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Simple Harmonic Motion With a String

Please could someone give me an explanation on how a particle attached to a string lying on a smooth horizontal surface can undergo SHM? Why wouldn't the particle stop and the string just go slack?

Thanks!
Original post by PhyM23
Please could someone give me an explanation on how a particle attached to a string lying on a smooth horizontal surface can undergo SHM? Why wouldn't the particle stop and the string just go slack?

Thanks!


Smooth = no frictional force so the only force acting on the particle in the horizontal field is the tension of the string, which changes with respect to the displacement from the equilibrium point, hence SHM
Reply 2
Original post by MathsAstronomy12
Smooth = no frictional force so the only force acting on the particle in the horizontal field is the tension of the string, which changes with respect to the displacement from the equilibrium point, hence SHM


Thanks for the reply

I understand that concept, but what I don't understand is how the motion of a particle attached to a spring can be oscillatory? A particle on a spring has a force due to the compression of the spring, but what causes the 'pushing back' force on a string?
Original post by PhyM23
Thanks for the reply

I understand that concept, but what I don't understand is how the motion of a particle attached to a spring can be oscillatory? A particle on a spring has a force due to the compression of the spring, but what causes the 'pushing back' force on a string?


Oh I think I get you now.. A spring has tension when both extended and compressed therefore SHM throughout, however a string has tension only when extended, therefore SHM then and constant velocity when compressed as no net force. Does that answer your question?
Reply 4
Original post by MathsAstronomy12
Oh I think I get you now.. A spring has tension when both extended and compressed therefore SHM throughout, however a string has tension only when extended, therefore SHM then and constant velocity when compressed as no net force. Does that answer your question?


Ah so for SHM, the motion of the particle doesn't have to be oscillatory, but it's acceleration has to be directed towards the equilibrium position, so it only undergoes SHM from the point to which it was stretched to the equilibrium position, then undergoes constant velocity?
Original post by PhyM23
Ah so for SHM, the motion of the particle doesn't have to be oscillatory, but it's acceleration has to be directed towards the equilibrium position, so it only undergoes SHM from the point to which it was stretched to the equilibrium position, then undergoes constant velocity?


Yes. So back to the original question, the particle will move with SHM from the amplitude point to the equilibrium point due the tension from the extension of the string however due to there being no tension from compression, the particle will move with constant velocity whilst the string is slack and then when the string becomes taut again on the other side, it'll then go back to SHM and repeat.
Reply 6
Original post by MathsAstronomy12
Yes. So back to the original question, the particle will move with SHM from the amplitude point to the equilibrium point due the tension from the extension of the string however due to there being no tension from compression, the particle will move with constant velocity whilst the string is slack and then when the string becomes taut again on the other side, it'll then go back to SHM and repeat.


Thank you very much. I understand it a lot more now :smile:

Oh and I've seen you over in the PAT forum - hopefully they won't keep us waiting too much longer haha! Good luck with your application :smile:
Original post by PhyM23
Thank you very much. I understand it a lot more now :smile:

Oh and I've seen you over in the PAT forum - hopefully they won't keep us waiting too much longer haha! Good luck with your application :smile:


Haha yeh the wait is torturous, best of luck to you too.

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