When a figure skater glides into a graceful spin on the ice, she rotates slowly at first, then faster as she tucks in her arms. Often, the skater spins so fast that you might wonder why she doesn’t fall down. This impressive skating technique relies on a physics phenomenon called the conservation of angular momentum. When the skater starts to spin, her arms have their own momentum. As she draws them near to her torso, her body gains some of that momentum, causing her to speed up. You can see angular momentum at work by spinning with a lazy susan.
I first start off on the lazy susan with my arms out holding to 5lb weights. Having someone push me in a circle starts me off with angular momentum.
When I first started spinning, the weights in my hands gained momentum. When I pulled in my arms to my chest, I reduced the distance between the axis of rotation and some of my mass, reducing my moment of inertia. Since angular momentum is conserved, my rotational velocity must increase to compensate.