In what circumstances can the angular velocity of system of particles change without any change in the system\'s angular momentum?

Question

This cannot happen under any circumstances.

This can happen if an external net torque is applied properly to the system.

This can happen if the only forces acting are internal to the system.

This can happen if a net external force acts on the system\'s center of mass.

Answer 1

This can happen if the only forces acting are internal to the system.

Think, spinning figure skater pulls arms in and spins faster

ang momentum L = I omega
for simple dumbell = m r^2 omega
decrease r ----> increase omega for same L

Answer 2

This can happen if the only forces acting are internal to the system