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Assume a rope of mass $M$ is connected to a fixed wall and is free from other endenter image description here

Now,I pull on the end of the rope enter image description here

My simple questions are:

1.What is the reaction force/Newton's 3rd law pair force to my pull(F) on the end of the rope?

2.What is the restoring force(force to make it go back to it's original length) produced in the rope?

3.What is the tension force?

4.Difference between the above 3 mentioned forces(Reaction force to my pull,restoring force and tension force)

Please consider I'm a beginner and explain the whole working mechanism in a basic layman and simple language

Thanks!

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  • $\begingroup$ Tension is very much like the force produced by a VERY still spring. $\endgroup$ Apr 29, 2023 at 1:04

2 Answers 2

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In the diagram you have drawn the rope exerts two horizontal forces:

1 a force on the wall to the right

2 a force on the object pulling the rope to the left.

The tension forces are force $1$ and force $2$.

If the rope is not accelerating the magnitude of these two forces are the same.

There are two other horizontal forces acting on the wall as well,

3 a force due to the wall to the left

4 a force due to object pulling the rope to the right.

Forces $1$ and $3$ are a Newton third pair, equal in magnitude and opposite in direction.

Forces $2$ and $4$ are a Newton third pair, equal in magnitude and opposite in direction.

Which you call the action and which you call the reaction is up to you.

In the context of this system the restoring force would be the sum of the internal forces within the rope.
If you think of the rope as made up of molecules with bonds ("springs") connecting the molecules together, it is the sum of the forces exerted by the stretched bonds.

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  • $\begingroup$ Isn't the sum of the internal forces equal to zero? $\endgroup$
    – nasu
    Apr 28, 2023 at 16:56
  • $\begingroup$ @nasu When you stretch a spring and release it, the string contracts. Think of a string consisting of 2 molecules with one stretched spring between. On each of the molecules there is a force towards the other molecule. Now extend it to a string with three molecules and again the molecules at the end are pulled towards the rest of the string. With 4 molecules the "end" molecules are pulled inwards whilst at the same time the middle molecules are pulled "inwards". $\endgroup$
    – Farcher
    Apr 28, 2023 at 22:31
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Its actually a good question, I had the same doubts so i think I can answer appropriately.

  1. Reaction force in reponse to the force you applied, now since you are the body that applied, the tension force you feel on your hands is the reaction force. (That tension force is due to reaction force of the particles of rope which were pulled as you pulled it, so in response to it , that particles exerted force on the particles that pulled them first, and at the end of the rope these particles pull your hand) So force on your hand is reaction force.

  2. (Answer in the diagram attached below)

  3. Tension force is nothing special , it is jut the force exerted by a string. Now as you know we always use strings to pull things , not push hence it is also called pulling force.

  4. The restoring force is actually due to the particles inside the rope (the forces that they exert on each other and due to the wall, since the particles at the end of rope will try to pull it, and since newtons law is followed , the wall will try to pull the rope back, hence it does not move.

enter image description here

This what typically happens inside the rope, all particles pull each other ( you can also call it interparticle force.

Such a similar thing happens at the end part of the rope where it is attached to the wall

enter image description here

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  • $\begingroup$ So,the reaction force of my pull on the rope,and the restoring force of the rope,both are tension forces??? $\endgroup$
    – Aakash
    Apr 29, 2023 at 1:28
  • $\begingroup$ YES OFCOURSE... $\endgroup$ Apr 29, 2023 at 17:21

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