Aim: How can we explain air pressure?

Air Pressure a.k.a. Barometric Pressure The weight of air above us pushing down

Measuring Air Pressure Measured by a Barometer Measured in inches of Hg (mercury) OR millibars

Air Pressure Conversions 1. 1013.2 mb = _______________ inches This is 1 atm (atmosphere), or the standard sea level pressure. 2. 1022.8 mb = _______________ inches 3. 1005. mb = _______________ inches 4. 985. mb = ________________ inches 5. _______________ mb = 30.53 inches 6. ________________ mb = 29.81 inches 7. ________________ mb = 29.12 inches 8. ________________ mb = 28.67 inches 29.92 30.20 29.68 29.09 1034.0 1009.5 986.0 971.0

Isobars Lines on a weather map connecting areas of equal pressure Isobars close together shows rapidly changing pressure

Picture of isobars

Factors Affecting Air Pressure

1. Temperature As temperature increases, air expands, so air density and pressure decrease As temperature decreases, air contracts, so air density and pressure increases

2. Water Vapor The MORE water vapor (humidity), the LESS air density and pressure WHY??? Water molecules weigh LESS than O2 and N2

3. Altitude As altitude INCREASES, air density and pressure DECREASES Why??? The higher you are, the LESS air above you pushing down

Pressure and Density Decrease with ALTITUDE

Summary As altitude, temperature, or water vapor in the air increase, the air density and pressure will DECREASE!!!

Questions

As air gets warmer in the atmosphere, the air pressure Decreases!

At sea level, the average air pressure in millibars is 1013.2 mb

At sea level, the average air pressure in inches of Hg is

As the altitude increases, the air pressure Decreases!

As air gets more humid in the atmosphere, the air pressure Decreases!

A barometer is used to measure Temperature Wind speed Pressure Humidity

As air absorbs moisture, its density Decreases Increases Remains the same

As you height above the surface of the Earth increases, the atmospheric pressure usually Decreases Increases Remains the same

Atmospheric pressure is often measured in oC oF g/cm3 millibars

Atmospheric pressure is a result of what property of air? Volume Temperature Transparency Weight