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191.
Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five
professional players are observed using high-speed video when taking curling free kicks with four different soccer balls.
The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s.
It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than
the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall
using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated.
Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount
of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it
is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free
kick by up to 1 m. 相似文献
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The purpose of this study was to answer 2 questions: (1) how important to 2-year-old children is fact-to-face contact with the mother, and (2) do attachment behaviors, such as looking at, talking to, and being close to mothers, interact in a compensatory fashion? 24 male and female children, 18 to 30 months, were observed with their mothers for 15 minutes in 3 conditions: (1) mother facing tethered toys, (2) mother facing away from toys, and (3) mother behind a partition and not visible from toys. Observations were made by time-lapse photography techniques. Results indicated that the potential for face-to-face contact was important: children spent 94% of their time in mother's visual field when she faced the toys and 50% of their time in her visual field when she either faced away or was behind the partition. Overall, they established face-to-face contact about 12% of the time. Some compensation was observed: talking and physical proximity increased as visual contact decreased. 相似文献
198.
Carr S 《Journal of sports sciences》2006,24(3):281-297
In this paper, I present data from two studies that sought to examine multiple achievement goals in the context of children's physical education (PE). Study 1 examined the links that multiple-goal profiles (i.e. mastery/performance-approach/performance-avoidance goals) for PE had with self-determined motivation, affective patterns and levels of extracurricular sporting activity in a sample of 193 Year 7 pupils. Results suggested that children endorsing high mastery/high performance-approach/high performance-avoidance, high mastery/high performance-approach/low performance-avoidance, or high mastery/ low performance-approach/low performance-avoidance profiles typically exhibited the most adaptive motivational responses. In contrast, children endorsing a low mastery/high performance-approach/high performance-avoidance profile typically experienced more maladaptive motivational outcomes. Study 2 examined the development of multiple achievement goals over two terms of PE in conjunction with retrospective perceptions of the motivational climate in the sample. The results of analysis of variance suggested that children exposed to a consistent high mastery/low performance climate experienced decreased performance-avoidance goals and maintained high levels of mastery goals for PE. In contrast, children exposed to a consistent low mastery/high performance climate experienced increased performance-avoidance goals and decreased mastery goals for PE. 相似文献
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Michael P I Nunns Sharon J Dixon James Clarke Matt Carré 《Journal of sports sciences》2016,34(8):730-737
Plantar loading may influence comfort, performance and injury risk in soccer boots. This study investigated the effect of cleat configuration and insole cushioning levels on perception of comfort and in-shoe plantar pressures at the heel and fifth metatarsal head region. Nine soccer academy players (age 15.7 ± 1.6 years; height 1.80 ± 0.40 m; body mass 71.9 ± 6.1 kg) took part in the study. Two boot models (8 and 6 cleats) and two insoles (Poron and Poron/gel) provided four footwear combinations assessed using pressure insoles during running and 180° turning. Mechanical and comfort perception tests differentiated boot and insole conditions. During biomechanical testing, the Poron insole generally provided lower peak pressures than the Poron/gel insole, particularly during the braking step of the turn. The boot model did not independently influence peak pressures at the fifth metatarsal, and had minimal influence on heel loads. Specific boot-insole combinations performed differently (P < 0.05). The 8-cleat boot and the Poron insole performed best biomechanically and perceptually, but the combined condition did not. Inclusion of kinematic data and improved control of the turning technique are recommended to strengthen future research. The mechanical, perception and biomechanical results highlight the need for a multi-faceted approach in the assessment of footwear. 相似文献