Understanding Pressure Let's say you took a 1 inch by 1 inch piece of wood 3 feet long, and let's say this piece of wood weighs a pound. If you were to stand that piece of wood on end on your big toe, it would place 1 pound of pressure on your toe. If you took a 30 foot long piece of the same wood and balanced it on your toe, it would apply 10 PSI of pressure. If it were 300 feet long it would apply 100 PSI, and so on. That is, a 1-inch square column of water a mile high weighs 2,270 pounds.
Air works the same way.
Our bodies think 14.7 PSI is completely normal. The way a gas like air exerts pressure inside a container like a tire or a balloon is through the action of the air atoms colliding with the sides of their container. Imagine that you have a single atom of nitrogen in a sealed container. That atom is in constant motion ricocheting off the sides of the container. By its collisions with the sides of the container the atom exerts a pressure outward.