2022年2017年秋高中物理第四章牛顿运动定律章末总结 .pdf
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1、1 第四章 牛顿运动定律章末总结知识点一、整体法、隔离法分析连接体问题1.连接体两个或两个以上相互作用的物体组成的具有相同加速度的整体叫连接体如几个物体叠放在一起,或并排挤放在一起,或用绳子、细杆等连在一起2处理连接体问题的方法(1)整体法:把整个系统作为一个研究对象来分析的方法不必 考虑系统内力的影响,只考虑系统受到的外力(2)隔离法:把系统中的各个部分(或某一部分)隔离,作为一个单独的研究对象来分析的方法此时系统的内力就有可能成为该研究对象的外力,在分析时要特别注意(3)整体法与隔离法的选用求解各部分加速度都相同的连接体问题时,要优先考虑整体法;如果还需要求物体之间的作用力,再用隔离法求解
2、连接体问题时,随着研究对象的转移,往往两种方法交叉运用一般的思路是先用其中一种方法求加速度,再用另一种方法求物体间的作用力或系统所受合力无论运用整体法还是隔离法,解题的关键还是在于对研究对象进行正确的受力分析【典型例题】【例题 1】如图,两个质量分别为m12 kg、m2=3 kg 的物体置于光滑的水平面上,中间用轻质弹簧秤连接。两个大小分别为F1=30N、F2=20N的水平拉力分别作用在m1、m2上,则A弹簧秤的示数是20 N B弹簧秤的示数是25 N C在突然撤去F2的瞬间,m1的加速度大小为5 m/s2D在突然撤去F1的瞬间,m1的加速度大小为13 m/s2【答案】D【解析】将两物体和弹簧
3、看做一个整体,根据牛顿第二定律可得2512123020/2/5FFamsmsmm,对1m分析可得11FFm a,联立解得11302226FFm aNN,AB错误;在突然撤去2F的瞬间,因为弹簧的弹力不能发生突变,所以1m的受力没有发生变化,故加速度大小仍为22m/s,故 C错误;突然撤去1F的瞬间,1m的受力仅剩弹簧的弹力,对1m列牛顿第二定律得:1Fm a,解得:213/ams,故 D正确2【名师点睛】两个大小分别为123020FNFN、的水平拉力导致物体受力不平衡,先选整体为研究对象进行受力分析,列牛顿第二定律解出加速度,再隔离单独分析一个物体,解出弹簧受力;在突然撤去2F的瞬间,弹簧的弹
4、力不变,对两物块分别列牛顿第二定律,解出其加速度【针 对训练】(多选)如图所示,在光滑的桌面上有M、m的两个物块,现用力F 推物块,使M、m两物块在桌上一起向右加速,则M、m间的相互作用力为A、若桌面光滑,作用力为MFMmB、若桌面光滑,作用力为mFMmC、若桌面的摩擦因数为,M、m仍向右加速,则M、m间的相互作用力为MFMgMmD、若桌面的摩擦因数为,M、m仍向右加速,则M、m间的相互作用力为MFMm【答案】AD【名师点睛】分析整体的受力时采用整体法可以不必分析整体内部的力,分析单个物体的受力时就要用隔离法采用整体隔离法可以较简单的分析问题知识点二、动力学的临界问题1.概念(1)临界问题:某
5、种物理现象(或物理状态)刚好要发生或刚好不发生的转折状态(2)极值问题:在满足一定的条件下,某物理量出现极大值或极小值的情况2关键词语在动力学问题中出现的“最大”、“最小”、“刚好”、“恰能”等词语,一般都暗示了临界状态的出现,隐含了相应的临界条件3常见类型文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编
6、码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D
7、6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y
8、5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K
9、10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8
10、M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5
11、A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z1
12、0C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C23 动力学中的常见临界问题主要有三类:一是弹力发生突变时接触物体间的脱离与不脱离的问题;二是绳子的绷紧与 松弛的问题;三是摩擦力发生突变的滑动与不滑动问题4解题关键解决此类问题的关键是对物体运动情况的正确描述,对临界状态的判断与分析,找出处于临界状态时存在的独特的物理关系,即临界条件常见的三类临界问题的临界条件:(1)相互接触的两个物体将要脱离的临界条件是:相互作用的弹力为零(2)绳子松弛的临界条件是:绳的拉力为零【典型 例题】【例题 2】如图所示,质量为m的光滑小球,用轻绳连接后,挂在三角劈的顶端,绳与
13、斜面平行,劈置于光滑水平面上,斜边与水平面夹角为30,求:(1)劈以加速度a1g/3 水平向左加速运动时,绳的拉力多大?(2)劈的加速度至少多大时小球对劈无压力?加速度方向如何?(3)当劈以加速度a32g向左运动时,绳的拉力多大?【答案】(1)336mg(2)3g,方向水平向左;(3)5mg【解析】(1)如图所示,水平方向:FT1cos FN1sin ma1竖直方向:FT1sin FN1cos mg文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y
14、5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K
15、10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8
16、M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5
17、A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z1
18、0C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编
19、码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D
20、6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C24 由得:FT1336mg.【针对训练】如图所示,有一块木板静止在光滑而且足够长的水平面上,木板的质量为M4 kg、长为L1.4 m,木板右端放着一个小滑块,小滑块质量m1 kg,其尺寸远小于L,小滑块与木板间的动摩擦因数为 0.4.(g取 10 m/s2)(1)现用恒力F作用在木板M上,为使m能从M上面滑落下来,问:F大小的范围是多少?(2)其他条件不变,若恒力
21、F22.8 N,且始终作用在M上,最终使得m能从M上滑落下来,问:m在M上面滑动的时间是多少?【答案】(1)F20 N(2)2 s 知识点三、动力帝的图象问题文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B
22、3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5
23、HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10
24、T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1
25、 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2X9Z10C2文档编码:CF5D6B3U1Y5 HN7K10T5C8M1 ZL5A2
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