Solving Confusions on Pulling a Spool

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The discussion centers on the mechanics of a spool and the application of forces, particularly static friction, during its motion. It clarifies that the Uniformly Accelerated Motion (UAM) equations cannot be used because the spool behaves as a rigid body rather than a point particle. Static friction does not perform work since the point of contact does not move relative to the surface, which is crucial for understanding the forces at play. The conversation also emphasizes the importance of analyzing the system from the cylinder's reference frame to determine the displacement of the hand in relation to the spool's movement. Overall, the thread provides insights into the dynamics of rolling motion and the role of static friction in such scenarios.
  • #91
haruspex said:
Yes,

No, you are free to define positive separately for each force, each displacement, each acceleration. Just be clear about it and do it consistently through the equations.

If all such variables are along the perpendicular axes, it is a good idea to pick one convention for them all. If not, you could decompose each oblique variable into such components or define the conventions individually.

Many prefer to guess which way each will act and define positive accordingly. That's ok as long as you handle each consistently and accept that some may turn out to have negative values.

That said, there may be cases where the equation does change if you guessed wrongly, but I can only think of quite contrived ones.
Thank you for your reply @haruspex! That is very interesting!

Many thanks!
 

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