CHAPTER 4
Energy in the
Earth System
How do radiation and convection currents
affect phenomena on Earth?
212
Lesson
1
Electromagnetic
Spectrum
PAGE
216
Lesson
2
Solar Radiation
PAGE
228
Lesson
3
The Power of
Convection Currents
PAGE
240
6 PS 4. Many phenomena on Earth’s surface are
affected by the transfer of energy through radiation
and convection currents.
213
Literature
MAGAZINE ARTICLE
ELA R 6.2.2.
Analyze text that
uses the compare-andcontrast organizational
pattern. • ELA W 6.2.2.
Write expository
compositions (e.g.,
description, explanation,
comparison and contrast,
problem and solution).
214
from MONKEYSHINES ON HEALTH AND SCIENCE
A Scientific Breakthrough
Most light, whether from a candle or a high-powered spotlight, is
composed of many different colors and quickly spreads over a wide
area as it travels away from its source. Laser light, however, can
be concentrated into a very fine line which can travel thousands
of miles unless something blocks it.
Lasers, invented in the early 1950s, have revolutionized
communications, astronomy, surgery, and a multitude of other
scientific fields. A laser is a specialized lamp producing light waves
which are extremely bright, are pure in color, and can be highly
focused.
Light, television, and radio signals are all forms of
electromagnetic waves. Microwaves, like those used to cook
food in microwave ovens, are a few inches long. Dr. Charles
Townes of New York’s Columbia University invented a way to
amplify and transmit microwaves in 1954, calling it a maser,
short for “microwave amplification by the stimulated emission of
radiation.”
Lasers consist of four basic parts: an energy source, an active
medium, an amplification system, and an output unit. Many lasers
are made using crystal rubies, but lasers also can be made using
various gases and liquids. Many recent laser designs incorporate
the same kinds of semiconductor materials found in computer
microchips. As laser research continues and industry continues to
develop new laser applications, lasers probably will come to play
an even greater role in our everyday lives.
Write About It
Response to Literature In this article the author
tells about the invention of the laser. How did this
invention come about? What impact has it had on
science? Write an essay comparing and contrasting
lasers and other forms of light. What do they have in
common? How do they differ?
-Journal Write about it online
@
www.macmillanmh.com
215
Lesson 1
Electromagnetic
Spectrum
A rainbow appears when falling raindrops bend
sunlight. Like a prism, each raindrop divides white
light into bands of different colors—the part of the
electromagnetic spectrum people can see. There are
other parts that people cannot see. Parts of the
electromagnetic spectrum warm the air on a hot day.
216
ENGAGE
6 PS 3.d. Students know heat energy is also transferred between objects by
radiation (radiation can travel through space). • 6 ES 4.b. Students know solar
energy reaches Earth through radiation, mostly in the form of visible light.
Materials
Which material best heats water?
Make a Prediction
Which material—white paper, black construction
paper, or aluminum foil—will most quickly raise
the temperature of water when placed in direct
sunlight? Write your answer as a prediction in the
form “If I wrap three jars using white paper, black
construction paper, and aluminum foil, then . . .”
• 3 medium-size jars
Test Your Prediction
• black construction
paper
Experiment Fill three jars with the same
amount of water. Wrap one of the materials
around each jar, and secure each with a piece
of tape. Place the jars on a level surface
in a location that receives direct sunlight.
Place a thermometer in each jar, and stir the water.
Record the temperature of the water in each jar.
Wait 30 minutes, stir the water, and record the
temperature of the water in each jar again.
• white paper
• aluminum foil
• tape
• 3 thermometers
Step
Draw Conclusions
Use Numbers For each jar, subtract the initial
temperature of the water from the temperature
recorded after 30 minutes in the sunlight.
In which jar was the temperature of the water
most increased? Was your prediction correct?
Infer What caused the water temperature in the
jars to rise?
Step
Explore More
Set the jars in a place that does not receive direct
sunlight. Which jar will lose the most heat? Wait 30
minutes, stir the water, and record the temperature.
Which jar lost the most heat? Analyze the data and
present your results.
6 IE 7.d. Communicate the steps and results from an investigation
in written reports and oral presentations. • 6 IE 7.e. Recognize
whether evidence is consistent with a proposed explanation.
217
EXPLORE
▶ Main Idea
6 PS 3.d
6 ES 4.b
Heat travels from the Sun
to Earth by radiation in the
form of electromagnetic
waves.
▶ Vocabulary
electromagnetic spectrum,
p. 218
radiation, p. 220
absorption, p. 220
emission, p. 221
-Glossary
@
www.macmillanmh.com
▶ Reading Skill
Sequencing
4W`ab
What is the electromagnetic
spectrum?
The Sun’s energy is carried to Earth by
electromagnetic waves. The electromagnetic
spectrum is the wide range of electromagnetic
radiation ordered by wavelength. A wavelength
is the distance along a wave before it repeats.
Shorter wavelengths have higher energy, while
longer wavelengths have lower energy.
The electromagnetic spectrum, arranged from
waves with the lowest amount of energy to waves
with the highest amount of energy, consists of
radio waves, microwaves, infrared rays, visible
light, ultraviolet light, X rays, and gamma rays.
Radio waves have the longest wavelengths and
include transmissions of AM radio, shortwave
radio, TV, and FM radio. Microwaves, used
to power radar and satellite systems, as well
<Sfb
:Oab
Explore the
elctromagnetic
spectrum with
an engineer.
▲ the colors of visible light
218
EXPLAIN
The Electromagnetic Spectrum
Reading Diagrams
Which has a wider range of frequencies:
visible light or radio waves?
as ovens that cook food quickly, are
in the next part of the spectrum.
Infrared rays, which people feel as
heat, are given off by the Sun and other
sources, such as active volcanoes. Some
restaurants use infrared lamps to keep
food warm.
In the middle of the spectrum are
the wavelengths of visible light. We see
these wavelengths as colors that range
from red to violet.
The next part of the spectrum
includes ultraviolet light waves.
Ultraviolet waves carry more energy
than visible light waves. Overexposure
to ultraviolet rays and other high-energy
waves can be harmful to humans. After
ultraviolet rays are X rays and gamma
rays. Gamma rays have very short
Clue: Compare the ranges of the
frequencies.
wavelengths and carry so much energy
that they can even pass through metals
and concrete.
Quick Check
Sequencing How are the forms of
electromagnetic radiation arranged
from lowest energy to highest
energy?
Critical Thinking Compare the
characteristics of radio waves and
gamma rays.
219
EXPLAIN
How does electromagnetic
radiation reach Earth?
Electromagnetic waves travel
about 150 million kilometers
(93 million miles) to reach Earth
from the Sun. There is no air in
the empty space between Earth’s
atmosphere and the Sun. Without
air, there is no substance for
waves to travel through. How do
electromagnetic waves reach Earth?
The answer is that they travel by
radiation. Radiation is the transfer of
energy by electromagnetic waves. The
energy given off by the Sun is called
radiant energy. It does not require two
objects to be touching, as conduction
does. Nor does it require that the
objects be joined by a liquid or a gas,
as convection does.
The light produced by the Sun is
the most common example of radiation,
but all objects give off a wide range
of electromagnetic waves. The strength
of each type of radiation depends on
the temperature of the object.
220
EXPLAIN
▲ The International Space Station collects
solar radiation to make electricity.
Absorption and Emission
of Radiant Energy
When radiant energy falls on an
object, part of it is reflected, and part of
it is absorbed. Absorption is the process
of taking in radiant energy. A perfect
absorber of electromagnetic radiation
appears black, because it absorbs all
colors of visible light as well as other
types of radiation. Objects that appear
dark absorb some electromagnetic
radiation, while objects that appear
white or light-colored reflect more
radiation than they absorb. That is
why the jar you wrapped in black
paper in the Explore activity heated
the water to a higher temperature.
You might notice that dark objects
absorb more radiant energy if, on a hot
day, you touch a black metal surface
such as a car. The surface will feel
hotter than a white metal surface. It
has absorbed more infrared radiation,
which people feel as heat energy.
Emission is the process of giving
off absorbed electromagnetic waves.
A good absorber is also a good emitter.
Therefore a black, metal object takes
in more electromagnetic radiation, but
it also emits more. This means that once
a dark object is away from the source
of radiation, it will cool off faster than
a similar, light-colored object.
Solar radiation is the electromagnetic
radiation emitted by the Sun. With
a surface temperature of about 5,500°C
to 6,000°C (9,900°F to 11,000°F),
the Sun emits a great amount of highenergy, short-wavelength radiation.
Most of it lies in the visible and nearvisible, or infrared, parts of the
electromagnetic spectrum. A small
percentage falls in the ultraviolet range
of the spectrum.
As the Sun’s incoming energy passes
through Earth’s atmosphere, it may
be absorbed, reflected, or scattered.
Air molecules, water vapor, clouds,
dust, and pollutants play a role in
this process.
Wavelengths of visible light are
not greatly absorbed by anything
in the atmosphere, so they are able
to reach Earth’s surface. Each visible
color has its own properties and
scatters differently. For example, blue
light, which has a shorter wavelength,
is scattered more easily than red or
yellow light. This is why the sky looks
blue and the Sun looks yellow.
Quick Check
Sequencing What events lead
up to the emission of radiation
from an object?
Critical Thinking Why might
light-colored clothing be more
suitable than dark-colored
clothing in hot weather?
Absorption and Emission
Reading Photos
Why do you think the hot desert air cools
quickly at night?
Clue: What is the difference between the
two photographs?
221
EXPLAIN
What forms of radiation are useful?
Radiation in the electromagnetic
spectrum can be divided into two
categories: ionizing radiation and
non-ionizing radiation. Non-ionizing
radiation falls at the long-wavelength
end of the spectrum. Every time you
use a microwave oven, you see nonionizing radiation at work. Microwave
energy shakes the water molecules in
beverages and foods, creating friction.
The friction caused by the moving water
molecules heats the beverage or food.
In a microwave oven, all foods do not
heat at the same rate. This is why you
have to stir some foods to distribute
the heat.
High-energy radiation falls at
the short-wavelength end of the
electromagnetic spectrum. This type
of radiation has extremely high energy.
High-energy radiation has the power
to generate electricity, kill cancer cells,
and drive manufacturing processes.
Uses of Radiation
infrared light
microwaves
non-ionizing
radiation
radio waves
visible light
222
EXPLAIN
Electromagnetic radiation is
generally safe in small quantities
when used properly. People can take
advantage of its properties for daily
tasks as well as special uses.
Quick Check
Sequencing Explain how a
microwave oven heats food.
Distance and Energy
What happens to the light beam
from a flashlight as you move the
flashlight farther from a piece
of paper? Tape a sheet of graph
paper to the wall, and write an x
in the middle of the paper.
Critical Thinking Why do you
think that the ionizing radiation
used for cancer treatment has to
be administered in small doses?
X rays
ionizing
radiation
Measure Hold a flashlight 2
centimeters away from the paper.
Turn on the light, and keep the x
in the middle of the beam. Trace
a circle around the spot of light.
Count and record the number of
squares inside the circle.
Predict What will happen to
the size of the circle if you move
the flashlight to 4 centimeters
and then 8 centimeters from the
paper? How will this affect the
brightness of the light and the
size of the circle? Why?
Infer How does distance from the
light source affect the amount of
energy each square receives?
Reading Diagrams
Does a microwave oven use a higher or
lower frequency than an X-ray machine?
Clue: Look at the part of the spectrum
where microwaves and X rays are marked.
Infer If a planet were twice as far
from the Sun as Earth is, would it
receive half as much energy from
the Sun as Earth does? Explain.
What effect would this have on
the planet’s temperature?
223
EXPLAIN
What forms of radiation are harmful?
Although radiation is used by
people in many ways, large quantities
of certain types of radiation can cause
harm. These types of radiation, which
include ultraviolet light, X rays, and
gamma rays, are the highest energy
on the electromagnetic spectrum.
blood cells that help the body fight
off infections. However, small doses
of X rays are not considered harmful.
A chest X ray exposes a person to
about the same level of radiation as
he or she would get while flying across
the United States in a jet plane.
Ultraviolet rays from the Sun can
cause suntans and sunburns. Ultraviolet
rays cause pigment-producing cells
in the skin to produce a brown color.
In addition, the radiation damages the
DNA in skin cells. This damage may
lead to skin cancer. Ultraviolet radiation
also ages the skin and can harm the
eyes. Children under the age of 18 are
at greater risk from ultraviolet radiation
because their skin is more sensitive.
Gamma rays are very highfrequency, high-energy waves that are
given off by nuclear explosions and in
nature by radioactive elements such as
uranium. Gamma rays have enough
energy to pass through several
centimeters of solid lead, and they are
very dangerous to living cells.
X rays, in large quantities, can
harm living tissue by damaging or
killing cells. The effects can include
reddened or burned skin, eye damage,
cancer, and a reduction of the white
sunburned lead to skin cancer?
Quick Check
Sequencing How can becoming
Critical Thinking Why do you think
dentists make you wear lead aprons
when they take X rays of your teeth?
Scientists take many precautions
when they work with gamma rays.
224
EXPLAIN
Summarize the Main Idea
The electromagnetic
spectrum is the
wide range of
electromagnetic
radiation organized
by wavelength.
(pp. 218–219)
Unlike conduction
and convection,
radiation can travel
through empty space.
(pp. 220–221)
Think, Talk, and Write
Main Idea How does solar energy
reach Earth?
Vocabulary The transfer of energy by
electromagnetic waves is
.
Sequencing What happens to the
Sun’s incoming energy as it passes
through Earth’s atmosphere?
4W`ab
<Sfb
:Oab
Small amounts of
ionizing radiation are
useful for medical and
energy needs.
(pp. 222–223)
Critical Thinking Provide arguments
against the common misunderstanding
that all radiation is harmful.
Test Practice Which of the following
Make a
Study Guide
Make a half-book (see pp. 487–490). Use
the title shown. On the inside of the fold,
write two sentences about the main idea
of the topic.
Writing Link
types of radiation is used for
communication?
A gamma ray
B ultraviolet
C microwave
D solar
Test Practice What type of radiation
from the Sun can cause sunburns?
A non-ionizing
B ultraviolet
C X-ray
D infrared
Social Studies Link
Exploratory Writing
Evaluate Limited Resource
Think about all the forms of radiation
that you have encountered. Write a
paragraph explaining the positive and
negative effects of radiation on your life.
Find out how the use of the radio-wave
part of the electromagnetic spectrum
is managed and regulated and why this
is important.
-Review Summaries and quizzes online @ www.macmillanmh.com
225
EVALUATE
Form a Hypothesis
The Sun emits a huge amount of
electromagnetic radiation, including
wavelengths we can see and some we cannot.
Waves with shorter wavelengths have higher
energy. Scientists use information like this that
they read, as well as the results of experiments
they do, to help them form a hypothesis, or
make an educated guess, about something.
Then they read more, experiment more, and
draw conclusions.
Learn It
When you form a hypothesis, you make a testable statement
about what you think is true. You can test the statement to
support or disprove the hypothesis. Record all your findings and
observations. You are gathering the evidence you need to support
or disprove the hypothesis.
Try It
▶ In this activity you will form a hypothesis about which part of the
electromagnetic spectrum emits the most heat. You will test your
hypothesis by measuring the temperatures in different parts of
the spectrum. You will need a cardboard box, white paper, tape,
a glass prism, 4 thermometers, and a watch or a clock.
▶ Tape white paper in the bottom of the box. Attach the prism
to one top edge of the box. Place the box by a window so
sunlight shines through the prism to make a spectrum. Tape
the thermometers in the box so you can read the numbers.
Tape one on the blue band of the spectrum, one on the yellow
band, one just beyond the red band, and one in a shaded area.
Form a hypothesis about which thermometer will register the
highest temperature and what the order of the readings will
be, from highest to lowest. Record your hypothesis on a chart
like the one on page 227. Wait 1 minute, and then read each
thermometer. Record the results on your chart. Continue to
read the thermometers at 1-minute intervals for a total of 6
minutes, and record the data.
226
EXTEND
▶ Now use your data to answer these questions. What part
of the spectrum emits the most heat? What is the order of
temperatures, from highest to lowest? Do your data support
your hypothesis?
Apply It
▶ Would the temperatures in this kind of experiment be the same if
the box were lined with black paper? With aluminum foil? If you
used a desk lamp instead of sunlight? If you had a deeper box?
▶ Choose one of these variables, or make up one of your own,
and form a hypothesis about what you believe would happen.
▶ Then test your idea, and record the results to either support or
disprove your hypothesis.
6 IE 7.a. Develop a hypothesis.
227
EXTEND
Lesson 2
Solar Radiation
The Sun is the major source of energy for
life on Earth. How does that energy
affect life on Earth?
228
ENGAGE
6 ES 4.a. Students know the sun is the major source of energy for
phenomena on Earth’s surface; it powers winds, ocean currents,
and the water cycle. • 6 ES 4.b. Students know solar energy reaches
Earth through radiation, mostly in the form of visible light.
Materials
How can light energy
create motion?
Form a Hypothesis
A radiometer spins when exposed to sunlight. What
do you think will happen if it is exposed to different
sources of light? Write your answer as a hypothesis
in the form “If a radiometer is exposed to different
light sources, then . . .”
Test Your Hypothesis
Place the radiometer in bright, natural sunlight.
Record your observations.
• radiometer
Try using different light sources and light
sources with different intensities. Record your
observations. Does the radiometer speed up,
slow down, or stay the same?
• light sources
• black cloth
Step
Place a black cloth over the radiometer. Look
underneath and observe the vanes. Record
your observations.
Draw Conclusions
Analyze How would you explain what you
observed?
Did your observations support your hypothesis?
Infer Do you think there is air inside the
radiometer? Why or why not?
Explore More
How do you think the motion of the radiometer would
change if it were placed in direct sunlight for a whole
day? Form a hypothesis and test it. Then analyze and
present your results.
6 IE 7.a. Develop a hypothesis. • 6 IE 7.b. Select and use appropriate tools
and technology (including calculators, computers, balances, spring scales,
microscopes, and binoculars) to perform tests, collect data, and display data.
229
EXPLORE
▶ Main Idea
6 ES 4.a
6 ES 4.b
Almost all energy on Earth
comes from the Sun in the
form of light.
▶ Vocabulary
solar radiation, p. 231
How is the Sun an important
energy source?
At any given moment, the Sun is shining on
some part of Earth’s surface. Sunlight warms
the surface of the planet. The heat from the Sun
causes air currents and water currents to form.
On Earth, living things use the Sun’s energy to
carry out everyday functions.
-Glossary
@
www.macmillanmh.com
▶ Reading Skill
Energy from the Sun
Summarize
6% reflected by
the atmosphere
Ac[[O`g
25% reflected
by clouds
15% absorbed by
the atmosphere
4% reflected from
Earth’s surface
50% directly
or indirectly
absorbed by
Earth’s surface
230
EXPLAIN
Solar Radiation
Energy from the Sun that
shines on Earth’s surface is called
solar radiation . Plants use it to carry
out photosynthesis. They convert solar
radiation to chemical energy, which
can be used by other organisms. This
energy is passed along the food chain.
When a plant or animal dies, the
energy it contains becomes food for
decomposers or in time, it may become
a fossil fuel.
Solar radiation helped create fossil
fuels such as coal, oil, and natural gas.
These fuels were formed from plant
and animal remains buried under
layers of mud and other materials. The
plants and animals contained stored
energy from the Sun. Over millions of
years, heat and pressure turned this
stored energy into fossil fuels that we
use today.
Energy from the Sun also affects
nonliving things. For example, uneven
heating of Earth’s surface causes winds
and contributes to ocean currents.
Solar energy drives the water cycle
and influences a region’s weather and
climate. All of these factors determine
the kinds of organisms that live in
the region.
Quick Check
Summarize How do animals
obtain energy from the Sun?
Critical Thinking How did the
Sun’s energy become trapped
in fossil fuels?
▲ Plants use energy from the Sun to carry
out photosynthesis and to produce
food. Animals, such as this giraffe, take
in some of this energy when they eat.
231
EXPLAIN
Solar Energy and the Water Cycle
Reading Diagrams
How does the Sun
affect the water cycle?
Solar radiation powers the water cycle,
or the movement of water between Earth’s
surface and the air. Energy from the Sun
helps recycle Earth’s supply of water, which
is essential to life.
What happens after water vapor
condenses?
Clue: Follow the arrows to trace
the path through this cycle.
Watch solar
energy and the water cycle
@ www.macmillanmh.com
The main processes that occur during the water cycle
are evaporation, condensation, and precipitation. During
evaporation, solar radiation warms the water on Earth’s
surface. The water molecules absorb energy from the Sun and
move faster. Then the molecules near the surface of the water
escape into the atmosphere as water vapor.
Evaporation of water from Earth’s surface requires a great
deal of energy. More than 70% of Earth’s surface is covered
by oceans, so an enormous amount of water vapor rises into
the atmosphere every day. The Sun supplies the energy for all
of this evaporation.
▶ Solar radiation provides
the energy to obtain salt
from seawater at this
salt-production facility.
232
EXPLAIN
Temperatures in the atmosphere are
cooler than those at Earth’s surface,
because the atmosphere absorbs less of
the Sun’s energy than the surface does.
With less energy from the Sun available,
the water molecules in the atmosphere
slow down. They begin to change from
water vapor into liquid water. The
molecules collide and join together as
drops of water through condensation,
and in time they form a cloud.
When enough water accumulates in
a cloud, the water falls as precipitation.
Depending on the air temperature, the
precipitation may take the form of rain,
sleet, snow, or hail. Precipitation provides
water for living things and fills Earth’s
oceans, lakes, rivers, and streams.
Quick Check
Solar Still
You can use the Sun’s energy to
separate a solution of salt and
water. Make a saltwater solution
by dissolving 2 tablespoons of salt
per cup of fresh water. Fill a large
bowl with salt water to a depth
of about 2 inches.
Place an empty glass in the center
of the bowl. The top of the glass
should be below the edge of the
bowl but above the surface of the
salt water.
Cover the bowl with plastic wrap.
Use tape, if necessary, to make
a tight seal.
Place a heavy object, such as a
rock, in the center of the plastic
wrap over the glass.
Summarize What happens to water
molecules in the air after they have
cooled due to a loss of energy?
Critical Thinking What part of the
water cycle does solar radiation
affect most directly?
Leave the still in direct sunlight
for a few hours. Then remove the
plastic wrap. Has water collected
in the glass?
Predict Do you think the water
in the glass is salty or fresh?
Why? How would you test your
prediction?
Sequence Explain the role of
evaporation and condensation
in transferring water to the glass.
233
EXPLAIN
How does the Sun affect
climate and weather?
The Sun is the major source of
heat energy for Earth. Earth’s surface
absorbs heat from sunlight, and the
surface heats the air above it. The
amount of heat energy that reaches
Earth in a place affects the area’s
climate and weather.
Climate
Climate is influenced by factors
such as temperature, precipitation,
wind, mountain ranges, ocean currents,
latitude, and altitude. Energy from
the Sun affects a region’s climate in a
variety of ways. It warms the air, land,
and oceans, and it helps determine
patterns of precipitation, wind, and
ocean currents.
Solar Radiation and Climate
Oga
a`
c\¸
A
`
Ob]
S_c
Reading Diagrams
How have the penguins adapted to life in a
region that receives limited solar radiation?
Clue: Look at the pictures of the penguins
and the camel. How do these animals differ?
234
EXPLAIN
To see how this works, shine a
flashlight at a sheet of graph paper.
Move the light upward from a low
angle to the paper until it is directly
above the paper. Notice that fewer
squares are lit as you move the
flashlight upward. In the same way,
when light from the Sun strikes
Earth at a higher angle, the energy
is concentrated in a smaller area.
high pressure
dry weather
low pressure
Sunlight does not strike Earth’s
surface at the same angle at all times or
in all places. It shines more directly at
the equator and more indirectly at the
poles. Areas near the equator receive
the most heat energy from the Sun and
generally have warm climates. Closer to
the poles, the Sun’s rays strike Earth at
a low angle, spreading their energy over
a large area and creating a cool climate.
wet weather
Weather
Weather is the state of the
atmosphere at a given place and
time. The local conditions that make
up weather are air temperature, air
pressure, humidity, wind, clouds,
and precipitation. All of these elements
are connected to the Sun’s energy.
For example, humidity, clouds, rain,
and snow result from evaporation,
which is caused by solar radiation.
Air pressure is the force put on an
area by the weight of the air above it.
Air pressure depends on the density of
the air. As air is heated by the Sun, the
molecules in the air move faster and
move farther apart from one another.
For this reason the heated air becomes
less dense and exerts less pressure on
Earth’s surface.
Differences in air pressure are also
the cause of wind, or moving air. Air
moves from areas of high pressure to
areas of low pressure. By determining
air pressure, heat energy from the Sun
also affects wind patterns. Winds, in
turn, drive the currents on the surfaces
of Earth’s oceans.
Quick Check
Summarize How does the angle at
which the Sun’s rays strike Earth’s
surface affect climate?
Critical Thinking What type of
weather often follows an increase
in air temperature?
235
EXPLAIN
How does Earth gain
and lose energy?
Almost all the heat on Earth comes
from the Sun. Earth also gives off,
or radiates, heat into space. If Earth
were not able to give off some of the
energy from the Sun, the planet would
be too hot for life. When the balance
of heat energy is maintained, Earth’s
average surface temperature remains
about 14°C (59°F). A disruption in
the balance can cause the average
temperature to rise or fall.
The atmosphere plays an important
role in maintaining the balance of
heat energy on Earth. When the Sun’s
energy reaches the atmosphere, part of
it is reflected back into space by water
droplets in clouds and dust particles.
Another part is absorbed by water vapor
in the atmosphere. Only about half of
incoming heat energy reaches Earth’s
surface and is absorbed by it.
Different materials on Earth
absorb energy differently. Darkcolored objects become hotter than
light-colored objects when exposed to
the same amount of sunlight. This is
why, on a hot day, people might walk
barefoot comfortably over a concrete
sidewalk but hop painfully over a
black, asphalt driveway.
The ocean and the land also absorb
heat energy differently. Water heats up
and cools down more slowly than land,
because it takes more heat to raise
the temperature of water than it takes
to raise the temperature of land. The
resulting differences in temperature
influence weather and climate.
Quick Check
Summarize What happens after
the Sun’s energy reaches Earth’s
atmosphere?
Critical Thinking Explain how
water vapor in the atmosphere
keeps Earth’s surface warm.
◀ Even on a warm day,
ocean water can be cool.
236
EXPLAIN
Summarize the Main Idea
Solar radiation is the
source for almost all
the energy on Earth.
(pp. 230–231)
Think, Talk, and Write
Main Idea How does energy from
sunlight affect Earth?
Vocabulary Energy from the Sun that
shines on Earth’s surface is
.
Summarize What happens as air is
heated by the Sun?
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The water cycle moves
water between Earth’s
surface and its air.
Solar radiation powers
the water cycle.
(pp. 232–233)
Energy from the Sun
affects the climate and
weather of a region.
(pp. 234–236)
Make a
Study Guide
Make a three-tab book (see pp. 487–
490). Use the titles shown. On the inside
of each tab, summarize how that topic
can help you
understand how
energy from
sunlight affects
Earth.
Writing Link
Ac[[O`g
Critical Thinking How might Earth’s
surface temperature be affected if it
had no oceans?
Test Practice Which of the following
processes is not a main part of the
water cycle?
A evaporation
B precipitation
C absorption
D condensation
Test Practice Which of the following
does not influence climate?
A temperature
B precipitation
C ocean currents
D moonlight
Math Link
Write a Story
Compare Temperatures
How important is the Sun to you?
Write a story about some of the things
that you can do because of the Sun’s
energy.
The average temperature on the
surface of Earth is 14°C. The surface
of the Sun is about 400 times hotter.
What is the average temperature of
the surface of the Sun?
-Review Summaries and quizzes online @ www.macmillanmh.com
237
EVALUATE
Wildfire Alert
Every year wildfires blaze throughout Southern
California. The wildfires are fueled by the Santa Ana
winds. These warm, dry winds blow out of the desert
when it is cold, from October through March. They can
gust up to 50 or 60 knots through canyons and passes,
nearly as fast as a car on the freeway. The winds occur
when high atmospheric pressure builds to the north
and east of Southern California. Cold air then begins
to sink and flow downhill from the mountains, where
it compresses and warms. As the temperature rises, this
air starts to dry up, creating the fast, hot, dry Santa
Ana winds.
These winds can bring disaster to the residential
areas of Southern California that have been built on
the grasslands. The extremely low humidity helps dry
out vegetation, making it a better fuel for a fire. In
addition, the winds can cause a fire to change direction
in ways that are complex and difficult to predict.
wildfire beginning
238
EXTEND
peak of wildfire
wildfire burning out
ELA R 6.2.3. Connect and clarify main ideas by identifying
their relationships to other sources and related topics.
Science, Technology, and Society
The USDA Forest Service monitors the speed and
direction of the Santa Ana winds to predict what impact
they may have on a fire.
Scientists also use data from satellites above Earth that
help them see fires from up above. Imagine if you had to
battle a wildfire using only information you could get from
the ground. By the time you got people out to the perimeter
of the fire, it might have spread in new directions. You
would need an incredible number of people and a lot of time
just to be able to survey the fire area.
NASA’s Terra and Aqua satellites fly 644 kilometers
(400 miles) above Earth. Data collected from these satellites
is transmitted rapidly to the forest service. The information
helps the forest service know the whereabouts of a fire
almost immediately. By working as a team, scientists and
firefighters are able to control wildfires better than before.
Sequencing
▶ Look for steps that
happen first and last.
Write About It
▶ Think about how steps
relate to each other.
Sequence
1. How do the Santa Ana winds affect
vegetation before the outbreak of a wildfire?
2. What happens if the Santa Ana winds blow
during a wildfire?
-Journal Write about it online @ www.macmillanmh.com
239
EXTEND
Lesson 3
The Power
of Convection
Currents
When glaciers flow into the sea, they break into huge
blocks of ice known as icebergs. As icebergs travel
toward the equator, they shrink in size and decrease in
number. Which portion of an iceberg melts faster, the
part above the water or the part that is submerged?
240
ENGAGE
6 ES 4.c. Students know heat from Earth’s interior reaches the surface
primarily through convection. • 6 ES 4.d. Students know convection
currents distribute heat in the atmosphere and oceans.
Materials
How does heat move
in liquids and gases?
Make a Prediction
When an ice cube melts in room-temperature
water, what do you think happens to the melted
water? Where does it go? Write your answer as
a prediction in the form “If an ice cube melts in
room-temperature water, then . . .”
• clear plastic
container
Test Your Prediction
• ice cube dyed
with blue food
coloring
Fill the plastic container about two-thirds full of
water. The water should be at room temperature
and perfectly still. Gently place the blue ice cube
in the water at one end of the container. Add
two drops of red food coloring to the water at
the opposite end of the container.
• red food coloring
• color pencils
• paper
Observe Carefully observe where the blue
water flows and where the red water flows.
Use color pencils to draw the flows of the two
different-color waters.
Step
Draw Conclusions
Analyze How would you explain what you
observed?
Did your observations support your prediction?
What caused the behavior of the blue water?
Why did the water in the tank appear to circulate?
What happens when warm and cool water
meet? Explain your answer.
Explore More
What would happen if you placed a dyed ice cube
in very cold water? Form a hypothesis and test it.
Then analyze and present your results. Does circulation
take place in air? What examples can you find to
demonstrate warm air’s rising or cold air’s sinking?
6 IE 7.a. Develop a hypothesis. • 6 IE 7.d. Communicate the steps and
results from an investigation in written reports and oral presentations.
241
EXPLORE
What are convection currents?
▶ Main Idea
6 ES 4.c
6 ES 4.d
Most heat transfer in the
atmosphere, in the ocean,
and in Earth’s interior
occurs through convection.
▶ Vocabulary
wind, p. 244
Santa Ana wind, p. 244
ocean current, p. 246
Gulf Stream, p. 246
California Current, p. 247
ENSO, p. 248
-Glossary
@
www.macmillanmh.com
▶ Reading Skill
Sequencing
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Explore convection
with a chef.
242
EXPLAIN
A hot-air balloon can rise only if the pilot
uses a burner to heat the air inside the balloon.
As the air is heated, the molecules in the air move
apart. As the air inside the balloon is heated,
it becomes less dense than the air surrounding
the balloon. This enables the balloon to rise.
To slow the motion of the balloon or to descend,
the pilot opens a valve located at the top of the
balloon. This releases hot air.
The Isles of Scilly
Reading Photos
Why are subtropical plants able
to grow in the Isles of Scilly, off
southwest England?
Currents at Work
The molecules in gases and in most
liquids are not as close to each other
as they are in solids. When cold air
sinks toward Earth’s surface, it is
heated by the ground, becomes less
dense, and rises. More cold air moves
in to take its place. This creates a
pattern of rising and sinking air called
a convection current.
As you saw in the Explore activity,
the same pattern takes place in water.
Convection also takes place in the
thick rock that flows in Earth’s
mantle. Convection currents affect
other things on Earth’s surface, such
as plate tectonics and different types
of weather. For example, the Isles
of Scilly, part of Great Britain, enjoy
a mild, almost tropical climate
Clue: Look at arrows that show the
Gulf Stream on the locator map.
despite their location in the northern
latitudes. The Gulf Stream and its warm
currents enable subtropical plants to
thrive in this unlikely spot. In the
following sections, you will learn
how convection powers wind, ocean
currents, and the transfer of heat in
the layers of Earth.
Quick Check
Sequencing What happens in
the atmosphere after cold air
sinks toward Earth’s surface?
Critical Thinking What
characteristics are shared by
the materials in the atmosphere,
the ocean, and Earth’s mantle?
243
EXPLAIN
What makes wind blow?
Wind is air that moves horizontally
near Earth’s surface. The ultimate
source of wind is the Sun. As you
know, the uneven heating of Earth’s
surface by the Sun produces convection
currents. The up-and-down motions
of air that occur during the convection
process cause differences in air
pressure. Wind is the air that flows
from areas of higher pressure to areas
of lower pressure.
Regions near the equator receive the
most direct and most intense sunlight,
which makes the air very warm. This
heat causes a great deal of water to
evaporate, so the air is moist. Warm,
moist air over the equator creates a
zone of low pressure.
Because of the low angles at which
the Sun’s rays strike Earth’s surface at
the poles, incoming energy is spread
out over a wider area. As a result the
temperatures are cold, and the air is
dense. The warm air from the equator
rises and moves toward the poles.
Meanwhile the cooler air at the poles
sinks and moves toward the equator.
This movement creates a global pattern
of air moving from high-pressure zones
to low-pressure zones.
There are two types of winds: local
winds and global winds. Local winds
can blow from any direction and cover
short distances. Global winds blow
from a specific direction and typically
cover longer distances.
Sometimes people who are affected
by local winds give them specific
names. The Santa Ana winds are
244
EXPLAIN
well-known in California. These
winds begin with an area of high
air pressure to the north and east of
Southern California. The air flows
down through the deserts toward low
pressure offshore. These hot winds dry
out vegetation in the area, providing
fuel for raging wildfires.
Factors That Affect Winds
The global pattern of air moving
from high-pressure zones to lowpressure zones does not follow a straight
north-to-south path. The rotation of
Earth toward the east curves the paths
of the winds. Winds in the Northern
Hemisphere curve to the right, or
clockwise, as they move, and winds in
the Southern Hemisphere curve to the
left, or counterclockwise. This deflection
of the winds is called the Coriolis effect.
Expanding and
Contracting Air
Place a balloon over the opening
of a bottle as shown in the picture.
What do you think will happen
if you heat or cool the air in the
bottle? Hold the bottle for a
minute or two in a pail of warm
water. Observe what happens
to the balloon.
wildfire in Sonoma
County, California
The land’s geography also affects
the movement of air. For example, land
features such as mountains affect local
winds. Between sunrise and midday,
mountains absorb a greater amount
of heat from the Sun than valleys do.
As a result warm air rises off the slopes
of mountains. Cool air moves out of the
valleys to replace the warm air. This is
called a valley breeze. In the afternoon
the valley radiates heat. The mountain
peaks circulate cool air into the valley.
This is called a mountain breeze.
Quick Check
Sequencing What happens after
warm air from the equator moves
toward the poles?
Critical Thinking Besides the
Coriolis effect and the geography of
the land, what might deflect winds?
Infer Explain what happened to
the air in the bottle. What evidence
do you have for your explanation?
Now hold the bottle in a pail of
ice water for a few minutes. What
happens to the balloon?
Infer Use your observations to
answer these questions. As the
bottle cooled, what happened
to the air pressure inside? How
did the pressure outside compare
to the pressure inside? What
caused the changes to the balloon?
Draw “before” and “after” pictures
of the bottle. Use arrows to show
what happened to the air pressure.
245
EXPLAIN
Major Ocean Currents
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What causes ocean
currents?
An ocean current is a continuous
flow of water along a definite path.
To visualize an ocean current, try to
imagine a river, such as the Mississippi
River, flowing through the sea. Like
wind currents, ocean currents form
because of the uneven heating of
Earth’s surface by the Sun. Ocean
currents carry warm water away from
areas near the equator to the polar
regions. These convection currents
also move cold water from the polar
regions to lower latitudes.
Winds propel some ocean currents
on the surface. Other currents move
deep beneath the surface. Factors such
as temperature and density influence the
movement of ocean currents. Salinity,
the amount of salt in water, changes the
density of the water. Salinity can also
affect the currents.
246
EXPLAIN
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Suppose you put a message in a
bottle and dropped it into the ocean
off the California coast. Where might
the bottle travel to?
Clue: Look at the map, and determine
where the currents flow off the coast
of California.
Surface Currents
Winds blowing steadily across the
ocean cause the top layer of water to
move in huge, circular patterns. Surface
currents can move at speeds of about
120 kilometers (75 miles) per day. These
currents may move water hundreds of
kilometers through the ocean.
As currents flow along the edges of
continents, the currents affect the land’s
climate. One of the strongest ocean
currents in the world is the Gulf Stream ,
which carries warm water from the
southern tip of Florida north along
the eastern coast of the United States.
The Gulf Stream not only keeps the
east coast of the United States warm
but also keeps parts of northern
Europe from freezing. By contrast
the California Current carries cold
water toward the equator along the
west coast of the United States, keeping
the climate of the northwest cool.
However, deepwater currents take up
a much larger part of the ocean than
surface currents do.
The Coriolis effect causes currents
to bend to the right, or clockwise,
in the Northern Hemisphere and to
the left, or counterclockwise, in the
Southern Hemisphere. The currents
then start flowing in huge circles,
forming a continuous global pattern
of water circulation. The presence of
coasts or landmasses also affects the
flow of the surface currents.
Sea Breezes
Deepwater Currents
Colder, saltier water is denser than
warmer, less-salty water. Cold, dense
water flowing from polar regions moves
under warmer, less-dense water. As
the colder currents move toward the
equator, they become warmer and rise
to the surface. Warm waters from these
regions flow toward the poles, where
they cool down and begin to sink.
The water in a deepwater
current moves much more
slowly than the water
in a surface current—
just a few meters per day.
Another example of convection at
work is a breeze that occurs along a
coastline. Because land heats up faster
than water, the air above land is warmer
during the day than the air over a
nearby body of water. The warm air
expands and rises. The cooler air above
the water moves in and replaces the
rising warm air. A sea breeze is a wind
that blows from the sea toward the land.
At night the process reverses. The
air over the land cools more rapidly
than the air over the water. Winds blow
from the land to the sea, producing
a land breeze.
Quick Check
Sequencing Describe the events
that produce a sea breeze.
Critical Thinking Why does the
water in a deepwater current move
more slowly than the water in a
surface current?
humpback whale
247
EXPLAIN
What is El Niño/
Southern Oscillation?
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Convection currents in oceans
have a tremendous influence on world
climates. Winds move currents as
they blow across the oceans. Ocean
currents, in turn, interact with the
atmosphere. Any disruption in these
systems can cause climate changes.
Results of El Niño
Under normal conditions the trade
winds near the equator blow toward the
west. Warm surface water builds up in
the western Pacific Ocean. Along the
western coast of South America, water
from deeper levels of the ocean moves
up to the surface. The cold, nutrient-rich
water supports large numbers of fish.
Every few years the surface waters
near Peru and Ecuador become
unusually warm. As a result the water
holds fewer nutrients, so there are
fewer fish, and fish-eating birds die.
People working in the area have been
aware of this pattern, called El Niño
(el NEEN•yoh), for centuries. During
most years strong winds from the
North American and South American
coastlines push warm water across the
Pacific toward Australia and Japan.
When the warm water moves to the
west, cold water rises to the surface to
replace it. During El Niño years, which
occur every three to seven years, the
wind is weak, and little water is pushed
across the Pacific. With no cold water
rising, the ocean stays warm.
Scientists use the term ENSO , or El
Niño/Southern Oscillation, to refer to
the disruption of the ocean-atmosphere
system in the Pacific Ocean and
248
EXPLAIN
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the impact that it has on weather
around the globe. The word oscillate
(AH•si•layt) means “to swing back and
forth.” The Southern Oscillation is a
back-and-forth pattern of reversing
surface air pressure between the eastern
and western Pacific Ocean along
the equator. ENSO may come and
go quickly, or it may last for several
months. When the equatorial Pacific
waters become unusually cold,
a La Niña (lah NEE•nyah) may form.
Effects of ENSO
Scientists are not sure of the causeand-effect relationship between the
changes in the atmosphere and the
changes in the ocean during El Niño.
They do not know whether pressure
reversals in the atmosphere cause
ENSO or ENSO causes the changes
in the atmosphere. They do know
that there are very dramatic climate
changes during ENSO. In the ocean the
cold water carries nutrients for marine
life. Without the new nutrients, large
numbers of fish and other organisms
die. During ENSO, the entire food
chain is affected.
On land, weather patterns across
the world change. Areas that are
usually dry may receive a great deal
of rain, and area that are usually wet
may experience droughts.
ENSO often brings heavy storms
to the Gulf of Mexico, Peru, Ecuador,
Bolivia, and Cuba, causing landslides
and floods. Other areas, such as
southern Africa, Central and South
America, Indonesia, the Philippines,
and India, are hit with extreme
drought. This can lead to famine and
loss of life. During the last ENSO,
California experienced serious storms
that led to floods and mudslides.
In addition to its impact on regions
in the Pacific, ENSO causes changes in
the path of the jet stream, a current of
fast-moving air in the upper atmosphere.
The jet stream is one factor that
determines weather in North America.
ENSO
normal year
Strong winds keep warm surface
water in the western Pacific Ocean.
Cooler water rises to the surface of
the eastern Pacific Ocean.
El Niño year
Warm waters in the western Pacific
Ocean move east and prevent cool
water from rising to the surface.
Quick Check
Sequencing What happens in the
regions of the eastern Pacific Ocean
during El Niño?
Critical Thinking Why does ENSO
affect weather around the globe?
La Niña year
Very strong winds push warm water to
the western Pacific Ocean. Cool water
surfaces near California, bringing drier
weather to much of the United States.
249
EXPLAIN
How do convection currents work underground?
Earth consists of three main
sections: the crust, the mantle, and
the core. The temperature of the
inner core reaches 5,500°C (9,932°F).
Temperatures in the mantle are much
cooler but still quite hot. The mantle
consists of soft, yielding rock material
that slowly moves in currents like other
fluids. This material is cooler and
denser closer to the crust.
Because rock is a poor conductor
of heat, most of the transfer of heat
in Earth’s interior occurs through
convection currents. The rock material
in Earth’s mantle rises and falls. The
cooler material sinks toward the core.
Warmer, less-dense material rises. This
cycle distributes heat from Earth’s core
throughout the mantle.
Earth’s Convection Currents
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Only a small amount of heat
from Earth’s interior reaches the
atmosphere. The rocks in Earth’s
interior insulate the surface from the
core’s heat better than the clouds and
atmosphere insulate the surface from
the Sun. Heat from the core takes
longer to reach Earth’s surface than
the Sun’s heat takes to reach Earth.
Because of this, most of the heat on
Earth’s surface is from the Sun, not
from Earth’s core.
Power for Plate Tectonics
Convection currents in the mantle
push rock against the bottom of Earth’s
crust. This movement causes Earth’s
plates to move along Earth’s surface,
causing earthquakes and slow motions
of the crust.
Sometimes convection rises as
a column, or plume, of molten rock,
producing a hot spot. These hot
spots erupt as volcanoes. Examples
of convection hot spots are the
Hawaiian Islands and the volcanic
features of Yellowstone National Park,
such as geysers and hot springs.
Quick Check
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250
EXPLAIN
relationship between the
convection currents in Earth’s
mantle and the movement of
Earth’s crust.
Critical Thinking What
characteristics of Earth’s layers
cause convection currents in
the mantle?
Summarize the Main Idea
Convection currents
distribute heat in the
atmosphere, the ocean,
and the thick molten
rock material in Earth’s
mantle.
(pp. 242–243)
Wind flows from areas
of higher pressure to
areas of lower pressure.
(pp. 244–245)
Think, Talk, and Write
Main Idea What causes most heat
transfer on Earth?
Vocabulary A continuous flow of water
along a definite path is a(n)
.
Sequencing Describe what causes the
Santa Ana winds.
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Ocean currents
form because of
uneven heating of
Earth’s surface.
(pp. 246–249)
Make a
Study Guide
Make a layeredlook book (see pp.
487–490). Use the
titles shown. On
the inside of each
tab, write several
sentences that
summarize each
of the topics.
Writing Link
Critical Thinking What causes the
variation in the density of the rock
material in Earth’s mantle?
Test Practice What causes winds
and water currents to bend to the
right in the Northern Hemisphere?
A ENSO
B the Coriolis effect
C the Gulf Stream
D convection currents
Test Practice What carries cold water
toward the equator along the west
coast of the United States?
A a sea breeze
B the Gulf Stream
C ENSO
D the California Current
Social Studies Link
Write a Short Story
Watch World Weather
Write an original short story that
helps younger students understand
the movement of convection currents
in Earth’s layers. Be sure your story
includes characters, setting, and plot.
Identify an area of the world that is
affected by ENSO. Determine what
weather patterns might be connected
to ENSO. Present your findings to
the class.
-Review Summaries and quizzes online @ www.macmillanmh.com
251
EVALUATE
Good expository
writing
▶ introduces the
main idea and
develops it with
facts and details.
▶ organizes facts
and details in a
logical order.
▶ draws a conclusion
based on the facts
and details.
A growing number of people in the United States
are moving to underground homes. Most of these
homes, however, are not completely underground.
They often have a roof that lets in sunlight and fresh
air. Many have one or two sides above ground level.
Underground homes have many advantages over
aboveground ones. Unlike aboveground houses, they
let in very little dust or pollen. They stay warm in
winter and cool in summer. Your family could save
money on oil, gas, and electricity.
Underground homes need less painting and repair.
They are also safer. The earth protects the house from
fires, storms, and earthquakes. If you add up these facts,
then the underground house may be a good choice.
Write About It
Expository Writing Choose one of these topics to compare and contrast:
1. Compare and contrast the price of an energy-saving air conditioner or
refrigerator to the savings in energy costs. How long would it take the
appliance to save as much as it cost?
2. Compare and contrast two brands of refrigerators. Which is more
energy efficient?
-Journal Write about it online @ www.macmillanmh.com
252
EXTEND
ELA W 6.2.2. Write expository compositions (e.g., description, explanation, comparison
and contrast, problem and solution): a. State the thesis or purpose. b. Explain the
situation. c. Follow an organizational pattern appropriate to the type of composition.
d. Offer persuasive evidence to validate arguments and conclusions as needed.
Solar Heating: What Are the Costs?
Solar energy is a renewable source of both heat
(thermal) energy and light energy. Solar collectors,
such as solar panels, absorb heat from the Sun and can
provide hot water or heat for homes and businesses.
Solve It
1. A 60-watt lightbulb uses 4 kilowatt hours (kWh)
per month. (A watt is a unit of electrical power;
a kilowatt is 1,000 watts.) How many kWh does
it use per year?
2. A home heated with solar panels uses 2,250
kWh of electricity per year. A home heated with
power plant–generated electricity uses 9,000
kWh of electricity per year. At a cost of 40 cents
per kWh for solar energy and 12 cents per kWh
for power plant–generated electricity, which
home has lower electricity costs per year? What
is the difference in electricity costs between the
two homes, expressed as a percent?
Finding yearly cost
▶ To determine the
yearly energy cost
for an item, multiply
the cost per day,
week, or month by
the appropriate
number.
▶ To determine the
cost of using either
solar or power plant–
generated electricity,
multiply the amount
of electricity used by
the cost per kWh.
3. Do you have the information you need to solve the following
problem? If not, what else do you need to know? One family
with solar heating spent $12,000 to install the solar panels. If
they spend $900 per year for electricity, how many years will
it take for them to use 10,000 kWh?
MA MR 6.1.1. Analyze problems by identifying relationships, distinguishing
relevant from irrelevant information, identifying missing information,
sequencing and prioritizing information, and observing patterns.
253
EXTEND
Materials
Inquiry Structured
What can convection currents do?
Form a Hypothesis
2 jars
small piece of
cardboard
Convection currents can be seen in air and in water. They even occur
in Earth’s mantle. The heating and cooling of air causes convection
currents. A circular pattern is created, in which warm air rises and
cooler air moves in to take the place of the warm air. Convection
currents cause wind and other weather patterns. How does the
temperature of the air affect the movement of convection currents?
Write your answer as a hypothesis in the form “If air is cooled, then . . .”
Be Careful. Be careful using matches.
Test Your Hypothesis
matches
ice
2 plastic tubs
(1 for ice, 1 for
warm water)
Experiment Place one jar in a
plastic tub filled with ice. Place the
other jar in a tub of warm water.
Leave the jars for 10 minutes.
Remove the jar from the tub of ice.
Have your teacher light a match
and immediately blow it out.
Hold the opening of the jar over
the smoking match to trap some
of the smoke. Place a piece of
cardboard on the opening of the
jar, and turn the jar right side up.
Make a Model Place the jar from
the tub of warm water over the
jar from the tub filled with ice.
Remove the cardboard. Make
sure to keep the jars together
so the smoke cannot escape.
Observe the movement of
the smoke, and record your
observations in your journal.
Observe While still keeping the
jars together, flip the jars over.
Observe the smoke, and record
your observations in your journal.
254
EXTEND
Step
6 IE 7.d. Communicate the steps and results
from an investigation in written reports and oral
presentations.
Step
Step
Step
Draw Conclusions
Define Based on Observations What did the smoke do when
you first removed the cardboard in step 3? Why did that
happen?
Communicate What happened to the smoke when you flipped
the jars over?
Infer What do you think the smoke would do if you placed the
model in a hot-water bath? Try it.
Inquiry Guided
What happens when cold
air meets warm air?
Form a Hypothesis
How do convection currents behave in the atmosphere? Write
your answer as a hypothesis in the form “If warm air and cold air
come together, then the warm air will . . .”
Test Your Hypothesis
Design an experiment to create and test a model that
demonstrates convection currents in the air. Write out the steps
you will follow. Record your results and observations.
Draw Conclusions
Did your experiment support your hypothesis? Why
or why not? What did you observe in your convection-current
model? Could your observations explain how wind is created?
Inquiry Open
What else can you learn about convection currents?
For example, how can convection currents be affected
by the rotation of Earth? Design an experiment to
answer your question. Your experiment must be
organized to test only one variable, or one item being
changed. Your experiment must be written so that
another group could complete the experiment by
following your instructions.
Remember to follow the
steps of the scientific process.
Ask a Question
Form a Hypothesis
Test Your Hypothesis
Draw Conclusions
255
EXTEND
CHAPTER
4 Review
Summarize the Main Ideas
Heat travels from
the Sun to Earth by
radiation in the form of
electromagnetic waves.
Fill each blank with the best term
from the list.
absorption, p. 220
ocean currents, p. 246
electromagnetic
spectrum, p. 218
Santa Ana
winds, p. 244
emission, p. 221
solar
radiation, p. 231
(pp. 216–225)
The Sun is the source
of almost all energy
on Earth.
(pp. 228–237)
Convection currents are
movements of materials
due to differences in
temperature.
(pp. 240–251)
Make a
Study Guide
Take a sheet of paper and tape
your lesson study guides as shown.
Use the study guides to answer
the questions on these pages.
ENSO, p. 248
wind, p. 244
1. Radio waves, microwaves, visible light,
infrared light, and X rays are all part of
the
. 6 PS 3.d; 6 ES 4.b; 6 LS 5.a
2. During photosynthesis plants convert
into chemical energy.
6 PS 3.d; 6 ES 4.b; 6 LS 5.a
3. Local winds that begin with an area
of high air pressure to the north and
east of Southern California are the
. 6 PS 3.d; 6 ES 4.d, e
4. When an object such as a black
seat in a car takes in radiant energy,
the process is called
.
6 PS 3.a, d; 6 ES 4.b
5. A disruption in the ocean-atmosphere
system in the Pacific Ocean that can
cause changes in global weather
patterns is commonly referred to as
. 6 PS 3.d; 6 ES 4.b
6. When an object gives off absorbed
electromagnetic waves, the process
is called
. 6 PS 3.d; 6 ES 4.b
7. Some
carry warm water
away from areas near the equator
toward the polar regions. 6 PS 3.d;
6 ES 4.b, d
8. The movement of air due to differences
in air pressure is
.
6 PS 3.d; 6 ES 4.b, d, e
256
-Review Summaries and quizzes online @ www.macmillanmh.com
Answer each of the following
in complete sentences.
9. Infer People recovering from burns
often wear protective clothing when
in the Sun. Explain why this clothing
is light in color. 6 PS 3.a, d; 6 ES 4.b
10. Critical Thinking On thermograms,
or heat pictures, brighter colors
indicate areas of greater heat. How
can these be used to detect ocean
currents? 6 PS 3.d; 6 ES 4.b, d
11. Cause and Effect What is the
relationship between wavelength on
the electromagnetic spectrum and
degree of harmfulness to humans?
6 PS 3.d; 6 ES 4.b
12. Sequence Follow the path of a rock
that has recently been submerged
and melted in Earth’s mantle. Point
out where it contributes to the
movement of Earth’s continents.
6 PS 3.d; 6 ES 4.c
13. Explanatory Writing South
American people who caught fish
in the ocean have been aware of El
Niño for centuries. Write a letter to
these people, explaining why this
phenomenon occurs. 6 PS 3.d; 6 ES 4.b
Save the Ozone
Ozone in Earth’s atmosphere absorbs
most of the harmful ultraviolet radiation
from the Sun. However, chemicals are
destroying the ozone layer. The dark
circles in the illustration below show an
area where the amount of ozone in the
atmosphere has been depleted. Your
task is to convince world leaders that
protecting the ozone layer is vital.
What to Do
1. Prepare a visual presentation that
explains what ultraviolet rays are
and why they are harmful.
2. Write a position paper that states
your opinion. Develop at least three
supporting details that defend your
position.
Analyze Your Results
▶ What are the risks involved with ozone
depletion?
▶ What can be done to reduce ozone
depletion?
How do radiation and convection
currents affect phenomena on
Earth?
257
1
Which kind of energy can be
transferred through empty
space? 6 PS 3.d
A
B
C
D
2
3
sound energy
potential energy
food energy
light energy
Which of the following is the
best example of heating by
radiation? 6 PS 3.d
A
B
C
D
The graph below shows temperatures
recorded at a lake on a sunny day.
It compares the temperature of the
water with that of the sandy beach.
4
If you wanted to measure the
temperature of an object sitting
in sunlight for an hour, you
would use 6 PS 3.d
A
B
C
D
5
a pan heating on the stove
an oven baking cookies
sunlight warming a pool
water boiling in a kettle
a microscope.
binoculars.
a balance scale.
a thermometer.
What kinds of radiation are the
most harmful? 6 ES 4.b
A gamma rays, X rays, and
ultraviolet light
B infrared light and magnetism
C radio waves and microwaves
D visible light, sound waves, and
solar waves
6
Solar energy from the Sun is changed
to chemical energy by 6 ES 4.a
A chemists who work in laboratories.
B plants that change solar energy
Based on the graph, which
conclusion can you draw?
A
B
C
D
258
6 IE 7.e
Water heats faster than sand.
Sand heats faster than water.
Many fish live in the lake.
The plants living in the lake
keep it cooler.
into food.
C animals that absorb the Sun’s
energy.
D animals that change solar energy
into food.
7
The picture below shows a hot-air
balloon in flight. The pilot uses
a burner to heat the air inside the
balloon.
9
How does the Sun affect the water
cycle? 6 ES 4.a
A
B
C
D
10
It slows condensation.
It causes evaporation.
It decreases photosynthesis.
It absorbs radiation.
For heat to be transferred by
convection, 6 ES 4.c
A the molecules must be in a liquid
or gas.
B both substances must be cold.
C both substances must be on the
surface of Earth.
D the molecules of the warmer
substance must sink to the bottom.
11
Why does the balloon rise when the
air inside it is heated? 6 ES 4.d
A The molecules absorb the heat
energy and move away from
each other.
B The molecules absorb the heat
energy and move closer to each
other.
C The molecules move closer to
the heat.
D The molecules change into other
substances.
A The balloon becomes smaller and
less heavy.
B The balloon becomes larger and
less heavy.
C The air in the balloon becomes less
dense than the surrounding air.
D The air in the balloon becomes
denser than the surrounding air.
8
What happens to air molecules as
they absorb solar radiation? 6 ES 4.a
A They move faster and farther apart.
B They move slower and closer
together.
C They absorb water and cause rain
to fall.
D They thicken and form clouds.
What happens to molecules in
a liquid or gas when they are
heated? 6 ES 4.c
12
What happens to cold air as it sinks
toward the ground? 6 ES 4.d
A It becomes drier.
B It turns into fog.
C It becomes warmer and less dense
and rises.
D It becomes denser and produces
rain and snow.
Materials prepared by PASS at
259
We open our eyes each day, trusting that what we see
is really there. As strange as it may seem, however,
other animals see the same world in very different
ways. What the world looks like—and therefore what
is “real” to you—depends on your sense of sight!
The Spectrum:
How Animals See It
We see the part of the electromagnetic
spectrum called visible light. This
light—in red, orange, yellow, green, blue,
and violet—illuminates our world. All
the radiation beyond these frequencies
is invisible to us. Certain other animals,
though, have a visible spectrum that
extends beyond ours. We can only begin
to imagine how they see the world.
are a bright shade of blue-green to
bees. Other flowers are decorated with
patterns and lines. Like lights on an
airport runway, they guide bees in for
a landing and direct them to the center
of the flower. There the bee gathers
nectar and may pollinate the flower.
flower seen in
normal light
Bees: Flower Finders
A bee’s visible range is shifted
slightly toward the higher-frequency
end of the spectrum. Bees do not see
the color red. They do see beyond
violet into the ultraviolet range. Our
eyes cannot detect ultraviolet light, but
we can use an ultraviolet filter to get
an idea of what a bee sees. Amazingly
some flowers that look white to us
260
6 ES 4. Many phenomena on Earth’s surface are affected by the transfer of
energy through radiation and convection currents. • ELA R 6.2.2. Analyze
text that uses the compare-and-contrast organizational pattern.
▼ pit viper
Pit Vipers: Heat Hunters
Beyond our visible spectrum on
the opposite side is the infrared range.
Although we cannot see it, we feel
infrared radiation on our skin as heat.
Other animals sense heat with much
greater accuracy. Snakes called pit
vipers see as we do through their eyes,
but they have other sensory organs
between their eyes and nostrils. These
“pits” detect very slight variations
in heat. This means that the snakes
can sense warm-blooded prey even
in darkness. A hungry snake “sees”
a mouse because the animal’s warm
body stands out from the cooler
environment around it. The snake adds
this information to what it sees with
its eyes to produce a picture of
the mouse’s exact location.
flower seen in
ultraviolet light
261
Heating-and-Air-Conditioning
Technician
Air conditioning helps people survive the
steamy days of summer. In northern climates
people depend on heating systems during cold
winters. What happens when these systems break
down? The problems are solved by heatingand-air-conditioning technicians. They install,
maintain, and repair heating, air-conditioning,
refrigeration, and ventilation systems. To
work in this profession, people would need a
high-school education as well as training and
apprenticeships, in which they learn, while
working alongside experienced workers. In most
areas certification and licensing are required
in order to work with refrigerant gases and
heating-and-air-conditioning units.
Physics Teacher
When you see a roller coaster
complete a loop, do you think about
the forces that keep the machine on
the track? If you like physics, would
you enjoy sharing your interest with
the next generation? If so, a career as
a physics teacher might be for you.
Physics teachers use their knowledge and
creativity to lead discussions, perform
scientific demonstrations, and even
do research with their students. Most
states require a college degree in physics
and science education as well as state
teaching certification. Advanced degrees
are needed to teach at the college or
university level.
262
-Careers @ www.macmillanmh.com