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AIR PRESSURE. What is Air Pressure ?. The weight of the atmosphere above a location per unit of area Measured in atmospheres, millimeters of Mercury or Millibars Standard Atmospheric Pressure (at Sea Level) = 1 atmosphere= 14.7 psi 760 mm or 29.92 inches
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What is Air Pressure ? • The weight of the atmosphere above a location per unit of area • Measured in atmospheres, millimeters of Mercury or Millibars • Standard Atmospheric Pressure (at Sea Level) = 1 atmosphere= 14.7 psi • 760 mm or 29.92 inches • 1013.25 mb BAROMETER
Factors that Affect Air Pressure • TEMPERATURE- as temperature increases, air pressure decreases ( warm air rises and expands) 2. Amount of WATER VAPOR- moist air weighs less than dry air- water weighs less than Nitrogen or Oxygen molecules 3. ALTITUDE- as you increase elevation, air pressure decreases, there are fewer molecules as you go up
Air Pressure Changes • WARM AIR weighs less than Cold Air warm air rises and expands, less dense • HUMID AIR weighs less than Dry Air water weighs less than Nitrogen or Oxygen gas
Weather Changes with A.P. Changes • FALLING BAROMETER – changeable weather (rain/snow/clouds) warmer, more humid air • RISING BAROMETER good (fair ) weather cooler, drier air