Determining Resonance of Rods for a Given Frequency

[Oblio]

Most of us have seen the experiment where a tuning fork that is resonating, makes another tuning fork resonant when brought close in proximity.

there's another one where small metal rods are mounted upright with plastic knobs on top (dont know if this is necessary), and two rods of same length, etc will resonate together in the same way.

Does anyone know how, with such a rod, to determine the specifications for a rod for a certain frequency?
say for 256 hz for example, how long, thick.. etc...

Much appreciated!

 

[Danger]

I don't know the answer to your question, but I suspect that the plastic knobs are simply a visual aid. It's hard to see a rod vibrating, but it's easy to see a coloured sphere moving back and forth.