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Homework Help: Torque Experiment

  1. Jan 16, 2009 #1
    1. The problem statement, all variables and given/known data
    So I'm conducting an experiment using simple torque at a set fulcrum, similar to an unbalanced scale (see below), where you know one of the masses and the radii are at equal distances from a central fulcrum and have to find the mass of the other side. I'm having difficulty figuring out how to do this mathematically, if it can be done using just the data given: radii, force of one side, fulcrum. Or perhaps I'm setting it up wrong? Like should there be a counter mass at the top of the fulcrum or something? See: http://is.gd/gasp

    Example masses:
    r = 6 in
    Total length of ruler = 18 inches
    Fulcrum at 9 inches
    Mass 1: 150g
    Mass 2: Unknown
    Theta: 25 degrees (let's say like one side is turning downwards at that degree)


    2. Relevant equations
    τ = rFsin(θ)

    3. The attempt at a solution
    r(m1)(g)sin(θ) = r(m2)(g)sin(90-θ)
    Last edited: Jan 16, 2009
  2. jcsd
  3. Jan 16, 2009 #2


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    Homework Helper

    What does that mean? I'm not seeing a complete question here.
    You say the radii are equal, so the masses must be equal if it is in balance.
    If not in balance, the angle of tilt doesn't have any meaning as far as I can see - the thing will just tilt until it runs into some kind of stop because tilting does not cause any balancing - the moments on each side are reduced identically from mgr to mgr*cos A and remain unbalanced.
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