众所周知，力是物体对物体的作用，我们在学习力的概念时应注意以下三点．一、力的物质性力是不能离开物体而存在的，凡是有力的作用时，至少存在着两个物体、如重力是发生在地球与物体之间，压力是发生在相互接触并且相互挤压的物体之间．二、力的相互性物体间力的作用是相互 As we all know, force is the effect of an object on an object. We should pay attention to the following three points when studying the concept of force. First, the material force of force cannot exist without leaving an object. When there is a powerful effect, there are at least two objects. For example, gravity occurs between the earth and the object. Pressure occurs in mutual contact and squeezes each other. Between objects. Second, the interaction of forces