判断液面升降对初中学生来说是一个难点 ,采用一题多变的方法分析这一类问题中的几种可能情况 ,进行归纳总结和迁移应用能收到良好的效果。例题　一块冰浮在烧杯内的水面上 ,冰熔化后 ,水面如何变化 ?解析　判断液面升降取决于冰排开水的体积V排 和冰熔化成水后的体积V冰化水 Judging the liquid level rise and fall is a difficult task for junior high school students. This paper uses several methods to analyze several possible situations in this type of problem. It can be concluded that the summary and migration application can receive good results. Example A piece of ice floats on the surface of the beaker. After the ice melts, how does the surface of the water change? Analyze Judging that the liquid level rises and falls depends on the volume of water in the ice row V and the volume of ice melted into water V iced water