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Lesson 1 Summary
Use with pp. 231–233
Lesson 1: How does air move?
Vocabulary
convection current when gases or liquids rise and sink in a circular path
Layers of Air
Do you know what is in the air you
breathe? Air is made of gases. About
8/10 of air is nitrogen. About 2/10 of air
is oxygen. The rest of the air is carbon
dioxide, water, and other gases. Earth is the
only planet with this kind of air.
The atmosphere of Earth has five layers.
The temperature changes as you go up
through the layers. As you go higher, the
altitude increases and the air pressure gets
lower. Altitude is how high you are in the
atmosphere. Air pressure is the amount of
air. The higher you are in the atmosphere,
the lower the air pressure is. The air
pressure changes because the gas particles
in the air are farther apart. The higher you
go, the less air there is above you.
Convection Currents
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Have you ever put your feet in a lake
to cool them off? Sunlight warms up land
quickly, but it takes longer to warm up
water. At night, land cools off faster than
water. This is why the air above land
and the air above water are different
temperatures.
Convection currents form when there
are different air temperatures. A convection
current happens when gases or liquids rise
and sink in a circular path.
Gas particles are closer together in cool
air. Gas particles are farther apart in warm
air.
This makes cool air heavier than warm
air. When warm and cool air are next
to each other, the cool air sinks and the
warm air rises. This is what happens to
convection currents near the ocean at
night.
There are six very large convection
currents in the air over Earth. The
convection currents over North America
and the spinning of Earth cause wind
patterns. In North America, this makes the
wind blow mainly from west to east.
There are jet streams high above the
ground. A jet stream is a very high fast
wind. The different temperatures between
the convection currents form jet streams.
Jet streams can change the temperature,
winds, and rain because it affects air
movement.
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Chapter 8, Lesson 1 Summary
Quick Study
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Lesson 1 Checkpoint
Use with pp. 231–233
Lesson 1 Checkpoint
1. As altitude increases, how does air pressure change? Why?
2. What causes convection currents?
3. In what direction do winds of North America generally blow?
Draw Conclusions At night, land cools more than water. Air
above land will be cooler than air above the water. What conclusion
can you draw about convection currents near the ocean at night?
© Pearson Education, Inc. 5
4.
Quick Study
Chapter 8, Lesson 1 Checkpoint
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