Would the friction be in the plane?

[Alem2000]

If you had two disks with the lower one rotating and dropped the one on top onto it they both come to the same angular speed b/c of friction. How come there is no torqu action on it? Would the friction be in the plane?

 

[Tide]

What exactly do you mean when you say "there is no torque action on it?"

If there is friction then eventually the two disks will rotate at the same rate and it will do so in conformance with the principle of angular momentum conservations since there is no net torque on the system of disks. However, and obviously, each disk will experience torque.

 

[Alem2000]

Okay what I don't understand is ...the conservation of angular momentum requres there to be no net torque...so are you saying that individually there is a torque but not on the system of the two disks?

 

[Tide]

That's exactly what I am saying! :-)