Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up.
Kinetic energy is conserved.

Question

Consider a situation where a skater pulls her arms inward, causing her rotation rate to speed up. 
Kinetic energy is conserved.

Quizplus · Accepted Answer

When a skater pulls her arms inward, her moment of inertia decreases, causing her rotation rate to increase to conserve angular momentum, not kinetic energy. This process does not conserve kinetic energy because the skater does work on her body by pulling her arms inward, which changes the distribution of her mass and thus her moment of inertia, leading to an increase in rotational kinetic energy.

Consider a Situation Where a Skater Pulls Her Arms Inward