Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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

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
Rm 2028
598-5710 ext 225

-----Original Message-----
From: on behalf
of Fakhruddin, Hasan
Sent: Mon 10/4/2010 1:31 PM
To: Forum for Physics Educators
Subject: [Phys-l] Clarification: A ball at the center
of a planet

Alright folks, Here is a little modification:

A solid elastic rubber ball is a perfect sphere of
radius r in free space. A solid homogeneous spherical
massive run away planet also in free space has a
spherical cavity formed at its center. The cavity is
much larger than the ball and has vacuum in it. The ball
is now transported to the center of the planet. Its
radius now is
(A)> r
(B)< r
(C) = r

(now come on....don't ask me to define free space)

How did you guys ever take any exam without giving your
instructor ulcers?!

'Burp'....excuse me; I just took Alka-Seltzer!

~ Hasan Fakhruddin