Frequency of oscillation

  • Thread starter goonking
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Homework Statement


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?


Homework Equations



I believe we need the imagine the leg as a rod, so the moment of inertia would be = 1/3 m L2

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?
 

Answers and Replies

  • #2
rude man
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so is the the pivot point at the hips and the whole leg is moving?
Yes
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?
No. It says 'pivoting about one end' so it's not pivoting about the knee.
 
  • #3
haruspex
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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?
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.
 
  • #4
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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.
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?
 
  • #5
haruspex
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so I would just use T = 2 pi sqrt(L/g)
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.
 
  • #6
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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.
ok, I got the the new answer to be .675 Hz after using the physical pendulum formula . Thanks.
 

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