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If I start spinning a raw egg very slowly in place, why does its angular velocity increase spontaneously? This is something I noticed the other day while cooking. It doesn't do the same thing with a hard-boiled egg, so I assume it has to do something with how the contents of the raw egg are distributed during the spinning process, but I was wondering if someone could fill in the details.

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Never seen that before, so I just tried it. Cool.

I believe that the membrane between the yolk and the white is elastic, so when you first, gently, give the egg a little angular momentum, you are only spinning the white. As the yolk catches up the effective moment of inertia drops, and conservation of momentum therefor implies a higher angular velocity.

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  • $\begingroup$ This appears to be reasonable for a short impulse, but for an application of force over a second would mean that the yolk doesn't rotate for most of that time. $\endgroup$ – LDC3 Jun 13 '15 at 17:30
  • $\begingroup$ @LDC3 Well, yes. And I only tested it with about a one radian twist given in about half a second. You need a pretty smooth surface to observe the effect under those condiction. $\endgroup$ – dmckee Jun 13 '15 at 17:35

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