Game Physics Engine Development, 2nd Edition

54 Chapter 3 The Laws of Motion

of 9.807 ms

−2

, although because of the variations in r and other effects, this is a global

average rather than a measured value).

Equation 3.3 tells us the force that a mass experiences. And using our simplifica-

tions, this force depen ds on the mass of the object. If we work out the acceleration

using Equation 3.2, then we get:

¨

p =

1

m

mg = g

In other words, no matter what mass the object has, it will always accelerate at the same

rate due to gravity. As the legend goes, Galileo dropped a heav y and a light object from

the Tower of Pisa and they hit the ground at the same time.

1

This means that the most significant force ...