Ch 19.1 Understanding Air Pressure

Vocabulary:

• air pressure
• barometer
• pressure gradient
• Coriolis effect
• jet stream

Describe how air pressure is exerted on all objects

Air pressure is exerted in all directions- down, up, and sideways.  Air pressure pushing down on an object balances the air pressure pushing up on an object.

Explain how changes in air pressure affect the mercury column of a barometer

When air pressure is increased, the mercury in the tube rises.  When air pressure decreases, the height of mercury in the tube falls.

Cold air has more pressure than warm air b/c in cold air the particles are spaced closer together than they are in warm air.

Identify the ultimate energy source for wind

Wind results from horizontal differences in air pressure.  Air pressure flows from areas of higher pressure to areas of lower pressure.

Since unequal heating of the Earth’s surface generates pressure differences, solar radiation is the ultimate energy source for most wind

What three factors combine to control wind?

1. pressure differences
2. Coriolis effect
3. friction

Describe how the Coriolis effect influences freely moving objects

All free-moving objects or fluids, including wind are deflected due to the rotation of the Earth.

• In the Northern Hemisphere, they are deflected to the right
• In the Southern Hemisphere, they are deflected to the left

Difference in pressure are expressed as a pressure gradient. 

• Closely spaced bars indicate a steep pressure gradient and high winds.
• Widely spaced bars indicate a weaker pressure gradient and light winds

Friction acts to slow air movement, which changes wind direction