Question about Centripetal force

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Discussion Overview

The discussion revolves around the nature of forces involved when a weight is swung around on a string, specifically examining whether the tension in the string is due to centripetal force, centrifugal force, or both. The conversation includes theoretical considerations and definitions of these forces, as well as their implications in different reference frames.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the tension in the string is due to centripetal force, while others argue that centrifugal force may also play a role depending on the frame of reference.
  • One participant suggests that centrifugal force is a reactive force that depends on the rigidity of the string.
  • Another participant emphasizes that centrifugal force is often considered a fictitious force that appears in rotating frames of reference.
  • There is a discussion about the action-reaction pairs, with some stating that the string pulls on the object (centripetal) and the object pulls on the string (often referred to as centrifugal), though this usage is debated.
  • One participant questions whether centrifugal force exists in the string at all, suggesting that the string might only transfer force to the weight.
  • Another participant clarifies that inertia is not a force and discusses the nature of forces in a rotating frame.
  • There are conflicting views on the terminology used, with some participants labeling centrifugal force as a misnomer and others defending its use in certain contexts.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the definitions and existence of centripetal and centrifugal forces, indicating that the discussion remains unresolved with no consensus reached.

Contextual Notes

Participants highlight the ambiguity in defining forces in different reference frames and the historical context of terms like "centrifugal." There are also unresolved questions about the nature of forces when considering inertia and the lack of external forces acting on the system.

nuby
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If a string is attached to a weight and swung around overhead, is the force that creates tension on the string centripetal, centrifugal, or both?
 
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What do you think?
 
nuby said:
If a string is attached to a weight and swung around overhead, is the force that creates tension on the string centripetal, centrifugal, or both?

Centripetal. Centrifugal force can only be measured in a rotating frame of reference.

Pete
 
I think centripetal would always exist in the string. But, centrifugal (reactive) force would depend on the rigidity of the string.
 
nuby said:
I think centripetal would always exist in the string. But, centrifugal (reactive) force would depend on the rigidity of the string.
Still insist on using that archaic meaning of centrifugal force as the "reaction" force to centripetal force? If so, then it's simple: The string pulls the object (centripetal) and the object pulls the string ("centrifugal"). Can't have one without the other.

One more time though: This is an old-fashioned usage of the term centrifugal. The modern usage is as a "fictitious" force that appears when viewing things from a rotating frame of reference.
 
Doc Al said:
Still insist on using that archaic meaning of centrifugal force as the "reaction" force to centripetal force? If so, then it's simple: The string pulls the object (centripetal) and the object pulls the string ("centrifugal"). Can't have one without the other.

One more time though: This is an old-fashioned usage of the term centrifugal. The modern usage is as a "fictitious" force that appears when viewing things from a rotating frame of reference.

Just to add to what Doc Al said, the concept of "force" is actually a very slippery one. Technically, a force is the rate of change of momentum away from what the natural trajectory would have been. In other words, it doesn't really make sense to talk about a force without fixing trajectories first. Normally, in an inertia frame, things move in straight lines (ignoring gravity). So if something moves in a circle, there must be a force to make it do so --- we call that "centripetal". However, if we're in a rotating frame, things tend to move away from the centre, so if something doesn't then you need a force --- we call that one "centrifugal".
 
Doc Al said:
Still insist on using that archaic meaning of centrifugal force as the "reaction" force to centripetal force? If so, then it's simple: The string pulls the object (centripetal) and the object pulls the string ("centrifugal"). Can't have one without the other.
archaic? Was it true? For the example which nuby explain,
a string is attached to a weight and swung around overhead
What are the action-reaction forces? Say the one is centripetal force, what is the other?
 
The "action/reaction" pair is: String pulls on object & object pulls on string. When considering the motion of the object, we call the first force the centripetal force. The second force has no particular name. (Some folks call that second force the "centrifugal" force--but that's nonstandard usage. Old-fashioned and out of date!)
 
Last edited:
Doc Al said:
The "action/reaction" pair is: String pulls on object & object pulls on string. When considering the motion of the string, we call the first force the centripetal force. The second force has no particular name. (Some folks call that second force the "centrifugal" force--but that's nonstandard usage. Old-fashioned and out of date!)
I thought the second one was inertia - the object's tendency to continue moving in a straight line.
 
  • #10
Inertia is not a force.
 
  • #11
Ok. centripetal-centrifugal forces pair never action-reaction forces.

Other hand, for this example, I suppose the pair of centripetal force is a force like so; say we pull a body by means of a string in space. There is no other force(friction, weight) then we apply. But anyway string will have has a tension. If this true, this is inertia force. But it is a pair-less fictitious force. Then how will we call it? :-/
 
  • #12
Net force?
 
  • #13
The string "pulls" on the body and the body "pulls" on the string, this forms a force-reaction pair. Equally, we "pull" on the string and the string "pulls" on us, again a force-reaction pair.

What is this fictitious force your talking about?
 
  • #14
Volcano said:
Other hand, for this example, I suppose the pair of centripetal force is a force like so; say we pull a body by means of a string in space. There is no other force(friction, weight) then we apply. But anyway string will have has a tension. If this true, this is inertia force. But it is a pair-less fictitious force. Then how will we call it? :-/
As Hootenanny already explained, the string pulls on the object and the object pulls on the string. Two very real forces--nothing "fictitious" here.
 
  • #15
Is it possible centrifugal force doesn't exist in the string at all? If you take the ball way and spin the string around by itself, the string would probably just get tangled around the axis. Would there be any centrifugal force in this example?

Maybe the string only transfers force to the weight? i.e. Weight pulls on spinning axis through string, and the rigidity of the string controls the rate force is transfered.
 
  • #16
nuby said:
Is it possible centrifugal force doesn't exist in the string at all?
According to your nonstandard definition of "centrifugal" force: NO. The string can't pull without being pulled.
 
  • #17
Hootenanny said:
What is this fictitious force your talking about?
I tried to understand second force on weight which asked in first post. Doc_Al said has no particular name and DaveC426913 said inertia. You and Doc_Al are right. I must be mad. Don't know how and why confused so much. Ok.
 
  • #18
centrifugal force is a misnomer. what people refer to as centrifugal force is actually centrepetal force to the best of my knowledge.
 
  • #19
patrickdt10 said:
centrifugal force is a misnomer. what people refer to as centrifugal force is actually centrepetal force to the best of my knowledge.
No, centripetal force is the force pulling inward. Centrigual force is plain-old garden variety inertia as seen from the rotating reference frame. (i.e. if the string tied to the rotating bucket of water were to break, the bucket would continue in a straight line tangential to the bucket's former circular path).
 

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