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Question

A spinning figure skater pulls his arms in as he rotates on the ice as he pulls his arms in. What happens to his angular momentum L and kinetic energy Ek?

Solution

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The angular momentum of an object depends on the moment of inertia and its angular velocity. So, what matters to us is the mass distribution in relation to the object's center of mass. The closer the total mass of the body is to the center of mass, the angular velocity of the body increases.

Kinetic energy depends on its angular velocity. The higher the speed of the body, the greater its kinetic energy.

So, this is the reason why the skater pulls his arms along his body while turning on the ice, reduces his moment of inertia, and his angular velocity increases, resulting in an increase in his kinetic energy.

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