A dancer girl is rotating over a turntable with her arms outstretched. If she lowers her arms, how does this affect her motion?

 Answer: Moment of inertia, I1 of dancer girl when her arms are outstretched is greater than moment of inertia, I2 of the same girl when she lowers her arms, If ⍵1 and ⍵2 are angular velocities of the table when arms are out stretched and folded respectively, then from principle of conservation of angular momentum , we have

I1⍵1 = I2⍵2

Since I1>I2, so ⍵2>⍵1

It means angular speed of the turntable is increased, when she lowers her arms. On the other hand, a ballet dancer stretches her arms to reduce her motion.