How Everything Works
How Everything Works How Everything Works

Question 541

How much natural pressure is around us when we are on the ground? Does this pressure decrease in higher places? Why don't people in aircraft explode because the pressure is lower?
Near sea level, the air around us has a pressure of about 100,000 newtons per square meter or 15 pounds per square inch. That means that each square meter of surface on your body is exposed to an inward force of 100,000 newtons or that each square inch of your body is exposed to an inward force of 15 pounds. Your body is thus exposed to enormous inward forces. However, you don't notice these forces because your body is composed of solids and liquids that resist compression ferociously. To see that this is so, try to squeeze a sealed bottle of soda or to squash a coin by stepping on it. It's very hard to shrink the volume of a solid or liquid by squeezing it.

The origin of the large pressure around us is the weight of the atmosphere overhead. The air near you is supporting the weight of several miles or kilometers of air overhead and the weight of this air is squeezing the air down here. When you ascend a mountain, the amount of air overhead decreases and so does the pressure of the air around you. Your body becomes less tightly squeezed by the air around it. However, you don't explode because releasing the pressure on you doesn't change your volume very much. Solids and liquids don't expand very much when the pressure on them is released.


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