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初中物理学課本上册第76節輪軸的一課,是通过槓桿原理進行解釋的,在这里把磨也列入,我覺得不妥当,因為“磨”不能和其它的輪軸一樣确定出一個重點和一個重臂來。我們推磨時,是克服它的摩擦力而做功,如果用槓桿原理來解釋它省力的原因,就应確定出它的重點所在。很明顯这個重點应是磨的摩擦力的合力點。在磨上產生摩擦力的接觸面,是以磨脐为中心的中心对称的圆形,所以在磨盤上任意找出一點A,就能找出它的一個对称点B,从磨的轉動情况和它的構造上看,这兩点的摩擦力是量值相等方向相反的兩個平
Middle school physics textbook Volume 76 axles lesson is explained by the lever principle, where the mill is also included, I think inappropriate, because the “grinding” can not be identified with the other axles as a focus and a Arm up. When we push the ground, it is to overcome its friction and work, if you use the principle of lever to explain the reasons for its effort, it should determine its focus. Obviously this focus should be on the friction point of friction. Friction in the grinding friction of the contact surface is based on the navel as the center of the center of a circular symmetry, so any point in the disc to find a point A, you can find a symmetrical point B, from the rotation of the mill and Its construction point of view, the friction between these two points is the same value of the opposite direction of the two flat