滚动实验的另一种演示

介绍了另一种滚动演示实验,并对演示结果进行了理论分析和解释     

几种演示影响刚体滚动因素的物理实验仪

改进和研制了几种演示刚体平面平行运动(滚动)的物理实验仪,突出演示了转动惯量、滚动半径、刚体质量等因素对运动的影响．仪器结构简单,构思巧妙,演示效果良好．     

质心运动定理演示实验

质心运动定理∑F=ma是刚体力学中的一个基本规律,是教学重点之一.为使学生理解质心运动定理及由此导出的结论,我们设计了下面的演示实验,验证静止刚体受力偶的作用时,刚体绕质心转动,而不是绕力偶中心转动.     

改进一个演示实验

九年义务教育三年制初中三年级物理教科书中，有关于“并联电路干路中的电流等于各支路中的电流之和”的演示实验，如图1所示．     

用注射器做的几个演示实验

用演示实验在给学生表明各种现象时,比口头叙述更直观、更清楚、更明确、更易于理解和记忆.但是由于目前许多乡镇中学仪器设备不足,使一些演示实验不能进行.由于注射器是一个既透明又透热的"气缸活塞"装置,用来演示各种现象便于观察;内部空腔的体积、压强、温度便于调节;可吸气也可排气.     

角动量的物理图象

根据角运量的定义，结合图形、分析和讨论角动量计算中各项以及各量的深刻意义，建立角动量的物理图象，明确对点的角动量和对轴的角动量的关系。     

“曲线运动”的速度方向演示实验缺陷及改进

曲线运动的速度方向是高一物理"曲线运动"一节的教学难点,教材试图通过"砂轮"和"转伞"的实例加以说明.可是很多学生没见过用砂轮磨刀具时形成的火星是何形状,课堂上演示此实验,既不现实,也不安全.     

刚体转动实验新测量方法的研究

本实验是用转动惯量实验仪和电脑计时、计速仪来测量数据，用转动定律和平行移动轴定理推导新的线性方程，再用方程中的自变量和变量关系进行画图，成一条斜直线，从而间接地验证了转动定律和平行移轴定理成立，计算出转动惯量的大小。这种测量方法可达到国内较高的测量水平。与原来的测量方法相比，可消除较大部分系统误差和偶然误差，使数据接近真值，测量方便，重复性好，节省时间，效率高，可实现设备资源共享，可以解决实际问题。     

利用J2432交流电特性演示仪做自感演示实验

利用J2432演示仪和指针式演示电表演示了自感过程中电感的电流与电压的相位关系。     

Rolling Friction

Doklady Physics - The dependence of rolling friction on velocity for various contact conditions is discussed. The principal difference between rolling and other types of relative motion (sliding...     

阿基米德实验和电磁振荡实验的改进

利用简易装置对阿基米德实验和电磁振荡实验进行了改进．     

声学小实验

取1支大试管,配上合适胶塞,在胶塞下悬挂1个蜂鸣器(可用生日贺卡上的音乐 IC片及蜂鸣器),联接好电源,待用. 实验时,先向试管中注入少量水,然后加热试管中的水. 此时不要盖紧胶塞,待水沸腾,水蒸气充满容器,空气大部分被排出大试管后,小心盖紧胶塞. 这时能清楚听见蜂鸣器的音乐声,停止加热后声音逐渐减弱,至水冷却后该声音听不见. 这是由于试管内水蒸气冷凝后使试管内接近真空状态,所以几乎听不见蜂鸣器的响声,从而说明声音的传播需要以空气等物质为媒质,在真空中不能传播.图1　实验装置图声学小实验@陈少康$珠海市第二中学!广东珠海5190…     

"三明治"靶型在间接驱动冲击波实验中的应用

间接驱动方式具有提供更高冲击波压力的潜力,对冲击波物理研究来说是一种很好的驱动方式.针对间接驱动下X射线离化对透明窗口造成的致盲问题,提出了新的"三明治"靶型结构,以完成间接驱动下冲击波实验.该靶型可以用两种方法避免致盲效应对实验的干扰.一种方法是从时间上避开致盲效应,使致盲效应与冲击波测量区错开,从而获得冲击波数据.另一种方法是从强度上屏蔽X射线,将X射线阻挡在透明材料之前,使其不能产生致盲效应.对单冲击实验而言,用增加烧蚀层厚度的方法,将X射线离化效应与冲击波信号从时间上错开,获得了蓝宝石和石英晶体中冲击波实验的结果.用增加阻挡层的方法,获得了间接驱动条件下石英晶体和聚苯乙烯材料中的冲击波实验结果.提出的"三明治"靶型,为间接驱动条件下状态方程和冲击波调速技术提供了技术支持. 关键词： 冲击波 光学诊断 离化效应 干涉仪     

浅谈滚动摩擦

详细地分析了阻碍滚动体向前滚动的原因及滚动摩擦力偶矩产生的机理，解释日常生活中有关滚动摩擦的一些问题．     

Twistor Space for Rolling Bodies

On a natural circle bundle ${\mathbb{T}(M)}$ over a 4-dimensional manifold M equipped with a split signature metric g, whose fibers are real totally null selfdual 2-planes, we consider a tautological rank 2 distribution ${\mathcal{D}}$ obtained by lifting each totally null plane horizontally to its point in the fiber. Over the open set where g is not antiselfdual, the distribution ${\mathcal{D}}$ is (2,3,5) in ${\mathbb{T}(M)}$ . We show that if M is a Cartesian product of two Riemann surfaces (Σ ₁, g ₁) and (Σ ₂, g ₂), and if ${g = g_{1} \oplus (-g_2)}$ , then the circle bundle ${\mathbb{T}(\Sigma_1 \times \Sigma_2)}$ is just the configuration space for the physical system of two surfaces Σ ₁ and Σ ₂ rolling on each other. The condition for the two surfaces to roll on each other ‘without slipping or twisting’ identifies the restricted velocity space for such a system with the tautological distribution ${\mathcal{D}}$ on ${\mathbb{T}(\Sigma_1 \times \Sigma_2)}$ . We call ${\mathbb{T}(\Sigma_1 \times \Sigma_2)}$ the twistor space, and ${\mathcal{D}}$ the twistor distribution for the rolling surfaces. Among others we address the following question: “For which pairs of surfaces does the restricted velocity distribution (which we identify with the twistor distribution ${\mathcal{D}}$ ) have the simple Lie group G ₂ as the group of its symmetries?” Apart from the well known situation when the surfaces Σ ₁ and Σ ₂ have constant curvatures whose ratio is 1:9, we unexpectedly find three different types of surfaces that when rolling ‘without slipping or twisting’ on a plane, have ${\mathcal{D}}$ with the symmetry group G ₂. Although we have found the differential equations for the curvatures of Σ ₁ and Σ ₂ that gives ${\mathcal{D}}$ with G ₂ symmetry, we are unable to solve them in full generality so far.     

F-theory and experiment

There is currently a wide gulf between string theory and experiment. This is compounded by the existence of a ‘landscape’ of solutions to the string theory equations of motion, many of which are in gross violation of experimental constraints. To make contact with experiment, it is then necessary to impose some additional criteria to find potentially realistic solutions. In this article we show that requiring that the forces of the Standard Model unify, while remaining decoupled from gravity, imposes sharp restrictions. A promising class of string based models which meet both these criteria are known as F-theory GUTs. We review the main ingredients of these constructions, and how they make contact with experiment.     

Negative theta-pinch experiment

Plasma temperature obtained with a negative theta-pinch experiment is somewhat lower than that with an ordinary thete-pinch. This is consistent with a numerical calculation assuming Sagdeev resistivity.