Introduction: In ski jumping, when the jumper performs his ski-jumping, the mechanical forces affect the body and skis. Such forces include the gravity, aerodynamic and friction forces. If the forces during the jump performance could be recorded, the mechanical quantity can be analyzed more easily. A jumper has to adapt his motion to the speed. The maximum speed reaches as fast as 85km/h in the approach run. It is important for a jumper to develop a large force in the high speed condition and to control his power production optimally on the take-off platform. However, physical conditions differ in the phases of the take-off and the aerial region. It is important to reveal the behaviors of forces in the transition. The purpose of this study is to reveal the influence of such forces during the period of transition. Methodology: Four jumpers jumped wearing a compact accelerometer during the season 2007-2008. The accelerometer was placed on the jumper`s back. The data was taken digitally with 200 Hz Sampling frequency. The data of three components on the local coordinate system are obtained by the accelerometer with gyroscope. The acceleration data were converted to the global coordinate system by the Eular`s rotation matrix. Result and discussion: Drastic change of forces were observed in two directions (the driving force and the perpendicular force to the velocity) on the sagittal plane. The driving force along the direction of velocity vector changes drastically in the transition. It can be considered that the drastic change is produced by the take-off action and aerodynamic forces at the take-off. Drastic change of perpendicular forces were also observed. So far, the reason why these changes of amplitude of the acceleration happen has yet to be known. Even in this study, drastic changes of the amplitude are confirmed at the transition of every jump. The amplitude converges to steady level in approximately 0.5 seconds. It can be suspected that the vibration of the skis may contribute to the large amplitude of the acceleration. Conclusion:The coordinate data conversion technique in this study produced precise data. It is difficult to monitort the noise for ski`s vibration perfectly. The aerodynamic forces after the take off can be precisely calculated.
© Copyright 2008 Abstractbook. The First International Low Lands Congress on Science and Skiing, Brussels, October 11th. Veröffentlicht von Vrije Universiteit Brussel. Alle Rechte vorbehalten.