Atmospheric pressure

Beginner

Pressure from the weight of the air above.

The weight of the air column above gives 101.3 kPa at sea level, falling with altitude (about half at 5.5 km).

Worked example

A 1 m² table top bears a 10 tonne load of air, balanced by pressure beneath.

Common mistake

It decreases exponentially, not linearly.

In more detail

Atmospheric pressure is the weight of the air above a surface per unit area. At sea level it is about 101,325 Pa, and it falls with altitude.

Aircraft cabins are pressurised because atmospheric pressure is lower at altitude.
Weather forecasting relies on changes in atmospheric pressure.
Pilots and weather forecasters track atmospheric pressure, which falls as altitude increases and as weather systems approach.

Why does pressure fall with height?

Because there is less air above, so less weight presses down.

What is standard atmospheric pressure?

101,325 Pa, or one atmosphere.

Why is air pressure lower on a mountain?

There is less air above the mountain, so the weight of the air column pressing down is smaller.