Apple Motion 4 - Manual (Page 603)

Anatomy of a Particle System
Every particle system is made up of an emitter and one or more particle cells. Each cell
appears inside of the emitter in the Layers tab and the Timeline.
Emitter
Cell
Original objects
(now disabled)
Behaviors applied to one
particle cell
The emitter and cells have separate sets of parameters that control the particle system’s
behavior. If you imagine that a garden hose is a particle system, the nozzle acts as the
emitter, while the water represents the flow of particles. Changing the parameters of the
emitter changes the shape from which the particles are emitted and their direction, while
changing the cell’s parameters affects each individual particle.
By changing a few parameters, it’s possible to create very different effects using the same
cell.
Note: In a particle system, cells and particles are not the same thing. A cell is a layer (in
the Layers tab) that acts as the “mold” for the particles (the multiple objects generated
in the Canvas). The cell itself is a copy of a source object (cell source) that appears dimmed
(disabled) in the Layers tab, and therefore is by default not visible in the Canvas.
As with any effect in Motion, particle system parameters can be keyframed in order to
change a particle effect’s dynamics over time. For example, you can create a path of
bubbles that follows an object onscreen by keyframing the emitter’s Position parameter.
For more information on keyframing, see
Keyframes and Curves .
603 Chapter 11 Working with Particles