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Why does it matter if the length of a pendulum is taken at at the center of mass?

  1. Nov 16, 2011 #1
    1. The problem statement, all variables and given/known data

    Does it matter whether you measure the length of the pendulum to the center of mass of the ball or to the bottom of the ball


    2. Relevant equations

    T=2pi*root(L/g)


    3. The attempt at a solution

    I can see that L (length) is a factor, but I'm not sure why it matters if it's taken from the COM or not??

    Any help is appreciated!!
     
  2. jcsd
  3. Nov 16, 2011 #2
    It is essential! A simple pendulum (small mass on the end of a massless string) of length 50cm will have the same time period as a wooden ruler of length 100cm (1 metre).
    The 1m ruler must be pivoted as near the end as possible.
    The centre of mass of a uniform wooden ruler is at the middle (50cm mark)
     
  4. Nov 16, 2011 #3
    Thank you!! That clears it up perfectly.
     
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