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   

浅论邓小平对青少年成长的关怀     

周慧敏 《六盘水师范高等专科学校学报》2004,16(5):33-34

邓小平同志始终以博大的胸怀和深邃的目光,站在党和国家前途命运的高度,十分关怀青少年的成长。多次向青年发出号召要做“四有”新人,要学习,要参加社会实践,并鼓励大量派遣青少年出国留学,培养了大量的青年专家。  相似文献   

Impact absorption of tennis shoe-surface combinations     

S.?J.?DixonEmail author  V.?H.?Stiles 《Sports Engineering》2003,6(1):1-9

The aim of this study was to investigate, for typical shoes and surfaces used in tennis, the relative role of the shoe and surface in providing cushioning during running. Five test surfaces ranging from concrete to artificial turf were selected, together with two shoe models. Impact absorbing ability was assessed mechanically using drop test procedures and biomechanically using peak magnitude and rate of loading of impact force and peak in-shoe pressure data at the lateral heel. Differences in biomechanical variables between shoe-surface combinations were identified using a two-way ANOVA (p < 0.05). Mechanical test results were found to rank the surfaces in the same order regardless of the shoe model, suggesting that the surface is influential in providing cushioning. However, for all mechanical and biomechanical (p < 0.05) variables representing impact absorbing ability, it was found that the difference between shoes was markedly greater than the differences between surfaces. The peak heel pressure data were found to rank the surfaces in the same order as the mechanical tests, while impact force data were not as sensitive to the changes in surface. Correlations between mechanical and biomechanical impact absorption highlighted the importance of testing the shoe-surface combination in mechanical tests, rather than the surface alone. In conclusion, mechanical testing of the shoe-surface combination was found to provide a strong predictor of the impact absorbing ability during running if pressure data were used. In addition, for typical shoe-surface combinations in tennis, the shoe was found to have more potential than the surface to influence impact loading during running. Finally, in-shoe pressure data were found to be more sensitive than force plate data to changes in material cushioning.  相似文献   

大型集装箱船的总纵强度实用计算方法     

吴善刚  邱文昌 《上海海事大学学报》1998,(3)

以我国１９９６年《钢质海船入级与建造规范》对大型集装箱船的总纵强度的要求为标准,讨论了具体装载状态下船舶总纵强度的校核方法,并着重探讨了在资料不完整的情况下与总纵强度校核有关的船舶资料的计算制作方法。  相似文献   

抗美援朝战争与我党对台政策     

迟萍萍 《英才高职论坛》2007,(2)

解放台湾,实现统一,是中共一直坚持的目标。从新中国成立到抗美援朝战争,中共坚持以武力歼灭国民党残余力量,解放台湾。然而,抗美援朝战争使中共中央面临的局势发生重大变化,中共中央被迫暂缓武力解放台湾的步伐。抗美援朝战争结束后,中共中央根据形势的变化,逐渐提出以和平的方式实现统一。  相似文献   

未经训练成年男性急性运动性疲劳的电刺激研究     

胡敏  邹亮畴  程蜀琳  周文良 《广州体育学院学报》2007,27(4):6-10

运用电刺激的方法研究未经训练成年男性的急性运动性疲劳机制。结果表明:在疲劳性伸膝运动后,最大随意收缩力下降17±15%(p<0.001),中枢激活水平从88±7%下降到84±6%(p=0.001),M波波幅基本不变,但电刺激诱发的最大颤搐张力和最大张力上升速度明显降低,半舒张时间延长,激活后增强效应(postactivation potentiation)下降19%(p<0.001)。疲劳过程中平均肌电图-力矩比值升高。结论:在未经训练成年男性间歇性大负荷运动导致疲劳过程中,中枢神经系统及肌肉本身均参与了运动性疲劳的形成,肌肉的兴奋性未发生明显变化,但收缩能力减弱。  相似文献   

三线扭摆法测刚体转动惯量所用近似方法的分析   总被引：1，自引：0，他引：1  

陈文清  陈林峰 《洛阳工业高等专科学校学报》2004,14(3):20-22

分析在推导转动惯量的测量公式时采用的近似方法和其对测量结果带来的影响，指出减小其影响的途径。  相似文献   

单人皮划艇500 m竞速结构与竞赛策略研究   总被引：2，自引：0，他引：2  

马祖长  曹景伟  刘爱杰  孙怡宁  梅涛 《体育科学》2007,27(5):47-51

通过对我国优秀皮划艇运动员测试数据的分析,提出了基于桨频曲线转折点的皮划艇500 m比赛竞速结构划分方法;根据全程桨频和船速的变化特点,对每个阶段重新命名,更准确地反映了皮划艇500 m竞速规律;冲刺阶段桨频的增加并不一定意味着船速的提高,船速是否增长取决于平均桨力,它才是船速的最终决定因素;对世界大赛中分段成绩的进行对比分析;以我国划艇运动员杨文军参加世界大赛成绩为例,说明了竞赛策略的重要性。  相似文献   

影响我国男子甲级排球队团队凝聚力水平的因素研究     

杜宁  张萍  刘娇娜 《沈阳体育学院学报》2008,27(6):100-102

以卡伦提出的凝聚力概念模式理论为依据,对参加2006年全国男子排球锦标赛的16支甲级运动队的运动员进行问卷调查,分析影响男子排球运动队凝聚力问题的各种因素,为教练员与俱乐部管理人员对球队管理及运动员心理整合与共溶性提出相应的理论参考。研究结果表明,影响我国男子甲级排球运动队凝聚力水平的主要因素依次为协调因子、团结因子、素质因子、个体因子、稳定性因子、巩固性因子。  相似文献   

创造教育是学校体育教学改革的永恒主题     

陈天石 《中国体育科技》1997,(10)

学校体育教学改革正面临从技术教学向健身教育转化，本文以创造教育的理论，以创造、发展的观点，对深化学校体育改革问题试作分析和探讨。  相似文献