Atmospheric pressure

The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude.

Air molecules colliding with a surface create atmospheric pressure. The number of air molecules (and so the weight of air) above a surface decreases as the height of the surface above ground level increases. So as height increases there is always less air above a surface than there is at a lower height. So atmospheric pressure decreases with an increase in height.

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Students should be able to:
- describe a simple model of the Earth’s atmosphere and of atmospheric pressure
- explain why atmospheric pressure varies with height above a surface.