Apple Motion 4 - Manual (Page 623)

For example, you can create a particle system that simulates an explosion by offsetting
the appearance of three different types of particles. First, dense white particles emerge
from the center. Half a second later, more diffuse orange particles appear around a larger
area. One second after that, small sparks emerge from underneath both of these layers
as they fade away.
You can offset a cell in the Timeline or mini-Timeline to start before the emitter. This
creates a “preroll” in which the particle simulation starts before the particles are drawn.
For more information on adjusting the timing of layers in the Timeline, see Using the
Timeline .
Creating Graphics and Animations for Particle Systems
Creating a new particle system from scratch begins with designing the particles you want
it to emit. You can use any image, shape, text, or movie supported by Motion as a source
for a cell. This section presents things to keep in mind when you create particle imagery.
Creating Still Image Graphics for Particle Systems
Particle systems that use still images as their cell sources render in real time much faster
than systems that use video or animation clips. A still image is often all you need to create
a compelling particle system. Here are some guidelines for creating graphics for use as
particles.
623 Chapter 11 Working with Particles