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Re: [Phys-l] Clarification: A ball at the center of a planet - retract

When dealing with angels dancing on pin heads, it is fair to accentuate the positive,
no doubt - but not to lie.
Fortunately, the august readership of this list passes lightly over my modest
contributions without much cerebration. Here, I seem to have passed on a
factoid worthy of Snopes: that rubber shrinks on heating.

Well, yes it does, sort of. You have undoubtedly heard popular accounts of fan belts
shrieking when cold, going silent when warm? Like that. Now there certainly ARE
materials with negative thermal coefficients of expansivity over some small even
wide temperature range, but you won't find rubber with a negative symbol
in the list (at least I didn't)
But wait a moment, didn't you hear of elastic bands shrinking when heated?
But the issue tends to become the anisotropic coefficients of a long chain
molecule that offers more of less untidy folding with temperature.

Sorry about that

Brian W

On 10/4/2010 8:50 PM, brian whatcott wrote:
I see merit in Brian's question: as I note (again and again); ignoring
radioactive heating (which occurs in most conceivable planetary bodies,)
leads one to Thomsonian error.
So the radiative heating would have its affect on the rubber ball,
after some equilibrating time period.
Rubber has the curious property of contracting when heated
which would be the dominating effect in this situation.

Unless it were spinning, I suppose? :-)

Brian W


On 10/4/2010 1:11 PM, Crawford MacCallum wrote:
I think there is no force on any particle anywhere in the
cavity, so (C).

On Mon, 4 Oct 2010 14:04:45 -0400
"Brian D. Shock"<> wrote:
Sounds like the net force acting on the ball before and
after is zero, so no change in the r. Is there a
temperature change?

Brian Shock