Mechanical Forces: Centrifugal/Centripetal Force Effects

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Discussion Overview

The discussion revolves around the forces acting on a rock tied to a rope and spun in a horizontal plane above the head of the person spinning it. Participants explore the roles of centrifugal and centripetal forces, as well as the tension in the rope and the effects of gravity.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions which force counteracts gravity to keep the rock fixed in its horizontal axis while being spun.
  • Another participant asserts that the tension in the rope is the key force, noting that the rope is not horizontal.
  • A participant seeks clarification on the orientation of the rope, expressing concern about the validity of their question.
  • One participant compares the scenario to an olive spinning inside an upside-down cup, questioning why the olive does not fall.
  • A participant explains that the rock is spinning around a vertical axis and that the forces acting on it include gravity downward and the rope's tension directed toward the center and slightly upward.
  • Another participant challenges the notion that the rope is horizontal, suggesting that it can be observed to be angled when viewed from the side during the spinning motion.
  • A later reply expresses gratitude for the clarification provided in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the orientation of the rope or the forces involved, indicating that multiple competing views remain regarding the mechanics of the situation.

Contextual Notes

There is an assumption that the reader understands the basic concepts of centrifugal and centripetal forces, as well as the role of tension in the rope. The discussion does not resolve the specifics of how these forces interact in this scenario.

pedro trindade
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i'm not really a phycisist and to be really sincere i usually cannot answear my questions in class... so yeah, a question i have for a long time now is, which force anulates the gravity preventing a rock tied on a rope spinning over my head to fall and just stay fixed in his horizontal axis, the centrifugal force and the centripetal are both horizontal in this case... what happens?
 
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Tension in the rope. The rope is not horizontal.
 
what do you mean? (i'm really sorry if it is a dumb question.). The rope in this case is spinning with the rock in the horizontal axis over my head.
 
Like in the case of a olive being spin inside a cup turned upside down... why it don't fall?
 
A rock spinning in a horizontal plane is spinning around a vertical axis. I think that this is what you mean. In order to spin around that axis it must be subject to a horizontal net force. The force from gravity is downward. The force from the rope is toward the center and slightly upward. The rope is not exactly horizontal. The upward component of force from the rope and the downward force from gravity are equal in magnitude.
 
pedro trindade said:
The rope in this case is spinning with the rock in the horizontal axis over my head.
No, it isn't. Get a relatively lightweight rope and a decently massive weight. Have someone who is shorter than you spin it at a moderate speed, and look at it from the side. You will see that the rope is not horizontal.
 
thanks... that answered well ^^
 

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