Pressure is defined as force per unit area. It can be measured in units such as pounds per square inch, atmospheres, or pascals. Air pressure in the atmosphere is caused by gas molecules constantly colliding with surfaces and exerting force. Standard air pressure at sea level is approximately 101 kPa or 14.7 psi. Pressure calculations involve dividing the total force by the area over which that force is applied.

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?