Centrifugal force and artificial gravity

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Discussion Overview

The discussion revolves around the concepts of centrifugal force and artificial gravity, particularly in the context of uniform circular motion. Participants explore the relationship between perceived gravity, forces acting on objects in circular motion, and the implications of Newton's laws in both inertial and non-inertial frames of reference.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the perceived gravity experienced during circular motion relates to Newton's 3rd law, suggesting that if the rope pulls on them, they must also be pulling on the rope.
  • Another participant compares two scenarios: holding a rope in strong gravity versus holding a rope being swung around a pivot, noting the differences in forces required to maintain position in each case.
  • It is proposed that in a rotating frame of reference, centrifugal force is perceived as an outward pull, while centripetal force acts inward, and both forces must balance to maintain circular motion.
  • A participant introduces the idea that inertia is the source of the perceived centrifugal force, explaining that one must exert force to counteract this inertia to remain at a fixed distance from the pivot.
  • One participant attempts to clarify their understanding by describing a scenario involving a turntable and a wall, suggesting that the wall provides the centripetal force and that the reaction force felt is akin to 'artificial gravity'.
  • There is a discussion about the perception of acceleration in a non-inertial frame, with a participant noting that one does not feel like they are accelerating but rather feels a force pushing them outward if friction is insufficient.

Areas of Agreement / Disagreement

Participants express various viewpoints on the nature of centrifugal force and its relationship to perceived gravity. There is no consensus on the interpretation of these forces, and the discussion remains unresolved regarding the exact nature of the forces at play in circular motion.

Contextual Notes

Participants rely on different frames of reference and definitions of forces, which may lead to varying interpretations of the concepts discussed. The discussion includes assumptions about the conditions under which these forces are felt and the role of friction in maintaining circular motion.

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In lecture 5 of MIT's OCW 8.01 , Prof. Lewin says that when you're in in uniform circular motion, the perceived gravity is always in the opposite direction as the push or pull (so if you're holding onto the end of a rope that's being spun around horziontally, the rope is pulling on you and you feel gravity in the opposite direction).

My question is does this perceived gravity have anything to do with Newton's 3rd law? If the rope is pulling on you then you're pulling on the rope as well?

And is this 'perceived gravity' due to what's called centrifugal force? How does it work and why does it make you feel as though gravity's pulling on you? Doesn't the centripetal force point inwards?
 
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Compare holding on a rope hanging in strong gravity to holding on a rope being swung around a pivot. In the first case, you and the rope must supply a force to keep you from falling down. Your grip on the rope has to hold your weight, so you are pulling yourself upwards to counteract gravity which is pulling you down. The rope is also pulling you up. In the second case, you and the rope must supply a force to keep pulling you inward, toward the pivot. But you feel a fictitious force, centrifugal force, pulling you outward from the pivot, so you must pull on the rope to keep yourself on the rope.

Centripetal force points inward. You and the rope supply the centripetal force.

In an inertial frame of reference, centrifugal force doesn't exist, and centripetal force points inward, pulling you in a circle. In a rotating frame of reference, centrifugal force points outward, and centripetal force points inward, canceling out the forces on your body, so you don't move (relative to the rotating frame).
 
Khashishi said:
Compare holding on a rope hanging in strong gravity to holding on a rope being swung around a pivot. In the first case, you and the rope must supply a force to keep you from falling down. Your grip on the rope has to hold your weight, so you are pulling yourself upwards to counteract gravity which is pulling you down. The rope is also pulling you up. In the second case, you and the rope must supply a force to keep pulling you inward, toward the pivot. But you feel a fictitious force, centrifugal force, pulling you outward from the pivot, so you must pull on the rope to keep yourself on the rope.

Why do ou feel the force pulling you outward?
 
Without any forces, you would move in a straight line, which would take you away from the pivot. Thus, inertia is the source of this centrifugal force. You have to fight inertia to stay a fixed distance from the pivot, hence it feels like a force is pulling you away.
 
Ok...let's see if I understand this...

Say you're on some sort of giant turntable with a wall. If the friction between the floor and you isn't enough to provide the centripetal force to keep you turning with the turntable, then you slide and hit the wall. Now the wall is pushing against you to provide the centripetal acceleration, and the reaction force of you against the wall is the force you feel - the 'artificial gravity'? Is that right?

And for the ball and the rope, the rope pulls on the rope and so the reaction force in the non-inertial frame is the ball pulling back on the rope, and it's this pulling is the gravity that the ball feels

Also, in the non-intertial frame, you don't think you are accelerating do you? You just feel a force pushing you outwards if the friction between you and the floor isn't enough to keep you going in a circle
 

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