1. AIR PRESSURE Air has pressure because gravity pulls air down on us.
Air’s Pressure = Air’s Density = Air’s Weight
If air density changes then air pressure changes.

2. The atmosphere is high and heavy.

3. Prove it with a straw

4. How do you drink through a straw?
Air Pressure
How do you drink through a straw?

5. The atmosphere is so heavy it can push water up about 30 feet!
Air
Pressure
The atmosphere is so heavy it can push water up about 30 feet!

6. 1 atmosphere is about a ton of weight on the average human.
About the weight of a Honda Civic!

7. Since gravity pulls air down, the higher you go the less air.
Less dense, less weight, less pressure.
Less Pressure!
More Pressure!

8. Water
Air
Pressure
Is using a 30 foot water tube a practical method to weigh the atmosphere?

9. Mercury is more dense than water and only rises 3 ft (1 m).
Add a scale, and a Mercury
Barometer measures air pressure.
(It weighs air!)

10. Barometers measure air’s pressure very accurately.
Mercury
Barometers measure air’s pressure very accurately.
BUT, mercury
is poison!

11. ANEROID BAROMETER

12. ANEROID BAROMETER

14. A barometric pressure of 1021
A barometric pressure of millibars is equal to how many inches of mercury?
(1) (3) 30.25
(2) (4) 30.50