The invisible motion of still objects - Ran Tivony

譯者: Helen Chang 審譯者: S Sung

Many of the inanimate objects around you probably seem perfectly still.

周遭許多無生命的物體 看似完全靜止。

But look deep into the atomic structure of any of them,

但如果深入觀察它們的原子結構，

and you'll see a world in constant flux.

就會看見一個不斷波動的世界。

Stretching,

伸展、收縮、彈跳、抖動

contracting,

springing,

jittering,

drifting atoms everywhere.

和飄移的原子無所不在。

And though that movement may seem chaotic, it's not random.

看似亂紛紛的動，其實並不亂。

Atoms that are bonded together,

幾乎所有物質的原子 都被鍵合在一起，

and that describes almost all substances,

根據一套原則而移動。

move according to a set of principles.

For example, take molecules, atoms held together by covalent bonds.

例如，分子的原子 由共價鍵結合在一起。

There are three basic ways molecules can move:

分子有三種移動的基本方式：

rotation,

旋轉、平移，和振動。

translation,

and vibration.

Rotation and translation move a molecule in space

旋轉和平移乃是分子在空間中移動，

while its atoms stay the same distance apart.

其原子間的距離保持不變。

Vibration, on the other hand, changes those distances,

另一方面，振動改變了原子的間距，

actually altering the molecule's shape.

實際上也改變了分子的形狀。

For any molecule, you can count up the number of different ways it can move.

任何分子的不同移動方式 都可以被算出來，

That corresponds to its degrees of freedom,

總數對應於它的自由度；

which in the context of mechanics

在機械學裡，自由度指的是

basically means the number of variables we need to take into account

為要了解整個系統 所需考慮的變數數目。

to understand the full system.

Three-dimensional space is defined by x, y, and z axes.

三維空間由 X、Y 和 Z 軸所定義。

Translation allows the molecule to move in the direction of any of them.

平移讓分子向其中的任何方向移動。

That's three degrees of freedom.

自由度是三。

It can also rotate around any of these three axes.

也可以繞其中一軸旋轉，

That's three more,

自由度加三；

unless it's a linear molecule, like carbon dioxide.

除非它是個線性分子， 例如二氧化碳，

There, one of the rotations just spins the molecule around its own axis,

它其中的一種，只是 分子依著自身的軸線旋轉，

which doesn't count because it doesn't change the position of the atoms.

因它的原子位置不變， 所以不計為旋轉。

Vibration is where it gets a bit tricky.

振動則有點複雜。

Let's take a simple molecule, like hydrogen.

取一簡單的分子，例如氫，

The length of the bond that holds the two atoms together is constantly changing

兩個原子間的共價鍵， 長短不斷地變化，

as if the atoms were connected by a spring.

彷彿由彈簧連結著原子。

That change in distance is tiny, less than a billionth of a meter.

長度的變化極小， 短於十億分之一公尺。

The more atoms and bonds a molecule has, the more vibrational modes.

分子的原子數和鍵數越多， 振動的方式也就越多。

For example, a water molecule has three atoms:

例如，水分子有三個原子：

one oxygen and two hydrogens, and two bonds.

一氧、二氫，和二鍵，

That gives it three modes of vibration:

使得它有三種振動模式：

symmetric stretching,

對稱伸縮，

asymmetric stretching,

非對稱伸縮，

and bending.

和屈折。

More complicated molecules have even fancier vibrational modes,

複雜的分子有更花俏的振動模式，

like rocking,

像晃動、

wagging,

搖擺

and twisting.

和扭轉。

If you know how many atoms a molecule has, you can count its vibrational modes.

如果知道分子的原子數， 即可算出它振動模式的總和。

Start with the total degrees of freedom,

從總自由度開始，

which is three times the number of atoms in the molecule.

也就是三乘以分子中的原子數；

That's because each atom can move in three different directions.

這是因為每個原子可以向 三個不同的方向移動；

Three of the total correspond to translation

其中有三個對應著平移，

when all the atoms are going in the same direction.

所有的原子均向同一方向移動；

And three, or two for linear molecules, correspond to rotations.

另有三個對應旋轉， 若是線性分子則對應兩個；

All the rest, 3N-6 or 3N-5 for linear molecules,

剩下的 3N-6， 或者線性分子的 3N-5，

are vibrations.

就是振動。

So what's causing all this motion?

這一切因何而動呢？

Molecules move because they absorb energy from their surroundings,

分子因自週遭吸收了能量而動，

mainly in the form of heat or electromagnetic radiation.

主要的能量形式 是熱能或電磁輻射能。

When this energy gets transferred to the molecules,

當能量被轉移至分子，

they vibrate,

分子就以更快的速度 振動、旋轉，或平移。

rotate,

or translate faster.

Faster motion increases the kinetic energy of the molecules and atoms.

加快的運動速度 提升了分子和原子的動能，

We define this as an increase in temperature and thermal energy.

我們定義為溫度升高或熱能增加。

This is the phenomenon your microwave oven uses to heat your food.

這是使用微波爐加熱食物的現象。

The oven emits microwave radiation, which is absorbed by the molecules,

微波爐射出微波輻射，由分子吸收，

especially those of water.

尤其是由水分子吸收。

They move around faster and faster,

它們四處移動，速度越來越快，

bumping into each other and increasing the food's temperature and thermal energy.

互相碰撞，提高食物的溫度和熱能。

The greenhouse effect is another example.

溫室效應是另一個例子。

Some of the solar radiation that hits the Earth's surface

一些太陽輻射擊中地球表面，

is reflected back to the atmosphere.

被反射回大氣中；

Greenhouse gases, like water vapor and carbon dioxide absorb this radiation

溫室氣體，如水蒸氣和二氧化碳，

吸收輻射能，速度加快。

and speed up.

These hotter, faster-moving molecules emit infrared radiation in all directions,

這些更熱、更快速移動的分子

向每個方向散射紅外輻射線，

including back to Earth, warming it.

包括射回地球，使地球變暖了。

Does all this molecular motion ever stop?

這一切分子運動會停止嗎？

You might think that would happen at absolute zero,

你或許認為，在絕對零度， 能達到的最低溫，分子可能就不動了。

the coldest possible temperature.

No one's ever managed to cool anything down that much,

沒有人曾降低至絕對零度，

but even if we could,

但即使辦得到，

molecules would still move due to a quantum mechanical principle

基於量子力學原理， 分子仍然會​​動，

called zero-point energy.

被稱為零點能。

In other words, everything has been moving since the universe's very first moments,

換句話說，自宇宙初始， 萬事萬物已經在動，

and will keep going long, long after we're gone.

並且還會在我們身後長久持續地動。