What is radius of gyration? What is it physical interpretation?
Imagine you took a normal, real-world object and condensed all the particles into a hollow sphere. Now imagine this hollow sphere (with no wall thickness) has the same rotational inertia as the original object. The radius of the sphere is the radius of gyration of the original object. (At least that’s what wikipedia said. If I remember from dynamics class, though, I’d say it’d be better to imagine a hollow cylinder with no end caps or an extremely thin torus/ring. You avoid the error from the mass at the poles this way.) Sit in a chair and spin with your arms out. When you pull them in, rotational momentum is conserved, and you spin faster because your rotational inertia decreased. This decrease in rotational inertia with the same mass was caused by a decrease in the radius of gyration.
