VOA标准英语2012.12.30
[audio]http://sound.yywz123.com/tingbbs/voab/voab20121230.mp3[/audio]__________________.Dipping a wand into regular water won't work because the water's surface tension is so strong that the molecules would rather bunch together in a puddle than be stretched across the opening of the wand.把吹泡泡用的"魔术棒"放进水里浸泡后再吹气不能形成泡泡,因为水面的表面张力太强,水分子会聚集在一起,不会在"魔术棒"的开口伸展开. The addition of soap helps because these molecules have two distinct ends, one that is attracted to water, and one that is not.加入肥皂有助于产生泡泡,因为这些分子有不同的两端,亲水端和疏水端. When a wand is dipped into soapy water, soap molecules cover the surface of the film, with their water-loving ends facing the water. Since the water molecules are now attracted not only to each other but also to one end of the soap molecules, the water is held in place as it stretches across the wand, forming a soapy film.把"魔术棒"放进肥皂水后,肥皂分子覆盖在薄膜表面,分子的亲水端朝向水.由于这时水分子不仅互相吸引,而且还被肥皂分子的亲水端吸引,水分子在"魔术棒"上伸展时,也能被固定从而产生肥皂薄膜.
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