What physical characteristic does the moment of inertia of a rotating object most directly and accurately measure? radius mass momentum rotational inertia

It is within the definition of moment of inertia itself that rotational inertia appears. Just like some people interpret an object's mass as a resistance to changes in its linear motion, some people interpret an object's moment of inertia (around a given axis) to be its resistance to changes in its rotational motion around that axis.

probably not the "magnets"in the magnet, so to speak, are thought to be electrons orbiting in shells. vurrent loops two sides to the loop

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.