英语听力文摘 English Digest 391、感受空气的存在
时间：2019-02-16 作者：英语课 分类：英语听力文摘 English Digest
What is Air?
空气
D: Strictly 1 speaking, air is mostly nitrogen–about seventy-eight percent, and about twenty-one percent oxygen, which leaves about one percent of other stuff, like water vapor 2 and carbon dioxide.
Y: So air is mostly empty space?
D: Yep, in fact, if you ever condensed a gallon of air into a solid, you’d end up with a little over one tenth of one percent of the air’s original volume.And the reason we don’t notice all this emptiness is because air molecules 3 are constantly moving around at the speed of sound, and bouncing against any surface that happens to fall in their path.
Y: So we’re constantly bombarded by air molecules.So how come we don't feel that?
D: Well, actually we do.The force these air molecules exert is what we measure when we measure air pressure.
D：严格地说，空气主要由大约78%的氮气和21%的氧气组成，另外还有1%的其他气体，像水蒸气和二氧化碳。
Y：所以，空气大部分都是真空吗？
D：是的。实际上，如果你将一加仑的空气凝结成固体，这个固体的体积只比空气原本体积的千分之一多一点。我们没有注意到这一点的原因是空气分子以音速在不停地移动，而当它们碰到任何表面时都会反弹回去。
Y：那么，我们一直被空气分子撞击着，可是为什么我们感觉不到呢？
D：其实我们能感觉到的。空气分子施加的压力就是我们平时测量的气压。
- His doctor is dieting him strictly.他的医生严格规定他的饮食。
- The guests were seated strictly in order of precedence.客人严格按照地位高低就座。
- The cold wind condenses vapor into rain.冷风使水蒸气凝结成雨。
- This new machine sometimes transpires a lot of hot vapor.这部机器有时排出大量的热气。