Discussion
An ice-skater starts spinning during her performance. As she retracts her arms and legs closer to her body, her angular velocity _________________.
Answer: A
Her angular velocity increases.
The ice exerts almost no torque about the vertical axis, so the skater's angular momentum \(L = I\omega\) is conserved. Pulling her arms and legs in brings mass closer to the axis and reduces her moment of inertia I, so \(\omega\) must increase to keep \(I\omega\) constant.
A decrease would happen if she extended her limbs. The angular velocity would stay the same only if I were unchanged, and it would go to zero only under an external braking torque.
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