This number is somewhat deceiving though because there is air on the other side of your eardrums that is pushing the other direction. It is really the difference in pressure over the eardrum that causes your ears to hurt. When you dive in water, the pressure of the water pushes in on your ears. When you fly in an airplane or go in the mountains, the outside pressure is less than inside, and the air in your ear pushes out on the eardrum. You have to go through a process of letting your ears "pop" which is really just letting the pressure inside and outside the ear come to an equilibrium.