英語聽力文摘 感受空氣的存在

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空氣

D: Strictly 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 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 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：嚴格地說，空氣主要由大約78%的氮氣和21%的氧氣組成，另外還有1%的其他氣體，像水蒸氣和二氧化碳。

Y：所以，空氣大部分都是真空嗎?

D：是的。實際上，如果你將一加侖的空氣凝結(jié)成固體，這個固體的體積只比空氣原本體積的千分之一多一點。我們沒有注意到這一點的原因是空氣分子以音速在不停地移動，而當它們碰到任何表面時都會反彈回去。

Y：那么，我們一直被空氣分子撞擊著，可是為什么我們感覺不到呢?

D：其實我們能感覺到的。空氣分子施加的壓力就是我們平時測量的氣壓。