Rotational motion can be characterized in terms of quantities analogous to those describing ordinary motion: position, velocity, acceleration—which become angular position, angular velocity, and angular acceleration; force, which becomes torque; and mass, which becomes rotational inertia. Together, rotational analogs of acceleration, force, and mass obey a law analogous to Newton’s second law. This, in turn, leads to the concept of angular momentum and the all-important conservation of angular momentum, which explains some surprising and seemingly counter-intuitive phenomena involving rotating objects.