Sound travels through air as a series of compressions and rarefactions moving outward.

The longer version

Air molecules shoved outward by a vibrating object crowd together, then spring apart again, and that alternating pattern of crowding and thinning is what moves through the room. Each push hands energy to neighbouring molecules, so the disturbance keeps travelling long after the source has stopped moving. The crowding raises local pressure slightly, the thinning lowers it, and your eardrum reads those swings.

Nothing material travels across the room; only the pattern does, which is why a pressure wave can pass through a closed window frame as vibration while the air itself stays put. Particle motion is tiny compared with the distance the wave covers. That distinction between motion of the medium and motion of the pattern sits at the heart of wave behaviour.

Where this entry sits

Sound and Music gathers facts about how vibrations move through air and water, how ears turn them into meaning, and how instruments and notation shape what listeners hear. Expect echoes, pitch, volume, acoustics, and the odd silence in between. The full list sits on the Sound and Music page, where every entry is listed in order.