Abstract
Aerodynamic behavior of forkball and fastball are studied in a stand point of fluid dynamic research. The fastball rotates in backspin and aerodynamic lift force acts on it is toward upward by Magnus effects. This lift force is the same magnitude with gravity force for good fastball. As a result, the fastball trajectory is nearly straight toward homebase after detaching pitcher's finger. The other hand, good forkball spins around vertical axis. In this case, less lift force and only the gravity force act on the ball. The flight trajectory of the forkball results in vertically sinking line only by the gravity force and laterally sliding one by side spinning effects in its final stage near the homebase.
