In this case the amplitude of oscillations appears to simply increase as the driving frequency increases. Think about the demonstration of standing waves on a string; is this what happened then?
The amplitude of vibration of a damped driven oscillator depends on how far the driving frequency is from the natural frequency of oscillation. The amplitude is biggest when these two frequencies coincide: this is the phenomenon of resonance.
In this case the amplitude of oscillations appears to get very large for very low driving frequencies. Think about how an oscillator responds in the case of a very low driving frequency; all that happens is the oscillator will follow the driver, so this figure must be wrong.
How can both be correct? They can’t!
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