一类质点组动能定理的推导方法

给出了质点组动能定理，不同于一般教材的一种推导方法，并对两种方法进行了比较。     

刚体动能的一种计算方法

根据克尼希定理和刚体转动的有关理论，导出了由关于质心对称的任两对称点的速度来计算刚体动能的一种算式。并用两个算例说明了该式的优越性。     

介词空间语义的"静态"与"动态"

文章重点讨论英语介词概括的典型意义，不涉及语义扩展隐喻意义。介词的静态投射关系由此tr，投射轨迹，lm三个相对静止的因素组成，介词的动态投射关系中,tr根据参照体做各种线性，改变投射距离的运动。     

宇宙速度及其简明计算

第三宇宙速度的计算是个繁杂的多体问题，利用系统逃逸动能的可叠加性，将多体问题化为二体问题的叠加给出了一个可以计算第三宇宙速度数值的主项。     

The relationship between segmental kinematics and ball spin in Type-2 cricket spin bowling

The techniques of spin bowling in cricket have been largely formulated from the collective intuitions of past players. A standard model of bowling technique has been generally prescribed for both off-spin and leg-spin bowlers, but there has been no biomechanics research to validate this approach. This study measured 20 Type-2 off-spin and 15 Type-2 leg-spin bowlers using a 3D Cortex motion analysis system. Correlation coefficients between segmental kinematic variables and spin rate in the off-spin and leg-spin bowlers revealed that off-spin bowling was associated with an earlier movement time of the thorax, whereas leg-spin bowling was associated with a greater magnitude and earlier movement time of pelvis rotation, as well as a greater magnitude of pelvis-shoulder separation movement. The maximum velocity of rear hip flexion differentiated between both groups of bowlers. The GLM suggested that for off-spinners, rear hip flexion velocity significantly explained the variance in spin rate (subject to sequential timing constraints), while for leg-spinners, the time of maximum rear hip flexion and maximum arm circumduction velocity significantly explained variance in spin rate. This study supports the notion that off-spinners and leg-spinners have significant differences in their joint kinematics, and should not be coached under a one-size-fits-all technical model.     

在高中物理教学中如何处理好“碰撞”的教学

“碰撞”问题是高中物理教学中的重点和难点。用通俗的语言和直观的方法对球的对心碰撞过程进行较详尽的讨论．便于中学生对碰撞过程中有一个较清晰的物理图像。     

Mechanics of Batting: Effect of Stride Technique on Ground Reaction Forces and Bat Velocities

The benefits associated with being physically active are well documented, but a significant proportion of the population is insufficiently active. Physical inactivity is a major health risk factor in our society, and physical education programs are consistently identified as a means to address this concern. The purpose of this article is to use the social-ecological model as a framework to examine ways in which physical education programs can play an important role in promoting physical activity. Policies that require time allocations and resources for physical education and physical activity in schools and community designs that provide infrastructure that makes being physically active accessible and convenient are important factors in making schools and communities healthier spaces. It is clear, however, that policies alone are not sufficient to address concerns about physical inactivity. We must consider individual factors that influence decisions to be physically active in efforts to engage children in physical education programs that promote active lifestyles. The learning climate that teachers create determines what students do and learn in physical education classes. Ensuring that students see value in the content presented and structuring classes so that students believe they can experience success when they exert effort are key elements in an effective motivational climate. Efforts to address public health concerns about physical inactivity require a comprehensive approach including quality physical education. It is critical that kinesiology professionals emerge as leaders in these efforts to place physical education programs at the center of promoting children's physical activity.     

Development and Validation of a Method for Determining Tridimensional Angular Displacements with Special Applications to Ice Hockey Motions

Abstract

Tridimensional angular displacements of the skates were determined with a single cinecamera used in conjunction with two orthogonal rods attached to the rear part of the skater's boots. The method was based on the commutative law with the imposed restrictions that two of the angles were small in relation to the other one, and that a sequence of angular displacements was defined. This approach required the sole determinations of the planar coordinates of the three points delimiting the orthogonal rods. An experimental setup was designed to validate the method: the criterion angles were approximated with less than 2 degrees of error. Subsequently, the method was applied to a practical situation: the two-legged stop in ice hockey. The combination of this tridimensional method with instrumented strain gauge skates for the measurement of forces provides a new and powerful tool for performing kinetic analyses in tridimensional skating activities.     

Tennis

The study investigated differences in the one‐ (SH) and two‐handed (DH) backhands when hit flat, across‐court (AC) and down‐the‐line (DL), and with heavy topspin DL (TDL). The ability to disguise each of these backhands when hitting the above strokes was also assessed. Eighteen college‐level male tennis players, identified as having a high performance topspin SH (n = 6) or DH (n = 12) backhand drive, participated in the study. Players were required to hit three AC, DL and TDL backhands from the baseline with their preferred technique, while being filmed with two high‐speed video cameras operating at 200 Hz. The highest horizontal velocity backhand for each stroke was analysed. Results indicated that the sequential coordination of five body segments (hips, shoulder, upper arm, forearm, and hand/racquet rotations) was required for the execution of the SH stroke. The same number of segments were generally coordinated in the DH stroke (hips, shoulders, and varying degrees of upper arm and forearm rotations followed by hand/racquet movement). Mature players produced comparable racquet horizontal velocities 0.005 s prior to impact using either the SH or DH backhand technique. The SH backhand was characterised by a more rotated shoulder alignment than the DH stroke (SH: 119.1°; DH: 83.4°) at the completion of the backswing. At impact the ball was impacted further in front (SH: 0.59 m; DH: 0.40 m) and a similar distance to the side of the body (SH: 0.75 m; DH: 0.70 m). Players using the DH backhand technique delayed the horizontal acceleration of the racquet towards the ball (SH: 0.13 s; DH: 0.08 s prior to impact) and thus were capable of displaying a similar hitting motion closer to impact than players with a SH technique.     

新旧动能转换背景下红色文化资源的开发利用——以“沂蒙精神”为例

新旧动能转换是新时代背景下第一、第二和第三产业协同融合发展的重大举措,红色文化资源作为重要生产要素,需通过“新科技”“新模式”“新资源”“新服务”等新动能的转换,实现自身政治价值、文化价值和经济价值更大更广范围的开发利用。“沂蒙精神”文化资源是红色文化资源的典型代表,该资源的开发,需结合其资源禀赋,包括自身特点、价值、类型等,通过加快数字转型、变革思维模式、完善人才战略、重构服务体系等路径,实现新旧动能的转换,完成开发利用的升级。