例1 如图1所示,质量为2 kg的石块用细绳悬挂后静止在半空中,分析石块受到哪些力的作用?各力的大小、方向如何? 分析和解:取石块为研究对象,因石块与地球和绳之间有相互作用,所以石块受重力G和拉力F两个力的作用,如图2所示.因石块静止,故其所受的重力和拉力是一对平衡力,其合力为零.根据G=mg Example 1 As shown in Fig. 1 , a stone with a mass of 2 kg is suspended in a mid air after being suspended by a string, and what force is applied to analyze the stone? How are each force’s size and direction? Analysis and Reconciliation: Taking stones as a research The object, because of the interaction between the stone and the earth and the rope, the stone is subject to the force of gravity G and tension force F, as shown in Figure 2. Because of the static stone, its gravity and tension are A pair of balancing forces with a resultant force of zero. According to G=mg