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慢动作展示猫空中转身的物理现象 – 译学馆
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慢动作展示猫空中转身的物理现象

Slow Motion Flipping Cat Physics | Smarter Every Day 58

嗨 我是丹斯汀
Hey it’s me Destin
欢迎回到Smarter Every Day
Welcome back to SmarterEveryDay
你大概留意到过猫在下落的时候
So you’ve probably observed that cats
几乎都是脚先着地的
almost always land on their feet
今天的问题就是 为什么会这样呢
Today’s question is why.
就如同很多简单的问题都会有一个复杂的答案
Like most simple questions there’s a very complex answer
我先重述一下这个问题
For instance let me reword this question
猫下降的时候 是怎样从脚朝上
How does a cat go from feet up
变成脚朝下的呢
To feet down
而且下降的时候 也没有违反参考坐标系中角动量守恒原理
In a falling reference frame without violating the conservation of angular momentum
我们这段时间一直在研究自由落体 我自己做实验
Now I’ve studied free falling bodies, my own in fact
在不同情况下 一旦开始朝一个方向旋转
in several different environments and once i get my angular rotation started
就很难停下来
in one direction, I can’t stop it.
今天 我们将用到一个高速摄像机记录 我们不会用艾利做实验
Today, we’re going to use a high speed camera- we’re not going to use Alley
因为它是我女儿的猫 我担心它会受伤
because this is my daughter’s cat, i don’t want to hurt it-
我们会用一只特效猫
we’re going to use a stunt cat
它叫吉吉
let me introduce you to Gi-Gi
一只特效猫
the stunt cat
(音乐)
(music)
我现在要翻转调整一下摄像机
I’ll just flip the uh, the video vertical
然后跟踪记录这只猫下落的轨迹
and then motion track the cat
等下上传的时候可能会更麻烦
it’s just going to take a lot more effort in post
我们尽量用一种不让人生气的方法
We’re going to try to do it in a way that doesn’t make anybody mad
这其实很难
That’s pretty hard to do.
我要开始扔了
You gotta drop the cat
吉吉 你准备好了吗
Ready Gi-Gi?
真乖
Good kitty
我们来看一下高速拍摄的数据吧 吉吉
Checking out the high speed data there Gi-Gi?
好的 当猫下落的时候 它做的第一件事就是试图分清
Ok the first thing a cat does when it’s falling is try to figure out
它的哪面朝上
which way is up.
它可以通过耳内测位
It does this either with the gyro in the ear
或者是眼睛观测做到
or with its eyes
准备好聊一聊猫的身体特性了么
Ready to talk cat physics?
我们来看一下这个 我用 Phantom Miro相机拍摄的连续镜头
Alright. So check out this footage i captured with the Phantom Miro
吉吉去喝水了
While Gi-Gi goes to get a drink of water.
我觉得这件事有意思的地方在于
So here’s what’s interesting about this to me.
你会发现 猫在开始坠落的时候
You’ll notice that at the beginning of the drop the cat
没有旋转
is not rotating
在坠落的过程中 它才开始旋转
halfway through the drop the cat is rotating
而且在最后 不知道怎么它又停止了旋转
and at the very end Gi-Gi somehow stopped rotating
牛顿第一定律说到 静止的物体将永远保持其静止状态
Newton’s first law says an object at rest will stay at rest
除非受到外力的作用 打破了这一状态
unless acted on by an external force
很显然它没有受到外力
I see no external forces on this cat
所以到底发生了什么呢
So what’s happening here?
这好像说不通
It’s not making sense to me
好吧 为了得到准确的数据
O.K. so in order to really get the right data
这次我们让它弯成90度
we’re going to have to drop her 90 degrees out of phase.
准备好了吗
Got it girl
这次看它的尾巴
This time watch her tail
3
3
2
2
1
1
【音乐】
[music]
好的 你认为你看明白了吗
Okay so you think you figured it out.
看看这个 你可能就会发现
Check this out you probably noticed that
猫在下落的过程中 尾巴与身体的旋转方向是相反的
when the cat was falling her tail was rotating in the direction opposite of where her body was rotating.
更有意思的是 那并不是它能安全着陆的原因
What’s interesting about that is that that’s not how it works.
事实上 短尾猫也可以做到这一点
In fact, even bobtail cats can do this.
这种现象叫做猫的翻正反射
It’s called the cat righting reflex.
我会向你证明这一点 我找了一些60年代记录的影像
I’ll prove it to you I came across some video from the 60s
当时空军正在研究微重力为宇航员未来上天做准备
when the Air Force was researching microgravity for future astronauts
通过调查 他们将猫按照抛物线抛射
turns out they took some cats up on parabolic flights.
猫会试图旋转它的尾巴 将自己翻过来 但失败了
He tries to rotate his tail to flip over but it doesn’t work he just ends up new tating wildly.
然后它做了一些有趣的事
Then he does something interesting.
它拱起它的后背 当后背弯曲的时候 一些有趣的行为发生了
he takes his back and he bends it and when he bends his back and then creates motion something interesting happens.
啊 我们看到了它做了什么
Ah now we’re getting somewhere.
再来看一遍猫翻转的镜头 我们就会更加清晰的明白事实是如何
So let me show you one more cat flip with the mirror and we’ll figure this out.
好的 弯曲的后背是十分重要的
Okay the arch back ends up being pretty important.
它所做的是就是将他的身体以旋转轴为中心朝相反方向倾斜
What he does is he divides his body up into two separate rotational axis that are tilted from one another
当男孩放开猫的前爪时 它会就像滑冰运动员做特技一样
when he’s released he pulls his front paws in and does the ice skater trick
降低身体前半部分惯性以便快速旋转
he decreases his moment of inertia in the front so he can spin fast up there.
而与此同时它会伸长后腿增加身体后半部分的惯性
But in the back he pushes his legs away from him increasing his moment of inertia.
所以身体前半部分巨大旋转 与身体后半部分反方向微小旋转相协调
So a really large twist in the front equals a really small twist in the back in the opposite direction
结果正反抵消
and the torques equal out.
要下落时 它要做的就是向后伸长它的后腿
So as soon as he gets his front paws in under him all he has to do is extend those legs back out to increase
来增加下落那个时刻的惯性 阻止身体前部分旋转
that moment of inertia and stop the front twist
而以轴为点伸展后腿
and extend his back legs along that rear axis that
使它得以快速旋转 旋转后它要做的就只是将后腿收回
allows him to twist those around really fast and then only has to do is pull them back in under his body
接着伸长四条腿作为支撑着陆 降低冲击
and then extend all four legs and brace for impact.
【音乐】
[music]
感谢您的观看 我希望你学到了一些关于猫的很酷的知识
So thank you for your attention I hope you learned something pretty cool about cats.
你不介意吧 是吧
You don’t mind oh okay.
好的好的 我松开
Okay okay I’m done I’m done.
如果可以的话 我抓住吉吉后 可以带你看看其他与猫相关视频
If you would, go check out your other cat videos after trying to catch Gigi.
假如你喜欢的话 请点击吉吉 订阅频道 我们会感谢你的
If you’d like to click Gigi the cat to subscribe we’d appreciate it.
我希望你会喜欢 抓球去
I hope you had a good one and with the ball.
看 多酷的猫 她让我们实验了很多次
Look. Very cool cat. She lets us drop her hundreds of times,
也或许只扔了5次 捡球去
or you know maybe just five punch ball. Go get it.
如果你想订阅就点击链接 我们现在玩球吧
Clicker if you want to subscribe oh but right now we’re playing bitch right.
【音乐】
[music]
嘿 这里是丹斯汀的Smarter Every Day 祝你开心
Destin here with Get Smarter Every Day. Have a good one.
吃吧 你应得的
One you earned it.
让我解释一下猫身体的奇特之处 首先 它们所有的身体部位都是为自己服务
Let me explain what cats are Wizards of physics first of all they have Physiology working for
他们没有像我们一样的锁骨 第二他们有非常灵活的背骨
them they have no working clavicle like I do and secondly they have very flexible back bones.
天才也需要休息啊
The talent needs a break.
实验的时候至少要有30厘米或者更高 否则我们就不能保证猫的安全
Thirty centimeters or higher anything below that is unsafe not that we condone dropping cats here.
【音乐】
[music]
嘿 过来到弹射器里
Hey go get in the catapult.
3 2 1哦伙计
Three two one oh man.
【音乐】
[music]

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视频概述

有一种传说,猫有九条命。可是,我们都知道这是不可能的,都是为什么有这种传闻呢?这就是猫转身的奥妙了!

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