Game Development Reference
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.
In the following sections we want to discuss certain aspects of the physics behind au‐
tomobile 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 topic, 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 transmis‐
sion 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.
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 of these two components:
R total = R air + R rolling