Here's why:

* Sound is a mechanical wave: Sound travels through a medium (like air) by causing the molecules in that medium to vibrate.

* Vibrations create pressure changes: As air molecules vibrate, they collide with their neighbors, creating areas of high and low pressure.

* These pressure changes propagate: These pressure changes travel outward from the source of the vibration, forming a wave.

* Our ears detect these pressure changes: Our ears are designed to pick up these pressure changes and convert them into electrical signals that our brains interpret as sound.

So, the vibration of air molecules is the very foundation of sound.