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Homework Help: Torque,rotational motion of an object

  1. Oct 25, 2012 #1
    1. The problem statement, all variables and given/known data
    We all know that
    T = Fd
    Where F = applied force,T=torque about the pivot.
    Mathematically,to produce the same size of torque,if F increases,d decreases.
    If F decreases,d increases.
    But,let's think about what's happening at the atomic level.
    Please see the attached.
    Suppose A is the pivot.
    In picture 1 and 2,you are applying a force at different position.
    By the formula,to produce the same size of clockwise torque about A,
    In fact the force is applied on the whole object,
    i.e.When you apply a force on E in figure 2,the force is actually acting on the atoms(or group of atoms) at E.By repulsive forces between atoms,force is "transmitted" to B,
    so the object rotates.
    In figure 1,you apply force at B,when the atoms at B move,they pull the other atoms forwards,so the whole object rotates about A.
    (These are what I thought about what's happening in atoms when an object rotate.)
    However,this analogy cannot explain why as d decreases F increases.
    1.Can someone give me an explanation of the equation in terms of movement of atoms and molecules?
    i.e. Why d decreases then F increases (for the same torque)

    2.And why the atoms at pivot point don't perform rotational and translational motion?
    Thx a lot.

    I have been solving this for one week though I can't figure it out....
    Please forgive for my foolishness.

    2. Relevant equations
    the equation of torque,which is T=Fd

    3. The attempt at a solution
    listed in the above and the attached

    Attached Files:

  2. jcsd
  3. Oct 25, 2012 #2
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