I Want to know if anybody knows the formula to find the resonant frequency of an object?

Question

Nikola Tesla found that the Earths resonant frequency is 7hz
How did he go about finding that?

Answer 1

I don't think there is a formula, because that would depend upon the object's density, shape, elasticity, how it is constructed physically, etc. Experimentation is the only thing that will find this, as far as I know.

I don't know how Tesla could have measured the resonant frequency of the entire planet, but earthquakes do send out infrasonic waves *before* the real shaking hits and some of those waves are in the 7Hz range.
Infrasonic vibrations are dangerous to work with, though--they can induce hysteria, paranoia, vomiting, and can cause tissue damage.