1. Understanding Air Pressure 19.1

2. Air Pressure The force exerted by the weight of a column of air above a given point.

3. Barometer An instrument that measures atmospheric pressure.

4. Pressure Gradient The amount of pressure change occurring over a given distance.

5. Coriolis Effect The apparent deflective force of Earth’s rotation on all free-moving objects, including the atmosphere and oceans; Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

6. Jet Stream Swift high-altitude winds.

7. Key Concept Describe how air pressure is exerted on objects. Air pressure is exerted in all directions down, up, and sideways. The air pressure pushing down on an object exactly balances the air pressure pushing up on the object.

8. Key Concept What happens to the mercury column of a barometer when air pressure changes? When air pressure increases, the mercury in the tubes rises. When air pressure decreases, so does the height of the mercury column.

9. Key Concept What is the ultimate energy source for wind? Wind is the result of horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure. The unequal heating of Earth’s surface generates pressure differences. Solar radiation is the ultimate energy source for most wind.

10. Key Concept How does the Coriolis effect influence free-moving objects? The Coriolis effect describes how Earth’s rotation affects moving objects. All free-moving objects or fluids, including the wind , are deflected to the right of their path of motion in the Northern Hemisphere. In the Southern Hemisphere, they are deflected to the left.