Why Does the String in a Pulley System Apply a Downward Force of 2T?

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Discussion Overview

The discussion revolves around understanding the forces in a string pulley system, specifically why the string applies a downward force of 2T on the pulley. Participants explore the mechanics involved in this scenario, including the roles of tension and the forces acting on the masses involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why the string applies a downward force of 2T on the pulley in a string pulley system.
  • Another participant explains that the net force from the string on the pulley is -T from each side, leading to a total of -2T.
  • A participant requests a detailed explanation of why the string applies a force T on the pulley from each side.
  • One suggestion is to draw a free body diagram to visualize the forces involved.
  • A participant describes the forces acting on one of the masses (m1), noting that it experiences both its weight and the tension in the string, and that this tension is equal on both sides of the pulley.
  • It is noted that if the string is assumed to be massless and non-stretchable, the tension remains constant throughout the string.

Areas of Agreement / Disagreement

Participants generally agree on the mechanics of tension and forces acting on the masses, but there is a lack of consensus on the initial reasoning behind the application of the downward force of 2T on the pulley, as some participants seek further clarification.

Contextual Notes

The discussion includes assumptions about the string being massless and non-stretchable, which may affect the conclusions drawn about the forces involved.

ajaysabarish
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in string pulley systems(like atwood machine),the string applies a force on pulley of force 2T downwards,but why is it so?

why should it apply that force?
explain in detail
 
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Think about net force. The force of the string on the pulley is -T on the left side and another -T on the right side. The total contribution of the string to the net force is -2T.
 
Dr. Courtney said:
Think about net force. The force of the string on the pulley is -T on the left side and another -T on the right side. The total contribution of the string to the net force is -2T.

thank you very much sir for replying,but please explain why should string apply that force T on the pulley on each side.please explain this part in detail sire.
 
Draw the free body diagram.
 
sir,unable to do that.i understand that the clamp connecting ceiling and pulley exerts some force but i couldn't understand the direction of force and why should that force be equal to 2T.sir,i would be really grateful to you if you can please attach it here,i am struggling with this doubt for the past 2 days,thinking of nothing else.
 
OK. So, let us go at it step by step. Call the two masses hanging from the ends of the string as m1 and m2. Concentrate on one mass, say m1.

1. There are two forces on m1. The weight, downwards, and the tension in the string, upwards. Agreed?
2. Since the string is pulling m1 up with the tension T, m1 is pulling down on the string with the same force T. Agreed?
3. The tension in the string is the same throughout. (This assumes that the string is massless, and it does not stretch). So the string is pulling up on m2 on the other side, with the same force T. Agreed?
4. So m2 is also pulling down on the string with the force T. Agreed?
5. So there are two forces on the string, each equal to T, and pointing downwards. Agreed?

Let me know if these steps are clear, and if you can continue on your own from here
 
Chandra Prayaga said:
OK. So, let us go at it step by step. Call the two masses hanging from the ends of the string as m1 and m2. Concentrate on one mass, say m1.

1. There are two forces on m1. The weight, downwards, and the tension in the string, upwards. Agreed?
2. Since the string is pulling m1 up with the tension T, m1 is pulling down on the string with the same force T. Agreed?
3. The tension in the string is the same throughout. (This assumes that the string is massless, and it does not stretch). So the string is pulling up on m2 on the other side, with the same force T. Agreed?
4. So m2 is also pulling down on the string with the force T. Agreed?
5. So there are two forces on the string, each equal to T, and pointing downwards. Agreed?

Let me know if these steps are clear, and if you can continue on your own from here
thank you very much sir,for replying i understand all those steps,please proceed on like this.
 

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