1. The Atmosphere’s Air Pressure Changes
Unit A Chapter 2 Section 1

2. Egg in a bottle: air pressure at work!
You can see more egg in a bottle tricks in YouTube videos.

3. Air Pressure
(Box 1) Defined as: the force of air molecules pushing on an area.
The greater the force, the higher the air pressure.
(Box 2) The greater the number of air molecules, the greater the air pressure.

4. *Air Pressure
Air molecules move in all directions so air pressure pushes in all directions.
Air pressure at any area on earth depends on the weight of the air above the area.

5. Air pressure is related to altitude and density!
(Box 3) Air pressure decreases as you move higher in the atmosphere because there is less air pushing on you from above.
(Box 4) Just as air pressure decreases with altitude, so does the DENSITY of the air.

6. Air pressure is related to altitude and density!
(Box 5) The air at sea level has greater air pressure than air at high altitudes because the greatest amount of the atmosphere is above you there.
It is also more dense!

7. Air moves from higher pressure areas to lower pressure areas.
Air pressure often varies in two locations at the same altitude.
(Box 6) Differences in air pressure causes air to move from areas of higher pressure toward areas of lower pressure.
The air may move only a short distance, or may travel many kilometers.

8. *Convection Currents Review*
The movement of energy from place to place by the flow of a heated material.
Warm water or air is less dense so it rises.
Cool water or air is more dense so it sinks. It moves in and helps push up warm air or water.

9. Barometers and Air Pressure
(Box 7) A barometer is an instrument that measures air pressure.
The flexible chamber on the barometer contracts when the air pressure increases.
The chamber expands when the air pressure decreases.

10. A2.1 Reflection On the back of your A2.1 Note Sheet:
Draw a quick sketch of the Earth and the four layers of its atmosphere. Show what happens to air pressure as you go up in altitude from Earth to outer space.
Show how differences in air pressure at the same altitude cause air to move. LABEL this drawing with the terms high pressure and low pressure.
Draw a picture of our class room barometer measuring air pressure and explain how it works.