An ice skater spins with his arms outstretched. When he pulls his arms in and raises them above his head he spins much faster than before. Did a torque act on the ice skater? If not how could his angular velocity have increased?

Answer 1

No torque was exerted on the skater to increase the spin rate. The angular momentum I*w remained the same. The angular velocity w increased while the moment of intertia (I) decreased.

Answer 2

Thank you.