void LateUpdate ()

{

ParticleSystem.Particle[] particles =?new?ParticleSystem.Particle[particleSystem.particleCount];

int?count = particleSystem.GetParticles(particles);

for(int?i = 0; i < count; i++)

{

particles[i].velocity =?new?Vector3(0, speed, 0);

}

particleSystem.SetParticles(particles, count);

}