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

[ajaysabarish]

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

 

[Dr. Courtney]

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.

 

[ajaysabarish]

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.

 

[Dr. Courtney]

Draw the free body diagram.

 

[ajaysabarish]

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.

 

[Chandra Prayaga]

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

 

[ajaysabarish]

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.