If two spinning cylinders with different MoIs and angular speeds and different radii come in contact with each other at the curved surfaces, how to find out the final angular speeds given all initial parameters? There will be a friction acting at the line of contact and perpendicular to it as long as the liner speeds of the surfaces differ. However once they are equal, there will be no friction. I can work it out by taking the angular impulse of friction on individual cylinders. But my question is, can we apply the conservation of angular momentum? I tried that but the expression differs than the one worked out considering the angular impulse of the friction. Please help.