The question I came across ,
If a semicircular disc rotates uniformly (const. angular velocity) about an axis passing through its Centre of mass , and prependicular to its plane , do we need an external torque to sustain its motion
My attempt includes going to the original definition of torque as rate of change of angular momentum , which I believe is constant here. The book mentions something of an assymetric axis , and thus not a constant angular momentum.
As per more reading I believe it has something to do with conditions where angular velocity and momentum of a rigid body are not parallel.
One condition that I can feel is when the axis is not fixed but how does assymetric axis fulfills this condition as in the question above.