使用任何机械，除了做有用功外，都不可避免地要做额外功．总功等于有用功加额外功。有用功跟总功的比值叫机械效率．用公式表示为有用功．利用机械时，对人有用的功是有用功．如利用斜面把重为G的物体拉到高为h的顶端，W6。一Gb．又如利用滑轮拉重物在水平面匀速运动，通过距 Using any machine, in addition to doing useful work, inevitably do extra work. Total work is equal to useful work plus extra work. The ratio of useful work to total work is called mechanical efficiency. Formulated as useful work. When using machinery, useful work for people is useful. For example, use an inclined surface to pull an object with weight G to the top of height h, W6. One Gb. Another example is the use of pulley weights to move at a uniform speed in the horizontal plane.