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静止物体的不可见运动 – 译学馆
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静止物体的不可见运动

The invisible motion of still objects - Ran Tivony

你周围许多物体看似是完全静止的
Many of the inanimate objects around you probably seem perfectly still.
但请从微观原子结构上观察它们
But look deep into the atomic structure of any of them,
你会发现一个永不停息运动着的世界扩张着
and you’ll see a world in constant flux.
压缩着
Stretching,
弹动着
contracting,
抖动着
springing,
原子
jittering,
动来动去
drifting atoms everywhere.
即使这种运动看似混乱 它们其实有规律可循
And though that movement may seem chaotic, it’s not random.
原子连接在一起
Atoms that are bonded together,
几乎构成了所有物质
and that describes almost all substances,
按照一定规律在运动着
move according to a set of principles.
例如分子中原子有着共价的联系
For example, take molecules, atoms held together by covalent bonds.
分子以三种基本规律运动:
There are three basic ways molecules can move:
旋转平移
rotation,

translation,
振动
and vibration.
旋转和转化时分子在空间中运动
Rotation and translation move a molecule in space
此时原子的间隙不变
while its atoms stay the same distance apart.
然而振动会改变原子间距
Vibration, on the other hand, changes those distances,
实际上这改变了分子的形状
actually altering the molecule’s shape.
每种分子都有一定数量的运动方式
For any molecule, you can count up the number of different ways it can move.
运动方式的多少与其自由度有关
That corresponds to its degrees of freedom,
用机械术语讲
which in the context of mechanics
就是我们为了全面了解一个整体
basically means the number of variables we need to take into account
而需要考虑的变量的数量
to understand the full system.
立体空间可用x y
Three-dimensional space is defined by x, y, and z axes.
z轴描述平移可让分子朝各个方向运动
Translation allows the molecule to move in the direction of any of them.
这种运动方式在三个维度上都完全自由
That’s three degrees of freedom.
分子也可以围绕这三个坐标轴旋转
It can also rotate around any of these three axes.
这是另外三种运动方式
That’s three more,
除非它是像二氧化碳一样的线型分子
unless it’s a linear molecule, like carbon dioxide.
线型分子的一种旋转方式是绕自己
There, one of the rotations just spins the molecule around its own axis,
的轴线旋转由于它的原子位置不变这种方式不纳入旋转方式的种类
which doesn’t count because it doesn’t change the position of the atoms.
振动就有一些复杂了
Vibration is where it gets a bit tricky.
以氢分子为例
Let’s take a simple molecule, like hydrogen.
它们的两原子间的间隙在不断变化
The length of the bond that holds the two atoms together is constantly changing
就像被弹簧连接一样
as if the atoms were connected by a spring.
这种间隙的改变很微小小于十亿分之一米
That change in distance is tiny, less than a billionth of a meter.
分子的原子越多它的振动方式就越多
The more atoms and bonds a molecule has, the more vibrational modes.
例如水分子有三个原子:
For example, a water molecule has three atoms:
一个氧原子 两个氢原子和两个相联点
one oxygen and two hydrogens, and two bonds.
这种结构让它有了三种振动方式:
That gives it three modes of vibration:
对称拉伸
symmetric stretching,
非对称拉伸和
asymmetric stretching,
弯折
and bending.
更复杂的分子有更剧烈的振动方式
More complicated molecules have even fancier vibrational modes,
比如强振动摇摆
like rocking,

wagging,
弯折
and twisting.
知道了分子中原子的个数就能知道其振动的种类数量
If you know how many atoms a molecule has, you can count its vibrational modes.
当运动不受阻碍时
Start with the total degrees of freedom,
振动种类数量是原子数量的三倍
which is three times the number of atoms in the molecule.
这是因为每个原子都可以从三个方向移动
That’s because each atom can move in three different directions.
三种运动种类属于平移
Three of the total correspond to translation
这时所有原子同方向移动
when all the atoms are going in the same direction.
旋转有三种运动方式(线型分子有两种)
And three, or two for linear molecules, correspond to rotations.
其余的3N-6种(线型分子3n-5种)
All the rest, 3N-6 or 3N-5 for linear molecules,
属于振动
are vibrations.
那么这些运动由什么引起呢?
So what’s causing all this motion?
分子吸收了周围的能量
Molecules move because they absorb energy from their surroundings,
而得以运动这些能量主要以热量或电磁波的形式存在
mainly in the form of heat or electromagnetic radiation.
当这些能量转移到分子上时
When this energy gets transferred to the molecules,
它们可能振动
they vibrate,
可能旋转
rotate,
或是更快地平移
or translate faster.
更快的运动速度导致了粒子的动能增大
Faster motion increases the kinetic energy of the molecules and atoms.
宏观上表现为温度升高
We define this as an increase in temperature and thermal energy.
内能增大微波炉工作正是应用了这一原理
This is the phenomenon your microwave oven uses to heat your food.
微波炉放射出电磁波
The oven emits microwave radiation, which is absorbed by the molecules,
被分子吸收尤其易被液体吸收
especially those of water.
分子运动速度加快
They move around faster and faster,
相互碰撞后增大了食物温度和内能
bumping into each other and increasing the food’s temperature and thermal energy.
温室效应则是另外一个例子
The greenhouse effect is another example.
太阳的辐射照射着地球表面
Some of the solar radiation that hits the Earth’s surface
被地表反射到大气层
is reflected back to the atmosphere.
水蒸气或二氧化碳之类的温室气体将这些辐射吸收
Greenhouse gases, like water vapor and carbon dioxide absorb this radiation
运动速度加快
and speed up.
这些炽热 高速运动的分子朝各个方向释放红外线
These hotter, faster-moving molecules emit infrared radiation in all directions,
有一些红外线回到地球
including back to Earth, warming it.
使之升温这种分子运动会停止吗?
Does all this molecular motion ever stop?
你可能认为在绝对零度时这有可能发生
You might think that would happen at absolute zero,
在可能到达的最低温度下
the coldest possible temperature.
至今没有人曾创造出那样的低温环境
No one’s ever managed to cool anything down that much,
但是即使我们可以
but even if we could,
根据量子力学的中零点能量的解释
molecules would still move due to a quantum mechanical principle
分子在那样的情况下仍能运动
called zero-point energy.
换句话说 自宇宙婴儿时期以来万事万物就在不断运动
In other words, everything has been moving since the universe’s very first moments,
在我们消逝幻灭之后仍会继续
and will keep going long, long after we’re gone.

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