is a tiny impurity. A touch of salt

一點點的鹽、泥沙

a grain of clay did absolutely crucial to the raindrops existence

都對雨滴的形成影響甚鉅

In fact, without these microscopic pieces of dirt there would be no rain because

實際上，水蒸氣若沒有這些微小的灰塵

water vapor can't condense into droplets on its own,

就無法自行凝結成水珠。

which is kind of weird because water molecules like each other

這說來奇怪，但水分子喜歡聚在一起。

If they didn't, they wouldn't cling to each other like this. And in the air

否則他們也不會像這樣聚攏。

vaporized water molecules collide and stick together all the time

大氣裡蒸氣型態的水分子總是連結在一起，

But they also break apart all the time thanks to bond breaking heat energy

當然它們也會因為熱能而被迫分開(斷鍵)。

Only when air cools down past a certain point called the dew point

只有當空氣冷卻到一定程度時，我們稱之為凝結點，

does this breaking apart slow down enough for little clusters of water

這一團團的水分子

molecules to grow into droplets

才會聚集成水滴。

But actually that's only true if the cluster is big

但事實上這也要水團夠大才能完成，

to start with. If it's too small, it's surface is curve

如果太小，表面不平整的話，

the molecules on the outside have few neighbors to bond to, which makes them

外層的分子很難與附近的分子做連結，

easy to break off

這也使它們容易被分開。

So the cluster as a whole has higher chances are losing molecules than gaining them

所以即使低於凝結點，失去分子還是比獲得分子容易，

even below dewpoint, which means that up until a certain critical size

這也說明如果水分子團沒有大到某個程度

a cluster chances of shrinking are better than it's odds of growing

比起集合成更大的水分子團，它們更有可能縮水。

Unfortunately that critical size is 150 million molecules

可惜的是，這決定性的大小要達到1.5億分子。

And while there are millions of 5 molecule clusters in a golf ball sized volume of air to dewpoint

而一顆高爾夫大的氣體中，有數以百萬計的5分子水團在等待凝結點。

odds are that only one of those clusters will grow to a size of 10

而只有一個會成長至10分子

and you'd need a golf ball of air ten million miles across to find a

所以如果你要找到50分子的水分子團

single fifty molecule cluster

你會需要直徑一千萬英里的高爾夫球大小的大氣

which basically means that clusters of water molecules never get to that 150 million mark on their own.

這意味著，水分子團無法單靠自己達到一億五千萬的標準

Fortunately they don't have to, they can start

可喜可賀的是，他們也不需要那樣做

of it that critical size by condensing onto one of the good Jillians of little pieces of little dirt

他們可以透過吸附大氣中數不盡的灰塵，

floating in our atmosphere, and then grow and grow until their are droplet in a rain cloud

以幫助他們形成雨雲裡的一顆水珠。

and ultimately if these little pieces of dirt surrounded by water

這些被水包覆的微小灰塵

that make life possible on our big piece of dirt surrounded by water

使我們能生存在水給包覆的地球裡。

Hi again before I go I wanna let you know that this video was sponsored by Lynda.com

在離開前，要讓你知道，這支影片是由Lynda.com提供

The online learning platform with over 3,000 on-demand video courses

有超過3000個課程能在這在這個線上學習平台找到

to help you strengthen your business, technology and creative skills

來幫助你增強在商業、科技或是創意上的技巧。

lynda.com has courses in a range of topics from negotiation tactics to Photoshop

從談判技巧到Photoshop等課程，都可以在lynda.com找到

I've personally clocked a lot of hours on Linda, learning about everything from

我自己則是在lynda上學了

JavaScript to the Adobe Creative Suite

JavaScript、Adobe Creative Suite等等的軟體

and without it there's a good chance I'd be googling right now instead of recording this message

而且如果沒有它，我可能現在會使用估狗，而不是錄這則語音。