英语听力文摘 English Digest 391、感受空气的存在

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。

 

 

1 strictly   

adv.严厉地，严格地；严密地

参考例句：

• 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。

2 vapor   

n.蒸汽，雾气

参考例句：

• 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。

3 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。