Physics for Game Developers, 2nd Edition

Chapter 17. Cars and Hovercraft

What cars and hovercraft have in common is that they operate in an essentially 2D manner. Unless they have jumped a ramp, both vehicles remain on the ground or water plane. In this chapter we’ll discuss the forces behind each vehicle’s method of travel and discuss how to accurately model them in your simulations.

Cars

In the following sections we want to discuss certain aspects of the physics behind automobile motion. Like the previous four chapters, the purpose of this chapter is to explain, by example, certain physical phenomena. We also want to give you a basic understanding of the mechanics involved in automobile motion in case you want to simulate one in your games. In keeping with the theme of this book, we’ll be talking about mechanics in the sense of rigid-body motion, and not in the sense of how an internal combustion engine works, or how power is transferred through the transmission system to the wheels, etc. Those are all internal to the car as a rigid body, and we’ll focus on the external forces. We will, however, discuss how the torque applied to the drive wheel is translated to a force that pushes the car along.

Resistance

Before we talk about why cars move forward, let’s talk about what slows them down. When a car drives down a road, it experiences two main components of resistance that try to slow it down. The first component is aerodynamic drag, and the second is called rolling resistance. The total resistance felt by the car is the sum ...