Video narration
How does a silent-looking school bell become something your ear can hear? When the bell is struck, its metal vibrates. That vibration pushes and pulls on the nearby air, making air particles vibrate too. Each particle moves back and forth, passing the disturbance to the next-not carrying the air all the way to you. The bell does not send a substance flying outward. It transfers vibration through a medium, such as air, until the disturbance reaches your ear. Faster vibrations mean a higher frequency, which you hear as a higher pitch. Bigger vibrations mean greater amplitude, heard as greater loudness. But without a medium, there is nothing to pass the vibration along: sound cannot travel through empty space, or a vacuum. So, how does the bell become sound? Its vibrating metal makes the air vibrate, those vibrations travel from particle to particle, and your ear detects them.