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Quick Gravity Question

  1. Jul 22, 2004 #1


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    just a really question about gravity, using the formula:
    F = (G * m1 * m2 ) / r^2

    where F is the force of attraction caused by gravity, G is the gravitational constant (6.673E-11), m1 is the first mass, m2 is the second mass, and r is the radius/distance between the two centers of mass.

    the force that is caused, is it shared between the two bodies or do each recieve that much force, for example if I just stick these numbers in:
    m1 = 1000000
    m2 = 1000000
    r^2 = 125
    then I get a force of .53384 newtons

    so do each of these bodies recievce the full .53384 newtons, or does it split up bwtween them and each gets half, .26692?
  2. jcsd
  3. Jul 22, 2004 #2
    The force is on one body M_1 due to the nearby presence of another body M_2. Newton's Third Law then states that the same magnitude of force acts on M_2 due to the presence of M_1.
  4. Jul 22, 2004 #3


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    so that formula finds the force that is applied on the first mass (but we know that the second mass gets the same force too).
    so in the example I gave earlier, they would both get the 53384 newtons.

    thanks, that solved my problem
  5. Jul 22, 2004 #4

    By the way, this is generally true of all force relationships. Whenever you see [tex]F = ...[/tex], then this is the force acting on the body in question (which we call the "system").

    So you always isolate a body to analyze the forces that act on it. The force equations (such as F = mg, F = kx, and so on) describe the magnitudes of the forces that act on THAT body.
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