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1、共点力平衡第二讲结果导向法2.1如图所示，光滑小球与斜面接触，悬挂小球的绳子处于竖直状态，则小球受到的作用力为（）A重力、绳子的拉力B重力、绳子的拉力和斜面的支持力C重力、斜面的支持力D重力、绳子的拉力、斜面的支持力和下滑力1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomeworkA121 1234U U have have knownknownU U should should knowknowU U need need pra
2、cticepracticeTest Test&homeworkhomework2.1结果导向法1.定义：由物体的运动状态反推出受力情况结果导向法绳子处于竖直：平衡状态物体合力为零121 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework2.1 结果导向法2、受力分析步骤“悬挂小球的绳子处于竖直状态”找对象11定状态223344=静止一重二弹三摩擦（不少力）检验（不多力）1 1234U U have have knownknow
3、nU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework可能处于平衡状态的受力情况2.1 结果导向法二力：三力：四力：121 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework(多选)如图,一个小球用两根轻绳挂于天花板上,球静止,绳1倾斜,绳2恰竖直。则小球所受的作用力个数()A一定是两个B一定是三个C不可能是一个D可
4、能是两个，也可能是三个AC1找对象1定状态2一重二弹三摩擦3检验421 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework小球与光滑水平面和斜面接触，正上方用一个细绳连接并竖直悬挂住。已知小球处于静止状态，下列判断正确的是（）A斜面一定没有支持力B水平面一定没有支持力C细绳一定没有拉力D小球一定受到三个力A找对象1定状态2一重二弹三摩擦3检验41 1234U U have have knownknownU U should s
5、hould knowknowU U need need practicepracticeTest Test&homeworkhomework如图，在A、B图中物体A均静止；C图中物体A匀速下滑；D图中斜面整体做匀速运动，A、B、C三物体相对静止.对A物体四幅受力图中，正确的是（）BAAAABCACDB1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomeworkAC（多选）如图所示，各接触面是光滑的，A、B 处于静止状态，则 A、B
6、间无弹力作用的是（）ABCDAAAABBBB1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework如图所示，一架梯子斜靠在光滑的竖直墙上，下端放在水平的粗糙地面上。关于梯子受力情况的判断，正确的是（）A.梯子受到两个竖直的力，一个水平的力B.梯子受到一个竖直的力，两个水平的力C.梯子受到两个竖直的力，两个水平的力D.梯子受到三个竖直的力，两个水平的力C1 1234U U have have knownknownU U shou
7、ld should knowknowU U need need practicepracticeTest Test&homeworkhomework如下图所示，容器内盛有水，器具壁AB呈倾斜状，有一个物块P处于图示状态，并保持静止，则该物体受力情况正确的是（）AP可能只受一个力BP可能只受三个力CP不可能只受两个力DP不是受两个力就是受4个力DBAPCD1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework（多选）如图所示，竖
8、直放置的轻弹簧一端固定在地面上，另一端与斜面P连接，P与斜放的固定挡板MN接触且处于静止状态，则斜面体P此刻所受到的外力个数有可能为 ()A2个B3个C4个D5个AC整体隔离法2.21 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework用轻质细线把两个质量未知的小球悬挂起来，如图(a)所示.现对小球a施加一个向左偏下30的恒力，并对小球b施加一个向右偏上30的同样大小的恒力，最后达到平衡，表示平衡状态的图可能是下图(b)中的(
9、).BACDab1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework平衡术1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework2.2 整体法最下方的酒瓶对地面的压力为多少？1 1234U U have have knownknownU U should s
10、hould knowknowU U need need practicepracticeTest Test&homeworkhomework2.2 整体法最下方的酒瓶对地面的压力为多少？1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework2.2 整体法1、触发条件1）大于等于两个物体2）运动状态一致（都是静止或者匀直）（具有相同的加速度）（秋季part）1 1234U U have have knownknownU U sh
11、ould should knowknowU U need need practicepracticeTest Test&homeworkhomework2、使用流程把所有物体当成一个物体（如用一个箱子装起来）研究外界对整体的力的作用（一重二弹三摩擦）2.2 整体法1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework用轻质细线把两个质量未知的小球悬挂起来，如图(a)所示.现对小球a施加一个向左偏下30的恒力，并对小球b施加一个
12、向右偏上30的同样大小的恒力，最后达到平衡，表示平衡状态的图可能是下图(b)中的().BACDabA1.地面对B的摩擦力2.A对B的摩擦力2.墙面对砖块1的摩擦力1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework判断下列静止物体受力分析是否使用整体法？研究系统外力对系统的作用可使用整体法12341 1234U U have have knownknownU U should should knowknowU U need
13、need practicepracticeTest Test&homeworkhomeworkD1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomeworkC1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework1 1234U U have have knownkn
14、ownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework整体AGA1隔离法：适用于研究系统内部的相互作用力。AB之间的力属于内部相互作用力一般先隔离受力较少的物体1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomeworkB如图所示，物体A、B叠放在物体C上，C置于水平地面上，水平力F作用于B，使A、B、C一起匀速运动，
15、各接触面间摩擦力的情况是（）AB对C有向左的摩擦力BC对A有向左的摩擦力C物体C受到三个摩擦力作用DC对地面有向右的摩擦力1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomeworkD1 1234U U have have knownknownP17-ex.3-2U U should should knowknowU U need need practicepracticeTest Test&homeworkhomework如图所示
16、，a、b两个质量相同的球用线连接，a球用线挂在天花板上，b球放在光滑斜面上，系统保持静止，以下图示哪个是正确的（）BaaaabbbbACDB整体法隔离法条件选用原则注意问题1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework2.2 整体隔离法运动状态受力少研究系统外的物体对系统整体的作用力或系统的加速度研究系统内物体之间的相互作用力受力分析时不要再考虑系统内物体间的相互作用力一般隔离_的物体（2017年广东佛山顺德区第一次模
17、拟）如图所示，斜面小车M静止在光滑水平面上，一边紧挨着墙壁。现再在斜面上加一物体m，再给m施加一个竖直向下的恒力F，M、m均保持相对静止，小车后来受力个数为（）A3B4C5D61 1234U U have have knownknownU U should should knowknowU U need need practicepracticeTest Test&homeworkhomework高考链接BM M m m 1 1234U U have have knownknownU U should should knowknowU U need need practicepracticeT
18、est Test&homeworkhomework如图所示，物块A放在直角三角形斜面体B上面，B放在弹簧上面并紧挨着竖直墙壁，初始时A、B静止，弹簧处于竖直。现用力F沿斜面向上推A，但AB并未运动。下列说法正确的是（）A施加F前，竖直墙壁对B的摩擦力可能向下B施加F前，弹簧弹力大小一定等于A、B两物体重力大小之和C施加F后，A、B之间的摩擦力大小可能为零D施加F后，B与竖直墙壁之间可能没有摩擦力志高行远BCB B A A 本课总结直接1、结果导向法：根据物体的_反推受力。2、整体隔离法：整体法：适用于多个_一致物体组成的 系统，只研究系统_。隔离法：先分析_的，研究的是系统 _。状态运动状态内外的受力情况外部的受力情况受力简单CongratulationsCongratulations第二讲