Does Using a Pulley Affect Acceleration in a Frictionless System?

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Discussion Overview

The discussion revolves around the impact of a pulley on the acceleration of a mass connected to another mass via a string in a frictionless system. Participants explore the relationship between the forces acting on the masses and how the pulley affects these forces, particularly in terms of tension and net force.

Discussion Character

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

Main Points Raised

  • One participant questions whether the presence of a pulley increases or decreases acceleration compared to the equation a=g(m), expressing confusion about how to approach the problem.
  • Another participant notes that the extra mass causes tension in the rope and asks how this tension affects the net force on the original block.
  • A different participant suggests that the net force on the original block would decrease, but questions whether this is solely due to friction or if there are more complex factors involved.
  • One participant clarifies that the decrease in net force is due to the weight of the second block creating tension in the rope, which pulls up on the first block, rather than the pulley itself affecting the force equation.
  • Another participant proposes simplifying the problem by considering a tilted table scenario to help visualize the forces at play.

Areas of Agreement / Disagreement

Participants generally agree that the net force on the original block decreases due to the tension created by the weight of the second block. However, there is some uncertainty regarding the role of friction and the complexity of the situation, indicating that multiple views remain on the factors influencing acceleration.

Contextual Notes

Participants have not fully resolved the implications of friction in the pulley system or how it interacts with the forces involved. The discussion also highlights the need for clearer definitions and assumptions regarding the setup of the problem.

Who May Find This Useful

This discussion may be useful for students or individuals interested in understanding the dynamics of pulley systems, tension forces, and acceleration in physics, particularly in frictionless contexts.

just.karl
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With a mass on a frictionless surface connected to a string that is sent over and down to a mass. Would that increase or decrease the acceleration compared to the equation, a=g(m). I'm just stumped on how to think of this. The pulley is not included in the equation but how would I figure out the difference?
 
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The extra mass attached to the rope will cause a tension in the rope correct? How does this tension affect the net force on the original block?
 
It would decrease the net force on the original block, correct? But would it be just because of friction or is it something more complicated than that?
 
Yes, the net force would decrease but not for the reason you are suggesting.

Consider the pulley to be frictionless. It's not the pulley that is decreasing the force on the block, but the weight of the second block that is added. The weight of the block causes a tension in the rope, and the rope thus pulls up on the first block, decreasing the net force on the first block. All the pulley really does is change the direction of the tension force so it pulls up on the block. This is why the pulley doesn't factor into the force equation, since it doesn't create any new forces.

(Of course, in reality, there is some friction in the pulley which will decrease the net force on the block, but it is not the primary cause of the decrease.)

Does this make sense? I suggest drawing a force/free-body diagram of the situation. It may help you visualize what's happening.
 
make it as simple as possible first

just.karl said:
With a mass on a frictionless surface connected to a string that is sent over and down to a mass. Would that increase or decrease the acceleration compared to the equation, a=g(m).

I assume by "frictionless surface", you mean a horizontal one, like a really smooth table?

Try an easier problem first: tilt the table, and put the pulley on the end of the table, so that the string always stays in the same direction.

Can you solve that problem?
 

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