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Why is this wrong? (gravitational flux)

  1. Sep 21, 2013 #1
    in my notes i have..

    [itex]\Phi[/itex] = [itex]\int[/itex] [itex]\vec{g}\cdot[/itex]dA = g(4[itex]\pi[/itex]r2) = -[itex]\frac{GM}{r^2}[/itex](4[itex]\pi[/itex]r2)

    which yields [itex]\vec{g}[/itex]=-[itex]\frac{GM}{r^2}[/itex]

    here's what i did independently..

    [itex]\Phi[/itex] = [itex]\int[/itex] [itex]\vec{g}\cdot[/itex]dA = -[itex]\frac{GM}{r^2}[/itex](4[itex]\pi[/itex]r2)

    but since [itex]\vec{g}[/itex]= -[itex]\vec{\nabla}[/itex][itex]\Phi[/itex]


    [itex]\vec{g}[/itex]=[itex]\frac{d \Phi}{dr}[/itex]=[itex]\frac{4 \pi GM}{r}[/itex]

    but this comes out to a different answer. is this still correct?

    *to admins/moderators/mentors/etc: before i get in trouble again, i appologize if this is considered another hw problem. but i thought it wasn't, so i posted in this section
    Last edited: Sep 21, 2013
  2. jcsd
  3. Sep 21, 2013 #2


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    Staff: Mentor

    The same symbol is used for flux and potential, but they are different physical concepts.
  4. Sep 21, 2013 #3
    oh darn i forgot about that.. thanks
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