Here is a displacement by attractors definition for grasshopper based on some real physics:

It allows you to set multiple ‘attractors’ which interact realistically just like electric charges, magnets, heat flows or ideal fluids. Sliders control whether each point is a source, sink, vortex or a combination of these.

Get the ghx here

edit 26/10/09 : Check out the new and improved 3D version – JellyFish

I’ve long been fascinated by this area of math/physics. For more on this, take a look at rheotomic surfaces (its a bit of a long read, but skip down to see all the pictures and videos)