Press your ear to any pipe. You should hear buzzing noises. Listen to the other pipes. Can you hear a difference.
How does it work
Inside each pipe the air is stimulated to vibration by the sounds coming from the surrounding area. 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’s size. The pipes differ in length, so the corresponding standing waves differ in frequency – as a result, each pipe produces sound of different pitch.
In a similar way, the sounds get amplified in wind instruments (aerophones). In the Science Garden there is a pipe organ – striking a chosen pipe generates inside the pipe a standing wave, whose frequency depends on the pipe’s length. Likewise, a humming sound of sea emerges from seashells. Exactly which sound is amplified depends on the shape and size of a seashell.