Air Pressure, Study notes of Earth, Atmospheric, and Planetary Sciences

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Air Pressure

Can you feel it?

Air Pressure

• Air pressure is the measure of the force with which air molecules push on a surface.
• Air Pressure is GREATEST at the surface of Earth because there is more of the atmosphere above you to push down on you.

Air Pressure is dependant on DENSITY

• More dense air will have a higher air pressure- there are more air molecules in a given space to push down on you
• Less dense air will have a lower air pressure- there are fewer air molecules to push down on you. More Dense= more particles to push down on you Less Dense= fewer particles to push down on you

Air Pressure is affected by 3 factors

• 1 - Elevation, or altitude
• 2 - Temperature
• 3 - Water content

Impact of Water Content , or humidity , on Air Pressure

• Moist air is less dense than dry air, and

therefore has a lower air pressure.

• A water molecule has less mass than other molecules that make up the air. If you replace some of the air molecules with water molecules, the water lowers the density (and lowers the air pressure) O N O (^) N H2O O (^) H2O N Weighs less since H2O is lighter than Nitrogen and Oxygen

Impact of Temperature on Air Pressure

• Warm air is less dense than cold air.

Therefore, warm air has a lower air

pressure and cold air has a higher air

pressure.

• The molecules in warm air are moving fast and are spread farther apart. Therefore there are fewer air molecules in a given area to push down on you. Warm Air Cold Air

Mercury Barometer

Air Pressure Affects the Weather

• Air pressure in a weather system reflects the amount of water in the air, which affects the

weather.

Low air pressure usually results in Bad weather: stormy, cloudy, overcast. High air pressure usually results in Good weather: clear skies, no precipitation