Science · 6 pages · 12 min

Why a spinning ice skater speeds up when arms come in

Pulling mass closer to the axis speeds the spin if angular momentum stays put.

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From the opening

A spinning ice skater speeds up when the arms come in because angular momentum stays roughly constant while mass moves closer to the axis. With a smaller moment of inertia, that same angular momentum is a faster spin. The opening covers moment of inertia and spin rate, why the ice must stay out of it, and where the extra energy comes from.

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Inside

Moment of inertia and spin rate
Why the ice must stay out of it
Where the extra energy comes from
The same tuck in a dive
Where the idea stops applying
A distinction worth keeping

Sources

Conservation of angular momentum
Moment of inertia about a spin axis

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Why a spinning ice skater speeds up when arms come in

From the opening

Inside

Sources

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