推理法就是根据题目给出的条件,按物理量的变化方向取值,当这个变化的量达到一定值时就可推断出结果的一种方法。学到杠杆时会遇到一类这样的问题,当力或力臂变化时,让我们判断杠杆哪端下沉,如根据杠杆平衡条件计算虽可判断,但比较繁琐。如用推理法就会很容易解决,下面通过几例 The reasoning method is based on the conditions given by the title, and the value is taken in the direction of the change of the physical quantity. When the quantity of this change reaches a certain value, a method can be inferred. When you learn leverage, you will encounter such a problem. When the force or power arm changes, let us judge which end of the lever sinks. Although it can be judged based on the balance condition of the lever, it is cumbersome. Such as using the reasoning method will be very easy to solve, following a few cases