Tension is causing me to be tensed

[nasu]

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?

 

[jbriggs444]

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.

 

[nasu]

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.

 

[Dale]

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.

 

[Dale]

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.

 

[nasu]

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.

 

[Dale]

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.

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.

 

[Sayam Banerjee]

EddiePhy ...u need to consider the free body concept...it'll clear as crystal...