Hi, Basically I have a point cloud that represents balls with different radii. They are all moving based on forces and sometimes they are intersecting with each other. Imagine the yellow ball is going in one direction while the blue balls goes in another direction. At one time they are colliding. How can I affect each sphere,s velocity or force so I can update it after the collision? What I know are these: 1. Since everything is represented as points, I know the position of the point that intersects with me given each of their radii. 2. I know the distance between them. 3. I know their velocity. 4. I know what forces are acting on these but they are integrated onto velocity at each iteration. 5. I know their radii. 6. I know their mass but it can be ignored. 7. I know their surface friction but this can also be ignored. If it was a simple repulsion, I would just negate the velocity but it will depend on where on the sphere the other sphere hits, right? That's where I have no idea how to solve this. Any ideas? Thanks a lot.