Particles Tutorial

http://www.youtube.com/watch?v=W7z-6HhPlbE&feature=relmfu

He has used parametric equations to make this helix path, for the tutorial.
Here's the expression he used:

for x,y:
t=time;
[400*Math.cos(t),400*Math.sin(t)]

for z:
50*time;

What is parametric equations?

http://en.wikipedia.org/wiki/Parametric_equation