The
moment of inertia, otherwise known as the
angular mass or
rotational inertia, of a
rigid body determines the
torque needed for a desired
angular acceleration about a rotational axis. It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rotation. It is an
extensive (additive) property: the moment of inertia of a composite system is the sum of the moments of inertia of its component subsystems (all taken about the same axis). One of its definitions is the second moment of mass with respect to distance from an axis
r, , integrating over the entire mass
.