The Essential Guide to Physics for Flash Games, Animation, and Simulations

Collisions between particles in 2D

We are now ready to look at general 2D collisions, in which the direction of approach of the particles is not necessarily along the line joining their centers. The way to handle such collisions is to resort to a trick similar to that used for a ball colliding with a wall: at the point of collision (when the particles are just touching), resolve the velocity of each particle into a normal component along the line joining them, and a tangential component perpendicular to that line (see Figure 11-13). The revelation is that, just like in a collision with a wall, only the normal velocity components are affected by the collision; the tangential components remain the same after the collision (provided it is frictionless). ...