The influence of moment of inertia on baseball/softball bat swing speed   总被引：1，自引：1，他引：0  

Keith?KoenigEmail author  Nan?Davis?Mitchell  Thomas?E.?Hannigan  J.?Keith?Clutter 《Sports Engineering》2004,7(2):105-117

The speed at which a player can swing a bat is central to the games of baseball and softball, determining, to a large extent, the hit speed of the ball. Experimental and analytical studies of bat swing speed were conducted with particular emphasis on the influence of bat moment of inertia on swing speed. Two distinct sets of experiments measured the swing speed of colege baseball and fast-pitch softball players using weighted rods and modified bats. The swing targets included flexible targets, balls on a tee and machine pitched balls. Internal mass alterations provided a range of inertial properties. The average measured speeds, from 22 to 31 m s⁻¹, are consistent with previous studies. Bat speed approximately correlates with the moment of inertia of the bat about a vertical axis of rotation through the batter's body, the speed generally decreasing as this moment of inertia increases. The analytical model assumes pure rotation of the batter/bat system about a vertical axis through the batter's body. Aerodynamic drag of the batter's arms and the bat is included in the model. The independent variable is bat moment of inertia about the rotation axis. There is reasonable agreement between the model and the measured speeds. Detailed differences between the two suggest the importance of additional degrees of freedom in determining swing speed.  相似文献   

Effect of verbal instructions and image size on visual search strategies in basketball free throw shooting     

Al-Abood SA  Bennett SJ  Hernandez FM  Ashford D  Davids K 《Journal of sports sciences》2002,20(3):271-278

We assessed the effects on basketball free throw performance of two types of verbal directions with an external attentional focus. Novices (n = 16) were pre-tested on free throw performance and assigned to two groups of similar ability (n = 8 in each). Both groups received verbal instructions with an external focus on either movement dynamics (movement form) or movement effects (e.g. ball trajectory relative to basket). The participants also observed a skilled model performing the task on either a small or large screen monitor, to ascertain the effects of visual presentation mode on task performance. After observation of six videotaped trials, all participants were given a post-test. Visual search patterns were monitored during observation and cross-referenced with performance on the pre- and post-test. Group effects were noted for verbal instructions and image size on visual search strategies and free throw performance. The 'movement effects' group saw a significant improvement in outcome scores between the pre-test and post-test. These results supported evidence that this group spent more viewing time on information outside the body than the 'movement dynamics' group. Image size affected both groups equally with more fixations of shorter duration when viewing the small screen. The results support the benefits of instructions when observing a model with an external focus on movement effects, not dynamics.  相似文献   

‘Skinhead’ in the classroom     

Keith Bardgett 《Children‘s Literature in Education》1972,3(2):56-64

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John A. Stormer and the Hofstadter hypothesis     

Keith R. Sanders  Robert P. Newman 《Communication Studies》2013,64(4):218-227

Does political rhetoric hold the key to an understanding of political pathology? Blending historical scholarship and behavioral research, this study tested empirically hypotheses derived from Richard Hofstadter's model of the “paranoid style” in American politics. The data were drawn from John A. Stormer's None Dare Call It Treason.  相似文献   

Editorial     

John Oxenham  Keith Watson 《International Journal of Educational Development》1985,5(3):139-140

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The application of artificial intelligence principles to teaching and training*     

Keith Shaw 《British journal of educational technology : journal of the Council for Educational Technology》2008,39(2):319-323

This paper compares and contrasts the use of AI principles in industrial training with more normal computer‐based training (CBT) approaches. A number of applications of CBT are illustrated (for example simulations, tutorial presentations, fault diagnosis, management games, industrial relations exercises) and compared with an alternative approach using AI. An evaluation of the relative merits of the two approaches will be given. Existing CBT packages are used to illustrate the points raised and the emphasis of the arguments will be on the effectiveness of AI and CBT in terms of both cost and learning. The position of AI applications within CBT is discussed, as is the task of getting started in applying these techniques.  相似文献   

Nicholson,T. (2005). The<Emphasis Type="Italic"> Phonics Handbook</Emphasis>. London. Whurr Publishers     

Keith Greaney 《Reading and writing》2007,20(9):945-946

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Dickens for All: Inclusive Approaches to Literature and Communication with People with Severe and Profound Learning Disabilities     

Keith Park 《British Journal of Special Education》1998,25(3):114-118

Keith Park, a teacher of children with visual impairment and learning disabilities with the Greenwich Visual Impairment Service, describes a series of multisensory interactive drama games re-telling the story of A Christmas Carol by Charles Dickens, following a discussion of the potential uses of literature with people with severe and profound learning disabilities.  相似文献   

The soil and air of academic life     

Marianne Weber 《Minerva》1977,15(2):200-213

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Undisclosed Flexibility in Computing and Reporting Structural Equation Models in Communication Science     

Christopher Scott Seaman  Rene Weber 《Communication methods and measures》2015,9(4):208-232

The use of structural equation modeling (SEM) in communication research has become increasingly popular in recent years, with SEM being commonly used as the primary method of data analysis in studies published within the field’s journals. However, despite its widespread use, there are persistent misapplications of SEM in published empirical studies in the communication sciences. Of these types of misuse, the most troubling are those related to the exploitation of flexibilities in data collection and analysis. Given the number of decisions that must be made when analyzing and reporting structural equation models, decisions which often remain undisclosed, the potential for researchers to exploit flexibilities in SEM research is high. To assess the extent of this problem, as well as the more longstanding types of misuse (i.e., omission of information and disclosed “bad practice”) identified by prior studies, we undertake a methodical review of studies employing structural equation modeling within major journals in the field of communication between the years 2007 and 2011. Articles were coded on the characteristics of the sample, characteristics of the model tested, as well as for various potential problems that we defined a priori. The most serious issues are identified, and recommendations for future standards in SEM research are suggested.  相似文献