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It is a very simple problem. a massless rope but with friction is climbed upon by a monkey. I need to understand the working of forces here. enter image description here

Suppose the monkey is applying a force F on the rope. So it in return feels the reaction force F towards the ceiling. Tension also develops here in the rope as well due to the force F and it is equal to F.

Now we know that the rope will pull the monkey up with tension force. so the monkey feels F upwards. But the monkey at the beginning also experiencing force F from the 3rd law reaction. So is it that the monkey applying a force of F downward will feel a force 2F upwards in return.

Now bringing friction into the play. When the monkey pulls down the friction pulls up.Let the friction be f. now the rope also feels a force of f. It means that the final tension should increase and become F+f. So the monkey will now feel an upward tension of F+f.

So eventually we have a monkey applying a force of F on a rope and getting 2F+f force in return.(one F from 3rd law reaction when it applied a force F in the first place. Another F+f from the tension in the rope.

So where am I wrong here ?

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  • $\begingroup$ Do you know what free body diagrams are? You are double-counting F because you haven't drawn the free body diagram. There is a separate FBD for the rope and the monkey. $\endgroup$ – DKNguyen May 12 at 20:41
  • $\begingroup$ yup I studied them but still I doubt regarding this that wether the tension is playing the part of the 3rd law reaction or not and other things in the question. $\endgroup$ – chittaranjan rout May 12 at 20:45
  • $\begingroup$ You're like quintuple counting forces. $\endgroup$ – Jerry Schirmer May 12 at 20:45
  • $\begingroup$ pls show me where I am wrong. I know I am terribly wrong $\endgroup$ – chittaranjan rout May 12 at 20:47
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    $\begingroup$ Draw the FBD first. Then you won't have silly mistakes like thinking "Suppose the monkey is applying a force F on the rope. So it in return feels the reaction force F towards the ceiling. Tension also develops here in the rope as well due to the force F and it is equal to F. Now we know that the rope will pull the monkey up with tension force. so the monkey feels F upwards. But the monkey at the beginning also experiencing force F from the 3rd law reaction. So is it that the monkey applying a force of F downward will feel a force 2F upwards in return." are two different forces. $\endgroup$ – DKNguyen May 12 at 20:47
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You need to organize the forces acting on each body, and which is the source of them.

Monkey: Gravity from Earth and friction from the rope.

Rope: Friction from the monkey and an upward force from the ceiling.

The rope is at rest, so the forces are equal on it. The monkey acceleration depends on the difference of forces on it.

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