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B What happen if i put r=0 into the formula F=(k)mm/r^2

  1. Nov 17, 2016 #1
    What happen if i put r=0 into the formula F=(k)mm/r^2
    So 1/0=infinity ?

    then F= infinite large in mathematical sense?
    is that statement correct ?

    thank
     
  2. jcsd
  3. Nov 17, 2016 #2

    BvU

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    That's what happens with the formula. In reality you can't have two masses in exactly one place, so the formula isn't endlessly applicable...

    Mathematically you have a singularity.
     
  4. Nov 17, 2016 #3
    But In reality i can have two mass put in r=0.000001m
    So the force still become very large?
     
  5. Nov 17, 2016 #4

    Math_QED

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    You cannot put in r = 0. That does not make sense. It does make sense to consider:

    ##\lim_{r \to 0}F = +\infty##. This means, intuitively, when ##r## approaches ##0##, ##F## becomes larger and larger (F grows without bound).
     
  6. Nov 17, 2016 #5

    BvU

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    Well, the masses become smaller too for such small particles. One micron diameter with a reasonable density gives a very small mass !

    On even smaller scales still other things happen. Protons, for example have a mass of only 1.67 10-31 kg and a diameter of 0.88 10-15 m. At such small scales other kinds of forces are much stronger.
     
  7. Nov 17, 2016 #6
    is it possible that the mass is very large but the r is very small?
     
  8. Nov 17, 2016 #7

    Demystifier

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    Yes. Moreover, in quantum physics mass is, in a certain sense, proportional to ##1/r##.
     
  9. Nov 17, 2016 #8

    mfb

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    Yes, then you get a very large force. But it is always finite. And if you want to put the masses too close, you have to consider quantum mechanics where the simple approach with a well-defined distance fails.
     
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