- #1
SprucerMoose
- 62
- 0
G'day all,
I have been reading that if there are no external torques on a system, then angular momentum will be conserved. Can a system be defined as anything or only a single rigid object. Could I define the "system" as 2 disks rotating side by side? If so then the total angular momentum of this system would be the sum of momentum of the 2 disks. What if these these disks had each edge pushed into each other by an equal force on either side so the net force on the system remained zero? Assuming friction is present each disk would exert and equal and opposite force on the other. If each disk has a different radius, wouldn't this create a non-zero net internal torque and cause a change in angular momentum of a closed system? This contradicts my first statement, so could someone please point out the error in my reasoning.
The only way I can see Newtons 3rd law and the conservation of angular momentum holding would be if the above circumstance results in a net torque on the two disks together causing them to rotate together (about each other), while exerting a torque on each other. I have no proof for this it is just my intuition. The reason I'm not sure is because today I was also told that you cannot define a net torque on a system of several objects like this, but to me this leads to a breakdown in the conservation of angular momentum, or do I have it wrong?
I have been reading that if there are no external torques on a system, then angular momentum will be conserved. Can a system be defined as anything or only a single rigid object. Could I define the "system" as 2 disks rotating side by side? If so then the total angular momentum of this system would be the sum of momentum of the 2 disks. What if these these disks had each edge pushed into each other by an equal force on either side so the net force on the system remained zero? Assuming friction is present each disk would exert and equal and opposite force on the other. If each disk has a different radius, wouldn't this create a non-zero net internal torque and cause a change in angular momentum of a closed system? This contradicts my first statement, so could someone please point out the error in my reasoning.
The only way I can see Newtons 3rd law and the conservation of angular momentum holding would be if the above circumstance results in a net torque on the two disks together causing them to rotate together (about each other), while exerting a torque on each other. I have no proof for this it is just my intuition. The reason I'm not sure is because today I was also told that you cannot define a net torque on a system of several objects like this, but to me this leads to a breakdown in the conservation of angular momentum, or do I have it wrong?