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Comprehension Skill
Main Idea and
Supporting Details
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Glossary
Science Content
Energy
Scott Foresman Science 3.13
ISBN 0-328-13846-0
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Vocabulary
Extended Vocabulary
absorb
electric charge
electric circuit
electric current
kinetic energy
potential energy
reflect
refract
thermal energy
lens
opaque
rainbow
shadow
spectrum
translucent
transparent
white light
What did you learn?
1. What is our most important natural
light source?
2. Explain how light travels.
3. A mirror and a leaf reflect light
differently. Why?
4.
by Marianne
Lenihan
In this
book you
have read about ways in which
people use the refraction of light in
their everyday lives. Write to explain
some ways in which refraction is
used. Use examples from the book.
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material.
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: John Lund/Corbis; 5 (TL) Getty Images; 6 Craig Tuttle/Corbis; 9 (B) Robert Holmes/Corbis;
14 Science Museum, London/DK Images; 17 John Lund/Corbis; 20 JS Productions/Corbis; 23 Craig Tuttle/Corbis.
Scott Foresman/Dorling Kindersley would also like to thank: 9 (TR) NASA/DK Images; 15 (BR) Stephen Oliver/DK Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.
ISBN: 0-328-13846-0
Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America.
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
5.
Main Idea and Supporting
Details Traveling light rays react
differently when they reach
different materials. What details
from the book support this idea?
What You Already Know
We live in a world filled with energy. Light
is a form of energy. Objects such as the Moon
reflect light. Light will also refract when it
passes through water.
Energy comes in many different forms other
than light. Potential energy has the ability to
change to another form in order to do work
or cause a change. When we burn
fuels, we release their potential energy.
Kinetic energy is the energy of
motion. Whenever we begin to walk
or run, potential energy changes
to kinetic energy.
Thermal energy is the total
energy of all the particles in
matter. The thermal energy in a
heated room is what warms us!
All matter is made up of small
particles that have electric charges.
An electric charge is a tiny amount
of energy. An electric charge can
move from one place to another as
an electric current. The path that a
controlled electric current flows
through is called an electric circuit.
light bulb
Light comes to us from
the Sun and from sources such as
electricity. We use light in many
different ways. Light has many
fascinating qualities! Keep reading
to find out more about light.
A swing changes
potential energy
to kinetic energy,
and kinetic energy
to potential energy.
2
3
Sources of Light
Daylight is the result of Earth receiving light
from the Sun as it turns on its axis. As Earth
rotates, part of it enters into darkness, and
another part comes into daylight. Most of Earth
experiences both day and night every 24 hours.
The Sun is not our only source of natural
light. The nighttime stars shine brightly. The
planets you see in the night sky, such as Venus,
shine also. But the light the planets give off is
not their own. Like the Moon, Venus reflects
the Sun’s light.
Stars are a source
of natural light.
The Sun is the star
nearest to Earth.
4
Light travels at
more than 186,000
miles per second.
Light from the
Sun takes about
eight minutes to
reach Earth.
Lightning is a form of electricity. It creates
huge amounts of light. Fireflies and some
kinds of fish also make natural light.
The Sun will always be our most important
source of light. But artificial light gives us light
when it’s dark outside. For the past century,
we have been using electric-powered lights in
our homes and schools, and on city streets.
Before electricity was used for light, people
used campfires, oil and gas lamps,
and wax candles. These types
of light sources are still
used today. However,
electric-powered lights
are our main source
of artificial light.
Flashlights use battery-powered
electricity to provide artificial light.
5
Traveling Light
Light travels very fast—much faster than
sound. That’s why you see a flash of lightning
before you hear the sound of thunder, even
though both happen at exactly the same time.
Light travels in straight lines. A flashlight’s
beam shows this. If you shine a flashlight on a
wall, you can mark where its beam of light hits.
The distance from the mark back to the flashlight
is always a straight line.
Light rays travel in a straight line from the Sun to Earth.
Traveling light rays react differently when they
reach different types of materials. Transparent
materials allow all light rays to travel through them.
Translucent materials allow some light to shine
through them. Frosted glass, stained-glass windows,
and dark sunglasses are translucent. Opaque
materials, such as doors, walls, and our bodies,
block out all light rays. Opaque materials absorb
and reflect light.
Does light pass through?
Colored water lets light rays pass through
easily. Milky water allows only some rays to
pass through, while ink blocks them completely.
flashlight
colored water
(transparent)
6
milky water
(translucent)
ink
(opaque)
7
Light and Shadow
Light rays travel from the Sun to Earth. When
they reach an opaque object on Earth’s surface,
they are unable to pass through it. This causes a
dark area, or shadow, to form on a surface on the
other side of the object. The shadow takes the
same form as the object.
Shadows change length throughout the day.
They are shortest at noon. Shadows get longer
as the Sun appears to move lower in the sky.
Shadows such as this one are caused by shining
a bright light on an opaque object in front of a
background surface.
The most amazing
shadow of all is seen
during a solar eclipse.
A solar eclipse is when
the Moon passes
between the Sun and
Earth. This causes the
During a solar eclipse, the
Moon casts its shadow on
Moon’s shadow to fall
Earth’s surface.
on Earth’s surface.
Shadows have been
used for centuries to tell time. A sundial is
a kind of clock. It tells time using a shadow
created by the Sun. Obviously, sundials can’t
measure the time at night!
This sundial is using the
shadow cast by the Sun to
measure the approximate
time of day.
8
9
Bouncing Light
Long ago, people thought that their eyes sent
out beams of light to the objects they saw around
them. But people have shown that idea to be
false. We now know that light rays bounce off
objects and enter our eyes.
When light bounces off an object it is called
reflected light. Light rays reflect differently off
smooth and rough surfaces. Suppose you shine a
flashlight on the surface of a smooth mirror. The
mirror reflects the light in only one direction.
How We See
We can see objects that are not light sources
because light rays bounce off the objects and
enter our eyes.
light source
some light
enters the eye
light rays
strike plant
plant reflects
light
Light bounces off mirrors
in only one direction.
Now, think about what would happen if you
shined a flashlight on a leaf. The leaf’s rough,
uneven surface would scatter the light in all
directions. These scattered, reflected light rays
allow you to see the leaf from all sides.
When light rays bounce off an object,
most of the light is reflected, but not all. Some
light is absorbed. All objects, no matter how
transparent, translucent, or opaque they are,
absorb some light.
10
11
Curved Surfaces
Reflections
Reflections are formed by shiny materials,
such as glass mirrors and smooth water surfaces.
Most metals reflect the light that falls on them.
Glass is not a metal. However, it is usually
very flat and smooth, like most metals. Since
glass does not reflect light rays well, how are
glass mirrors able to reflect our image?
Mirrors are made by putting metal sheeting
behind a piece of glass. The glass protects the
metal. It also makes a smooth surface. It is
the metal that reflects our image back to us,
not the glass.
Not all mirrors are made by
humans. A lake’s smooth,
calm surface reflects light
rays very well.
12
Have you ever looked at your
reflection in a spoon? The
way the front of a spoon is
curved can make your image
appear larger and upside
down. The curve of the back
of the spoon can make your
image appear smaller.
Mirrors can be used in many different ways.
We can use them to see our appearance. Mirrors
can also help us stay safe. Bicycle riders, car drivers,
and other vehicle operators use mirrors to help
them see while they are driving or riding. Finally,
mirrors can be used to send flashes of light over
long distances. This is a form of communication.
13
Lenses
Bending Light
A lens is a specially shaped piece of glass or plastic. It
refracts light in a precise way.
You already know that light moves through air
at an amazing speed. When light travels through
other materials, such as water or glass, its speed
decreases. The slowing down of light rays causes
them to change direction.
Refraction is the name given to the slowing
down of light rays. Because of the way that light
gets refracted through water, underwater objects
appear larger than they actually are. Refraction
also causes our skin to absorb more of the
Sun’s heat energy while we’re in the water.
That makes it very important to wear
sunscreen while swimming!
A light ray changes
direction as it
enters and leaves
a glass block.
14
A concave lens
spreads light rays
apart, which makes
objects appear
smaller than normal.
A convex lens
focuses, or brings
to a point, the light
rays of an object
that is far away.
We can find many examples
of refraction in our daily lives.
A spoon placed at an angle in a
glass of water appears bent. A
pencil seen through a water-filled
jar may appear to be broken.
Lenses are used in eyeglasses,
microscopes, telescopes, and
magnifying glasses. By using
refraction, these lenses help
people see better.
This pen placed
in a glass of
water appears
to be broken.
15
Using Refraction
We use refraction created by lenses every day
for many different things. Lenses can be used to
make objects that are far away look larger. They
can also correct poor eyesight and focus light
rays into a very strong beam.
People are born with two very important
lenses. Each eye contains a lens. The lens is
located just behind the pupil of each eye.
The pupil is the black dot located in the
very middle of each eye.
A magnifying glass is a type of
convex lens. It can make objects
such as stamps appear much
larger than they actually are.
16
This lighthouse
light uses a specially
shaped lens to create
a very strong beam
of light.
As we move our eyes from near to distant
objects, special muscles attached to the lenses
pull the lenses into different shapes. By changing
shapes, the lenses allow us to focus clearly on
objects both near and far. As people get older,
their eyes’ lenses can change shape. This can
cause their vision to blur. We can wear contact
lenses or eyeglasses to correct our eyesight.
A camera works a lot like our eyes do. A
convex lens uses light coming into the camera
to help create a clear, focused picture or image.
17
Splitting Light
Have you ever wondered what white light
is? Sunlight and light from an electric light bulb
seem to be colorless. We call these two kinds of
light white light.
White light is a mixture of many different
colors of light. Those colors become separated
when white light passes through a prism. A prism
is a triangular, transparent block. Light passing
through a prism forms a band of colors called
a spectrum.
This prism is splitting
white light into a
spectrum. Notice all the
different colors of light.
18
This tea set’s different
colors indicate which
colors are being absorbed
and which are being reflected.
An object’s color tells us which color it
reflects. Grass is green because that is the only
color it reflects. The grass absorbs the other
colors in the spectrum. If an object appears red,
it is because it is absorbing every color except
red. The red rays are reflected off the object.
Most of the light that you see each day is
white light. However, not all light is white light.
Red, green, and blue light only give off those
colors. Light can be any color found in the
color spectrum!
19
Rainbow Colors
You can see a rainbow because raindrops act
like tiny prisms. White light enters a droplet of
water. The water bends, or refracts, each color
in the light differently. Then the light passes out
through the droplet. But it no longer appears
as white light. Instead, the light is split into
its colors.
Rainbows occur most often after
rainfall or when there is fog. That
is when a lot of water hangs
in the air. That water
creates rainbows.
To view a rainbow, you
must have your back to
the Sun.
20
How a Rainbow Forms
Light from the Sun passes through raindrops
in the air and gets refracted. The refraction
causes rainbows to form.
sunlight
raindrop
spectrum
Curved bands
of colored light are
produced when a rainbow
forms. The sharpest rainbows are
called primary rainbows. They show
the full spectrum of colors. The colors in
a primary rainbow are: violet, indigo, blue,
green, yellow, orange, and red. People are able
to see these colors.
21
Light in Our Lives
The Sun gives us daylight. It provides our
planet with energy. Light makes plants grow.
Light makes it possible for people and animals
to live on Earth. Stars and the Moon’s reflected
light brighten the night sky.
Natural light does much more than give us
day and night. It allows us to see different colors,
reflections, and shadows. Light rays reflect and
refract. These properties are used in many
light-based inventions. Our lives are made
happier, healthier, and safer with lighthouse
lights, mirrors, eyeglasses, and other inventions.
It’s very easy for us to take light for granted.
After all, the Sun appears to rise every day.
We flip a switch and our homes, offices, and
streets are lit by electric-powered lights. So it’s
important to remember that light is one of our
most important resources. Without light, we
would not be here. The universe would be
left in the dark.
22
23
Vocabulary
Glossary
absorb
Extended Vocabulary
lens
electric charge
opaque
lenses
specially shaped
pieces of glass or
electric circuitplastic that
rainbow
refract light
electric current
shadow
opaque
the qualityspectrum
that prevents light
kinetic energy
from passing
through something
potential energy
translucent
reflect
transparent
rainbow
a curved spectrum
that forms in
refract
white
light
the sky
thermal energy
shadow
the dark area cast on a surface
by an opaque object, and forms
when light shines on the front of
the object
spectrum
the complete band of colors
found in white light
translucent
the quality that lets some amount
of light pass through something
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material.
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
transparent
the quality that allows light to
Scott Foresman/Dorling Kindersley would
also like
to thank: 9 (TR)
NASA/DK Images; 15 (BR)
Stephen Oliver/DK Images.
pass
almost
completely
through
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.
something
Opener: John Lund/Corbis; 5 (TL) Getty Images; 6 Craig Tuttle/Corbis; 9 (B) Robert Holmes/Corbis;
14 Science Museum, London/DK Images; 17 John Lund/Corbis; 20 JS Productions/Corbis; 23 Craig Tuttle/Corbis.
white light
ISBN: 0-328-13846-0
ordinary light, such as sunlight,
which appears to be colorless
Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America.
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
24
What did you learn?
1. What is our most important natural
light source?
2. Explain how light travels.
3. A mirror and a leaf reflect light
differently. Why?
4.
In this book you
have read about ways in which
people use the refraction of light in
their everyday lives. Write to explain
some ways in which refraction is
used. Use examples from the book.
5.
Main Idea and Supporting
Details Traveling light rays react
differently when they reach
different materials. What details
from the book support this idea?