Atmospheric pressure

Air particles are pulled towards the Earth by its gravitational field. This forms a layer of air around the Earth called the atmosphere.
Atmospheric pressure is the pressure air molecules exert on a surface as they collide with it.
Atmospheric pressure decreases with height above the Earth’s surface.
- This is because the air density decreases, and so there are fewer air molecules.
- This means collisions between air molecules and surfaces happen less frequently, so the force exerted by the molecules is smaller.

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