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2 rods' interaction

  1. Jun 4, 2009 #1
    There are 2 identical rods of mass "m" and length "l" separated by a distance "l" in such a way that the 2 rods are in a straight line. Find the Gravitational force between these two rods.



    2. Relevant equations



    3. The attempt at a solution

    I'm unable to analyse a calculus based strategy such as chosing the small elemnt of mass "dm" length "dx" and so on..
     
  2. jcsd
  3. Jun 4, 2009 #2

    berkeman

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    Staff: Mentor

    Just use their centers of mass, and the gravitational force equation. Write that out for us.
     
  4. Jun 4, 2009 #3
    so u mean to say that the interaction is nothing but...


    F= Gm.m/4 l.l ??
     
  5. Jun 4, 2009 #4

    berkeman

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    Almost. What is the separation of the centers of mass in terms of l?
     
  6. Jun 4, 2009 #5
    the situation is like this :

    |<___________________>|
    _____l_____ (l+l/2+l/2) _____l_____


    the separation between the centres of the 2 rods is l+l/2 +l/2 =2l
     
  7. Jun 5, 2009 #6

    berkeman

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    Two rods of length L have their centers of mass separated by L/2 or 2L? Why? Not.
     
  8. Jun 5, 2009 #7
    the centres are separated by a lenght of 2l
     
  9. Jun 5, 2009 #8

    berkeman

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    If each rod is length L, then I don't think so. Just use a practical example. What if each rod is 1 meter long, and you stack them end-to-end. How far apart are the centers of the rods?
     
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