Physics
How does pulling in their arms make figure skaters spin faster?
Quick fact
This is conservation of angular momentum: pulling mass closer to the spin axis reduces rotational inertia, so the spin speed must increase to keep total momentum constant.
Why this is interesting
A spinning skater can go from one rotation per second to over five rotations per second just by hugging their arms to their chest—with no external push.
Read the full explanation
Understanding How does pulling in their arms make figure skaters spin faster?
When arms are stretched out, mass is far from the center, creating high inertia and a slow spin. Pulling arms in brings that mass close, lowering inertia and forcing the spin to accelerate—like a figure skater becoming a human top.
A deeper explanation
The math is breathtaking: reducing the arm radius from 1.2 meters to 0.2 meters decreases the moment of inertia by over 80%. To conserve angular momentum, the rotation speed skyrockets from 1 revolution per second to over 5 rev/s. This exact principle governs everything from a collapsing star forming a rapidly spinning neutron star to a diver tucking into a somersault. Pulling in those arms doesn't just win gold medals—it's a live demonstration of the universe's most fundamental rotational law.