"Until now our discussion of the dynamics of rigid bodies has dealt only with two-dimensional motion. But for many engineering applications of dynamics, such as the design of airplanes and other vehicles, we must consider three-dimensional motion. Our first step is to explain how three-dimensional motion of a rigid body is described. We then derive the equations of motion and use them to analyze simple three-dimensional motions. Finally, we introduce the Eulerian angles used to specify the orientation of a rigid body in three dimensions and express the equations of angular motion in terms of them." p421

ANGLE
A MEASURE OF A CHANGE IN DIRECTION THAT COMMONLY USES UNITS OF DEGREES OR RADIANS

EULERIAN ANGLES
THREE ANGLES THAT SPECIFY THE ORIENTATION OF AN OBJECT RELATIVE TO A REFERENCE AXIS

INERTIA
A PROPERTY OF A BODY THAT RESISTS ANY CHANGE IN MOTION. FOR TRANSLATION MOTION, MASS IS A MEASURE OF THE BODY INERTIA. IT IS HARD TO CHANGE THE STATE OF MOTION OF A HIGH MASS OBJECT. FOR ROTATION, THE MOMENT OF INERTIA OF A BODY IS A MEASURE OF BODY INERTIA.

INERTIA MATRIX
A 3X3 ARRAY OF NUMBERS THAT CHARACTERIZES THE ROTATIONAL INERTIA OF AN OBJECT FOR ANY CHOICE OF ROTATIONAL AXIS.

MATRIX
A RECTANGULARLY SHAPED ARRAY OF NUMBERS USED FOR SIMPLIFYING THE MANIPULATION OF COMPLEX EQUATIONS.

PRINCIPAL AXES
THREE SPECIAL AXES OF SYMMETRY OF AN OBJECT USED FOR PREDICTING THE ROTATIONAL BEHAVIOR OF THE OBJECT.