Imagine for a moment standing in a pool of water—up to your ears. The water is perfectly still. A rock is dropped in the pool 20 feet away and the waves ripple outward, eventually reaching your ear. The individual drops of water don’t move from the rock to your ear, but the disturbance—the waves—do. That is a good way to visualize sound waves. But instead of water, the medium is air. What we call “sound” is a disturbance in the air caused by, say, a tuning fork, or a guitar, or your voice. Sound waves are nothing more than air molecules slamming into each other, creating ripples in the air like the waves in a still pool. Eventually this chain reaction reaches your eardrums. The air molecules collide with your eardrums at varying rates—which your brain interprets as varying sounds.
The tuning fork animation (below) shows the vibrations the fork creates in the air—that we perceive as sound.