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Using Physics and Earths wobble

A response to something seen on the discussion recently.
 Subject: Re: Warm- vs. Cold-blooded Dinos

>I am not suggesting anything about the pole behavior of the earth, but a
>non-symmetric rigid body spinning about its intermediate inertia tensor will
>spin stablely for a period inversely related to the initial deviation of the
>intermediate intertia tensor from the spin axis.

A little knowledge........

The Physics here is that a rotating object such as the earth or a child's top
has three mutually perpendicular axes (usually axes of symmetry) which have
different moments of inertia. If we spin such a body about the axis which has
the intermediate value (middle value) then it will be unstable. However if we
spin the body about either of the other two axes it may wobble but the wobble
will not increase with time i.e. it will be stable. This means that for the
earth which is spinning about its poles (the largest moment of inertia) it
will have a 'stable' wobble called a precession. Clearly such motion will not
create long term climate effects (the wobble for the earth has a period of
only about a year). 

Glen Moore
Senior Lecturer in Physics (and still trying to purchase a dinosaur!)