A simple movable pulley not at equilibrium

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    Equilibrium Pulley
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SUMMARY

The discussion focuses on the dynamics of a movable pulley system when not in equilibrium. When a force greater than half the weight of the object is applied to the free end of a frictionless rope, the object accelerates upwards. The tension in the rope becomes uniform at mg, leading to a total upward force of 2mg, resulting in an acceleration equal to g. This analysis is grounded in Newton's 2nd law, emphasizing the relationship between force, mass, and acceleration in pulley systems.

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  • Understanding of Newton's 2nd law of motion
  • Familiarity with concepts of tension in ropes
  • Basic knowledge of pulley systems and their mechanics
  • Ability to analyze forces in a non-equilibrium system
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  • Study the mechanics of non-equilibrium pulley systems
  • Learn about tension distribution in ropes under varying forces
  • Explore advanced applications of Newton's laws in dynamic systems
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Students of physics, mechanical engineers, and anyone interested in the principles of dynamics and pulley systems will benefit from this discussion.

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Note: This is not a homework question. I have constructed this question to help me understand a concept.

If I have an object hanging off a single (frictionless, negligible mass) movable pulley, the equilibrium system entails me pulling on the free end of the (frictionless, negligible mass) rope with half as much force as the object weighs.

What happens if I pull harder than that?

See the attached GIF. What would be the behavior of the weight? Would it accelerate up? If so, at what acceleration? What would be the tension in the left side of the rope?

Every resource I have access to that mentions pulleys keeps talking about pulleys in this type of setup in equilibrium. I am interested in furthering my understanding in regards to pulleys not in equilibrium.

Thank you for any help.
 

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The tension is uniform throughout the rope. The upward force on the pulley/mass will equal twice the tension. To find the acceleration, just add the vertical forces and apply Newton's 2nd law.
 
So me increasing my pulling force from an equilibrium inducing (1/2)mg to mg will cause the rope to have a uniform tension of mg, thus making the total upward force 2mg (the tension of the rope being a uniform "mg"). This accelerate the weight, which weighs mg, upwards at acceleration = g.

Is that correct?
 
Yes, that's correct.
 

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