2016年5月,我在讲授《简单机械》“杠杆”中阻力和动力的定义时,突然一位学生举手问道:“老师,教科书P76图12.1—1杠杆中阻力F_2是重力吗?”我不假思索地回答说,是啊!他反问我说:“如果F_2是重力,为什么没有画在石头的重心处而画在杠杆上呢?”我回答说:“在画力的示意图时,只要力的大小相等、方向相同,力的作用点可以平移到其他点,这一知识点到高中会具体学习,所以画重力作用线时画在石头重心处跟画在杠 In May 2016, when I was teaching the definition of resistance and motivation in ”Simple Mechanisms,“ ”Leverage,“ a student suddenly raised his hand and asked: ”Teacher, Textbook P76 Figure 12.1-1 Leverage Resistance F_2 is gravity “I answered without hesitation, yes! He asked me:” If F_2 is gravity, why not draw on the lever at the center of gravity of the stone? “I replied:” In painting Force diagram, as long as the force of the same size, the same direction, the role of the force point can be translated to other points, this knowledge to the high school will be specific to learn, so draw the line of gravity painting the center of gravity in the stone with the draw bar