What is the moment of inertia defined as in rotational motion?

• A. Reluctance to rotate.
• B. Speed of rotation.
• C. Angular velocity.
• D. Mass distribution.

Answer: (A)

In rotational motion, the moment of inertia tells you how hard it is to change an object's rotation about a given axis. It’s a measure of resistance to angular acceleration: the more mass you have farther from the axis, the harder it is to start or stop spinning. This is why a ring, with mass mostly at the outer edge, has a larger moment of inertia than a solid disk of the same mass and size. The essence is resistance to rotation, not the speed of rotation itself (that would be angular velocity). Mass distribution matters because it determines how much mass lies away from the axis, which increases the inertia and makes changes in rotation more difficult.