After working hard to understand KDtree and implement it, here is a quick video. In this video, no friction is integrated (why is alway move like a bowl of jello), only really simple collision. But collision response depend to the mass of each collided body.Here, blue spheres have a density of 700 kg/cu.meter , yellow spheres 500 kg/cu.meter , green spheres 750 kg/cu.meter and red 4000 kg/cu.meter. Look how each react depend of it’s mass:
Now , I need to work on more accurate collision response and friction.