Coupled Pendula - 100 To 1 Mass Ratio
To illustrate mechanical resonance.
Two pendula hanging in series from a fixed point as photographed.
This idea is used to amplify the oscillation of a gravitational wave antenna bar so that it can then be sensed by a sensitive transducer or by laser interferometry techniques.
The two pendula have the same length, but the mass of the upper bob is 100 times that of the lower bob. With the masses hanging motionless, gently tap the bigger mass. Its energy will couple to the smaller mass, causing the smaller mass to oscillate with a much larger amplitude. The energy then couples back to the larger mass, and the cycle repeats.◙
J. -P. Richard, Approaching the Quantum Limit with Optically Instrumented Multimode Gravitational-Wave Bar Detectors,