Hi,
I have tried to formulate my question as short as possible…=) to me it is quite tricky, hence I turn to this forum - where I have gotten excellent advice earlier 
I am working on animating a physical principle called ‘sputtering’, which is basic sphere-sphere elastic collisions.
But in large numbers = array + particle system needed. I can model very small scale by keyframing but this is TEDIOUS!!
Basicly I have an array of UVspheres; say fx. x=100, y=100, z=10. This is a surface within a square chamber.
I need to have a particle system of, different, UVspheres hitting this array and when doing so - (i) will cause the incoming UVsphere from the particle system to bounce back into the chamber, and (ii) also dislodge 1-2 of the array UVspheres from the surface, while leaving the rest in place.
This event should run until UVspheres from the array have been eroded to something like z=5-7. This is to model how a surface is cleaned in a plasma environment.
Status - array part:
Array done, separate objects, rigid bodies, made the lower 5 layers (in Z-dim) passive, removed gravity in scene.
Challenges/problems: When something collides with array, some spheres may be removed but very slowly and with widely different speeds. Is it possible to set a binary value determining if a sphere is dislodged or remains in array.
Status - particle system:
Plane emitting UVsphere particles into a chamber in random directions.
Challeges/problems: Is it possible to have something like ‘homogeneous/even’ bombardment of the array-surface?
Kind Regards,
Søren