"动量守恒"实验中落点的位置关系

笔者在讲授“验证动量守恒定律”实验时，不少学生提出以下两个问题：（1）为什么入射小球的质量m1一定要大于被碰小球的质量m2？（2）为什么M、P、N依次为碰后入射小球的落点、碰前入射小球的落点、以及当相碰后被碰小球的落点？对于第（1）问，我们通常是定性说明避免碰后入射小球反弹，显然学生对这样的解释是不满意的．对于第（2）问，     

竖直平面内“ 轻绳模型”的运动规律研究

利用理论研究与“ 仿真物理实验室”实验验证相结合的方法, 研究了竖直平面内的“ 轻绳模型”这一重 要的单轨道模型问题, 分析了小球速度、 加速度图像和规律, 研究得到了小球不能完成完整圆周运动的初速度条件; 小球做完整的竖直平面内圆周运动的初速度条件; 小球沿圆弧“ 轨道”返回的初速度条件; 小球离开圆弧“ 轨道”做 斜抛运动的最低点初速度条件以及斜抛运动的速度大小和方向; 阐述了小球从最低点水平方向出发经圆弧上某点 斜抛运动后能返回初始点的初速度条件; 并给出落点在最低点( 出发点)左右两侧侧圆弧上的初速度条件     

投影法和直接打点法研究平抛运动

高中物理第一册中“研究平抛物体的运动”的学生实验,采用有孔的纸卡片找小球的落点.在教学中我们觉得,该方法费时问,描出的抛物线也往往不是一条平滑曲线.因此,我们现在采用如下所示两种方法.     

集成霍尔开关传感器测量非透明液体的黏度

针对落球法无法测量非透明液体的黏滞系数的问题,改进了实验中测量小球下落时间t的方法.该方法的测量电路由多片高灵敏度的集成开关式霍尔传感器、指示LED灯、与门逻辑芯片和计时器等顺序组成.电路板A和B上的信号分别驱动计时器开始和停止计时,最后计时器显示出磁性小球下落一定距离所用的时间t.该测量方法直观方便,并且具有比较高的测量精度.     

关于研究平抛物体运动实验的改进

贵刊在2004年第2期的“实验改进与创新”栏目中刊有《改进用斜槽做的两个力学实验》一文，笔者读罢，深受启发，很是赞同吴文炎老师利用这一装置研究平抛物体运动的实验．但就这一装置中利用带孔的硬纸片来确定小球通过的任何位置的设计，笔者做些改进．因为利用带孔的硬纸片确定小球通过的任意位置，不仅需要反复多次的移动硬纸片来寻找落点，而且小球落到硬纸片上常常反弹不能落入设计的槽中，从而导致实验者满地找球，既费时又费事．笔者现将自己在实际教学中设计的简易装置介绍如下，希望能和贵刊的广大读者共同切     

利用Scratch软件实现落球法测量液体粘滞系数实验的仿真

利用Scratch软件实现了对"落球法测量液体粘滞系数"实验的演示与仿真,对实验中小球从静止下落过渡到匀速运动状态这一较复杂的微小变化过程进行了完整演示,同时给出了小球运动速度、位移随时间变化的图像,加深了学生对实验内容的理解。     

验证动量守恒定律实验的探究

1问题的引出验证"碰撞中的动量守恒"实验课的分组实验中,一位学生发现了问题:如图1所示中,在等位板处释放小球a,去碰撞放在水平轨道的另外一个完全相同的小球b时,不能出现小球a静止,小球b获     

浅谈“离心浮力”参与作用下小球的运动

流体在做匀速旋转运动时会产生与静止状态不同的动力学效应,主要体现在液体内部的压强变化以及由此带来的附加浮力,可形象地称之为"离心浮力".本文就V形管惯性离心力演示仪中的小球运动问题进行深入讨论,通过求解曲面积分求得小球所受"离心浮力"公式,进而求出小球的运动方程,并对实验中出现的现象进行定量分析解释.     

低黏度透明液体黏滞系数测量实验的研究

研究小球在低黏度透明黏性液体中以初速度为零状态下落的加速运动过程, 通过分析小球在加速下 落过程中下落速度与对应时间的关系而得到液体的黏滞系数值. 新方法改进了原变速落球法研究拟合小球下落位 移与对应时间得到黏滞系数的实验方法. 实验结果表明, 新方法提高了实验的稳定性和拟合的准确度     

用智能手机App Video Physics研究竖直平面内的圆周运动

本实验用智能手机App Video Physics追踪小球在竖直平面内做圆周运动的情况,研究了不同质量的小球从同一高度静止释放到达最低点的速度关系,研究了从不同高度静止释放小球的速度与运动轨迹之间的关系,计算了小球在圆形轨道上运动时的向心力、角速度,以及当小球与圆形轨道等高静止释放时小球的脱离点速度.     

Passive adaptive control of chaos in synchronous reluctance motor

The performance of synchronous reluctance motor (SynRM) degrades due to chaos when its systemic parameters fall into a certain area. To control the undesirable chaos in SynRM, a passive control law is presented in this paper, which transforms the chaotic SynRM into an equivalent passive system. It is proved that the equivalent system can be asymptotically stabilized at the set equilibrium point, namely, chaos in SynRM can be controlled. Moreover, in order to eliminate the influence of undeterministic parameters, an adaptive law is introduced into the designed controller. Computer simulation results show that the proposed controller is very effective and robust against the uncertainties in systemic parameters. The present study may help to maintain the secure operation of industrial servo drive system.     

Passive adaptive control of chaos in synchronous reluctance motor

The performance of synchronous reluctance motor （SynRM） degrades due to chaos when its systemic parameters fall into a certain area. To control the undesirable chaos in SynRM, a passive control law is presented in this paper, which transforms the chaotic SynRM into an equivalent passive system. It is proved that the equivalent system can be asymptotically stabilized at the set equilibrium point, namely, chaos in SynRM can be controlled. Moreover, in order to eliminate the influence of undeterministic parameters, an adaptive law is introduced into the designed controller. Computer simulation results show that the proposed controller is very effective and robust against the uncertainties in systemic parameters. The present study may help to maintain the secure operation of industrial servo drive system.     

电磁脉冲弹对相控阵雷达毁伤能力的仿真研究

在建立电磁脉冲弹和相控阵雷达天线阵面弹目关系数学模型的基础上,对电磁脉冲弹使用过程中涉及到的天线阵面覆盖率等问题进行了研究,分析了弹道偏差等因素对天线阵面毁伤区域的影响,并进行了仿真计算。仿真结果分析表明,弹头引爆高度、落点精度等弹道参数对毁伤覆盖区域均会产生影响。为实现对目标的最佳毁伤效果,应综合考虑弹头引爆高度、弹道倾角、滚转角等参数精度,以及目标处功率密度等要求。     

超导隧道结中的电流相位关系

计算了等自旋配对超导隧道结中的直流Josephson电流.结果表明,当两侧超导体中配对势的轨道对称性分别属于磁点群D₄的A不可约表示和 ²E不可约表示的情况下,电流相位关系是I∝sin4φ. 关键词： 超导隧道结 Josephson电流     

Time-dependent Benioff strain release diagrams

New time-dependent Benioff strain (TDBS) release diagrams were analyzed for acoustic emission during various loading tests and for electromagnetic (EM) radiation emanating during compression and, tension, which end in failure. TDBS diagrams are Benioff diagrams that are built consecutively, each time using a greater number of events (acoustic or EM emissions) using the last event as if it were associated with the ‘actual failure’. An examination of such TDBS diagrams shows that at a certain time point (this time point is denoted by the term ‘alarm’ time), a comparatively short interval prior to actual collapse, their decreasing part is broken by a positive ‘bulge’. This ‘bulge’ is quantified and an algorithm proposed for its assessment. Using the alarm time and other parameters of the failure process (fall, bulge size and escalation factors, bulge slope and slope fall time), a criterion for estimating the time of the actual collapse is developed and shown to agree well with laboratory experimental results.     

Multiaperture telecentric lens for 3D reconstruction

We present a telecentric lens that is able to gain 3D information. The proposed lens system has multiple aperture stops, which enable it to capture multidirectional parallel light rays, while a conventional telecentric lens has only one aperture stop and can capture only light rays that are perpendicular to the lens. We explain the geometry of the multiaperture telecentric system and show that correspondences fall on a line like those in a conventional stereo. As it is a single-lens sensor, we also introduce the principles of 3D reconstruction. Unlike a conventional stereo camera, the disparity of a scene point measured by the proposed lens system is linearly proportional to the depth of a scene point.     

Deformation hardening and temperature dependence of mechanical properties in ternary ordered alloys based on Ni3Fe I

The variation of hardening factor and resistance to deformation with the quenching and testing temperatures for ordered alloys based on Ni₃Fe was investigated. It was shown that the yield point _0.2 and flow stresses are independent of the quenching temperature right up to about 450 ° C. At higher quenching temperatures there are increases in _0.2 and in the flow stresses corresponding to small degrees of deformation ( < 10%); the highest mechanical properties are found when the quenching temperature is near the Curie point. In quenching from a temperature above the Curie point the mechanical properties and hardening factor fall suddenly to values corresponding to the disordered state of the alloys. The temperature variation of _0.2 is similar to that mentioned above. The deformation stress at high values and the hardening factor decrease with increase in testing temperature, and below the Curie point they reach values corresponding to the disordered state. The temperature variation of mechanical properties for specimens in which the formation of long-range order is suppressed by special treatment is characterized by the absence of substantial change near the Curie point. The results obtained are discussed in relation to modern dislocation theories of hardening of alloys with long-range order.     

Quantum cosmology and conformal invariance

According to Belinsky, Khalatnikov, and Lifshitz, gravity near a spacelike singularity reduces to a set of decoupled one-dimensional mechanical models at each point in space. We point out that these models fall into a class of conformal mechanical models first introduced by de Alfaro, Fubini, and Furlan (DFF). The deformation used by DFF to render the spectrum discrete corresponds to a negative cosmological constant. The wave function of the Universe is the zero-energy eigenmode of the Hamiltonian, or the spherical vector of the representation of the conformal group SO(1,2). A new class of conformal quantum mechanical models with enhanced ADE symmetry is constructed, based on the quantization of nilpotent coadjoint orbits.     

Topics in surface structure and crystal growth

Crystal growth occurs following widely different modes; in particular the transition from layer-by-layer to continuous growth, and the transition from stable to dendritic growth have attracted much theoretical attention. The former transition (corresponding, for equilibrium surfaces, to the roughening transition) is considered from the point of view of atom-surface scattering used as a tool to probe the state of the surface, and the effects of roughness on the height, width and shape of the incoherent peaks are studied. As an approach to the latter transition, simulations of cluster growth are considered where dendritic shapes are obtained by letting “atoms” fall along random straight trajectories from a “vapour” onto the growing cluster. Two geometries are considered: either the “atoms” fall along the cords from an outer large circle, or they fall obliquely on to a line from points of a parallel line. In both cases ramified structures are obtained, although less open that from diffusion-limited aggregation (DLA), and their fractal nature is studied.