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

[chuck britton <cvbritton@mac.com>]

But since our instructors already HAD their PhD's - we were just 
playing out this same game.

Are you concerned about General Relativity or Gauss's Law for gravity.

GenRel plays a hand if the 'Free Space' scenario still has any Grav 
PE due to the planet.

If not - it 'just' seems to be a gravitational Gauss's Law exercise.


At 12:38 PM -0500 10/4/10, Rauber, Joel wrote:
> They probably did give their instructors ulcers.  I wonder if that 
> is a pre-condition for wanting to get your Phd in Physics.
>
> :-)
>
>  >
> >  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!