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Chapter 3

Forces And Pressure

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Pull PullVacuum

Atmosphericpressure

Gas Pressure And Atmospheric Pressure (I)

Atmospheric Pressure Decreases

With Altitude

1 atmosphere = 760 mm Hg

= 10.3 m water

= 101 300 Pa

1 millibar = 100 Pa

Atmospheric Pressure

Decreasing atmospheric pressure

40 km

30 km

20 km

10 km

0 km

Ozone layer

Stratosphere

Cloud cirrus

Troposphere

Sea levelCloud cumulus

Mount

Everest

Magdeburg hemispheres needed

18 horses to be pulled apart.

The gas pressure inside a container

depends on the rate of collision of gas

molecules with the walls.

At higher temperature, molecules move

faster and the rate of collision increases.

Hence, pressure increases.

Gas Pressure In A Container

Temperature = T

Gas pressure = P

Temperature > T

Gas pressure >PVelocity of molecules increasesat higher temperature

Temperature = TGas pressure >P because moremolecules collide with the wallof container

The metal can becomes distorted on cooling as the

atmospheric pressure is greater than the air pressureinside the can.

Cyclone moving at high speed

surrounding a centre of lowatmospheric pressure.

Water vapour

Metalcan

Water

Heat

Lowpressure

Atmosphericpressure

Metal can is cooled bypouring cold water