Apple Motion 4 - Manual (Page 527)

Example 3: Using the Vortex Simulation Behavior
The Vortex behavior is the opposite of the Orbit Around behavior—Orbit Around causes
one object to orbit around another target object, whereas Vortex exerts a force on all
objects surrounding the object to which the Vortex behavior is applied. You can specify
whether All Objects, Related Objects, or Specific Objects are affected by the Vortex.
The following examples use the same group of layers (stars) used in Example 2: Using
the Orbit Around Behavior . For this example, the layers are repositioned in the Canvas.
To use the Vortex behavior
1 Using the result of the previous example, delete the Orbit Around behavior from the
project.
2 Apply the Vortex behavior to the “center star” layer in the Center group.
By default, Related Objects is selected in the Affect parameter of the Vortex behavior.
When Related Objects is selected, all objects that exist in the same group as the object
to which the behavior is applied move around that object. Because the star is the only
object in the Center group, nothing happens.
527 Chapter 9 Using Behaviors