1. Air Pressure

2. Air Pressure
Air is matter and is made of gasses and therefore has weight and mass to it.

3. Air Pressure
Because air has mass it pushes down on objects in all directions.
This is called air pressure.

4. Why doesn't air pressure crush us?
Because we have air inside pushing out.
And this balances the forces so we
Do not feel it.

5. Air Pressure We measure air Pressure with a barometer.
There are two basic types of barometers:

6. Mercury Barometer
This is a tube of mercury with the open end in a dish of mercury.
The higher the air pressure the further the mercury rises.

8. Water can also be used to show changes in air pressure.

9. Aneroid Barometer This works without liquid.
When the air pressure increases it squeezes the can causing needle to move.

11. Measuring Air Pressure
Air pressure is measured by the height of the column of mercury.
- inches of mercury or millimeters of mercury.

12. Measuring Air Pressure
A more common measurement is based on the average barometric pressure.
This unit is called a millibar.
Use can use your ESRT to convert from Millibars to Inches of Mercury.

13. Factors Effecting Air pressure
Temperature:
As air heats it expands, increases in volume, becomes less dense and exerts less pressure.
As air cools it contracts, decreases in volume, becomes more dense and exerts more pressure.

14. Factors Effecting Air pressure
WARM AIR ---- LOW PRESSURE
COLD AIR ---- HIGH PRESSURE

15. Factors Effecting Air pressure
Increasing Altitude
As you go higher in the atmosphere there is less air pushing down from above.
This causes the air pressure to decrease with an increase in altitude.
ESRT shows this in a graph.

16. The greatest air pressure is at the surface of earth
As you go up in the atmosphere pressure becomes less and less

17. Factors Effecting Air pressure

18. Humidity and Air Pressure
Air containing a lot of water vapor (high relative humidity) has a lower pressure then dry air.

19. Humidity and Air Pressure
The more water vapor in air causes the air to be expanded and take up more volume.
This results in air that is less dense and exerts less pressure.
Dry air would be more dense and exert more pressure.

21. Common Trends Low Pressure usually happens when:
-the weather is changing (windy)
-it is raining
-it is cloudy
High Pressure usually happens when:
-the weather is stable (not changing)
-it is clear and sunny
-it is not raining

22. Directions of Movement….
Low pressure systems spin counter clockwise, the air moves towards the center, and the air rises.

23. Directions of Movement…
High pressure systems spin clockwise, the air sink to the bottom, and moves away from the center of the High.

24. Acting Together they look like this……