Tension is causing me to be tensed

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    Newton Tension
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Discussion Overview

This discussion revolves around the concept of tension in ropes and the forces involved when multiple individuals pull on a rope. Participants explore various scenarios involving forces applied by individuals and the resulting tension in the rope, including cases with and without mass in the rope, and the implications of equilibrium and acceleration.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that if person A pulls with 100N and person B also pulls with 100N, the tension in the rope should be 100N, as both forces are equal and in opposite directions.
  • Others question how person A can experience a reaction force if person B does not also apply a force, suggesting that the scenario lacks clarity without additional context.
  • One participant explains that if person A pulls with 100N and person B pulls with 200N, the tension in the rope would not remain at 100N, as person A would accelerate towards person B due to the net force difference.
  • Another participant emphasizes that the tension throughout a rope must be consistent unless the endpoints are fixed, leading to discussions about the implications of fixed versus free endpoints.
  • Some participants discuss the role of acceleration and equilibrium, noting that without knowing all forces acting on person A, the situation remains ambiguous.
  • There are mentions of scenarios involving a rope attached to a pole or another person, raising questions about how tension and reaction forces are generated in these contexts.

Areas of Agreement / Disagreement

Participants express differing views on the nature of tension in the rope under various conditions. There is no consensus on how to interpret the forces at play, especially regarding equilibrium and the effects of acceleration. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants note that assumptions about the mass of the rope, the fixed or free nature of the endpoints, and the conditions of equilibrium are crucial to understanding the tension in the scenarios presented. The lack of clarity around these assumptions contributes to the ongoing debate.

  • #31
Why would he let go? He can be pulled with any force, even 100 times larger than his "strength". And he doesn't have to do anything to be pulled.
He does not have to do anything for the "reaction" force on the first one to equal his "action" force.

When you are water-skying and are pulled by a motor boat, do you have to have the same strength as the engine of the boat?
 
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  • #32
nasu said:
Why would he let go?
This sort of disagreement is what results when one tries to understand poorly defined terms like "all his strength".

On the one hand, Dale may have in mind the force limit at which an astronaut can pull in a rope hand over hand with some non-zero progress made and Nasu apparently has in mind the force limit at which a rope tied around the astronaut's body will cut him in twain.
 
  • #33
You are right.
But my point was (tried to be) that what the second astronaut does (or can do) does not change the fact that the action-reaction pair between the first astronaut and the rope will always consist in forces with same magnitude. The forces at the other end of the rope are not "reaction" to the force of the first astronaut.
 
  • #34
nasu said:
He does not have to do anything for the "reaction" force on the first one to equal his "action" force.
He has to hold on.
 
  • #35
nasu said:
The forces at the other end of the rope are not "reaction" to the force of the first astronaut.
Correct. They are constrained to be equal and opposite by Newtons 2nd law (and the massless rope assumption). Newtons 3rd law is not relevant to the relationship between those two forces since both forces are acting in the same object.
 
  • #36
Dale said:
He has to hold on.
Yes, I see what you mean.
His muscles in the hand have to be strong enough to either hold on by friction with the rope (enough normal force) or to keep his fingers "hooked" around some handle.
If the acceleration is too high he may not be able to.

But as you said (for the n-th time), this is not relevant for the reaction on the first astronaut. Maybe just indirectly. If he let go then the interaction at the other end changes.
 
  • #37
nasu said:
His muscles in the hand have to be strong enough to either hold on by friction with the rope (enough normal force) or to keep his fingers "hooked" around some handle.
If the acceleration is too high he may not be able to.
Yes. Your earlier example of the boat and the water skier is very appropriate. I learned that lesson the hard way when I was quite young, much to my embarrassment. The maximum amount of force that the rope could exert on was limited by my grip strength.

nasu said:
But as you said (for the n-th time), this is not relevant for the reaction on the first astronaut. Maybe just indirectly. If he let go then the interaction at the other end changes.
Yes, and if the rope is modeled more realistically (non zero mass and non infinite stiffness) then the disconnect becomes more obvious.
 
  • #38
EddiePhy ...u need to consider the free body concept...it'll clear as crystal...
 

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