1. At 1
1. 3ppt
Air Pressure
Section 1.3
Pages 25-30

2. Under Pressure Pressure is… Air Pressure is…
The force pushing on an area or surface
Air Pressure is…
The force of air pushing on an area
Why doesn’t air pressure crush us?
It presses in all directions.
David Bowie

3. D M = V M D V Density The amount of mass in a given volume of air.
Density = Mass / Volume M D V x M D V =

4. Air Molecule Model Gases consist of molecules which have:
Mass and occupy a Volume. Therefore, they have…
Density
Gas molecules move randomly and bump into each other.

5. Air Molecule Model D M = V 1g = M = ? 13g M = ? V 10cm3 = V 10cm3 =
Calculate the density in each box. 1g = M = ?
13g M = ? V
10cm3 = V
10cm3 =
13g
13g D =
D=1.3 g/cm3
D=1.3 g/cm3
10cm3
10cm3

6. Air Molecule Model Situation 1V =
Calculate the density for each side.
Draw a line to show where the wall should move? 1g = M = ?
13g
26g M = ? V
10cm3 = V
10cm3 =
26g
13g D =
D=2.6 g/cm3
D=1.3 g/cm3
10cm3
10cm3

7. Air Molecule Model Situation 1
D=2.6 g/cm3
D=1.3 g/cm3
The density is greater on the left, therefore pressure is higher
There are more molecules on the left side and there will be more molecules striking the wall.
As a result, the wall will move to the right.

8. Air Molecule Model Situation 2
Calculate the density for each side. Draw a line to show where the wall will move. 1g = M = ?
13g M = ? V
20cm3 = V
10cm3 =
13g
13g D =
D=0.65 g/cm3
D=1.3 g/cm3
20cm3
10cm3

9. Air Molecule Model Situation 2
D=0.65 g/cm3
D=1.3 g/cm3
The density of air is higher on the right, therefore the pressure is greater
The molecules on the right side will hit the wall more frequently
Therefore the wall will move to the left.

10. Temperature
The average amount of energy of motion in the molecules of a substance.
It is a measure of how hot or cold something is.
More Energy
Warmer
Less Energy
Cooler

11. Air Molecule Model Situation 3
Faster
Molecules
Slower
Molecules
Heating air molecules increases their energy, making them move faster.
Will hit the wall more often, moving it to right.

12. Mercury Measuring Pressure
Use a Barometer
Measured in Bars (millibars)
Mercury
Mercury in tube is forced upwards by mercury in the dish as pressure increases

13. Connected to a dial and needle.
Measuring Pressure
Aneroid
Walls of the barometer are pushed in or expand out as pressure changes.
Connected to a dial and needle.

15. Altitude Effects Altitude (or elevation) is height above sea level
As you increase altitude, what happens to air pressure?
Decreases because fewer molecules are above you.

16. Exit Pass
As you increase Altitude, what happens to the density of the air?
What would happen to air pressure if you went down into a mine?