What on Earth is spin? - Brian Jones

Translator: Andrea McDonough Reviewer: Jessica Ruby

翻译人员: Gabriella Hu 校对人员: Luyao Zou

The next time you see a news report of a hurricane

当你看到关于台风，

or a tropical storm

或者一个热带风暴的报道，

showing high winds battering trees and houses,

看到狂风席卷树木和房屋时，

ask yourself, "How did the wind get going so fast?"

问问你自己：“风的威力怎样变得那么大？”

Amazingly enough, this is a motion that started

神奇的是，这个运动早在五十亿年前

more than five billion years ago.

就已经开始了

But, to understand why, we need to understand spin.

但是想要了解其中的原因，首先要了解自旋

In physics, we talk about two types of motion.

在物理中，我们会谈到两种运动：

The first is straight-line motion.

第一种是直线运动，

You push on something, and it moves forward.

当你推动一个物体时，它会向前进；

The second type, spin, involves an object rotating,

第二种，自旋，是一个物体的旋转，

or turning on its axis in place.

也就是在原地绕它的轴线旋转

An object in straight-line motion will move forever

一个直线运动的物体会永远保持直线运动状态，

unless something,

直到有东西，

like the friction of the ground beneath it,

比如与地面的摩擦力，

causes it to slow down and stop.

使它减慢速度，然后停止运动

The same thing happens when you get something spinning.

物体旋转时也是同样的原理

It will keep on spinning until something stops it.

它会一直旋转直到有东西使它停止

But the spin can speed up.

但是自旋可以加快速度

If an ice skater is gliding across the ice

如果一个滑冰运动员冰面上，

in straight-line motion and she pulls her arms in,

直线滑行，然后收缩手臂，

she keeps on gliding at the same speed.

她会继续以同样的速度滑行；

But if she is spinning on the ice

但是如果她在冰上旋转，

and she pulls her arms in,

然后把手臂收紧，

you know what happens next.

你知道接下来会发生什么——

She spins faster.

她的旋转加速

This is called the conservation of angular momentum.

这叫做角动量守恒定律

Mathematically, angular momentum is a product of two numbers,

从数学的角度来讲，角动量是两个数的积

one that gives the spin rate

一个数是旋转速度，

and one that gives the distance of the mass from the axis.

另一个是该物体与定点的距离

If something is freely spinning,

当一个物体自由旋转时，

as one number gets bigger,

当一个数据增大，

the other gets smaller.

另一个就会减小

Arms closer, spin faster.

手臂收紧，旋转加速，

Arms farther, spin slower.

手臂张开，旋转减速

Spin causes other effects, too.

旋转也会产生其它的效应

If you are riding on a spinning merry-go-round

如果你在旋转木马上，

and you toss a ball to a friend,

向你的朋友扔一个球，

it will appear to follow a curving path.

它的轨道看上去世弯曲的

It doesn't actually curve, though.

其实，它并没有弯曲

It really goes in a straight line.

其实是直线运动

You were the one who was following a curving path,

你才是走弯曲路线的，

but, from your point of view,

但是从你的视角，

the ball appears to curve.

抛出去的球看上去走弯路了

We call this the coriolis effect.

我们把这个称作科里奥利力

Oh, and you are riding on a speeding merry-go-round

你现在就骑在一个旋转木马上

right now at this very moment.

就在此时此刻

We call it the Earth.

这个“旋转木马”就是地球

The Earth spins on its axis once each day.

地球每天都绕它的轴旋转一圈

But why does the Earth spin?

但是为什么地球会旋转呢？

Now, that's a story that starts billions of years ago.

这就要回到几十亿年前

A cloud of dust and gas that form

构成太阳，地球，所有的行星

the Sun and the Earth and the planets

还有我和你的

and you and me

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,

在它塌下之前，

this cloud had a very gentle spin.

这团星云一直轻微的旋转

And, as it collapsed,

在它崩塌时，

like that ice skater pulling her arms in,

就像滑冰运动员收紧手臂一样，

the spin got faster and faster.

它旋转的越来越快

And everything that formed out of the cloud,

这团星云构成的所有的物体，

the Sun

太阳，

and the planets around the Sun

还有围绕太阳的行星

and the moons around the planets,

和围绕行星的月亮，

all inherited this spin.

都从原始星云中得到了一定的旋转

And this inherited spin is what gives us night and day.

这个旋转就是我们有昼夜的原因

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,

地球的白天一侧是暖和的，

cool on the nighttime side,

黑夜一侧凉爽一些，

and it's warmer at the equator than at the poles.

赤道比两级更加暖和

The differences in temperature

不同的温度

make differences in air pressure,

形成了不同的气压，

and the differences in air pressure

而气压之间的差别

make air move.

使空气流动

They make the wind blow.

它们使风吹动

But, because the Earth spins,

但是，因为地球在不停地旋转，

the moving air curves to the right

在北半球，

in the Northern Hemisphere

流动的空气向右偏转

because of the coriolis effect.

因为有科里奥利力

If there's a region of low pressure in the atmosphere,

如果在大气层中有一片低压区域，

air is pushed toward it,

空气就会被推动到那里，

like water going down a drain.

就像水流进排水孔一样

But the air curves to the right as it goes,

但是流动的空气向右偏转，

and this gives it a spin.

这给予了它旋转

With the dramatic low pressure in a storm,

暴风雨中有极度的低压，

the air gets pulled in tighter and tighter,

空气就一直向中间流动，

so it gets going faster and faster,

所以旋转的越来越快，

and this is how we get the high winds of a hurricane.

这就是为什么飓风吹得那么烈。

So, when you see a spinning storm on a weather report,

所以，当你在天气预报中看到暴风雨，

think about this:

想一想：

The spin ultimately came from the spin of the Earth,

这个旋转最终来源于地球的旋转，

and the Earth's spin is a remnant,

而地球的旋转只是残存的

a fossil relic,

化石遗迹，

of the gentle spin of the cloud of dust and gas

是五十亿年前，

that collapsed to make the Earth

那团崩塌后构成地球的

some five billion years ago.

轻微旋转的尘埃和气体留下的。

You are watching something, the spin,

你所看到的旋转，

that is older than dirt,

它的历史比比尘土还要古老，

that's older than rocks,

比岩石还要古老，

that's older than the Earth itself.

比地球本身还要古老