all comfy and warm, thinking,

暖洋洋地想著：

"Man, it'd be cool to be an astronaut!

「啊！要是能當個太空人就酷斃了！

You could float out in outer space,

你可以在外太空漂浮

look down at the Earth and everything.

鳥瞰地球的一切

It'd be so neat!"

這種感覺肯定棒透了！」

Only that's not how it is at all.

遺憾的是，現實是殘酷的。

If you are in outer space,

你如果在外太空，

you are orbiting the Earth,

你會繞著地球運轉，

it's called free fall.

這就是所謂「自由落體」。

You're actually falling towards the Earth.

你其實正筆直地朝地球落下，

Alright, think about this for a moment.

嗯，這樣想一下好了，

That's the feeling you get

這種感覺就像是，

if you're going over the top of a roller coaster,

「你坐的雲霄飛車爬到至高點，然後

going, like, "Whoooooaaaahhhh!"

咻－哇哇挖嗄啊啊啊！」的那種感覺

Only you're doing this the whole time

只差在你會這樣下去，

you're orbiting the Earth

繞著地球轉。

for two,

兩個，

three,

三個，

four

四個，

hours,

小時

days,

甚至好幾天，

whatever it takes, right?

無論多久，是吧？

So, how does orbiting work?

那繞地公轉的原理是什麼呢？

Let's take a page from Isaac Newton.

這時候就有請牛頓老師為我們解釋了，

He had this idea,

他先這麼想的，

a little mental experiment.

進行一個小小的思想實驗。

You take a cannon,

你搬出一座大砲，

you put it on top of a hill.

放在小山巔上，

If you shoot the cannon ball,

假使你發射一枚砲彈，

it goes a little bit away.

它飛不遠就落地了。

But if you shoot it harder,

但若你發射的更有力一些，

it goes far enough so that it lands

它就能飛衝地更遠，最終落在

a little bit past the curvature of Earth.

地球曲線的較深處。

Well, you can imagine

想得更遠些，

if you shot it really, really, really hard,

如果你以很快很快的速度把炮彈發射出去，

it would go all the way around the Earth

它會開始一路繞地球轉，

and come back, boom!

踅了一圈回來，咚！

and, like, hit you in the backside or something.

命中你的屁屁或之類的。

Let's zoom way back

現在把鏡頭拉回外太空，

and put you in a little satellite

將你放進一個人造衛星，

over the North Pole of the Earth

以北極上空為起始點，

and consider north to be up.

並視北方為向上的方向。

You're going to fall down and hit the Earth.

你理應落下然後撞上地球，

But you are actually moving sideways really fast.

但實際上你沿切線方向快速移動，

So, when you fall down,

因此當你落下時，

you're going to miss.

你會與地球擦身而過。

You're going to end up on the side of the Earth,

最終你飛到地球的西端點，

falling down,

向南方掉下去，

and now the Earth is pulling you back in sideways.

但現在地球把你往側面拉，

Alright, and so it's pulling you back in

於是把你吸回來，

and you fall down,

然而你持續落下，

and so you miss the Earth again,

你再度與它擦肩而過。

and now you're under the Earth.

現在你位於地球正下方，

And the Earth is going to pull you up,

它會將你往上拉，

but you're moving sideways still.

但你依然沿切線移動，

So, you're going to miss the Earth again.

結果你三度與地球失之交臂。

Now, you're on the other side of the Earth,

現在你位處地球的東端點，

moving upward and the Earth's pulling you sideways.

向上移動的同時，地球把你拉往一旁，

Alright, so you're going to fall sideways,

於是你會往一旁落向地球，

but you're going to be moving up and to a miss.

但正因你向上移動，搞到最後仍然與地球無緣。

And now you're back on top of the Earth again,

現在，你再次回到地球的正上方，

over the North Pole,

北極上空，

going sideways and falling down,

不斷沿切線移動，同時往地球落下。

and yep, you guessed it.

沒錯，同你猜測的，

You'll keep missing because you're moving so fast.

你會因為移動迅速而持續與地球擦身而過。

In this way, astronauts orbit the Earth.

太空人就是照這個原理繞著地球轉。

They're always falling towards the Earth,

他們不停落向地球，

but they're always missing,

但終究還是撞不著它。

and therefore, they're falling all the time.

所以他們始終都在落下，

They feel like they're falling,

他們也感到自己正在落下，

so you just have to kind of get over it.

所以，嗯，習慣就好啦。

So, technically, if you ran fast enough and tripped,

從技術上說，假設你衝得夠快，猛然跌飛出去，

you could miss the Earth.

你也許再也碰不著地球了。

But there's a big problem.

但，問題來了。

First, you have to be going 8 kilometers a second.

首先，你必須每秒狂奔8公里，

That's 18,000 miles an hour,

相當於時速18,000英里，

just over Mach 23!

甚至比23倍音速還快！

The second problem:

問題二：

If you're going that fast,

要是你真能跑那麼快，

yes, you would orbit the Earth

你的確會繞著地球轉，

and come back where you came from,

然後回到原點，

but there's a lot of air in the way,

然而一路上會有大量的空氣等著你，

alright, much less people and things.

甭提更礙事的人們和東西。

So, you would burn up due to atmospheric friction.

你會因與大氣過度摩擦而燒得精光。

So, I do not recommend this.

所以，我勸你別這麼做。