ELI5: Explain Like I'm 5

Brass instrument valve

Ok, so imagine you have a straw and you blow into it. You can make different sounds by blowing harder or softer. Now, imagine that straw is made of brass.

A brass instrument valve is like a special straw that helps you change the notes you can play on the instrument by making it easier or harder for air to get through. It has buttons that you press down which change the way the air flows through the instrument.

When you press down the valve, it makes the air take a different path through the instrument, changing the length of the tubing the air has to travel through. This makes a different note come out of the instrument.

With the valves, a brass instrument like a trumpet or a tuba can play all kinds of different notes and songs.