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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,影响滑动摩擦力的大小因素,What affects sliding friction,Review,1. Recall the force,2. What can the force do ?,Change shape,（形变）,Change velocity,（改变物体的运动状态）,twist,一、,Sliding force in daily life,（生活中的摩擦力）,说一说,1,、,Definition :,一个物体在另一个物体表面上发生相对滑动时,受阻碍,的现象，称为滑动摩擦现象，在滑动摩擦过程中受到的力叫滑动摩擦力。,二、,Sliding friction force,（滑动摩擦力）,2,、,Direction,：,friction always opposes motion,。,Describe,（描述）,the,steps of a practical report,1,、,Purpose,（目的）,：,2,、,Hypothesis,（假设）,6,、,Conclusion,（结论）,5,、,Data and Analysis,（数据及分析,）,4,、,Procedure,（步骤）,3,、,Materials,（材料）,三、,What affects sliding friction ?,滑动摩擦力的大小和什么有关系,Variables,Independent variable,（自变量）,Dependent variable,（因变量）,Controlled variable,（不变量）,（,1,）可能与,正压力,F,N,（,normal force),有关,?,一次数据,primary data,2.,定量的数据,quantitative,Variables,Independent variable,Dependent variable,Controlled variable,1.,F,N,F,f,控制变量法,Normal force,F,N,/N,Sliding friction,F,f,/N,1.0 1.5 2.0 2.5 3.0,0.2 0.3 0.4 0.5 0.6,F,N,/,N,F,f,/,N,0.2,0.3,0.4,0.5,1.0 1.5 2.0 2.5 3.0,0,0.6,secondary data,二次数据,结论：滑动摩擦力的大小跟压力成正比,Compare,（比较）,Secondary data,primary data,Conclusion,几种材料间的动摩擦因数,材料,动摩擦因数,材料,动摩擦因数,钢,钢,0.25,钢,冰,0.02,木,木,0.30,木头,冰,0.03,木,金属,0.20,橡胶轮胎,路面（干）,0.71,皮革,铸铁,0.28,Coefficient of sliding friction,（滑动摩擦系数）,（,2,）可能与接触面的,粗糙程度,有关,?,（,2,）可能与接触面的,粗糙程度,有关,?,Compare,secondary data,Primary data,Conclusion,一次数据,first data,2.,定量的描述,quantitative,Variables,Independent variable,Dependent variable,Controlled variable,1.,F,f,控制变量法,Equation,：,F,f,= F,N,F,N,为正压力；,为动摩擦因数，无单位，,与接触面的材料 粗糙程度,有关。,Problem 1 :,Explain why it is easier to push a toy chest along the floor,when it is empty than it is full.,A full toy chest is harder to push than an empty toy chest because the full chest has more weight. Friction relates to weight of an object.,Problem 2,What horizontal force has to be applied to a 50 kg sled on,an ice surface ( = 0.3) as shown in the figure to make it,move,at constant speed,?,Problem 3,A spring balance reads 3N as it is used horizontally to,drag a 750 g block of wood along a laboratory bench.,Calculate the coefficient of friction:,Key Ideas:,Describe the,Sliding force in our life,Summary:,（小结）,Sliding friction :definition,、,direction,what affects sliding friction,Calculation about the equation,F,f,= F,N,Thank You,
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