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Can someone explain to me this about gravity please

  1. Sep 1, 2013 #1
    Does gravity have a limited range in which it can attract objects? I looked up on google, most people are saying it's infinite.. if it really is infinite then I'm confused, because if the denominator is infinite, then the result is just zero.. and in gravity's law F=[g(m1m2)] / r^2 .. if r is so big doesn't gravity simply become ineffective? so how would gravity have an infinite range?

    Sorry if this question is silly I'm not a specialist.. I'm just curious
     
  2. jcsd
  3. Sep 1, 2013 #2

    tom.stoer

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    The basic equation is - as you have said

    ##F = G \frac{m_1\,m_2}{r^2}##

    Of course the force F goes to zero if r goes to infinity. But that's not how we would interpret infinite range. We should better say that if we let the distance r become arbitrary large but finite, then the force F becomes small but not zero.
     
  4. Sep 1, 2013 #3

    HallsofIvy

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    The problem is that you are trying to treat infinity as if it were a number- and it isn't. Yes, if you were to replace "r" with infinity you would get a force of 0. But saying that the "range of gravity is infinite" just means that if you were to put any distance in for r you would get a non-zero gravitational force. That does not include setting r equal to "infinity" because, as I said, infinity is not a number and you cannot be an infinite distance away from a gravitating body.
     
  5. Sep 1, 2013 #4

    BruceW

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    yeah. Something with a finite range would have some cut-off ##r## value, and for any ##r## greater than this, the force is zero. (and gravity does not have this property).
     
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