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Re: Warm- vs. Cold-blooded Dinos



In a message dated 95-07-11 18:32:59 EDT, pwillis@ozemail.com.au writes:

>>
>>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.
>
>Obvious really, I'm glad you cleared that up for me.
>
>>
>>Try this: take an expendable book and wrap it with a rubber band to
>keep it
>>closed.  Hold the book so that the title faces you and throw the
>book up in
>>the air so that it spins top over bottom.  No matter how hard you
>try, you
>>will not be able to spin the book stablely for any length of time.
>The book
>>might spin stablely for a moment or two but it will suffer a "pole
>flip."  If
>>the spinning book is completely isolated, no energy is being lost or
>added to
>>it and that is my point.
>
>I may well have missed the point here, but are books held together
>with
>rubberbands adequate models of a rotating earth with a molten center
>and
>crusty layer on the outside? What about gravity (completely different
>between your analogy and the real earth).
>
>OK, lets start a-fresh. Imagine a rotating jam-donut, 95% jam and 5%
>donut
>crust. Now I am not sure about all the technobabble that makes this
>correct, but as I see it, providing the donut is rotating on a stable
>axis,
>no problem. But begin to change that axis of rotation and the rotating jam
>will be have differently to the rotating donut crust (liquid vsolid).
 
Inertia tensors represent the current mass distribution of a body in 3D.  In
a rigid body as I described, they do not change at all.
 
>this difference in movement is great enough, the friction between the
>donut
>crust and the jam could be considerable. If, instead of a jam donut
>we have
>an earth with a molten core, the friction generated between crust and
>mantle when the axis changes would be enormous, ... wouldn't it? And
>one
>way that friction could be disapated could be as heat across the
>crust, ...
>couldn't it?
>
>Anyway, I am just a very dead croc person, physics was never my
>strong point.

I never claimed that the earth met the criteria for a non-symmetric rigid
body, I was only illustrating that a rotating body's motion can become
apparantly unstable with no exterior forces at all being applied.  The motion
I described above -- which is cyclic with periods of stability and
instability -- is merely the natural motion of a bodies that are rotating as
I described.

If the axis of rotation fell near the intermediate intertia tensor of the
earth and a period of instability were to occur, then either the earth would
wobble and flip (over a considerable period of time) and/or the mass of the
earth would redistribute to move the intermediate intertia tenor to lessen or
cancel the wobble.  If this mass redistribution occurred, it is likely that
it would initiate much vulcanism and climate changes.

I do not believe that the earth rotates as I described (even with contenental
drift, ice ages, etc. I do not think enough mass would ever be moved to bring
the intermedate intertia tensor close enough to the poles), but I have not
performed any calculations to test my strong hunch.

And besides, I think most of the readers here know that I favor a villian
other than polar wobble in the KT extinction.

V.S.