1. SECTION A.3
Pressure

2. PRESSURE
Refers to force and space
Pressure = force/area

3. WOULDYOU RATHER?
Pressure = force/area
Have a 180 pound person or a 110 pound person
step on your foot?
What if the 110 pound person was wearing spiky
heeled shoes?

4. AIR PRESSURE
Gas molecules exert pressure on their surrounding
Units to report air pressure:
 psi
 mmHg
 atm
 torr

5. SI UNITS OF PRESSURE
Force = Newton (N)
Area = meter squared (m2)
Pressure = N/m2 : called a pascal (Pa)

6. WHAT CAUSES AIR PRESSURE IN A TIRE OR
ANY SEALED CONTAINER?
The air molecules are moving and bounce off the
sides of the container. These collisions exert a
force on the walls of the container.

7. MEASURING AIR PRESSURE
Use a barometer typically with mercury in it.

8. TYPICAL AIR PRESSURE MEASUREMENTS
AT SEA LEVEL
101.3 kPa
1 atm
760 mmHg
Air pressure video

9. In Osseo, MN, the Earth’s atmosphere has a force
of about 15 pounds per square inch (psi).
Dimensions Area (in2) Force (pounds)
1 x 1 1 12
2 x2
3 x 3
4 x 4
5 x 5
6 x 6
7 x 7
8 x 8
9 x 9
10 x 10
newspaper

10. CALCULATING PRESSURE
Pressure = force/area
Calculate the pressure of a block that is exerting a
force of 18 N that has the measurements of .25 m
x .5 m.

11. CALCULATING PRESSURE
Pressure = force/area
What pressure is exerted by a block that weighs 25
pounds and is 3 inches x 5 inches?