谈自制教具的材料

利用生活中的易得材料和废弃材料，通过简单的加工，设计制作出一些教具．通过这些实例，说明了自制教具的可行性．     

非均匀弦的驻波实验

用自制的线密度为ρ（ｘ）＝ａｘ形式的非均匀弦进行驻波实验，取得较好效果，它可以作为对原有的均匀弦驻波实验的改进或开放性实验安排到普物实验中去。     

一种磁场优化结构电磁超声传感器设计*

为了进一步增强电磁超声检测技术在管道厚度测量领域的检测能力,该文对电磁超声传感器(EMAT)的结构进行了优化。提出了多磁铁对称分布型EMAT,能实现更小的磁铁体积,产生更强的表面剩磁强度。采用在硅钢表面开槽的方式限制涡流形成的区域,解决了涡流对测量的影响。建立厚度测量实验系统,对比出单磁铁型与多磁铁对称分布型EMAT在不同提离距离上检测信号的变化规律。结果表明,多磁铁对称分布型结构可通过增强EMAT的偏置磁场达到信噪比更优的效果。采用耐高温探头外壳和钐钴磁铁,提高了EMAT探头在高温环境下的检测性能。     

探究电磁驱动现象组合教具的研发与自制

高中物理<选修3-2>第四章电磁感应第七节讲到电磁驱动:当磁场以某种方式运动时,导体中的安培力阻碍导体与磁场间的相对运动.本人通过对比法、实验法,用轴承制作旋转的磁场,用强磁铁代替U型磁铁,用易拉罐做不同形状不同厚度的铝框,在摸索中自制了探究电磁驱动现象的组合教具,它具有现象明显、直观、物美价廉的优点.     

重力对弦振动特征频率的影响

本文从非均匀弦波动方程出发探讨重力对弦振 动特征频率的影响．讨论了两种不同边界条件下竖直 均质弦驻波特征频率与其重量之间的关系，给出了在 弦重量远小于其张力时两端固定的竖直均质弦驻波特 征频率修正项的解析表达式．     

自制教具在中学物理教学中的必要性

在新课程理念下,利用生活中常见的材料和器具自制成教具进行中学物理实验教学,能激起学生的学习兴趣,培养学生的主动性、创新意识和动手实践能力.因此,研究自制教具在中学物理教学中的应用非常重要.本文对新课程背景下对实验器材的创新要求进行了分析,深入探讨了自制教具在中学物理教学中的必要性及自制教具对物理教学的作用,并列举了自制教具的案例,说明自制教具在中学物理教学中的作用.     

弦振动实验装置的改进

弦振动实验装置的改进郑稷（重庆师范专科学校６３２１６８）弦振动实验是力学实验中一个重要而典型的实验．该实验的主要内容是研究弦振动的基频与弦长（其他条件不变）和基频与张力（其他条件不变）的关系．实验方法有两种：（１）采用振动频率固定的振动体，通过改变弦...     

小制作 大用途

在通用技术教学中,我们教师可以自制一些小教具来辅助教学。虽然很多教具都是简单的小制作,但只要有创意,能切合教学实际,它们就能有大用途。其作用主要表现为以下几点:1.自制教具可以让课堂教学更轻松;2.自制教具能有效激发学生学习兴趣;3.自制教具能促进教师的成长;4.学生自制教具可以提高学生的动手能力和创新能力。本文通过一些作者教学中制作的实例来阐述以上观点。     

自制教具在实际运用中的效果反思

结合自制的一些教具,展示了自制教具在教学中所取得的效果     

自制教具系列化 — — — 以食盐水为核心的教具及实验开发

自制教具在物理教学过程中具有重要的作用, 但自制教具也存在着一些困难. 通过以食盐水为例, 阐 述以某一核心资源进行自制教具系列化和实验开发的一些参考路径     

Vibration of a string wrapping and unwrapping around an obstacle

The problem of a string vibrating against a smooth obstacle is investigated in this paper. The obstacle is located at one of the boundaries and the string is assumed to wrap and unwrap around the obstacle during vibration. The wrapping of the obstacle is modeled by a series of perfectly inelastic collisions between the obstacle and adjacent segments of the string and unwrapping is assumed to be energy conserving. The geometry of the string is determined iteratively starting from an initial configuration where the string is vibrating in a single mode and is not in contact with the obstacle. The obstacle can be regarded as a passive mechanism for vibration suppression in which the energy lost during each cycle of oscillation depends on the energy content of the string at the beginning of the cycle. Numerical simulation results are provided for the string vibrating in different modes for circular- and elliptic-shaped obstacles. The loss of energy is found to be greater for higher modes of oscillation and for obstacles that induce greater length of wrapping.     

对FD-DB-Ⅱ型单摆实验仪功能的拓展

通过对FD-DB-Ⅱ型单摆实验仪的研究,对该装置作了改进,增加了可计算振幅的刻度板,并使用电磁铁控制摆球的释放,由此可以研究周期T和角振幅θ0的关系,也可利用T-(sinθ0/2)~2 曲线外推后计算重力加速度g.     

电磁控制陀螺转子进动角速度的计算

分析了现代激光制导武器中陀螺稳定光学系统式位标器的两种进动控制方式———受控磁环轴向充磁与控制线圈径向布置和受控磁饼径向充磁与控制线圈轴向布置。由现代电磁场理论 ,磁体在磁场中的受力及进动理论 ,分别推导出了它们的进动角速度的计算公式 ,并进行了第一种进动控制方式的计算机模拟计算 ,结果与实际相符     

A novel multimode negative inductance negative resistance shunted electromagnetic damping and its application on a cantilever plate

Based on the characteristic of the electromagnetic damping, a novel multimode vibration control treatment, negative inductance negative resistance electromagnetic shunt damping (NINR-EMSD), is proposed and employed to control multimode vibration of a cantilever plate. The negative inductance of the shunt impedance can cancel the inherent inductance of the electromagnet, and the impedance of circuit consisted of the coils and shunt will be a pure resistance and the shunt current will be frequency independent when the inductance of the shunt and the electromagnet are equal with each other. The negative resistance cancels the resistance of electromagnet, and as a result the resistance and the current of the closed circuit will change, which make it feasible to control the multimode vibration of the system. Electromechanical coupling coefficient is obtained based on the equivalent current method. The governing equation of the plate with the electromagnetic shunt damping (EMSD) is established according to Hamilton's principle. Multimode vibration control of the system is simulated and experiments are carried out to verify the performance of the NINR-EMSD. The numerical predictions and experimental results agree well with each other and show that: the negative inductance negative resistance (NINR) of the shunt impedance can increase the damping of the structure notably; the decrease of the resistance of shunt impedance have a significant contribution to the improvement of vibration control performance; the first four modes vibration of the plate can be suppressed simultaneously with the NINR-EMSD.     

The violin: Chladni patterns,plates, shells and sounds

In this article we consider the vibrations and radiated sound of the bowed violin. The vibrations are discussed in terms of the normal modes of the instrument involving the coupled vibrations of the bowed string, the supporting bridge, the hollow shell comprising the body of the instrument and, ultimately, the acoustic modes of the performance space in which the instrument is played. We show that damping plays an important role in characterizing the normal modes in what can be distinguished as weak and strong coupling limits. The historic and modern application of Chladni pattern measurements to enhance our understanding of the acoustics and as an aid to the making of violins is highlighted, alongside the modern equivalents of experimental modal and computational finite-element analysis. The symmetry-breaking properties of the internal soundpost is shown to have a profound affect on the intensity and quality of sound radiated by the bowed instrument.     

Optimizing parametric oscillators with tunable boundary conditions

Parametric excitation or pumping is an effective method to create large oscillations by periodically altering a physical parameter of the governing dynamics. Precisely tuned pumping frequencies can lead to exponentially growing oscillations limited only by nonlinear effects like axial stretching of transversely vibrating string. It is demonstrated that a tuned passive dynamical system amplifies the otherwise limited transverse vibrations amplitudes of a nonlinear string considerably and thus increasing the selectivity of the system. This effect becomes more noticeable for shorter wavelengths where nonlinear stretching limits the obtainable vibration amplitudes severely. The present work analyses a passive dynamical system connected to one end of a taught string which parametrically couples its axial motion to transverse vibration. Analysis shows that a specific selection of parameters can reduce the limiting effect of nonlinear stretching thus allowing one to excite high-order modes with small external forces. The result can possibly affect other disciplines where effective parametric amplification is necessary.     

The string of variable density: Perturbative and non-perturbative results

We obtain systematic approximations for the modes of vibration of a string of variable density, which is held fixed at its ends. These approximations are obtained iteratively applying three theorems which are proved in the paper and which hold regardless of the inhomogeneity of the string. Working on specific examples we obtain very accurate approximations which are compared both with the results of WKB method and with the numerical results obtained with a collocation approach. Finally, we show that the asymptotic behaviour of the energies of the string obtained with perturbation theory, worked to second order in the inhomogeneities, agrees with that obtained with the WKB method and implies a different functional dependence on the density that in two and higher dimensions.     

Frequency upshifting by an ionization front in a magnetized plasma

The interaction of a light wave with a relativistic ionization front in the presence of an applied DC magnetic field which is perpendicular or parallel to the incident wave is considered. In both cases, four transmitted modes are generated in the magnetized plasma by an incident linearly polarized wave. The frequency upshifts of the various modes are calculated and compared to the unmagnetized case. The corresponding reflection and transmission coefficients are also obtained. Finally, the density ripple associated with the free streaming mode in a magnetized plasma for the perpendicular case is discussed     

The vibration of a rotating circular string subject to a fixed elastic restraint

The natural frequencies of a rotating circular string, subject to a fixed elastic restraint, are calculated. This simple system is important because its dynamic behavior has most of the characteristics of more complex rotating systems. The variation of the natural frequencies with change in rotation speed and spring constant is examined. The results show “avoided crossing”, a characteristics of eigenvalue problems where there is coupling between modes. When the string is rotating, the vibration is harmonic, but it does not have a uniform phase at all points in space. At particular rotation speeds, standing waves are formed which have stationary nodal points. The phase within these standing waves is also non-uniform, except when the string is stationary. The critical rotation speed, at which all the natural frequencies degenerate to zero, is independent of spring stiffness.     

Normal modes of a model radiating system

In order to gain insight into normal modes of realistic radiating systems, we study the simple model problem of a finite string and a semi-infinite string coupled by a spring. As expected there is a family of modes which are basically the modes of the finite string slowly damped by the radiation of energy to infinity on the semi-infinite string. But we also study another family of modes, found by Dyson in a different model problem, which are strongly damped modes of the semi-infinite string itself. These may be analogous to the modes of black holes, and they are likely to be present in relativistic stars as well. The question of whether the instability in these modes which Dyson found is present in realistic stars remains open.