简单机械-复习教学设计.docx

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1、复习课-教案刘少敏1第十二章复习课2一、简单机械杠杆1．杠杆的五要素①支点O、动力F1、阻力F2、动力臂l1、阻力臂l2②图示杠杆的力臂例：画出图中力F对支点O的力臂l。lOF3例一块截面积为矩形ABCD的均匀金属块重2000N，它的长宽之比为4:3，将它置于水平地面上如图所示，若在A点用力F抬起金属块的一端，则力F至少为800N。ABFl1l1Gl2Dl2CG_____________________________________________________________________

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4、__________________________________________________________________________________________________________________________________________________________________42．探究杠杆的平衡条件①调节杠杆在水平位置平衡；②获取实验数据；③归纳结论。实验阻力阻力臂阻力×阻力动力动力臂动力×动力次数F2/Nl2/m臂F2l2/N·mF1/Nl1/m臂F

5、1l1/N·m110.150.15210.150.151.50.100.15330.050.15410.30.351.50.20.320.150.3630.10.353．杠杆的平衡条件①动力×动力臂=阻力×阻力臂F1×l1=F2×l2F1l2②两个力与它们的力臂成反比。l1F2例右图所示杠杆平衡吗？作如下变化，杠杆能平衡吗？若左侧加一个相同钩码；若右侧减一个钩码；支点右移一格；左侧钩码组左移一格。64．杠杆分类①省力杠杆：动力臂大于阻力臂。省力，但费距离。例：钓鱼杆、使用筷子、用大扫帚扫地②费力杠杆

6、：动力臂小于阻力臂。省距离，但费力。例：开瓶起子、羊角锤起钉子、剪铁皮的剪子③等臂杠杆：动力臂等于阻力臂。不省力也不费力。例：天平__________________________________________________________________________________________________________________________________________________________________________________________

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