步行与竞走运动--物理与体育系列专题之十一

双足直立行走是人类移动自身的运动形式，直立行走并不容易，原始人从四足爬行到直立站起用双足行走经历了一千多万年的漫长历程．从力学观点考察，四肢落地与双足直立的根本差别在于：四肢与地面接触点联线围成一个四边形，无论躯体怎样动，其重心在地面的投影都不会越出这个范围．因此四肢落地可保证静平衡条件得到满足，由支撑点围成的区域可称做静态稳定域。     

对竞走速度的运动学分析--物理与体育系列专题之四

竞走速度公式的导出 竞走和普通行走一样，是一脚支撑和双脚交替进行的．竞走规则要求，支撑腿必须伸直，从单脚支撑过渡到双脚支撑，在摆腿的脚跟接触地面前，后蹬腿的脚尖不得离开地面，这样就能保证用双脚支撑，不会出现腾空现象．即运动员必须至少一个脚在地面上，那就是他必须“走”．竞走的速度取决于步频和步长，并与运动员身体重心上下起伏有关系．     

从多视角审视物理与体育之关系--物理与体育专题之二

联合国把2005年既定为“国际物理年”，又定为“国际运动与体育年”，这是一种巧合，还是有某种内在的联系?因此，有必要从多视角去考察物理与体育的关系．     

乒乓球旋转的力学分析--物理与体育专题之五

乒乓球运动是我国普及性和水平最高的一项全民运动项目．作为一项竞技性很强的运动，其技巧性、灵活性和反应性都是运动员所追逐的目标，其中技巧性是首位的．对于乒乓球的技巧来说，莫过于接、发球和对攻环节中的加旋技术．本文就旋转技术中的物理学简介于下．     

投篮球、推铅球和掷手榴弹的力学--物理与体育系列专题之九

投篮球入篮、推铅球和掷手榴弹这三种常见的运动，可以用比较简单的抛射体运动的计算方法和公式来统一处理．这是因为，篮球、铅球和手榴弹在空中运动的速度不大，我们主要关心重心位置的变化，空气阻力影响可以忽略不计(参看下面所给的参考数据)．本文将分别讨论有关这三种运动的一些有实际意义的有趣味的问题．     

浅析短跑运动的力学规律--物理与体育专题之十

为了初浅地阐明短跑运动的力学规律，我们先以优秀短跑运动员在赛跑全过程(从起跑到冲过终点线)中位置变化情况的实测结果为典型实例，分析百米赛跑的运动学特点，然后采用一个短跑运动的数学模型，用能量法阐明短跑运动的动力学特点．     

从物理看乐音的和谐(续)--物理与音乐专题之一

研究表明，人类的耳朵除了对基频外，较易听辨的就是二倍(频率)音、三倍音和四倍音．所以当一个基频为f1：f2：f3=400：500：600的三个音同时发声时，各音的二次谐频，三次谐频，四次谐频被加强，听感就变得和谐、明亮．而频率比不是简单整数比关     

腾空运动:从猫空中转体谈起--物理与体育系列专题之八

从高处下落的猫总是四肢先着地的现象很早就引起注意．1894年法国科学院的Marey用当时的摄影技术记录猫的下落过程，发现猫能在1／8秒钟内从四足朝天姿势自动翻转过来．这一事实使物理学家陷入困惑．根据牛顿力学的动量矩守恒原理，腾空的猫处于无力矩状态，在下落过程中应维持初始状态的零动量矩不变，不可能产生实现180度翻转所需要的动量矩增量．1894年法国科学院另一位物理学家Guyou对此提出一种解释．他认为猫分两阶殷实现前后半身的转体，     

室内音质设计的物理原理及应用--物理与音乐专题之五

无论是乐器还是喉咙发出的音乐声，总要经过传播才能被人听到．声波在空气中传播当然以直线传播为主，但反射和衍射不可避免的存在，而且对音乐的效果有重要影响．音乐在旷野、山颠、院落或室内，听起来强度和音色各不相同，无论是听者还是演唱者，感受都大不一样，可见环境对乐音的响度或音色是有影响的，这里的区别主要是反射的效果．     

打击乐器和膜、棒、板的振动--物理与音乐专题之四

藉助捶打、敲击、抓奏、刮奏、摇奏、弹拨等方法几乎可以使任何刚性物体发声．打击乐器就是利用这种方式发出乐音的乐器．它们大致可以分为两类：一类是有调打击乐器如木琴、钟琴、钢板琴、定音鼓和中国编钟等，此类乐器有音阶的变化，可以独立表演乐曲；另一类是无调打击乐器，如各种鼓、     

语音清晰度和平均混响时间在车内声学中的应用

乘用车的车内声学性能直接影响人的主观感受,但仅靠主观评价来判定是不够的;必须通过引入有力的客观参量来刻画车内听觉的舒适度效果。而如何来设计车内噪声试验方案来诊断和改善声学水平则成了一个重要的环节。在乘用车车内噪声品质的开发过程中,综合应用语音清晰度和平均混响时间两个指标对车内吸声性能进行了对比分析。通过对实车主观评价和客观测试,讨论了语音清晰度、车内平均混响时间、吸声系数和声压衰减斜率的概念及相互关系,从而确定了高速道路行驶工况下的语音清晰度主要取决于车内吸声材料的性能。提出了将车内相关部位进行材料吸声改进作为改善语音清晰度的主要措施之一。     

关于声波教学中的几个关系

在声波的教学中,由于学生知识结构的关系,对于声波性质的了解有一定的欠缺,为了让学生充分认识声波的特性,在实际教学过程中,通过对如下几个关系的认识,学生对知识的了解将会更加清晰、明了.1 声波的传播与波速的关系 在教材中,列出了声波在各种不同介质中的传播速度,以及它们随温度变化的情况,     

The Millimeter Wave Radiation of a Traveling Wave Sinusoidal Wire Antenna

In this paper, investigation of radiation properties of the traveling-wave sinusoidal wire antennas is extended to the millimeter-wave frequencies (Ka-band) for the antennas whose geometrical dimensions vary in a wide range. Far-field patterns and S-parameters of composed three antenna sets were measured. A mathematical model was constructed for the structure and a MATLAB code based on this theoretical approach was written to calculate patterns, phase and attenuation constants of all investigated antennas. Frequency characteristics and the relation of antenna dimensions with wave parameters were investigated. Measured and calculated patterns were also compared with the constructed far-field patterns obtained by MoM (method of moments) and the MoM current distributions were used to explain the loss mechanisms of antennas. A directive, undistorted and smooth radiation can be achieved only choosing small undulated antennas whose peak-to-peak amplitude to period ratio κ is smaller than 0.4 (κ < 0.4). It is shown that wavelength of broadside radiation is not equal to antenna period for all antennas, except for very small undulated antennas (κ < 0.2). This antenna type can be used as a frequency-scan antenna for millimeter wave radars.

一种简便的表达声波波动特性的演示方法

1引言 普通扬声器发出的声波不是强指向性的；当声源发出的直达声波到达接收传声器后，由房间内对应各个反射面向声源产生的声波也陆续到达，造成严重的干扰．由于室内反射面状况较复杂，对时域中具有一定持续时间的信号，其直达声与反射声完全混叠，无法将各个像声源所对应的声波一一辨别出，因此直接采用扬声器发出的窄带或单频信号作为波源的实验方法就无法应用于普通的课堂教学．     

普通物理教学中进述声波问题的几点体会

声波这一概念在普通物理中是相当重要的.在多年的普通物理教学中我们发现,有的学生根本不知道声波可以在固体中传播,即使知道的学生也认为声波在固体内传播时一定是纵波.而地震波既有横波又有纵波,那么地震波和声波在本质上有什么区别吗?我们知道实际上地震波和声波本质是一样的,这样一来学生就弄不明白了.     

空间衍射声波波前与压力场的计算机层析三维重建

应用脉冲载波电子散斑干涉（ｐｕｌｓｅｄｃａｒｒｉｅｄ－ＥＳＰＩ）与计算机层析技术（ＣＴ），实现了由高压电极放电激励所产生的瞬态传输声场在经过不同孔径模板衍射后波前与压力场的三维重建，给出了数值结果，并对噪声条件下的计算机层析重建进行了讨论。     

Sound Wave of Spin-Orbit Coupled Bose-Einstein Condensates in Optical Lattice

We study the phonon mode excitation of spin-orbit(SO) coupled Bose-Einstein condensates trapped in a one-dimensional optical lattice. The sound speed of the system is obtained analytically. Softening of the phonon mode,i.e., the vanishing of sound speed, in the optical lattice is revealed. When the lattice is absent, the softening of phonon mode occurs only at the phase transition point, which is not influenced by the atomic interaction and Raman coupling when the SO coupling is strong. However, when the lattice is present, the softening of phonon modes can take place in a regime near the phase transition point. Particularly, the regime is widened as lattice strength and SO coupling increase or atomic interaction decreases. The suppression of sound speed by the lattice strongly depends on atomic interaction, Raman coupling, and SO coupling. Furthermore, we find that the sound speed in plane wave phase regime and zero-momentum phase regime behaves with very different characteristics as Raman coupling and SO coupling change. In zero-momentum phase regime, sound speed monotonically increases/decreases with Raman coupling/SO coupling, while in plane wave phase regime, sound speed can either increase or decrease with Raman coupling and SO coupling, which depends on atomic interaction.     

Stable Components of the Wave Field in Underwater Sound Waveguides

A technique is proposed for determining which sound field components are weakly sensitive to variations in the parameters of the speed of sound field in a marine waveguide. Such components are formed by narrow ray beams, with the dispersion of their vertical coordinates on the distance to the point of observation being less than the vertical scale of the perturbation. Since these rays pass through the same inhomogeneities, their phases in the presence of perturbations acquire approximately the same increment. For a monochromatic field, such components in perturbed and unperturbed waveguides differ only by their phase factors. With a pulsed field, perturbations lead only to some additional delays of the stable components. A procedure based on decomposing the field into coherent states is proposed to select stable components from the total field. The solution to the problem of finding the location of a source using the stable components is illustrated by a simple example.     

利用虚拟技术演示声波的拍现象

将虚拟技术与多媒体计算机教学技术相结合,演示正弦波的拍现象。方法是用麦克风采集拍音信号输入到计算机中,利用频谱分析软件进行实时分析,同时将拍信号投影在大屏幕上,以使学生全面、直观地认识而掌握拍的概念。     

Saser (Sound Amplification by Stimulated Emission of Radiation)

A theoretical scheme of a saser (Sound Amplification by Stimulated Emission of Radiation) is proposed. A liquid with gas bubbles is used as the active medium. Pumping is performed with an alternating electric field or mechanical vibrations of the resonator. Phase bunching of initially incoherent radiators (bubbles) occurs under the action of acoustic radiation forces. The proposed scheme is similar to that of a free-electron laser. Two models of an active medium are studied. In the first model it is assumed that all bubbles have the same radius. In the second model a continuous distribution of bubble radii is studied. The starting values for sasers with square and cylindrical resonators are calculated. It is shown that in all cases studied these conditions are identical, to within a numerical factor. The operation of a saser in a nonlinear regime and the directional pattern of a saser in the saturation regime are studied. Zh. Tekh. Fiz. 67, 92–100 (April 1997)