Put simply, sound is our perception of differences in .

The air molecules hit other air molecules, causing a longitudinal wave to propagate until it hits our ear. Our ear takes the vibrations and sends a signal to our brain, where the frequency is translated into “sound.” So the mechanism for transfer is particle to particle collisions in the medium transmitting the sound wave. This is why (unlike light waves) require a medium in order to propagate.

Here is an image of sound waves: