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高中《物理》第一册(必修)“液体的表面张力”后有一练习题:“布的雨伞和帐篷,虽然纱线间有空隙,却不漏雨水,试解释这种现象。”人民教育出版社《教学参考书》第一册第340页上的解答是:“雨水将纱线浸湿后,在纱线间隙中形成一层水膜,当雨水顺着伞面流过水膜时,水膜微微下凹,表面张力支持住雨水,使雨水不会漏下(图1)。”上述的解答是说水能浸润纱线的情况,这时雨水就能附着在纱线上,其下半部的水层,就像水滴能附着在天花板上一样(如图2)。
In the high school “Physics” Book 1 (required) “Liquid Surface Tension”, there is an exercise title: “The cloth umbrellas and tents, although there are gaps between the yarns, but do not leak rain, try to explain this phenomenon.” People’s Education The answer to the “Teaching Reference Book” of Book One of the first volume on page 340 is: “After wetting the yarn, rainwater forms a film of water in the yarn gap. When rain flows along the umbrella surface through the water film, The water film is slightly concave, and the surface tension supports the rain so that the rain does not leak (Figure 1).” The above solution is to say that the water can infiltrate the yarn, and then the rain can adhere to the yarn. Half of the water layer, like water droplets can be attached to the ceiling (Figure 2).