Quick question about a man running on a Merry-go-round

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Discussion Overview

The discussion revolves around the dynamics of a man running on the edge of a frictionless carousel and the implications for torque and rotational momentum conservation. Participants explore the conditions under which the man may run in place and how this affects the overall system's rotational momentum.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant posits that the man will run in place while generating torque on the carousel, raising questions about how rotational momentum is conserved in this scenario.
  • Another participant expresses confusion regarding the conservation of rotational momentum, suggesting that if the man is stationary relative to the carousel, only the carousel would be rotating, leading to a discrepancy in momentum conservation.
  • A third participant questions whether the carousel will turn at the same rate as the man runs, implying that the relationship between their motions may not be straightforward.
  • Another participant suggests that the assertion of the man running in place is only valid under specific conditions, particularly when considering the carousel's rotational inertia and proposes using a free body diagram and Newton's laws for clarity.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views regarding the man's motion and the conservation of rotational momentum in the system.

Contextual Notes

Participants mention special cases regarding the carousel's mass and inertia, indicating that the discussion may depend on these definitions and assumptions. There are unresolved mathematical steps related to the application of Newton's laws and the implications for torque.

ecoo
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Hey there,

If a man is on the edge of a carousel and starts to run perpendicularly to cause a torque on the carousel (no friction on axis of rotation), will the man be running in place? And if he is running in place, how is rotational momentum conserved of the man-carousel system?

I think that the man will run in place, and so I'm not sure how rotational momentum is conserved.

Thanks!
 
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The reason I am confused about the conservation of rotational momentum is because if the man is running in place and not moving, then only the carousel will be turning and so there will be rotational momentum, whereas initially there was none when both the man and carousel were at rest.
 
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ecoo said:
... to cause a torque on the carousel ...
ecoo said:
...only the carousel will be turning...
Will it be turning at the same rate?
 
ecoo said:
I think that the man will run in place
That is only true for a special case...
And in that case the carousel has no rotational inertia...
draw a free body diagram and apply Newtons laws.
Consider the two special cases; where the carousel has infinite mass and where it is weightless
 
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