ABSTRACT
Definition of Rotational Motion Rotating machine parts are everywhere: the shaft on an electric motor, a gear inside a reducer, or a winch drum and shaft on its bearings, are all common examples. A wide variety of rotating scenery is less obvious beyond the turntables that might first come to mind, but pivoting panels, doors, periaktoi, and jack-knife stages for instance all turn about a single stationary axis of rotation. As was true in the linear motion section, the complexity of the mathematics describing rotation can be considerably reduced by a number of assumptions. In the following chapters, rotation will be assumed to involve only rigid solid materials traveling in a simple circular motion around a single fixed axis of rotation. Rigid solids insures that all points on that material are spinning at the same speed around the same axis. This is not true in fluids and elastic solids, but we do not make liquid doors, or turntables with sheets of rubber. The circular motion assumption is similar to restriction of movement to a straight line made earlier, as this confines all moves to changes in a single dimension. Wheels alone will be the one exception to these assumptions that will be covered here as wheels do both rotate and translate, but that discussion will wait until a later chapter.
