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在讲完初二物理第十四章《功》之后,一位善于动脑筋的学生问我:在作关于杠杆平衡的计算题时,是否应将动力×动力臂的结果的单位和阻力×阻力臂的结果的单位都写成“焦耳”? 我们应当这样来认识这个问题。动力×动力臂即动力矩,阻力×阻力臂即阻力矩,它在普通物理学中是一个矢量积(即高等数学中的叉乘)。力矩是有方向的,在高中要讲到力矩是矢量、有正负,力矩的作用效果是使物体转动。功=力×距离是标量乘法(即高等
After finishing the second chapter of the physical physics in Chapter XIV, a good-natured student asked me whether or not the unit of the result of the power x power arm and the resistance x resistance should be used when making calculations on the balance of the lever. The unit of the result of the arm is written as “joules”? We should recognize this problem in this way. Power x dynamic arm is dynamic torque, resistance x resistance arm is resistance torque, which is a vector product in general physics (that is, multiplication in higher mathematics). Torque is directional. In high school, torque is vector and positive and negative. The effect of torque is to rotate the object. Work = force × distance is scalar multiplication (ie higher