Upward force on a object spinning on on string

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    Force Spinning String
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Discussion Overview

The discussion centers on the forces acting on an object spinning horizontally on a string, particularly focusing on how these forces counteract gravity and the implications for the plane of rotation. Participants explore the components of tension in the string and the conditions under which the plane of rotation remains stable.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Ramana questions how the force counteracting gravity arises and whether it is responsible for the plane of rotation rising when spinning starts.
  • Some participants propose that the vertical component of tension balances the weight of the object, while the horizontal component provides the necessary centripetal force for rotation.
  • Others express confusion about the existence of a vertical component when the force is primarily horizontal, prompting further clarification and exploration of the dynamics involved.
  • A later reply suggests that as the plane tilts, the vertical component of tension adjusts to restore equilibrium.
  • One participant asserts that in a uniform horizontal circular motion, the vertical component of tension is zero, leading to a discussion about the conditions under which the plane of rotation can remain level.
  • Another participant emphasizes that the plane of rotation cannot remain perfectly horizontal in a steady-state condition, as there will always be a slight downward angle in the string.

Areas of Agreement / Disagreement

Participants express differing views on the existence and role of the vertical component of tension in maintaining the plane of rotation. While some agree that there is a balance of forces, others contest the conditions under which this balance occurs, indicating that the discussion remains unresolved.

Contextual Notes

There are limitations in the assumptions made regarding the forces acting on the object, particularly concerning the definitions of vertical and horizontal components of tension in different scenarios of motion.

ramanakumars
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Hi everyone,
I was wondering what forces would counteract the force of gravity on an object which is spinning horizontally on a string. I realize its a component of the tension, but how does the force come about?
Is this force also the reason that the object's plane of rotation rises when we start the spinning from when the object was at rest?

Thanks,
Ramana
 
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From what I think, yes, that is the reason the string would go up, i.e., would become slanted instead of horizontal.

In suck a case, the vertical component of the tension would balance the weight and the horizontal component would act as the centrifugal force required for rotation.
 
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Thanks for the reply...
What I was wondering was how a vertical component could exist for a horizontal force... Anything I'm missing here?
 
I just realized something... Is it that as soon as the rotating plane tilts away from the horizontal, the vertical component "steps in" to ensure that the plane is set back?
 
An object "spinning on a vertical string" has NO vertical component. The force on the string is just the weight of the object. IF you mean an object moving in a horizontal circle, held by a string from a point above the center of the circle, then the object does NOT move outward on its own. There must have been a additional force initially to move the object horizontally. The vertical component is still the weight of the object.
 
I believe there is some confusion... I am sorry if I wasn't clear.
The situation is a uniform horizontal circular motion (parallel to a level ground). I was wondering why the plane of the circle stays at that level and does not drop, despite the obvious force of gravity 'pulling down' on the object. At this point, the vertical component of the tension on the string is zero, as there simply is no vertical component.
I believe Siddharth answered the question by saying that at the point where the plane of the circle dips, the vertical component of the tension forces the plane back to its original position. This does seem logical to me... But I am not entirely sure..

Thanks...
 
It is not that the plane of rotation rises up so that a rock-on-a-string is level with the hand that is swinging it. It is a matter of equilibrium.

If the plane of rotation is far below the hand, the vertical component of tension will tend to cause it to rise.

If the plane of rotation is level with the hand, gravity will tend to cause it to fall.

Somewhere in between is an equuilibrium level where the force of gravity and the vertical component of tension are in balance. No matter how fast you spin the rock, this level will be somewhere below the hand.
 
ramanakumars said:
I was wondering why the plane of the circle stays at that level and does not drop, despite the obvious force of gravity 'pulling down' on the object. At this point, the vertical component of the tension on the string is zero, as there simply is no vertical component.

This is the part that is wrong. There is a vertical component. You will never get the string perfectly horizontal, at least not in a steady-state condition. The string will be slightly angled downwards, and the vertical component of the tension will balance the weight of the object.
 
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Ok... I understand...
Thanks a lot guys... :D
 
  • #10
Exactly. It will never remain in the horizontal plane.
Cheers.
 

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