Game Development Reference
In-Depth Information
Figure 1-8. Example body consisting of car, driver, and fuel
The properties of each component in this example are given in Table 1-2 . Note that
length is measured along the x-axis, width along the y-axis, and height would be coming
out of the screen. Also note that the coordinates—in the form ( x , y )—to the centroid of
each component are referenced to the global origin.
Table 1-2. Example properties
Car
Driver (seated)
Fuel
Length = 4.70 m
Length = 0.90 m
Length = 0.50 m
Width = 1.80 m
Width = 0.50 m
Width = 0.90 m
Height = 1.25 m
Height = 1.10 m
Height = 0.30 m
Weight = 17,500 N
Weight = 850 N
Density of fuel = 750 kg/m 3
Centroid = (30.5, 30.5) m
Centroid = (31.50, 31.00) m
Centroid = (28.00, 30.50) m
The first mass property we want to calculate is the mass of the body. This is a simple
calculation since we are already given the weight of the car and the driver. The only
other component of weight we need is that of the fuel. Since we are given the mass
density of the fuel and the geometry of the tank, we can calculate the volume of the tank
and multiply by the density and the acceleration due to gravity to get the weight of the
fuel in the tank. This yields 920.6 N of fuel, as shown here:
W fuel = ρvg = (750 kg/m 3 ) (0.50 m) (0.90 m) (0.30 m) (9.81 m/s 2 )
= 993 N
Acceleration due to gravity is the acceleration of a falling object as it
falls toward the earth. The weight of an object is equal to its mass times
the acceleration due to gravity. The symbol g is used to represent the
acceleration due to gravity, and on Earth the value of g is approximately
9.8 m/s 2 at sea level. Units for weight in the metric system are Newtons,
N .