小球在空气阻力下弹跳实验的建模与仿真

使用Matlab/Simulink软件,建立了小球在空气阻力下反复弹跳的实验模型,讨论了小球在不同空气阻尼系数下的位移和速度,加深了学生对质点落体运动以及碰撞问题的认识。     

非磁性旋转导体盘阻尼效应的定量研究

应用法拉第电磁感应定律推导出非磁性旋转导体盘的转动衰减方程;定义并测量了导体盘的摩擦阻尼系数和电磁阻尼系数;分析研究了电磁阻尼系数与励磁电流平方间的关系.     

关于“电磁阻尼“教学的一点思考与探索

人教社2020版高中物理选择性必修二第二章第四节内容是“涡流、电磁阻尼和电磁驱动”,其中在“电磁阻尼”部分,教材中安排了做一做栏目.在备课的过程中,发现了问题,通过对问题的解决,经历了一次成功的科学探究过程.经过反思,觉得这是一个绝好的科学探究素材,于是在实际教学中尝试设计了一节基于电磁阻尼的实验探究课.这是一节基于实际问题解决的探究课,非常自然而真实,收到了很好的效果.     

斜塔实验与伽利略结论差异性的分析讨论

利用Matlab对比萨斜塔的真实落体实验进行模拟和数值计算,发现所得结果与伽利略的落体结论存在一定的差异性,并因此对亚里士多德落体定律和伽利略落体结论跟实验事实的统一性问题进行讨论。     

阻尼落体运动的分析力学研究

应用分析力学理论和方法,研究了两种情况下的阻尼落体运动:1)阻力大小与速度成正比;2)阻力大小与速度平方成正比.对两种运动分别给出了等效的Lagrange函数和Hamilton函数,并应用第一积分法、点变换法、正则变换法和Ham-ilton-Jacobi方程法等不同的求解方法进行了求解.     

用于绝对重力仪的落体旋转评估方法

介绍了一种自主搭建的测量落体在自由下落过程中旋转角速度的装置,评估了不同落体旋转角速度引入的旋转误差对重力测量的影响。针对具有旋转初速度的落体在真空腔内自由下落的运动模型,该装置采用光杠杆原理,将高精度位置传感器(PSD)作为光跟踪设备,研究并推导出落体由旋转所导致的反射光位移与下落时间的关系。然后,对PSD采集记录的时间位移曲线进行拟合,求解落体单次下落的旋转角速度值。在调整真空腔垂直度后,最大旋转角速度值可减小为16.88 mrad/s,引入的重力测值不确定度为0.57μGal,即该状态下落体的释放更加平稳。实验表明,该装置不仅可以进一步提升绝对重力仪中落体传动机构的装调精度,还可以对光学干涉绝对重力仪工作过程中的落体姿态进行监测,进一步降低落体旋转所引入的测量不确定度。     

落体偏东和空气阻力

通过在落体的动力学方程中引入空气阻力，研究空气阻力对落体偏东的影响．指出空气阻力将使落体的科里奥利向东偏斜增加，从而消除空气阻力将使落体偏东减小的误解．     

利用电磁阻尼单摆测量金属球的电导率

通过设计有无电磁阻尼作用的单摆实验,精确测定金属球的摆幅随时间的变化规律,拟合实验数据得到空气阻尼系数和电磁阻尼系数,采用对比法得出金属球的电导率.该实验可加深学生对单摆作为简谐振动理想模型的理解,也为研究梯度磁场中金属小球的电磁感应现象提供了新思路.     

受迫振动法研究压强变化对气体阻尼系数的影响

采用弹性摆受迫振动时幅频特性对阻尼的依赖关系为依据,借助非接触电磁激振装置和（AX1001）单片机,通过测量所得的幅频特性曲线算出相应的阻尼系数。在密闭的环境下,改变空气的压强得到相应数值下的空气阻尼系数,最终,给出空气阻尼系数与压强之间的关系。     

空气阻力对落体东偏的影响

利用Matlab软件,计算了空气阻力对落体东偏的影响并与无空气阻力时的结果进行比较.结果表明,空气阻力将使落体东偏的数值减小,从而纠正了空气阻力将使落体东偏增大的错误观点.     

垂直下落球体运动的数值分析

在考虑空气浮力和阻力情况下,对垂直下落物体运动进行了分析.通过数值计算的方法,对比萨斜塔铁球下落及雨滴下落两个运动进行了描述.     

落体法测量刚体转动惯量实验中引起测量值偏离的因素分析

测量并分析了落体法测量刚体转动惯量实验中拉绳与转轴的不垂直对刚体转动惯量测量值偏离的影响,得出了转动体系在阻力矩作用下的角加速度与转速的关系.该值偏离的测量与分析可作为刚体转动惯量实验的拓展性、创新性实验内容,有利于启发学生实验思维和培养学生实验创新意识.     

On the notion of a rotating fluid force induced by swirling flow

The Bently/Muszynska (B/M) model shows that oil whirl and oil whip are both self-sustained vibrations associated with two unstable modes of a rotor–fluid system. The model includes a rotating fluid damping and inertia force. In certain configurations, the rotating damping force overcomes the frictional internal damping of the rotor and pushes the rotor into a stable limit cycle of circular orbiting. Such a notion of a rotating fluid force is based on bulk-flow models of fluid-filled clearances that could be approximated as narrow since the tangential velocity of the fluid then translates to one angular velocity at a certain radial distance defined by an average radius. This paper scrutinizes the assumption of a rotating fluid inertia force and pinpoints the additional inertial effects of the swirling flow as the gap width increases. These effects are clarified by deriving the equation of motion of a body with a mass subjected to motion-induced fluid forces of a confined swirling flow. We show that the inertial effects of the swirling flow counteract the destabilizing effect of the rotating damping force. However, if the body mass is larger than the displaced fluid mass, instability follows. The frequency of the unstable mode is unchanged by the additional inertial effects and is always equal to the frequency of the damping that induces the instability.     

Viscoelastic analysis of multi-body systems using the finite element method

A study of the effect of viscoelastic material damping on the dynamic response of multibody systems, consisting of interconnected rigid, elastic and viscoelastic components, is presented. The motion of each elastic or viscoelastic body is identified by using three sets of modes: rigid body, reference and normal modes. Rigid body modes describe translation and large angular rotation of a body reference. Reference modes are the result of imposing the body-axis conditions. Normal modes define the deformation of the body relative to the body reference. Constraints between different components are formulated by using a set of non-linear algebraic equations that can be introduced to the dynamic formulation by using a Lagrange multiplier technique or can be utilized to eliminate dependent co-ordinates by partitioning the constraint Jacobian matrix. In developing the system equations of motion of the viscoelastic component, an assumption of a linear viscoelastic model is made. A Kelvin-Voigt model is employed, wherein the stress is assumed to be proportional to the strain and its time derivative. The formulation yields a constant damping matrix and the damping forces depend only on the local deformation; thus, no additional coupling between the reference and elastic co-ordinates appears in the formulation when considering the viscoelastic effects. It is demonstrated, by a numerical example, that the viscoelastic material damping can have a significant effect on the dynamic response of multibody systems.     

The eastward displacement of a freely falling body on the rotating Earth: Newton and Hooke's debate of 1679

In this article I would like to tell the story of the beginning of modern theoretical physics, freed from all kinds of questionable anecdotes which have entered the scientific literature over the centuries. It all began in the seventeenth century when the mathematical theory of astronomy began to take shape. A major step in the history of modern science was taken when a few members of The Royal Society in London realized that the laws ruling the motions of heavenly bodies as manifested in Kepler's three laws are also effective in the dynamics of Earth‐bound particle motion. Everything started, not with I. Newton, but with R. Hooke. Not Newton's falling apple (Voltaire's invention), but a far‐reaching response by R. Hooke to a letter by I. Newton, dated November 28, 1679, ignited Newton's interest in gravity. That letter contained the famous spiral which a falling body would follow when released from a certain height above the surface of the Earth. Hooke's answer, based on Keplerian orbits, expressed the opinion that the body's trajectory would rather follow an elliptical path. In his spiral sketch Newton, however, predicted correctly that the falling body would be found to suffer an eastward deviation from the vertical in consequence of the Earth's rotation. In the course of time, many a researcher, including Hooke himself, was able to verify this conjecture. But it took until 1803 for the first satisfactory calculation of the eastward displacement of a freely falling body to be performed, and was provided by C.F. Gauss.     

Bryan's effect and isotropic nonlinear damping

Bryan's effect is the phenomenon of the rotation of the vibration pattern within the body of a rotating, vibrating body. In this paper we generalise Rayleigh's dissipation function whereby we include isotropic, nonlinear damping in the Euler–Lagrange equations. We then derive the equations of motion of a slowly rotating, vibrating, symmetric body. In so doing we analyse the effect that such damping has on Bryan's effect. Using a combination of linear and nonlinear damping in the equations of motion of a slowly rotating symmetric body, a numerical experiment indicates that underdamping, critical damping and overdamping scenarios appear to exist. For the underdamped case we compare the effect on amplitude of vibration made by linear, quadratic and a combination of these types of damping. Our final result for light, isotropic, nonlinear damping, mimicks a known result for light, isotropic, linear damping, namely for a slowly rotating symmetric body, Bryan's effect is invariant and the rate of rotation of the damped pattern is the same as it would be for the pattern of an ideal slowly rotating symmetric body.     

改进的自由落体运动实验

通过2个光电门记录铁球通过的时间,利用Excel对实验数据进行分析处理,探究下落高度和时间的关系,从而得出自由落体运动是匀变速直线运动的结论.     

上海光源储存环主支撑减振研究

 上海光源是一台在建的第三代同步辐射光源,对束流轨道稳定性要求很高。由磁铁和支架组成的支撑组件的机械稳定性是影响束流轨道稳定性的重要因素。对主支撑组件样机的测试结果表明,其最低共振频率处放大倍数为50左右,超过要求5倍。因此,需要研究相应的减振措施。利用阻尼减振原理设计了一种约束阻尼结构。在样机上的测试结果表明,安装该装置后,支撑组件的共振放大倍数最大可以降低91.8%,对应的功率谱密度的峰值可以降低25 dB。因此,该装置可以用来增加支撑的稳定性。