Game Development Reference
In-Depth Information
is equal to zero. In this case, the car and the object it collided with would stick together, and
they would have the same post-collision velocity shown in Equation (8.43).
mv
+
m v
′
==
vv
11
2 2
(8.43)
1
2
mm
+
1
2
In most cases, the collision won't be completely inelastic, and the coefficient of restitution
will have some nonzero value. The car will suffer a certain amount of damage, and it will bounce off
the object it hits. The F1-Spirit Formula One racing game uses a value of 0.25 for the coefficient
of restitution.
Motorcycles
Motorcycles are another type of motor vehicle that can be used to create exciting game scenarios.
Generally speaking, motorcycles are lighter, more agile, and have greater acceleration poten-
tial than cars, but much of the general physics to describe the acceleration and braking is the
same between motorcycles and cars. Motorcycle engines generate torque that is applied to the
back wheel, and friction between the wheel and the ground propels the motorcycle forward.
Motorcycles are subject to the forces of aerodynamic drag, rolling friction, and traction, just as
cars are.
Table 8-4 compares some physical and performance characteristics between a sports car
and a performance motorcycle. The sports car is the 2004 Porsche Boxster S we used in the
“Cars” section of this chapter. The motorcycle is the 2004 Honda CBR1000RR. As you would
expect, the mass of the motorcycle is considerably less than that of the car. The Boxster S has a
higher top speed, but the motorcycle has greater acceleration. It can reach 100
km/hr
in a little
over half the time it takes the car. The car engine is more powerful in terms of peak torque, but
the motorcycle engine has a much higher redline
rpm
value (which is one reason why the
acceleration potential is higher).
Table 8-4.
A Comparison of Motorcycle and Car Characteristics
Quantity
Honda CBR1000RR
Porsche Boxster S
Vehicle mass (
kg
)
180
1323
0-100
km/hr
(
sec
)
2.95
5.5
Top speed (
km/hr
)
225
266
Redline
rpm
11650
7200
Peak engine torque (
N-m
)
106 @ 8500
rpm
310 @ 4600
rpm
Peak engine horsepower
153.5 @ 11000
rpm
258 @ 6400
rpm
As we said before, many similarities exist in the physics that describe the motion of a
motorcycle and car. There is one important area of difference that we will explore in a little
more detail—how a motorcycle turns.
