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

为什么冰漂浮在水中? - George Zaidan 和 Charles Morton

翻译人员: Tina Zhao 校对人员: Zhiting Chen

Water is the liquid of life.

水是生命的体液。

We drink it,

人喝水，

we bathe in it,

用水洗澡，

we farm,

cook,

耕种，

做饭，

and clean with it.

清洁。

It's the most abundant molecule in our bodies.

水是人身体中数量最多的分子。

In fact, every life form we know of

事实上，如果没有水，所有的生命

would die without it.

都会死亡。

But most importantly, without water,

但最重要的是，如果没有水，

we wouldn't have

就没有

iced tea.

冰茶了。

Mmmm, iced tea.

嗯，冰茶。

Why do these ice cubes float?

为什么冰块会浮在上面呢？

If these were cubes of solid argon

如果这些冰块是固体氩气做成的，

in a cup of liquid argon,

被放入一杯液体氩气中，

they would sink.

他们就会下沉。

And the same goes for most other substances.

大多数其他物质都是固态重于液态。

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

但是，不知为何，固态水，又称冰，

is somehow less dense than liquid water.

密度比液态水小。

How's that possible?

怎么会呢？

You already know that every water molecule

众所周知，一个水分子

is made up of two hydrogen atoms

是两个氢原子和一个氧原子

bonded to one oxygen atom.

组成的。

Let's look at a few of the molecules

请看一滴水中的

in a drop of water,

几个分子，

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

假设温度是 25 摄氏度。

The molecules are bending,

这时，分子在弯曲

stretching,

伸展，

spinning,

and moving through space.

旋转，

在空间里移动。

Now, let's lower the temperature,

现在，降低温度，

which will reduce the amount of kinetic energy

每个分子里所含的

each of these molecules has

动能也随之减少，

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

那么分子弯曲，拉伸、 旋转，移动地自然会较少。

And that means that on average,

平均而言，这意味着

they'll take up less space.

分子所占空间变小。

Now, you'd think that as the liquid water

那么，你可能以为，液态水

starts to freeze,

在冻结时，

the molecules would just pack together

分子只是挤在一起

more and more closely,

贴得越来越紧，

but that's not what happens.

但事实并非如此。

Water has a special kind

水，同大多数其他物质不同，

of interaction between molecules

水分子之间

that most other substances don't have,

有一种独特的的相互作用

and it's called a hydrogen bond.

叫做氢键。

Now, remember that in a covalent bond

那么，通常，在共价键里，

two electrons are shared,

两个电子

usually unequally,

在原子之间

between atoms.

被不平等共享。

In a hydrogen bond,

在氢键里，

a hydrogen atom is shared, also unequally,

氢原子在原子之间也

between atoms.

被不平等共享。

One hydrogen bond looks like this.

一个氢键是这样的。

Two look like this.

两个是这样。

Here's three

这是三个

and four

四个

and five,

五、

six,

六、

seven,

eight,

七、

八、

nine,

ten,

九、

十、

eleven,

twelve,

十一、

十二、

I could go on.

我还可以加下去哦。

In a single drop of water,

一滴水里，

hydrogen bonds form extended networks

数百、 数千、 数以百万，

between hundreds, thousands, millions,

数十亿，数万亿的分子之间，

billions, trillions of molecules,

氢键由此而形成大范围网络,

and these bonds are constantly breaking and reforming.

这种连接又不断地断开再重新形成。

Now, back to our water as it cools down.

现在还是回头讲水凉了的情况吧。

Above 4 degrees Celcius,

4 摄氏度以上时，

the kinetic energy of the water molecules

水分子的动能

keeps their interactions with each other short.

使其之间的互动时间很短。

Hydrogen bonds form and break

氢键快速形成再断开，

like high school relationships,

就好比是高中生之间的关系，

that is to say, quickly.

真的是速战速决。

But below 4 degrees,

但温度低于4 度时，

the kinetic energy of the water molecules

水分子的动能

starts to fall below the energy

开始跌落低于氢键内

of the hydrogen bonds.

能源量。

So, hydrogen bonds form much more frequently

所以，氢键形成比断开

than they break

还频繁，

and beautiful structures start to emerge

混乱中，开始呈现出

from the chaos.

新的美妙结构。

This is what solid water, ice,

固态水、 冰、

looks like on the molecular level.

从分子图上是这样的。

Notice that the ordered, hexagonal structure

请注意，这种有序的 六角形结构的

is less dense than the disordered structure

密度低于无序结构

of liquid water.

的液态水。

And you know that if an object is less dense

大家都知道，如果物体放入

than the fluid it's in,

比其密度低的液体中

it will float.

该物体就会浮起来。

So, ice floats on water,

好吧，冰浮于水上

so what?

又有什么了不起的？

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

好，设想一下没有浮冰的世界吧。

The coldest part of the ocean

海洋最冷的部分

would be the pitch-black ocean floor,

将是漆黑不见五指的海底，

once frozen, always frozen.

一旦冻结，永远冻结。

Forget lobster rolls

别指望再吃到龙虾卷了，

since crustaceans would lose their habitats,

因为甲壳类动物就会失去它们的栖息地，

or sushi since kelp forests wouldn't grow.

寿司也永别了，因为海藻森林不会增长。

What would Canadian kids do in winter

加拿大的孩子们在冬天要做什么？

without pond hockey or ice fishing?

如果他们没法玩冰球或冰中钓鱼了？

And forget James Cameron's Oscar

詹姆斯 · 卡梅隆也可以忘记他的奥斯卡奖了，

because the Titanic totally would have made it.

因为泰坦尼克号根本没机会沉。

Say goodbye to the white polar ice caps

永别了! 那反射着阳光的

reflecting sunlight

雪白的极地冰帽，

that would otherwise bake the planet.

而阳光则烘烤着我们星球。

In fact, forget the oceans as we know them,

事实上，连我们熟知的海洋也将不复存在，

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

现在地球表面面积的 70%以上是海洋，

regulate the atmosphere of the whole planet.

调节着整个地球的大气层。

But worst of all,

但最糟的是，

there would be no iced tea.

那样就没有冰茶了。

Mmmmm, iced tea.

嗯，冰茶。