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Homework Help: Torsion pendulum

  1. Oct 1, 2009 #1
    1. The problem statement, all variables and given/known data
    In the experiment, you will study an oscillator called a "torsion pendulum." In this case, the restoring "force" is the torsion constant of the wire that suspends the weight X and the inertial term is the rotational inertia of the suspended mass. You will compare the periods of a suspended sphere and of a suspended cube. The rotational inertia of a sphere is Is = 110msD2 where ms is the mass of the sphere and D is its diameter. The rotational inertia of a cube is Ic = 61mcS2 where mc is the mass of the cube and S is the length of its side. If the cube and the sphere are suspended from the same wire, what is the expected ratio of their periods, Tc/Ts?
    Assume that D = S
    ms = 020kg
    and mc = 12 kg

    2. Relevant equations

    3. The attempt at a solution

    I'm pretty lost with this one.
  2. jcsd
  3. Oct 1, 2009 #2


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  4. Oct 1, 2009 #3
    I wonder why they gave those moments of inertia. the real values are

    [tex] I_s = \frac { m_s d^2 } {10} [/tex]


    [tex] I_c = \frac { m_c s^2 } {6} [/tex]

    Do you know the solution of a simple harmonic oscillator?

    [tex] F = m\frac {d^2x}{dt^2} = - k x [/tex]

    you don't know the torsion constant, but because you only need the ratio of the periods
    that isn't a problem.
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