A Study of Fluid Dynamics on A Tennis Ball and Racket Using the Digital Image Processing - A View on the Degree of Wear of a Tennis Ball and its Trajectory-
【Supercategory：7. DESCENTE SPORTS SCIENCE Subcategory：7.13 Vol.13】
A relation between the degree of wear of a tennis ball and its motion trajectory has been quantitatively analized by using the digital image processing. The degree of wear of the tennis ball and its spinning speed having been taken as experimental parameters, the influence of these two parameters on the trajectory has been examined statistically through numerous experiments.
The trajectory of a brandy new ball and an old one have been measured under three different spinning conditions, while maintaining the initial speed of these two balls, By taking the image of the initial movement of the balls with a high speed video camera when it has just come out of the tennis machine and analyzing those image through the digital image processing, the traveling speed, the spinning speed, and the flying angle of the balls are measured automatically.
Furthermore, the height of the moving ball from the court is measured when it passes over the line of the net, and the flying distance between the line of the net and the reaching position of the ball at court is also measured. The trajectory of the ball is decided by four positions ; the leaving spot of the ball at the tennis machine, the initial position of the ball near the tennis machine right after flying, the position of the flying ball over the net, and the reaching position of the ball at court.
The main results are as follows :
1) The influence of the degree of wear of the ball on its trajectory, descreases as the ball is spinning.
2) The trajectories of the balls with spinning forward (gravity direction) for the trajectry are similar, even if the degree of wear of those balls are different. And the variance of those trajectory are also small.
3) The flying distance (reaching distance of the ball) of the more worn balls is farther than that of the brandy new ones when the balls are spinning backward for the trajectory.
4) The variance of the trajectory of those two kinds of the balls is large when these balls are little spinning.
Concerning the above, the mutual influence of the initial spinning speed and spinning direction of the balls on the relation between the degree of wear and the trajectory of the balls is different.
DESCENTE SPORTS SCIENCE Vol.13/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
The trajectory of a brandy new ball and an old one have been measured under three different spinning conditions, while maintaining the initial speed of these two balls, By taking the image of the initial movement of the balls with a high speed video camera when it has just come out of the tennis machine and analyzing those image through the digital image processing, the traveling speed, the spinning speed, and the flying angle of the balls are measured automatically.
Furthermore, the height of the moving ball from the court is measured when it passes over the line of the net, and the flying distance between the line of the net and the reaching position of the ball at court is also measured. The trajectory of the ball is decided by four positions ; the leaving spot of the ball at the tennis machine, the initial position of the ball near the tennis machine right after flying, the position of the flying ball over the net, and the reaching position of the ball at court.
The main results are as follows :
1) The influence of the degree of wear of the ball on its trajectory, descreases as the ball is spinning.
2) The trajectories of the balls with spinning forward (gravity direction) for the trajectry are similar, even if the degree of wear of those balls are different. And the variance of those trajectory are also small.
3) The flying distance (reaching distance of the ball) of the more worn balls is farther than that of the brandy new ones when the balls are spinning backward for the trajectory.
4) The variance of the trajectory of those two kinds of the balls is large when these balls are little spinning.
Concerning the above, the mutual influence of the initial spinning speed and spinning direction of the balls on the relation between the degree of wear and the trajectory of the balls is different.
DESCENTE SPORTS SCIENCE Vol.13/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE
| Researcher | Toshio Kobayashi*1, W. Frank.*2, Tetsuo Saga*3, Shigeki Segawa*3, Hisako Nagase*3 |
|---|---|
| University or institution | *1 Institute of Industrial Science, University of Tokyo, *2 Institut fur Stromungsleher and StrOmungsmaschinen Universitat Karlsruhe, *3 Institute of Industrial Science, University of Tokyo |
Keywords
degree of wear, tennis ball, motion trajectory, digital image processing, spinning speed