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Modern tennis rackets are manufactured from composite materials with high stiffness-to-weight ratios. In this paper, a finite
element (FE) model was constructed to simulate an impact of a tennis ball on a freely suspended racket. The FE model was in
good agreement with experimental data collected in a laboratory. The model showed racket stiffness to have no influence on
the rebound characteristics of the ball, when simulating oblique spinning impacts at the geometric stringbed centre. The rebound
velocity and topspin of the ball increased with the resultant impact velocity. It is likely that the maximum speed at which
a player can swing a racket will increase as the moment of inertia (swingweight) decreases. Therefore, a player has the capacity
to hit the ball faster, and with more topspin, when using a racket with a low swingweight. 相似文献
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The study was designed to investigate the extent to which expectancies and performance of emotionally handicapped children could be altered by success- or failure-induced experiences. Students were randomly assigned to either of two experimental conditions during five trials of a guessing task. Immediately following the initial experience, all children were asked to estimate their expectancy of success on a novel learning task; students were then given a progressive matrix worksheet with ten problems which required adding and/or subtracting. It was hypothesized that those students in the success condition would have higher expectancies and actual performance scores than the children in the failure condition. It was further hypothesized that expectancy levels and performance scores would be related. An analysis of the results indicated that success and failure on a task were influential on subsequent expectancy estimates and performance; a discussion of these results is presented. 相似文献
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