Particle speed and density I am using a Particle system to simulate falling dust / debris. The particle start and end fairly quickly. They should look like a short burst of falling dust.

I cant figure out how to get the particles to fall at slightly different speeds.

The particles should be falling downwards with very little Brownian motion.

The fact that the particles are falling at the same speed makes them look odd / too uniform (almost like a static image of some particles which is moving down rather than individual particles.

Also the particles end at a set frame so I get a uniform trailing edge (as below).


A bit of air drag helps a bit but not much.

Question 1. how to vary the downward speed of the particles?

Question2. Can the density of particles be animated so I can brake up the distribution?

Thanks
Oliver
Yesterday I found out how to control the particle's speed.
You can do this from "Timestep"! 



You can find it in the "Particles" tab in the "Properties" window. Then go to "Physics" menu. Over there is the "Timestep" slide, which by default is on "0.040" which is quite fast. So if you want slower the particles you can change this to "0.005" or even for very slow motion you can set it to "0.0005".

And most of all!!! You can keyframe the particles "Timestep", so you can do nice and cool animations. I have made a quick demo in which you can see that. It's here: Particles speed test in Blender .

I hope I was helpful!

P.S.
I want to apologize about my bad english (it's not perfect).