Dynamics of Particles
The emission and lifetime settings affect the overall behaviour of the system but the individual particles can also change over time. Each one has a velocity vector that determines the direction and distance the particle moves with each frame update. The velocity can be changed by forces and gravity applied by the system itself or when the particles are blown around by a wind zone on a Terrain. The color, size and rotation of each particle can also change over its lifetime or in proportion to its current speed of movement. The color includes an alpha (transparency) component, so a particle can be made to fade gradually in and out of existence rather than simply appearing and disappearing abruptly.
Used in combination, particle dynamics can be used to simulate many kinds of fluid effects quite convincingly. For example, a waterfall can be simulated by using a thin emission shape and letting the water particles simply fall under gravity, accelerating as they go. Smoke from a fire tends to rise, expand and eventually dissipate, so the system should use an upward force on the smoke particles and increase their size and transparency over their lifetimes.