To measure and analyze the golf swing form, there is a method that uses a high-speed camera or video camera. However, it is difficult to measure the motion of a thin part like the wrist or ankle by using this method. In golf, the cock motion is one of the wrist motions that is done at the near point of contact between the body and the club. It is regarded as the position that transmits the energy stored in the rotation of the body to the club. In this paper, we proposed a new measurement method that uses a gyro sensor in order to measure cock motion. To measure this motion, the sensor was attached to the left wrist and the forearm. Finally, the features of the cock motions that middle and novice class players exhibit were measured by the experiment. Although this method was developed for cock motion measurement in golf swing, it can be applied to baseball, tennis and so on.
The authors have already proposed a numerical approach for calculating flexural rigidities of a ski's cross section. In the present study, to discuss the accuracy and practical usefulness of the numerical approach, an experimental approach is developed. The experimental approach estimates the flexural rigidities of a ski using experimental results obtained by bending test and torsional test. Although the ski has a laminated construction, the flexural rigidities for non-uniform orthotropic plates are estimated. Three kinds of test pieces with uniform laminated cross sections in the longitudinal direction and five test pieces with non-uniform laminated cross sections, which is similar to the ski, were used for the numerical calculations and experimental estimations. From comparisons of numerical values with values estimated experimentally, it was shown that the differences between numerical and estimated values areless than 15% of the maximum value of flexural rigidities. Furthermore, from the simulation of a skiing turn for five test pieces similar to the ski, it was shown that the maximum difference of "characteristic of ski turn" is less than 4% of the maximum "characteristic of ski turn". This means, the difference of "characteristic of ski turn" due to the difference of the flexural rigidities becomes far less than the difference of the flexural rigidities itself. From the abovementioned reasons it was concluded that the numerical approach for calculating flexural rigidities of a ski's cross section, and the experimental approach for estimating flexural rigidities are useful.
The surfaces of athletic stadiums have improved since 1970. However, no classification has been made regarding the scars on surfaces. A standard of the surface was announced by the IAAF(International Association of Athletics Federations) in 1998. This standard consists of 10 properties such as force reduction, friction and modified vertical deformation. These properties and precedence studies are mostly in regard to vertical direction but few are related to the characteristics of level direction. The purposes of this study were to classify the scars on surfaces of athletic stadiums and to develop a wear test device. The characteristics of 3 kinds of track surfaces were investigated by using this device. Theresults are as follows;1) Scars on surfaces of the athletic stadiums were classified into three categories, a) abrasive wear (scratch damage), b) abrasive wear (brake damage), c) fatigue wear.2) The wear test device is able to simulate the contact phase of human running and can carry out various tests. This device detects the forces of spike pins and surface.3) It became clear that the vertical direction force is big on a hard surface.
The present study focused on the behavior of the ball at the time of the stroke in soft tennis, and it aimed at exploring the relations of many kinematic values at impact, and the flight behavior of the ball, while checking whether there might be an abnormal flight behavior. The flight of the ball was videotaped by three sets of video cameras, and the ball at impact was videotaped with two high speed cameras. The behaviors of these balls were analyzed. These experiments investigated the conditions of the flights of soft tennis balls, both when given a lift from an applied drive rotation and when given a sinking flight from a slice rotation. It was suggested that the difference in rate of spin given by a stroke influenced the abnormal flight behavior of a soft tennis ball, and also that when there was drive rotation or slice rotation of 40rps or more, the possibility of abnormal flight behavior occurring was high.