Air Is Pressing on You

Step 1 of 5

Air is not nothing — it has weight.

A cubic metre of air weighs about 1.2 kg. The air in an average bedroom weighs roughly as much as a small child.

Step 2 of 5

The whole column above you presses down.

The atmosphere stacks 100 km high. All of that weight rests on the layer below it, and eventually on you — about 10 tonnes across your whole surface.

Step 3 of 5

So why does it not crush you?

Because you are full of fluid and air pushing back with exactly the same pressure. Balanced pushes cancel, and you feel nothing at all.

Step 4 of 5

Remove the balance and it is obvious.

Suck the air out of a can and the outside pressure crushes it flat instantly. Nothing pushed harder — the inside just stopped pushing back.

Step 5 of 5

It drops as you go up.

Less air above you means less weight. At the top of Everest the pressure is a third of sea level, which is why climbers need bottled oxygen.

A drinking straw does not pull liquid up. You lower the pressure inside and the air outside pushes the drink up for you.