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Why is the distance that two objects are apart (r) when it should be half of it?

  1. Feb 17, 2010 #1
    1. The problem statement, all variables and given/known data

    what is the gravitational force of atraction between
    two oranges of 0.12kg each placed 0.2m apart


    2. Relevant equations

    F=(Gm1m2)/r^2

    3. The attempt at a solution
    it works when i put r = 0.2 but shouldnt it be 0.1 (half the diameter is the radius isnt it?)
     
  2. jcsd
  3. Feb 17, 2010 #2

    Matterwave

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    Your intuition for F is correct for things like the Earth, where we are a distance r=radius from the Earth's center. But, more generally, r just represents the distance between the two objects. In this case, the distance is just .2m.
     
  4. Feb 17, 2010 #3
    what i know about r in these kinds of questions that it is the distance from the centre of object1 to the centre of object2, so if that 0.2 represents:

    radius of object1+raduis of object2+the distance between the two surfaces , then your work is done .. but becareful with other questions this one i assume that they meant that 0.2 is the distance from centre object1 to centre object2 ..
     
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