化一般为特殊,巧解弹性正碰问题

本文由贵刊2017年第11期和2018年第5期刊登的两篇文章提出思考,通过选择恰当的参考系,化一般为特殊,巧妙地解决了学生在处理弹性正碰问题中的困难。该方法既不会给学生增加太大的理解困难,又能够不冲淡解题过程的“物理味”,且完全不需要进行解方程组之类的数学运算。     

“弹性正碰”中的两个重要结论及应用

设发生碰撞的两物体质量分别为m1、m2，碰撞前、后速度分别为V10、V20和V1、V2。由弹性碰撞中，动量和动能都守恒有：     

“隐形的”弹性正碰

所谓碰撞,是指两个物体经过极短时间的相互作用而使各自的动量发生明显的变化.而正碰即对心碰撞,碰撞前后若无机械能损失则为弹性碰撞.我们先看看弹性正碰的基本规律.设两个物体质量分别为m1和m2,碰前的速度分别为v1和v2,碰后速度分别为v′1     

两球一维弹性正碰规律例析

两个(或两个以上)物体相遇,物体之间的相互作用仅持续一个极为短暂的时间,而运动状态发生显著变化,这种现象称为碰撞.由于碰撞是在极短的时间内发生的,当满足"相互作用的内力远大于外力"的条件时,不管系统是否受到外力,一般都满足动量守恒."碰撞"问题在高中阶段的要求仅限于一维正碰:即两个物体碰撞前沿同一直线运动,碰撞后仍沿同一直线运动."碰撞"问题所依循的基本定律是系统动量守恒定律,然后再根据碰撞的具体类型有选择性地应用机械能守恒定律.弹性形变是指撤去外力后能够恢复原状的形变,     

巧求两小球对心弹性碰撞后的速度

本文用对称性原理推导出两小球对心弹性碰撞后的速度公式,具有求解简单,宜于推广,以高中生学习物理有很大的帮助。     

解答弹性碰撞问题的一种新方法

在完全弹性碰撞中，动量守恒，动能也守恒，根据两个守恒关系，可列出二元二次方程组，以达到解决问题的目的，本文探讨一种不必列出二次方程组的一种方法，用该方法可以很方便地解决弹性碰撞的有关问题。     

剖析弹性碰撞 巧解竞赛题

第22届全国中学生物理竞赛预赛第五题是求解由弹性碰撞引发的临界值问题．在弹性碰撞中，动量守恒，动能也守恒，根椐两个守恒关系，可列出二元二次方程组，以达到解决问题的目的．本文通过剖析弹性碰撞，探寻一种不必列出二次方程组的方法，巧解有关弹性碰撞的问题．     

两小球对心弹性碰撞后速度的计算与分析

用对称性原理推导出两小球对心弹性碰撞后的速度公式，该公式求解简单，宜于推广，对高中生学习物理有很大的帮助。     

守恒原理在多球弹性碰撞中的应用

本文应用守恒原理分析球与地球及球与球之间的弹性碰撞 ,得到了某些令人感兴趣的结果     

求解矩形布局问题的一种混合SAGA算法

矩形布局问题属于NP-Hard问题,是一种复杂的组合优化问题.模拟退火算法(SA)和遗传算法(GA),经常被用于求解组合优化问题.但是当问题规模较大时,存在一些难以解决的问题,如早熟现象.针对二维矩形布局问题,以动态吸引子为依据,根据各优化算法的特点,提出了一种将模拟退火算法和遗传算法思想融合的SAGA混合算法.最后通过实例证明该算法的合理性和高效性.     

利用传感器研究碰撞问题

碰撞是日常生活中常见的现象，也是物理学广泛研究的一个基本现象．在科学研究中也是常用的试验方法，如，为测定汽车的耐碰撞性能而进行的汽车碰撞试验、为研究物质结构进行的粒子碰撞试验等．在高中物理教学中碰撞是重点教学内容．     

Head-on collision of two balls revisited

We present a dramatic demonstration which is also a simple, and an extremely low-cost experiment of head-on collision of two balls in a vertical direction. The advantages of this phenomenon in the vertical direction are clarified. Some simple estimates are made. A thorough analysis of this simple topic is then made, which includes various special and limiting cases, conditions of collision, change of reference frame, etc.     

力学中"两体碰撞"的程序实现

“两体碰撞”是力学教学中的重要内容，也是教学中的一个难点，本以物理规律为基础，提出了在一般情况下如何用计算机模拟“两体碰撞”的程序实现方法，详细介绍了由程序控制碰撞初值进行多次碰撞的基本算法以及编写程序应注意的问题；有坐标变换方法有效地解决了任意条件下的两体碰撞问题，使教材中正碰和斜碰的分离问题有机地统一起来。     

Solving composite scheduling problems using the hybrid genetic algorithm

This paper dealt with composite scheduling problems which combine manufacturing scheduling problems and/or transportation routing problems.Two scheduling models were formulated as the elements of the composite scheduling model,and the composite model was formulated composing these models with indispensable additional constraints.A hybrid genetic algorithm was developed to solve the composite scheduling problems.An improved representation based on random keys was developed to search permutation space.A genetic algorithm based dynamic programming approach was applied to select resource.The proposed technique and a previous technique are compared by three types of problems.All results indicate that the proposed technique is superior to the previous one.     

Charting the waves of prevention: two steps forward,one step back

BACKGROUND: Over the past 30 years, the political response to child maltreatment and its prevention in the US has experienced periods of frantic activity, often followed by long periods of benign neglect. In reflecting on this history, Dick Krugman has referred to this uneven level of attention as a series of "waves" in which apparent progress is often minimized by an inability to sustain political commitment to a given reform or course of action. To an extent, this pattern reflects deep differences among child welfare advocates, researchers, and practitioners on how best to proceed. While most everyone agrees that "it shouldn't hurt to be a child," how to prevent this hurt and at what cost is less clear. METHOD: To address this dilemma, prevention advocates, researchers, and practitioners have struggled with a variety of conceptual frameworks and programmatic reforms. This article summarizes the relative gains and limitation of three such efforts and outlines the lessons these efforts offer those formulating future prevention policies and programs. RESULTS: Specifically, the authors suggest that future prevention efforts will need to take care in avoiding some of the most common mistakes experienced by earlier efforts. CONCLUSIONS: These mistakes or pitfalls include oversimplifying the problem of child abuse; overstating preventions' potential and appropriate target populations; failing to establish a significant partnership with child protective services; compromising depth or quality in an effort to maximize breadth or coverage; and failing to fully engage the public.