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Q & A: liquid moments of inertia

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Most recent answer: 04/05/2011
Q:
Why do non rigid bodies (like liquids) not have / contribute to moment of inertia?
- Niharika (age 18)
India
A:
If you have an object with some liquid parts (say an uncooked egg), even if the rigid parts are rotating, the liquid parts may not (depending on the geometry) have to rotate along with the rest. However, over time the friction (viscosity) of the liquid will cause it to rotate along with everything else. So you actually get a frequency-dependent effective moment of inertia. If the object is rotated back and forth quickly, the liquid only partly contributes. If it rotates back and forth on a longer time-scale, the liquid contributes almost fully.

More interesting things happen for superfluid quantum liquids, but I don't think that's what you were asking about.

Mike W.

(published on 04/05/2011)

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