Theory Analysis On The Determination Of The Ping-pong Edge Ball And Research On The Introduction Of Video Playback Technology

With the high ratio of edge balls in current table tennis competitions, it’s a trend to introduce high-tech methods to assist referees make correct judgments.The category of edge balls is classified in this study. Profound experiments are conducted base on the elastic collision principle of physics to construct a mathematical model of ball gravity. By analyzing the mathematical model, it’s found out that the key factors of affecting edge balls is the horizontal tangent of ball gravity and the vertical dimension of the horizontal plane of the table. When it’s verified by the actual camera of video playback, it’s proved that it’s feasible and maneuverable to judge the category of edge balls by using video playback technology to determine the gravity center of the ball.This study can be divided into four parts in structure.In the first part, the category of edge balls is classified according to five basic routes of the ball, including the ball direction, placement and gravity point when impacting the table, with all the gravity functioning on the surface of the table, partial gravity functioning on the surface of the table, gravity functioning on the side of the table and gravity functioning on the outside of the table.In the second part, experiments of different kinds of edge balls are conducted through serve machine. It’s observed that it’s surely an edge ball when a diagonal edge ball, a linear edge ball or a linear edge ball flying to the sideline is impacting the surface of the table. What troubles the referees most is to identify whether it is an edge ball when a ball is flying from the overlap sideline and when a ball is flying from the both upper and lower sidelines impacting the surface of the table.In the third part, by constructing the mathematical model, the key physic factors affecting the edge balls and the bounce direction and range of a sideline edge ball affecting the judgment are analyzed. It shows that an edge ball occurs only when the horizontal tangent of ball gravity is higher than the vertical dimension of the horizontal plane of the table. Therefore, the key physic factor of producing an edge ball is the relative height between the ball gravity point and the table surface. The ball gravity point affects not only the edge ball but also the ball bounce direction and range, which determines the different bounce directions when the ball gravity point is higher than the table surface. If there exists an alternative bounce direction of an edge ball from up or down, the direction of a non-edge ball tends to be inertial downslide or bouncing downside. The cognition of the bounce direction of an edge ball is further confirmed from the perspective of physics.In the fourth part, four groups of videos of edge balls and non-edge balls recorded from the experiments are played back to the experts. It’s widely accepted by the experts that it’s necessary to assist edge ball judgment by using video playback technology to capture the gravity point at the moment when the ball impacting the surface of the table, and that the video playback technology can provide data support for referees to penalize the state and bounce direction of an edge ball.This study is of great practical significance and theoretical value for television sports broadcasting and in-field judgment.