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Homework Help: Is a simple pendulum simple harmonic motion?

  1. Oct 17, 2009 #1
    I'm wondering this because my textbook says that for small angles it is, but we learned that for simple harmonic motion to occur there must be a linear restoring force.. eg F= -kx.. but for the simple pendulum the restoring force is F= -mgsin(theta).. wouldn't this not be linear?
  2. jcsd
  3. Oct 17, 2009 #2


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    Well you see for small angles θ, sinθ≈θ so that the restoring force is F=-mgθ.

    And now you know θ=x/l (x=arc length and l=length of pendulum)

    so F=-mgx/l
  4. Oct 17, 2009 #3
    Ohh okay, makes sense. Thank you!
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