Sound is produced when something vibrates quickly — this fast shaking is called a «vibration». When you hit a drum, its skin vibrates rapidly and makes a sound. When you pluck a guitar string, it also vibrates and produces a musical note.
These vibrations travel through the air as invisible waves until they reach your ear, much like the ripples that form when you drop a stone into calm water. Sound can also travel through water and even through solid objects, but it cannot travel through empty space because there is no air there.
Inside your ear is a very thin membrane called the «eardrum». When sound waves reach it, it vibrates, and this vibration sends a signal to the brain, which turns it into a sound we understand — whether it's your mom calling you or a song you love.
