Expanding loop torque division

[FusionJim]

Hey folks,

It seems I have a problem understanding a thought experiment I myself thought of. Not saying I was the first to think of it, but it puzzles me nevertheless.

Assume there is a conducting rectangular loop, the red loop side legs have a frictionless and perfect electrical contact with the black legs, I pull each leg towards each side such that the loop area expands. there is an infinite static magnetic field on each side over where I pull the loop legs.
But here is the difference I do not pull them equally, I pull one leg , for example, 10x faster than the other.

How do the required torque divides between the legs considering I try to pull one faster than the other?

My own intuition tells me that just because i try to pull one leg faster than the other doesn't mean the other isn't affected by the one I pull faster. since the loop EMF and current acts simultaneously on the whole loop, my own guess is that by pulling one side leg faster the other leg also experiences an increased torque on it, so even if it is pulled slower it becomes harder to pull on it, correct?
So how exactly the forces divide between the identical side legs being pulled towards either side?

 

[hutchphd]

Hey folks,

It seems I have a problem understanding a thought experiment I myself thought of. Not saying I was the first to think of it, but it puzzles me nevertheless.

Assume there is a conducting rectangular loop, the red loop side legs have a frictionless and perfect electrical contact with the black legs, I pull each leg towards each side such that the loop area expands. there is an infinite static magnetic field on each side over where I pull the loop legs.
But here is the difference I do not pull them equally, I pull one leg , for example, 10x faster than the other.

How do the required torque divides between the legs considering I try to pull one faster than the other?

My own intuition tells me that just because i try to pull one leg faster than the other doesn't mean the other isn't affected by the one I pull faster. since the loop EMF and current acts simultaneously on the whole loop, my own guess is that by pulling one side leg faster the other leg also experiences an increased torque on it, so even if it is pulled slower it becomes harder to pull on it, correct?
So how exactly the forces divide between the identical side legs being pulled towards either http://watch.spectrum.net/livetvside?View attachment 370420

"Torque on each leg" is not well well defined. I think you are confused......if these wires are rigid, force on each will resist the applied force. These forces will all lie in the plane of the paper. Note also that center of the "loop' is moving as well.

 

[FusionJim]

"Torque on each leg" is not well well defined. I think you are confused......if these wires are rigid, force on each will resist the applied force. These forces will all lie in the plane of the paper. Note also that center of the "loop' is moving as well.

@hutchphd Pardon, but I don't understand how can the forces be "not well defined"? Because if I would construct this loop in real life with sliding contacts and then pull the side bars outwards with different speeds, there would be real measurable torque that I would need to apply to each in order to pull it at the speed I want. Isn't there a way to calculate this? Or is it complex because the whole loop is acting as "one" so if I pull one side leg outwards faster then that increases the EMF and also the torque required to pull the other side leg even if I was pulling it slower?

 

[hutchphd]

@hutchphd Pardon, but I don't understand how can the forces be "not well defined"? Because if I would construct this loop in real life with sliding contacts and then pull the side bars outwards with different speeds, there would be real measurable torque that I would need to apply to each in order to pull it at the speed I want. Isn't there a way to calculate this? Or is it complex because the whole loop is acting as "one" so if I pull one side leg outwards faster then that increases the EMF and also the torque required to pull the other side leg even if I was pulling it slower?

Please read. I said torques not well defined. torques need to reference an axis.