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I remember the following fact about a rigid pendulum:

The point when the pendulum weight is lowest is a stable equilibrium while the point where the pendulum weight is highest is an unstable one.

But if you perturb the suspension point of the pendulum with small, quick oscillations, the upper point becomes a stable equilibrium.

Now, my question:

Can someone give me a reference for the stability of the second equilibrium point of a pendulum with small perturbation?

Has this been actually replicated in an experiment (preferably on youtube :) ) or are the necessary parameters impractical?

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up vote 2 down vote accepted

I believe you are referring to Kapitza's Pendulum. The Wikipedia site is a decent introduction: and has references to further reading (like his original paper).

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Thanks, with this name, I found a simulation on youtube: – Phira May 20 '11 at 20:05

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