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

  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. rock.freak667

    rock.freak667 6,231
    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. 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. 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. 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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