我们都知道机械效率的计算公式是η=W有/W总,所以要想正确计算出机械效率,首先必须正确判断出哪一部分是有用功,哪一部分是总功。而我们在实际生活中,大部分都是利用简单机械,故在判断时候,可以从以下两方面来考虑:(1)动力所做的功就是总功,动力就是使机械转动的力,这个是很容易找到的,也就确定了总功的大小。(2)有用功就是为达到目的必须做的功,在做题时候,我们可以这样设想,有用功就等于不用机械时候,达到同样目的,人所做 We all know that the mechanical efficiency formula is η = W / W total, so in order to correctly calculate the mechanical efficiency, we must first correctly determine which part is useful work, which part is the total work. However, in real life, most of us use simple machinery. Therefore, in judging, we can consider from the following two aspects: (1) The work done by the power is the total work, and the power is the force that makes the machine rotate. This is Very easy to find, it also determines the size of the total work. (2) The useful work is the work that must be done to achieve the goal. When doing the question, we can imagine that the useful work is equivalent to the same goal