Sports
Angular Momentum in Figure Skating
Quick fact
A figure skater can increase their spin speed by 2–3 times just by pulling their arms in close to their body.
Why this is interesting
Have you ever watched a figure skater pull their arms in to spin faster? That seemingly simple motion is a perfect demonstration of a fundamental law of physics.
Read the full explanation
Understanding Angular Momentum in Figure Skating
When a figure skater spins, they possess angular momentum—a measure of how much rotation they have. This quantity remains constant if no external force (like friction) acts on them. By pulling their arms and legs inward, they reduce their moment of inertia (the resistance to spinning). Since angular momentum is conserved, their rotational speed must increase to compensate. This is why skaters spin faster when they tuck in, and slow down when they spread out.
A deeper explanation
The key principle is conservation of angular momentum: L = I × ω, where L is angular momentum, I is moment of inertia, and ω is angular velocity. When a skater changes their body shape, I changes. Because L stays constant (assuming minimal external torque), ω must change inversely. The moment of inertia depends on how mass is distributed from the axis of rotation. Arms extended far from the body create a larger I; arms close to the body create a smaller I. This mechanism is why skaters can control spin speed without any external push. In practice, skaters also use the friction of the blade on the ice to initiate the spin and then rely on conservation for the rest. Understanding this helps skaters improve their spins and shows how physics governs even graceful movements.