An Ocean of Air
We don't usually think of air as having weight, but it does. We live at the very bottom of an 'ocean' of air that is about 60 miles deep. Every mile of air above you is pressing down because of gravity. This pressure is constant, but because we are born in it, our bodies are built to push back with the exact same strength.
The Mountain Effect
As you go higher up—like driving up a mountain or flying in a plane—there is less air above you. This means the 'weight' or pressure of the air decreases. The air also becomes 'thinner,' which is why it’s harder to catch your breath on top of Mount Everest than it is at the beach.
The Ear Pop Riddle
Inside your head, behind your eardrums, is a small pocket of air. When you go up in a plane, the pressure outside your ear drops quickly, but the air inside stays at high pressure. This makes your eardrum bulge outward! When you swallow or yawn, a tiny tube opens, letting the pressure equalize with a 'pop.'