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Homework Help: Calculating force required to keep pendulum in motion

  1. Mar 25, 2009 #1

    I am interested in calculating the force required to keep a pendulum in motion. I believe This force will be same as the frictional loss + other dampening loss happening in the oscillations.


    I know the initial push or force that i am giving to the pendulum. let initial force given to pendulum be 3.5 Kg force-cm.

    I also know the displacement angle of pendulum. The displacement angle A= 20 Degrees.

    The length of the pendulum is L=30 cm. and the weight of the pendulum is W=10 Kg.

    The pendulum oscillations dies out after say 40 cycles.

    Can i calculate how much energy is lost in the pedulum during this 40 cycles?

    How can i calculate the energy loss per cycle from this?

    My ultimate aim is to calculate the force required to be given to the pendulum to keep it moving.

    Can some one please help?

  2. jcsd
  3. Mar 25, 2009 #2
    Force times distance (F dx) is work (energy), while force times time (F dt) is impulse or momentum transfer. Push is not a recognized term for either work or momentum transfer.

    Force is measured in Newtons. Sometimes a Newton is called a kilogram-force, but it does not properly connotate the correct units.

    1 Newton = 1 kilogram-meter / sec2
    Last edited: Mar 25, 2009
  4. Mar 25, 2009 #3
    sorry about that...my mistake,

    I am actually pushing rather pulling the pendulum with 3.5 kgf force. i have a spring gauge which i am using for measurement. I lift the pendulum weighing 10 kg's to about 20 degrees. the spring gauge reads 3.5 kg. then i release the pendulum.

    The time for one oscillation is about 1.4 seconds. the pendulum comes to rest in about 30 oscillations. the total time taken for it to come to rest is say around 40 seconds.

    i am interested in find the amount of force that must be supplied to pendulum to keep it in motion.
  5. Mar 27, 2009 #4
    can some one please help?
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