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Frequency of oscillation

  1. Apr 24, 2015 #1
    1. The problem statement, all variables and given/known data
    Consider a human leg to be a rod of uniform density pivoting about one end. What will the frequency of oscillation be for a leg with a length of 0.82 meters?


    2. Relevant equations

    I believe we need the imagine the leg as a rod, so the moment of inertia would be = 1/3 m L2
    3. The attempt at a solution
    so is the the pivot point at the hips and the whole leg is moving?

    or just the shin is moving and the knee is the pivot point? if this it the case, then do be divide .82m by 2?
     
  2. jcsd
  3. Apr 24, 2015 #2

    rude man

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    Yes
    No. It says 'pivoting about one end' so it's not pivoting about the knee.
     
  4. Apr 24, 2015 #3

    haruspex

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    It doesn't matter whether it represents the shin or the whole leg, just do as it says: treat it as a rod of length .82m pivoted at one end.
     
  5. Apr 24, 2015 #4
    so I would just use T = 2 pi sqrt(L/g)?

    which comes out to be 1.81 seconds

    frequency = 1/T = 1/1.81 = .55 Hz

    is that correct?
     
  6. Apr 24, 2015 #5

    haruspex

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    No, I said a rod of that length, not a simple pendulum of that length. Use the moment of inertia you mentioned in the OP.
     
  7. Apr 24, 2015 #6
    ok, I got the the new answer to be .675 Hz after using the physical pendulum formula . Thanks.
     
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