Apple Motion 2 Tutorials - Manual (Page 208)

208 Tutorial 4 Working With Particles
The particles with a long enough life now collide with the edges of the Canvas and
bounce back before finally disappearing.
Now, add Gravity to the same particle emitter.
To add Gravity to the particle emitter:
1 In the stack, select Gravity.
2 In the Preview area, click the Apply button.
The particles are pulled down by the force of gravity. The default Gravity settings do
not have much of a visible effect, so increase the pull of gravity.
3 In the Gravity Dashboard, drag the Acceleration value to 80.
Note: You can set an Acceleration value greater than 100 in the Behaviors tab of the
Inspector.