earticle

영어

Because tennis ball has spherical shape, tennis kinematics must be Poincaré conjecture in order to have best contact with the ball. They are open kinematics and close kinematics. The open one has expansive sphere while the close one has contractive sphere. They are composed of two spherical circles or two shuttle lines. Timing function has trigonometric shape. It has slow part and quick one. In a real play, one must adjust the timing with the ball speed. Volley and service have the same principles as in rally.