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Two mobile phone, A and B, are placed on the top of a wooden desk without direct contact, the gap between these two phones is about 5 centimeters.

When A is vibrating, e.g., a call comes in, a time series data is captured by B's accelerator sensor, which represents the acceleration in x, y, and z axis.

After transforming this time series data into frequency domain, I notice there is a significant power around 22 Hz.

Besides, from some paper, I have read a statement:

“If an object is struck by a rod, it will vibrate at its natural frequency no matter how hard it is struck. The magnitude of the strike will increase the amplitude of vibration, but not its frequency...if a periodic force is applied at the same natural frequency of the object, the object exhibits amplified vibration – resonance.”

If this is true, does it suggestion the 22 Hz is the natural frequency of wooden desk? or it is just the vibration frequency of phone A? or even the resonance frequency of phone A?

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  • $\begingroup$ I'd say it's the fequency of the vibration of phone A. $\endgroup$ – David Jun 23 '15 at 9:12
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My bet is it's the vibration frequency of phone A. The vibrator in phone A causes pressure waves through the material to end up driving a 22 Hz oscillation on phone B's accelerometer.

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  • $\begingroup$ I've read a statement that "If an object is struck by a rod, it will vibrate at its natural frequency no matter how hard it is struck. The magnitude of the strike will increase the amplitude of vibration, but not its frequency", is this statement correct? $\endgroup$ – ice_lin Jun 23 '15 at 12:17
  • $\begingroup$ Striking something with a hard object excites a broad range of frequencies, but the struck object will only have a sustained response at those frequencies where it is resonant. When exciting something with a vibration, the source is maintaining the excitation for a long time, and we don't need resonance to sustain the response. In differential equations you should have learned about natural and forced responses. That's exactly what we're comparing here. $\endgroup$ – The Photon Jun 23 '15 at 14:56

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