Re: Axis of rotation

matt271829-news@xxxxxxxxxxx wrote:

OK then, I'm confused. At
http://www.uwgb.edu/dutchs/PLATETEC/RotationQk2004.HTM, which seems a
reputable site, it says, of the earth's axis wobble: "Objects that are
not perfectly spherical do not rotate around a single axis. That's just
the laws of physics."

Is this really true? I always thought that any rotating rigid object,
in the absence of any external forces, will (and indeed *must*) rotate
about a single, fixed axis. Who's right?

J, the angular momentum, remains fixed in spatial orientation in the
absence of external torques. For sufficiently asymmetrical objects
however, J and w, the instantaneous axis of rotation, need not be
co-linear, and in fact the latter may wander in orientation ("wobble").

.

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