How heavy is air? - Dan Quinn

空氣有多重？ － 丹·昆

Transcriber: Jessica Ruby Reviewer: Caroline Cristal

譯者: Denise Tso 審譯者: woo liu

你可能沒有發現，

You may not realize it,

but from the moment you got out of bed today

從今天起床的第一瞬間，

to the point where you sat down to watch this video,

到你坐下觀看這段影片的時候，

you've essentially been swimming.

本質上， 你正在游泳。

Why? Because air is a fluid just like water.

為甚麼呢？ 因為空氣像水一樣是流體。

It has waves and eddies.

它有波浪和漩渦。

It flows.

它會流動。

And when you push air out of the way,

如果你把前面的空氣推開，

it rushes around you into a wake.

它就會被你擠到後面， 從後面包圍你。

So why don't we notice it most of the time?

那麼為甚麼在大部份情況下， 我們都沒有留意到它呢？

We commonly think of air as empty space.

因為我們通常視 空氣為沒有空間的。

But while one cubic centimeter of interstellar space,

其實一立方厘米 的外太空空間，

the volume in the tip of your pinky finger,

相當於 小拇指指尖的體積，

contains roughly one atom,

大約包含1個原子。

the same volume of air has about 10 quintillion molecules.

同樣體積的空氣則有 約10的18次方個分子。

If that sounds hard to wrap your head around,

如果你對這個數字沒有概念，

it happens to be about the same

這數目剛好，

as the number of insects alive on the planet,

跟地球上昆蟲的數量差不多。

all crawling, climbing, and flying over each other

它們擠在一個緊密的空間裏，

in an enormous, tightly packed swarm.

互相交疊地爬行、飛來飛去。

When this swarm of molecules runs into things,

當這群分子撞到其他東西時，

it exerts a force, pressing against the boundaries of the fluid,

它們就會貼緊空間的邊緣施加壓力，

like water pressing against the glass of a bottle.

像水貼緊瓶邊一樣，

This is known as air pressure.

這就叫做氣壓。

And while air is lighter than water,

雖然空氣比水輕，

all those molecules still get pretty heavy,

但這些分子其實蠻重的。

with the total air filling a typical school gym,

一個標準學校體育場的所有空氣，

weighing about as much as an adult elephant.

重量相當於一頭成年大象。

So when you walk into a gym,

那麼當我們走進體育場時，

how come you're not immediately crushed

為甚麼沒有被大象一樣重的空氣

by the elephant of air in the room?

壓垮呢？

Well, first of all,

這個嘛，首先

because most of it is pressing on the floor and the walls,

是因為大部份空氣的壓力 都施加在地板和牆上，

and the part that is pressing on you

而落在我們身上的壓力，

is pushed back by the pressure inside you!

都被體內的壓力抵消了！

You see, the air, as well as the water and everything else,

你看，在我們身體內的

that fills our bodies exerts an amount of pressure

空氣、水和其他物質都在施加相同的壓力，

equal to that of the air outside.

和體外的壓力抗衡。

Of course, this is no accident.

當然，這並不是機緣巧合。

It's precisely what allows us to survive

正是如此，

in the normal atmosphere,

我們才得以在正常氣壓下生存。

and what makes it more difficult

但這個設計也讓我們的身體

at high altitudes or deep water.

更難適應高海拔或深水。

And we normally don't feel the air pressing on us

我們通常感覺不到空氣壓迫在我們身上，

because it's generally uniform.

因為它整體上是一致的。

So even though different amounts of air molecules

所以即使在不同的時間，

are hitting you at different times,

撞擊你的空氣分子數量不同

the swarm is so thick

但由於分子實在是太多了，

that all those little differences average out.

這麼小的差異就變得不那麼明顯了。

What happens when air pressure isn't uniform?

那麼，氣壓不一致會發生什麼情況？

This means that the molecules are pushing harder

這種情況下， 代表一個區域的空氣分子的壓力

in one region of air than another,

比其他區域的要大。

driving the air flow from the higher pressure region

壓力的不均等， 會造成高氣壓流向

to the lower.

較低氣壓的位置，

We feel this flow directly as wind,

形成風。

and the pressure systems

而氣象學家常談到的

that meteorologists are always going on about

壓力系統，

are responsible for other weather changes,

負責著日常的天氣變化

from the mundane to the catastrophic.

到災難性的氣候改變。

But differences in air pressure

但是，氣壓差並不只讓我們

do more than just let us complain about the weather;

對惡劣的天氣有所抱怨，

they're the very reason we're alive.

它還讓我們得以生存。

We breathe by lowering the pressure in our lungs,

我們呼吸時，會將肺內的氣壓降低，

allowing air to rush in.

使得外面的空氣得以進入體內。

So the next time you take a deep breath,

所以下次你深呼吸的時候，

think of the unfathomable number of air molecules

試想想有無數的空氣分子，

you're commanding to move.

跟隨著你的指揮在運動。

We look up at the night sky

我們仰望夜空，

to ponder the infinity of space,

思索宇宙的無限。

but unless you're watching this video

但除非你是在太空深處

from that deep space,

看這段影片。

there are more air molecules

不然，圍繞著你和在你體內

in and around your body

的空氣分子，

than there are grains of sand in all the world's beaches and deserts,

比全世界所有沙灘 和沙漠堆起來的沙，

stars in the visible universe,

或是可見的星星，

or both of those numbers combined.

或兩者相加的數目還要來的多。

The vastness of the universe

宏大的宇宙，

is right in front of you

不但近在眼前，

and inside you.

還暗藏在你我的軀體內。