Physics
Angular Momentum in Figure Skating
Quick fact
A figure skater can increase their spin rate by up to four times simply by pulling their arms from outstretched to tightly crossed over their chest.
Why this is interesting
Have you ever watched a figure skater pull their arms in during a spin and suddenly whirl much faster? What’s the physics behind this dramatic change in speed?
Read the full explanation
Understanding Angular Momentum in Figure Skating
Imagine spinning on a swivel chair with your arms stretched out. If you suddenly pull your arms in, you spin faster. This happens because of a property called angular momentum—a measure of how much rotation an object has. In a closed system (no external forces), angular momentum stays constant. When the skater pulls their arms in, they decrease their 'moment of inertia' (resistance to spinning). To keep angular momentum the same, the rotation rate must increase. It’s like an ice skater becoming a smaller, tighter wheel, spinning more rapidly.
A deeper explanation
Angular momentum (L) is given by L = I ω, where I is moment of inertia and ω is angular velocity (spin rate). For a figure skater spinning on ice, friction and air resistance are minimal, so angular momentum is conserved. Moment of inertia depends on how mass is distributed relative to the axis of rotation: arms extended means mass is far from the axis (large I), arms pulled in brings mass closer (small I). As I decreases, ω must increase proportionally to conserve L. This is why skaters can speed up without applying extra torque from the ice. During jumps, skaters use this principle to control rotation—they tuck to increase spin for multiple rotations, then extend to slow down for landing. Understanding this mechanism allows athletes to optimize performance and execute complex spins and jumps with precision.