Atwood Machine Problem: Analyzing Friction & KE

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Discussion Overview

The discussion revolves around analyzing the Atwood machine problem, specifically focusing on the effects of friction and the kinetic energy of the pulley. Participants explore how these factors influence the system's behavior, particularly in scenarios involving initial pulls and varying masses.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the relative importance of friction versus the kinetic energy of the pulley in the Atwood machine setup.
  • Another suggests comparing energy lost from friction to the kinetic energy of the pulley and rope, noting that the outcome depends on the specific setup.
  • A participant seeks clarification on how to determine friction when an initial pull is applied to the system.
  • Concerns are raised about understanding the initial conditions and the specific forces involved in the experiment.
  • It is proposed that more information about the system, such as the force of the initial pull and resulting acceleration, is necessary to distinguish between friction and kinetic energy effects.
  • One participant emphasizes the need to consider torque when the pulley has mass and the hanging masses are unequal, suggesting a different approach to solving the problem.
  • Another participant notes that if the rope does not slip over the pulley, friction may not significantly affect the analysis.
  • A later reply indicates that the initial pull may relate to overcoming static friction, implying that energy loss is primarily due to kinetic friction.
  • One participant mentions that a rotating wheel will also experience friction, adding another layer to the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the significance of friction and kinetic energy in the Atwood machine problem, with no consensus reached on how to analyze these factors effectively. The discussion remains unresolved regarding the specific methods to quantify friction and energy loss in various scenarios.

Contextual Notes

Participants acknowledge the need for additional data, such as measurements of external forces and system parameters, to accurately analyze the effects of friction and kinetic energy in the Atwood machine setup.

tigigi
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I'm actually grading this stuff, and have a question. Ideally there's no friction and no kinetic energy of pulley. If we take them into account, which one is more important? I wonder how to analyze this? Thanks a lot.
 
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You can compare the energy lost from friction to the energy of the kinetic energy of the pulley and rope.
Which one will win depends on the specific setup.
 
Thanks. And if there's initial pull to give a bit speed in the beginning, how to know the friction from this experiment?
 
I don't understand that question at all. What do you know, what do you want to find?
 
The situation was, two objects with same mass release at the same height without initial velocity. But now it gives the object a little pull ( I guess it means it gives it some initial velocity) then how can you find / decide friction force from this situation.
 
You have to know more about the system - like the force of this pull and the resulting acceleration. To distinguish between friction and the kinetic energy in the pulley, you'll need even more data, like measurements with different external forces.
 
Thanks. I'll see the manual again on Monday, and I'll post the exact complete situation and question from it. It seems to be something simpler, no need to know the exact force pulling it.
 
By kinetic energy on the pulley, if you mean rotational kinetic energy and that the pulley has a mass then we have to solve the problem in totally different way.
try considering the toque acting on the pulley due to the tension (if the two hanging masses are different) and then solving a problem

PLease note:- NO ONE asks question on atwood machine when the rope slips over the pulley. So even if there is friction, it won't make ANY difference as the rope doesn't slip on the pulley.
The only difference comes when the pulley is not massless and then we have to use the concept of torque to solve it.

PS:- if you meant by kinetic energy that the pulley is also moving i.e the pulley is attached to another pulley, then try using constrained motion relationships and solve the problem
 
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Thanks for these answers. I take a look at the question and figure you can find total energy loss from the data, graph, and from there find friction, which cause the energy loss. The initial pull (more conceptual) means overcomeing static friction, so the energy loss is due to only kinetic friction.
 

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