1. Aim: How can we explain air pressure?

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

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

13. Air Pressure Conversions
mb = _______________ inches
This is 1 atm (atmosphere), or
the standard sea level pressure.
mb = _______________ inches
mb = _______________ inches
mb = ________________ inches
5. _______________ mb = inches
6. ________________ mb = inches
7. ________________ mb = inches
8. ________________ mb = inches
29.92
30.20
29.68
29.09
1034.0
1009.5
986.0
971.0

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

15. Picture of isobars

17. Factors Affecting Air Pressure

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

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

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

22. Pressure and Density Decrease with ALTITUDE

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

24. Questions

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

26. At sea level, the average air pressure in millibars ismb

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

28. As the altitude increases, the air pressure
Decreases!

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

30. A barometer is used to measure
Temperature
Wind speed
Pressure
Humidity

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

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

33. Atmospheric pressure is often measured inoC oF
g/cm3
millibars

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