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

[John Denker <jsd@av8n.com>]

On 10/04/2010 02:12 PM, Fakhruddin, Hasan wrote:
> I believe the radius will decrease due to the planets pull on the
> particles of the ball, directed toward the center of the planet. So
> Choice C.

Not a chance.

The only parts of the planet that could have produced such
an effect were removed when you created a cavity big enough
for the ball to sit in.

It's a famous result, published by Sir Isaac himself.  The 
field inside a spherical shell is zero.

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Nitpickers note:  This assumes Newtonian gravity, symmetry, 
and other conventional simplifications.