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Shift in vibrating resonance with decreasing amplitude.

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Circlotron:
Plugged my guitar into one channel of the scope, as you do, and the sig gen into the other channel. Synced to the sig gen and adjusted the pitch of the strings so that the plucked note trace drifted neither to the right or left. What I noticed is that the frequency of the plucked note would initially be dead on, then after maybe half a second it would drift to the right because it's frequency had dropped slightly. Why would this happen? I would have expected it to stay constant.

ejeffrey:
Because the frequency depends on tension and the tension depends on amplitude.  The larger the amplitude the longer the string and the higher the tension.

Circlotron:
Okay. I note that the frequency of oscillation of a pendulum is somewhat amplitude dependent as well, but for different reasons. But physics being what it is, maybe there is a relationship.

https://en.wikipedia.org/wiki/Pendulum#Period_of_oscillation

If this is the case then, this begs the question - why doesn't an LC tuned circuit behave this way?

Tomorokoshi:
Is it a coiled steel string, a steel wire string, or a nylon string?

twospoons:

--- Quote from: Circlotron on April 11, 2023, 01:38:16 am ---
If this is the case then, this begs the question - why doesn't an LC tuned circuit behave this way?

--- End quote ---

If L and/or C are non-linear then this would happen to LC tuned circuits too. e.g inductor core heading towards saturation at peak current.  One outcome of this is the oscillation is no-longer purely sinusoidal.

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