Sound is just patterns of air pressure.

If you were able to go “puh puh puh” in someone’s ear 440 times per second, they’d hear a middle A note if they didn’t punch you first.

Imagine a delicate needle in front of your mouth. If you “puh” at it, it wiggles. If you play an A on a violin, the violin string wiggles 440 times per second. That vibrates the air around the string at the same speed. That air vibrates your ear drum 440 times per second, so you hear it. But it also vibrates the needle. Now let that needle carve a pattern in a spinning disc. That pattern of pressure is now recorded. If you harden that disc and balance a needle over it and spin it again at the same speed, the needle will vibrate 440 times per second. You can use that to make a big floppy piece of paper vibrate 440 times per second. That vibrates the air, which vibrates your ear drum just like the original violin string would’ve.

Magnets