This simulation shows the physics of two ball collide in 2D (without any rotation motion).
    Physics processes:
  1. when two ball meets, the program shows two components of the velocity for each ball (along the line connect two ball and perpendicular to it)
  2. Interaction (force) between balls is along the line connect two balls
  3. Velocitys perpendicular to connection line are not changed (No force/interaction in that direction)
  4. The rest of the problem is similar to 1D collision problem for ball with velocity along the line