SECTION A.3Pressure

PRESSURE

Refers to force and space

Pressure = force/area

WOULD YOU 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?

AIR PRESSURE

Gas molecules exert pressure on their surrounding

Units to report air pressure: psi mmHg atm torr

SI UNITS OF PRESSURE

Force = Newton (N) Area = meter squared (m2)

Pressure = N/m2 : called a pascal (Pa)

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.

MEASURING AIR PRESSURE

Use a barometer typically with mercury in it.

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

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

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CALCULATING PRESSUREPressure = 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.

CALCULATING PRESSURE

Pressure = force/area

What pressure is exerted by a block that weighs 25 pounds and is 3 inches x 5 inches?