在高中物理教学中 ,经常遇到一些平衡问题 ,运用相似形法解决这类问题 ,往往能收到简捷的效果 .例如 n个共点力作用使物体平衡 ,且能找到一个几何 n边形与力的 n边形相似 ,则可利用相似形对应边成比例的规律直接给出力的关系 .例 1　如图 1所示 ,半径为 0 .6 m的半球固定在水平 In high school physics teaching, some balance problems are often encountered. Using the similarity method to solve such problems can often receive simple effects. For example, n common point forces can balance objects and find a geometric n-angle shape. The n-angles of the force are similar, and the force relationship can be directly given by the proportionality law of the corresponding sides of the similarity. Example 1 As shown in Figure 1, the hemisphere with a radius of 0.6 m is fixed at the horizontal