Why does angular momentum conservation differ from angular impulse for spinning cylinders?

[thephysicist]

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.

 

[BvU]

In PF the use of the template is mandatory. Gives you an opportunity to tell us which way the things are running: that makes a considerable difference!

And what are Mols of a centrifuge ?

 

[haruspex]

can we apply the conservation of angular momentum?

No. The cylinders (though this is not clearly stated) are presumably mounted on axles, which are held fixed. That implies external forces applied to the system. Since there are two axles, there is no reference point you can use for the angular momentum that will eliminate both forces.