This velocity is used for effects that are based on physics. Examples of features that use this type of velocity are the Force module, Gravity, and Start Speed. This velocity is remembered across frames, and will be reapplied to the particle position of each frame.
The velocity is also used by the ParticleSystemRenderer if Render Mode is set to ParticleSystemRenderMode.Stretch.
See Also: ParticleSystem.Particle.animatedVelocity, ParticleSystem.Particle.totalVelocity.