africa counted sheep in their flocks by colored shells based on
10, and 10 had evolved as a “base” of most numbering schemes. Some historians
believe the reason 10 developed as a base number had more to do with ease: 10 is
easily counted on figures and the rules of addition, subtraction, multiplication, and
division for the number 10 are easily memorized.
What is so special about the number 2?
The number 2 is called the “oddest” even prime number. 2 is a unique even prime
number because all even numbers are divisible by 2. But any number apart from 2
that is divisible by 2 is not a prime number.
What are Roman numerals?
Roman numerals are symbols that stand for numbers. They are written using seven
basic symbols: I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000). Sometimes
a bar is placed over a numeral to multiply it by 1,000. A smaller numeral
appearing before a larger numeral indicates that the smaller numeral is subtracted
from the larger one. This notation is generally used for 4s and 9s; for example, 4 is
written IV, 9 is IX, 40 is XL, and 90 is XC.
Roman numerals were developed around 500 B.C.E. at least partially from primitive
Greek alphabet symbols that were not incorporated into Latin. Using mainly
addition, they are read from left to right. Historians believe the long usage of
Roman numerals is due to a number of factors, including the widespread influence
of the Roman Empire, tradition, and the fact that the system had many advantages
over other European systems of the time. For example, the majority of users had to
memorize only a few symbols and their values. You can see Roman numerals every- 181
MATH, MEASUREMENT, AND TIME
How long will it take me to count to one billion?
Probably longer than your lifetime. Most of the numbers between one and
one billion are long and challenging to pronounce. When you start
counting the larger numbers like 482,051,341, you will likely start to slow
down. If you allow just three seconds to say each number, which is probably
faster than most people can count, and you take no breaks at all, it will take
you three billion seconds to finish counting. How many years is that? More
than 95 years! Here’s how you arrive at that figure: three billion seconds divided
by 60 (seconds per minute) = 50,000,000 minutes; 50,000,000 minutes
divided by 60 (minutes per hour) = 833,333.333 hours; 833,333.333 hours
divided by 24 (hours per day) = 34,722.22 days; 34,722.22 days divided by 365
(days per year) = 95.1 years.
where today—in the appendices in books, in the credits of feature films, on building
faces for dates, and on watches and clocks.
What is an abacus, and how long has it been used?
An abacus, also called a counting frame, is a calculating tool used for mathematical
problems. Abaci are often constructed as a wooden frame with beads sliding on
wires, but originally they were beans or stones moved in grooves in sand or on
tablets of wood, stone, or metal. These early abaci were documented in
Mesopotamia around 3500 B.C.E. The modern form, with beads sliding on rods,
dates back to at least fifteenth-century China. Before the use of decimal number
systems, which allowed the familiar pencil-and-paper methods of calculation, the
abacus was used for almost all multiplication and division. The abacus is still used
in many countries where modern calculators are not available. It is also widely used
in Japan and China, both of which have long traditions of abacus use.
Is zero a number?
Yes. 0 (zero) is both a number and the numerical digit used to represent that number
in numerals. The idea to use zero as a number was probably not recognized until
the early centuries C.E., when the Hindus and Arabs tried to solve mathematical
equations and organized a systematic study of the properties of operations on numbers.
In about 850 C.E. Mahavir, a Hindu mathematician, wrote in his book The Compendium
of Calculation: “A number multiplied by zero is zero, 182 and that number
The abacus can be thought of as an old-fashioned adding machine. It uses beads to represent numbers that can be added
and subtracted by moving them back and forth along columns.
remains unchanged which is divided by,
added to, or diminished by zero.” Today’s
mathematicians agree with most of what
this ancient thinker wrote. We can add
or subtract zero to a number and get
back that number. When we multiply a
number by zero the answer is zero.
However, division by zero is undefined.
Why is learning math important?
Galileo once said, “The great book of
nature can be read only by those who
know the language in which it was written.
And that language is mathematics.”
Math is one way we understand the
world around us. Math is the most
widely used subject in the world, and
every career—from retail work to rocket
science—uses some sort of math.
More importantly, doing math helps
the mind to reason and organize complicated
situations or problems into
clear, simple, and logical steps. Thus, as
students learn more math, they become
critical thinkers and problem solvers
that can resolve difficult situations in everyday life. Taking math is important if
you are considering attending a college, university, or technical school—nationwide
studies have found that students who take algebra and geometry in high
school have about an 80 percent chance of attending college regardless of race,
religion, and family income.
What is a googol?
A googol is a very large number: the number 1 followed by 100 zeros, or 10100. Unlike
most other names for numbers, it does not relate to any other numbering scale. The
American mathematician Edward Kasner first used the term in 1938; when searching
for a term for this large number, Kasner asked his nephew, Milton Sirotta, then about
nine years old, to suggest a name. The googolplex is 10 followed by a googol of zeros.
The popular Web search engine Google.com is named after the concept of a googol.
Is it possible to count to infinity?
No. Very large finite numbers are not the same as infinite numbers. Infinite numbers
are defined as being unbounded, or without boundaries or limits. Any number
that can be reached by counting or by representation of a number followed by billions
of zeros is a finite number. 183
For some, learning math is fun, while other kids might not
enjoy it so much. Still, math is used in everyday life and is
important for everyone to learn.
MATH, MEASUREMENT, AND TIME
WE IGHTS AND MEASURE S
How are measuring units related to the human body?
In all traditional measuring systems, short-distance units are based on the dimensions
of the adult human body. The inch represents the width of a thumb; in fact,
in many languages, the word for “inch” is also the word for “thumb.” The foot (12
inches) was originally the length of a human foot, although today it is longer than
most people’s feet. The yard (3 feet) is the name of a 3-foot measuring stick in England,
but it is also approximately the distance from the tip of the nose to the end of
the middle finger of the outstretched hand. Finally, if you ask an adult to stretch
their arms out to the sides as far as possible, their total “arm span,” from one fingertip
to the other, is called a fathom (6 feet).
Other early measures were derived from physical activity, such as a pace, a
league (the distances that equaled an hour’s walking), an acre (the amount of land
plowed in a day), a furlong (the length of a plowed ditch). The ell, based on the distance
between the elbow and the index finger, was used to measure out cloth. It
ranged from 20 to 91 inches (0.513 to 2.322 meters) depending upon where it was
used and the type of goods measured.
What is a cubit?
In ancient Egypt and Mesopotamia, the basic unit of length was the cubit, based on
a forearm measured from the elbow to the tip of the outstretched middle finger.
Indeed, the word cubit comes from the Latin word cubitum, meaning “elbow.” This
distance is approximately 18 inches (roughly 45 centimeters). In ancient times, the
cubit was usually defined as equal to 24 digits or 6 palms. The Egyptian “royal” or
“long” cubit, however, was equal to 28 digits or 7 palms.
How were stones used as weights and measures?
Babylonians made important improvements upon the invention of weights and balance
using stones. Instead of just comparing the weights of two objects, they compared
the weight of each object with a set of stones kept just for that purpose. In the ruins of
their cities, archaeologists have found some of these stones finely shaped and polished.
It is believed that these were the world’s first weight standards. The Babylonians used
different stones for weighing different items. In modern English history, the same basis
has been used for weight measurements. For the horseman, the stone weight was 14
pounds (6 kilograms). In weighing wool the stone weight was 16 pounds (7.3 kilograms).
For the butcher and fisherman, the stone weight was 8 pounds (3.6 kilograms).
The only legal stone weight in the king’s legal system was 14 pounds.
Is a mile the same distance on land and at sea?
No. A mile on the ocean and a mile on land are not the same distance. On the ocean,
184 a mile is called a nautical mile and measures 6,076 feet (1,852 meters). A land mile
(or statute mile) is 5,280 feet (1,609 meters). Queen Elizabeth I of England established
the statute mile. This measure, based on walking distance, originated with
the Romans, who designated 1,000 paces as a land mile.
How are carats and carob seeds related?
The weight of a carat (200 milligrams), the standard unit of measurement for gemstones,
is based on the weight of the carob seed, which was once used as a weighing
standard by jewelers in Africa and the Middle East. Historians believe the word
“carat” is derived from an Arabic word meaning “bean” or “seed.”
How can U.S. money be used to measure items around the house?
All U.S. paper currency is 6 1/8 inches wide by 2 5/8 inches long. The diameter of a
quarter is approximately one inch. The diameter of a penny is approximately threequarters
of an inch. So if you want to measure the length of your pencil, simply line
up some coins and begin measuring!
What is an acre used to measure?
An acre is a unit of area used for measuring real estate. The word “acre” is an Old
English word meaning “a field.” The acre was originally defined as the area that
could be plowed in a day by a yoke of oxen. An acre is 43,560 square feet (4,840
square yards). There are exactly 640 acres in a square mile.
What is a cord used to measure?
A cord is a traditional unit of volume used to measure stacked firewood. In the United
States, the cord is defined legally as the volume of a stack of firewood 4 feet (1.2
meter) wide, 8 feet (2.4 meter) long, and 4 feet (1.2 meter) high. (In Maryland, the
law specifies that the wood be stacked “tight enough that a chipmunk cannot run 185
How can you know that the pound used to weigh your apples is
the same whether you are in New York City or Los Angeles?
The weights and measures officials in each U.S. state use standards that are
checked against the national standards in Washington, D.C. The standards
are kept at the National Institute of Standards and Technology (NIST), an
agency of the U.S. Department of Commerce. The NIST (previously known as
the National Bureau of Standards between 1901 and 1988) was established by
Congress as the central measurement laboratory of the federal government.
So no matter where you are in the United States, 16 ounces will always equal
1 pound; 8 fluid ounces will always equal 1 cup; 2 cups will always equal 1
pint; 2 pints will always equal 1 quart; and 4 quarts will always equal 1 gallon.
MATH, MEASUREMENT, AND TIME
through it.”) The name comes from an old method of measuring a stack of firewood
using a cord or string. In the U.S. timber industry, the cord is also used as a unit of
weight for pulpwood. The weight varies with tree species, ranging from about 5,200
pounds (2,358 kilograms) for pine to about 5,800 pounds for hardwood.
How is a baker’s dozen different from a standard dozen?
A dozen is a unit of quantity, equal to 12. A baker’s dozen is an informal unit of
quantity, equal to 13. Bakers often toss in an extra item for each dozen bought,
making a total of 13. This custom is very old, dating at least from the thirteenth
century, when the weights and prices of loaves of bread were strictly regulated by
royal proclamations called assizes, and bakers could be jailed if they failed to provide
fair weight at the listed prices.
Are the terms “gnat’s eye” and “hair’s breadth” true units of measure?
Yes, but both are slang units of distance and diameter. The eyes of typical gnats tend
to have diameters similar in size to a hair’s breadth—roughly 100–150 micrometers.
An item would have to be very short in order to be gnat’s eye in length! A hair’s
breadth is an informal unit of distance: it is used to denote a measurement of
approximately 70 to 100 micrometers in diameter, or 0.1 millimeter, which is similar
in thickness to real human hair.
What is horsepower?
Horsepower is a unit of power representing the power exerted by a horse when it pulls
an object. James Watt, the inventor of the steam engine, defined the term horsepower
after determining through careful measurements that a horse is typically capable of a
power rate of 550 foot-pounds per second. This means that a horse, harnessed to an
appropriate machine, such as a plough or wagon, can lift 550 pounds at the rate of one
foot per second. Today the standard unit of power is named for Watt, and one horsepower
is equal to approximately 745.6999 watts. Outside the United States, the English word
“horsepower” is often used to mean the metric horsepower, a slightly smaller unit.
What is the metric system?
The metric system is a decimalized system of measurement. Designed during the
French Revolution of the 1790s, the metric system brought order out of the conflicting
and confusing traditional systems of weights and measures that were being
used in Europe at the time. Prior to the introduction of the metric system, it was
common for units of length, land area, and weight to vary, not just from one country
to another but from one region to another within the same country. As the modern
nations gradually developed from smaller kingdoms and principalities, confusion
multiplied. Length, for example, could be measured in feet, inches, miles,
spans, cubits, hands, furlongs, palms, rods, chains, and leagues. Merchants, scientists,
and educated people throughout Europe realized that a uniform system was
needed, and in 1790 the French National Assembly commissioned the Academy of
186 Science to design a simple decimal-based system of units.
The three most common base units in the metric system are the meter, gram,
and liter. The meter is a unit of length equal to 3.28 feet; the gram is a unit of mass
equal to approximately 0.0022 pounds (about the mass of a paper clip); and the liter
is a unit of volume equal to 1.05 quarts. Temperature is expressed in degrees Celsius;
0 degrees Celsius equals 32 degrees Fahrenheit.
Why is the metric system called a decimal-based system?
The metric system is a called a decimal-based system because it is based on multiples
of 10. Any measurement given in one metric unit (such as a kilogram) can be
converted to another metric unit (such as a gram) simply by moving the decimal
place. For example, if your father told you he weighed 82,500.0 grams (181.8
pounds), you can convert this to kilograms simply by moving the decimal three
places to the left; in other words, your father weighs 82.5 kilograms.
How big is a hectare?
The hectare (abbreviated ha) is a unit of area equal to 10,000 square meters and
used exclusively for measuring land. To get a sense of how big this is, imagine a
football field. A football field is almost exactly 100 meters from one end line to the
opposite goal line. Imagine a square of that length on each side, and you’ve got an
area of one hectare. There are 100 hectares in one square kilometer, so one square
kilometer is the same area as a square that is ten football fields on one side.
Which countries of the world have not formally begun converting to the
metric system?
In 1960, the metric system was officially named the Système International d’Unités
(or SI) and is now used in nearly every country in the world except the United 187
The horsepower number used to describe engine power literally relates to the strength of an average horse. The man in this
picture is using a four-horsepower plow!
MATH, MEASUREMENT, AND TIME
States, Burma (also known as Myanmar, in Southeast Asia), and Liberia. As early as
1790, Thomas Jefferson, then the U.S. secretary of state, proposed adoption of the
metric system. It was not implemented because Great Britain, America’s major
trading source had not yet begun to use the system.
What is the difference between avoirdupois measurements and troy
measurements?
Troy weight is a system of mass units used primarily to measure gold and silver. A
troy ounce is 480 grains, or 31.1 grams. Avoirdupois (pronounced AV-er-deh-POIZ)
weight is a system of units that is used to measure mass, except for precious metals.
It is based on the pound, which is approximately 454 grams. In both systems,
the weight of a grain is the same: 65 milligrams.
CALENDARS AND
TE LLING TIME
How did ancient civilizations develop calendars, or ways for tracking days,
months, and years?
Celestial bodies, such as the Sun, Moon, planets, and stars, provided peoples of
ancient civilizations a reference for measuring the passage of time. Ancient civilizations
relied upon the apparent motion of these bodies through the sky to determine
seasons, months, and years. Historians know little about the details of timekeeping
in prehistoric eras, but wherever archaeologists dig up records and artifacts, they
usually discover that in every culture some people were preoccupied with measuring
and recording the passage of time. Ice-age hunters in Europe over 20,000 years
ago scratched lines and gouged holes in sticks and bones, possibly counting the
days between phases of the Moon. Five thousand years ago, Sumerians in the Tigris-
Euphrates valley (in present-day Iraq) developed a calendar that divided the year
into 30-day months, divided the day into 12 periods (each corresponding to two of
our hours), and divided these periods into 30 parts (each like four of our minutes).
188 Historians have no written records of Stonehenge, built over 4,000 years ago in
Which is heavier, a pound of gold or a pound a feathers?
Apound of feathers is heavier than a pound of gold because gold is measured
in troy pounds, while feathers are measured in avoirdupois pounds.
Troy pounds are made of 12 ounces and avoirdupois pounds have 16 ounces.
A troy pound contains 372 grams in the metric system, and an avoirdupois
pound contains 454 grams.
England, but its alignments show one of
its reasons for existence was to determine
seasonal or celestial events, such
as lunar eclipses and solstices.
Was one of the early Egyptian
calendars a 365-day calendar?
Yes. The earliest Egyptian calendar was
based on the Moon’s cycles, but later the
Egyptians realized that the “Dog Star” in
Canis Major (which today’s astro nomers
call Sirius), rose next to the Sun every
365 days, about when the annual inundation
of the Nile began. Based on this
knowledge, they devised a 365-day calendar
that seems to have begun around
3100 B.C.E., which thus seems to be one
of the earliest years recorded in history.
Before 2000 B.C.E., the Babylonians (in today’s Iraq) used a year of 12 alternating
29-day and 30-day lunar months, giving a 354-day year. In contrast, the Mayans
of Central America relied not only on the Sun and Moon, but also the planet Venus,
to establish 260-day and 365-day calendars. This culture and its related predecessors
spread across Central America between 2600 B.C.E. and 1500 C.E., reaching
their apex between 250 and 900 C.E. They left celestial-cycle records indicating their
belief that the creation of the world occurred in 3114 B.C.E. Their calendars later
became portions of the great Aztec calendar stones.
What is the basis for modern timekeeping?
Modern society has adopted a 365-day solar calendar with a leap year occurring
every fourth year (except century years not evenly divisible by 400). The modern
clock is based on the number 60. In about 3000 B.C.E. the Sumerians used a base 10
counting system and also a base 60 counting system. The timekeeping system
inherited this pattern with 60 seconds per minute and 60 minutes per hour. Ten and
60 fit together to form the notion of time: 10 hours is 600 minutes; 10 minutes is
600 seconds; 1 minute is 60 seconds.
How long is each year?
Each calendar year is exactly 365 days, 5 hours, 48 minutes, and 46 seconds. This is
the amount of time between two successive crossings of the celestial equator by the
Sun at the vernal equinox (the first day of spring). The fact that the year is not a
whole number of days has affected the development of calendars, which over time
generate an error. The current calendar we use, called the Gregorian calendar,
attempts to fix this by adding an extra day to the month of February every four
years. These years are called “leap years.” 189
The Mayans, who once had a thriving civilization in Central
America, developed a sophisticated calendar for tracking time.
MATH, MEASUREMENT, AND TIME
When and why were leap years introduced?
The use of a 365-day calendar year with occasional leap years was introduced in 46
B.C.E. with the Julian calendar. The Julian calendar was formed by Julius Caesar,
who had commissioned the Alexandrian astronomer Sosigenes to revise the calendar
system. Sosigenes used a tropical solar year, which calculates to 365.25 days per
year. This was slightly off, because the actual tropical solar year is 365.242199 days.
This discrepancy caused there to be 10 days missing by the year 1582. That year,
Pope Gregory XIII issued a papal bull (decree) to fix the Julian calendar. The Jesuit
astronomer Christoph Clavius undertook the Pope’s decree and designed what is
now known as the Gregorian calendar. In order to correct for the loss of one day
every 130 years, the Gregorian calendar drops 3 leap years every 400 years. According
to this system, years are leap years only if divisible by 400—thus, 1600 and 2000
are leap years; 1700, 1800, and 1900 are not. Because the solar year is shortening,
today a one-second adjustment—called a leap second—is made (usually on December
31 at midnight) when necessary to compensate.
When was the last leap second added, and why?
Scientists added an extra second—called a leap second—to 2008 to make up for the
slowing down of Earth’s rotation. The International Earth Rotation and Reference
Systems Service (IERS) in Paris, France, keeps track of time by measuring Earth’s
rotation, which has been slowing down over time, and by an atomic clock, which
never changes. When a difference in the two clocks shows up, the IERS adds or subtracts
a second to the year. Time has been measured by the planet’s rotation for
thousands of years; however, it was not until 1949 that scientists developed a clock
that kept perfect time. The IERS atomic clock keeps time by viewing the fundamental
vibrations of atoms. As far as scientists know, the cesium atom—which vibrates
9,192,631,770 times per second—does not change over time and is the same everywhere
on Earth and in space.
What is the Chinese lunar calendar?
The Chinese lunar calendar is based on the cycles of the Moon, and is constructed in
a different fashion than the Western solar calendar. In the Chinese calendar, the
beginning of the year falls somewhere between late January and early February, and
contains 354 days. Each year is given an animal designation, such as “Year of the Ox.”
A total of 12 different animal names are used, and they rotate in the following
sequence: Rat, Ox, Tiger, Hare (Rabbit), Dragon, Snake, Horse, Sheep (Goat), Monkey,
Rooster, Dog, and Pig. The Chinese have adopted the Western calendar since 1911,
but the lunar calendar is still used for festive occasions such as the Chinese New Year.
Many Chinese calendars print both the solar dates and the Chinese lunar dates.
What is the difference between B.C. and A.D.?
The term B.C. stands for “Before Christ,” and is used to date events before the birth
190 of Jesus Christ. A.D. is the abbreviation for the Latin phrase anno domini, which
means “in the year of our Lord,” and is used to date events after Jesus’s birth. This
system of dating has been used for many years by Western archaeologists. Today,
however, with a growing understanding that not all archaeologists are Christians,
some archaeologists prefer to use the terms B.C.E. (meaning Before the Common
Era) and C.E. (meaning Common Era). These terms are exactly the same as B.C. and
A.D., but are not related to Christianity.
What is the difference between a millennium and a century?
A millennium is an interval of 1,000 years. A century is 100 consecutive calendar years.
The first century consisted of years 1 through 100. The twentieth century started with
1901 and ended with 2000. The twenty-first century began on January 1, 2001.
How are the months of the year named?
The origins of our calendar came from the old Roman practice of starting each
month on a new moon. Roman bookkeepers would keep their records in a ledger
called a kalendarium, from which comes the English word “calendar.” The original
Roman calendar was 304 days long and had 10 months that began with March and
ended with December. The Roman political leader Julius Caesar reorganized the calendar
year to start with the month of January. Thus, the first month was named for
Janus, the Roman god of beginnings and endings. February was named for the god
of purification, Februus. March was
named for Mars, the Roman god of war.
April comes from the Roman word
aperire, meaning “to open”; this is the
month when the trees and flower buds
open. May is named for Maiesta (Maia),
the Roman goddess of honor and reverence.
June is named for Juno, the
Roman queen of the gods. July is named
after Caesar himself, who was born in
this month, and August is named for
Augustus, the Roman emperor. And the
last four months of the year have
numerical meanings: September comes
from the word septem,meaning “seven”;
October from the word “octo,” meaning
“eight”; November from the word
novem, meaning “nine”; and December
from the word decem, meaning “ten.”
How are the days of the
week named?
The English days of the week are named
after a mixture of figures in Roman and 191
The Roman emperor Julius Caesar was responsible for
reorganizing the Western calendar so that years began with
the month of January.
MATH, MEASUREMENT, AND TIME
Anglo-Saxon mythology. The English language has inherited and changed those
names a bit, but the ones we use today resemble those names. For example, Sunday
is named after the Sun, and it was originally called “Sun’s Day.” The Sun gave people
light and warmth every day. Monday is named after the Moon, and it was originally
called “Moon’s Day.” The Moon was considered very important in the lives of
people and their crops. Tuesday was Tiw’s Day. Tiw (sometimes spelled Tiu or Tyr)
was a Norse god known for his sense of justice. Wednesday was Woden’s Day; Woden
(or Odin) was a powerful Norse god. Thursday was Thor’s Day, named for Thor, the
Norse god of thunder. Friday was Frigg’s Day, named for Frigg, the Norse god of love
and fertility. Saturday was Seater’s Day (or Saturn’s Day); Saturn was the Roman
god of agriculture.
Is there a simple rhyme to help recall how many days are in each month?
Yes. Many children learn this simple poem to help them remember how many days
are in each month. Although the origin of the lyrics to “Thirty Days Hath September”
is unclear, the use of old English dates this poem to at least the sixteenth century:
Thirty days hath September,
April, June and November
All the rest have thirty-one,
excepting only February
Which hath but twenty eight-days clear
And twenty-nine in each leap year.
What is the International Date Line?
Located at 0 degrees longitude, the prime meridian passes through Greenwich,
England. Halfway around the world in the middle of the Pacific Ocean (180 degrees
from Greenwich) is the International Date Line (IDL), where the date changes
across the boundary of the time zone. The entire world is on the same date only at
the instant when it is noon in Greenwich, England, and midnight at the IDL. At all
other times, there are different dates on each side of the IDL.
When and why were time zones established?
Earth is divided into 24 time zones so that everyone in the world can be on roughly
similar schedules. Until about 100 years ago, each city set its clocks to local time.
Noon was the time when the Sun was at its highest in the sky, as viewed from that
city. In order to make this happen, however, even neighboring cities needed to set
their clocks differently. For example, when it was 8:00 in New York City, it was 8:12
in Boston (because Boston is about three degrees east of New York). Before modern
transportation and communication, this time difference did not really affect society.
As railroads were being constructed in the late 1800s, however, the Canadian
railway planner and engineer Sir Sandford Fleming proposed a world time zone system.
He did this so that train schedules could be written using common time set-
192 tings. In November 1883 the U.S. and Canadian railroad companies instituted stanhandy
dard time in time zones. (Standard time in time zones was established by U.S. law
with the Standard Time Act of 1918.) The concept was soon adopted internationally,
with the world being divided into 24 time zones, each one a long strip from
North Pole to South Pole, about 15 degrees of longitude wide. All the people in one
time zone set their clock the same way, to the local time in the center of the time
zone. Today, most countries use this time zone system.
When do the seasons officially start?
There are four traditional seasons on Earth—spring, summer, fall (or autumn), and
winter—and each is marked by the movement of the Sun in the sky. In the Northern
Hemisphere, spring starts at the moment the Sun is directly over the equator, going
from south to north, called the vernal equinox. Summer starts the moment the Sun
is farthest north, called the summer solstice. Fall begins the moment when the Sun
is directly over the equator, going from north to south, called autumnal equinox.
Winter starts the moment the Sun is farthest south, called the winter solstice.
What is Daylight Saving Time?
Sometimes called “fast time” or “summer time,” Daylight Saving Time (DST) temporarily
extends the length of daylight because we move our clocks forward an hour
in the spring, creating longer days. In the United States, we change our clocks in
March. Most of the United States begins Daylight Saving Time at 2:00 A.M. on the second
Sunday in March and reverts to standard
time on the first Sunday in November
(when we set our clocks back one
hour). In the United States, each time
zone switches at a different time. Different
countries have different change
dates. Although DST was first proposed by
Benjamin Franklin in 1784, it began in
the United States during World War I, primarily
to save fuel by reducing the need to
use artificial lighting. Although some
states and communities observed DST
between the wars, it was not observed
nationally again until World War II. Today,
most Americans continue to participate in
DST to save energy, although Arizona and
Hawaii are the two states that are exceptions
to the rule.
What is a sundial and how does
it work?
The sundial, one of the first instruments
used to measure time, works by 193
MATH, MEASUREMENT, AND TIME
Sundials tell time by casting a shadow on a base plate
marked with the different hours of the day.
simulating the movements of the Sun. The Sun shines on a gnomon (pronounced
NO-men), a triangle or device set perpendicular to a base plate, and casts its shadow
on the appropriate hour line, thus displaying the time of day. The angle on the
gnomon has to be parallel to the Earth’s axis and must be equal to your location’s
latitude if it is to display accurate clock time.
What is a water clock?
Water clocks were among the earliest timekeepers that didn’t depend on the observation
of celestial bodies. One of the oldest was found in the tomb of the Egyptian
pharaoh Amenhotep I, buried around 1500 B.C.E. Later named clepsydras (“water
thieves”) by the Greeks, who began using them about 325 B.C.E., these were stone
vessels with sloping sides that allowed water to drip at a nearly constant rate from
a small hole near the bottom. Other clepsydras were cylindrical or bowl-shaped containers
designed to slowly fill with water coming in at a constant rate. Markings on
the inside surfaces measured the passage of “hours” as the water level reached
them. These clocks were used to determine hours at night, but may have been used
in daylight as well. Another version consisted of a metal bowl with a hole in the bottom;
when placed in a container of water the bowl would fill and sink in a certain
time. These were still in use in North Africa in the twentieth century.
When and how did the first modern clocks develop?
In Europe during most of the Middle Ages (roughly 500 to 1500 C.E.), simple sundials
placed above doorways were used to identify midday and four “tides” (important
times or periods) of the sunlit day. By the tenth century, several types of pocket
sundials were used. One English model even compensated for seasonal changes
of the Sun’s altitude. Then, in the first half of the fourteenth century, large mechanical
clocks began to appear in the towers of several large Italian cities. Historians do
not have any evidence or record of the working models that preceded these public
clocks, which were weight-driven. Another advance was the invention of springpowered
clocks between 1500 and 1510 by Peter Henlein of Nuremberg. Replacing
the heavy drive weights permitted smaller, portable, clocks and watches. Although
they ran slower as the mainspring unwound, they were popular among wealthy
individuals due to their small size and the fact that they could be put on a shelf or
table instead of hanging on the wall or being housed in tall cases. These advances
in design were precursors to truly accurate timekeeping.
What is a grandfather clock?
A grandfather clock, also called a long case clock or floor clock, is a freestanding,
weight-driven, pendulum clock. Its pendulum, which swings back and forth, is kept
inside its tower. Clocks of this style are commonly 6 to 8 feet (1.8 to 2.4 meters) tall.
The case often features carved ornamentation on the hood, called a bonnet, which
surrounds and frames the dial, or clock face. These clocks have a long history. In
1582 the Italian astronomer Galileo Galilei discovered that a pendulum could be
194 used to keep time. He studied pendulum clocks, and drew the first designs for a
grandfather clock. In 1656 the Dutch mathematician Christiaan Huygens applied
what Galileo had discovered and built the first working grandfather clock (he also
patented a pocket watch in 1675.) The first grandfather clocks did not keep time
well, often losing as much as 12 minutes a day. In 1670 the English clockmaker
William Clement noticed that by making the pendulum in the clock longer he could
make the clock keep better time. His longer pendulums required longer cases,
which led to the name “long case” clock, and later grandfather clock. Most grandfather
clocks are “striking” clocks, which means they sound the time on each hour.
When was the wristwatch invented?
The wristwatch, today the most common watch available, was first manufactured by
the Swiss watch manufacturer Patek Philippe in 1868. During World War I, military
personnel found that the wristwatch was far more beneficial on the battlefield than
the day’s popular pocket watches. Soldiers fitted their watches into primitive
“cupped” leather straps so they could be worn on the wrist, thereby freeing up their
hands to operate weaponry. It is believed that the Swiss watchmaker Girard-Perregaux
equipped the German Imperial Navy with similar pieces as early as the 1880s,
which they wore on their wrists while synchronizing naval attacks. Many European
and American officers kept their wristwatches once the war was over, thus popularizing
wristwatches in America and Europe. In 1926, the Swiss watch manufacturer
Rolex patented the first waterproof and
dustproof wristwatch, the Oyster.
Who invented the alarm clock?
The clockmaker Levi Hutchins of Concord,
New Hampshire, invented an
alarm clock in 1787. His alarm clock
rang at only one time—4:00 A.M. He
invented his device so that he would
never sleep past his usual waking time.
It was his “firm rule” to awaken before
sunrise, whatever the season. But sometimes
he slept past that hour, and was
distraught the rest of the day. Although
he lived to the age of 94, Hutchins never
patented or manufactured his clock. He
wrote about his clock: “It was the idea of
a clock that could sound an alarm that
was difficult, not the execution of the
idea. It was simplicity itself to arrange
for the bell to sound at the predetermined
hour.” The French inventor
Antoine Redier was the first person to
patent an adjustable mechanical alarm 195
MATH, MEASUREMENT, AND TIME
Alarm clocks are a pain when we want to sleep. You can
thank eighteenth-century American clockmaker Levi
Hutchins for waking you up.
clock, in 1847. In 1876, a small mechanical wind-up clock patented in the United
States by Seth E. Thomas was the most inspirational of those invented in this era—
soon all the major U.S. clockmakers were making small alarm clocks and the German
clockmakers soon followed. The electric alarm clock was invented around 1890.
What do A.M. and P.M. stand for?
The initials A.M. stand for ante meridian, which is Latin for “before noon.” The initials
P.M. stand for post meridian, which is Latin for “after noon.”
How long is a fortnight?
The word fortnight is a unit of time that equals fourteen days. It comes from the Old
English word feorwertyne niht, meaning “fourteen nights.” The term is used in
Great Britain, where salaries and most social security benefits are paid on a fortnightly
basis, but in the United States people use the term “two weeks.” In many languages,
there is no single word for a two-week period and the equivalent of “fourteen
days” has to be used. In Spanish, Italian, French, and Portuguese, the terms quince
días, quindicina, quinzaine, and quinzena—all meaning “fifteen days”—are used.
196
What is a jiffy?
Ajiffy is a unit of time—about 1/100 of a second. A jiffy is often used in
chemistry and physics to discuss time equal to a “light centimeter,” that
is, the time required for light to travel a distance of one centimeter. The definition
of the jiffy was proposed by the early-twentieth-century American
physical chemist Gilbert N. Lewis, who was one of the first scientists to apply
principles of quantum physics in chemistry.
BONE S AND JOINTS
How many bones are there in the human body?
Babies are born with about 300 to 350 bones, but many of these fuse together
between birth and maturity to produce an average adult total of 206. Bone counts
vary according to the method used to count them, because a structure may be treated
as either multiple bones or as a single bone with multiple parts. There are four
major types of bones: long bones, short bones, flat bones, and irregular bones. The
name of each type of bone reflects the shape of the bone. The shape of the bone also
tells about its mechanical function. Bones that do not fall into any of these categories
are sesamoid bones and accessory bones.
How do bones grow?
Bones are made of a network of calcium laid down by cells. As children grow, special
cells at the end of bones add new calcium to the network of bone. Children have
layers of these cells in the shape of plates at the ends of their bones. These are called
“growth plates,” and they close up when kids reach their full adult height. To grow
in a healthy way, bones need protein, calcium, and other minerals. In addition,
bones need the hormones that increase at puberty, including estrogen and testosterone.
Bones also need vitamin D, to help absorb calcium, and regular exercise to
keep bones strong.
Are bones hard as a rock?
Yes and no. Bones are hard connective tissue, made up of bone cells, fat cells, and
blood vessels, as well as nonliving materials, including water and minerals. Some
bones have a very hard, heavy outer layer made out of compact bone. Under this 197
ALL ABOUT
MY BODY
layer is a lighter layer called spongy bone, which is located inside the end, or head,
of a long bone. Spongy bone is tough and hard, but light, because it has lots of
irregularly-shaped sheets and spikes of bone (called trabeculae) that make it porous
(full of tiny holes). The soft, jelly-like inner core of bone is called the bone marrow.
It is where red blood cells, certain white blood cells, and blood platelets are formed.
The jawbone is the hardest bone in your body. Although bones are hard, they are
not the hardest substance in the human body: the enamel on your teeth is harder.
Which are the biggest and smallest bones?
The femur, or thighbone, is the biggest bone in the body. The average femur is 18
inches (45.72 centimeters) long. The longest bone ever recorded was 29.9 inches
(75.95 centimeters) long. It was from an 8-foot-tall (2.45 meters) German who died
in 1902 in Belgium. The stirrup (also called the stapes) in the middle ear is the
smallest bone in the body. A tiny, U-shaped bone that passes vibrations from the
stirrup to the cochlea, it weighs about 0.0004 ounces (0.011 grams) and can measure
just one-tenth of an inch.
Where is my rib cage?
The ribs are thin, flat, curved bones in your upper body that form a protective
“cage” around the heart and lungs. The ribs are comprised of 24 bones arranged
in 12 pairs that form a kind of cage that encloses the upper body and gives the
chest its familiar shape. The ribs serve several important functions. They protect
the heart and lungs from injuries and shocks that might damage them. Ribs also
protect parts of the stomach, spleen, and kidneys. The ribs help you to breathe. As
you inhale, the muscles in between the ribs lift the rib cage up, allowing the lungs
to expand. When you exhale, the rib cage moves down again, squeezing the air out
of your lungs.
Where is my spine?
Your spine, also called the backbone,
runs down the length of your back from
the base of your neck to your pelvis. The
spine has 25 joints connecting 33 individual
bones. (The bottom four bones of
the spine are fused together to form the
terminal vertebrae called the coccyx, or
tailbone—and the five bones above that
are fused together to form the sacrum.
They are caged within the bones of the
pelvis.) Each bone in the spine is called
a vertebra and they are grouped together
to perform specific tasks. The spine
supports your head, lets you twist and
198 bend, and holds your body upright. It
The “rib cage” includes the curved ribs in your chest that
protect vital organs like the heart and lungs.
also protects the spinal cord, a large bundle of nerves that sends information from
your brain to the rest of your body.
How is the body able to bend?
The human skeleton moves at its more than 230 joints, which are the places where
bones connect. Those joints give you a basic range of motion. For example, everyone’s
shoulder joints can rotate 360 degrees, and elbows can open and close to just
under a 180 degree arc. The pull of ligaments—ropelike connective tissues that
anchor one bone to the next around a joint—lengthen a bit to allow a joint to move,
but keep the range of motion limited so that you don’t hurt yourself. So, the next
time you are tempted to do a backbend or stretch your leg up to your ear, think of
your joints and ligaments!
Why do my knuckles sometimes make a cracking sound if I bend them?
Knuckles—as well as your knees, back, and neck—sometimes make a popping or
grinding sound thanks to the body’s synovial fluid, which acts as a lubricant in your
bone joints. This fluid contains the gases oxygen, nitrogen, and carbon dioxide.
When you pop or crack a joint, the joint capsule is stretched, gas is rapidly released,
and bubbles form. If you want to crack the same knuckle again, you have to wait
until the gases return to the synovial fluid. Other sounds, like snapping or the
plucking of a rubber band, sometimes happen when your ligaments temporarily
slide off your bone as you move your joints.
MUSCLE POWER
What are muscles made of?
Our muscles, which make up about half of our body mass, control the way the body
moves. Muscles work together all the time, whether we are actively playing sports,
or quietly reading and writing. Muscles lie in bands just beneath the surface of the 199
Is there such a thing as a funny bone?
The funny bone exists in your body, but it’s not a bone at all! The funny bone
is a part of the ulnar nerve located at the back of the elbow. If you accidentally
bump this area it can cause a tingling sensation toward the front of your
forearm. This tingling or dull pain is caused by the ulnar nerve bumping up
against the humerus, the long bone that starts at your elbow and goes up to
your shoulder. Although it might feel weird, tapping your funny bone doesn’t
do any damage to your elbow, arm, or ulnar nerve.
ALL ABOUT MY BODY
skin. A muscle is made up of thousands
of fibers bundled together
within a protective sheath that
consists of blood vessels and
nerves. These nerves can be up to
12 inches (30 centimeters) long. A
muscle becomes stronger when
you work it, which is why people
who regularly exercise have more
defined muscle tone than those
who do not exercise.
There are about 660 muscles
in the human body. The three types
of muscle tissue are skeletal, cardiac,
and smooth. The main and
most unique characteristic of muscle
tissue is its ability to contract,
or shorten, making some type of
movement possible. Skeletal muscles
hold the bones together, and
are often called “voluntary” muscles
because the brain controls
them. The cardiac muscle, which is
found only in the heart, contracts
to send blood from the heart into
the arteries. The brain sends signals
to the cardiac muscle to speed
up or slow down its contractions,
called the heartbeat. Smooth muscles,
located in the internal organs such as the stomach and intestines, help these
organs or tissues do their job, such as help you digest and eliminate your food.
What’s an Achilles heel?
Muscles are attached to bones by tendons, the longest and strongest of which is
called the Achilles tendon in your heel. This thick band of tissue attaches the muscles
of the calf to the heel bone and is the key to the foot’s ability to flex. The Achilles
tendon allows you to push off of your foot when walking or running. In ancient
Greek myth, the hero Achilles died from a wound to his heel, so the popular expression
“Achilles heel” often refers to a physical weakness or limitation.
Which muscles are the largest, and which ones are the smallest?
The largest muscle is the buttock muscle (gluteus maximus), which moves the
thighbone away from the body and straightens out the hip joint. It is also one of the
200 stronger muscles in the body. The smallest muscle is the stapedius, in the middle
The human body contains about 660 different muscles that are used
to move our bodies as well as control our organs.
ear. It is thinner than a thread and 0.05 inches (0.127 centimeters) in length. It activates
the stirrup that sends vibrations from the eardrum to the inner ear. The
longest muscle is the sartorius, which runs from the waist to the knee. Its purpose
is to flex the hip and knee.
What’s a charley horse?
A charley horse a muscle cramp, or sudden, uncontrolled contraction of a muscle.
This type of pain is generally felt in the legs, sometimes after heavy exercise, and
usually lasts just a few minutes. The expression probably came from the word
“charley,” which is used to describe a horse that is lame.
What causes “growing pains”?
“Growing pains” usually refers to the aches and pains that children feel in their legs
at night when they are lying in bed. Kids seem to get them during growth spurts,
times when they are growing a lot. Doctors think that the tendons—the tough elastic
straps, or bands, that attach muscles to bones—of affected children do not grow
quite as fast as their bones do. The tendons eventually catch up, but in the meantime
this condition puts muscles under extra stress during an active day and causes
them to ache and even spasm (contract abnormally) when they are finally at rest
at night. Growing pains are not dangerous. They don’t bother children during the
day, and they usually come and go at nighttime. Regular stretching exercises—
keeping the muscles and tendons relaxed—often solve the problem for good. But if
the pains are very bad and continue for a long time, a doctor should be seen. In rare
cases, an infection, disease, injury, or unnoticed malformation of the legs is causing
the problem.
MY BUI LDING BLOCKS
How is the human body a living machine?
The human body is a complicated living machine in which various systems work
together as a functioning whole. All the parts of the body—including hundreds of
rock-hard bones and quarts of blood—are made up of cells, about 100 trillion
(100,000,000,000,000) cells in all! Twenty-two internal organs—the large body parts
like the heart, lungs, liver, and kidneys—perform special jobs and work together to
form the different body systems. There are eight key systems in the body. The muscu- 201
Is it easier for my face to laugh or frown?
It is much easier to smile. Smiling takes about 17 facial muscles while you
use 43 muscles to make a frown. Smiling also makes you feel happier!
ALL ABOUT MY BODY
lar system, made up of more than 600 muscles, enables our bodies to make all of their
movements. The circulatory system carries oxygen-rich blood throughout the body.
The skeletal system is made of the bones that form the skeleton and give the body its
shape. People breathe using the respiratory system. The body’s heat-control system is
called the integumentary system, which is made up of skin, hair, nails, and sweat
glands. The reproductive system creates new life. The nervous system processes information
from both inside and outside the body and sends messages, via its nerves, to
different parts of the body. And the digestive system helps us digest our food and
nutrients and gives us energy to go through the day. There are other systems, too,
that help the body sustain life, including the immune system, which fights off invading
viruses and diseases, and the urinary system, which helps keep the inside of the
body clean and eliminates waste. The endocrine system, made up of glands, sends hormones
around the body to trigger growth and to control other activities. These body
systems work together to keep all human beings alive and healthy.
How did my life begin?
All living things are made up of cells. They are so small that you need a microscope
to see them. Your body contains trillions and trillions of cells. Each person begins
life as a single fertilized cell. This single cell contains all the information needed for
202 a new human being to grow and live. The information—coded chemical instruc-
Millions of sperm cells try to fertilize a single egg, but (usually) only one sperm will complete its mission.
tions known as genes—is found on 23 pairs of chromosomes in the nucleus, or control
center, of the cell.
That special fertilized cell began with a single egg cell from your mother. Each
month a woman releases a mature, or ripe, egg cell from reproductive organs called
ovaries. This egg contains half the genes needed to create a new life. A man produces
millions of sperm cells in reproductive organs called testes. Each sperm cell contains
half the genes needed to create a new life. When a sperm cell from your father joined
with and fertilized the released egg cell inside your mother’s body, the cell that
would become you was complete. It had all the coded instructions it needed to begin
dividing and growing into a baby. Within a few hours, the fertilized cell split into two
complete cells, each with a full set of genes inside. Before long the cells divided
again. After five or six days a ball of hundreds of cells existed. The size of the head of
a pin, this ball of cells attached to the lining of your mother’s uterus, or womb, the
reproductive organ in which babies grow. There, in the nourishing lining of the
uterus, the cells continued to multiply. Gradually the cells began to specialize, turning
into nerve cells, muscle cells, and so on. A tiny baby began to take shape.
As you grew, you received nutrients and oxygen from your mother’s blood
through a special tube that was attached to your abdomen called the umbilical cord.
After 40 weeks (between nine and ten months), all of your organs and body systems
were developed enough to work on their own, and you were ready to enter the
world. Then you made your grand entrance and were born!
How do I grow?
Just as the tiny fertilized egg cell from which you began divided again and again to
become a baby, the trillions of cells now making up your body continue to divide as
you grow. The more cells you have, the bigger you become. Some cells divide to
replace worn out cells and others divide to increase the size and change the shape of
your body as you mature. Hormones—chemicals that are produced by glands and circulate
in your blood—help direct the growth of cells in your body during the process
of growing up. Usually people are fully grown by the time they reach the age of 20. By
the time a person is 30, however, the rate at which body cells renew themselves begins
to slow down, and signs of aging appear. As time goes on, certain body cells—like
those of the brain and nerves—are not replaced when they wear out and die.
How big will I become?
Several different factors determine how big a person will grow. The most important
one is heredity, the passing of physical traits from parents to children. When you
began as a single fertilized cell, your mother and father each contributed half the
genes—coded chemical information—needed for you to live and grow. These genes
are responsible for your physical traits, like the color of your eyes and hair, how your
body will be shaped, and how tall you will become. That is why children look a lot
like their parents, or even their grandparents: they have inherited family characteristics
that may have been passed on for several generations. If your parents are big
or tall, chances are good that you will be big or tall, too. The average height of a 203
ALL ABOUT MY BODY
woman in the United States is about 5 feet, 4 inches (1.6 meters), and the average
height for an American man is 5 feet, 9 inches (1.75 meters). In spite of genetic coding,
certain conditions can keep people from growing as large as their genes say they
should. Bad nutrition keeps a body from reaching its maximum size. Poor health and
disease do the same. That is why people who lived in generations before us, when
food was sometimes scarce and health care was poor, were quite a bit smaller than
we are today. Taking good care of your body, then, helps it become the best it can be.
Why are cells called building blocks?
All living things are made up of cells, which are the basic units of life. The human
body contains about 100 trillion cells, which live in our brain, bones, muscles, nerves,
skin, and blood. Humans have about 200 different types of cells that come in different
shapes and sizes, and each has a specific job to do in the human body. However,
no matter what job they perform, all cells have a similar structure. Holding the cell
together around its outside is the cell membrane. Openings in the membrane allow
certain chemicals to travel in and out. The membrane is made up of a watery fluid
called cytoplasm, which contains structures called organelles, specialized subunits
that play specific roles in making the cell work. The nucleus is the cell’s control center,
which sends the organelles chemical instructions and which also contains chromosomes,
the packaging for our genetic material, or DNA (deoxyribonucleic acid).
What is DNA?
DNA, or deoxyribonucleic acid, is a very important molecule found in all living cells.
It contains information used in everyday metabolism and growth and influences
most human characteristics, including the color of our skin, the color of our eyes,
and whether we have curly or straight hair. DNA is often called the blueprint of an
organism because it enables various cells to develop and work together to form a
fully functional body. When an egg and sperm met to form the first cell that was to
become a life, you were given the complete genetic code that all of your cells will use
for the rest of your life. The information that DNA contains is passed from one generation
to the next. Using gene technology, DNA can be modified or transferred from
one animal, plant, or human to another. Genes are made up of short lengths of DNA
and modern gene technology is able to make changes at the level of individual genes.
BLOOD
How much blood is inside my body?
The human body contains approximately 6 quarts (5.6 liters) of blood. Blood acts as
your body’s transportation system—in one day, your blood travels nearly 12,000 miles
(19,312 kilometers). Pumped along by your heart, blood brings oxygen from the air
you breathe and nutrients from the food you eat to all the cells of your body. (Your
heart pumps 1 million barrels of blood during your lifetime—204 enough to fill three
supertankers.) Blood also keeps cells clean and healthy by taking waste products away
after the nutrients and oxygen have been used for processes like growth and repair. In
addition, blood transports hormones—chemicals made in glands that control a variety
of processes—throughout your body. Blood also carries heat throughout your body.
What do plasma, red blood cells, and white blood cells have to do
with blood?
More than half of your blood is a light yellow watery liquid called plasma. Plasma
contains things like nutrients and waste products, along with chemicals and matter
needed for clotting, or sealing a wound before too much blood escapes. The rest
of blood is made of tiny cells. Most are red blood cells, which distribute oxygen
throughout your body and carry away the waste gas carbon dioxide, which is
released from your lungs. The remaining cells are white blood cells, which protect
you from infection by attacking and destroying disease-causing germs that enter
your body. Red blood cells are the smallest cells in your body. But what they lack in
size they make up for in number: in a drop of blood the size of the head of a pin
there are 5 million red blood cells. In that same drop there are 10,000 white blood
cells and 250,000 platelets, small ovals of matter that gather wherever a blood vessel
is injured to plug the hole and help form a clot.
Why is blood red?
As the young red blood cell grows and takes on an adult form in the marrow of the
bone, it loses its nucleus, and it increases its production of hemoglobin. Hemoglobin 205
Our blood contains a variety of cells, including red cells for transporting oxygen and white cells that help defend against germs.
ALL ABOUT MY BODY
is the red pigment, or color of blood, and contains iron, combined with protein. (Oxygen
combined with iron is red; the more oxygen iron has bound to it, the redder it is.)
When blood passes through the lungs, oxygen attaches itself to the hemoglobin of the
red cells. From there, the red cells carry the oxygen through the arteries and the capillaries
to all other cells of the body. The arteries appear reddish because the iron in
the blood gives up its oxygen to the cells that need it as the red blood cells travel
throughout the body. By the time the blood is back on its way to the heart and then
to the lungs it has less than half as much oxygen as it did before. The veins, therefore,
do not get as much oxygen as the other tissues and they appear bluish.
ORGANS
What does my brain do, besides think?
The brain is the body’s command center; everything we do—eating, talking, walking,
thinking, remembering, sleeping—is controlled and processed by the brain. As the
most complex organ in the human body, the brain tells us what’s going on outside
our bodies (whether we are cold or hot, for instance, or whether the person we see
coming toward us is a friend or a stranger) as well as what’s going on inside our bodies
(whether we have an infection or a broken bone, or whether we feel happy or sad).
The key to the body’s nervous system, the brain contains between 10 billion and
100 billion nerve cells, or neurons. Neurons combine to form the body’s nerves,
thin cords that spread from head to toe and all parts in between. Neurons take in
and send out electrical signals, called impulses, that control or respond to everything
your body does and feels. The brain is like a very busy, high-speed post office,
constantly receiving messages and sending them out all the time; it handles millions
of nerve impulses every second.
How many parts are there to the brain?
The human brain is divided into three main parts: the cerebrum, the cerebellum,
and the brain stem. The cerebrum is the largest part of the brain (about 85 percent
of its total weight). It controls emotions, thought, memory, and speech. It is divided
into a right and left side, called hemispheres, and each side is divided further into
parts called lobes. Its thick outer covering, called the cortex, is made up of a type of
tissue called gray matter. The cerebellum coordinates the kinds of movements we
don’t usually think about: it helps us walk upright and in a straight line, it keeps us
balanced so we don’t tip over, and it gives us coordination so we can run and play.
The brain stem connects the brain with the spinal cord. It controls our body’s vital
processes, like breathing, digestion, and heart rate.
How can you measure a heartbeat?
Doctors measure heart rate—the number of contractions of the heart (or heart-
206 beats) in one minute—by taking a person’s pulse or listening to the heart with a
stethoscope. Your heart rate can be taken at any spot on the body at which an artery
is close to the surface and a pulse can be felt, such as the wrist or the neck. When
resting, the average adult human heartbeats at about 70 beats per minute (for
males) and 75 beats per minute (for females), although this rate is often less for athletes.
A toddler’s heart beats about 100 to 130 times per minute; the older child’s
about 90 to 110 times per minute, and the adolescent’s about 80 to 100 times per
minute. If you add it all up, 75 beats per minute translates to 4,500 beats an hour,
108,000 beats per day, or about 39.4 million beats in a year!
How do people breathe in and out?
You usually don’t have to think much about your breathing because your brain controls
it automatically. When you have a lot of carbon dioxide—the waste gas produced
by body processes—in your blood, your brain gets the message and tells your
lungs to exhale and get rid of it. This action then causes you to inhale, drawing in
air that eventually delivers oxygen to every cell in your body. This carefully regulated
exhaling and inhaling takes place about 10 to 14 times each minute when you
are breathing calmly.
When you need more oxygen than usual, your brain takes care of that, too.
When you are exercising or working hard, your brain tells you to breathe more
quickly, taking in 15 to 20 times more air. If that still doesn’t deliver all the oxygen
that your muscles need, you may “run out of breath,” which forces you to rest. You
will still breathe hard at that point—every second or so—until your muscles are
able to work again.
Are the lungs connected to my voice?
Yes. The human voice, whether singing, speaking, or yelling, is made by a combination
of factors. It all begins with air. Air from your lungs rushes through your trachea
(also called the windpipe) and vibrates your vocal chords, a tiny, two-part muscle
located in the larynx (also called the voice box) in your throat. The pitch of the
note depends on the distance between the vocal chords: if you almost close the
space between your vocal chords, the result is a high-pitched sound. If you open the
space, the result is a low-pitched sound. And the speed of your breath determines
just how loud the note is. Your lips and tongue shape these sounds into words. 207
Does the brain feel pain?
Technically, no. While it is responsible for receiving and transmitting all
messages of pain for the whole body, the brain itself does not have pain
receptors. That means that, if you could somehow gain access to another
person’s brain, you could poke it or pinch it and that person would not feel
the pain.
ALL ABOUT MY BODY
How much air does a person breathe in a lifetime?
During a person’s life, he or she will breathe about 75 million gallons (284 million
liters) of air. Every minute, the human body needs 2 gallons (7.5 liters) of air when
lying down, 4 gallons (15 liters) when sitting, 6 gallons (23 liters) when walking,
and 12 gallons (45 liters) or more when running.
Which is the body’s biggest organ?
Your skin is your body’s largest organ and acts as a barrier to the outside world. It
covers your entire body and has a surface area of around 21.5 square feet (2 square
meters). Its thickness ranges from .02 inches (0.5 millimeters) on your eyelids to
0.16 inches (4 millimeters) or more in “tougher” areas, like on the palms of your
hands and the soles of your feet. In total, it accounts for around 16 percent of your
body weight. Your skin protects your internal organs from infection and helps control
body temperature.
Many people say that your skin is like layers of an onion, but your skin really
consists of three main layers. The outer layer, called the epidermis, contains skin
cells, pigment, and proteins. The middle layer, called the dermis, contains blood vessels,
nerves, hair follicles, and oil glands, and provides nutrients to the epidermis.
The layer under the dermis, called the subcutaneous layer, contains sweat glands,
some hair follicles, blood vessels, and fat. Each layer also contains connective tissue
with collagen fibers to give support and elastin fibers to provide flexibility and
strength. Cells in the deepest layer of your epidermis are constantly dividing to make
new cells, providing your skin with a durable overcoat, which protects 208 deeper cells
Our skin is a lot more complicated than it looks at first glance. Skin contains cells that sense touch and temperature, grow
hair, excrete perspiration, and perform other functions, too.
from damage, infection, and dryness. Cells on the surface of your epidermis flake off
and are continuously replaced with new ones, so that about every 30 days your body
produces a whole new set of skin. A human body sheds about 600,000 particles of
skin every hour—that’s about 1.5 pounds (0.68 kilograms) a year. By age 70, an average
human will have lost 105 pounds (47.6 kilograms) of skin.
What causes a bruise?
A bruise is a common skin injury that causes discoloration of the skin, usually yellowish,
brownish, or purplish spots. Blood from damaged blood vessels deep
beneath the skin collects near the surface of the skin, resulting in a “black and blue”
mark. You can get a bruise by bumping into something or someone, or by something
or someone bumping into you.
Why do scabs form?
As soon as you scrape or break the skin anywhere on your body, special blood cells
called platelets get to work. Platelets stick together like glue at the cut site, forming
a clot. This clot is like a protective bandage over your cut that keeps more blood and
other fluids from flowing out. The clot is also full of other blood cells and thread-like
matter called fibrin that help hold the clot together. As the clot starts to get hard and
dries out, a scab forms. Crusty and dark red or brown, the scab protects the cut by
keeping germs out and giving the skin cells underneath a chance to heal. All by itself,
usually after a week or two, a scab falls off, revealing pinkish, new skin underneath.
What is pus?
Pus is a thick, whitish-yellow fluid that oozes from a cut because white blood cells, bacteria,
and dead skin cells have accumulated there. Eventually the white blood cells eat
up all the bacteria and dead skin cells and the puss clears up on its own. Sometimes
antibiotics are needed to kill off bacteria and help the wound heal more quickly. If a
pimple gets infected with bacteria, the result is a pustule, or small amount of pus.
HAIR, SKIN, AND NAI LS
How many hairs do I have on my head?
Scientists estimate that both children and adults have about 100,000 strands of hair
on their heads. Redheads have fewer because their individual strands are thicker.
Although you may lose an average of 40 to 100 strands of hair every day, it’s hard to
notice because you have so many!
Which hair grows the fastest?
The fastest growing hairs on the human body are men’s beard hairs. If the average
male never trimmed his beard, it would grow to almost 30 feet (9 meters) long in
his lifetime. 209
ALL ABOUT MY BODY
Why do people have different
color skin?
Skin color—which ranges from light
pink to dark brown—is determined by
the amount and type of the pigment
melanin there is in the skin. Melanin
comes in two types: phaeomelanin (red
to yellow) and eumelanin (dark brown to
black). Both amount and type are determined
by four to six genes. One copy of
each of those genes is inherited from
your father and one from your mother.
Each gene comes in several coding
sequences, which results in a variety of
skin colors around the world.
Why do some people have freckles?
People with light skin and eyes are more
likely to have freckles because they have
less melanin, a chemical in the skin that
protects it from sun damage by reflecting
and absorbing ultraviolet (UV) rays.
Instead of tanning, they freckle. Some
people’s freckles fade away almost completely
in the winter, and then return in the summer, when the person is more likely
to sunburn. Sunscreen can help protect everyone (freckled or not) from the Sun’s
harmful rays.
How does the body cool off?
The human body cools off by utilizing its three million sweat glands. Nerves in your
skin tell your brain that your body is getting hot, and the brain signals the sweat
glands to get busy. Each gland is like a little pump that draws water from nearby capillaries
and delivers it to the skin, cooling it off. Since up to 60 percent of the body is
water, sweat glands are like wells tapping into a giant ocean. There are two types of
sweat glands: eccrine glands and apocrine glands. The eccrine glands are specifically
designed for cooling the body off, and can pump up to 2 quarts (1.9 liters) of water an
hour during intense activity or exercise. The apocrine glands are triggered by emotional
stimuli, not heat. These glands secrete sweat in the hair follicles of the armpit,
groin, and nipples, where the sweat mixes with bacteria and oils, giving it color and
odor. As the sweat dries up, your skin cools off, and your body temperature drops.
Why do my fingers get all “pruney” in the bathtub?
During long baths (or while swimming in a lake or pool) our fingers and toes soak
210 up water like a sponge, which makes them swell. This happens because the top layer
Freckles tend to form more easily on the skin of kids who
have pale skin.
of skin (called the stratum corneum) on fingers and toes is more porous than the
layers of skin underneath, and thus better at absorbing water. But instead of ballooning
up, our fingers and toes shrivel like raisins because of the way the layers of
skin are connected: The top, swelling layer of skin is connected underneath to tissue
that does not swell, so the skin buckles to accommodate the increased surface
area. Once you dry off, the water from your skin evaporates into the air and your
skin quickly returns to normal.
My grandmother has a lump on her chin that sprouts hair. What is this?
Chances are that your grandmother has a mole, a spot on the skin that is usually
round or oval in shape. Moles can be small or large, smooth or lumpy, and range in
color from pink, brown, red, or black. Skin moles can occur on any area of the body
and even sprout hair. Moles are melanocytes—or cell factories that make pigments
to give skin its color—that have grown in clusters rather than spreading throughout
the skin. Moles can appear at any time or at any age; even babies are born with
them occasionally. In fact, if you look carefully enough, you may find between 10
and 50 moles on your own body!
Will a wart go away if I wrap it in duct tape?
Maybe. Warts are skin infections caused by a common virus called HPV (human papillomavirus).
They are perfectly “normal,” in that health researchers estimate that
three out of four people will develop a wart some time in their lives, usually on their
hands or feet. It can take months or years for a wart to disappear on its own. To speed
up the process, some skin doctors recommend wrapping the wart in duct tape until
it disappears. The duct tape removes dead skin from the wart, thereby gradually
killing off the wart virus that lives in the skin. It may also trigger the body’s immune
system to attack the wart virus. Otherwise the wart can be removed by a doctor with
a laser or liquid nitrogen, a substance that freezes the skin, killing the cells.
Why is the skin between my toes sometimes red and itchy?
Itchy, red skin may be the sign of athlete’s foot, a skin infection caused by a moldlike
fungus. The fungus needs a warm, moist environment to live and often grows 211
Why doesn’t it hurt to cut my hair?
Haircuts don’t hurt because your hair is not alive. Hair is made out of a protein
called keratin. Only the root of the hair—the part that grows inside
the skin on your head from tiny holes called follicles—is alive and growing. So
if you pluck out a hair by the roots, it hurts. But trimming or cutting your hair
is painless. And that is also the same reason why it doesn’t hurt to trim your
fingernails or toenails, which are also made of keratin. And because fingernails
grow faster than toenails, you need to trim them more often!
ALL ABOUT MY BODY
on the floors of locker rooms and public showers and in swimming pools and
whirlpools. It also loves stinky old tennis shoes. When a foot comes in contact with
the fungus, it becomes red and itchy. Sometimes, moist, white, scaly lesions or
sores develop between the toes and spread to the soles of the feet. In boys, sometimes
athlete’s foot fungus spreads to the groin area, where it is called “jock itch.”
The fungus sometimes spreads from one location to another as it is picked up on a
bath towel, and the groin area, which is warm and moist, helps the fungus flourish.
Why do I have a belly button?
Your belly button, or navel, is a scar where your umbilical cord once was. The tubelike
cord connected you to your mother when you were inside her uterus, growing
into a baby. It carried oxygen and nourishment to you from the placenta, an organ
that develops in the uterus during pregnancy, connecting you to your mother’s blood
supply. (It also carried away waste products from your blood.) Once you were born,
the umbilical cord was no longer needed, because you began to breathe and eat on
your own. The cord was clamped off and cut, and what was left of it withered and
dropped off about a week after your birth. Doctors clamp the cord and cut it, leaving
a remnant two to three inches long that eventually shrivels up and falls away. Skin
grows over the area, and it then becomes the belly button shape you have for life.
What causes goose bumps?
Goose bumps or goose pimples are little bumps on your skin that appear when you
are cold or afraid. They are named that because they look like the bumpy flesh of a
goose that has had its feathers plucked. When you are cold the muscles in your skin
raise the hairs on your body so that they can trap a thicker layer of air next to your
skin, which may keep you a bit warmer. And, as with all muscular activity, this contraction
of the skin muscles also produces heat.
Why do zits always form in the middle of the forehead?
Acne, a red, irritating skin rash, that mostly affects children approaching puberty,
usually appears in the oil-producing areas of the body. These include the face (forehead,
nose, and chin), chest, and back. Hyperactive glands produce oil (sebum) at a
faster than normal pace due to tweens’ rapid changes in hormone levels. Excessive
oil clogs pores and creates acne, or pimples. Many times hair—which hangs down
onto the forehead or sides of face—contains grease-like gels and styling products
that contribute to acne.
Why do people get wrinkles and gray hair as they get older?
As people age, their bodies change in many ways that affect the ways their cells and
organ systems function. These changes occur little by little, progress over time, and
are different for every man and woman. We all lose height as we age, and by the time
we reach 80 years old, our height may have decreased by two inches (five centimeters).
Changes in posture, in the growth of our spine’s vertebrae, and joint changes
212 all contribute to our loss of height. With aging, the hair follicles produce less
melanin, the pigment that gives hair its color. Hair becomes lighter, gray, and eventually
turns white. The nails also change with aging: they grow slower, may become
dull and brittle, and may become yellowed and opaque. With aging, the outer skin
layer (epidermis) thins and the number of pigment-containing cells (called
melanocytes) decreases, but the remaining melanocytes increase in size. Aging skin
thus appears thinner, more pale, and translucent. Changes in the connective tissue
reduce the skin’s strength and elasticity, resulting in a wrinkly, leathery skin.
MY S ENS E S
What are the five main senses?
The five main senses of the human body—the ways in which people perceive stimuli
from outside the body—are sight, hearing, taste, smell, and touch. But there are
many other senses, like balance, hunger, thirst, and fatigue. No one sense is more
important than another; all your senses work together to allow you to gather information
from the world around you.
How often does a person blink?
Humans blink once every five or six seconds, and each blink lasts about one-sixth
of a second. If you add it up, you blink more than three million times per year. The
main purpose of blinking is to moisten and clean the cornea and the conjunctiva,
two membranes of the eye. In fact, your eyes would dry out if they stayed open all
the time. But the eye also blinks if an object or person approaches quickly.
What do eyelashes do?
Eyelashes protect our eyes. They help
keep small particles and dust out of our
eyes, especially when the wind is blowing.
Eyelashes are also super-sensitive,
and they alert the eyelids to shut when
something touches them. If you rub
your finger against your eyelashes, you
will find that your eyelid automatically
shuts. But be careful not to rub too
hard—if you lose a lash it will take
about four to eight weeks to grow back!
Fortunately, your upper eyelid has
between 100 and 150 lashes.
Are tears good for me?
Absolutely! Tears, which flow from tear
glands into your eyes through tiny tear 213
Tears form when we are sad, but tears have another
purpose, too: they help keep dirt and dust out of our eyes.
ALL ABOUT MY BODY
ducts, wash the eyeballs and carry away dust and dirt. Tears, which contain salt, kill
germs and keep the cornea (the transparent front part of the eye) moist. Some of
the tears drain out of your eyes through tear ducts, which are tiny tubes that run
between your eyes and your nose. That is why people almost always blow their nose
after they cry.
Why do our ears sometimes pop in airplanes?
Your ears sometimes pop in airplanes, while driving through high mountainous
areas, and at other high altitudes because of air pressure changes. As you ascend
in an airplane, for example, and the air pressure decreases, the air trapped in
your inner ear will cause your eardrums to push outward. This expansion causes
the discomfort you feel before your ears “pop.” Your hearing ability also
decreases because the pressure on your ear drums makes the sound harder to
transmit. When you yawn or swallow, your body can equalize the pressure
between your inner ear and the atmosphere by allowing some air from your
inner ear to escape through the Eustachian tubes, two small channels that connect
the inner ears to the throat. When they open, you feel the pressure release
and you hear a popping sound.
Why do I have two ears?
You have two ears so that you can hear which direction sounds are coming from.
The brain detects long lines of sound waves or sound patterns that we hear by comparing
the information coming from each of our ears. If a dog is barking on the left
side of you, the sound will arrive to your left ear a little faster than to your right ear.
Also, the sound of the barking will be louder in your left ear than in your right ear.
Your brain notes the miniscule difference in time and loudness, and lets you know
214 where the sound is coming from.
Why can’t I see just after I turn off the lights?
It is hard to see in the dark immediately after you turn out the lights, just
as it can take a few minutes for your eyes to adjust when you walk from a
dark place into a bright, sunny day. Why? Your eyes’ pupils are responsible.
The size of your pupil—the black circle in the center of your eye controlled
by the iris—determines the amount of light that enters the eye and adjusts to
light and darkness. Pupils dilate (widen) in dim light or darkness to let more
light into the eyes; they constrict (narrow) in bright light to prevent too much
light from entering the eyes. When you move from dark to light, pupils widen,
and the retinas become six times more sensitive after one minute in darkness
than they are after the first few seconds. After a half hour, they are even more
sensitive, and you can begin to see more comfortably in the dark.
Why do I get dizzy after
spinning around?
The fluid in your inner ear is responsible
for dizziness. After you spin around,
your ear fluid keeps spinning, sending
conflicting messages to your brain.
These mixed signals cause dizziness,
lack of balance, and lightheadedness.
After a few seconds, the liquid levels out
and the dizziness goes away.
Why do some people get sick when
they read in the car?
Motion sickness happens when your
body is feeling the sensation of movement.
This can happen when you are
riding in a school bus, sailing on a boat, or riding in the backseat of a car. When you
are reading a book, your eyes do not see the movement, which confuses your brain
and causes some people to feel sick. If you get car sick, the solution is to look out
the window, not down at your book, so your brain and body will be in sync.
What are taste buds?
The human tongue contains about 10,000 tiny bumps (called papillae), and every
bump has about 250 taste buds. Each taste bud has a pore that opens out to the surface
of the tongue, which allows molecules going into the mouth to reach the
receptor cells inside. Receptor cells live for only one to two weeks and then are
replaced by new receptor cells. Taste buds detect the four basic flavors of salty,
sweet, bitter, and sour, and work together with other taste buds on the roof of your
mouth to give you the taste of your food.
But taste buds also need help from your nose. While you’re chewing, the food
releases chemicals that immediately travel up into your nose, triggering your nose’s
olfactory receptors. Your nose is at least 20,000 times more sensitive than your
tongue—and it can remember about 50,000 different scents! Smell cells work with
your taste buds to create a rich taste experience. In fact, you may notice that if your
nose is stuffed and you can’t smell your food you also can’t taste it very well!
Is it true that people have “tongue prints”?
Yes. All human beings have some traits that are the same, but each individual person
also has a set of traits that are different from any other. Among these individual
traits are fingerprints, tongue prints, patterns in the iris of the eye, and voice
patterns. Because fingerprints and tongue prints are unique in every person (even
identical twins), they can be used to identify an individual. (But next time someone
calls out your name, it’s best to answer rather than stick out your tongue!) 215
Different parts of our tongues are used for tasting bitter,
salty, sweet, and sour flavors.
ALL ABOUT MY BODY
How do you stop a brain freeze?
Quickly gobbling up cold ice cream may result in “brain freeze,” also know as an ice
cream headache. When the cold object touches the roof of your mouth, the blood
vessels contract in order to prevent loss of body heat. As the coldness stops, the blood
vessels relax again, quickly increasing blood flow to the brain. This sudden release is
what causes the intense headache sensation. You can relieve brain freeze by quickly
warming the roof of your mouth: Touch your tongue to the top of your mouth or, if
you can roll your tongue in a ball, press the underside of your tongue (which is
warmer) to the roof of your mouth. Slowly sipping room-temperature water or
pressing a warm thumb against the roof of the mouth also works for some people.
How do dust mites make a person sneeze?
Dust mites are microscopic organisms that live in dust. These unwelcome visitors
invade your nose and can irritate your mucous membranes, triggering nerve cells
that signal the lungs to fill with air. When the air passages close and pressure builds
up, your nose tingles and twitches, and you sneeze—forcing mucus (the slimy,
moisturizing substance), dust, pollen, and mites out of your nose at speeds of up to
525 feet (160 meters) per second! Sneezing is one of the body’s reflexes, an automatic
way it rids itself of harmful substances like bacteria and germs. It also keeps
the tubes that carry the air from your nose to your lungs healthy.
What is a booger?
The mucous membrane that lines your nose is moist and sticky. That environment
helps trap dust and other things in the air before they can pass into your lungs.
When moisture evaporates from the thick film of mucus that covers the lining of
your nose—which happens all the time as air passes over it—the mucus, combining
with the particles you’ve breathed in, becomes dried and crusty, forming boogers.
EATING AND DRINKING
Do I have to brush my teeth?
Absolutely! Strong, healthy teeth help you speak clearly, chew harder vegetables
and meats, and help you look your best. Brushing your teeth helps prevent plaque,
a clear film that sticks to your teeth. The sticky film acts like a magnet for bacteria
and sugar. Bacteria eats the sugar on your teeth, breaking it down into acids that
deteriorate tooth enamel, causing holes called cavities. Plaque also causes the gum
disease gingivitis, which make your gums red, swollen, and sore. At around age six,
you lose your baby teeth and a larger set of teeth begin to surface. Eventually, 32
new teeth will line your growing jaws, the last coming in around the age of 18.
These permanent teeth will perform all of your eating tasks for the rest of your life,
216 so they are worth taking care of! Your four front teeth (on top and bottom) are sharp
incisors that cut and tear off food when you bite, along with your four pointed
canine teeth. The flat-topped bicuspids (premolars) and molars near the back of
your mouth crush and chew your food.
What is a healthy diet?
Although everyone eats different foods, doctors and nutritionists (people who plan
food and nutrition programs) generally agree that a healthy diet is one loaded with
fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products; one
that includes lean meats, poultry, fish, beans, eggs, and nuts; and one that is low in
saturated fats (like those fats found in butter), trans fats (also called partially hydrogenated
oils, found in foods like French fries and donuts), cholesterol, salt (sodium),
and added sugars. Foods like processed cheese that squirts from a can, frosted
pastries filled with sugary jam, and deep-fried fish, nuggets, or French fries do
not provide the types of nutrients your body needs to grow, and are sometimes
called “empty” foods. For example, 1 ounce of potato chips has 152 calories and 10
grams of fat (3 grams of which are saturated fat).
Why does the body need vitamins and minerals?
Vitamins are chemicals that the body needs to function well; minerals are metals
and salts that the body also needs in tiny amounts to run properly. Both help the
human body grow. Different foods, like vegetables, contain different amounts of
vitamins and minerals, so it is important to have variety in your diet so you can get
a good balance. When it comes to vitamins, each one works differently in your body.
Vitamin D in milk helps your bones grow; vitamin A in carrots helps you see at 217
What did people use before toothbrushes were invented?
Early in human history, people used anything that they could find to keep
their teeth clean. Usually a thin, sharp object, like a stick, was used to pick
out food left between teeth. Chewing on the end of certain sticks would fray the
wood, making a kind of brush, which could then be rubbed across the teeth.
(Even today, members of primitive tribes chew sticks to keep their teeth clean.
The constant chewing produces more saliva than usual, which helps wash food
away.) Later, people found that if they rubbed abrasive elements, like salt or
chalk, across their teeth, they could get rid of grime. They also used water and
pieces of rough cloth to clean their teeth. Toothpicks made of all kinds of materials
also became popular. Rich people had jeweled toothpicks made of gold and
silver. Toothbrushes for the wealthy, with fancy handles and hog bristles, came
into use in the eighteenth century. Only much later, when cheaper, woodenhandled
toothbrushes were made, and the importance of good dental hygiene
became known, did most people start to regularly use them.
ALL ABOUT MY BODY
night; vitamin C in oranges helps boost your immune system and helps your body
heal if you get a wound; and the B vitamins in leafy green vegetables help your body
make protein and energy. And although some vitamins like A (which helps your eyesight)
and D are stored in your body (for several days or up to several months), others,
like C and the B vitamins, quickly pass through your bloodstream. So it’s
important to replace your vitamins every day.
How much food does the average person eat in a year?
Some doctors say that the average American adult eats about 525 pounds (238 kilograms)
of food each year of his or her life! If a person lives to be 70 years old, he or
she will eat about 35 turkeys, 12 sheep, 880 chickens, and 770 pounds (349 kilograms)
of fish.
Why should I drink lots of water?
All living things need water to survive. Without water, the human body stops working
properly. Water makes up more than 50 percent of your body weight and a person
cannot survive for more than a few days without it. Water flushes toxins out of
your organs, carries nutrients to your cells, and provides a moist environment for
ear, nose, and throat tissues. Water is also in lymph, a fluid that is part of your
immune system, which helps you fight off illness. You need water to digest your
food, to get rid of waste, and to sweat. Too little water in your body leads to dehydration,
and it can make you tired and unable to function. Your body gets water
from drinking it, but lots of foods, such as fruits and vegetables, contain water too.
What does the esophagus do?
It takes about 4 to 8 seconds for food to travel from your mouth to your stomach,
and your esophagus plays a big part in that action. The esophagus is part of your
body’s digestive system, which is about 30 feet (9 meters) in length and runs from
218 the mouth to the anus. The main part of the digestive system is the alimentary
Why is Jell-O® so wobbly?
Jell-O® is made from gelatin, a processed protein that makes it wobbly. Gelatin
is made from the collagen in cow or pig bones and skins. Gelatin melts
when heated and solidifies when cooled again. When you add the Jell-O® powder
to boiling water, the powder dissolves and the weak bonds that hold together
the protein chains start breaking apart. The chains float around in the mixing
bowl until you add cold water. As the Jell-O® cools, the chains start bonding
again. The chains become tangled when they are stirred, and water gets
into gaps between the chains. Once it is refrigerated, the gelatin “chains” harden
and the trapped water and flavor make Jell-O® wobbly.
canal, a long tube that is made up of the
mouth, esophagus, stomach, small
intestine, and large intestine. Other
parts of the body are also linked to the
canal, such as your teeth, tongue, salivary
glands (which make saliva to help
break down food), pancreas, liver, and
gallbladder. Food and liquids from your
mouth pass down through the esophagus,
an 11-inch- (25-centimeter-) long
tube, into the stomach, where a wave of
gastric juices helps break down food
into smaller parts, or molecules, which
are small enough to be absorbed into
the bloodstream and carried throughout
the body.
Does the red color in fruit juice
really come from a beetle?
Yes. The red coloring that makes many
juices and jams red is from a natural dye
called carmine. Carmine is derived from
conchineal, or conchineal extract,
which comes from the bodies of a
female beetle (Dactylopius coccus) that lives on the Opuntia cactus. The insect is
boiled and the scales of the insect are crushed into a red powder. It takes about
70,000 insects to make one pound of cochineal. The ancient Aztecs used cochineal
as a dye for cloth and other items, and today it is widely used as a coloring agent for
food, beverages, and cosmetics.
Are soap, booger, and earwax really jellybean flavors?
Yes! And so are dirt, earthworm, vomit, and grass. It’s not really clear how the folks
at the jelly belly company figured out the flavor recipe for each bean, but those that
have tried them say they are authentic tasting! Jellybeans, a type of candy made
from sugar, corn syrup, and food starch, have traditionally been made with fruit flavoring.
One company, called Jelly Belly, made flavors like butter popcorn, cotton
candy, and watermelon in the 1980s. These jellybeans were endorsed by U.S. President
Ronald Reagan, who kept a jar of them on his desk in the White House, and
who also made them the first jelly beans in outer space, sending them on the 1983
Challenger shuttle as a surprise for the astronauts.
Why do some people throw up when they eat spicy food?
Throw up, also called vomit, puke, and upchuck, is half-digested food and liquid
that gets mixed up with your stomach juices and comes out of your mouth. Vomit 219
It is the gelatin in Jell-O® that makes this fun dessert
wobble and jiggle.
ALL ABOUT MY BODY
happens when your stomach starts to feel queasy (or nauseated), sometimes after
you exercise or run around too much after eating, eat too much food, or eat food
that is spicy and therefore irritating to your stomach. Normally, your stomach
processes your food well through the digestive system, but if you eat food with lots
of bacteria or if you have a virus in your stomach, the quickest way for your body to
get rid of the irritants is to vomit them out. Your brain tells the muscles in your
stomach walls to spasm (contract abnormally); it also tells your diaphragm—the
large sheet of muscles that separates your chest from your abdomen and is most
responsible for your breathing—to press downward on your stomach. These activities
combine to force the contents of your stomach up and out.
Why do people sometimes burp?
A burp, sometimes called a belch, is gas that your body needs to get rid of. When
you eat or drink, you swallow air at the same time you swallow food or liquid. The
air contains gases such as nitrogen and oxygen. The extra gas you ingest is forced
out of the stomach, up through the esophagus, and out of the mouth as a burp.
Some kids discover that drinking soda or other carbonated beverages makes them
burp more, and this is because these drinks contain carbon dioxide, the gas that
makes them fizzy. Sometimes eating or drinking too fast, which sends more air into
the stomach, can make a person burp. The same thing happens when you drink
through a straw: the straw brings extra air into your stomach, causing you to burp.
What causes hiccups?
A hiccup is a noise that your body makes when your diaphragm, the muscle barrier
between your stomach and lungs, gets irritated and has spasms. The “hic” part of
the sound is caused when air is sucked into your lungs, and the “cup” part of the
sound happens when a special flap called the epiglottis, located between your
tongue and vocal cords, slams closed over your windpipe. Your diaphragm can
become irritated from eating too much food, which causes an enlarged stomach to
press against the wall of the muscle. Your diaphragm can also become irritated from
lifting a heavy object or from breathing in too much air, which affects your normal
breathing pattern. Hiccups may last a minute or two, but generally go away with
220 time. Holding your breath, drinking a glass of water, or having someone scare you
What do potato chips have to do with the heart?
Potato chips often contain saturated fats, which over time can clog the
arteries that carry blood to the heart. The oils used to cook the chips are
made up of saturated fats, which increases cholesterol production in the body,
a known risk factor for heart disease. Heart disease results from a condition
known as atherosclerosis, which happens when a waxy substance forms inside
the arteries that supply blood to your heart.
generally does not work to get rid of hiccups, since your diaphragm needs time to
relax again.
What causes people to pass gas?
When there is too much air in your digestive system, there are two ways to get rid
of it. It can exit from the top, through your mouth, in the form of a burp. Or it can
exit from the bottom, through your anus, in the form of passed gas, better known
as a fart.
Some of the gas in your digestive system comes from the air you swallow when
you eat, while some of it is a natural by-product of food digestion in your large
intestine. When your intestine encounters foods that are difficult to digest—including
greasy or high-fat foods—it produces more gas than with foods that are digested
easily. This gas travels through your intestine to your rectum and eventually
passes out through your anus. While some may not like to admit it, everyone passes
gas several times a day.
What is constipation?
Constipation occurs when your body has a hard time having a bowel movement, or
going poop. When you digest your food, it collects in the last part of the colon, or
the end of the large intestine. If the feces doesn’t have lot of fiber or bulk to it, it
stays in the colon longer than it normally would. Water continues to draw out of
the feces, making it hard and compact instead of squishy and moveable. The rectum
has to push extra hard to get your poop out. Constipation usually resolves itself, but
your body can avoid constipation by eating plenty of fresh fruit, vegetables, and
bran, and drinking plenty of water each day.
S ICKNE SS AND HEALTH
Why do I get sick?
When you get sick, part or all of your body is not working as it should. The cause of
sickness can come from inside your body or from the outside world. Diseases that
start on the inside are usually inherited in the genes that you receive from your parents,
which make up the master plan that determines how your body will grow and
run. Abnormal development or functioning of different body systems is the cause of
many chronic (long-lasting) diseases.
Things in the outside world can cause sickness, too. Poisons in the environment
can cause illnesses in people. Not eating the right foods, with their important nutrients,
can also cause diseases. But the most common cause of sickness from the outside
world is infectious agents. These agents are usually microscopic organisms (living
things so small that they can only be seen with the help of microscopes) like bacteria
and viruses, which we commonly refer to as germs. Bacteria and viruses and 221
ALL ABOUT MY BODY
other microscopic organisms live in the air, water, and soil that make up our world.
They are on the things and people we touch and in the food we eat. Many of them
are beneficial: bacteria are needed to make cheese, some bacteria help vegetables like
peas and beans grow, and some bacteria clean the environment and enrich the soil
by feeding on dead plants and animals. But there are other microscopic organisms
that invade the bodies of plants and animals—and people—and cause diseases.
How do the disease-causing germs invade my body?
Your skin is a wonderful protective barrier that keeps a lot of the disease-causing
germs that you run into each day from entering your body. Only when you have an
opening in your skin—like a cut or a scrape—are germs likely to enter there. Most
222 germs enter through your mouth and nose, making their way farther into your
How the human immune system works is really pretty complicated. Many types of cells are used by the body to defend
against viruses and other invaders.
body through your respiratory or digestive tracts. But even then, certain chemicals
in body tissues and fluids keep many harmful germs from causing problems. When
an infection does begin—with the germs multiplying inside your body—your
immune, or defense, system goes into action to get rid of the foreign organisms.
Your white blood cells produce special substances called antibodies that attack and
destroy the invaders, helping you to recover.
What does the immune system do?
The immune system protects the human body against germs, which are microorganisms
that cause sickness and disease. There are four major types of germs—
harmful bacteria (pathogens), viruses, fungi, and protozoa. This defense system
begins with the skin, which stops germs from getting into your blood or tissues. If
germs get into your body, for example through your nose or mouth, white blood
cells called phagocytes and lymphocytes attack them. Phagocytes scout out and
destroy invaders, and long-living lymphocytes remember the invaders and release
chemicals called antibodies to make the body resistant, or immune, to them. White
blood cells live in the bloodstream, lymphatic system, and spleen.
The lymphatic system (or lymph system, for short) is a far-reaching network
that extends throughout your entire body. A clear liquid called lymph runs throughout
the system, washing the body’s cells with nutrients and water and detecting and
removing pathogens. Lymph is filtered through the lymph nodes, and then passes
into the body’s bloodstream.
What is the difference between bacteria and viruses?
Bacteria are single-celled organisms that have the ability to feed themselves and to
reproduce. They are found everywhere, including the air, water, and soil. They
divide and multiply very quickly, which means that one cell can become 1 million
cells in just a few hours! Viruses are microorganisms that are smaller than bacteria,
but they cannot grow or reproduce without the help of a separate living cell.
Once the virus gets inside your body, it attaches itself to a healthy cell and uses the
cell’s nucleus to reproduce itself.
Do our intestines contain germs?
Yes. Germs aren’t all bad—in fact, some are helpful. For example, the common bacterium,
E. coli, is found in our intestines and helps us digest green vegetables and
beans (also making gases). These same bacteria also make vitamin K, which causes
blood to clot. If we didn’t have this bacteria inside of us, we could bleed to death
whenever we got a small cut.
Where are some other places that germs hide?
Germs are everywhere! Most germs spread through the air, invading our homes,
pets, and family, and sometimes they make us sick. Besides your bathroom toilet
and the kitchen sink, everyday items like shopping-carts, restaurant menus, com- 223
ALL ABOUT MY BODY
puter keyboards, and the shower curtain contain germs. These items contain bacteria,
mold, and rhinoviruses (instigators of the common cold) that can lead to sickness.
In fact, cold and flu viruses can survive for 18 hours on hard surfaces. Common
household items can be swabbed with a disinfectant wipe easily before use in
order to prevent germs from spreading. Washing your hands with soap and water,
using a hand sanitizer, and avoiding touching your face with your hands after using
these items also helps keep germs away from you. To eliminate dust mites—those
little critters that live in your bed sheets and feed on dead skin cells—don’t make
your bed for a while. Studies have found that dust mites need humidity levels above
50 percent to survive and cannot live in the arid conditions of an unmade bed.
What are allergies?
An allergic reaction is a reaction to a substance that is normally harmless to most
other people. Allergies happen when a person’s immune system overreacts to a normally
harmless substance that the person has breathed in, touched, or eaten. Allergens—
the antigens that bring on an allergic reaction—may be foods, medications,
plants or animals, chemicals, dust, or molds. Some common allergic reactions are
hay fever, allergic conjunctivitis (an eye reaction); asthma, pet-dander allergies, and
skin reactions, such as hives. A common cause for allergies are dust mites, a large part
of household dust. If they are breathed in by an allergic person, the body parts of the
dead mites can trigger asthma, a lung condition that causes a person to have difficulty
breathing. Cat and dog dander, or skin flakes, can cause an allergic reaction, such
as sneezing, wheezing, and running eyes and nose. Common food allergy triggers are
the proteins in cow’s milk, eggs, peanuts, wheat, soy, fish, shellfish, and tree nuts.
What are antibiotics?
Antibiotics are medicines that help the human body fight bacteria, either by directly
killing the offending germs or by weakening them so that the body’s own
immune system can fight and kill them more easily. The most widely known antibiotic
is penicillin, which is made from mold. Penicillin kills bacteria by interfering
with the formation of the cell walls or cell contents of the bacteria.
Was penicillin discovered by accident?
Yes. In 1928, the Scottish research scientist Alexander Fleming found that mold had
accidentally contaminated one of his experiments. The mold created a bacteria-free circle
around itself, and Fleming deduced that the mold was an antibacterial agent that
could kill many harmful bacteria. He named the active agent penicillin. By the middle
of the twentieth century, Fleming’s discovery birthed a pharmaceutical industry that
made synthetic penicillin to treat many bacterial diseases of the day, including syphilis,
gangrene, and tuberculosis. He won the Nobel Prize in 1945 for his discovery.
Who discovered vaccination?
Edward Jenner, an army surgeon and country doctor from Gloucestershire,
England, tried his first experimental vaccination in 1796. At 224 the time smallpox
was a fatal disease that mostly affected infants and young children. Jenner recognized
that dairymaids infected with cowpox virus (a minor virus that affected
cows) were immune to smallpox. He used material from the arm of Sarah Nells,
a dairymaid who had contracted cowpox, to infect James Phipps, an eight-yearold
boy. He then exposed Phipps to smallpox, which Phipps did not contract. It
worked because cowpox and smallpox have common antigens (proteins), which
aroused the young boy’s immune system. After repeating the experiment on
other children, including his own son, Jenner concluded that vaccination provided
immunity to smallpox without the risk of the person contracting the disease.
Jenner used the word “vaccination” for his treatment, which comes from
the Latin word vacca, meaning “cow.” Jenner’s findings were published two
years later, in 1798, and today vaccines are used around the world to produce
immunity to disease.
Who was Louis Pasteur?
The French research chemist Louis Pasteur continued Jenner’s work with vaccination.
Vaccinations work by presenting a foreign antigen to the body’s immune
system in order to evoke an immune response. Pasteur reasoned that if a vaccine
could be found for smallpox, then a vaccine could be found for all diseases. In the
summer of 1880, he accidentally found a vaccine for chicken cholera, a disease
that affected many poultry farmers. He also found a vaccine for rabies, a disease
that affected animals and that humans contracted after being bitten by infected
animals, mainly dogs. Pasteur and his research team discovered that the rabies
germ attacked the nervous system only after it had made its way to the brain. The
team traced the germ to the brain and spinal cord of infected animals and by 225
Antibiotics like penicillin fight against bacteria. Antibiotics do not kill viruses, however. For viruses, doctors use antiviral drugs.
Antiviral drugs do not kill viruses; they only keep them from spreading.
ALL ABOUT MY BODY
using dried spinal cords, produced a vaccine for rabies. The vaccine was first
tried out on animals, and in 1885 it was used successfully on a young boy who
was bit by a rabid dog.
Can chicken soup help a cold go away?
It doesn’t cure a cold but it can help lessen the symptoms. For centuries, people
around the world have used chicken soup to help cure the common cold. Chicken
soup can help people feel better, but scientists learned that chicken fat may
help relieve cold and flu symptoms in two ways. First, the chicken broth acts as
an anti-inflammatory by slowing down the movement of neutrophils (immune
system cells that play a role in the body’s inflammatory response). Second, it temporarily
speeds up the movement of mucus through the nose. This movement
helps relieve congestion and limits the amount of time viruses are in contact with
the nose lining.
Why is exercise important to health?
Exercise—like playing tag on the playground, participating in a team sport, or
twirling in dance class—is good for your health. Regular physical activity helps
a person have stronger bones and muscles, helps control body fat, helps prevent
certain illnesses, and contributes to a good outlook on life. Regular exercise
helps promote digestion and a good night’s sleep. When children exercise
as part of their busy lives, they are better equipped to manage the physical and
emotional challenges of a busy day, like walking to school, climbing stairs,
catching a school bus, or studying for a test. According to the Department of
Health and Human Services (HHS), all children two years and older should get
at least 60 minutes of moderate to vigorous exercise on most, if not all, days of
226 the week.
Why is laughter called “medicine” for the human body?
Research shows that laughter has many health benefits—in fact, it is so
good for you, that doctors sometimes call it “medicine.” Why? Laughter
can help strengthen the body’s immune system by increasing the number of
antibody-producing cells and boosting T cells (a white blood cell that protects
the body from infection). Humor also relieves the stresses and pressures
of everyday living, by reducing the body’s stress hormones like cortisol,
epinephrine (adrenaline), dopamine, and growth hormone. It also
increases the level of good hormones like endorphins, which promote a feeling
of happiness. A deep belly laugh exercises the diaphragm and contracts
the abdominal muscles, leaving them more relaxed afterward. And it provides
a good workout for the heart.
Can my cat or dog benefit my
health?
As a matter of fact, yes! Researchers
believe that regular contact with pets
can reduce levels of stress and reduce
blood pressure (the force of blood pushing
against the walls of the arteries as
the heart pumps out blood). Pets offer
stability, comfort, security, affection, and
intimacy. Owning a dog also provides a
great opportunity to get exercise and
fresh air, since it will need to go for a
walk every day.
What causes a yawn?
Some people yawn when they are bored,
tired, or in the presence of another yawner. Yawning happens when a person is not
getting enough oxygen. Oxygen, the gas needed to run body processes, and carbon
dioxide, the waste gas produced by these processes, travel in your bloodstream and
enter and exit your body through your lungs. When you don’t breathe deeply
enough, too much carbon dioxide builds up in your body and your brain gets the
message, telling you to breathe more deeply to fix the problem. A yawn is a great
big breath that clears carbon dioxide from your lungs and forces you to take in
fresh, oxygen-rich air.
Why do I need sleep?
Scientists do not know exactly why people need sleep, but studies show that sleep is
necessary for survival. Sleep appears to be necessary for the nervous system to work
properly. While too little sleep one night may leave us feeling drowsy and unable to
concentrate the next day, a long period of too little sleep leads to poor memory and
physical performance. Hallucinations (seeing things that aren’t really there), vision
problems, and mood swings may develop if sleep deprivation continues.
Do people dream every night?
Yes. The average person has three or four dreams each night, with each dream lasting
10 minutes or more. Almost all dreams occur during REM sleep, a period of
sleep characterized by fast breathing and heart rates. Scientists do not understand
why dreaming is important, but one theory is that the brain is either cataloging the
information it acquired during the day and discarding the data it does not want, or
is creating scenarios to work through situations that may be causing emotional distress.
Like sleep, most people who are deprived of dreams become disoriented, are
unable to concentrate, and may even have hallucinations. Sometimes it is hard to
remember our dreams because they are stored in our short-term memory. 227
Yawning is a reflex action that is your body’s way of telling
you that you need more oxygen.
ALL ABOUT MY BODY
DI SABI LITI E S AND
SUBSTANCE ABUS E
What is a disability?
The word “disabled” usually refers to a person who has a physical or mental handicap
that keeps him or her from doing certain tasks—or makes performing them
unusually difficult. Most physical disabilities, like blindness or paralysis, are easily
noticed, but many mental disabilities are harder to detect. Mental disabilities
can include diseases like schizophrenia, which causes severe disturbances in people’s
thoughts and emotions. Another type of disability is a learning disability,
such as dyslexia, which is a learning disorder that makes reading very difficult
because the brain reverses the order of letters and words. Many disabled people
prefer the term “differently abled,” a description that doesn’t divide people into
categories like “normal” and “disabled” but addresses the idea that every person
has different abilities.
Why do people become disabled?
A disability can be the result of a disease, an accident, or of genetics, which means
that it is a condition that a person is born with. A lot of times disabled people can
learn new ways to do things or use special machines or specially trained animals to
help them work around their disability.
Why are some people blind?
Blindness is complete loss of sight. It can happen when the optic nerves, which
carry visual signals from the eyes to the brain, or the sight centers of the brain are
damaged. Such damage can occur as a result of injuries or diseases. A person can
also be born with eye or brain abnormalities that cause blindness. In many cases,
particularly in very poor countries, infectious diseases and poor diets can also cause
blindness. A lack of vitamin A, in fact, is the leading cause of blindness worldwide.
With basic medicines and proper nutrition, such cases could be prevented.
For every one person in the United States who is totally blind, there are four
others who are visually impaired or “legally blind.” These people have some ability
to see, but they see so poorly—even with eyeglasses—that they cannot do things
that require good vision, like driving a car.
How do blind people get around in the community?
Some people use canes or guide dogs to get around. A white cane indicates that the
person using it is visually impaired. Blind people use their canes on sidewalks,
floors, and streets. They learn to identify the locations of things—like steps, walls,
or doors—simply by the different sounds that their cane taps make. Various hightech
devices have been invented, such as laser canes, which use sound or light
228 waves that bounce off objects and send signals to the user about where these objects
are located, what they might be made of, and how big they are. Guide dogs are
specifically trained to lead blind people around, with the guide dog following commands
that help the blind person go about his or her day.
Why can’t some people hear?
The inability to hear, or deafness, can occur for many reasons. Some types of hearing
loss result from something blocking sound as it travels from the outer ear to
the eardrum and the tiny bones in the middle ear. Other types of loss arise from
damage to or a defect of the inner ear or the auditory nerve, which is the nerve that
carries sound signals from the inner ear to the brain. Deafness can happen as a
result of disease, including severe ear infections, or it can be inherited, with the
deafness being apparent at birth or sometimes showing up years later. Injuries and
accidents also account for many cases of deafness. Extremely loud noises, like those
that come from an explosion, can cause deafness, though that loss of hearing is
sometimes temporary. People who work in noisy factories or those who are frequently
exposed to very loud music can also develop hearing loss over time. Many
people gradually lose some or all of their hearing when they reach old age, but some
of those types of hearing loss can be overcome by wearing a hearing aid, which
makes noises like speech or music louder.
What is substance abuse?
Substance abuse means taking drugs (other than those prescribed by a doctor for a
specific illness) in amounts that are dangerous or that prevent a person from doing
everyday things, like going to school or work. The substance being abused can be
alcohol, marijuana, pills called tranquilizers that make people feel very tired or
relaxed, household products that are inhaled, or a number of other drugs. Drug
abuse happens all over the world, to all kinds of people, young and old. It frequently
causes terrible damage to a person’s body, to relationships with family and
friends, and to career or education. In some cases, substance abuse leads to death,
because the abuser gets involved in an accident or because he or she overdoses, or
takes enough of the substance to cause the body to completely shut down.
Why is alcohol bad for your health?
Alcohol is a type of drug known as a depressant that slows down the body’s central
nervous system. After a person has had a few drinks, it immediately affects the way
he or she thinks and acts. Alcohol can make a person feel sleepy, less coordinated,
and slow to react to things. And it can cause your brain to feel foggy, and make you
think and see differently. After years of drinking, alcohol use can cause stomach and
intestinal problems, liver damage, nerve and muscle damage, heart problems, and
brain damage. Alcohol is difficult for the brain to process, and can cause everything
from blackouts to permanent loss of brain function and memory. Researchers have
also linked long-term drinking to cancer of the throat, mouth, liver, esophagus, and
larynx. Drinking alcohol can also lead to emotional and psychological problems like
sadness, depression, and even hallucinations (seeing and hearing things that are not 229
ALL ABOUT MY BODY
real). If a pregnant woman drinks too
much alcohol, it can seriously injure her
unborn baby and lead to birth defects.
Why is smoking cigarettes bad for
your health?
In addition to the stimulant nicotine,
cigarettes contain many harmful chemicals,
like tar and the poisonous gas carbon
monoxide. These chemicals present
health risks that range from bronchitis
to cancer. Doctors believe that cigarette
smoking is the cause of 90 percent of all
cases of lung cancer. Heart disease,
heart attack, and stroke are far more
common in smokers. One of the effects
of nicotine is constricting the blood vessels,
which causes high blood pressure.
Another effect is that smoking raises
your heart rate, which adds extra stress
on your heart. Smoking also affects
every part of the body’s circulatory system.
Your blood becomes thicker and
stickier, making it harder for your heart
to work well. The lining of the blood
vessels is damaged, allowing fat deposits to stick, which most likely causes arteriosclerosis,
or hardening of the arteries. Smoking also stains teeth, fingernails, and
lung tissue and causes bad breath.
Is second-hand smoke bad?
Yes. Secondhand smoke, also know as environmental tobacco smoke (ETS), is a
mixture of the smoke given off by the burning end of a cigarette, pipe, or cigar and
the smoke exhaled from the lungs of smokers. It is involuntarily inhaled by nonsmokers,
lingers in the air hours after cigarettes have been out, and can cause a
wide range of illnesses, including cancer, respiratory infections, and asthma.
Why do I see “No Smoking” signs in the windows of restaurants?
In the 1990s, when the dangers of second-hand smoke became widely known, may
laws were passed in the United States to protect nonsmokers from having to inhale
another person’s smoke. Some of these laws prevent people from smoking in public
or government buildings. Nonsmoking sections in restaurants have grown larger
and larger, with many restaurants banning smoking altogether. Smoking is
banned in most office buildings. California and New York have also passed state-
230 wide laws banning smoking in public places.
Smoking is legal for Americans who are 18 or over. At any
age, though, smoking is really bad for your health and is
banned from many public places.
HOME LI FE
Why do people work?
People usually work to get the things that they need to live. The most basic needs are
food, clothing, and shelter. In some places, people grow their own food, make their
own clothes, and build their own shelters, living much as their ancestors have for
thousands of years. In other places people earn money to buy those things. Work in
industrialized, or developed, nations frequently takes place in office buildings or factories,
while some people still make their livings as farmers. The economies of such
countries are based on advanced technologies and large-scale manufacturing, which
create products and services that earn workers more money than people can make in
the less industrial, or developing, countries of the world, where farming is the main
industry (and most farmers can barely grow enough food for their own families). People
who live in industrialized nations—like the United States, Canada, Japan, Australia,
and many countries in Europe—are able to buy far more than the basic things
they need to live. They are able to make their lives easier and safer by paying for clean
water, electricity, good medical care, reliable transportation, and much more. Those
who live in developing countries, located mainly in Africa, Asia, and Latin America,
still struggle to acquire the most basic necessities. It may be hard to believe, but half
of the world’s people do not have enough of the right foods to be healthy.
When were coins first used?
Coins were first made in the seventh century B.C.E. in Lydia, Asia Minor (presentday
Turkey). They were issued by the early Lydian kings—probably Alyattes or Sadyattes—
about 600 B.C.E., several decades before the reign of the famous Lydian king
Croesus. Lydian coins were made out of electrum, a mixture of gold and silver, and 231
DAILY LIFE
each was weighed and stamped with a lion’s head, the king’s symbol. About 0.03
pounds (14 grams) of electrum was one stater (meaning “standard”). A stater was
about one month’s pay for a soldier. Today’s coins are not made from precious metals
like gold and silver, but from inexpensive alloys such as cupro-nickel, which is a
combination of copper and nickel. Unlike early coins, the metal in today’s coins is
worth far less than its value in the marketplace.
What is an allowance?
An allowance is an amount of money usually given each week to a child by his or
her parents. Kids can use this money to pay for their personal expenses, for things
like special snacks, toys, or activities with their friends. In some families, parents do
not give their kids allowances, and children just ask their parents when money is
needed. But allowances are useful because they help teach kids how to manage
money—including spending, saving, and donating money to charity. Children learn
how to control their expenses by staying within their weekly budgets. And children
learn to save—if they want to buy something expensive, such as a new bicycle—by
holding onto a portion of their allowances each week. In some families, allowances
are considered payment for doing household chores, and they increase when children
get older and do more work around the house.
Does everyone in the world live in a house or apartment?
No. Although people need houses for the same reason—to provide shelter—people
live in different styles or types of houses. Their homes are determined by their country’s
climate (wet, dry, cold, or hot), location (in the desert, near a river, in a big city),
natural resources (such as wood, stone, or snow), number of people living in the
dwelling, and the amount of money they have to spend on a home. In China, for
example, families who fish may still live on boats called junks, while city dwellers
usually live in apartments. The Mongolians of Inner Mongolia in northern China live
in transportable homes called yurts, a dome-shaped tent made of dried grass, animal
wool, and leather hides. Herdsmen sleep in them when they are driving their herds,
because they can carry them easily and set them up in an hour. In parts of the Philippines,
near rivers that often flood, families live in homes on stilts. Some Navajo families
today live in traditional eight-sided homes called hogans, but most of them live
in ranch-style homes. The Inuits, who live along the northern coast of Canada, live
in homes called igloos or snowhouses, which are made from blocks of snow fitted
and shaped together in an arc. In some villages in Tanzania people live in mud
homes, with roofs made from dried grass and banana and palm leaves.
Do these homes have fireplaces, stoves, running water, and electricity?
Many homes around the world, like igloos, tepees, and mud huts, do not have running
water, stoves, bathrooms, electricity, or many of today’s modern appliances.
In the United States, running water and electricity were not introduced until
232 the mid-1800s, when power-driven machinery came into use. Sawmills, using
steam power, provided abundant lumber. Nails and other metal products became
cheap and plentiful. Steamships, canals, and finally railroads made these materials
available in all settled communities. Inventors and manufacturers introduced many
household conveniences. By the 1850s, fireplaces were being replaced by coal-burning
stoves. Later in the nineteenth century, central heating by furnaces and radiators
became available. Many homes today enjoy modern plumbing and use gas or
electricity for cooking and lighting.
Where does the water from my toilet go?
When you flush the toilet or wash your clothes, the used water, called wastewater,
goes down the drain. This wastewater travels through a network of
underground pipes known as the sewer system. The city system treats the
wastewater to keep it clean. Both large objects, such as sticks, cans, rocks, and
small debris, such as gravel and sand, are separated from the wastewater. It is
treated with oxygen, which allows micro-organisms to grow and eat small bits
of organics. The wastewater is then recycled and clarified again. The wastewater
is then disinfected with chlorine to kill harmful pathogens before being released
into a nearby river, lake, or sea. In towns that do not have a sewer system, each
house has its own septic system. Toilet water flows into a big underground tank
where bacteria helps break down the waste. Then the water flows out into the
soil, where it is absorbed.
Why do I have to do
household chores?
Running a household is a lot of work.
Your parents do most of the chores
required to take care of your family’s
food, clothing, house, and yard, especially
when you are young. But as you
become older, your strength and skills
increase, and you can help out. Household
chores are called chores because
they aren’t fun to do. But these things—
like taking out the trash, doing the dishes,
and vacuuming—are necessary. When
all family members pitch in, household
chores get done more quickly, and everyone
has more time to do the things they
like. So when you do household chores,
you are showing that you care about your
family. Also, taking on additional responsibilities
is a part of growing up, preparing
you for the time when you will have
to do those jobs by yourself. 233
Helping around the house with chores not only keeps the
home clean but is also an important part of contributing to
your family.
DAILY LIFE
What is dust, exactly, and why might it be bad for me?
Dust is made up of particles of all sorts of things. In places where people live, a
great deal of dust comes from flakes of dead skin, which are being shed all the
time. Dust mites, tiny microscopic creatures that feed on this dead skin, make up
dust, too (including their waste and tiny skeletons). Particles of the environment
contribute to dust as well: grit from the sidewalk, salt from the sea, dry earth,
pollen from plants, pet dander, molds, and smoke from burning materials. And
Earth gets 10 tons of dust from outer space every day, from the meteors that burn
up as they enter our atmosphere. Sometimes these ingredients cause allergic reactions,
such as sneezing and coughing.
What’s a cobweb?
A cobweb is an old, abandoned spider web that has collected dirt and dust. Sometimes
the cobwebs you see in ceiling crevices and along floorboards are several
draglines that spiders no longer use. The common house spider—which feeds on
many insects daily—often abandons webs that do not yield prey, and then constructs
new ones until it finds a productive site. It’s best to sweep these old cobwebs
away, and let your house spiders spin new webs, preferably outdoors!
How many spiders live around the house?
Probably too many to count. Spiders live everywhere, and tens of thousands can be
found in a 1-acre (0.4 hectare) grassy field. There are more than 3,000 species in
North America alone. No matter how clean your home is, most have a spider population
that feeds on household insects, mites, and stray flies. They often live in dark,
neglected areas, like closets, attics, and basements, and behind and under furniture,
bookcases, or curtains. Corners and baseboards are two of their favorite locations.
Most house spiders are seldom seen except during housecleaning, but some of the
larger species mature and become more active from late August to early October.
But spider specialists say this is no cause for alarm—very few spider species have
venom that can harm humans, dogs, or cats.
Can houseplants help the quality of air in my house?
Yes. The air inside your home might be filled with toxins from tobacco smoke,
cleaning products, ceiling tiles, and upholstery. Scientists have discovered that
many types of houseplants absorb airborne pollutants as part of their normal
“breathing” process—they take carbon dioxide in through their leaves, and let oxygen
out. The plant transports these toxins to their roots, where microbes feed on
and detoxify them. Although scientists disagree about how many—and what types
of—houseplants it takes to clean the air, they suggest using a mix of plants. Bill
Wolverton, a former NASA scientist and environmental engineer, studies the
effects that plants have on air quality and has rated the areca palm, lady palm,
bamboo palm, rubber plant, and dracaena as highly effective at clearing pollutants
234 from the air.
Why does the floor creak at night?
All matter—gases, liquids, and solids—expands when heated and shrinks when
cooled. This principle explains some of the funny and unexpected sounds that your
house makes at night. During the day, the Sun’s rays warm the materials your
house is made of—like the wooden frame that supports its roof and walls—and they
expand. Heat from the Sun may also make the interior of your house warmer and
even shine on some of its furniture. When night comes, the temperature outside
can drop 30 degrees or more as Earth turns away from the Sun. Things like wooden
floors, house-building materials, and furniture become cooler, too, shrinking
and slipping a little, which can sometimes cause creaking and groaning sounds.
These noises are particularly noticeable at night because your home and neighborhood
are so much quieter than they are during the day.
Why does the wind make noise outside my window?
When the wind (moving air) blows outside your window, you can often hear it. When
the air speed increases, the friction over objects, such as leaves, tree branches, bushes,
and the glass in your window, increases also. The process of friction can release
whistling sounds and swooshing sounds, especially as wind speed becomes very high.
FAMI LI E S
Why do people get married?
Throughout the centuries—and in different parts of the world—men and women
have married for a variety of reasons. It used to be common for young people to
marry the person their parents chose for them, and some cultures continue to practice
arranged marriages. Throughout most of the world today, however, a man and
a woman usually marry because they love each other and want to be together and
care for one another for the rest of their lives. Adults often want to have children
together and raise them in a family. While people don’t have to be married in order
to have children, many people feel more comfortable raising a family as part of a
married couple. When a man and a woman marry they make their permanent partnership
public. After a marriage ceremony, they are connected by a legal contract—
a marriage license—that can be dissolved by another legal decree known as a
divorce (though death legally ends a marriage as well). Marriage grants a couple a
new legal and social status, changing such things as the way they pay taxes and the
amount they pay for health insurance.
Where do babies come from?
Babies grow in their mother’s uterus, a special organ that houses the baby until it
is born. At the start of pregnancy, a mother’s egg is fertilized, which makes a new
cell. The cell divides quickly into many more cells. At about one week, this tiny
mass, called an embryo, sticks to the wall of the uterus, and begins to grow. From 235
DAILY LIFE
the moment of conception, 46 chromosomes and tens of thousands of genes combine
to determine a baby’s physical characteristics—the sex, facial features, body
type, and color of hair, eyes, and skin. At the eighth week, the embryo is called a
fetus. By the end of the twelfth week, the fetus is completely formed and is able to
make a fist, can turn his or her head, and can squint and frown. Until the baby is
ready to come out, it grows inside its mother’s uterus. When the baby is ready to be
born, at about 40 weeks, the mother starts to feel labor contractions. The uterus
squeezes and pushes the baby out of the uterus and into the world.
What is a test-tube baby?
Sometimes, a man and a woman who want to have a baby have trouble conceiving.
Many factors can contribute to a fertility problem, and sometimes medical science can
help fix it. One solution to infertility is called in vitro fertilization. With this method a
woman’s eggs are fertilized with a man’s sperm outside the woman’s body. Fertilization
takes place in a laboratory, in a glass dish (not really a test tube). Once fertilization
occurs and the fertilized eggs begin to grow, they are placed inside the woman’s uterus
to develop further. Eventually a baby is born—and sometimes multiple babies are born
if more than one of the fertilized eggs attaches to the uterus and develops fully. Children
who originate from this method of fertilization are no different from other kids.
They are simply children who began their lives outside of their mothers’ bodies.
Who decides what is right and wrong?
When you are young, it is mainly your parents, but also teachers and other grownups
close to you, who decide what is right and wrong. They are the ones who make
the rules that they believe will keep you safe and help you learn 236 how to become a
Sometimes parents have a hard time having a baby in the usual way, so the mother has her egg fertilized in a laboratory
using the father’s sperm. Then the fertilized egg is put back in the mom, where it grows in the womb naturally.
good person and get along in the world. Adults make the best teachers because they
have experienced a lot of different situations while growing up themselves, and they
have learned lessons from those experiences that they can share with you. Grownups
are wiser than children, who have lived just a short time in the world. But, as
you continue to mature, you will have your own experiences and learn your own lessons.
You may begin to question certain rules, and your ideas about what is right and
wrong may change. This development is a normal part of growing up, the point at
which you start to become the independent and unique person you are meant to be.
Why are “please” and “thank you” magic words?
Saying “please” and “thank you” is a part of etiquette, or good manners. And good
manners make both your home and the world a more thoughtful and generous
place. The words “please” and “thank you” are special words because they make dealing
with other people go more smoothly. People have to ask for help or permission
all the time. Saying “please” shows that your request also comes with respect for the
person you are asking. People are usually more willing to fulfill the requests of those
who treat them with respect. And after someone gives you something or assists you,
it is polite to say “thank you” to show your appreciation. Someone whose actions are
appreciated will be more likely to help you out or be generous again.
Why do I sometimes need a time out?
When troubling situations and conflict occur, our feelings come first before our
thinking takes over. When someone does something we don’t like, or that upsets us,
our first reaction is to act on our feelings, which might include yelling or hitting. 237
How can I get a baby brother instead of a baby sister?
There is no way specific way to place an order for a baby brother or a baby
sister. The gender (boy or girl) of a baby is determined by whether the
father’s fertilizing sperm has an X or a Y chromosome. An X chromosome will
lead to a girl, and a Y to a boy. (Mothers always contribute an X chromosome.)
Although scientific methods are available to help parents organize their chromosomes
and take advantage of the fact that the “boy” sperm has less DNA
than “girl” sperm, they can be expensive and unreliable. One method, called
the Shettles method, recommends that if parents want a girl, they should plan
to make a baby right around the time of ovulation. At this time, the egg is as
far away as possible from the incoming sperm so the long-distance runners of
the sperm world, the X sperm, have a better chance of making it to the egg.
For a boy, the method suggests that parents plan to make a baby about two to
four days after ovulation. That way, the short-distance sprinting Y sperm can
make it to the egg first. Many doctors say that although this method is based
in science, it is no guarantee that a couple will have a baby boy or a baby girl.
DAILY LIFE
A person can get pretty worked up physically, which doesn’t allow him or her to listen
to the thinking messages that are going on inside the brain. When an adult
makes you take a “time out,” it takes you away from the upsetting situation. Your
body and feelings can settle down then, and you can start to think. It is normal and
natural to react strongly to things that put your body on alert, but as you get older
you begin to recognize that most situations can be handled calmly, using your
words. You will be able to control your feelings better and use thinking to guide
your actions. It is this development of self-control that shows you are growing up!
Why do I sometimes wet my bed at night?
Bed-wetting is fairly common and is often just a developmental (age-related) stage.
Twenty percent of five-year-olds and 10 percent of six-year-olds wet the bed, according
to the American Academy of Pediatrics. And it’s twice as common in boys as it
is in girls. Although there are many reasons for wetting the bed at night, doctors
say it is often because these children have a difficult time waking up from their deep
nighttime sleep. Some children have a small bladder that is more easily overfilled.
Since bedwetting is physical, the child has no control over it when it is happening.
However, there are things that you can do to help limit bed-wetting accidents, such
as not drinking liquids after dinnertime and using the bathroom right before you
go to bed. The majority of children grow out of bed-wetting naturally.
Why do my clothes need to be washed?
If you want to look clean and smell nice, your clothes need to be washed frequently.
Most clothing is made of tiny threads that are woven together. As you go about your
day, dirt and odors get trapped in the weave of your clothes and can only be removed
by washing. Clothes must be jiggled and swished around quite a bit in water—as is
done in a washing machine—to best remove dirt and odors. Detergent is added to
the water to help the process: it can
break up oily particles into smaller
pieces that can be whisked away, and it
can surround other dirt particles and
pull them away from fabric.
Should I wash my hands before
I eat?
Yes. Washing your hands with soap and
water cleans them of pathogens (bacteria
and viruses) and chemicals that can
cause disease. Hot water is not enough
to clean your hands. Using soap adds to
the time spent washing and breaks
down the grease and dirt that carry
most germs. The most important times
238 to wash your hands with soap and water
Your hands can get very dirty with germs and gunk that you
might not see, but the dirt is there! That is why it is
important to always wash your hands before eating.
are after you use the toilet or before handling food. When not washed with soap,
hands that have been in contact with human or animal feces, bodily fluids like
mucus, and contaminated foods or water can transport bacteria, viruses, and parasites
to others. When done thoroughly and at least for 20 seconds, hand washing
can prevent all types of illness and disease, skin infections, and eye infections.
Why do we need table manners?
It does seem that there are more rules about eating at a table with others than just
about anything else. Put your napkin in your lap. Don’t take huge bites. Don’t talk with
your mouth full. Ask for something to be passed to you instead of reaching for it. Don’t
start eating until everyone is seated and food has been offered all around. How can a
person remember so many rules? And why are there so many in the first place?
Meals bring people into very close contact with each other. When you’re sitting
so near to one another, you can’t help but notice everyone’s behavior. Table manners
were developed to make the dining experience as pleasant as possible, focusing on
safety and consideration for others. Believe it or not, when you examine each rule
separately, it actually makes sense. You shouldn’t take big bites, for instance, because
you could choke if you have too much food in your mouth. You shouldn’t talk with
your mouth full because that too increases the risk of choking, and because other
diners will be able to see your half-chewed food, which is unpleasant. Reaching for
things far away on the table could lead to knocking something else over along the
way, including someone else’s drink, for example, creating a real mess. The good reasons
for different table manners go on and on. Maybe if you think about the reasons
behind the rules, it will be easier to remember and follow them.
Why do hugs and kisses make me feel good?
Human beings communicate through language, a complicated system of vocal symbols
that our complex brains allow us to learn after we are born. But we also communicate
through our bodies and senses. Our organ of touch is our skin, covering the outside
of our bodies. (Nerve endings under the surface of skin give us our sense of touch.) 239
My older sister says it’s a bad idea
to stick jellybeans up my nose. Why?
The nasal cavity is made up of two narrow passages that lead from the nostrils
to the nasopharynx. In the nasal cavity, air is prepared for its journey
into the lower airways and lungs. It is a sensitive space. Jellybeans (as well as
other candies, nuts, and peas) are about the size of a child’s nostril, and when
lodged inside might get stuck there, or travel too far backward to manually
remove. It may take a special trip to a doctor to get any foreign objects removed.
Your older sister (or brother) is right: don’t stick anything up your nose, ever.
DAILY LIFE
Hugging and kissing are ways to share love and caring through touch. When
you were born, well before you knew language and could understand caring words,
you were learning about love through your sense of touch. As a newborn, when
everything was frighteningly new, you immediately experienced the comfort of
touch when you were held in your mother’s arms, feeling the warmth of her body
and the beat of her heart, sensations familiar to you when you were inside her
womb. You were held close when you first learned about food and about how good
it felt to have milk in your empty stomach. Your parents’ caring hands kept you
clean and dressed in dry clothes when you could not yet do those things for yourself.
So, from your earliest days, you learned that someone’s touch usually made
you feel comfortable and safe.
Loving and caring about special people in our lives is a feeling inside that is
hard to describe in words. But hugs and kisses make it easy to show that love—and
their message is clear. Giving hugs and kisses feels as good as getting them.
(Because the lips have an extra supply of nerve endings, kissing is an especially
intense way to touch.) The human need to share affection through touch is something
we all experience throughout our lives.
Why do I cry when I’m unhappy or hurt myself?
Scientists don’t really know why we cry when we’re unhappy or hurt (or sometimes,
even joyful). But tears help express deeply felt emotions and often release stress and
tension from the body. From our earliest days, when we were babies and could not
yet communicate through language, crying let the people around us know that we
needed something. Frequently, even after we become older, crying still serves as a
wordless signal that something—help or comfort—is needed. In places all over the
world, no matter what language is spoken, crying expresses emotions that are easily
understood by all.
When will I be a grown-up?
In the United States you are considered a grown-up when you reach the age of 18.
You are no longer legally connected with your parents, and you are entitled to the
rights—and expected to fulfill the duties—of an adult American citizen. (You may
vote and be called for military service, for instance.) There is a good chance, though,
that when you are 18 your body has not yet reached full maturity. Many people continue
to grow for a few more years. Most are fully grown—at least in height—by the
time they are 20 years old, though boys may keep on growing until they are 23.
PETS
What is the most common household pet in the United States?
According to a national survey conducted by the American Pet Products Manufac-
240 turers Association in 2008, Americans owned about 75 million dogs and 88 million
cats. Approximately 39 percent of U.S.
households own at least one dog, and 34
percent own at least one cat. According
to the American Kennel Club, Labrador
retrievers are the most popular dog
breed, followed by Yorkshire terriers,
German shepherds, and golden retrievers.
Persian cats are the most popular
feline breed, followed by the Maine coon
and the Siamese. Combined reptiles are
the next popular type of pet, followed by
birds and horses.
What kinds of household pets are
common around the world?
Not all people own dogs and cats. While
many Europeans, including the British,
French, and Italians, own dogs and cats, other people have different relationships to
them. In Islamic tradition, dogs are shunned as unclean and dangerous, and thus it
has never been common for Arabs to own pets. However, in Saudi Arabia and Egypt
it has become fashionable among the upper class to own dogs and cats. (As early as
3500 B.C.E., Egyptians domesticated wildcats from Africa, which became their treasured
pets and honored for their skill in hunting snakes, rats, and mice.) In China,
cats are thought to bring good luck and are kept in shops and homes; the country
also has about 150 million pet dogs—about one for every nine people. The Japanese
keep birds and crickets as pets. The Inuit Eskimo of northern Canada adopt bear
cubs, foxes, birds, and baby seals. And Australian Aborigines capture dingo (wild
dog) puppies and raise them for a time before letting them go.
Why does my dog wag its tail when it’s happy to see me?
Because a dog cannot use words to communicate, it uses its tail wagging, facial
expressions, ear position, posture, and vocalization to communicate. Puppies start
wagging their tails when they are about six or seven weeks old, as they begin to interact
with their fellow littermates and humans. At this time, puppies begin using their
tails as a means of communication and social interaction. You may have noticed that
if your dog is happy, content, and confident, he will wag his tail. Animal specialists
believe that tail wagging is in the dog’s genes: since wolves (the ancestors of today’s
domesticated dogs,) ran in packs, communication—whether by barking, growling, or
wagging tails—was essential to survival. Researchers agree that a dog with a loosely
wagging tail is usually “saying” that he is friendly or excited. However, a wagging tail
is not always a sign of friendliness: an aggressive dog might hold its tail high and wag
only the tip, while a submissive or scared dog is more likely to hold its tail low and
wag it stiffly. Look for these clues in your own dog. If you ever approach anyone else’s,
ask the owner for permission to pet the animal before making contact. 241
According to surveys, cats are now the number one pet in
America, but dogs are still a very strong number two.
DAILY LIFE
Why do dogs bark?
Dogs bark to communicate with other dogs and with humans. Dogs are descendants
of wolves, which are social animals that live in packs, and they share many of the
behaviors that define the complex relationships that exist within such animal
groups. Few domestic dogs live together in packs (though they often consider their
human family their group), but they still use complicated behaviors that involve
smell, sight, and hearing to communicate.
A dog has many scent-producing glands that it uses to communicate. The scent
that a dog leaves behind (in its urine, feces, and paw prints) can reveal its sex, age, and
even its mood to other dogs that come sniffing by. A dog uses its posture, facial expression,
and ear and tail position to communicate with other dogs, too. And it uses its
voice to communicate by whining, growling, howling, or barking. A dog usually
whines or whimpers when it is in distress: when it is hungry, cold, or in pain. Growls
indicate that a dog is angry and ready to fight. Barks usually show excitement.
Why does my dog sometimes howl?
Like barking, growling, and whining, howling is one of the few forms of verbal communication
that dogs have. Its roots go back to dogs’ wolf ancestry, when wild wolves
used howling to communicate over long distances. The howl swept through different
pitches, which helped the sound carry over longer distances. Wolves use howling
to let other pack members know
their precise location if they happen to
get separated. Other members of the
pack howl back in reply—an acknowledgement
that the sent message has
been received. Wolves also howl to discourage
a rival pack from encroaching
on their territory. Dogs today still display
some of this behavior. If you leave
your house or apartment, your dog may
howl to try to reestablish contact with
you. If the howling persists after you’ve
left, it could be a sign of separation anxiety.
And sometimes dogs howl to establish
their territory.
Why don’t dogs get hoarse when
they bark a lot?
It seems like some dogs can bark and
bark for hours. Yet they never seem to
get hoarse or lose their voice (bark) like
people do when they talk, yell, or sing
242 too much. Veterinarians (animal doc-
Dogs bark and howl for a lot of different reasons. The sounds
they make can mean they are excited, mad, happy, afraid, or
guarding their territory.
Can a pet help me when I am having a bad day?
Yes! Research shows that regular contact with pets benefits a person’s overall
health by reducing heart rate, blood pressure, and levels of stress. Pets
offer stability, comfort, security, affection, and intimacy. They teach children
how to care for others, and they help teach children responsibility as they feed
them and tend to their daily needs. In addition, studies show that playing with
pets helps people feel happy and may contribute to fewer feelings of loneliness
and depression. The whole family can bond around an animal as they share
the tasks of walking, feeding, grooming, and interacting with a household pet.
tors) think that is because a dog’s voice box, or larynx, is not as complicated as the
larynx of a human, who needs to make a wide range of different sounds to speak. So
the stress that results from excessive barking doesn’t do nearly as much damage as
overusing a human voice does.
Why does my cat purr?
Animal specialists believe that cats purr to show contentment. Cats are born with
the ability to purr; kittens make tiny rumbling sounds when they are nursing. Scientists
think that purring starts out as a form of communication between a mother
cat and her kittens. The purr lets the mother cat know that her babies are happy
and feeding well, and she may purr back in response. Later, cats continue to purr
when they are in a contented mood or as a friendly greeting. But scientists aren’t
really sure how cats purr. Many think that it comes from the vibration of blood in
a large vein in the cat’s chest, caused when surrounding muscles repeatedly squeeze
and release the blood vessel. Air in a cat’s lungs and windpipe increase the sound of
the vibrations that can be heard (although sometimes the purring is silent and can
only be felt). Other scientists think that cats purr when membranes called false
vocal chords, located in a cat’s throat near the real ones, start to vibrate.
Why does my cat arch its back?
Like meowing and purring, a cat’s arching back is part of its complex body language
system, usually associated with feeling threatened. The arch is able to get so high
because the cat’s spine contains nearly 60 vertebrae, which fit loosely together.
Humans have only 34 vertebrae.
How does a cat’s tail help keep the animal balanced?
Almost 10 percent of a cat’s bones are in its tail, and the tail is used to maintain the
animal’s balance. A cat’s tail plays a vital part in its “righting reflex” that allows it
to land on its feet after falling from a height. Cats often survive a long fall based on
their agility and balance, which they develop as kittens. When falling, the fluid in
the inner ear shifts and the cat rotates its head until it equalizes and the fluid is 243
DAILY LIFE
level. The body automatically shifts to follow the head, and the cat lands on its feet.
A cat also uses its tail to communicate. A cat’s tail held high means that it is happy.
A twitching tail is a warning sign that it may be angry or on guard, and a tail tucked
in close to the body is a sign of insecurity or fearfulness.
Why do mice cry red tears?
People who own rats and mice may be shocked when they see their pet rodent has
red tears and nasal secretions. Red crusts may also develop around your pet’s eyes
and nose, and the forepaws may be red from rubbing the face. This redness is not
caused by blood, but by the secretion of a red pigment called porphyrin. This pigment
is released from a gland behind the eye called the Harderian gland. (The scientific
name for the colored tears is chromodacryorrhea.) Although the red coloration
is not blood, the red tears suggest your pet rodent may be ill because they
cry these tears when they are sick or stressed.
Why does my guinea pig have buck teeth?
Pet rodents—hamsters, rats, mice, gerbils, and guinea pigs—are very popular pets.
Common to these pets is large front teeth, called incisors, which grow continuously
throughout the pet’s life. Overgrown incisors are a common problem and can be prevented
by allowing the pet to chew on pieces of wood chewing sticks. Often a veterinary
surgeon (a pet doctor) can trim these front teeth. Rodents are herbivorous (planteating)
animals, and the digestive tract is, in some ways, similar to that of other planteaters,
such as horses and cattle. They love to use their front teeth to nibble and chew!
Can my turtle take off its shell?
No. The turtle’s outer shell is made of a thin layer of keratin, like your fingernails.
But underneath that layer, there is a layer of bony plates that give the shell its
244 shape. The ribs and vertebrae (backbones) are part of the shell, too. So removing
My pet iguana was tiny and now it’s more than
3 feet (0.91 meters) long! What happened?
If cared for properly, green iguanas can live more than 20 years. But they
do indeed grow … grow … and grow along the way. Although iguanas
make popular pets, they need lots of time, attention, care, and room to
grow. A healthy iguana will grow to be 5 to 6 feet (1.5 to 1.8 meters) in
length, and will require a very large cage or an entire room to live in. Iguanas
need tall cages because they are tree-dwelling (arboreal) creatures, and
prefer to spend the majority of their time as high off the ground as possible.
Iguanas also need a special diet, plenty of sun, places to climb, and human
interaction and stimulation.
the shell would remove part of the skeleton of the turtle—which is why it is impossible
for a turtle to remove its shell.
Why do I have to wash my hands after handling my pet turtle?
Turtles and other reptiles, such as snakes and lizards, can carry salmonella bacteria.
Although this does not affect the animal’s health, it can make humans very sick.
In order to avoid getting salmonella, a few rules of hygiene should be followed.
First, don’t put reptiles in your mouth. Wash your hands carefully with soap and
hot water after you handle the turtle. Very young children should just look, and not
touch, reptiles. Don’t let reptiles walk (or slither) around in the house—keep them
in their cages and tanks. The most common source of the salmonella bacteria is
undercooked food, especially eggs and poultry, so be sure to tell your parents or
adult caregiver to thoroughly cook your eggs and chicken. (And don’t lick the cake
batter if it contains raw eggs!)
Is it okay to bring my pet snake to school for show and tell?
Because animals are unpredictable and because schools have rules, it is never okay to
bring animals out in public without the permission of both a parent and teacher. Even
if you have permission, these creatures—such as snakes, rabbits, hamsters, gerbils,
lizards, frogs, and other small critters—should be contained in their habitats and
handled very carefully. Sometimes in public animals are outside of their natural habitats
because they play a role in helping humans. Guide dogs (also called seeing-eye
dogs) help the blind or visually impaired move around cities and neighborhoods.
These dogs are trained to behave properly on public transportation, in restaurants, in
stores, and in any other place their masters go. Other times people carry their dogs
and cats in pet carriers to the vet, to the park, or on shopping trips. However, they 245
Kissing a reptile like a snake or turtle is not a great idea. Reptiles can carry germs that cause salmonella, which will make
you very sick to your stomach.
DAILY LIFE
must have the store’s permission to enter, since many businesses (like restaurants and
supermarkets) do not allow pets or require them to be contained and/or on leashes.
Why should I walk my dog every day?
Walking with your dog strengthens the bond between you and your pet, and it is
also the healthy thing to do. Dogs, like people, benefit from exercise to help control
weight and to maintain a healthy heart, lungs, and muscles. They love going for a
walk, running and jumping, and retrieving a ball or Frisbee. Aging pets must be
kept as agile and fit as possible, but may not be motivated to exercise without
encouragement. The pleasure of your company is one of your dog’s greatest motivations
to exercise. In addition to exercise, dogs also need social interaction, positive
attention from their owner, and mental stimulation. Many of these needs can
be met by simply taking your dog for a walk. Always remember to walk your dog on
a secure leash (with identification tags) and pick up after your pet. During warm
weather carry water for your pet, and always pause when your dog needs a rest.
What do I do if my pet dies?
Like all living things, your pet will die someday. A pet can die from old age, an accident,
or an illness. Even when a veterinarian (an animal doctor) helps, there are
some illnesses that can’t be cured. If your pet is in a lot of pain and will never get
better, your parents and the vet may decide that the animal should be allowed to die,
or “put to sleep.” To make the process pain-free and peaceful, the vet can give the
pet a special kind of injection (shot) to help it die. If your pet dies naturally, you may
want to bury it in your back yard. But check with your town or city first to make
sure burial on your property is legal. Some laws permit homeowners to bury their
pets on their property, while others do not. Other options include burying your pet
at a pet cemetery or cremating the animal, then scattering the ashes throughout
your garden or under a favorite tree.
No matter what you decide to do when your pet dies, many emotions are likely
to surface, such as sadness, loneliness, or even anger. Talk to your parents about
how you are feeling. You and your family may want to find special ways to remember
your pet. You might have a ceremony, tell stories, write a poem, or make a
scrapbook. And there are animal organizations, such as the ASPCA (the American
Society for the Prevention of Cruelty to Animals) that can help you with the grieving
process. A new animal can’t replace your old pet, but someday the time might
be right for you and your family to adopt a new animal for everyone to love.
GOING TO SCHOOL
Why do I have to go to school?
Much of what you need to know to live successfully as an adult does not come naturally—
it has to be learned and studied and memorized. Children 246 learn to speak nathandy
urally, for example, by listening to those around them, but reading and writing must
be specifically taught. The complicated process of learning the alphabet and the
sounds it represents, putting letter sounds together to make words, and learning the
meaning of words in order to read and write are skills that only come with special
effort. Knowing how to figure out problems that involve numbers, and learning how
the world is run or how nature works are important things to learn, too.
Although your parents might be able to teach you these things, they would need
many hours each day to do it. Most parents work outside the home and wouldn’t
have the time to give proper instruction (although some kids are “home schooled”
by their parents instead of going to school). In the United States, a public school
system provides years of free education for all children. Teachers, who are specially
trained to know what children should learn, and how, and when, are the people who
do the job. To ensure that children learn what they need to, state governments now
require that all children go to school for a certain number of years (usually until
age 16). Kids who skip school a lot can find themselves in court. (Children who go
to private schools or whose parents have received special permission to teach them
at home are exceptions.)
What is home schooling?
Home schooling (also called home education or home learning) is the education of
children at home, typically by parents or professional tutors, rather than in a public
or private school. Most parents cite family togetherness, more control over curriculum,
and having a say over what their children learn as reasons to home school.
Many of the families who home school also do so for religious reasons. Because each
state makes its own laws for education and schooling, home schooling is defined
differently in each state. According to different surveys, between 1.7 and 2 million
children in grades kindergarten through 12 were home schooled in the United
States during the 2002-2003 school year
(the most recent data available).
Did our Founding Fathers discuss
school in the country’s founding
documents?
America’s founders did debate a bit as to
whether or not to force children to
attend schools, and they decided to
leave such decisions to individual families
and local and state governments.
The words “education” and “school” do
not appear in any of our founding documents,
such as the Declaration of Independence,
the Constitution, or the Bill
of Rights. Some of our most famous
inventors, writers, and politicians were 247
Many parents teach their children at home rather than sending
them to a public or private school because they feel they can
give their kids a lot more attention and help them learn more.
DAILY LIFE
self-taught, learning through mentoring or apprenticeships, conversation, and
reading. In 1850, Massachusetts became the first state to institute a compulsory
schooling law.
What is school like in other countries?
Schools are different in every country in the world. A school may have lots of classrooms,
books, play equipment, and a playground, or lessons may take place under
trees or in an open outdoor space. A temple, a tent, or a building on stilts may serve
as a classroom for some children. In poor places that have no money to build
schools, children may learn their lessons outdoors. In isolated places—such as the
Australian outback or the Alaskan wilderness—where families live hundreds of
miles apart and far from cities or towns, children may get their lessons from teachers
over two-way radios or the Internet. All around the world, schools are a reflection
of the culture in which they are formed. In Japan, as students enter school,
they remove their shoes and put on slippers, a Japanese custom. They do not write
with pencils; instead, each child has his or her own ink well, brush, and ink for writing
the kanji (Japanese characters). Children often clean their classrooms (including
dusting cubbies and mopping floors), and at the end of each class the students
thank their teacher and bow. In schools in Brazil and other South American countries,
children often go to school barefoot. In India, children practice yoga in
school. And many children that go to public schools in European countries, such as
Germany and France, ride their bikes to school or take public transportation, rather
than school buses.
My friend says he’s a genius. Is that possible?
Some people use the term “genius” to mean a genius I.Q. or extreme intelligence.
I.Q. stands for intelligence quotient, and it is supposed to be a measurement of how
248 naturally intelligent a person is. Scientists think that each person is born with a
How long has home schooling
been practiced in the United States?
The concept of home schooling was first introduced by early republic families,
before schools were built and made in America. Family, community,
religious institutions, and work were all integrated into the daily lives and
upbringing of children. Through involvement in daily life, children gathered
knowledge of everything from growing food, construction, caring for livestock,
and making tools, clothing, and soap. Sometimes families hired or
shared professional or informal tutors who instructed children at various
times for short periods each year; other families used daily chores, apprenticeships,
and internships to educate their children. Many home schoolers incorporate
these traditions into their home school curriculum today.
certain amount of intelligence or mental ability. Still, how well a person uses his or
her natural intelligence has a lot to do with the person’s desire to learn and the
learning environment he or she grows up in. I.Q. tests measure things like the ability
to use words, the ability to see how things relate to one another, and the ability
to store and use information. The term “intelligence quotient” comes from the
mathematical equation used to score intelligence tests. A person’s mental age—
which is determined by how many questions he or she has answered correctly on
such a test—is divided by his or her actual age. Then that number is multiplied by
100 to give an I.Q. score. A person whose mental and actual age are the same will
have an I.Q. that is 100, which is average. A person with an I.Q. of 170 or greater is
considered a genius.
When people think of geniuses, they often think of great men and women from
history, including the Italian painter of the Mona Lisa, Leonardo da Vinci, the great
scientist Albert Einstein, and the child genius Wolfgang Amadeus Mozart, the
famous Austrian musical composer. Before he was even five years old, Mozart could
master complicated musical compositions in just a half an hour. Even at this early
age, before most of today’s children start formal schooling, Mozart was composing
his own works. He is called “gifted” and a “child prodigy,” because he mastered
many talents at an early age.
Why are some kids better at schoolwork than others?
Some children do better in school than others for many reasons. All kids have different
talents and abilities, and some of these just show up better in school. Some
children may be naturally better at reading and writing, working with numbers, and
at storing and using information. Some children are very organized, good with
managing their time, and diligent about doing their homework. Most schoolwork
requires these skills, so kids who are strong in these areas are likely to be better students.
Still, most kids have enough ability to earn the basic skills taught in schools,
things that they will need to know to get along well in the world once they graduate.
Kids succeed by putting a lot of time and effort into their studies, by getting
help when they need it, and by not giving up!
What is a learning disability?
Learning disabilities are disorders that keep people from understanding or using
spoken or written language in typical ways. Learning disabilities are not due to
physical handicaps, like blindness or deafness. Instead, they have to do with problems
in the brain and the way it perceives things. About 10 percent of all children
in the United States have some type of learning disability. The most common of
these are dyslexia—where the brain has trouble understanding words, sometimes
reversing the order of letters and words—and attention deficit hyperactivity disorder
(ADHD), which is marked by difficulty with concentration. Special teaching
methods have been developed to help such children learn successfully despite their
disorders. The teaching is done either in the regular classroom, in special classes,
or at a specialized school. 249
DAILY LIFE
Why do I have to do homework?
The hours in a school day and the amount of time a teacher can spend individually
with students are limited. As a result, teachers need the understanding and help of
their students, parents, and families in supporting classroom instruction and learning
outside school hours. Homework has been part of school life since the beginning
of formal schooling in the United States. It is important because it can
improve your thinking and memory. It can help you develop positive study habits
and skills that will serve you well throughout your life. Homework also can encourage
you to use time well, learn independently, and take responsibility for your work.
And if you have an adult supervise you, it benefits them as well. It helps your mom
and dad see what you are learning in school and helps your family communicate
with you and your teachers.
Where did the English alphabet come from?
An alphabet is a system of writing in which symbols or letters represent all the
sounds of language. Because ancient Egyptian hieroglyphics sometimes used symbols
to represent language sounds, they are considered the root of true alphabets.
The English alphabet came from the ancient Romans, who based theirs on the
ancient Greeks. Modern English uses a modified form of this Latin alphabet. The
written languages of western Europe, Africa, and the Americas, as well as scientific
writing, all use the Roman, or Latin, alphabet. It has 26 letters, and is written
from left to right.
What is American Sign Language, and does it have an alphabet?
American Sign Language (ASL) is a complete, complex language that uses signs
made with the hands and other movements, including facial expressions and postures
of the body. It is the first language of many deaf North Americans, and one of
several communication options available to deaf people. ASL is the fourth most
commonly used language in the United States. Even though ASL is used in Ameri-
250 ca, it is a language completely separate from English. It contains all the basic fea-
American Sign Language is a system of hand gestures used to communicate to people with severe hearing impairments.
tures a language needs to function on its own, including a finger alphabet, and rules
for grammar, punctuation, and sentence order.
What does it mean to be bilingual?
A bilingual person is able to speak two languages. A person who speaks more than
two languages is called “multilingual.” A person does not have to speak two languages
with equal fluency to be considered bilingual; usually, a person will be
stronger in one language than another. It is common for most of the world’s societies
to be multilingual; in the United States, one in five children enters school
speaking a language other than English, according to the 2000 Census. Some
children who learn English in school speak their native language at home. Bilingualism
often allows children to communicate with their grandparents, which
can strengthen family bonds across both generations and countries. Bilingualism
teaches an appreciation of the arts and traditions of two cultures. It promotes tolerance
and cross-cultural understanding; research indicates that children who
are raised with a bicultural identity tend to be more accepting of cultural differences
in others.
What is literacy?
Literacy is more than just the ability to read and write. According to the Department
of Education and other government sites, literacy is defined as an individual’s
ability to read, write, speak in one’s native language, and compute and solve problems
at levels of proficiency necessary to function on the job, in the family, and in
society. This is a broader view of literacy than just an individual’s ability to read. As
information and technology have increasingly shaped society, the skills we need to
function successfully have gone beyond reading. 251
Which library has the most books?
According to the American Library Association, there are an estimated
123,291 libraries of all kinds in the United States today. The Library of
Congress, founded in Washington, D.C., in 1800, is both the oldest and largest
library in the United States. On August 24, 1814, British troops burned the
Capitol building (where the library was housed) and destroyed the library’s
core collection of 3,000 volumes. The following year, Congress approved the
purchase of statesman Thomas Jefferson’s personal library of 6,487 books for
$23,950. Today, the Library of Congress is the largest library in the world,
with more than 138 million items on approximately 650 miles of bookshelves.
The collections include more than 32 million books and other print materials,
2.9 million recordings, 12.5 million photographs, 5.3 million maps, 5.5
million pieces of sheet music, and 61 million manuscripts. DAILY LIFE
What is a pen pal?
Pen pals (also called pen friends) are people who regularly write to each other, particularly
via postal mail. They are often located in faraway places, such as other
states and countries. A pen pal relationship is often used to practice reading and
writing in a foreign language, to improve literacy, to learn more about other countries
and lifestyles, and to feel connected to people in other parts of the world—
which helps the world feel like a much smaller place!
Pen pals come in all ages, nationalities, and cultures. Pals may seek new pals
based on their own age group or a shared common interest, such as a specific sport
or hobby, or they may select someone totally different to gain knowledge about a
foreign culture (such as the Far East, Europe, or South America). With the advent
of the Internet, a modern version on the traditional pen pal arrangement has developed,
and many pen pals also exchange e-mail addresses as well as, or instead of,
paper letters. In order to connect with a pen pal, get your mom or dad’s permission
first. Often, online sites dedicated to pen pal communication can help you connect
with a student your own age.
Why should I visit the library often?
Libraries offer books for people of all ages, and much, much more—they are places
of learning and discovery for everyone. Besides books, public libraries offer videos,
DVDs, free access to computers and the
Internet, and many literacy-related programs.
For elementary school children,
there are variations of the read-alouds
and storytelling hours that often include
discussions and presentations by the
children themselves, as well as summer
reading programs. For middle-school
kids, there may also be book talks, summer
reading programs, creative writing
seminars, drama groups, and poetry
readings. The more you read, the more
you learn! In addition, the library is a
place to find information and help with
schoolwork. Your school library may
offer some of these services as well.
What is the librarian’s job?
Librarians have many responsibilities.
One of the most important ones is to
help the public (called patrons) find the
books and materials that they are looking
for—this is their specialty. For
252 example, if you don’t know which books
Librarians are not just people who tell you to be quiet at the
library. They love to help kids and adults find information
and learn new things!
to select, the librarian can help you select books that are both fun and suitable to
your age level. They can also show you the other programs and services the library
has to offer. Ask a librarian for help when looking for books and materials, so that
you become comfortable with the library system and the process for getting the
information you need. Keep in mind, however, that a librarian is there to point out
different choices, not to decide what you should read. If you are unsure if a book is
appropriate for you, ask a parent to help you select books and participate in your
reading programs.
What can parents do to help kids with their library assignments?
Very often school-age children will ask their parents for help with library assignments.
And very often parents will find themselves gradually taking over and doing
a report for their son or daughter. Instead, ask your parents to try the following
ideas to motivate you and increase confidence in wading through a book report or
library assignment (courtesy of Reading Rockets, a nonprofit educational service of
WETA, Washington, D.C.’s leading public broadcasting station):
• Ask your children questions about the assignment and encourage them to ask
their teacher questions. This helps children to clarify what they are trying to
do. Help them to identify smaller components of the topic they are researching
or to see the topic as part of a larger topic. (For example, brontosaurus is
a subgroup of dinosaurs, which is a subgroup of extinct animals.) These classifications
will help them to identify useful references.
• Suggest that they look up the topic in the library catalog, periodical guides,
and reference books. The librarian will direct them and help them get started.
Be sure they know how to use a table of contents and index. Suggest they start
with something general about the subject and be prepared to consult more
than one source.
• Help them to break assignments into logical segments and avoid last-minute
panics by setting deadlines for each phase of the work. Allow them plenty of
time to gather the materials they need.
• Help them to determine if the community library has the resources they need
or if they need to check other information sources.
• Encourage your kids to ask the librarian for help in locating materials and let
them do their own talking.
• Give them encouragement, advice, and a ride if they need it, but resist the
temptation to take over an assignment. Let your children assume responsibility
for researching and writing reports. It is the best way for them to library
skills that they will able to use for the rest of their lives.
What’s the best way to make friends at a new school?
Although it might be overwhelming your first few days at a new school, you’ll find
it’s easier to make friends than you might think. Especially if you try to behave in a
way that you think would make a good friend. By being inviting, smiling, and mak- 253
DAILY LIFE
ing eye contact, people will naturally greet you. If you see someone you recognize
from class, the basketball court, or the community, give a smile or say hi. Introduce
yourself. Tell them your name and where you’re from. Asking questions, such as
“What sports do you like to play?” or “Have you been here since kindergarten?”, is
a good way to begin a friendship.
And it’s always good “friend etiquette” to do something nice for someone, such
as saving someone a seat, saying hi in the hall, or offering congratulations on a good
test score. Even a simple compliment, such as “I like your backpack,” can go a long
way toward making friendships. Other ways to make new friends is to join a sports
team, engage in school activities, such as choir or theater, or form or join a study
group. All are great ways to make potential friends, establish common bonds, and
get academic support. And guidance counselors can arrange for “buddies” with similar
interests and the same classes to introduce new students to the school campus
the first few days of school.
And here’s a fun tip: Look for other people who are new to the school. You’ll discover
you’re probably not the only new student. At the very least, you’ll share the
fact that you’re both in an unfamiliar environment. And if you are starting at a new
school in start-up year, almost everyone is new! Talk about your old school, your
new school, your opinions, grades, teachers, and interests with a wide variety of
people—you’ll soon find you have more than one new friend, but several or many!
What is stress?
Stress is your body’s way of responding to any kind of demand. It can be caused by both
good and bad experiences. When people feel stressed by something going on around
them, their bodies react by releasing chemicals into the blood. These chemicals give
people more energy and strength, which can be a good thing if their stress is caused
by physical danger—such as steering a bike out of a driveway if a car is approaching.
But stress can also be a bad thing, if yours is in response to something emotional and
there is no outlet for this extra energy and strength. Young people experience stress at
a high rate, and females more than males, an extensive Associated Press/MTV survey
showed in 2007. People under large amounts of stress can become tired, sick, irritable,
and unable to concentrate or sleep, so it’s important to identify when you might be
“feeling stressed” and take steps to lessen your stress level.
Why do I have to be a “good sport” when I lose a game?
Sports games, board games, and competitions—such as spelling bees and gymnastics
competitions—always have winners and losers. When you agree to play a game
you have to prepare yourself for the fact that you may not win. If you can see the
game as a way to improve your own skills and to have fun, you may even be able to
admire (and learn from) the talent of the person who beats you and congratulate
him or her. After all, it’s only a game.
So remember that when you play a game, the object is not to win, but to par-
254 ticipate well. Play fairly, with courtesy and respect for your teammates and oppohandy
nents, and with your best effort. It is also important to show good behavior following
the game, whether you win or lose (which is why many coaches have all teammates
shake hands with or “high five” members of the opposite team post-game).
What do I do if I am being bullied?
Lots of kids have been picked on by a bully, for many different reasons. Bullying is
intentional tormenting in physical, verbal, or psychological ways, and can range
from hitting, shoving, name-calling, threats, and mocking to taking lunch money
or personal items. If you’ve been the target of a bully, you know it can be very scary
and upsetting to be teased, hit, or threatened. Sometimes it helps to simply ignore
what the bully is saying—most bullies tease or threaten other kids to get a reaction
from those they tease, and if they get no reaction at all, it’s a lot less fun for
them. It usually helps to have friends around. A kid walking alone is more vulnerable
than a group of kids. And even if you don’t feel confident, sometimes acting
confident helps. If you hold your head high and tell a bully to stop calling you 255
How can I manage my stress?
Stress usually comes from a combination of your schedule and schoolwork.
Notice whether your schedule allows you enough time to get all your
schoolwork done or whether you need to budget your time better to accomplish
all your assignments. If finding time to get your schoolwork done seems
almost impossible, plan to find a quiet place (like a library or study hall) to
spend the first hour or two after school to do your homework. If scheduling
is not the problem and the schoolwork is too difficult for you, plan to spend
the first few hours after school in your teacher’s classroom, at study hall, or
in a tutoring program to get the help you need. Avoiding budgeting your time
or asking for help may be unnecessarily increasing your stress level at school.
And, if you have trouble discerning what kind of help you need, ask your parents
and teacher to help you decide where your stress is coming from.
Three of the easiest and best ways to deal with stress are to get plenty of
exercise, eat a good breakfast every day, and get lots of sleep (7 to 10 hours per
night, depending upon your age). It is also important to stay away from caffeine
and sugar, because they do not help your body manage stress in the long
term. Stress experts say it’s also important to have practical expectations
about school, make to-do lists when necessary, and take creative study breaks,
such as going rollerblading or biking. Do not make grades the most important—
or only—thing in your life. It is important to have friends and find hobbies
and activities that you like. If you feel overwhelmed, remember to talk to
friends, a parent, a teacher, or your guidance counselor about what’s going on
in your school life. Often, there are several ways to juggle assignments, extend
deadlines, or work together as a team to get a project done.
DAILY LIFE
names, you may just surprise that bully into silence. One approach to avoid is
responding to bullying with fighting or bullying back—aggressive responses will
only make matters worse.
Should I tell my parents I am being bullied?
Yes. Even though it may feel awkward or embarrassing, it helps to tell your parents,
a teacher, or a counselor about a bullying experience. A trusted adult can
make you feel better by explaining why bullies behave the way they do and by
reassuring you that what a bully says about you has nothing to do with who you
really are. Adults can help keep you safe if you’re being threatened, and come up
with solutions to deal with the bullying. Many states have bullying laws and policies,
and many schools have programs in place that educate parents and kids
about bullying.
What do I do if witness bullying on the playground?
If you are on a playground and you see a kid hurting or making fun of another kid,
your first impulse might be to turn around and pretend you don’t see it. But imagine
how that bullied kid is feeling, and you’ll know that the right thing to do is to
try to put a stop to it. The best thing to do is to find a teacher or another adult and
tell that person what is happening. Or, if the situation doesn’t feel like it could
256 threaten your personal safety, the best thing you can do is stand up for the kid being
Bullying can be a big problem at school or just around the neighborhood. If you are being bullied by someone, you should
not keep it a secret. You should tell an adult and ask for help.
bullied. Kids who make fun of others usually expect to get a laugh from their
friends, and if you show the bully that his or her teasing isn’t funny and that you
support the person being teased, it could end the teasing.
What is head lice?
The head louse is a tiny, wingless insect that lives in human hairs and feeds on very
small amounts of blood drawn from the scalp. Although they may sound kind of disgusting,
lice appear often on young children in common settings, such as school.
Lice aren’t dangerous and they don’t spread disease, but they are contagious and
can be very annoying. Their bites may cause the scalp to become itchy and inflamed,
and scratching may lead to skin irritation. They can be hard to get rid of, and take
lots of work to make them go away and stay away. Usually, using special medicated
shampoos and thoroughly cleaning sheets, carpets, clothing, and personal products,
like combs and brushes, gets rid of the pesky insects. Kids should try to avoid
head-to-head contact at school (both in classrooms and on the playground) and
while playing at home with other children. They also shouldn’t share combs, brushes,
hats, scarves, bandanas, ribbons, barrettes, towels, helmets, or other personal
care items with anyone else, whether they may have lice or not.
S ERVING MY COMMUNITY
What type of people help make a community operate well?
Firefighters, police officers, ambulance drivers, garbage collectors, mail carriers,
crossing guards public-school teachers, school-grounds and maintenance workers,
public librarians, bus drivers, and parks and recreation workers are just a few of the
city-service people that make a town or city run well. Every day, these and hundreds
of other workers labor to make communities across the United States safe, clean,
and healthy. Many of these workers are paid for their jobs, but many also volunteer
(work without pay) to help their neighborhoods be safe. The government estimates
that about 60 million people volunteer each year, most often in religious, educational,
youth, or community service organizations. Volunteers commonly perform
activities such as firefighting, coaching, campaigning, fundraising, delivering
goods, and serving on boards or neighborhood associations.
How do police officers help the community?
There are about 800,000 police officers in the United States. Police officers protect
the lives and property of citizens. They maintain order, catch lawbreakers, and work
to prevent crimes. Also called “peace offers,” police officers have different responsibilities
depending upon the size and structure of the communities in which they
serve. Police officers may patrol the streets on foot or in squad cars, control traffic,
or work as detectives investigating crimes. At the police station, officers may be
assigned to work in the crime laboratory or the records department. All officers file
reports of incidents, and many testify at trials and hearings. 257
DAILY LIFE
How do firefighters help the community?
There are about 355,000 firefighters working in communities across the United States.
Firefighters work under extremely dangerous conditions, risking their own lives to save
others as they battle fires. Called “first responders,” they are usually the first emergency
personnel at traffic accidents or explosions and may be called upon to put out fires or
treat injuries. Once at a fire, they use axes to break down walls or windows so they can
evacuate people trapped by flames and other obstacles. Rescue squads take first-aid
equipment to fires and help the injured until ambulances arrive. They also may be called
for injuries and accidents not caused by fire, such as heart attacks. Despite the dangers,
firefighters take satisfaction from providing an important public service.
What is philanthropy?
The word “philanthropy” comes from two Greek words, philos (meaning “loving”) and
anthropos (meaning “man”), and is translated as “love for mankind.” Today’s definition
includes the concept of voluntary giving of money by an individual or group to promote
the common good and improve people’s quality of life. The modern notion of philanthropy
began with steel tycoon Andrew Carnegie, who, in an essay titled “The
Gospel of Wealth” published in 1889, gave birth to the idea that the rich should, instead
of leaving their wealth to their families, “administer it as a public trust during life.”
Why is it important to volunteer?
In 2007, many Americans—about 60 million people, or about 26 percent of Ameri-
258 cans age 16 or older—volunteered, or performed unpaid work for a nonprofit
Lots of kids dream of being firefighters or police officers when they grow up. A desire to help your community is a great thing,
and you should pursue it if you are really interested.
organization (or charity), according to the Corporation for National and Community
Service. They understood that volunteering is an important part of life. It provides
an opportunity for us to see our world from a different perspective, gain exposure
to new people, places, and situations, and make a difference in someone’s life.
Volunteering provides us with a chance to interact with people from different backgrounds,
who come together to support a common cause. Whether you serve in the
arts, music, parks and recreation, sports, technology, or education, your neighborhood
schools and nonprofit organizations always appreciate reliable and dedicated
volunteers. Your reward is the feeling you get inside when you give your time and
energy to help a person less fortunate.
Why do people beg for money and push grocery carts around town?
In the United States, millions or people are hungry or homeless. Many people do
not have the necessary amount of money to live each month, some do not live in
homes or apartments, and some do not have jobs. A grocery cart may carry all of
their belongings. Some people are too ill to work and don’t have money to afford a
house or apartment. Being homeless means that a person does not have a place to
live. It might be for a day or two or for many weeks or months. The person (or family)
might live in a shelter with a lot of other people, or in a car, or have no structure
surrounding them. Homelessness is not necessarily permanent and often people
just need some help to get settled again.
What is a homeless shelter?
A homeless shelter is a building that helps homeless people by giving them a place
to stay for awhile. It can include beds, bathrooms, showers, clothing, and hot meals. 259
Why do people wear uniforms?
Some jobs require special clothing or uniforms. Sometimes these special
clothes are meant to protect workers or the people they work with. An
emergency room doctor, for instance, may wear special clothes to protect herself
from blood and infectious agents as well as to protect patients from the
germs and impurities that may be present on ordinary clothing. Most often,
though, special clothes or uniforms are worn so that workers can be easily
recognized by other people. Occupations that require uniforms are frequently
service jobs, where workers help or perform services for other people.
Workers in stores and restaurants frequently wear uniforms so that customers
know whom to ask for help or service. Uniforms help police officers do
their jobs better, because people recognize them and go to them for help or
give them the cooperation they need to maintain the law. On the battlefield,
soldiers wear uniforms to identify which country they are from, signaling
whether they are friends or enemies.
DAILY LIFE
They also have activities for children.
Some homeless people also move into
“transitional housing,” which are housing
facilities that also have job training
and other services to help the homeless
eventually get their own homes.
How can kids help the homeless?
Kids can help the homeless in a number
of ways. You can collect canned food or
freshly baked items and take them to a
shelter. You can ask your parents if you
can clean out your closet and give some
of your old clothes to homeless children.
You can collect toys from your
friends, and then donate them to a local
shelter. You can open a lemonade stand
or have a bake sale and give the money
you make to a shelter or an organization that helps the homeless. And, if you are
old enough, you can volunteer to help out at a local shelter—you can baby sit, read,
help with homework, or play games with the children.
What is a food bank?
A food bank is a warehouse or “bank” where contributed food is collected, sorted,
and distributed to different agencies, such as shelters and church pantries, who
then give or prepare and serve the food to those in need. There are many ways to
help out at your local food bank. You can donate money. You can donate food. If
your school does not already collect food for your community’s food bank, you can
speak to your principal about setting up a food drive one day per month to collect
food from your student body. (Perhaps each child brings from home one can of nonperishable
food the first Tuesday of every month.) You can volunteer. And you can
take political action by writing to your congressman, state senator, or representative,
and telling them that you will not accept hunger in your town or city.
INTERNET SAFETY
What is cyberbullying?
Cyberbullying (also called griefing) is the act of harassing someone online. It is
illegal to communicate repeatedly with someone if your communication causes
them to fear for their own safety or the safety of others. Always speak to a responsible
adult if you are uncomfortable with any conversations occurring online.
You can block the person sending the harassing messages 260 using the block
Homelessness is a problem in the United States and
countries all over the world. You can help by collecting food
or other items and taking them to a church or local shelter.
options that come in many e-mail and instant messaging programs. And your
parents can help you save any harassing e-mail messages and forward them to
your e-mail service provider. Most providers have appropriate-use policies that
restrict users from harassing others over the Internet. If the harassment consists
of comments posted on a Web site, you can contact your Internet service
provider (ISP) and ask for help locating the ISP hosting the site. You can then
contact the ISP and bring the offensive comments to their attention. You can
also contact your local police department.
What are house rules and family contracts for Internet use?
Often parents and guardians work with their kids to create an online agreement
that outlines the rights and obligations of computer use at home. It might be a list
of rules that you agree to together, or it might be a more formal contract that both
the parent and the child sign. It covers topics like where kids can go online and
what they can do there; how much time they can spend on the Internet (and how
much of that time is dedicated to school work); and what they should do if anything
or anyone makes them feel uncomfortable. You can write down the rules for protecting
your personal information and how to use chat rooms, newsgroups, and
instant messaging services. Families often print the rules out and keep them by the
family computer to remind everyone of the rules.
What should I do if someone asks for my name when I am online?
The Internet is an amazing place where you can find information on all kinds of
things. You can chat with friends, e-mail long-distance pen pals, and read what 261
My friend spends all his free time playing games online.
Is he addicted?
Kids often use the Internet for many things—doing research for homework,
exploring new cultures, and building relationships with other kids.
Kids who are shy in person may feel more comfortable initially connecting
with people over the Internet. Excessive computer use, however, might further
isolate shy kids from their friends. Or it can take away from other activities
such as homework, exercise, sleep, or spending time with others. Parents
and teachers are often unaware that a child has an Internet problem until it
is serious, because it is easy to hide online activity and because Internet addiction
is not yet widely recognized. You may want to talk to your friend and his
parents; have an adult accompany you if you feel you need support. It is
important to promote healthy Internet use in your home, whether through
limiting online time, balancing computer time with physical and social activities,
or making sure your Internet-connected computer is in a public space
in your home.
DAILY LIFE
other people are saying about things
you are interested in. But just as you
should not talk to strangers when you
are in the outside world, you should also
use caution when chatting in the cyber
world. Unfortunately, there are people
surfing the Web who present a threat to
kids. They may be adults posing as
another kid or somehow lying to you
about who they are and what they want.
To be safe, never give anyone you don’t
know personal information about yourself
online—including your name,
address, phone number, or e-mail password.
And never agree to meet a person
you’ve chatted with online, even if that
person seems friendly or harmless. Let
your parents know if a stranger is sending
you e-mail or instant messages.
Can I register at any Web
site I choose?
No—it’s important to ask your parents
first before registering at a Web site.
Many sites offer special benefits if you
register as a member, which involves providing your name, e-mail address, and
sometimes home address, phone number, and other information. While some sites
protect your privacy and only use that information to send you things you want,
others sell your information to advertisers or organizations. As a result of registering
at a Web site, your family may end up getting lots of unwanted e-mail, regular
mail, and phone calls from companies trying to sell you things. And even if you find
a great deal online for something you really want, never give out your parents’ credit
card information unless they say it’s okay.
What is a computer virus?
A virus is a malicious software program that infects computer files or hard disk
drives and then makes copies of itself. Many activities that kids do online can leave
computers vulnerable to viruses. E-mail attachments are a common means of distributing
viruses, but viruses can also be downloaded when you share files and open
instant message attachments. In order to keep your computer safe, never open an
e-mail attachment you haven’t requested. Send an e-mail to friends to confirm that
they meant to send you an attachment. Also, you can configure your instant messaging
program so you can’t receive files from other users. Never download any pro-
262 gram without checking with a parent first. You can protect your computer by
Computer games are really fun, but playing them all the
time is called an addiction. It is not healthy for you or your
friends to do nothing but play video games all the time.
always running up-to-date firewall software, by running antivirus software regularly,
and by periodically scanning your computer for spyware or other unwanted software
and immediately removing it.
BICYCLE TI PS
How does a bicycle work?
A bicycle is a simple device that increases the power that you have in the muscles
of your legs, taking you faster and farther than you could ever run. When you push
the pedals of your bike around once, the pedal sprocket—the wheel with teeth to
which the pedals are attached—goes around once, too. But it pulls a chain along,
one that is connected to a much smaller sprocket (with fewer teeth to grip each link
of the chain) in the center of your bike’s rear wheel. This smaller sprocket moves
around a number of times for each single turn of your pedals, moving your bike
wheels a lot faster than you’re moving your feet!
Some bicycles have several “speeds,” which means that they have a number of
gears (called derailleurs) that vary the rate at which the wheels turn. These extra
sprockets are located at the pedals and rear wheel of a bike, where levers move the
driving chain sideways, from one to another. A special spring system keeps the
chain tight when it changes from a larger to a smaller sprocket. Although you
might think that a rider would always want the wheels of his or her bike to move as
fast as possible for each pedal turn, that is not always the case. When going uphill,
for instance, a rider can get more force out of a wheel that turns fewer times, making
the task easier.
How do I brake?
Brakes can quickly stop the rotating wheels of a bicycle. On some bikes you can stop
by pedaling backwards, which activates a braking mechanism (coaster brake). On
other bikes, you activate the brakes by squeezing levers located on the bike’s handlebars.
While a person’s leg strength is far greater than the strength in his or her
hands, a hand brake uses a set of three levers that increase the original squeezing
force, making it strong enough to stop a speeding bike. A compressed hand brake
pulls a cable connected to two metal arms with rubber pads that grip a bicycle tire
rim, causing enough friction to stop it. After a quick stop, feel the brake blocks on
your bike—the friction makes them hot.
Why do bicycle tires lose air so fast?
Early bicycle tires were made out of solid rubber. (Before that, iron covered the edges
of wooden bicycle wheels.) Solid rubber tires made bicycling a bumpy experience
because they were unable to provide any cushioning on rough roads. When the airfilled
rubber bicycle tire was invented, it made riding a lot more comfortable. 263
DAILY LIFE
But along with the comfort of air-filled tires came the frequent task of filling
them up. The rubber that is used to make bicycle tires is thin and porous, which
means that it has tiny microscopic pores, or holes, through which air can escape
over time. Air that is pumped into bicycle tires is pressurized, meaning it is compressed
into a much smaller space than it would ordinarily occupy. Without pressurized
air inside, a bicycle tire would not have its firm shape. Air under high pressure,
like all gases, moves or migrates to surrounding areas that have lower pressure,
traveling even through fairly solid materials. Air in a bicycle tire naturally
tries to escape through the valve stem that is used to fill it and the inner tube that
holds it. So even bicycles that don’t undergo the wear-and-tear of frequent use eventually
end up with flat tires.
Why do little kids ride tricycles instead of bikes?
The triangular shape of a tricycle, with its three wheels spread apart, is much more
stable than a regular bicycle, which balances on two aligned wheels. (The “tri”
[three] and “bi” [two] before “cycle” refers to the number of wheels each vehicle
has.) Tricycles suit young children well; with larger heads and undeveloped muscles,
little ones lack the coordination and balance needed to ride regular bikes. But
as soon as they can learn to pedal, children can ride a tricycle, turning leg power
into wheel power.
A tricycle is built for stability and not for speed: its pedals are attached to a
sprocket in the center of its large front wheel, which moves around once for each
completed pedal turn. So the larger the front wheel of a tricycle, the faster it will
264 go—but it cannot be so large that young legs cannot reach the pedals! This design
Why are men’s and women’s bicycles built differently?
The crossbars on bicycle frames give them added strength. On a man’s or
boy’s bike the crossbar extends straight across the top of the frame, just
below the seat. On a woman’s or girl’s bike the crossbar is attached to the seat
tube at an angle, far below the seat. Because of this structure, women’s bikes
are not nearly as sturdy as men’s bikes.
When bicycles were first built, women didn’t wear pants; they always wore
skirts or dresses. The low crossbars on their bikes allowed them to get on,
ride, and get off with dignity—without showing their underwear! The design
of bicycles for women and girls, then, is based on a long-standing tradition
and still offers the advantage of easier mounting and dismounting. But today,
women and girl bicyclists wear pants or shorts when riding and can easily use
bikes designed for men. As a matter of fact, serious female bicyclists who do a
lot of riding or travel through tough terrain and need bikes with sturdier
frames buy those made for men.
makes a tricycle unlike a regular bike,
which has chain-driven sprockets that
move its wheels a lot faster than its
rider’s feet. Tricycles are also easier for
little ones to steer and turn because
they are pulled forward by the movement
of their front wheels; regular
bikes are powered by their rear wheels.
What were high-wheelers?
A high-wheeler was an early type of
bicycle that had pedals attached to its
front wheels, just like tricycles. To give
high-wheelers greater speed, bike
designers kept enlarging the front
wheels, some of which measured up to
64 inches (163 centimeters) across.
Known as “high-wheelers,” they were
quite dangerous to ride—bicyclists
couldn’t touch the ground with their
feet when they stopped, and they often
fell forward over their handlebars when
they hit bumps. A high-wheeler was also
hard to balance because it had only one
rear wheel, not two.
Can I ride my bike or scooter anywhere or whenever I want to?
While riding bicycles and scooters are a lot of fun, it is important to remember that
these items are not just toys. They are machines that can sometimes be involved in
accidents that result in injury. So all bike riders—as well as in-line skaters, skateboarders,
and scooter riders—must follow certain rules, for their own safety and the
safety of others.
Bicyclists have to follow some of the same traffic laws as people who drive cars
do, like stopping at stop signs and obeying traffic lights. But bike riders also have
their own special set of safety rules. They have to make sure that their bikes have
reflectors in order to ride safely at night. They can’t let other people ride with them
on their bike—like on bicycle handlebars—because that threatens their balance
and could lead to accidents. One of the most important of all bicycling rules is wearing
a protective helmet. So, it doesn’t matter where you will be riding or for how
long—you should always follow traffic laws and safety tips.
Why is it important to always wear my helmet?
Each year, about 150,000 children are treated in emergency rooms for head injuries
that occurred while riding their bikes. Many bike-related injuries could be avoided 265
It’s important to wear a helmet whenever you ride your bike.
Accidents leading to head injuries can happen when you
least except them. Be prepared!
DAILY LIFE
Why don’t school buses have seatbelts?
School buses provide students with the safest form of transportation to and
from school, according to research by the National Academy of Sciences.
School buses have to meet rigid federal construction standards for the sides
and top of the bus, fuel tanks, and inside of each bus. The thick padded seats
and seatbacks provide a passive form of crash protection known as “compartmentalization.”
This padding, combined with the placement of the seating area
high above the impact zone (with most other vehicles), offers a protection that
has resulted in an unmatched record of passenger safety. Especially for small
students, seatbelts can be more harmful than helpful, and in most states these
are being phased out from school buses. Only since the early 2000s have lapshoulder
seatbelts been available on school buses in some states.
if riders wore their helmets properly. Wearing a bike helmet reduces the risk of
brain injury by as much as 88 percent and reduces the risk of injury to the face by
65 percent. That is why many state laws say that bicyclists under the age of 14 are
required to wear approved bicycle helmets when they ride their bicycles. If your
friends don’t wear helmets when you bicycle together, teach them by your wise
example. In the United States, bicycle helmets save one life every day and prevent
one head injury from happening every four minutes.
What are the reflectors on my bike or scooter for?
Reflectors help keep you safe if you are riding in the dark. When a car approaches
you the light waves produced by its headlights hit your reflectors and bounce back
into the eyes of the driver, making him or her aware of where you are. This helps
that person drive past you carefully. Reflectors are usually made of hard colored
plastic with a backing of reflective material. The inner surface of the plastic is cut
into many tiny angles, kind of like the sides, or facets, of a diamond. These bounce
light waves around inside before they are reflected away, which explains why they
are so startlingly bright. Reflectors are located at the front and back of your bike, as
well as on your pedals. That way you can be seen regardless of the direction in
which you are heading.
OTHER SAFETY TI PS
Why do I need to wear a seatbelt in the car?
Seatbelts rock! Studies have found that wearing a seatbelt can save your life in the
event of an automobile accident. In fact, you are 45 percent more likely to survive
266 a crash if you’re wearing a belt. According to the National Highway Traffic Safety
Administration (NHTSA), an estimated
5,500 lives could be saved each year by
increasing the level of safety belt use in
the United States to 90 percent. That is
why there are mandatory safety belt
laws in 49 states and the District of
Columbia. In most states, these laws
cover those riding in the front seats,
although belt laws in 19 states and the
District of Columbia cover all rear seat
occupants, too.
How can I stay safe when I
am walking?
Walking is a great way to exercise. Walking
burns calories, strengthens back
muscles, strengthens bones, reduces
stress, helps improve your mood, helps
you sleep better, and requires no equipment. Best of all, it is free and can be done
almost anywhere! Walking also helps build community. A simple wave as you walk
by your neighbors’ yard helps strengthen community connections. Walking, instead
of driving, also reduces traffic congestion and pollution.
It is important to be careful when you walk. During the day, wear bright, light
clothing; at dusk, dawn, or nighttime, wear reflective clothing, with strips of material
or tape attached that bounce back light. Be careful. Always look both ways
before crossing the street, obey traffic signals, and use the crosswalk. Be aware of
all traffic, and make sure that drivers see you by making eye contact with them
before you cross the street. Walk against the direction of traffic whenever possible.
And remember, too, that walking with a friend is always safer than walking on your
own. Encourage a friend or family member to join you! Be thoroughly familiar with
your route. Know the location of phones, police or fire stations, and businesses, and
always bring along some form of identification, like a school ID card.
Should I talk to a stranger?
No. Although most of the strangers you encounter treat children with respect, there
are dangerous people who do harmful things to children. Sometimes hurtful people
can fool kids into thinking they are gentle and helpful. They may have pleasant
faces and friendly voices, and they may say nice things. So it’s important to follow
personal safety rules with all strangers. What can you do to stay safe when you are
outside or away from home? Play with at least one other kid in familiar places. Don’t
go near a car with a stranger in it, even if the person says he or she has a gift for
you, or needs your help to find a lost pet, or is asking for directions. Think about it
this way: if an adult really needed help, he or she would ask another adult, not a kid.
Do not accept a ride home from school or anywhere from someone you don’t know, 267
Even in the daytime, crossing the street can be dangerous.
Be aware of your surroundings, wear bright-colored clothes,
and walk with friends and family whenever you can.
DAILY LIFE
even if that person says your parents asked him or her to pick you up, and even if
that person knows your name. Avoid situations where you are alone with an adult
you don’t know unless it is a person your parents have arranged for you to meet
with, like a doctor, teacher, or counselor.
If a stranger approaches you, tell that person to please not speak to you because
you don’t know him or her. If the stranger continues toward you, start yelling and
run away. If you need help, your best bet is to go to a public space like a store, a
library, or a police station. Afterward, be sure to tell your parents about your experience
with the stranger.
What should I do if I find a gun?
Studies have shown that hundreds, perhaps even thousands, of children and
teenagers are accidentally killed by guns in the United States each year. Millions of
American kids have access to guns in their homes. People use guns all the time in
movies and television shows, and the action scenes in these shows make guns look
exciting and powerful. What these shows can’t really convey is the massive, painful
destruction an exploding bullet causes when it hits a person’s body.
While many kids understand that, in real life, guns can be very dangerous and
can cause great harm, most still find guns fascinating. If an adult is supervising and
your parents have given their approval, it’s okay to look at and even touch an
unloaded gun. But if you are alone or with other kids and you come across a gun,
remember that it is not a toy and should not be handled. Guns should never be
pointed at another person, even if you intend it as a joke. If you find a gun in your
own house, a friend’s house, or elsewhere, as tempting as it might be to play with
it, remember the damage that guns can cause and leave it alone. If you’re away from
home, leave right away and tell your parents what happened. Your parents may be
upset and worried that you found a gun, but they will be very glad that you told
them about it because then they can help you stay safe.
What is a Neighborhood Watch?
Neighborhood Watch is a crime-prevention program based on safety education and
common sense. It teaches citizens how to help themselves by identifying and
reporting suspicious activity in their neighborhoods. It allows you, your family
members, and your neighbors the opportunity to participate in your neighborhood,
make your neighborhood safer, and improve the quality of life in your area. There
are many Neighborhood Watch programs in towns and cities across the United
States, and each one is a bit different. The groups typically focus on observation and
awareness as a means of preventing crime. People in the neighborhood meet (usually
at potlucks or backyard barbeques), get to know one another, agree to look out
for the welfare of each other, and sometimes patrol their neighborhood on bikes or
by car, much as a police officer would. They report suspicious activity to the local
authorities. Most neighborhood groups are organized around a block or a subdivi-
268 sion and are started with help from a local law-enforcement agency, such as the
police or sheriff’s department. Often there is a sign in the area that states that it is
a Neighborhood Watch neighborhood.
What safety rules should be followed during a thunderstorm?
If you find yourself in a thunderstorm, the government’s National Weather Service
recommends following a few safety rules. First, get away from metal fences at ball
fields. Drop metal objects such as golf clubs, and backpacks. Remember: metal is a
very good electrical conductor, and you don’t want to attract lightning! Lightning
may be ready to strike near you if you feel your hair stand on end or your skin tingle.
Crouch down or drop to your knees, but do not lie flat on the ground. The safest
place in a lightning storm is inside a sturdy structure—such as your home, school,
or a local business. Get inside the building, but do not stand by open windows,
doors, or patios during a storm. Experts also recommend unplugging unnecessary
appliances and staying off the phone.
My nose sometimes bleeds while I play sports or after practice. Why?
Nosebleeds are fairly common because the nose is located in a vulnerable area (the
center of the face!) and filled with blood vessels that can easily bleed. In some cases,
nosebleeds can be severe and involve lots of blood; in other situations, bleeding is
minor. The sensitive nose can bleed easily when hit or when fractured—even a
brush against the nose can cause it to bleed. Often this happens in contact sports,
and if practice takes place outdoors, where it is cold and dry, there may be a higher
chance of getting a nosebleed. A dry climate or heated indoor air irritates and
dries out nasal membranes, causing crusts that may itch and then bleed when
picked. The common cold may also irritate the lining of the nose, and bleeding may
happen after repeated tissue blowing. When you combine a cold with dry winter air,
you have the perfect formula for a nosebleed!
What items should be in a first-aid kit?
Whether you go to the store with an adult to buy a first-aid kit or work with an adult
to put one together, it should include all the items you may need in case of an emergency.
Make sure an adult includes any personal items such as medications and
emergency phone numbers or other items your doctor may suggest. Check the kit
regularly. Make sure the flashlight batteries work. Check expiration dates and 269
What are the odds against being struck by lightning?
The National Oceanic and Atmospheric Administration estimates the odds
of being struck by lightning are 1 in 700,000. However, the odds drop to 1
in 240,000 based on the number of unreported lightning strikes. The odds of
being stuck by lightning in one’s lifetime are 1 in 3,000.
DAILY LIFE
replace any used or out-of-date contents.
If you are compiling your own,
the Red Cross and the American Medical
Association recommend that all first-aid
kits include the following items:
• absorbent compress dressings
• adhesive bandages, in assorted sizes
• adhesive cloth tape
• antibiotic ointment packets
• five antiseptic wipe packets
• aspirin or aspirin substitute
• blanket
• breathing barrier (with one-way valve)
• first-aid manual
• hydrocortisone ointment packets
• instant cold compress
• nonlatex gloves
• oral thermometers
• roller bandages
• scissors
• sterile gauze pads
• triangular bandages
• tweezers
TOUGH QUE STIONS:
DIVORCE, DEATH, AND GOD
Why do husbands and wives divorce?
Husbands and wives divorce when they can no longer live happily together. It is
usually a sad thing, because when people marry they expect to be with their partner
for the rest of their lives. But over the course of a marriage things happen,
people can change, and the happiness that the couple was so sure of in the beginning
sometimes disappears. When couples with children get divorced it is even
more unfortunate because more people are affected. Many children feel bad when
their parents divorce because their family will not be the same. After a divorce,
they generally do not see one of their parents as much as they did before. Still,
just because the feelings between a mother and a father change doesn’t mean
that their love for their children changes in any way. It’s important to remember
that divorce is something that happens between a husband and wife—it has
nothing to do with the kids. Many children feel that if they adjust their behavior
somehow their parents will want to stay together, but divorces are not caused by
anything 270 children do.
A well-supplied first-aid kit is a good thing to always keep
at your house and in the car.
Who decides which of the divorced parents their children will live with?
Because a marriage is a legal partnership, its dissolution, or end, takes place by a
judgment of a court. The court, then, awards custody of children after a divorce. The
judge that presides over the court makes this decision, ideally keeping the best interests
of the children in mind. A judge’s involvement is especially important when parents
cannot agree about who should be the main caregiver for their children and
provide their main home. But in the best cases, both parents and children decide
together how they would like custody to be awarded, and they let the court know
their preferences. Sometimes joint custody is the solution, which means that the
parents share responsibility for the kids and the children divide their time equally
between their mother and father and their separate homes. Most of the time, however,
one parent becomes the custodial parent and the children live with her or him,
while the other parent has visitation rights, which means that he or she can see the
children at certain times, like on weekends or during summer vacations.
Why do people have to grow old?
Growing old is part of being a living thing. Every plant and animal must go through
a cycle of life that involves a beginning, a middle, and an end. Actually, as soon as
we are born we begin aging or growing older. But when we talk of growing old we
think of the physical changes that occur when bodies cannot grow and repair themselves
as they once did. At about age 30 the signs of aging start to appear, though
for most people the physical changes are not really obvious until many years later.
Why do people have to die?
All living things must die. It is a part—the final part—of the biological cycle of
life. A flowering plant, for instance, springs from a seed, grows, blossoms, pro- 271
What happens as we age?
As people age, skin may begin to sag and wrinkle, and hair may turn thin
or gray. Over time muscles become less strong and flexible, and bones
may become more brittle and breakable. Blood may not flow through the body
as well as it once did, which slows the activity of the brain and the senses. The
immune system becomes weaker and does not fight off sickness as well as
before. People experience these changes at different ages, but all will grow old
as they near the end of their life cycle. It may seem sad that a person has
grown old and cannot do all the things they once did, but try to look at it this
way: When people grow old, that means they have been lucky enough to avoid
things like accidents and diseases that could have cut their lives short. And
better yet, regardless of the physical changes of old age, many people remain
healthy and lead full and happy lives. DAILY LIFE
duces seeds for the next season, fades,
and dies. Similarly, an animal is born,
grows and matures, reproduces, ages,
and dies. Old plants and animals must
make way for new plants and animals,
through which the cycle of life can
continue. If plants and animals did not
die, eventually there would not be
enough food, water, or space in the
world for life to flourish. Even dead
plants and animals contribute to the
cycle of life, for their remains enrich
the soil for the next generation of living
things.
New generations of plants and animals
are needed to ensure the survival
of life on our planet. The world’s environment
is constantly changing, and
new plants and animals—with unique characteristics resulting from the combined
genetic contributions of their parents—may be better equipped to survive
under the evolving conditions. This process of change and improved survival,
which has taken place gradually over millions of years (ever since life began), is
called evolution.
Just like all plants and other animals, people also experience this biological
cycle of life. A person is born, grows into physical maturity during adolescence,
experiences adulthood, ages, and then dies. At death, the cycle of life is completed
as that individual makes way for following generations.
What happens when people die?
When death occurs, blood—which carries oxygen to all the cells of the body—
has stopped circulating. This stoppage may be caused by damage to the heart,
which is the muscle that pumps blood throughout the body, or by damage to the
brain, which gives the signals that direct the heart to do its pumping. (Other circumstances,
like severe accidents, also stop blood flow.) But whatever the reason,
once blood stops bringing its life-giving oxygen to the body’s billions of
cells—the building blocks that make up the human body—the death of those
cells starts to occur. When the brain, which is the body’s command center, goes
without oxygen for about 15 minutes, all cells there die. While machines can
help our lungs breathe or our hearts pump blood, no machine can assume the
complex functions of the brain. Without a brain, we cannot live. Soon after a person
dies, an official document called a death certificate is filled out and later filed
as a record with the local government. It includes such information as time,
place, 272 and cause of death.
Dealing with the death of a loved one is never easy, but it is
a natural part of life. Don’t be afraid to talk to your family
about this issue if you have questions.
Does it hurt to die?
Nobody who has died has been able to come back to tell us about it, so it is impossible
to know whether dying hurts. But people who have had “near-death” experiences—
those whose hearts have stopped, for instance, but were later restarted—
have only good things to report. Most tell of a peaceful sensation of floating above
their bodies. A number also describe traveling through a tunnel toward a beautiful
light or having loving meetings with friends and relatives who have died before
them. Scientists know that when a person is in a state of very low oxygen—often a
condition that precedes death—he or she experiences feelings of euphoria, or great
happiness. So as far as we know, the act of dying is not painful at all.
Many sick people welcome death. The same wonders of medicine that have
allowed people to reach old age have also enabled them to live through long, and
sometimes painful, illnesses. Often, death is seen as a welcome end to pain, both for
the ill person and for the family and friends who have watched their loved one suffer.
People with strong religious faith, too, may fear death less because they believe
they will journey to a better place.
What do we do after a person dies?
Throughout human history and in places around the world, people have done many
different things with their dead. The ancient Egyptians, for instance, took great care
when preparing the bodies of their dead rulers; it was believed that their leaders were
immortal and would need their bodies in another world after death (the afterworld). In
a process that took several months, ancient Egyptians carefully preserved dead bodies
through a process called embalming. They wrapped the bodies with layers of linen,
wax, and spices. Some of these mummies still exist today, some 6,000 years later. 273
Can people who die see and talk
with living people after they are gone?
Although for centuries living people have reported seeing and talking to
people who have died, there is no scientific proof that this can be done or
that visiting with “ghosts” is possible. Although some people claim they have
special skills allowing them to contact and receive messages from the
deceased (such people are known as spiritualist mediums), their communications—
usually conducted during meetings called séances—have generally
proven to be fake. Sometimes, though, people who have recently had a loved
one die feel that they can sense that person’s presence with them; they may
even talk to the deceased. It is likely that these sensations arise out of very
powerful feelings of loss and vivid memories of the loved one. For many people,
believing that a physical connection continues after death lessens their
sorrow. It is one of many ways through which people keep alive the memories
of those who have died.
DAILY LIFE
In the United States today, most people are buried in coffins. Funeral ceremonies
take place so that people can honor the deceased and give comfort and
support to his or her family and friends. Music, prayers, and eulogies—speeches
remembering and praising the dead person—are often a part of these ceremonies.
A funeral usually ends when the deceased is taken to a cemetery, a place where
bodies are buried in the ground. A headstone or marker listing the person’s name,
birth and death date, and other information is placed at the burial spot. Family
members and friends may later visit and decorate the grave site with flowers in
memory of their loved one.
Many times, too, people choose to be cremated instead of buried. In a cremation,
the body is burned until nothing but ashes remain. According to the wishes of
the person who died, these ashes might then be buried, or kept in an urn, or sometimes
they are scattered over the land of a place that was important to the deceased.
One of the most creative things that were done with somebody’s ashes happened
when Gene Roddenberry (the creator of the Star Trek series) had his ashes put
aboard the space shuttle Columbia after his death in 1991. Later, his wife Majel’s
ashes were also launched into space, as were the ashes of James Doohan, who played
Scotty in the original series.
Why do people cry when someone dies?
Crying is a way of expressing sadness. It helps people who have lost someone
close to them express their grief and sorrow. (Talking about the dead person also
helps.) People cry because they will never again see the person who has died and
they know they will miss that person. If the death is unexpected, the tears may
also be caused by feelings of shock and anger. During the period immediately following
a person’s death, when the loss of that loved one is felt most sharply,
grieving people usually are not comforted by the fact that dying is a natural and
necessary process that happens to all living things. As time passes, however,
many people begin to accept the loss of their loved one, and the pain of that loss
becomes a bit easier to bear. Thinking of the person after some time has passed
brings less sadness and maybe even some pleasure as good times with the loved
one are remembered.
Where do people go after they die?
Because no one has come back to our world after dying, it is not possible to know
for sure what happens to people after death. Nearly all the religions of the world
believe that some kind of existence continues after life on Earth stops, that a person’s
soul or spirit continues to exist—in a way we can’t really imagine—even after
his or her body is dead. In fact, a lot of religions teach the belief that our life on
Earth is a stage or time of preparation (or a test by which we’re judged) that leads
to a final, perfect state of existence that we will share with God in a spiritual realm
after we die. Some people who don’t subscribe to religious beliefs about an afterlife
think that people simply end when they die, that once the physical body has died,
274 all awareness and existence ceases.
What is heaven?
According to many religions based on
Judaism and Christianity, heaven is a
state of existence where a person’s spirit
is at last united with God forever. In a
number of Christian religions, heaven is
believed to be the reward for people who
have lived good lives according to certain
rules of thought and behavior that
God has made known through scriptures
(sacred writings, like the Bible)
and through the teachings of churches
and religious leaders. (Those who have
not followed these rules, it is believed by
many, go to a place of punishment
known as hell.) Many Christians believe
that at the end of the world their human
forms will be resurrected in a perfect
state—just as the body of Jesus Christ
was, when he arose from the dead on
Easter morning—and join their souls or
spirits in heaven for eternity. This idea
has led to the concept that heaven is an
actual place—located above—with
physical characteristics. Over the centuries,
through pictures and writings, people have tried to create images of heaven,
imagining a place of perfect happiness perched atop fluffy white clouds. It has often
been portrayed as a place full of things that would bring happiness on Earth, possessing,
for instance, pearly gates and streets of gold.
What is hell?
In many Christian religions, hell is the place of punishment where people go after
death if they have not lived good lives and followed the rules of thought and behavior
set forth by God in scriptures (sacred writings, like the Bible) and in the teachings
of churches and religious leaders. Hell is believed to be a horrible place because
it is the opposite of heaven; hell is a place where a person’s spirit will forever be
deprived of the presence of God. To never know the joy of God’s presence, believers
feel, is so painful that it is compared to burning in fire forever, one of the most awful
things that can be imagined. Just like with heaven, people have tried over the centuries,
through paintings and writings, to create images of hell, a place of enormous
suffering. And as heaven is thought to be located above, hell is said to be down below.
Satan, or Lucifer—who, according to the Bible, was a favorite angel of God’s until he
disobeyed God—is the ruler of hell. In many Christian religions, Satan and his
wicked angel followers (devils) are thought to be the cause of evil in the world,
always tempting people to be bad. Many non-Christian religions also teach of a place 275
Is there a heaven? Are angels real? Many people believe
they are, but only you can decide for yourself whether you
believe in these religious issues.
DAILY LIFE
like hell where people who have led bad lives on Earth must go after they die. Even
the ancient Greeks and Romans (who lived before the development of Christianity)
believed in an underworld, a place where people traveled to after death. Good and bad
people lived in different places in this ancient underworld.
Are angels real?
In many religions, angels are powerful spiritual beings who live with God but who
sometimes become involved in the lives of people on Earth, often bringing God’s
messages to them. According to the Bible, for instance, the angel Gabriel appeared
before the Virgin Mary and announced that she would become the mother of Jesus
Christ. In the Muslim religion, Gabriel revealed to the Prophet Muhammad the
words of Allah (God), which were recorded in the Koran, the sacred book of Islam.
Angels are not believed to have physical bodies, but they may look like people when
visiting Earth. Over the centuries, artists have portrayed them in many ways: neither
men nor women, angels have human forms (appearing as babies, children, or
adults) and are winged for travel to their heavenly home. In a few religions, like
Roman Catholicism, it is believed that each person on Earth has a special angel who
watches over him or her and gives protection from the temptations of the devil;
such a being is called one’s guardian angel. The answer to the question of whether
angels are real, then, is a matter of faith.
Who is God?
It is believed by many people that God is the perfect spiritual being who has always
existed and who created everything. (Although having no physical form and therefore
no gender, God is usually referred to as a male.) Believers feel that God made
the universe and all that is in it. God is thought by many to be all-knowing and allpowerful.
In many religions, it is thought that the souls of people who have led good
lives on Earth join God after they die.
While many of the world’s most widely practiced religions—Christianity, Islam,
Judaism—teach of the existence of a single supreme being (called God in Judeo-
Christian religions and Allah in Islam), some religions teach that there are many
gods. Hinduism (practiced by many people in India and elsewhere) teaches that
there are many gods, but all are part of one divine being, called Brahman. Some
people feel that God is everywhere and part of everything—the universe itself, and
all life, and all natural occurrences, are divine. Others, called atheists, do not believe
a supreme being exists in any form.
276
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Macaulay, David. The New Way Things
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Oxlade, Chris. Houses and Homes.
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Parker, Steve, and Giovanni Caselli.
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Pascoe, Elaine, Deborah Kops, and
Jenifer Morse. Scholastic Kids
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Tucci, Paul A. The Handy Geography
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Silverstein, Alvin, and Virginia Silverstein.
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Things around Us. New York: Time-
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The Ultimate Book of Knowledge. New
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The Universe (First Facts series). New
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Visual Encyclopedia of Science. London:
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Waldbauer, Gilbert. The Handy Bug
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Wood, Robert W. The McGraw-Hill Big
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The American Presidency:
http://ap.grolier.com.
ASPCA Animaland:
http://www.animaland.org.
Ben’s Guide to U.S. Government for
Kids: http://bensguide.gpo.gov.
DiscoverySchool.com:
http://school.discovery.com.
Enchanted Learning:
http://www.enchantedlearning.com.
Flags of the World:
http://www.fotw.net/flags/index.html.
50 states.com:
http://www.50states.com.
Guinness World Records:
http://www.guinnessworldrecords.com.
Infoplease.com:
http://www.infoplease.com.
Kidport Reference Library:
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KidsHealth: http://kidshealth.org.
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279
FOR MORE INFORMATION

A
abacus, 163–64, 182, 182 (ill.)
Achilles heel, 200
acid rain, 46–47
acorns, 98–99
acre, 185
adulthood, 240
Africa, 22–23, 23 (ill.)
afterlife, 274–76
aging, 212–13, 271
agriculture. See farming
air, 27, 234
air pollution, 47
airplanes, 40, 214
airports, 113–14
alarm clock, 195–96, 196
(ill.)
Alaska, 140
alcohol, 229–30
alginates, 102
Allah, 276
allergies, 224
alligator, 73 (ill.), 73–74
allowance, 232
aloe vera, 102
alphabet, 250
Alyattes, 231
A.M., 196
Amazing Flynapping Arum of
Sardinia, 90
Amazon ants, 66
Amazon water lily, 88
amendments, 134
Amenhotep I, 194
American Sign Language,
250 (ill.), 250–51
ammonia, 173
amphibians, 74
analytical engine, 163
Andromeda galaxy, 4
angels, 275 (ill.), 276
angiosperms, 81–82
animals, 56–64. See also
mammals
coral, 71
first, 50
kinds of, 56–57
and seeds, 82–83
in space, 19
vs. plants, 79–80
annual flowers, 85, 86 (ill.)
Antarctica, 22–23, 23 (ill.),
28, 34, 42
anteater, 64
antibiotics, 224, 225 (ill.)
apocrine glands, 210
apple trees, 100
April, 191
aquaculture, 120–21
arachnids, 67
arch bridge, 148–49
arching back, 243
Arctic tundra, 24–25
Aristotle, 2
Arizona, 141
armor, 128–29, 129 (ill.)
Armstrong, Neil, 19
Arrhenius, Svante, 43
Asia, 22–23, 23 (ill.), 106
Asia-Pacific region, 107
ASIMO (Advanced Step in
Innovative Mobility), 177
asteroid, 14
astronauts, 16–17, 18–20, 20
(ill.)
Atlantis (lost civilization),
127
Atlantis (space shuttle), 16
atoms, 114
attention deficit hyperactivity
disorder (ADHD), 249
“Audion,” 158–59
August, 191
Augustus, 191
Australia, 22–23, 23 (ill.)
authoritarian governments,
130
autocracy, 130
Autolycus, 180
automobile, 147
autumnal equinox, 193
avalanche, 36–37
avoirdupois weight, 188
B
Babbage, Charles, 163
babies, 235–36
Babylonians, 179, 184
backbone, 198–99
bacteria, 221–22, 223–24
Bain, Alexander, 161
baker’s dozen, 186
bald eagle, 136
Baldwin, Anna, 117
“ballooning,” 68
banyan tree, 97
bar codes, 170
barking, 242 (ill.), 242–43
barns, 118 (ill.), 118–19
bats, 57 (ill.), 57–58
bay, 38–39
B.C., 190–91
beam bridge, 148
beard, 209
bears, 62
bed-wetting, 238
beetles, 64, 219
belly button, 212 281
Index
Note: (ill.) indicates photos and illustrations.
Benz, Karl, 147
Bermuda Triangle, 40
bicycles
brakes, 263
high-wheelers, 265
men vs. women, 264
operation of, 263
reflectors, 266
scooters, 265
tires, 263–64
traffic laws, 265
tricycles, 264–65
biennial flowers, 85–86
Big Bang theory, 1, 3 (ill.)
Big Crunch theory, 2
bighorn sheep, 63
bilingual, 251
Bill of Rights, 134
billion, 181
bimetal switch, 175
binary digits (bits), 162
birds
bald eagle, 76
beak, 76
“birds of prey,” 77
breeds that don’t fly, 75
crashing into windows, 77
eagle, 77–78, 78 (ill.)
eyesight of, 77
feathers, 76
flying capability, 74–75
flying south for winter,
75–76
hummingbird, 78
peacock, 78
worms, 77
black hole, 13
blindness, 228–29
blinking, 213
blood, 204–6
blue sky, 28
blue whale, 59–60
Bluford, Guion S., Jr., 18
boats, 154–55
body temperature, 168
bones, 170, 197–99
bonsai tree, 99, 99 (ill.)
booger, 216
Borglum, Gutzon, 37
Bosporus Straight, 22
botany, 81
bowel movement, 221
Brachiosaurus, 51–52
bracket fungus, 95
brain, 206, 207
brain freeze, 216
brain stem, 206
brakes, 263
breathing, 207, 208
bridges, 148–51
bristle-cone pine tree, 96
Brooklyn Bridge, 150 (ill.),
150–51
Brown, Samuel, 147
bruise, 209
brushing teeth, 216–17
buck teeth, 244
Buddhism, 110
building blocks, 204
buildings, 144–46
bulb, 85
bullying, 255–57, 256 (ill.)
burial, 274
Burj Dubai skyscraper, 145,
145 (ill.)
burning, 175–76
burp, 220
buses, 266
butterflies, 65–66
buttock, 200
C
cable car, 147
cacti, 92
Caesar, Julius, 190, 191, 191
(ill.)
calendars, 188–89, 189–90
California, 116, 140–41
camera, 169
cantilever bridge, 149
car seatbelts, 266–67
carats, 185
carbon footprint, 44–45
cardiac muscle, 200
carmine, 219
Carnegie, Andrew, 258
carnivorous plants, 88–90, 89
(ill.)
carob seeds, 185
carrageenans, 102
carrion flower, 88
Castro, Fidel, 130
cat, 227
caves, 37
cells, 201–4
cellular phones, 161–62
Celsius, Anders, 34–35
cemetery, 274
census, 106
century, 191
cerebellum, 206
cerebrum, 206
Challenger (space shuttle),
16, 20
Chapman, John, 100
charley horse, 201
cheetah, 58
chicken soup, 226
child custody, 271
children, 106
Chinese language, 109
Chinese lunar calendar, 190
chlorophyll, 80
chores, 233, 233 (ill.)
Chrétien, Jean-Loup, 19
Christianity, 110
chromosome, 237
cigarettes, 230, 230 (ill.)
circulatory system, 202
cities
airports, 113–14
dams, 113–14
factories, 112
landmarks, 112
largest, 111
megalopolis, 111
metropolitan area, 111
nuclear energy, 114–15,
115 (ill.)
smallest, 111
subway system, 112–13,
113 (ill.)
citizen, 135
Civil War, 128
Clavius, Christoph, 190
Clement, William, 195
climate, 35
climate change, 43
clocks, 194–96
clot, 209
clothes, 109, 238
clouds, 28–30
cobweb, 234
coco de mer tree, 100
coconuts, 100
coffeemaker, 174
coins, 231–32
coldest days, 33–34
colonies, 138, 138 (ill.)
Colorado, 141
Colossus computers, 164
Columbia (space shuttle), 16
Columbus, Christopher, 106,
139
Colvin, Lee, 117
combine harvester, 116–17
comets, 13–14, 14 (ill.)
282 common cold, 226
community
firefighters, 258, 258 (ill.)
food bank, 260
homeless, 259–60, 260
(ill.)
homeless shelter, 259–60
philanthropy, 258
police officers, 257
uniforms, 259
volunteers, 257, 258–59
compact disk (CD), 170–71
Compsognathus, 52
computer virus, 262–63
computers, 157, 162–66
Congress, 106, 132–33
coniferous trees, 99
constellations, 13
constipation, 221
Constitution, 134
constitutional governments,
130
continents, 22–23, 23 (ill.)
contrails, 29
convex lens, 171
Copernicus, Nicolai, 3
coral reefs, 39 (ill.), 39–40
cord, 185–86
corm, 85
cosmonaut, 18
cotton, 101
countries. See also
governments
Atlantis, 127
biggest, 125
flags, 127
formation of, 126
“landlocked,” 126–27
most with neighbors, 126
newest, 125
number of, 125
smallest, 126
United States, 126
war, 127–29, 129 (ill.)
cows, 117, 117 (ill.), 121–22
crabs, 70–71
craters, 27
creaking floor, 235
cremation, 274
cricket chirps, 34
crime prevention, 268–69
crocodiles, 55, 72, 73–74
Croesus, 231
crops, 120
cross-pollination, 84
crying, 240, 274
cubit, 184
Cugnot, Nicolas-Joseph, 147
culture
clothing, 109
definition of, 108
melting pot, 110–11
religions, 110
veils, 109 (ill.), 109–10
Curie, Marie, 144
cyberbullying, 260–61
D
Daguerre, Louis, 169
daguerreotype, 169–70
Daimler, Gottleib, 147
dams, 113–14
dandelion, 83, 83 (ill.)
dark energy, 17
Darwin, Charles, 58
Daylight Saving Time, 193
days, 191–92
deafness, 229, 250 (ill.),
250–51
death and dying, 271–76, 272
(ill.)
December, 191
deciduous trees, 98
decimal-based system, 187
deepest hole, 38
democracy, 130–31
deoxyribonucleic (DNA), 204
dermis, 208
deserts, 24, 92
detergent, 238
diaphragm, 220–21
diet, 217
digestive system, 202
digital cameras, 169
digital television, 159–60
dinosaurs
biggest, 51–52
communication, 54
crocodiles, 73–74
definition of, 52
eating habits of, 52–53
eggs, 53 (ill.), 53–54
era of, 51
extinction, 55 (ill.), 55–56
fastest, 55
fossils, 49, 50 (ill.)
return of, 56
skin, 54
smallest, 52
teeth, 53
warm-blooded vs. cold
blooded, 54
diplomacy, 128
disabilities, 228–29
discovery, 143
Discovery (space shuttle), 16
disease, 107
District of Columbia, 139
divorce, 270–71
dizziness, 215
DNA, 204
“dog days,” 34
dog racing, 140
dogs, 140, 227, 246
Dolly (sheep), 121
dolphin, 71–72
Doohan, James, 274
dozen, 186
dreams, 227
drugs, 229
dust, 234
dust mites, 216
dyslexia, 249
E
E. coli, 223
e-mail, 165–66
eagle, 76, 77–78, 78 (ill.)
ear thermometer, 168, 168
(ill.)
ears, 214–15, 229
Earth. See also planets
age of, 21
blue, 23
continents, 22–23, 23 (ill.)
covered in ice, 23
craters, 27
land and water coverage,
38
life on, 23–24
onion-like, 22
ozone layer, 27 (ill.),
27–28
shape of, 21–22
size of, 21
temperature, 35
Earth Day, 47
earthquakes, 41–42
eccrine glands, 210
echolocation, 58
eclipse, 11–12
Edison, Thomas, 143, 168
Egyptian calendars, 189
Egyptians, 105, 179
Einstein, Albert, 144, 249
Eisenhower, Dwight, 149
electric car, 147–48, 148 (ill.) 283
INDEX
electric eel, 69–70
electricity, 232–33
Elements (Euclid), 180
elephants, 62
elevators, 145–46
embalming, 273
Empire State Building, 112
endangered species, 60, 103
Endeavour (space shuttle), 16
endocrine system, 202
Enterprise (space shuttle), 16
epidermis, 208–9
epiphytic plants, 93
Eriksson, Leif, 105
escalator, 146
esophagus, 218–19
estuary, 40
etiquette, 237
Euclid, 180
Eudoxus of Cnidos, 180
Europa, 8
Europe, 22–23, 23 (ill.)
exercise, 226
Explorer 1, 16
explorers, 105–6
eyelashes, 213
eyes, 213, 214, 228–29
F
factories, 112
fading newsprint, 157
Fahrenheit, Gabriel, 34–35
Fairbanks, Richard, 166
faith, 276
farming
barns, 118 (ill.), 118–19
biggest farm states, 116
changes in, 116
cloning, 121
combine harvester,
116–17
cows, 121–22
crops, 120
fish farm, 120–21
flies, 122
food, 115–16
horses, 122–23
milk, 121–22
milking machines, 117,
117 (ill.)
organic farming, 120
pesticides, 120
pigs, 123, 123 (ill.)
rooster crowing, 121
seed drill, 117–18
windmills, 118
fart, 221
fax machine, 161
feathers, 76, 78
February, 191
Februus, 191
feces, 122
federal government, 131–32
femur, 198
Ferdania, Saudi Arabia, 111
ferns, 94
fertilization, 86, 236, 236
(ill.)
fiddleheads, 94
fingernails, 211
fingers, 210–11
fir trees, 99
fire extinguisher, 176 (ill.),
176–77
firefighters, 258, 258 (ill.)
fireplaces, 232–33
first-aid kit, 269–70, 270 (ill.)
first responders, 258, 258
(ill.)
fish
breathing underwater,
68–69
dolphin, 71–72
eel, 69–70
flying, 69, 69 (ill.)
living without water, 69
nest of bubbles, 70
porpoise, 71–72
salmon, 70
seahorse, 71, 71 (ill.)
shape of, 70
fish farm, 120–21
flags, 127, 136–37
flax plant, 101
Fleming, Alexander, 224
Fleming, Sandford, 192
flies, 122
floating, 88, 100
flooding, 114
floor, 235
Florida, 139–40
flowers
Amazing Flynapping
Arum of Sardinia, 90
annual, 85, 86 (ill.)
biennial, 85–86
bloom, 85
brightly colored, 86
closing up at night, 86–87
edible, 87
first, 85
largest, 87, 87 (ill.)
plants without, 81–82
Flowers, Tommy, 164
flying fish, 69, 69 (ill.)
food, 115–16, 218
food bank, 260
Ford, Henry, 148
forehead, 212
Forest, Lee de, 158–59
fortnight, 196
fossils, 50 (ill.)
definition, 49
entire animal, 50
future, 51
Founding Fathers, 247–48
Four Corners, 141
Franco, Francisco, 130
Franklin, Benjamin, 193
freckles, 210, 210 (ill.)
Friday, 192
friends, 253–54
frogs, 74
frown, 201
fruit, 99
fruit juice, 219
funeral, 274
fungus, 95, 211–12
funny bone, 199
G
Gabriel (angel), 276
Gagarin, Yuri, 18, 18 (ill.)
Galapagos Islands, 58
galaxies, 17
Galilei, Galileo, 15, 183, 194
games, 254–55
gamma-ray bursts, 17
garbage, 45, 45 (ill.)
gas giants, 6, 221
gelatin, 218, 219 (ill.)
gender, 237
genes, 203–4
genius, 248–49
germs, 222–23, 223–24
ghosts, 273
giant puffball, 95
“Giant Water Platter,” 88
Girard-Perregaux
(watchmaker), 195
Global Positioning Satellite
(GPS), 18
global warming, 43
glow-in-the-dark, 169
gnat’s eye, 186
284 God, 276
Goddard, William, 167
gold, 45
Golden Gate Bridge, 150
Gondwanaland, 23
good sport, 254–55
googol, 183
goose bumps, 212
governments. See also
countries; United States
democracy, 130–31
existence of, 129–30
federal, 131–32
involvement in, 132
types of, 130
U.S., 131
governor, 133
Grand Canyon, 37
grandfather clock, 194–95
grass, 102
gravity, 2
gray clouds, 29–30
gray hair, 212–13
Great Banyan Tree, 97
“green” (environment), 42,
43
greenhouse effect, 43
greenhouse gases, 43, 44
Greenland, 39
Gregory XIII, Pope, 190
grief, 274
groin, 212
growing old, 271
growing pains, 201
growth plates, 197
guinea pig, 244
gulf, 38–39
guns, 268
Gutenberg, Johannes, 157
gymnosperms, 82
H
hair, 209, 211
hair’s breadth, 186
Hallidie, Andrew S., 147
Hanno the Navigator, 105
Hartsfield-Jackson Atlanta
International Airport
(Atlanta, GA), 113
Hawaii, 141, 141 (ill.)
head, 209
head lice, 257
health, 221–27
heart, 220
heartbeat, 206–7
heaven, 275
hectare, 187
hedgehog, 60
helicopters, 153–54
hell, 275–76
helmet, 265 (ill.), 265–66
hemlock, 91
Henlein, Peter, 194
Henry, Joseph, 158
hermit crabs, 70–71
hibernation, 62
hiccups, 220–21
high-definition television,
159–60
high-wheelers, 265
highways, 149
Hinduism, 110
Hippocrates of Chios, 180
Hitler, Adolf, 130
Home Insurance Company
Building, 146
home schooling, 247, 247
(ill.), 248
homeless, 259–60, 260 (ill.)
homeless shelter, 259–60
homes, 232
homework, 250
Hoover, William, 172
hormones, 203, 226
hornbook, 157
horsepower, 186, 187 (ill.)
horses, 122–23
hottest days, 33–34
House of Representatives,
106
household chores, 233, 233
(ill.)
houseplants, 234
housework, 177
Howard, Albert, 120
howling, 242
Hubble, Edwin, 2, 16
Hubble Space Telescope, 15
(ill.), 16, 17
hugs, 239–40
Hum, Croatia, 111
human body
blood, 204–6
bones and joints, 197–99
death, 272
disabilities, 228–30
eating and drinking,
216–21
growth, 201–4
hair, skin, nails, 209–13
measuring units, 184
muscles, 199–201, 200
(ill.)
organs, 206–9
senses, 213–16
sickness and health,
221–27
substance abuse, 228–30
humerus, 199
humidity, 34
hummingbird, 78
humps, 60–61
hurricanes, 31–32
Hutchins, Levi, 195
Huygens, Christiaan, 195
hybrid cars, 148
I
ice, 34
ice cream headache, 216
iceberg, 39
icequakes, 42
igneous rocks, 36
iguana, 244
immune system, 202, 222
(ill.), 223, 226
in vitro fertilization, 236, 236
(ill.)
incisors, 244
industrial cities, 112
Industrial Revolution, 144
infinity, 183
inner ear, 215
insects
butterflies, 65–66
drown in pitcher plant, 89
eyes, 65, 65 (ill.)
growth of, 65
kinds of, 64
largest, 66–67
leeches, 68
maggots, 68
number of, 64
slaves, 66
and spiders, 67
“vicious predator,” 67
“instant” cameras, 169
integumentary system, 202
International Date Line, 192
International Earth Rotation
and Reference Systems
Service (IERS), 190
Internet, 164–65
computer virus, 262–63
cyberbullying, 260–61
family rules regarding,
261
identity on, 261–62 285
INDEX
playing games online, 261,
262 (ill.)
Web site, 262
interstate highways, 149
intestines, 223
invention, 143
I.Q. (intelligence quotient),
249
Islam, 110
J
Jackfruit, 99
January, 191
Janus, 191
Japan, 107, 109
Jefferson, Thomas, 36 (ill.),
37, 188, 251
Jell-O, 218, 219 (ill.)
jellybean, 219
jellyfish, 50
Jemison, Mae C., 18–19
Jenner, Edward, 224–25
Jenny, William Le Baron, 146
jet airplanes, 29
jiffy, 196
jock itch, 212
Johnny Appleseed, 100
joints, 199
Joshua tree, 97–98
Judaism, 110
judicial branch, 134–35
Judson, Whitcomb, 172
Julian calendar, 190
July, 191
June, 191
Juno, 191
Jupiter, 6–7, 7 (ill.), 8
Jupiter, 19
K
Kalakaua, David, 141
Kamehameha I, King, 141,
141 (ill.)
Kasner, Edward, 183
Keck Telescopes, 15–16
keratin, 211
Key, Francis Scott, 137
Kilby, Jack, 163
King Khalid International
Airport (Riyadh, Saudi
Arabia), 113
kisses, 239–40
kissing bridge, 151
knuckles, 199
Kola Superdeep Borehole, 38
Kosovo, 125
L
Laika (space dog), 19
Lake Pontchartrain
Causeway, 149
land and water coverage, 38
land mile, 184–85
“landlocked,” 126–27
landmarks, 112
languages, 108–9, 250 (ill.),
250–51
lasers, 170–71
laughter, 226
laundry, 238
Laurasia, 23
laws, 134–35
Lazarus, Emma, 136
leap second, 190
leap years, 190
learning disability, 228, 249
leaves, 98
leeches, 68
Leibniz, Gottfried Wilhelm,
164
Lenoire, J. J. Etienne, 147
Leonardo da Vinci, 147, 249
Lewis, Gilbert N., 196
librarian, 252–53
library, 251, 252 (ill.), 252–53
Library of Congress, 251
Libya, 34
lichen, 93–94
light bulb, 168
light year, 2
lightning, 30, 31 (ill.), 269
Lincoln, Abraham, 36 (ill.),
37, 131 (ill.), 169
Linde, Carl von, 173
linen, 101
lion, 61
Lippershey, Hans, 15
literacy, 251
Little Ice Age, 35
liverwarts, 49
lizard, 72, 74
Lloro, Colombia, 30
London, England, 112
losing a game, 254–55
Lowell, Percival, 6
Lucifer, 275
Luna 1 (space probe), 17
lungs, 207
M
machinery, 144
Mackinac Straits suspension
bridge, 150
maggots, 68
magnifying glass, 171, 171
(ill.)
Mahavir, 182–83
Mahru (robot), 177
maiden-hair tree, 96
Maiesta, 191
mail, 166–67
Maiman, Theodore, 170
mammals
anteater, 64
bears, 62
biggest, 59–60
bighorn sheep, 63
camels, 60–61
definition of, 57
fastest, 58
flying, 57 (ill.), 57–58
poisonous, 58
polar bears, 62, 63
shark, 63
sleeping, 60
slowest, 59
smelliest, 60
walrus, 63
wild African elephant, 62
zebras, 61
Man in the Moon, 25
Mandarin Chinese language,
109
mangrove killfish, 69
mangrove tree, 98
manners, 237, 239
March, 191
Marconi, Guglielmo, 158
marine plants, 102
marram grass, 102
marriages, 235, 270–71
Mars, 6–7, 9–10, 191
marsupials, 57
mathematics, 183, 183 (ill.)
May, 191
Mayans, 189, 189 (ill.)
mayor, 133
Maza, North Dakota, 111
McAuliffe, Christa, 20
measurement
acre, 185
avoirdupois weight, 188
baker’s dozen, 186
carats vs. carob seeds, 185
286 cord, 185–86
cubit, 184
decimal-based system, 187
gnat’s eye, 186
hair’s breadth, 186
hectare, 187
horsepower, 186, 187 (ill.)
human body, 184
metric system, 186–87,
187–88
mile, 184–85
money, 185
standards, 185
stones, 184
troy weight, 188
mechanical energy, 173
megalopolis, 111
melanin, 210
melanocytes, 213
melting pot, 110–11
membrane, 204
mental disabilities, 228
Mercury, 6–7, 8
metamorphic rocks, 36
metamorphosis, 65
meteor, 14–15
meteorites, 15
metric system, 186–87,
187–88
metropolitan area, 111
Mexico City, Mexico, 111
mice, 244
microwave, 175
mile, 184–85
milk, 121–22
milking machines, 117, 117
(ill.)
Milky Way, 3–4
millennium, 191
minerals, 217–18
mirrors, 171
mobile telephone switching
office (MTSO), 162
mold, 224
mole, 211
molting, 76
Monday, 192
money, 185, 231–32
monotremes, 57
monster storms, 31–32
months, 191, 192
Moon, 25, 25 (ill.), 26, 27.
See also planets
craters, 27
definition of, 25
distance from Earth, 26
jumping on, 26
Man in the Moon, 25
moonquakes, 25–26
ocean tides, 26
volcanoes, 26
moonquakes, 25–26
Morse, Samuel F. B., 157–58
moss, 94–95
moths, 65–66
motion sickness, 215
motors, 172
Mount Rushmore, 36 (ill.), 37
mountains, 36
Mozart, Wolfgang Amadeus,
249
MP3 player, 165, 165 (ill.)
Muhammad, 276
multilingual, 251
mummies, 273
muscles, 199–201, 200 (ill.)
mushrooms, 94 (ill.), 95
N
nails, 211, 213
Napier, John, 164
Napier’s Bones, 164
nasal cavity, 239
national anthem, 137
National Institute of
Standards and Technology
(NIST), 185
nautical mile, 184–85
Neale, Thomas, 167
near-death experiences, 273
Neighborhood Watch, 268–69
Nells, Sarah, 225
Nelson, Gaylord, 47
Neptune, 6, 7, 7 (ill.), 8
nervous system, 202, 206
nettles, 91–92
neurons, 206
“The New Colossus”
(Lazarus), 136
New Delhi, India, 107 (ill.)
New Mexico, 141
New York City, 111, 112
Newman, Max, 164
newspapers, 156
Nichomachus of Gerasa,
180–81
Nigeria, 109
Nobel, Alfred, 144
Nobel Prize, 144
North America, 22–23, 23
(ill.)
nose, 216, 239
nosebleeds, 269
November, 191
Noyce, Robert, 163
nuclear energy, 114–15, 115
(ill.)
numbers
abacus, 182, 182 (ill.)
counting to one billion,
181
Euclid, 180
googol, 183
infinity, 183
mathematics, 183, 183
(ill.)
origin of, 180
“perfect” number, 180
Pythagoras, 180
Roman numerals, 181–82
ten, 180–81
two, 181
zero, 182–83
nut, 100
nutrition, 217
O
oak trees, 98–99, 100–101
ocean, 38
ocean tides, 26
October, 191
oil, 44
Okinawa, Japan, 107
Old Reliable (space monkey),
19
oligarchy, 130
“Open sesame!,” 84
orb web, 67–68
orbit, 4
organelles, 204
organic farming, 120
organs, 206–9
Orion (space vehicle), 16
Ornithomimus, 55
Osaka-Kobe-Kyoto, Japan,
111
ostriches, 75, 75 (ill.)
Otis, Elisha, 146
outer space, 3
oxygen, 27–28
ozone, 42, 43
ozone layer, 27 (ill.), 27–28
P
pain, 207
Pangaea, 22–23
paper, 101–2
Pascal, Blaise, 164 287
INDEX
passed gas, 221
Pasteur, Louis, 225–26
patent, 143
Pauling, Linus, 144
Pavlov, Ivan, 144
peacock, 78
pen pal, 252
pendulum, 194–95
penicillin, 224
Penn, William, 167
perennial flowers, 85
“perfect” number, 180
periscope, 155
personal computer, 163
pesticides, 120
pets
cats, 240–41, 241 (ill.),
243–44
death of, 246
dogs, 240–43, 242 (ill.)
guinea pig, 244
health benefits of, 243
iguana, 244
mice, 244
most common household,
240–41
in public, 245–46
salmonella, 245
turtle, 244–45, 245 (ill.)
philanthropy, 258
Philippe, Patek, 195
Phipps, James, 225
phosphorescent materials,
169
photographs, 169–70
photons, 171
photosynthesis, 79, 80
physical disabilities, 228
pigs, 123, 123 (ill.)
pilots, 152
pine trees, 99
pitcher plant, 89
placental mammals, 57
Planet X, 6
planets, 5, 5 (ill.). See also
Earth; Moon
derivation of, 5
floating on water, 7–8
gas giants, 6
greenhouse effect, 8, 9
(ill.)
ice skating on, 8
length of day, 7
life on, 10
Mars vs. Earth, 9–10
melting metal on, 8
and moons, 10
names of, 6–7
number of, 5
Planet X, 6
Pluto, 6
red, 7
rings, 7
rocky, 5
and stars, 10–11
Venus, 8, 9 (ill.)
windiest, 8
plants, 49–50, 71, 234. See
also flowers; trees
aloe vera, 102
and animals, 79–80
blooming time, 86
bulb, 85
cacti, 92
carnivorous, 88–90, 89
(ill.)
coral, 71
corm, 85
cotton, 101
dandelion, 83, 83 (ill.)
defense mechanisms, 90
desert, 92
digestion, 89
drowning bugs, 89
endangered species, 103
epiphytic, 93
ferns, 94
fiddleheads, 94
food, 80
fruit, 99
growing in ice and snow,
93
growing process, 80
growing without seeds,
84–85
hemlock, 91
leaves, 81
with leaves that can support
weight of child, 88
lichen, 93–94
linen, 101
marine, 102
marram grass, 102
nettles, 91–92
perennial, 85
poison ivy, 91, 91 (ill.)
poisonous, 90–91
rotting fragrance, 88
seeding process, 83–84
seeds, 82–85
self-pollination vs. crosspollination,
84
smallest, 87–88
spices, 102–3
spines, 92
stinging, 91–92
Theophrastus, 81
tropical rain forests,
92–93
tuber, 85
types of, 80–81
Venus flytrap, 90
water lily, 81, 81 (ill.)
without flowers, 81–82
plasma, 205
Plateau theory, 2
platelets, 209
“please,” 237
Pluto, 6
P.M., 196
poison ivy, 91, 91 (ill.)
poisonous plants, 90–91
polar bears, 62, 63
police officers, 257
pollen, 65
pollution, 47
Polynesians, 105
Ponce de León, Juan, 139
pond ice, 34
poop, 221
popping ears, 214
population, 105–7
porcupine fish, 70
porpoise, 71–72
post office, 167
Postal Service, 166–67
potato chips, 220
poverty, 107
praying mantis, 67
pregnancy, 235–36
president, 131 (ill.), 132
primitive plants, 49–50
protoplanetary disks, 17
puffer fish, 70
pulpwood logs, 101
pupils, 214
purr, 243
pus, 209
Pythagoras, 180
Q
quasar, 13
R
rabies, 225–26
radio, 158
288 rafflesia, 87, 87 (ill.)
rain, 29
rain forests, 24, 92–93, 103–4
rainbow, 30
rays (fish), 70
Reagan, Ronald, 219
recycled paper products,
101–2
recycling, 45–46
red barns, 119
red blood cells, 205 (ill.),
205–6
red coloring, 219
red planet, 7
red tears, 244
Redier, Antoine, 195
“Reduce, Reuse, and
Recycle,” 45
redwoods, 96–97, 97 (ill.)
reflection, 171
reflectors, 266
refrigerator, 34, 173
religions, 110
representative, 132–33
reproductive system, 202
reptiles, 72–73, 74, 245
resistance heating, 172
respiratory system, 202
Revolutionary War, 128, 138
Rhode Island, 140
rib cage, 198, 198 (ill.)
Ride, Sally K., 18, 19, 20 (ill.)
right and wrong, 236–37
Ring of Fire, 41
rings, 7, 7 (ill.), 96
rivers, 40
Robinson, Doane, 37
robots, 177
rocket, 16
rocks, 35–36
Roddenbery, Gene and Majel,
274
Roebling, John A., 150 (ill.),
150–51
Roebling, Washington A., 151
roller coaster, 151–52
Roman numerals, 181–82
Roosevelt, Theodore, 36 (ill.),
37
rubber, 263–64
running water, 232–33
Russia, 125
S
sadness, 274
Sadyattes, 231
safety
first-aid kit, 269–70, 270
(ill.)
guns, 268
lightning strikes, 269
Neighborhood Watch,
268–69
nosebleeds, 269
seatbelt, 266–67
talking to strangers,
267–68
thunderstorm, 269
walking, 267, 267 (ill.)
salamanders, 74
sand dunes, 102
São Paulo, Brazil, 111
sartorius, 201
Satan, 275
satellite, 18
saturated fats, 220
Saturday, 192
Saturn, 6–7, 7 (ill.), 7–8
Saudi Arabia, 109
scabs, 209
scaly skin, 72–73
scanners, 170
school
alphabet, 250
American Sign Language,
250 (ill.), 250–51
attending, 246–47
attending new, 253–54
bilingual, 251
bullying, 255–57, 256 (ill.)
Founding Fathers, 247–48
genius, 248–49
head lice, 257
home schooling, 247, 247
(ill.), 248
homework, 250
learning disability, 249
library, 251
literacy, 251
making friends, 253–54
other countries, 248
pen pal, 252
schoolwork, 249
school buses, 266
scooters, 265
sea, 38
seahorse, 71, 71 (ill.)
séances, 273
search engine, 165
Sears Tower, 144, 145
seasons, 193
seatbelts, 266–67
second-hand smoke, 230
sedimentary rocks, 35–36
seed drill, 117–18
seeds, 82–85
self-pollination, 84
Senate, 106
senator, 132–33
Seoul-Incheon, South Korea,
111
September, 191
sequoias, 96–97
sesame seeds, 84
Seward, William H., 140
shadow, 167–68
shark, 63–64
shell, 244–45
shelter, 232
shipbuilding industry,
100–101
shooting star, 14–15
Siamese fighting fish, 70
sickness, 221–27
silicon chip, 162 (ill.), 162–63
silo, 119
skeletal muscles, 200
skeletal system, 202
skin, 208 (ill.), 208–9
skin color, 210–13
skunk, 60
sky, 28
Skylab (space station), 19
skyscrapers, 144–46
sleep, 227
sloth, 59
smallpox, 224–25
smartphone, 162
smiling, 201
smog, 42–43
smoke, 175–76
smoke detectors, 176
smoking, 230, 230 (ill.)
smooth muscles, 200
snail mail, 166–67
sneezing, 216
snowflakes, 32
snowstorms, 31
soap, 238 (ill.), 238–39
solar system, 4
soldiers, 128–29
sonar, 155–56
Sosigenes, 190
South America, 22–23, 23
(ill.)
space exploration. See also
planets; universe
animals in space, 19
astronauts, 16–17, 19 289
INDEX
Challlenger disaster, 20
first African American in
space, 18
first man in space, 18, 18
(ill.)
first woman in space, 18
Hubble Space Telescope,
15 (ill.), 17
Moon landing, 19
people living in space, 20
rocket, 16
satellite, 18
Skylab (space station), 19
space probes, 17
space shuttle, 16
spacecraft, 16
telescopes, 15 (ill.), 15–16
space probes, 17
space shuttle, 16
space station, 19
spacecraft, 16
Spangler, James, 172
sperm cells, 202 (ill.), 203
spices, 102–3
spiders, 67–68, 234
spine (human), 198– 199
spines (plants), 92
spring, 193
Sputnik 1, 16
Sputnik 2, 19
Stalin, Joseph, 130
standards, 185
stapedius, 200–201
stapes, 198
“The Star-Spangled Banner”
(Key), 137
stars, 11–12, 13
stars and stripes, 136–37
Statue of Liberty, 112
steam-driven vehicles, 147
steel, 144–45
stinging, 91–92
stirrup, 198
stomachs, 122, 219–20
Stonehenge, 188–89
stones, 184
stoves, 232–33
strangers, 267–68
stress, 254, 255
stripes, 61
sub-Saharan, Africa, 107
subcutaneous layer, 208
submarines, 155 (ill.), 155–56
substance abuse, 229–30
subway system, 112–13, 113
(ill.)
Sullivan, Kathryn, 20 (ill.)
summer, 193
summer solstice, 193
Sun
consistency, 11
eclipse of, 11–12
heat of, 11
lack of, 11
locations receiving most,
12, 12 (ill.)
non-rising, 12
size of, 12, 12 (ill.)
Sunday, 192
Sundback, Gideon, 172
sundial, 193 (ill.), 193–94
supernova, 13
supersonic airplane, 153
suspension bridge, 149
Swade, Doron, 163
sweat glands, 210
T
table manners, 239
tail, 241, 243–44
tail wagging, 241
Taipei 101 (skyscraper), 145
talking to strangers, 267–68
talking with the dead, 273
taste buds, 215, 215 (ill.)
tears, 213 (ill.), 213–14
teeth, 53, 216–17
telegraphy, 157–58, 158 (ill.)
telephone, 160, 160 (ill.),
161–62
telescopes, 15 (ill.), 15–16
television, 159–60
temperature, 34, 168
Tereshkova-Nikolaeva,
Valentina V., 18
test-tube baby, 236, 236 (ill.)
“thank you,” 237
Theaetetus of Athens, 180
Theophrastus, 81
thermal energy, 173
thermometers, 34–35, 168,
168 (ill.)
thermos, 173–74, 174 (ill.)
thighbone, 198
“Thirty Days hath
September,” 192
Thomas, Seth E., 196
thunder, 30
thunderstorm, 269
Thursday, 192
time
alarm clock, 195–96, 196
(ill.)
A.M., 196
B.C. vs. A.D., 190–91
calendars, 188–89, 189–90
Chinese lunar calendar,
190
clocks, 194–96
Daylight Saving Time, 193
days, 191–92
Egyptian calendars, 189
fortnight, 196
grandfather clock, 194–95
International Date Line,
192
jiffy, 196
leap second, 190
leap years, 190
millennium vs. century,
191
months, 191, 192
P.M., 196
seasons, 193
sundial, 193 (ill.), 193–94
time zones, 192–93
timekeeping, 189
water clock, 194
wristwatch, 195
year, 189
time out, 237–38
time zones, 192–93
tires, 263–64
toadstools, 95
toaster, 174, 175
toenails, 211
toes, 210–11, 211–12
toilet, 233
Tokyo, Japan, 111
tongue, 215, 215 (ill.)
tongue prints, 215
toothbrushes, 217
toothpaste, 102
tornadoes, 32–33, 33 (ill.)
totalitarian governments, 130
town meeting, 133–34
traffic laws, 265
transformer, 172
transportation
automobile, 147
boats, 154–55
bridges, 148–51
Brooklyn Bridge, 150
(ill.), 150–51
cable car, 147
electric car, 147–48, 148
290 (ill.)
gasoline-driven vehicles,
147
helicopters, 153–54
interstate highways, 149
roller coaster, 151–52
steam-driven vehicles, 147
submarines, 155 (ill.),
155–56
supersonic airplane, 153
tunnels, 151
trees. See also flowers; plants
age of, 96
apple, 100
biggest, 96–97
bonsai, 99, 99 (ill.)
coconuts, 100
coniferous, 99
deciduous, 98
fir, 99
grows on stilts, 98
Joshua, 97–98
largest nut, 100
leaves, 98
longest-living, 96
oak, 98–99, 100–101
pine, 99
rings, 96
tallest, 96–97, 97 (ill.)
thousands of trunks, 97
Trevithick, Richard, 147
tricycles, 264–65
tropical rain forests, 92–93,
103–4
troy weight, 188
trunks, 97
tsunami, 42
tuber, 85
Tuesday, 192
Tull, Jethro, 117
tunnels, 151
Turing, Alan M., 164
turtle, 244–45, 245 (ill.)
twinkling stars, 11
two-way radio, 161
U
ulnar nerve, 199
umbilical cord, 212
uniforms, 259
United States, 126, 131–32.
See also governments
Alaska, 140
bald eagle, 136
beginning of, 137–39, 138
(ill.)
Bill of Rights, 134
citizen, 135
Congress, 132–33
District of Columbia, 139
flag, 136–37
Four Corners, 141
government, 133
governor, 133
Hawaii, 141, 141 (ill.)
largest state, 140
laws, 134–35
mayor, 133
most populous state,
140–41
national anthem, 137
president, 131 (ill.), 132
smallest state, 140
state nicknames, 139–40
states not originally territories,
139
Statue of Liberty, 135–36,
136 (ill.)
symbol of, 136
town meeting, 133–34
voting, 135
universe, 1, 2, 14, 17. See
also planets; space
exploration
asteroid, 14
beginning of, 1
black hole, 13
center of, 2–3
collapse of, 2
comets, 13–14, 14 (ill.)
constellations, 13
expansion of, 2
galaxies, 3
gravity, 2
light year, 2
meteor, 14–15
meteorites, 15
orbit, 4
outer space, 3
quasar, 13
shooting star, 14–15
size of, 1
solar system, 4
Sun, 11
supernova, 13
Uranus, 7, 7 (ill.)
urinary system, 202
Utah, 141
V
vaccination, 224–26
vacuum bottle, 173–74, 174
(ill.)
vacuum cleaner, 172
Vail, Alfred, 158
veils, 109 (ill.), 109–10
Venus, 6–7, 8
Venus flytrap, 90
vernal equinox, 193
Verrazano, Giovanni da, 150
Verrazano-Narrows Bridge,
150
vertebra, 198
Vikings, 105
Virgin Mary, 276
viruses, 221–22, 223
vitamins, 217–18
voice, 207
volcanoes, 26, 40–41, 41 (ill.)
volunteers, 257, 258–59
vomit, 219–20
voting, 135
Voyager 1 (space probe), 17
W Walker, Lewis, 172
walking, 246, 267, 267 (ill.)
walking sticks, 66, 66 (ill.)
walrus, 63, 63 (ill.)
wars, 127–29, 129 (ill.)
wart, 211
washing hands, 238 (ill.),
238–39
washing machine, 173
Washington, George, 36 (ill.),
37
wastewater, 233
water, 46, 233
water clock, 194
water erosion, 37
water lily, 81, 81 (ill.)
watermeal, 87–88
Watt, James, 186
Web site, 262
webs, 67–68
Wednesday, 192
wettest location, 30
whales, 59–60
white blood cells, 205, 205
(ill.), 209
whorls, 96
wild African elephant, 62
Williams, Venus, 22
wind, 28, 235
windmills, 118
winter, 193
winter solstice, 193
Wolverton, Bill, 234
woolly mammoths, 50, 51 291
INDEX
working for a living, 231
World Wide Web, 164–65
worms, 50, 77
Wright brothers, 152–53, 153
(ill.)
wrinkles, 212–13
wristwatch, 195
X
X chromosome, 237
X-ray, 170
Y
Y chromosome, 237
yawn, 227, 227 (ill.)
year, 189
Z
zebras, 61 (ill.), 61–62
zero, 182–83
zipper, 172
zits, 212
292
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