Shive Wave Machine - Fabrey-Perot Interferometer
To demonstrate the mechanical analog of the optical Fabrey-Perot interferometer.
Shive Wave Machine, 4 crossarm weights, wave generator, dashpot, ruler.
This effect is subtle, in that it is not readily observable, so it must be actually measured to be convincing.
Pairs of small weights are connected to two arms six inches apart in the center of the machine. The dashpot is attached to the end of the machine opposite the wave generator to prevent reflections (It must be adjusted.). Measure the difference in amplitude of the transmitted wave by measuring the amplitude of the oscillation of the dashpot, and compare that with the amplitude of the incoming wave as measured by the amplitude of the generator. The maximum transmitted wave occurs when the reflected wave is minimized, that is, when the two arms with the weights are one-quarter wavelength apart.
John N. Shive, Similarities In Wave Behavior, Bell Laboraties, (1961).