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

[Idrees]

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

Homework Statement

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 happened to the other two? please give me some hints or full answer

Homework Equations

we don't use equations but we can think about the different heights of each pendulum

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 happened to the third pendulum, it will have no motion

 

[godtripp]

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.

 

[Idrees]

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? please help out

 

[godtripp]

They might start out at a different oscillation 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.

 

[Idrees]

thank you for the second reply.. and i think by energy transformation they mean what will happen to kinetic and gravitational energy.. which i can answer easily

 

[godtripp]

well more correctly it's gravitational potential to kinetic energy, but you have the right idea.

 

[nasu]

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.

 

[Idrees]

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 gravitational energy transforms to kinetic energy... can please help me on how to write this part aswell? thanks heaps.