The particles that the emitter I set up is creating are born with a speed of 0 so that they don't move off of the motion track i set up. However, at the end of the animation, I want the particles to scatter. I tried keyframing the speed from 0 up to a value, but the particles do not move. It seems like the speed parameter only affects particles that are being born... not existing particles. How can I (using any method in Motion 4) get pre-existing particles to scatter off the screen from their current, stationary locations?