What can you do here
Hit the triangles with the beater. Examine how the pitch and timbre of resulting sounds changes with the triangle size, the spot you are striking, and the hitting technique.

How does it work
Solid body vibrations, standing wave, acoustic wave formation, idiophones.

Triangle vibrations caused by your hits are travelling along the metal bar. Once they have reached one end, they are coming back and overlapping with new vibrations from the source. In short, a standing wave is forming. The oscillations are exciting air molecules and the acoustic wave, whose properties depend on the triangle size and shape, is generated.

Interesting facts
This is musical instrument used in the percussion section of a symphony orchestra.

The origin of this instrument is obscure but it features in many mediaeval paintings where it is played by angels.