Apple Motion 3 - Manual (Page 489)

Chapter 5 Using Behaviors 489
When the Edge Collision behavior is applied to a group, and the Affect Subobjects
parameter is turned off, the entire group is “bounced” off the bottom of the screen at
the anchor point of the group.
3 In the Edge Collision HUD (or Inspector), turn on Affect Subobjects.
Note: The Edge Collision behavior Inspector parameters also include Active Edges
controls for turning on and off the edge of the screen (or Z space) against which an
object collides. By default, an object is deflected from all edges of the screen.
When the bottom edge of each circle hits the lower edge of the screen, the circles are
deflected and bounce upward.
As the project plays, each circle bounces up and down.
When the Edge Collision behavior is applied to a
group and Affect Subobjects is turned off, the object
(group) bounces at the edge of the screen at its
anchor point.