1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gauss's Law applied to Gravational Flux

  1. May 25, 2009 #1
    1. The problem statement, all variables and given/known data
    Gauss's Law states that the gravatational flux crossing a closed surface is -4piGM, where M is the mass inside the surface.

    A Long straight cylinder has a radius R and is made of material of a constant density of p
    Show that the gravatational field at a distance r from the axis of the cylinder is proportional to r, for r<R.

    2. Relevant equations

    f.da = (closed integral) -4piGM

    3. The attempt at a solution

    I enclosed the cylinder in a Gaussian surface

    Mass Enclosed is pi(r)^2lp
    f is constant therefore, f.da = f.2(pi)rl

    So by gauss's law:

    f.2(pi)rl = -4piG[pi(r)^2lp]

    So f = -2G(pi)pr.

    The problem is when i compare with people they get f = -G(pi)pr.

    Is this correct? Either shows that f proportional to r. But the constant 2 is confusing me, should it be there or not?

    Any help would be greatly appreciated
  2. jcsd
  3. May 25, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    I think the factor of 2 is correct.
  4. May 26, 2009 #3
    Thanks for confirming that
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Gauss's Law applied to Gravational Flux
  1. Gausses Law (Replies: 1)