Introduction: It has been reported that the aerodynamic force applied to the ball changes in accordance with the number of panels and their orientation, consequently changing the flight trajectory (Goff et al., 2014; Hong & Asai, 2014; Hong et al., 2015). However, as the shapes on the surface of a soccer ball are a combination of various forms of panels and complicated seams, the influence that these shapes have on the aerodynamic force acting on the soccer ball is mostly unclear. Hence, in this study we aerodynamically studied the shape of the panels and the surface design (presence or absence of dimples). Methods: In this study, we introduced dimples on the surface of a soccer ball and examined their effect on the aerodynamic forces acting on the ball using a wind tunnel. We targeted three types of soccer balls in this study, namely, a soccer balls constructed from 32 panels, 12 panels and 6 panels, all of which are made out of the same material (leather). In addition, for each type of soccer ball, we constructed a type with dimples (dimple width of 3 mm and depth of 1 mm) and a type without dimples, making a total of six types of soccer balls. We then studied and measured the effect of the number of panels and the presence or absence of dimples on these six types of soccer balls using a wind tunnel experiment and revealed the aerodynamic characteristics. Results: The drag coefficient of soccer balls with dimples in the supercritical region, the soccer ball with 32 panels had the smallest drag value of approximately 0.10 (Re = 2.3×10 ) whereas the soccer ball with 12 and 6 panels had a value of approximately 0.15 (Re = 2.1×10 ) and 0.17 (Re = 2.1×10 ). However, for the case of soccer balls without dimples, the soccer ball with 32 panels had a drag coefficient value of approximately 0.13 (Re = 3.5×10 ) and the soccer ball with 2 and 6 panels had a value of approximately 0.12 (Re = 3.5×10 ) and 0.12 (Re = 3.4×10 ). Furthermore, in a wind speed of 30 m/s, the variations in the lift and side force in the case of a soccer ball with 32 panels without dimples were 2.5 N and 2.6 N, respectively. Likewise, the dimple soccer balls with 32 panels were 1.3 N and 1.7 N, respectively. Conclusion: The presence or absence of dimples on the surface of a soccer ball greatly varied the drag working on the ball. From this, it is plausible that, in the speed range used during a pass and a long kick, soccer balls with dimples have the possibility of flying faster, whereas, in the speed range used during powerful shots, soccer balls without dimples have the possibility of flying faster. In addition, during the flight of a soccer ball, horizontal motion is believed to be more stable for soccer balls with dimples than for soccer balls without dimples. ABSTRACT FROM AUTHOR
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