California science grade 3 (13)

CHAPTER

8

Light

What is light and how does it travel?

342


Lesson 1

How Light Moves

PAGE

346

Lesson 2

Seeing Light and Color

PAGE

356

Lesson 3

Shadows

PAGE

368

3 PS 2. Light has a source and travels in a direction.

343


Literature
Poem
ELA R 3.2.3.
Demonstrate
comprehension by identifying
answers in the text.
ELA W 3.2.1. Write narratives:
a. Provide a context within
which an action takes place.
b. Include well-chosen details
to develop the plot. c. Provide
insight into why the selected
incident is memorable.

A prism separates white
light into all the colors
of the rainbow.

344

from Spectacular

Science

by Lawrence Schimel
The prism bends a beam of light
And pulls it into colored bands.
My fingers tremble with delight:
I hold a rainbow in my hands.

Write About It
Response to Literature The poet tells about
an experience he had with light. How did the
experience make him feel? Write a personal
narrative about an experience you have had
with light. It might be a rainbow, a sunrise,
or a sunset. Tell how you felt about the
experience and why it is memorable.

-Journal Write about it online
@

www.macmillanmh.com

345


Lesson 1

How Light

Moves

When you look at a mirror, glass,
water, or other shiny thing, you can see
yourself. Why does this happen? How
does light make this possible?

346
ENGAGE

3 PS 2.b. Students know light is reflected from mirrors and other surfaces.


How does light move?

Materials

Make a Prediction
What happens to light when it hits a mirror?

Test Your Prediction

mirror

Hold a mirror in front of you. Have a partner
shine the flashlight onto the mirror.

Observe What happens to the
flashlight’s beam?

flashlight

Experiment Pick a spot on the wall or
chalkboard. Can you make light bounce off the
mirror and shine on that spot? How? Do you
have to move the mirror, the flashlight, or both?

Step

Draw Conclusions
What happened to the beam of light when
it hit the mirror? What happened when you
moved the mirror? What happened when
you moved the flashlight?

Communicate Make a drawing to show
how light moves.
Step

Explore

More

Experiment Sit next to your partner and hold
the mirror so that you can see your partner. Can
your partner see you in the mirror? Can you see
yourself and your partner in the mirror at the
same time?
3 IE 5.e. Collect data in an investigation and analyze
those data to develop a logical conclusion.

347
EXPLORE


What is light?
C Main Idea

From blue skies to green grass and
golden sunshine, you live in a world of
color. What is color? Why do we see color?
To understand color, you must learn about
light. Light is a form of energy. Light is
made up of transverse waves that move up
and down.

3 PS 2.b

Light is a form of
energy. When light hits
an object, some light
is reflected. Reflected
light changes direction
and keeps moving in a
straight line.

Visible Light

C Vocabulary

You can see some waves of light energy.
Color is light energy we can see. Light you
can see is called visible light. The beam of a
flashlight and flash of a camera are visible
light. Everything you see with your eyes is
because of visible light.

light , p. 348
reflection , p. 350

-Glossary
@

www.macmillanmh.com

C Reading Skill
Problem and Solution

Forms of Light Energy

>`]PZS[

B Radio waves are
used to transmit
signals for cellular
phones, radios, and
televisions.

AbS^ab]A]ZcbW]\

A]ZcbW]\

C Technology
Explore how
light travels
with the
Secret
Agents.

radio waves

348
EXPLAIN

Infrared waves
are felt as heat.
This photo was
taken with film
that shows
infrared light.

B Microwaves are
used to cook food.

microwaves

infrared waves


Invisible Light

Other forms of light energy are not visible.
X-ray waves are a form of light energy that
you cannot see. We use X-ray waves to take
pictures of bones and teeth. The waves given
off inside a microwave oven are another
form of invisible light energy. You cannot see
microwaves but you can see how they change
uncooked foods.
Quick Check
Problem and Solution You fell and hurt

your ankle. How can you find out if you
broke it?
Critical Thinking How are light and

sound similar?

Visible light waves are the
only light energy we can see.
We see these waves as the
colors of the rainbow.

An X-ray wave
is invisible light
energy used to
take pictures of
bones. B

High-energy
gamma waves

are used in
nuclear power
plants. B

Ultraviolet
waves tan
your skin
but can also
give you a
sunburn. C

visible waves

ultraviolet waves

X-ray waves

gamma waves

349
EXPLAIN


How does light travel?
All forms of light energy are alike
in one way. Light always travels in
a straight path. Visible light moves
outward from a lamp in a straight
path. The microwaves in a microwave
oven move in a straight path. Even

light energy from the Sun travels
millions of miles through space in
straight paths.

Reflection
Have you ever played tennis?
After you hit the ball toward the
ground, it bounces upward. Light
acts much like a tennis ball. When
light hits an object, it bounces
off in a different direction. Then
it continues moving in a straight
path. The bouncing of light waves
off an object is called reflection
(ri•FLEK•shuhn) .

Reflection

Light is like a
bouncing tennis
ball. When it
hits a surface, it
bounces off in a
new direction.

Read a Photo
How is the path taken
by the tennis ball similar
to the path of light that
reflects off a mirror?

Clue: Pictures can show
movement and direction.

350
EXPLAIN


Movement of Light

What do you notice about
the path of the laser light?

Smooth, shiny surfaces reflect
almost all the light that strikes
them. These surfaces can be used
as mirrors. Light bounces off
them in one direction and forms
a picture called an image.
Quick Check
Problem and Solution How

can you see yourself if you do
not have a mirror?
Critical Thinking Is it possible

to see in the dark? Explain.

Use a pencil and carefully poke
a hole in two index cards. Hold
the cards upright on a flat

surface so that the holes are
lined up.
Observe Place a lit flashlight
directly behind the last card.
Then bend your body so that
you are eye level
with the first card.
Can you see the
flashlight’s beam?
Predict What will
happen if you move
one of the cards?
Will you still be able
to see the light?
Write down your prediction and
make a drawing of how you
think the light will move.
Observe Move the second card
a little to the right. Again bend
your body so that you are eye
level with the first card. Can you
see the flashlight’s beam now?
Draw Conclusions What caused
differences in your observations?
Make another sketch to explain
how light travels.

D When you look in
a mirror you see an
image of yourself.

351
EXPLAIN


What happens when light hits
a rough surface?
A smooth, shiny mirror reflects light very
well and shows a clear image. A mirror with
a scratched surface will not reflect a clear
image. Why?

A When light hits a rough
pond, it bounces off
in different directions.
You cannot see a clear
image on the surface.

When light hits a rough surface, it
bounces off in different directions. Because
of this, a clear image does not form. You can
see yourself on the surface of a calm pond. If
the water is rough and swirling, a clear image
does not form. This is because the light is
reflected in many different directions.
Quick Check
Problem and Solution If you were

planning a building that reflects the sky,
what kind of material would you use?

Critical Thinking Have you ever looked

at your reflection in a pool of water? Why
do you think a pool of water can act like
a mirror?
352
EXPLAIN

A Light that hits a rough
surface is reflected in
different directions.


Summarize the Main Idea
Light is a form of
energy. Some light
energy is visible.
Some is invisible.
(pp. 348–349)

Light travels in a
straight path. The
light that bounces
off an object is a
reflection. (p. 350–351)

Think, Talk, and Write
Main Idea What is light?
Vocabulary What is a reflection?
Problem and Solution Why can you

see yourself in the base of a silver
spoon but not at the bottom of a
plastic bowl?
>`]PZS[

AbS^ab]A]ZcbW]\

If light hits a smooth
surface, a clear image
forms. Light that
hits a rough surface
scatters. (pp. 350–352)

Make a
Study Guide
Make a layeredlook book. Use
it to summarize
what you read
about light.

Writing Link
Write a Paragraph
Count the number of mirrors in
your home. Are there many? We
don’t think about mirrors, but
they are very useful tools. Write a
paragraph listing at least five uses
for mirrors.

A]ZcbW]\

Critical Thinking How is a reflection
in a mirror different from the object
in front of the mirror?
Test Practice How does light travel?
A

in a zigzag path
B in a curved path
C in a circular path
D in a straight path

Math Link
Solve a Problem
One side of a rectangular mirror
is 8 feet long. Another side of the
rectangular mirror is 10 feet long.
What are the lengths of the other
two sides of the mirror?

-Review Summaries and quizzes online @ www.macmillanmh.com

353
EVALUATE


Experiment
You just read that light moves in a straight
path. How did scientists figure this out? They did
an experiment, recorded what they observed,

and analyzed the data to draw a conclusion.

Learn It
When you experiment, you make and follow a
procedure to test a hypothesis. It is important to record
what you observe during an experiment. Once you
have enough information, you can decide whether your
hypothesis is supported or disproved.

Try It
In the following experiment, you will test the
hypothesis that light moves in a straight path. Follow the
steps of the procedure. Then use your observations to
draw a conclusion.

354
EXTEND


Procedure
Draw a target on a sheet of white
paper. Hang it on a wall near your
desk or table.
Stand two mirrors in clay as
shown. Then shine a flashlight into
one mirror. Draw or write your
observations on a chart.
Move the light or the mirror until the
light is reflected in the other mirror.
Record your observations.

Continue to move the light or
mirrors until the light is reflected
off your target.
Shine the flashlight from a higher,
then a lower angle. Record your
observations.

What I Did

What I Observed

shine the light
in one mirror

Draw Conclusions
C How did you make the light hit the
target? Does light always move in a
straight path?

made light
reflect in the
other mirror

C Did your observations support or
disprove the hypothesis?

shine the light
from a higher
angle

Apply It
Now do another experiment. Put the
mirrors back in place. Place a small object
between them. How many reflections do
you see? Move the mirrors closer together,
then farther apart. How many reflections
do you see each time? Remember to
record your observations.

shine the light
from a lower
angle

3 PS 2.b. Students know light is reflected from mirrors and other surfaces.

355
EXTEND


Lesson 2

Seeing Light
and Color

Have you ever looked through colored
glass? How does colored glass change
the way an object looks?

356
ENGAGE

3 PS 2.c. Students know the color of light striking an object affects the way the
object is seen. • 3 PS 2.d. Students know an object is seen when light traveling from
the object enters the eye.


How does light affect the color
you see?

Materials

Form a Hypothesis
Will the color of an object appear to be different
if you look at it through a colored filter?

sheets of colored paper

Test Your Hypothesis
Predict Look at a sheet of white paper and
a few sheets of colored paper. What color
will each sheet of paper appear to be if you
observe it through the blue filter? The red?
The green? Write down your predictions.

Experiment Look at the white paper and

sheets of colored plastic
Step

the colored paper through the red filter.

Repeat for each of your colored filters. Make
a list of all the colors that you see.

Draw Conclusions
Compare How do your observations
compare to your predictions? How do
they differ?

Analyze Data Why did you see
different colors?

Explore

More

Experiment What color will a white object be
if you look at it through a blue filter? What if you
look through both a blue and a red filter at the
same time? Try it and explain what you see.
3 IE 5.d. Predict the outcome of a simple investigation
and compare the result with the prediction.

357
EXPLORE


How do you see?
C Main Idea

3 PS 2.c

3 PS 2.d

You see an object when
reflected light enters
your eyes. The color of
light that bounces off an
object gives the object
its color.

C Vocabulary
cornea , p. 358
pupil , p. 358
iris , p. 358
lens , p. 359
prism , p. 360
absorb , p. 360

-Glossary
@

www.macmillanmh.com

You know that light reflects or bounces off
objects it strikes. If the reflected light enters
your eyes, you see an image of the object. The
light first strikes the cornea. The cornea is
the clear outer covering of the eye. After light
passes through the cornea, it enters the pupil.
The pupil is an opening into the eye.
Your pupils change size to let in more or

less light. Your pupils are small when there
is a lot of light. They grow larger and let in
more light as the amount of light around
you decreases. This change in your pupil’s
size is caused by the iris. The iris is the
colored circle that surrounds the pupil. It
controls how much light enters the eye by
changing the size of the pupil.

C Reading Skill
Main Idea

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cornea
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pupil

lens

358
EXPLAIN

iris

Light that moves into your
eye must be focused. This is just
like light from a movie projector
that must be focused on a screen.
The part of the eye that focuses
incoming light is the lens . It is
located behind the pupil and
iris. The lens focuses light on the
back of the eyeball. Information
about the picture that forms is
sent to the brain. The brain then
makes sense out of the picture.
Quick Check

How Light Affects
Your Pupils
Predict Does the amount of
light in a room affect your pupils?
Write down your prediction.
Observe Dim the classroom
lights. Look at your pupils in a
mirror. Make a sketch of what
you see.
Observe Turn on the classroom
lights. Again, look at your pupils
in the mirror. Make a sketch of
what you see.

Main Idea How does reflected

light allow you to see?
Critical Thinking Why does

the size of a pupil change?
Compare How do your
sketches differ?
Draw Conclusions What
caused differences in your
sketches? What does this show
about the amount of light that
enters your eyes?

D Light entering the eye passes
through the cornea, the
pupil, and the lens. The light
is focused on the eyeball to
form an image.

359
EXPLAIN


Why can you see colors?

When light passes
through a prism, it
is separated into
different colors.

Red, orange, yellow,
green, blue, indigo,
and violet are the
colored lights that
form white light.

360
EXPLAIN

Have you ever seen a rainbow? If so, you
probably saw bands of different colors. This
happens when white light is separated by an
object called a prism (PRIZ•uhm). A prism
is a special lens that separates white light.
Drops of water in the sky can act like prisms
and separate sunlight. When this happens,
a rainbow forms. A rainbow has seven
different colors. That is because white light
is made up of seven different colors of light.
When white light strikes an object, some
colors of light are absorbed , or taken in.
Some colors of light are reflected. If you
look at the object, some of the reflected
light enters your pupils. You see the object
as the color of this reflected light.


Seeing Colors
The leaf
looks

green.

The flower
looks red.

Read a Diagram

White light that strikes a leaf is
made up of seven different colors.
The leaf absorbs all of the colors
except for green. Only green light
bounces off the leaf. It is reflected to
your eyes. You see the leaf as green.

Why is the leaf green but the
flower red?
Clue: Look at the pictures of
reflected light.
Learn
about seeing color
@ www.macmillanmh.com

Something quite different happens
when the same white light strikes
a red flower. Now the green light
is absorbed. All of the colors are
absorbed except for red. Only the
red light is reflected to your eyes.
You see the flower as red.
Quick Check

Main Idea What happens when white light

passes through a prism?
Critical Thinking Why does a banana appear

to be yellow?

361
EXPLAIN


Why do objects appear black
or white?
When white light hits a tar-covered road,
all the colors of light are absorbed. Almost no
light is reflected. This is why the road looks black.
When white light strikes a snowman, all the
colors of light are reflected. No light is absorbed.
The snowman looks white.
What happens when you view a white object
through a colored filter? Because a white object
reflects all the colors of light, the object will
look the same color as the filter. If you shine
a red light on a white sheet of paper the paper
will look red. The filter only allows red light
to pass through it. It absorbs all other colors
of light. If you look at the same sheet of paper
through a blue filter, it will look blue. Only blue
light can pass through the blue filter. All the
other colors of light are absorbed. An object’s

color is affected by the light shining on it.
A Why do the
objects appear to
be the same color
as the filter?

Quick Check
Main Idea Why does a tar-covered road

look black?
Critical Thinking What color do you see if

you look at a white sheet of paper through
a yellow filter? Why?

D Light is absorbed by
the black sections
and reflected off the
white sections.

362
EXPLAIN


Summarize the Main Idea
When reflected light
enters your eye, you
see an image.
(pp. 358–359)

White light is made
up of seven colors.
(pp. 360–361)

Think, Talk, and Write
Main Idea What must happen for an
object to be seen? Talk about it.

Vocabulary What is a prism?

Main Idea Why does a school
bus appear yellow and a fire truck
appear red?
;OW\7RSO

Black objects absorb
all colors. White
objects reflect all
colors. (p. 362)

Make a
Study Guide
Make a trifold book.
Use it to summarize
what you learned
about color.

Writing Link
Write a Story
Is color important? Write a story

about a world without color. What
would life in your story be like?

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Critical Thinking A chalkboard
appears black whether you shine
red light or white light on it. But, an
index card appears red in red light
and white in white light. What causes
this to happen?

Test Practice How many colors
make up white light?
A four
B five
C six
D seven

Math Link
Make a Chart
A spinner landed on “Red” 6
times, “Blue” 4 times, and “Green”
5 times. Construct a tally chart to
show these results.

-Review Summaries and quizzes online @ www.macmillanmh.com

363
EVALUATE


A laser is a
tiny tool that
uses a beam
of light.

urgeons are doctors who
perform operations to fix
injuries or treat diseases. They
use scalpels, special tools with
sharp blades, to cut through
tissues such as skin, muscles,
and organs. Today, they have
another tool they can use to do
operations that were impossible
in the past. That tool is a beam
of light!

Lasers were first used to fix
marks on children’s skin. Today,
surgeons use lasers to treat
injuries to the brain, the heart,
and many other parts of the
human body. Lasers are even
used to help people see better.

This beam of light is called
a laser. Not many people know
that LASER stands for Light
Amplification by Stimulated
Emission of Radiation. Lasers
are very powerful and precise.
Lasers can cut though tissue
without causing a lot of
blood loss.

Doctors perform laser eye
surgery on people who have
vision problems. The laser is
tapped, or “pulsed,” on the
surface of the eye to change its
shape. After the surgery, the
patient’s vision is improved. The
patient usually does not have to
wear glasses or contact lenses.

364
EXTEND

ELA R 3.2.6. Extract appropriate and significant information
from text, including problems and solutions.


Science, Technology, and Society

A problem and
solution
C gives a problem
C tells how to solve the
problem

Write About It
Problem and Solution
How have lasers helped
patients? Read the
article again. Then write
about ways lasers solve
problems.

-Journal Write about it online
@ www.macmillanmh.com

Laser surgery is very
precise. Surgeons use lasers
instead of scalpels in many
surgical procedures.

365
EXTEND


Materials

Inquiry Structured

How can you mix colors of light?
Form a Hypothesis

white paper plate

You learned that drops of water in the sky can act like a
prism. The prism separates white light into bands of color.
Can you mix bands of color to get white light? Write a
hypothesis. Start with, “If I mix the right colors, then . . .”

Test Your Hypothesis
colored
crayons

Divide the white paper plate into eight equal sections
by folding the plate three times. Color each
section of the spinner in a different color.

pencil

Step

Observe Carefully push a pencil
into the center of the plate. Spin your
spinner away from your body. What
color do you see while the spinner is
spinning?

Experiment Repeat steps 1–3 to
make another spinner. This time

choose colors that you think
will make the spinner
appear white when you
spin it. If necessary,
make several
spinners to find the
color combinations
that work best.

366
EXTEND