小球与轴线位置可变定轴杆垂直碰撞

文章讨论了小球与轴线可以变化的定轴均质细杆在杆上任一点垂直碰撞的问题,并对有关碰撞的结果进行了分析讨论。     

非光滑小球的完全弹性斜碰

本文根据动量守恒定律和恢复系数定义,分析计算了非光滑小球完全弹性斜碰后的运动,研究了滑动摩擦力在小球斜碰中的作用及对小球碰撞后运动的影响.     

例析一道物理竞赛题

原题:(2005年第22届全国中学生物理竞赛预赛题试卷)如图1所示,一根长为l的细刚性轻杆的两端分别连结小球a和b,它们的质量分别为ma和mb.杆可绕距a球为14l处的水平定轴O在竖直平面内转动,初始时杆处于竖直位置.小球b几乎接触桌面.在杆的右边水平桌面上,紧挨着细杆放着一个质量为m     

对一道习题的深入思考

<正>一次,在课堂中老师曾经讲过一道习题,内容如下:在竖直向下的匀强电场中,有一轻质细杆,在该轻质细杆的两端各固定一质量为m的小球A、B,A球带电量为-q,B球带电量为+q,在该轻质细杆的中点处有一固定转动轴,如图1所示。将球由水平位置静止释放后,求小球的速度最大时该轻质细杆对轴的作用力。当时,老师对此题的分析与解答步骤如下:     

07年高考物理实验题创新视点

一、实验目的创新 例1 碰撞的恢复系统的定义为e= ｜v2-v1｜/｜v20-v10｜,其中v10和v20分别是碰撞前两物质的速度,v1和v2分别是碰撞前两物体的速度．弹性碰撞的恢复系数e=1．非弹性碰撞的e〈1,某同学借用验证动量守恒定律的实验装置（如图所示）验证弹性碰撞的恢复系数是否为1,实验中使用半径相等的钢质小球1和2,[第一段]     

叠加消项,化变为恒(高二、高三)

例1 如图1所示,同一竖直平面内固定着两根水平绝缘细杆AB、CD,长均为L,两杆的竖直距离为h,两杆在B、D两端与光滑绝缘的半圆形细杆相切,O为AD、BC连线的交点.在O点固定一电量为Q的正电荷,质量为m的小球P带正电,电量为q,穿在细杆上,从A以一定的初速度出发,沿杆滑动,最后可到达C点.已知小球与两水平杆之间的动摩擦因数为μ,小球所受的库仑力始终小于重力.求: (1)P在水平细杆上滑动时所受摩擦力的极大     

从一道习题谈力电综合习题的教学

例题 如图1所示将一质量为m电荷量为＋q的小球固定在绝缘杆的一端，杆的另一端可绕通过O点的固定轴转动，杆长为L，杆的质量忽略不计，杆和小球置于场强为E的匀强电场中，电场的方向如图（1）所示，将杆拉至水平位置OA，并在此处将小球自由释放，求杆运动到竖直位置OB时小球的动能？     

小球平衡的物理机制

本文分析了固连于细杆一端的小球平衡条件,比较了小球的质点模型与刚体模型相应的受力状态,应用杆的弯曲弹性模型解释杆与球间的力矩作用,由此说明采用恰当的模型对解决问题所具有的重要意义。     

一道高考题的运动学特征

题 如图1所示,质量M=2kg的滑块套在光滑的水平轨道上,质量m=1kg的小球通过长L=0．5m的轻质细杆与滑块上的光滑轴O连接,小球和轻杆可在竖直平面内绕O轴自由转动,开始轻杆处于水平状态,     

电场力做功的几种计算方法

电荷q在电场中运动时,电场力所做的功只取决于始末位置而与路径无关,所以计算电场力做功可有多种方法.1.根据功的定义W=FScosθ计算.例1带电量分别为+q和-q的小球,固定在长度为l的绝缘细杆的两端,置于电场强度为E的匀强电场中,杆与场强方向平行,如图1所示,若细杆绕中心O垂直于杆的方向转过180°,则转动过程中电场力做的功为     

Firmness measurement of peach by impact force response

The impact force response of a peach impacting on a metal flat-surface was considered as nondestructive determination of firmness. The objectives were to analyze the effect of firmness, drop height, fruit mass, and impact orientation on the impact force parameters, and to establish a relationship between the impact force parameter and firmness. The effect of fruit firmness, drop height and fruit mass on the impact force parameters (coefficient of restitution, percentage of energy absorbed, and coefficient of force-time) was evaluated. The study found that the coefficient of restitution, percentage of energy absorbed, and force-time impact coefficient were significantly affected by fruit ripeness, but not affected by drop height, impact position (fruit cheek), and mass. The percentage of absorbed energy increased with ripeness, while the force-time impact coefficient and coefficient of restitution decreased with ripeness. Relationships were obtained between the three impact characteristic parameters (force-time impact coefficient, coefficient of restitution, and percentage of energy absorbed) and peach firmness using a polynomial model (R~2=0.932), S model (R~2=0.910), and exponential model (R~2=0.941), respectively.     

Equivalent Kelvin Impact Model for Seismic Pounding Analysis of Bridges

Based on Hertz contact theory, a method to determine the parameters of Kelvin impact model for seismic pounding analysis of bridges is proposed. The impact stiffness of Kelvin model is determined by the ratio of maximum impact force to maximum contact deformation, which is calculated based on Hertz contact theory with considering the vibration effect. The restitution coefficient which has great influence on the damping coefficient of Kelvin impact model is investigated by numerical analysis. Numerical results indicate that the impact stiffness of Kelvin impact model increases with the increment of the Hertz contact stiffness, approaching velocity or the length ratio of short to long girders. Vibration effect has remarkable influence on the impact stiffness and cannot be neglected. The restitution coefficient decreases when approaching velocity increases or the length ratio of short girder to long girder decreasing. The practical ranges of impact stiffness and restitution coefficient are obtained as 3×108-6×108 N/m and 0.6-0.95 respectively.     

Bearing capacity of composite columns reinforced by concrete filled steel tube

In this study, nine simplified short composite columns consisting of core CFST (concrete filled steel tube) of different diameters and outer reinforced concrete were constructed to study their compressive performance under axial or eccentric compression. The failure mode is characterized by the crush of the outer concrete. The bearing capacity increases at first and then decreases with further increase of the position coefficient. It can be concluded that position coefficient is an important structural parameter that has considerable influences on the ultimate bearing capacity of the composite columns. The outer concrete, steel tubes and longitudinal reinforcement are found to work in a cooperative manner under axial or eccentric compression when the position coefficient is about 0.5. An improved bearing capacity algorithm that takes the position coefficient into account has been proposed based on the experimental and simulation results and current technical specification in China. It has been proven to be precise and safe.     

西方文化对大学生职业观形成的影响研究

高校是东西方文化互相交流、碰撞、融合的主阵地。围绕西方文化对大学生职业观形成的影响问题,辩证阐述了西方文化对大学生职业观形成的积极影响和消极影响,并就引导大学生正确看待西方文化、树立正确的职业观提出了对策建议。     

The action researcher as tempered radical and strategic entrepreneur in higher education: a personal reflection

This article describes the discovery of action research by a ‘conscious incompetent’ in higher education. The influences on the development of an action researcher’s individual philosophy are discussed. These shape a specific investigation into the implementation of international staff exchange in a post-1992 UK university from the position of an ‘outsider within’, a tempered radical. Ontological and epistemological concepts of quasi-objectivity, subjectivity, participation and commitment are discussed in relation to entrepreneurship in the higher education context, concluding that action research is a methodology suitable for tempered radicals and strategic entrepreneurs and that the action researcher can play these roles to research the execution of international faculty mobility in higher education.     

Pyrolysis model of single biomass pellet in downdraft gasifier

By coupling the heat transfer equation with semi-global chemical reaction kinetic equations, a onedimensional, unsteady mathematical model is developed to describe the pyrolysis of single biomass pellet in the pyrolysis zone of downdraft gasifier. The simulation results in inert atmosphere and pyrolysis zone agree well with the published experimental results. The pyrolysis of biomass pellets in pyrolysis zone is investigated, and the results show that the estimated convective heat transfer coefficient and emissivity coefficient are suitable. The mean pyrolysis time is 15.22%, shorter than that in inert atmosphere, and the pellet pyrolysis process in pyrolysis zone belongs to fast pyrolysis. Among the pyrolysis products, tar yield is the most, gas the second, and char the least. During pyrolysis, the temperature change near the center is contrary to that near the surface. Pyrolysis gradually moves inwards layer by layer. With the increase of pyrolysis temperature and pellet diameter, the total pyrolysis time, tar yield, char yield and gas yield change in different ways. The height of pyrolysis zone is calculated to be 1.51—3.51 times of the characteristic pellet diameter.     

一维复杂颗粒气体的速度分布特性

利用蒙特卡罗方法,采用计算机模拟研究粒径呈连续分布的一维颗粒气体在均匀加热机制下的速度分布特性。研究表明颗粒气体的速度分布不再遵从高斯分布。系统的颗粒速度分布偏离高斯分布的程度及各个组分之间颗粒速度分布的差异程度受到颗粒的非弹性恢复系数及粒子粒径分布宽度的影响。     

Numerical Simulations of Pile Supported Protective System Subjected to Ship Impact

The head-on collision process between ship and concrete pile supported protective system is simulated by software LS-DYNA. The influences of pile non-linearity and soil non-linearity on impact force, ship crush depth and the cap displacement of pile supported protective system are discussed. It's shown that for both severe impact case and non-severe impact case, the non-linearity of pile material influence the impact force history, ship crush depth. The non-linearity of pile material and soil has remarkable influence on the cap displacement especially for severe impact case. These issues should not be ignored in the analysis of pile supported protective system subjected to ship impact.     

碰撞规律分析

对物体间的碰撞做了简化分析，给出了质点的和质点组的动量定理及动量矩定理，并用恢复系数对碰撞类型作了归类。