3D Compositing with Action > Action: The Particle System > About Action's Particle System >
Manipulators

Particle manipulators are used to influence either the position or the speed of particles. Manipulators can simulate the effects of a vortex, gravitational pull, or the pull toward a point, line, or plane. Manipulators are parented by the particle stream that they influence.

Action offers eight manipulators. Instructions on how to use each manipulator are provided in Manipulating Particles.