To simulate a realistic collision, you need to assign masses and velocities to both balls. If you want the two balls to move toward each other, you should give one of the balls a negative velocity. For example, if Ball A is moving to the right with a velocity of +4 m/s, and Ball B is moving to the left with -2 m/s, they will collide in the center. If both balls move in the same direction, ensure Ball A has a higher velocity.
