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高中物理教材第一册“固体和液体的性质”一章中有一个小实验：要求学生用棉纸把缝衣针漂浮在水面上，并说明缝衣针被水的表面托住的原因．许多学生甚至有的教师都认为缝衣针是受重力和液体表面张力作用而平衡，使缝衣针被水的表面托住，并画出了如图１所示的受力图；也有些教
There is a small experiment in the first chapter of the “Physical and Liquid Nature” chapter of the High School Physics Teaching Materials Book 1. Students are required to use cotton paper to float needles on the surface of the water and explain why the sewing needle is supported by the water surface. Many students and even some teachers think that the sewing needle is balanced by gravity and liquid surface tension, so that the sewing needle is supported by the surface of the water, and the force diagram shown in Figure 1 is drawn;