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How to explain there cannot be a case where r=0 in F=G(Mm/r^2)

  1. Feb 24, 2013 #1
    Hi. This is my first post here. In one of our science groups in Facebook, a member is asking about a case where r=0 in Newton's Equation F=G(Mm/r^2)

    The best i could do was to state that there cannot be two point masses with a distance r=0 between them. He seems to accept my explanation but his intuition that it should be 'infinity' still remains. I would like to explain it better. Can you please help?

    I have searched the site but could not find the answer. If there is already a thread, I would be glad if you could point me towards it.
  2. jcsd
  3. Feb 24, 2013 #2


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    Homework Helper

    The gravitational force of attraction between two point masses, M & m2, separated by a distance 'r' is given by:

    F= GMm/r2

    If r=0, then you don't have two masses anymore but one mass. In which cases, gravity would vary with depth of the planet. Read more here.
  4. Feb 24, 2013 #3
    When r=0, you no longer have two masses, you have one. This condition actually does occur at a black hole, where all mass is (believed to be) contained in a singularity, i.e., a single point.
  5. Feb 25, 2013 #4
    I don't think the gravity law works well on a quantum scale since the nuclear forces and electromagnetic forces become very strong at small distances.
  6. Feb 25, 2013 #5
    Thank you guys for your insights, we managed to resolve the question.

    When we are talking about classical physics, I think we sometimes tend to grab ideas from Relativity and Quantum Mechanics and get confused and this seems to be the root of the problem.
    Last edited: Feb 25, 2013
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