Motion is a theme that will appear in one form or another throughout this entire book. Although we all have intuition about motion, based on our experiences, some of the important aspects of motion turn out to be rather subtle. So rather than jumping immediately into a lot of mathematics and calculations, this first chapter focuses on visualizing motion and becoming familiar with the concepts needed to describe a moving object. Our goal is to lay the foundations for understanding motion.

To begin, let’s define motion as the change of an object’s position with time. FIGURE 1.1 shows four basic types of motion that we will study in this book. The first three—linear, circular, and projectile motion—in which the object moves through space are called translational motion. The path along which the object moves, whether straight or curved, is called the object’s trajectory. Rotational motion is somewhat different because there’s movement but the object as a whole doesn’t change position. We’ll defer rotational motion until later and, for now, focus on translational motion.

FIGURE 1.1 Four basic types of motion.