中文摘要：

在求平行力系中心位置的过程中,要用到合力矩定理.现有方法把合力的作用点设为平行力系中心,较难理解.该文应用合力矩定理时,把合力作用点假设为合力作用线上任意一点,平行力系合力作用线总是通过一个固定点的物理意义非常明确.

英文摘要：

The moment of the resultant, equivalent force about a given point of a force system, is equal to the sum of the moment of all acting forces about the same point. This theorem is usually used to determine the center of a parallel force system. In a conventional way the acting point of the resultant is set to be the center, which is difficult to be understood. In this work, an arbitrary point on the acting line of the resultant is assumed in using the theorem. The physical meaning of the center is clear and the line of action of the resultant must always pass through a fixed point.