Understanding Air Pressure

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Chapter 19

• Understanding Air Pressure

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Air Pressure

• Pressure exerted by the air in all directions
  down, up, sideways.
• At sea level 1kg/cm2 1 atmosphere
• (about 15 pounds/inch2)
• Our bodies are built to withstand the pressure of
  1 atms

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Measuring Air Pressure

• Barometer measures air pressure
• Bar pressure
• Metron measuring instrument
• Scientist Torricelli invented the mercury
  barometer

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Mercury barometer
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• There is also an aneroid barometer
• Empty chamber that expands or contracts with
  changing pressure
• Used in airplanes to help determine altitude.
• Why would a barometer help determine altitude?

Air pressure changes with altitude
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Aneroid barometer
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• Your ears
• Water bottle example

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Wind

• Air that moves HORIZONTALLY
• Solar radiation is the ultimate energy source for
  wind (heats the air)
• 3 factors that control wind
• Pressure differences
• The Coriolis Effect
• Friction

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Pressure Differences

• Air will always flow from areas of HIGH pressure
  to LOW pressure

HiLow
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HIGH pressure to LOW pressure

• Can also mean
• Cold (sinking) to Warm (rising)

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• How do we determine the air pressure?
• Data points are plotted on a map
• Isobars lines that connect points of equal air
  pressure
• Similar to contour lines on a topographic map

Barometer
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• The closer the lines are together.
• Faster the pressure changes
• Faster the wind

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The Coriolis Effect

• The earths rotation affects moving objects
• all-free moving objects (fluids including wind)
  are deflected
• Northern hemisphere deflects to the RIGHT
• Southern hemisphere deflects to the LEFT

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Friction

• The earth rotates (spins)
• Therefore, there is FRICTION between the air and
  the Earths surface.
• Friction acts to slow air movement
• Higher up in atmosphere there is less friction,
  so air can move faster.
• Example Jet Streams