Need alittle more help.

Hi again, i need a little more help.

You know when objects collide with each other you get thouse small balls of bust forming when they move againest each other (often seen when objects spaz out) and the sparks that are created. Is there any way of turning these off? they are really screwing up my green screen shots. BTW these objects must collide since im running a cart along a rail, but i cannot have any of these spark and dust balls in the shot.

Thanks for your help.