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I've noticed occasionally that if I put a metal pan on the stove and it gets very hot, it will vibrate or shake. I know metal expands, and that heat increases the kinetic energy of molecules. But do the molecules actually start moving back forth in the same direction in a way that actually causes the whole object to shake or is it uneven expansion that causes it?
Many years ago I read somwhere of a sound effect (it probably had even a precise name) generated by cold metal bodies resting on hot surfaces; I remember the case of a lead bar resting on the surface with two points or two segments: one of the two, casually, heats more than the other expanding it and giving the bar a momentum which lift it that side; then that side cools and goes down while the other is pushed up, and so on, many times per second, generating a distinct sound.Someone remember the name of this effect?
... The fourth point of contact will then be heated, while the third point, no longer in contact with the metal will cool, and the balance will be reversed, and so on...