论合力的作用点是一个实用的概念

The action point of resultant force is a practical concept

介绍了作用在刚体上力系的简化知识,指出作用在刚体上力的三要素宜改为大小、方向、作用线.通过分析重力、浮力、匀强电场力的做功特点,详细地论证了合力的作用点在本质上是一个实用的概念;指出重心、匀强电场中电荷系的荷心、浸没在液体中物体的浮心可以分别被看作重力、电场力、浮力的作用点,而漂浮物的浮心则不宜被看作浮力的作用点.指出一般力系合力的作用线要比作用点更客观、真实,并且后者也并非必需.

Introduces the knowledge of reduction of force system acting on the rigid body,and points out that the three elements of the force acting on the rigid body should be changed into size,direction and action line.By analyzing the work characteristics of gravity,buoyancy and uniform electric field force,it is demonstrated in detail that the action point of resultant force is a practical concept in essence.It is pointed out that the center of gravity,the charge center of the charge system in the uniform electric field and the floating center of the object immersed in the liquid can be regarded as the action points of gravity,electric field force and buoyancy respectively,while the floating center of the floating object should not be regarded as the action point of buoyancy.It is pointed out that in general,the action line of the resultant force of force system is more objective and true than the action point,and the latter is not necessary in essence.