A recorder is a little tube you blow into to make music. It has holes down the front, and you cover them with your fingers to play different notes. But how does covering holes change the sound?

When you blow into a recorder, the air wiggles all the way down the tube. The amount of tube the air travels through decides how high or low the note sounds.

Covering more holes on a recorder makes the note lower, because the air gets a longer tube to travel through. When you lift your fingers off the bottom holes, the air can escape sooner, and the tube it uses is shorter.

Here is the big idea: longer tubes make lower sounds, and shorter tubes make higher sounds. That is why a giant tuba rumbles low and a tiny whistle squeaks high.

You can hear this rule almost everywhere, not just on a recorder. A long organ pipe booms deep, while a short one sings high and bright.

So the next time you cover the holes on a recorder, remember you are making the air travel a longer path. A longer path means a longer tube, and a longer tube means a lower, deeper sound.