1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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
    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
    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? ):
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook