and you've probably seen it lots of times without even realizing it.

而且你可能早已看過無數次，只是沒發覺罷了。

Ever notice how cereal tends to stick together in the middle of the bowl? Or it clumps to the edges.

你有注意過早餐穀片似乎會聚集在碗的正中央嗎？或是堆積在碗的邊緣。

That makes it easy to eat, but why does it happen?

這讓他們更容易用湯匙舀起來吃，但這種現象的成因是什麼？

We see this same clumpage with other objects too: paper clips, thumb tacks, even bubbles in a beverage will snap together.

我們也能在許多的物品上看到類似的堆積現象：迴紋針、大頭針，甚至是飲料裡的泡泡也都會聚集在一起。

Maybe you've noticed this, but scientists didn't fully understand what was going on until 2005, when a pair of mathematicians decided to hit the lab, hit the kitchen, and hit the books.

或許你有注意到這個現象過，但科學家們直到 2005 年時，兩位科學家決定前往實驗室、廚房和圖書館一探究竟後才知道這究竟是怎麼回事。

What they found is cool.

而他們發現了相當有趣的原因。

I'm super cereal. Check this out.

我超認真的。看看這個吧。

Breakfast cereal is less dense than water, and milk is mostly water.

早餐穀片的密度比水還低，而牛奶的主要成分是水。

It's buoyant, it weighs less than the milk it displaces.

因此穀片具有浮力，因為它比推擠出去的牛奶還要輕。

That force of buoyancy pushes up on each ring, until it matches the downward force of gravity.

浮力會把一顆顆穀片往上推，直到與穀片受到的向下地吸引力相符為止。

This interaction holds the Cheerios at the surface of the liquid, like little toasty rafts drifting together on top of a sea of cereal milk.

這種作用力間的互動讓穀片能保持在液體的表面上飄浮著，就像是一艘在牛奶汪洋中漂泊的酥脆小船一樣。

It's a really complicated way of saying cereal floats.

這是用比較複雜的方式來解釋穀片漂浮著的原因。

But look closely at where the cereal meets the liquid. It's curved up.

但是仔細看看穀片與液體之間的交界處吧。液體的邊緣捲曲了起來。

The same thing happens at the edge of the container, thanks to the meniscus effect.

在容器的邊緣也有同樣的狀況，而這都是因為彎液面作用的緣故。

Water molecules are sticky — they're attracted to each other, but they're even more attracted to the edges of your bowl or glass, or to the edge of the cereal itself.

水分子具有黏性，它們會互相吸引，但它們更容易被碗或是玻璃杯的邊緣吸引，或是受到穀片本身的吸引。

That "adhesion" forms a U-shape wherever the liquid meets an edge.

這種「黏性」導致當液體碰到物體表面時形成了一個 U 型的界線。

A buoyant object will always be pushed up the liquid to the highest point on a meniscus.

具有浮力的物體總是會被推擠到液體表面上，彎液面的最高點。

That's what makes them stick to the edge, and what causes the cheerios to become cheeri-amigos.

這就是為什麼它們都會黏到邊緣上，並讓穀片們黏在一塊變成穀片哥倆好的原因。

Any two nearby Os are pushed to a high point between them, and clumps are pushed towards the overall highest point in the bowl, around the edge.

任何相鄰的兩個穀片會被推擠到兩者之間液面的最高點，而結成一塊之後就會被推到整個碗裡的最高點，也就是碗的邊緣。

Let's try something denser.

讓我們試試看其他密度更高一點的東西吧。

I don't recommend eating paperclips, but toss them in water and they sink.

我並不建議把迴紋針吃下肚，但總之，我們如果直接把它丟進水裡，它便會沉下去。

Place them carefully though, and you can get them to float.

不過只要小心輕放，便能讓他們浮在水上。

They're too dense to be buoyant. They float because of surface tension.

它們密度太高，因此浮力不足。它們是因為表面張力才能漂浮在水上的。

Water molecules like to stick to each other so much, they can behave like a membrane that's strong enough to hold up tiny things.

水分子非常喜歡黏在一起，讓它們能形成像是一層膜那樣，足以支撐住較小的東西。

Let's try it with these thumbtacks.

接下來試試看大頭針吧。

Like the paper clips, you can see that they're pushing that membrane down, just not hard enough to break through.

就像迴紋針一樣，你能看到它們正向下推擠水膜，但力道不足以穿破它。

If I place another one nearby, watch what happens.

仔細看在我放下另一個大頭針之後發生了什麼是。

They're attracted to each other, just like the Cheerios.

它們倍互相吸引，就像是穀片一樣。

But the water around each one is curving down.

但是它們周圍的水面是朝下彎曲的。

Instead of climbing up the water like the cereal did, they fall into each other's sinkhole.

不像穀片是往水面的高處爬去，大頭針們反而是掉進了各自形成的凹洞中。

We can mess this whole scenario up just by adding soap.

只要加點肥皂水便能破壞這個現象。

The chemical properties of soap lower the surface tension of water, so anything relying on surface tension to stay afloat will sink.

肥皂的化學特性會降低水的表面張力，讓任何依靠表面張力飄在上面的東西沉下去。

But buoyant objects don't rely on surface tension, so they continue surfing the meniscus.

然而具有浮力的物體由於靠的不是表面張力，因此仍能在彎液面上悠游。

The first time I did this, I wondered if the tacks were being pulled together by static attraction on the plastic coating or something.

我第一次嘗試的時候，心想大頭針之所以會互相吸引，是不是其實是因為上面塑膠塗層所導致的靜電吸引力或其他的原因。

So I put in just the plastic bit to see.

因此我只放入塑膠的部分想試試看。

But instead of being pulled towards the tack, something strange happens… they repel each other.

但它們不但沒有互相吸引，奇怪的事情發生了... 它們竟然在互相排斥。

The same thing happens with Cheerios and a paper clip.

同樣的現象也發生在當把穀片與迴紋針放在一起時。

That's because light, floaty objects run away from the low points caused by the heavy objects.

這是因為輕盈、會漂浮的物體會遠離沉重的物體所形陳的凹陷水面。

A buoyant object will always repel something held up by surface tension's stretchy membrane.

一個具有浮力的物體永遠都會與表面張力所造成的延展性液面互斥。

Just to be clear, you should never put thumbtacks in your cereal. But this is what would happen if you did.

在此說清楚，絕對不要把大頭針放進穀片裡。但如果這麼做了的畫，看起來會像是這樣。

All of this made me wonder: What could happen if we could reverse the direction of water's meniscus?

而這讓我不禁心想：要是我們能反轉彎液面的方向呢？

I coated this glass with a hydrophobic coating that does just that.

我在這個玻璃試管裡塗上了疏水性塗層後，成功達成了這點。

When I put thumbtacks on top of the water in here, they floated to the edge instead of the center.

當我把大頭針放到這個試管裡的水面上時，它們會漂到靠近邊緣的地方，而不是漂到中心點。

And that buoyant object did the opposite. It floated to the middle.

而具有浮力的物品則相反，漂到了中心點。

So that's cool and all, but does the physics of cereal clumping actually matter in the real world?

這些現象確實挺酷的，但穀片聚集方法倍後的物理原理，在真實世界中有什麼實際用途？

It does if you're a tiny insect. Take water striders.

如果你是隻小小隻的昆蟲，那就很重要了。就以水黽為例子吧。

These pond skaters are nature's Cheerios.

這些在池塘裡自在滑走的小蟲就像自然界的穀片一樣。

They float so well that even a load 15 times their body weight won't make them sink. They can even jump on water.

牠們的飄浮能力之好，就算身體乘載了體重 15 倍的重量也不會沉下去。牠們甚至能在水上跳躍。

Tiny hairs on their legs trap air bubbles and increase their buoyancy.

牠們腳上的纖毛能困住氣泡，藉此來提升牠們的浮力。

They're basically wearing swim floaties on their feet.

牠們就好像在腳上穿了游泳浮具一樣。

Other aquatic insects like water treaders exploit surface tension, just like thumbtacks and paper clips.

而像是水蝽等的其他水生昆蟲則是利用了表面張力，就像是大頭針和迴紋針一樣。

But they get in trouble when it's time to get out.

但牠們很難脫離水面。

Gravity is pushing them into the depressions under their feet, but they've come up with a clever way to climb the meniscus.

重力將牠們的腿拖住，困在了腳下的凹陷液面上。不過牠們用了相當聰明的方法來爬上彎液面。

A running start doesn't work.

助跑沒什麼用。

But by arching their bodies and lifting their front and back ends, the bugs curve the water up, and are pulled to the edge just like the Cheerios were.

但是藉由將牠們的身體彎曲並把前端與尾端抬起，牠們能將水面向上彎曲，然後像是穀片那樣被拉往液面邊緣。

They're carried uphill by a physics-powered water escalator.

牠們簡直就是被物理學驅動的水扶梯給扛起並向上移動。

That's pretty cool.

真的挺酷的。

If you can find science like this at breakfast, imagine what else you might see the rest of day.

如果光是在早餐就能發現這麼酷炫的科學原理，想想看看一天下來還能發現些什麼。

Try this for yourself, and see what other floating objects you can get to attract or repel.

自己動手試試看吧，看看你能讓那些其他漂浮著的物品互相吸引或排斥。

Leave a comment and let me know what you find.

在底下留言，讓我知道你找到了些什麼吧。

And if you see any cool physics in everyday life I should check out in a future video, let me know.

如果你在日常生活中發現了任何想要我在之後的影片中介紹的酷炫物理原理，在底下跟我說。

Stay curious.

保持好奇，求知若渴。