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Lab Question - Pendulum

  1. Oct 1, 2011 #1
    Hi guys,

    I was doing my lab report and stumbled onto this question and I would really appriciate it if you guys could assist me on this. (:

    1. The problem statement, all variables and given/known data

    For a simple pendulum consisting of a mass M attached to a very thin light string of length L, in the absence of air resistance, derive the equation of motion for the simple pendulum in terms of the angular displacement θ relative to its equilibrium position? For “small” oscillation, namely θ is less than 5˚, what is the period T of oscillation? Compare with the derived result in Exercise 4 above.

    2. Relevant equations

    From Exercise 4:
    T = 2π√(I/(MgLg))

    3. The attempt at a solution

    I'm guessing that I will just be M for a simple pendulum and I'll end up with:
    T = 2π√(1/(gLg ))
    which doesn't make much sense.

    Looking forward to your replies! (:
    Last edited: Oct 1, 2011
  2. jcsd
  3. Oct 1, 2011 #2


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    Gold Member

    What are you using for I?
  4. Oct 1, 2011 #3
    It's the moment of Inertia of the pendulum (taken to be a I = MLg2.

    We assume that the pendulum of mass M is attached to a very light thin string of length Lg.

    I googled and found out that the answer should be:

    T = 2π√(Lg/g) but I have no clue how I am to get to this. ):
    Last edited: Oct 1, 2011
  5. Oct 2, 2011 #4


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    I goes as L^2. In your first equation if you substitute for I you should get L in the numerator and not the denominator as you have.
  6. Oct 2, 2011 #5
    Why does I become L^2? ):
  7. Oct 3, 2011 #6
    Can anyone assit me with this? ):
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