Rope, tension and Newtons third law

In summary, the problem asks to find the magnitude of the force exerted on segment R by segment L, given that segment R exerts a force of magnitude T on segment L. The solution involves using Newton's third law, which states that every force has an equal and opposite force. In this case, the force exerted by segment L on segment R would be equal in magnitude but opposite in direction to the force exerted by segment R on segment L. The use of g in the problem is to throw off the solution and is not actually needed.
  • #1
DakE_FeatH
6
0
This is more of a conceptual question, meant to help us understand how tension forces work.

Homework Statement



Assume that segment R exerts a force of magnitude T on segment L. What is the magnitude FRL of the force exerted on segment R by segment L?
Give your answer in terms of T and other constants such as g.

Homework Equations



Fnet = ma

The Attempt at a Solution



Fnet = FR on L + FL on R = 0 (I assume it's 0)

I also know that Fnet = ma, but I don't know if I should use any mass, since it's a rope, and in first year undergraduate class, I understood that ropes are massless.

The question says in terms of g and I know that FG=m*g (g = -9.81)

I don't know how to indroduce the g in the equations.
 

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  • #2
Consider Newton's 3rd law. (It's way easier than you think.)
 
  • #3
Ok, Newtons third law states that "every force occurs as one member of an action/reaction pair of forces". So the two objects have forces acting on them of the same magnitude but opposite directions.

I think I understand how the tension forces work horizontally, but I have no idea how to add the g in there. Is there also a normal force that is equal and opposite to g? If so, how? It's in the air so I don't understand where that would come from :(
 
  • #4
Welcome to PF!

DakE_FeatH said:
Ok, Newtons third law states that "every force occurs as one member of an action/reaction pair of forces". So the two objects have forces acting on them of the same magnitude but opposite directions.

I think I understand how the tension forces work horizontally, but I have no idea how to add the g in there. Is there also a normal force that is equal and opposite to g? If so, how? It's in the air so I don't understand where that would come from :(

Hi DakE_FeatH! Welcome to PF! :smile:

What makes you think g is involved? :wink:
 
  • #5


tiny-tim said:
What makes you think g is involved? :wink:

They say in the problem to give my answer in terms of T and "constants such as g"

So I can't just use Fnet = FR on L + FL on R = 0
 
  • #6


DakE_FeatH said:
They say in the problem to give my answer in terms of T and "constants such as g"
I think you are overly constraining yourself. I'm sure they meant: "... in terms of T and constants such as g if you need them".

If A exerts a force on B, then B exerts an equal and opposite force on A. That's Newton's 3rd law. Case closed. :wink:
 
  • #7
Ok I got it, it was |-T|, they just put in the g to mess me up. Thank you guys!
 

1. How does tension affect the movement of a rope?

Tension is the force applied on an object when it is pulled or stretched. In the case of a rope, tension affects its movement by creating a force that pulls the rope in the direction of the force. The greater the tension, the faster the rope will move.

2. How is Newton's Third Law related to rope and tension?

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when a force is applied to a rope, the rope will exert an equal force in the opposite direction. In the case of tension, when a rope is pulled in one direction, the rope will exert an equal tension force in the opposite direction.

3. How can the tension in a rope be calculated?

The tension in a rope can be calculated using the formula T = μ * mg, where T is the tension force, μ is the coefficient of friction, m is the mass of the object, and g is the acceleration due to gravity. This formula applies to a rope that is hanging vertically with one end attached to a fixed point.

4. Can tension in a rope be negative?

No, tension in a rope cannot be negative. Tension is a force that is always directed away from the object, and its magnitude is always positive. If a rope is being pulled in opposite directions by two equal forces, the net tension will be zero.

5. How does the length and thickness of a rope affect tension?

The length and thickness of a rope do not affect tension directly. However, the length and thickness can affect the maximum tension that a rope can withstand before breaking. A longer and thicker rope can withstand greater tension before breaking compared to a shorter and thinner rope.

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