It’s a simple but crowd-pleasing trick from Figure Skating 101. Skaters pull into a spin, cross their free leg over their other knee, then tuck in their arms. The tighter the tuck, the faster the spin, until the skater looks like a tornado on ice. But while the “scratch spin” – aka the “blur spin” – is relatively easy to pull off, the physics behind it goes by the complicated name of the “conservation of angular momentum.” We’ll keep it simple: Because of a force known as inertia, wider objects require more energy to spin than narrower ones. Apply the same amount of spin force to two objects – a wide one and a narrow one – and the narrow one will spin much more rapidly. So when figure skaters perform scratch spins, their goal is to start wide – with arms and leg outstretched – and end narrow. As they pull in their arms and free leg, they gradually require less energy to spin, which increases the speed of their rotations until they’re a blur of sequined tights and pearly whites.
Picture Credit : Google
