How does ParticleSystem.Particle.velocity behave?

• What I want to do: Emit an amount of particles, they all start from 1 point and have randomly different velocity.

• What I coded:

     [SerializeField]
       int numberOfParticles = 10;       
       [SerializeField]
       float speedMin = 10;
       [SerializeField]
       float speedMax = 20;
  
       ParticleSystem.Particle[] particles = new ParticleSystem.Particle[100];
  
       [ContextMenu("Emit")]
       void Emit()
       {
            targetParticleSystem = GetComponent<ParticleSystem>();
           targetParticleSystem.Emit(numberOfParticles);
           int spawnedParticlesCount = TargetParticleSystem.GetParticles(particles);
           for (int i = 0; i < spawnedParticlesCount; i++)
           {
               particles[i].velocity = Random.Range(speedMin, speedMax) * Random.onUnitSphere;
               particles[i].position = Vector3.zero;
           }
           targetParticleSystem.SetParticles(particles, spawnedParticlesCount);
       }
  
  
  

• What I got:

• When I set both speedMin and speedMax to zero, it emits all particles right at the center as expected.

• When I set speedMin, and speedMax other than zero, particles's initial positions diverge from the center, and as speed got bigger the initial positions got further from the center.

There's only 1 clue that I could come up with, that is there's a code that applies the velocity after I set the velocity and before first render of particles. But it doesn't seems right, first because you don't have delta time in a same frame. Secondly the step can't be that big.

• So, can you guys explain why or give me some help to achieve what I want? P/s: I'm using Unity 5.4.0f3