英语听力文摘 English Digest 391、感受空气的存在

（单词翻译）

What is Air?
空气

D: Strictly¹ 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 vapor² 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 molecules³ 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。