that cats almost always land on their feet. Today's question is why.

所以你可能已經發現貓咪幾乎總是用腳落地。

Like most simple questions there's a very complex answer. For instance

今天的問題是為什麼？

let me re-word this question. How does a cat go from feet up

就像是大部分的簡單問題一樣，這有個很複雜的答案。

to feet down in a falling reference frame without violating

舉例來說... 所以讓我改寫一下這問題。

the conservation of angular momentum. Now I've studied free falling bodies,

一隻貓如何在墜落過程的參考系統中

my own in fact, in several different environments and once I get my angular rotation started

從四腳朝天轉變成腳朝下，而不違反角動量守恆定律？

in one direction, I can't stop it. Today, we're gonna use a high speed camera, we're not

現在我已經研究過自由落體，實際上是以我自己，在幾種不同的環境之下做實驗，

gonna use Alley, cause this is my daughter's cat, I don't want to hurt it. We're gonna use a stunt cat.

而一旦我讓角動量起始往某個方向，我停不下來。

Let me introduce you to Gigi the stunt cat.

今天，我們要用一部高速攝影機，我們不會使用Alley，因為這是我女兒的貓咪。

[music]

我不想弄傷牠。

I'll just flip the video vertical, and then motion track

我們要使用一隻特技貓。

the cat. It's just gonna take a lot more effort in post. We're gonna try to do

讓我向你介紹特技貓：Gigi。

it in a way that doesn't make anybody mad. That's pretty hard to do.

我要把影像轉成垂直的，然後動態追蹤那貓咪。

You've gotta drop a cat. Ready Gigi? Good.

只是要費更大的勁在後製上。

Checking out the high speed data there Gigi?

我們要試著以不讓任何人生氣的方式來做這件事。那很難。

[music]

我要丟一隻貓。

OK the first thing a cat does when it's falling is try to figure out which way is up.

準備好了嗎，Gigi？

It does this either with a gyro in the ear, or with it's eyes.

很好。

3..2..

妳在檢查那兒的高速資料嗎，Gigi？

Ready to talk cat physics? Alright, so check out this footage I captured with the Phantom Miro

好，一隻貓在墜落過程中所做的第一件事是嘗試去分出上下。

while Gigi goes to get a drink of water. So here's what's interesting about this to me. If you'll notice

牠要不是用耳朵中的陀螺儀(內耳半規管)，要不就是用眼睛，來做這件事。

at the beginning of the drop the cat is not rotating. Half way through the drop

3… 2…

the cat is rotating, and then at the very end Gigi somehow stops rotating.

準備好談談貓咪物理學了嗎？

Newton's first law says that an object at rest will stay at rest unless acted

好吧，那麼趁Gigi去喝水的時候，看看這段用Phantom Miro(攝影機型號)所捕捉到的影片。

on by an external force. I see no external forces on this cat.

所以這個是讓我感到興趣的東西。如果你注意到在墜落過程的開端，貓咪並沒有轉動。

So what's happening here? It's not making sense to me. OK so in order to

掉到一半的時候貓咪才轉動，然後最後Gigi用某種方式停止轉動。

really get the right data, we're gonna have to drop her 90 degrees out of phase. Ready girl?

牛頓第一定律說一個靜止物體將保持靜止除非接觸到一個外在力量。

This time watch her tail. 3.. 2.. 1..

我在這貓咪身上沒看到外在力量。所以這裡發生什麼事？

[music]

對我來說一點道理也沒有。

OK so you think you've figured it out? Check this out.

好的，所以為了要真正得到正確的資料，我們必須要把她反轉90度丟下。

You probably noticed that when the cat was falling, her tail was rotating in the

好了嗎，女孩？這次注意她的尾巴。3… 2… 1…

direction opposite of where her body was rotating. What's interesting about that

好的，所以你以為你已經搞清楚了？來看看吧。

is that that's not how it works. In fact even Bobtail cats

你也許注意到當貓咪在墜落時，

can do this. It's called the cat righting reflex. I'll prove it to you.

她的尾巴會以一個和身體轉動相反的方向轉動。

I came across some video from the 60s when the air force was researching micro gravity for

有趣的是，那不是它的運作方式。

future astronauts. Turns out they took some cats up on parabolic flights.

事實上，甚至連短尾貓也可以這樣做。它叫做貓咪翻正反射(一種貓的本能)。

He tries to rotate his tail to flip over but it doesn't work. He just ends up

我會證明給你看。

nutating wildly. Then he does something interesting. He takes his back

我發現一些60年代的影片，當空軍為了未來的太空人在做微引力研究時。

and he bends it, and when he bends his back and then creates motion, something interesting happens.

結果他們帶了一些貓咪上去無重力飛行。他試著轉動他的尾巴去翻身，但沒有用。

Aah. Now we're getting somewhere. So let me

他只是變得失去控制地下墜。

show you one more cat flip with the Miro and we'll figure this out.

然後他做了件有趣的事情。

OK the arched back ends up being pretty

他拱起背部，

important. What he does is he divides his body up into two separate rotational

然後當他拱起背部然後做出動作，有趣的事情發生了。

axes that are tilted from one another. When he's released he pulls his front paws in

啊，現在我們有點頭緒了。

and does the ice skater trick. He decreases his moment of inertia in the front so he can spin

所以讓我用Miro再展示一次貓的翻轉給你看，然後我們會找出答案。

fast up there, but in the back he pushes his legs away from him, increasing his moment

好，拱起的身體看來是很重要的。

of inertia, so a really large twist in the front equals a really small

他所做的是把身體分成兩個分開且互相傾斜的旋轉軸。

twist in the back in the opposite direction and the torques equal out. So as soon as

當他被放開時，他收起前爪，然後使出冰上曲棍球的招式。

he gets his front paws in under him, all he has to do is extend those legs back out to

他降低前方的轉動慣量以使他能夠在上面快速轉動，

increase that moment of intertia and stop the front twist, and extend his back

但他在後面踢腿，增加他的轉動慣量，

legs along that rear axis. That allows him to twist those around

所以前方非常強力的扭動等同於是後方很小力、相反方向的扭動，而力矩互相抵消。

really fast, and then all he has to do is pull them back in under his body and then extend

所以一旦他將前爪收到身體下面，他所要做的只是將腿伸展回

all four legs and brace for impact.

去增加轉動慣量並停止前半身轉動，然後沿著後方軸線伸展他的腿。

[music]

那讓他能夠非常快速的扭轉，然後他所要做的只是將它們收回身體下方

So thank you for your attention. I hope you learned something

並伸展全部的四條腿並為衝擊做準備。

pretty cool about cats. If you don't mind.. [Angry meowing] Ooh! OK OK I'm done!

所以謝謝觀賞。我希望你學到了一些關於貓咪很酷的事情。

If you would, go check out your other cat videos after trying

如果你不介意…噢！好 好 我弄完了！

to catch Gigi. Wooh! A little too rowdy. If you'd like to, click Gigi

如果你想，抓到Gigi後去看看其他的貓咪影片。

the cat to subscribe, we'd appreciate it. I hope you had a good one. And aah

哇！有點太粗暴了。

Get the ball! You gotta catch her first. I got it, you want it?

如果你願意，按一下Gigi貓來訂閱，我們會很感激。

Look... Very cool cat.

希望你喜歡這影片。還有啊…撿球！!

She let us drop her hundreds of times. Or, you know, maybe just 5.

你得先抓到她。

Want your ball? Go get it!

我撿到球了，妳想要嗎？

Click her if you want to subscribe, but right now we're playing fetch.

看...很酷的貓咪。

Ready? Go get it!

她讓我們丟了幾百次。或，你知道，也許只有5次。

I'm Destin. You're getting Smarter Every Day. Have a good one.

想要你的球嗎？去撿吧！

[Whispered] There you go.

如果你想訂閱請點她，但現在我們在玩撿球遊戲。

You earned it.

準備好了？去撿吧！

Let me explain why cats are

我是Destin。你每天都變得更聰明。掰掰。

wizards at physics. First of all they have physiology working for them. They have no working clavicle

那就對了。

like I do, and secondly they have very flexible back bones.

那就對了。你應得的。

The talent needs a break.

讓我解釋為何貓咪是物理界的魔術師。

30 centimeters or higher. Anything below that is unsafe.

首先，他們有適用的生理構造。

Not that we condone dropping cats. C'mere!

他們沒有像我一樣有作用的鎖骨，而且第二，他們有非常有彈性的背骨。

C'mere.. There you go. Go get in the catapult.

小天才需要休息。

3.. 2.. 1.. Oh man.

30公分或更高。任何比那低的高度都不安全。

[ Captions by Andrew Jackson ] captionsbyandrew.wordpress.com

不是我們在容許丟貓咪。

Captioning in different languages welcome. Please contact Destin if you can help.

來！過來.. 這就對了。