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. The system stores this velocity across frames, and reapplies it to the particle position on each simulation step.
The velocity is also used by the ParticleSystemRenderer if Render Mode is set to ParticleSystemRenderMode.Stretch.
See Also: ParticleSystem.Particle.animatedVelocity, ParticleSystem.Particle.totalVelocity.