Game Development Reference
T HE L AWS
OF M OTION
begin to use results that were added to Newton's original work, but the funda-
mentals are his.
Newton created three laws of motion that describe with great accuracy how a
point mass behaves. A point mass is what we call a “particle,” but shouldn't be con-
fused with particle physics, which studies tiny particles such as electrons or photons
that definitely do not conform to Newton's laws. For this topic we'll use particle rather
than point mass .
Beyond particles we need the physics of rotating, which introduces additional
complications that were added to Newton's laws. Even in these cases, however, the
point-mass laws still can be seen at work.
Before we look at the laws themselves, and how they are implemented, we need to
look at what a particle is within our engine and how it is built in code.
Physics engines are based on Newton's laws of motion. In later sections we will
A particle has a position, but no orientation. In other words, we can't tell in what
direction a particle is pointing: it either doesn't matter or doesn't make sense. In the
former category are bullets: in a game we don't really care in what direction a bullet is
pointing; we just care in what direction it is traveling and whether it hits the target. In
the second category are pinpricks of light, from an explosion, for example: the light
is a dot of light, and it doesn't make sense to ask in which direction a spot of light is