Notes 11-1 Pressure. What Is Pressure? The amount of pressure you exert depends on the area over...

Notes 11-1

Pressure

What Is Pressure?

• The amount of pressure you exert depends on the area over which you exert a force.

Calculating Pressure

Pressure = Force Area = Length x Width

Area

Units:

Force- Newton (N)Area-square meters (m2)Pressure- Pascal (Pa)

Area • The area of a surface is the number of square units that it

covers. To find the area of a rectangle, multiply its length by its width. The area of the rectangle below is 2 cm X 3 cm, or 6 cm2.

Area

• Practice Problem

• Which has a greater area: a rectangle that is 4 cm X 20 cm or a square that is 10 cm X 10 cm?

• The square has the greater area.• 4 cm X 20 cm = 80 cm2

• 10 cm X 10 cm = 100 cm2

Fluids

• A material that can easily flow.

• Examples?• Liquids• Gases

• Tiny particles are constantly moving and colliding with surfaces, which exerts forces on the surfaces.

Fluid Pressure• All of the forces exerted by the individual

particles in a fluid combine to make up the pressure exerted by the fluid.

Air Pressure

• Right now, there is approximately 100 km of fluid on top of you…

• AIR!• The weight of the air exerts a force which

causes air pressure or atmospheric pressure.• Why are you not crushed by these fluids?• The forces are exerted from all directions so

they are balanced.

Variations in Fluid Pressure• As your elevation

increases, atmospheric pressure decreases.

Variations in Fluid Pressure

• Water pressure increases as depth increases.

Measuring Pressure• You can measure atmospheric pressure with a

barometer• Meteorologists use barometers to measure

pressure to help forecast the weather• Decrease in pressure = storm

Air Pressure and Altitude

• http://youtu.be/7_yf-iRf8Vc