The next time you see a news report of a hurricane or a tropical storm showing high winds battering trees and houses,
下次你看到新闻报导有飓风或热带风暴正席卷树木和房屋时，
ask yourself, "How did the wind get going so fast?"
问问自己：“风为什么可以这么快？”
Amazingly enough, this is a motion that started more than five billion years ago.
令人惊奇的是，这个空气的运动源自于五十多亿年前。
But, to understand why, we need to understand spin.
然而，要了解原因，我们比须了解“旋转”。
In physics, we talk about two types of motion.
在物理学中，我们会谈论两种运动。
The first is straight-line motion. You push on something, and it moves forward.
第一种是直线运动。你推某样东西，它就向前移动。
The second type, spin, involves an object rotating, or turning on its axis in place.
第二种是转动，涉及了物体的旋转，或者说是沿着旋转轴旋转。
An object in straight-line motion will move forever unless something,
直线运动的物体，不断向前运动，
like the friction of the ground beneath it, causes it to slow down and stop.
除非有像地板上摩擦力的这类力量让它变慢，然后停止。
The same thing happens when you get something spinning.
同样的事也发生在转动上。
It will keep on spinning until something stops it. But the spin can speed up.
旋转会持续到有力量将它停下来，但旋转也可以加速。
If an ice skater is gliding across the ice in straight-line motion and she pulls her arms in, she keeps on gliding at the same speed.
如果溜冰的选手沿着直线滑过冰场，然后把手臂收回来，她会以等速继续滑行。
But if she is spinning on the ice and she pulls her arms in, you know what happens next.
但如果她是在冰上转动，然后把手臂收回来，你很清楚会发生什么事。
She spins faster. This is called the conservation of angular momentum.
她会转得更快。这叫做“角动量守恒”。
Mathematically, angular momentum is a product of two numbers,
数学上，角动量是两个数的相乘，
one that gives the spin rate and one that gives the distance of the mass from the axis.
一个是转动的速度、一个是质量到旋转轴的距离。
If something is freely spinning, as one number gets bigger, the other gets smaller.
所以当物体自由转动时，一个数字变大，另一个就变小。
Arms closer, spin faster. Arms farther, spin slower. Spin causes other effects, too.
当手收回来，就转得快。当手伸出去，就转得慢。转动还会造成其他效应。
If you are riding on a spinning merry-go-round and you toss a ball to a friend, it will appear to follow a curving path.
如果你骑着旋转木马，然后朝着朋友丢球，看起来球的路径是曲线。
It doesn't actually curve, though. It really goes in a straight line.
但实际上并不是这样的。它走的是直线。
You were the one who was following a curving path, but, from your point of view, the ball appears to curve.
你才是沿着曲线运动的人。但从你的角度看，球变成了曲线运动。

We call this the coriolis effect. Oh, and you are riding on a speeding merry-go-round right now at this very moment.
这种现象叫做“科里奥利效应”。你正坐在超高速的旋转木马上，就在此时此刻。
We call it the Earth. The Earth spins on its axis once each day.
这个“旋转木马”我们称之为地球。地球沿着地轴，每天自转一圈。
But why does the Earth spin? Now, that's a story that starts billions of years ago.
但为什么地球会转动？这是几十亿年前的故事了。
A cloud of dust and gas that form the Sun and the Earth and the planets and you and me
构成太阳、地球、所有的行星，还有我和你的一团尘埃和气体，
started to collapse as gravity pulled it all together.
在引力的作用下开始崩塌。
Before it started to collapse, this cloud had a very gentle spin.
在崩塌前，这团星云一直轻微的旋转。
And, as it collapsed, like that ice skater pulling her arms in, the spin got faster and faster.
在它崩塌时，就像滑冰运动员收紧手臂一样，它旋转的越来越快。
And everything that formed out of the cloud, the Sun
这团星云构成的所有的物体、太阳、
and the planets around the Sun and the moons around the planets, all inherited this spin.
还有围绕太阳的行星和围绕行星的月亮，都继承了这股转动力量。
And this inherited spin is what gives us night and day.
就是这个转动让我们有了白天与黑夜。
And this day-night cycle is what drives our weather.
昼夜节律推进了气候变化。
The Earth is warm on the daytime side, cool on the nighttime side, and it's warmer at the equator than at the poles.
地球上白天的那面较暖，夜晚的那面较凉，赤道也比南北极更加温暖。
The differences in temperature make differences in air pressure,
不同的温度形成了不同的气压，
and the differences in air pressure make air move. They make the wind blow.
而气压的不同造成了空气的流动，造成了风。
But, because the Earth spins, the moving air curves to the right in the Northern Hemisphere because of the coriolis effect.
但是，因为地球在不停地旋转，北半球流动的空气会向右偏转。这是科里奥利效应的缘故。
If there's a region of low pressure in the atmosphere, air is pushed toward it, like water going down a drain.
如果在大气层中有一片低压区域，空气就会被推动到那里，就像水流进排水孔一样。
But the air curves to the right as it goes, and this gives it a spin.
但是流动的空气向右偏转，这就造成了旋转。
With the dramatic low pressure in a storm, the air gets pulled in tighter and tighter,
由于风暴中心的超级低压，空气吸进来的力量越来越强，
so it gets going faster and faster, and this is how we get the high winds of a hurricane.
风速就越来越快，这就是飓风的风速极快的原因。
So, when you see a spinning storm on a weather report, think about this:
所以，当你在天气预报中看到暴风雨，想一想：
The spin ultimately came from the spin of the Earth, and the Earth's spin is a remnant, a fossil relic,
这个旋转最终来源于地球的转动，而地球的转动是种遗迹、是化石级的遗迹，
of the gentle spin of the cloud of dust and gas that collapsed to make the Earth some five billion years ago.
是五十亿年前，那团崩塌后构成地球的轻微旋转的尘埃和气体留下的。
You are watching something, the spin, that is older than dirt, that's older than rocks, that's older than the Earth itself.
你所看到的旋转，它的历史比尘埃还要古老，比岩石还要古老，比地球本身还要古老。