CHAPTER 16

Rotational Motion

IN THIS CHAPTER
Summary: The mechanics of rotating objects make up a significant chunk of the AP Physics C exam. But, rotational motion has many direct
analogs from linear motion. If you understand the mechanics unit from your first-year physics course, rotational motion can be learned by
analogy.

Key Ideas
Rotational kinematics uses essentially the same equations as kinematics, but distances, speeds, and
accelerations are rotational quantities expressed with radians instead of with meters.
The rotational inertia defines an object’s resistance to rotation. It is the rotational analog of mass.
An object can possess rotational kinetic energy in addition to translational kinetic energy.
Angular momentum is conserved anytime no external torque acts on a system of objects. This includes
planets in orbit.

Relevant Equations

Rotational kinematics equations.
First, for constant angular acceleration:

And, in all cases: