What is the rotational analog of mass known as?

The correct answer is moment of inertia, which serves as the rotational analog of mass. In classical mechanics, mass quantifies an object’s resistance to linear motion when a force is applied; similarly, moment of inertia quantifies an object's resistance to rotational motion about an axis. It depends not only on the mass of the object but also on the distribution of that mass relative to the axis of rotation.

Moment of inertia is calculated as the sum of the mass of each particle multiplied by the square of its distance from the axis of rotation. This means that objects with mass distributed farther from the axis of rotation will have a larger moment of inertia and therefore be more difficult to rotate compared to those with mass concentrated close to the axis.

Understanding moment of inertia is crucial in applications ranging from engineering to physics, as it plays a significant role in determining how objects behave when subjected to rotational forces.