What Causes the ‘Hum’ in Empty Rooms?

The hum in empty rooms is caused by sound waves from things you can’t see, like lights and machines.

Imagine you're sitting in a quiet room, and all of a sudden, there's a soft buzz or a low hum. It’s not coming from your toys or your TV, it's coming from the lights on the ceiling or the refrigerator in the kitchen. These things are always working, even when you're not looking at them.

Lights and machines have tiny parts inside that vibrate, like tiny engines. When these parts move back and forth really fast, they push air around them, which makes sound waves. Those sound waves travel through the room until they reach your ears.

It’s kind of like when you shake a drum, even if no one is playing it, sometimes you can still hear it humming because the skin on the drum is moving just a little bit from inside.

So next time you hear that soft hum, remember, something invisible is working hard to make sound!