Physics for Game Developers, 2nd Edition

Chapter 2. Kinematics

In this chapter we’ll explain the fundamental aspects of the subject of kinematics. Specifically, we’ll explain the concepts of linear and angular displacement, velocity, and acceleration. We’ve prepared an example program for this chapter that shows you how to implement the kinematic equations for particle motion. After discussing particle motion, we go on to explain the specific aspects of rigid-body motion. This chapter, along with the next chapter on force, is prerequisite to understanding the subject of kinetics, which you’ll study in Chapter 4.

In the preface, we told you that kinematics is the study of the motion of bodies without regard to the forces acting on the body. Therefore, in kinematics, attention is focused on position, velocity, and acceleration of a body, how these properties are related, and how they change over time.

Here you’ll look at two types of bodies, particles and rigid bodies. A rigid body is a system of particles that remain at fixed distances from one another with no relative translation or rotation among them. In other words, a rigid body does not change its shape as it moves—or any changes in its shape are so small or unimportant that they can safely be neglected. When you are considering a rigid body, its dimensions and orientation are important, and you must account for both the body’s linear motion and its angular motion.

A particle, on the other hand, is a body that has mass but whose dimensions are negligible or unimportant ...