"In Chapter 6 we analyzed two-dimensional motions of rigid bodies without considering the forces and couples causing them. You have used Newton's second law to determine the motions of the centers of mass of objects, but how can you determine their rotational motions? In this chapter we derive two-dimensional equations of angular motion for a rigid body. By drawing the free-body diagram of an object such as an excavator's shovel, we can determine both the acceleration of its center of mass and its angular acceleration in terms of the forces and couples to which it is subjected." p303

AXIS
AN IMAGINARY LINE THAT SERVES AS A CENTER OF ROTATION OR A REFERENCE LINE

FREE-BODY DIAGRAM
A DRAWING OF THE OBJECT UNDER STUDY, SHOWING ONLY THE OBJECT AND ALL FORCES APPLIED TO THE OBJECT.

GENERAL PLANAR MOTION
ANY KIND OF OBJECT MOTION THAT REMAINS WITHIN A FLAT PLANE (OR SURFACE)

PLANAR MOTION
MOTION OF AN OBJECT WHERE THE CENTER OF MASS OF THE OBJECT REMAINS IN A SINGLE (UNCHANGING) PLANE (IMAGINARY FLAT SURFACE).

ROTATION
MOTION OF ALL PARTS OF A BODY IN CIRCLES AROUND AN AXIS.

ROTATION ABOUT A FIXED AXIS
MOTION OF ALL PARTS OF A BODY IN CIRCLES AROUND AN AXIS THAT IS FIXED IN POSITION AND ORIENTATION.