Humming pipes

What you can do here
Press your ear to any pipe. You should hear buzzing noises. Listen to the other pipes. Can you hear a difference?

How it works
Inside each pipe, the air is stimulated to vibration by the sounds coming from the outside. Only the sound whose wave length corresponds to the pipe’s length and forms a standing wave is amplified. The characteristics of the resulting wave depend on the pipe size. The pipes differ in length, so the corresponding standing waves differ in frequency – as a result, each pipe produces a sound of different pitch.

Interesting facts
In a similar way, the sounds get amplified in wind instruments (aerophones). In the Science Garden there is a pipe organ – striking a selected pipe generates a standing wave inside whose frequency depends on the pipe length.
Likewise, you get a humming sound of the sea from seashells. The exact sound which is amplified depends on the shape and size of the seashell.