通过对一道动态平衡问题展开讨论,指出了在利用“动态平衡三角形”法求解力的变化时,在某些给定的条件下容易掉入错误推理的陷阱,比如在一个力的大小和方向不变,而其余两个力的方向在同时变化的情况下,则其余两个力的大小变化是没有确定结论的。文中首先给出了错误推论的反例,然后结合一道此类问题的求解,指出了正确求解的关键在于能否在几何上充分展现题中所给条件。最后,通过转换参考系、引入同心圆的等效处理,达到精确求解。 By discussing a dynamic equilibrium problem, it is pointed out that it is easy to fall into the trap of false reasoning under some given conditions when using the “dynamic equilibrium triangle” method to solve the force variation, for example, in a force size The same direction, while the remaining two forces in the direction of change at the same time, then the size of the remaining two changes in force is not conclusive. In the paper, firstly, the counterexamples of wrong inference are given, and then the solution of one such problem is pointed out. The key point of the correct solution lies in whether it can fully demonstrate the conditions given in the article. Finally, through the conversion of the reference frame, the concentric equivalent processing is introduced to achieve accurate solution.