While resonance is generally avoided in machinery, some devices take advantage of resonance. Most obvious examples are musical instruments, soil compactors, pneumatic hammers...
What else? What other machinery is designed around the principle of resonance and is designed to work in resonance?
Would you know of any devices working in higher modes?
Densitometers and Coriolis flow meters drive a system at its natural frequency (using the tube etc as the frequency determining element in an oscillator).
Mass determinations in weightless conditions use the resonant frequency of mass and spring.
Vibrating conveyors and vibrating screens are often used to convey powders and granular materials, even up hill. They typically use a motor with out-of-balance weights (masses) at each end of the motor shaft to excite the device at its natural frequency - which, ideally, should be close to an harmonic of the motor speed.
Some micromachined inertia sensors measure the change in frequency when subject to acceleration or rotation (angular acceleration). Sensonor of Norway made a accelerometer utilizing the 9'th eigenfrequency. Christopher
The original Stewart Warner balance machines spun a part thru its mounted resonance probably to get a big output signal and more "sensitivity." Not too tough to detect 0.0002 inch ecentricity.
When my daughters were smaller I endeavored to time my pushes to coincide with the resonant frequecy of them, while sitting on their swings.
I think those fat loud mufflers kids put on their Honda Civics must have some resonant frequency excitation goin' on.
OH, and the "thump" so popular with young folks' stereos seem to only play one note real well, so I'm guessing the sub aims for typical body panel resonance. Or maybe the poor car effectively provides the passive filtering ensuring that frequency's just what innocent civilians are going to hear.
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