Why do spinning skaters speed up?
Show answer & explanation
Answer: Conservation of angular momentum
Conservation of angular momentum ✓ — Correct! Angular momentum (L = I×ω) is conserved without external torque. Moment of inertia I = mass × radius². Arms out: large radius, large I, slower rotation ω. Arms in: small radius, small I—to conserve L, rotation ω increases! Same physics: divers tuck for spins, planets orbit faster when closer to sun. Skater doesn't add energy—redistributes existing rotational energy. Pull arms in = speed up dramatically!
Friction decreases with arms in — Wrong. Friction change is minimal. Speed increase is from angular momentum conservation—pulling arms in reduces moment of inertia, increasing rotation rate.
Muscles push harder when tucked — Wrong. Muscles don't create the spin increase—they pull arms in. Angular momentum conservation (L = I×ω constant) automatically increases rotation when reducing radius.