Rotational mechanics is a challenging area in mechanics because the knowledge of many concepts is required to solve a single problem. Rotational motion is also extremely important in mechanical devices. In every case, the rotation of an extended, rigid body can be mathematically described as a collection of circular motions by the particles making up the body relative to the axis of rotation. Two very important quantities for dealing with such collections of particles in rotation are the dynamics of rolling, rotational kinetic energy, and the angular momentum.