The motion of the center of mass is invariant of internal forces. COM moves in a parabolic path even after the collision. In this simulation green tracer represents the locus of the center of mass of blue and orange bodies. Both bodies are projected on the ground with respective velocities. Green tracer always moves in a parabolic path like a projectile thrown with a velocity and its motion seems to be unaltered by the collision of balls, although individual motions become complex after the collision.
