geometric primitives that define the boundaries of the
surface such as polygons or triangles, but as a great
accumulation of primitive particles that define its volume.
Second point, a particle system is not a static entity as the
particles change shape and move with the passage of time.
The new particles are "born" and old particles "die." Third
point, an object represented by a particle system is not
deterministic because its shape and appearance are not
completely defined, however stochastic processes are used
to create and change the shape and appearance of the
object.