What you can do here
Strike the triangles with the wand. Examine how the pitch and the timbre of the resulting sounds change with the triangle size, the spot you strike, and your technique.

How it works
Triangle vibrations caused by striking it with a wand travel along the metal bar. Once they have reached one end, they come back and overlap with new vibrations from the source. In short, standing wave forms. The oscillations excite air molecules and an acoustic wave whose properties depend on the triangle size and shape is generated.

Interesting facts
The triangle is a 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.