Game Development Reference
In-Depth Information
CHAPTER 5
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Projectiles
T
he previous two chapters explored the subjects of Newtonian mechanics and kinematics,
and presented the basic equations that govern linear and rotational motion. It's time now to
apply those basic relations to a more specific problem, namely modeling the flight of a projec-
tile. You will probably work with projectiles quite a lot in your game programming. There are,
of course, obvious things like bullets and cannonballs, but other objects such as golf balls or
tennis balls are essentially projectiles as well. The good news is that this topic has already
covered almost everything you need to know to model a projectile in flight. For the most part,
projectile physics are straightforward application of Newtonian mechanics and kinematics.
This chapter will take a building-block approach to modeling projectile motion. We'll start
with a quick-and-dirty model in which the only external force on an object is due to gravity.
This is the least accurate model, but also the easiest one to program and the fastest one to
compute. As the chapter progresses, we'll add more and more physics to the model including
the effects of aerodynamic drag, wind, and spin effects. The differences between laminar and
turbulent flow will be explored. You'll learn about things called lift and drag coefficients and
how they are used to characterize the forces experienced by a projectile in flight. In the latter
part of the chapter, we will discuss specific modeling issues for specific types of projectiles.
The topics that will be covered in this chapter include the following:
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The basic concepts that apply to all projectile trajectory models
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The gravity-only model
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Aerodynamic drag
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Laminar and turbulent flow
•
Wind effects
•
Spin effects
•
Details on specific types of projectiles including bullets, cannonballs, and arrows
You may have noticed from the previous list that some important projectile topics are
missing. A football can certainly be considered a projectile as can a missile fired from an airplane.
Modeling the balls used in sporting events will be covered in Chapter 7. Rockets and missiles
are discussed in Chapter 11.
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