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What happends when we oscillate three pendulums next to each other?

  1. Dec 12, 2009 #1
    what happends when we oscillate three pendulums next to each other???????????

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

    if we have three pendula hanging from one string...and each of them separated by 5 cm, and each pendulum has same amount of mass hanging from it,, but the first two pendulums are 2.0 m long and the third one is 2.5 m long... if i set the first 2.0 m long pendulum to oscillate what will happend to the other two?????????? please give me some hints or full answer

    2. Relevant equations

    we dont use equations but we can think about the different heights of each pendulum

    3. The attempt at a solution

    i would think once you start oscillating the first pendulum, it will moeve and strt oscillating the 2nd pendulum which are both of same height, but nothing will happend to the third pendulum, it will have no motion
     
  2. jcsd
  3. Dec 12, 2009 #2
    Re: what happends when we oscillate three pendulums next to each other???????????

    you don't use equations? well the pendulum will simply start oscillating at a specific angular frequency. It won't necessarily oscillate like a simple pendulum however. There's a different moment of inertia and center of mass. Without using equations, I'd say average out the distances apart to find your center of mass. As a rule of thumb, I'd imagine that the moment of inertia of this physical pendulum would probably be similar to a point mass at that center of mass.
     
  4. Dec 13, 2009 #3
    Re: what happends when we oscillate three pendulums next to each other???????????

    Thanks for youre reply,, its very useful.. but also i wanted to know what will simply happen to the motion, would one pendulum moving oscillate the second one ,, please eloborate on what will simply happpen to the motion and how will the energy be transformed when this happends??? plz help out
     
  5. Dec 13, 2009 #4
    Re: what happends when we oscillate three pendulums next to each other???????????

    They might start out at a different oscilation periods, but a forced oscillation will quickly take over if that would happen. In which the system will resonate and oscillate all together about the center of mass.
     
  6. Dec 13, 2009 #5
    Re: what happends when we oscillate three pendulums next to each other???????????

    thank you for the second reply.. and i think by energy transformation they mean what will happen to kinetic and gravitional energy.. which i can answer easily
     
  7. Dec 14, 2009 #6
    Re: what happends when we oscillate three pendulums next to each other???????????

    well more correctly it's gravitational potential to kinetic energy, but you have the right idea.
     
  8. Dec 14, 2009 #7
    Re: what happends when we oscillate three pendulums next to each other???????????

    I think you have a problem related to forced oscillations and resonance.
    The first pendulum will "transmit" some of its energy to the other two. The one with the same length is at resonance with the first one so it will oscillate with a relatively large amplitude. The third one will oscillate with a smaller amplitude, as it's out of resonance (but not by much).
    After a while the energy will be transmitted back to the first pendulum and so on.
     
  9. Dec 15, 2009 #8
    Re: what happends when we oscillate three pendulums next to each other???????????

    thank you nasu heaps.. i completely understood your answer properly and thank you to godtripp aswell.. the question asked "DESCRIBE THE TRANSFORMATION OF THE ENERGY THAT OCCURS WHEN THESE PENDULAS are oscillated?? should i wirte about how the gravitional energy transforms to kinetic energy... can please help me on how to write this part aswell??? thanks heaps.
     
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