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Newton's third law problem

  1. Jan 11, 2007 #1
    1. The problem statement, all variables and given/known data
    "Identify at least five pairs of action reaction forces in the following diagram"
    [​IMG]
    Source: http://www.physicsclassroom.com/Class/newtlaws/U2L4b.html problem 2

    2. Relevant equations
    Newton's third law


    3. The attempt at a solution
    1) Man and monkey
    2)monkey and scale
    3)scale and tree
    4)man and tree
    5) monkey and tree
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 11, 2007 #2

    Doc Al

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    Staff: Mentor

    You would be better off sticking to things that are in actual contact and thus can push/pull against each other. For example, the man is touching the rope, so man and rope can exert forces on each other. But the man is not directly touching the tree, so man and tree do not directly exert forces on each other. (Note: A long range force, like gravity, does not require direct contact.)
     
  4. Jan 11, 2007 #3
    The best way to deal with things is to draw "bags" around things and see how the forces are acting on that single thing.

    * Note *
    You might want to think about tension =).
     
  5. Jan 11, 2007 #4
    Are my attempts to the solutions valid? Man exerts force on Monkey and vice versa. Do indirect forces count in newton's third law? Like the one between the tree and man.
     
  6. Jan 11, 2007 #5

    Doc Al

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    Staff: Mentor

    Strictly speaking: No. Only include forces between objects that are in direct contact. (We ignore the teeny tiny gravitational force between man and tree!) The man doesn't really pull on the tree; he pulls on the rope! Redo your answers with this in mind and you'll have a deeper (and more correct) understanding of forces and Newton's 3rd law.
     
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