教课书上指出:弹力的方向总是垂直于支承面而指向被压或被支承的物体.因此,判断弹力方向的关键是寻找支承面.一般情况下,支承面是显见的,如图1所示.但有些情况下,支承面很难从直观上判断.此时,应该从牛顿第三定律和物体处的状态入手分析. The textbook states that the direction of the elastic force is always perpendicular to the supporting surface and points to the object being pressed or supported. Therefore, the key to determining the direction of the elastic force is to find the supporting surface. In general, the supporting surface is obvious, as shown in Figure 1. In some cases, the bearing surface is difficult to judge intuitively. At this point, we should start with Newton’s third law and the state of the object.