8.2 - Pressure

Pressure

Pressure – the amount of force acting over a given area on an object.

Compression

Compression – a decrease in volume because of a force.

Why do you think the volume decreases? Shouldn’t it stay the same??

Gases are Compressible (con’t)Some uses for compressed gases:

Pressure and Kinetic Energy in Gases• Pressure can cause the particles energy to increase,

which makes the particles move faster.

• This can cause explosions!!

Pressure and Kinetic Energy in Gases (con’t)

• Pressure can also cause implosions!!!• An implosion is a collapse inward.

Liquids and Solids are VERY Difficult to Compress

• The volume does NOT change much in liquids and solids. Instead, the force is passed on to the particles directly.

• This makes solids and liquids incompressible.

Compression and Deformation

• Solids can also appear compressed when they are deformed.

Deformation – a change of shape without being forced into a smaller volume.

Comparing Pressure

Or,

Comparing Pressure (con’t)UNITS:Force – N (Newton)Area - m² (square metres, or SQUAREA!!)

Thus,Pressure is , or simply, Pa (Pascal)

NOTE: 1 Pa is VERY small, so it is more common to see kPa (kiloPascal).

Calculating PressureYou can calculate the pressure an object exerts on a surface if you know its weight and the dimensions of the surfaceExample:• A BMX rider and bike weigh 1200 N. They are on a piece of sheet metal that is 1.0 m by 2.0

m. How much pressure does the sheet metal exert on the ground?

P = P = P = P =

P = 600 Pa

The Diving Bell

• Why do you think the balloon shrinks??

The Diving Bell