Re: If air pressure is so strong, why doesn't it hurt humans?

Dear Nancy,

You are right, air does exert pressure equally on all sides of the body.  
However, the human body is mostly water.  In fact, you could think of the 
human body as a combination of water and oil with some proteins thrown in 
to give the whole thing a shape and to provide for some interesting 
functions.  Water and oil are essentially non-compressible.  So, no matter 
how much pressure you place them under they occupy the same volume.  They 
might change state and become more solid.  But, they would still occupy 
relatively the same volume.  So the pressure that the body exerts in an 
outward direction to counteract the air pressure is due to the molecular 
nature of the water and oil that make up our bodies.

A good example of this is a ping-pong ball.  If you take a ping-pong ball 
down to the bottom of the ocean it ends up looking like a shriveled up 
white pea because the water pressure crushes the air filled ball because 
air is compressible.  If you completely fill the ping-pong ball with water 
and then bring it down to the bottom of the ocean, it still looks like a 
ping-pong ball because the water is relatively non-compressible.

Our body has two additional problems created indirectly by air pressure.  
First, we have air filled lungs.  However, as long as our lungs are open to 
the outside air via all the airways and our mouth and nose, the air 
pressure is the same inside the lung and outside.  Second, we have air 
filled ears.  Actually, only our middle ear is filled with air.  You feel 
the direct effects of this when you fly in a plane and your ears begin to 
hurt.  The air pressure in the plane’s cabin is maintained at about the air 
pressure at 5000 ft. above sea level.  However, the air pressure in our 
middle ear is that found at sea level. Fortunately, the middle ear is 
directly connected to the outside by the eustachian tube which opens in the 
back of our mouth.  The mouth end of the eustachian tube is normally 
closed.  Whenever we swallow, the eustachian tube opens and the air 
pressure inside our middle ear is equalized to the pressure outside.  This 
is why it helps to chew gum when you fly on a plane.  Chewing leads to 
swallowing.  Fortunately, I don’t have to chew gum and walk at the same 
time while flying in a plane.