John Murphy, age 7, of Stanley, N.C., for his question:

Why do heights make our ears pop?

The outer ears are the ones on the outside of your head. The inner ears that do the hearing work are deep down in the bones of your skull. Each outer ear leads into an inner ear by a small tunnel. The eardrum is a flap of skin like a little door across this tunnel. It is sensitive to air pressure, the weight of the air around.

On the ground the air pressure is the same on both sides of the eardrum. When we go up a mountain or up in a plane the air pressure becomes less. The pressure is less on the outside of the eardrum and greater on the inside. The eardrum bulges and feels stopped up. But when you swallow, the air inside escapes down your throat and the eardrum pops back to its proper shape.