Abstract
Trajectories of the billiard balls have long been assumed to behave as the collision of mass points. As a matter of fact, the beginners can enjoy the games with this simple approximation. On the contrary, the professional players know the differences from the theory by their plentiful experiences and adjust them by intuitions. For example, the target ball does not go in the direction which is perpendicular to the surface of contact. This difference from the theory is well known as "throw". In order to investigate the mechanisms of the differences from the theory and to quantify them under various conditions, the authors of this study have visualized the motions of the balls by the high-speed camera and have investigated the trajectories of the balls quantitatively by using the digital image processing techniques. As a result, the maximum "throw" is found to occur at the contact angle of 30 degree.
