What is the rotational analog of mass?

The correct answer is moment of inertia, which serves as the rotational analog of mass in mechanics. Just as mass is a scalar quantity that measures an object's resistance to linear acceleration when a force is applied, moment of inertia measures an object's resistance to angular acceleration around a given axis when a torque is applied. It depends on both the mass of an object and the distribution of that mass relative to the axis of rotation. An object with a larger moment of inertia will require more torque to achieve the same angular acceleration as an object with a smaller moment of inertia.

In contrast, torque refers to the rotational equivalent of a force and is not a measure of an object's inertia but rather the effectiveness of a force in producing rotational motion. Angular momentum describes the quantity of rotation of an object and is a product of its moment of inertia and angular velocity, making it dependent on both the distribution of mass and its rotational speed. Velocity is a linear measure of how fast an object is moving in a straight line and does not relate specifically to rotational dynamics. Thus, moment of inertia is the most appropriate choice as it directly parallels the concept of mass in translational motion.