Re: [Phys-l] Gauss' Law

[Robert Carlson <rcarlson@physicstoolkit.com>]

John and Joel,

Thanks for your comments.

Alfredo,

Your comment below cleared things up for me.

Thank you,

Bob Carlson

--- Alfredo Louro <louro.alfredo@gmail.com> wrote:

> On Tue, Mar 4, 2008 at 11:09 AM, Robert Carlson
> <rcarlson@physicstoolkit.com> wrote:
>
> >  Now, my understanding of Gauss' Law is that it
> only
> >  tells me what the gravitational field is on the
> >  Gaussian surface due to the mass inside the
> Gaussian
> >  surface.  It does not tell me anything about the
> >  gravitational field on the Gaussian surface due
> to
> >  mass outside the surface.
>
> Actually, Gauss' theorem does tell you something
> about the sources
> outside the Gaussian surface, and if the field is
> nice and
> symmetrical, it tells you everything you need to
> know.
>
> Gauss' theorem implies that the flux through a
> closed surface due to
> sources outside it, is zero. If the field has, for
> example, spherical
> symmetry and you choose a sphere as a Gaussian
> surface, then the field
> over the surface is uniform, and perpendicular to
> the surface. Then
> the only way you can get zero flux is if the field
> is uniformly zero
> over the surface.
>
> By integrating, numerically or analytically, of
> course you will get
> the same result, but this does not give more
> information than Gauss'
> theorem. G's theorem is just a very elegant way of
> doing the
> integration for you.
>
> Alfredo
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