Air pressure Crush
why are we not crushed by air that is as heavy as a volkswagon?
Air is pretty light actually, about 1000 times lighter than water or
milk. That is why a one-gallon milk container is so light when the milk is
poured out (although there is air in it).
I suspect that your question is about air PRESSURE. The air around us is
pressured (called atmospheric pressure) and you can see its force by a
simple experiment in which a small amount of water is boiled inside a can
of coke and then the can turned upside down into a tank of water. As the
water vapor that has displaced the air in the can is condensed (turned into
water), the pressure inside the can drops. But the pressure outside the can
is still atmospheric pressure. This excess external force crushes the can.
Why doesn't air pressure crush us? The pressure inside our body is roughly
the same as the pressure outside and therefore there is no net pressure
(and thus, force) on us.
But what if we go to an environment with higher or lower pressure?
The magnitude of air pressure around us is like that of a 10-m-tall column
of water. If a diver goes 10 m under water, the pressure on his body is
doubled but this still will not crush him because much of his body is
composed of liquid (and not gas) and cannot be compressed (shrunk). Human
organs or areas filled with air, such as middle ear or the lung, however
will be pressurized (squeezed) as one dives deeper and expands as one comes
to the surface. Proper training and slow descent and ascent are necessary
to make sure the air inside the body does not expand or contact too rapidly
You can experience the force exerted by pressure differences by noting that
the volume of an air-filled balloon will shrink by as it is pushed under
water. The pressure outside due to atmosphere and water is higher than
inside and this lead to the shrinkage.
Dr. Ali Khounsary
This is a very good question. It is because the air is a fluid. It
flows around us and into us. From inside us (in our lungs) it exerts
the same force as it exerts from outside. The result is the force of
the external air trying to 'crush' us is exactly equal to the force of
the internal air trying to 'explode' us.
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Update: June 2012