Why does ice float in water? - George Zaidan and Charles Morton

為什麼冰塊會浮在水裡? - 喬治賽登 (George Zaidan) 和查理莫頓 (Charles Morton)

譯者: Nathalie Cheng 審譯者: Regina Chu

Water is the liquid of life.

水是生命的液體。

We drink it,

我們喝它，

we bathe in it,

我們用它來洗澡，

we farm,

cook,

來耕種，

煮飯，

and clean with it.

也用它來清理。

It's the most abundant molecule in our bodies.

它是我們身體內最主要的分子成分。

In fact, every life form we know of

事實上，我們所知道的所有生命體，

would die without it.

如果沒有它都會死去。

But most importantly, without water,

但最重要的是，如果沒有水分，

we wouldn't have

我們不會有

iced tea.

冰茶。

Mmmm, iced tea.

嗯，冰茶。

Why do these ice cubes float?

為什麼這些冰塊會漂浮？

If these were cubes of solid argon

如果這些是塊狀的固體氬，

in a cup of liquid argon,

在一杯液狀的氬當中，

they would sink.

它們會沈下去。

And the same goes for most other substances.

同樣的狀況也會發生在其他的物質身上。

But solid water, a.k.a. ice,

但是固體的水，也就是冰塊，

is somehow less dense than liquid water.

因為某種原因，密度就是比液體的水小。

How's that possible?

這怎麼有可能呢？

You already know that every water molecule

你已經知道每一個水分子

is made up of two hydrogen atoms

都是由兩個氫原子

bonded to one oxygen atom.

和一個氧原子組成的。

Let's look at a few of the molecules

讓我們來看看在一滴水裡面的

in a drop of water,

一些分子，

and let's say the temperature is 25 degrees Celcius.

讓我們假設在攝氏 25 度的溫度下，

The molecules are bending,

這些分子在彎曲，

stretching,

在伸展，

spinning,

and moving through space.

在旋轉，

也在空間中移動。

Now, let's lower the temperature,

現在，讓我們把溫度降下來，

which will reduce the amount of kinetic energy

這會降低每一個分子

each of these molecules has

所含有的動能，

so they'll bend, stretch, spin, and move less.

所以它們將會減少彎曲、 伸展、旋轉和移動的程度。

And that means that on average,

一般來說這就表示

they'll take up less space.

它們會佔用比較小的空間。

Now, you'd think that as the liquid water

現在，你會想到就像是液態的水

starts to freeze,

開始凝結，

the molecules would just pack together

分子會開始擠在一起，

more and more closely,

越來越靠近，

but that's not what happens.

但是這並不是實際上發生的狀況。

Water has a special kind

水有一種很特別的

of interaction between molecules

原子間交互影響作用，

that most other substances don't have,

是大部份其他物質所沒有的，

and it's called a hydrogen bond.

它叫做氫鍵 (Hydrogen bond)。

Now, remember that in a covalent bond

現在，記得在共價鍵(Covalent bond)裡，

two electrons are shared,

會共用兩個電子，

usually unequally,

通常原子之間對電子

between atoms.

是不均等共用。

In a hydrogen bond,

但在氫鍵的情況下，

a hydrogen atom is shared, also unequally,

原子間會共用一個氫原子，

between atoms.

一樣也是在不均等的狀況下。

One hydrogen bond looks like this.

一個氫鍵長得像這樣，

Two look like this.

兩個長得像這樣。

Here's three

這樣是三個，

and four

再來是四個，

and five,

然後是五個，

six,

六個，

seven,

eight,

七個，

八個，

nine,

ten,

九個，

十個，

eleven,

twelve,

十一個，

十二個，

I could go on.

我可以繼續下去。

In a single drop of water,

在一滴水裡面，

hydrogen bonds form extended networks

氫鍵形成延伸的網絡，

between hundreds, thousands, millions,

由數百個，數千個，數百萬個，

billions, trillions of molecules,

數十億個，數兆個分子所組成，

and these bonds are constantly breaking and reforming.

而且這些連結鍵持續的斷裂與重組。

Now, back to our water as it cools down.

現在，回到我們冷卻的水。

Above 4 degrees Celcius,

當溫度在攝氏4度以上時，

the kinetic energy of the water molecules

水分子的動能

keeps their interactions with each other short.

會使它們之間的交互作用時間短暫。

Hydrogen bonds form and break

氫鍵會連結然後斷裂，

like high school relationships,

就像是高中時的感情關係，

that is to say, quickly.

像是大家說的，都很短暫。

But below 4 degrees,

但是當溫度降到 4 度以下，

the kinetic energy of the water molecules

水分子的動能

starts to fall below the energy

開始降到低於

of the hydrogen bonds.

氫鍵的動能。

So, hydrogen bonds form much more frequently

這樣一來，氫鍵建立的頻率

than they break

會高於它們斷裂的頻率，

and beautiful structures start to emerge

這個時候從一團混亂之中，

from the chaos.

一個美麗的架構開始出現。

This is what solid water, ice,

這就是固態的水 - 冰，

looks like on the molecular level.

從分子組合的角度來看，

Notice that the ordered, hexagonal structure

注意那些有秩序的六角形，

is less dense than the disordered structure

比起液態水的無秩序結構

of liquid water.

來得鬆散。

And you know that if an object is less dense

你知道如果一個物體的密度低於

than the fluid it's in,

液體的密度，

it will float.

它會浮起來。

So, ice floats on water,

所以冰塊會浮在水裡。

so what?

那又如何？

Well, let's consider a world without floating ice.

那讓我們來想想 一個沒有漂浮冰塊的世界。

The coldest part of the ocean

這樣一來，海洋最寒冷的部分

would be the pitch-black ocean floor,

就會在漆黑海底，

once frozen, always frozen.

一旦結凍，永遠凍結。

Forget lobster rolls

別再想龍蝦捲，

since crustaceans would lose their habitats,

因為甲殼類動物會失去牠們的棲息地，

or sushi since kelp forests wouldn't grow.

也不用想吃壽司，因為海草也長不出來。

What would Canadian kids do in winter

當沒有了結冰池塘曲棍球和冰釣，

without pond hockey or ice fishing?

加拿大小孩冬天能夠做什麼？

And forget James Cameron's Oscar

我們也可以忘記 詹姆士卡麥隆贏得的奧斯卡獎，

because the Titanic totally would have made it.

因為鐵達尼一定可以安然到達目的地。

Say goodbye to the white polar ice caps

我們也要跟極地的白色冰帽說再見，

reflecting sunlight

它們反射陽光，

that would otherwise bake the planet.

不然地球就會被烤熟。

In fact, forget the oceans as we know them,

實際上，我們可以忘掉我們知道的這些海洋，

which at over 70% of the Earth's surface area,

它們覆蓋地球超過百分之七十的表面，

regulate the atmosphere of the whole planet.

調節整個地球的氣候。

But worst of all,

但最糟的是，

there would be no iced tea.

我們就不會有冰茶了。

Mmmmm, iced tea.

嗯，冰茶。