B1 中級 6609 分類 收藏
Hey it's me Destin welcome back to Smarter Every Day. So you've probably observed
that cats almost always land on their feet. Today's question is why.
Like most simple questions there's a very complex answer. For instance
let me re-word this question. How does a cat go from feet up
to feet down in a falling reference frame without violating
the conservation of angular momentum. Now I've studied free falling bodies,
my own in fact, in several different environments and once I get my angular rotation started
in one direction, I can't stop it. Today, we're gonna use a high speed camera, we're not
gonna use Alley, cause this is my daughter's cat, I don't want to hurt it. We're gonna use a stunt cat.
Let me introduce you to Gigi the stunt cat.
I'll just flip the video vertical, and then motion track
the cat. It's just gonna take a lot more effort in post. We're gonna try to do
it in a way that doesn't make anybody mad. That's pretty hard to do.
You've gotta drop a cat. Ready Gigi? Good.
Checking out the high speed data there Gigi?
OK the first thing a cat does when it's falling is try to figure out which way is up.
It does this either with a gyro in the ear, or with it's eyes.
Ready to talk cat physics? Alright, so check out this footage I captured with the Phantom Miro
while Gigi goes to get a drink of water. So here's what's interesting about this to me. If you'll notice
at the beginning of the drop the cat is not rotating. Half way through the drop
the cat is rotating, and then at the very end Gigi somehow stops rotating.
Newton's first law says that an object at rest will stay at rest unless acted
on by an external force. I see no external forces on this cat.
So what's happening here? It's not making sense to me. OK so in order to
really get the right data, we're gonna have to drop her 90 degrees out of phase. Ready girl?
This time watch her tail. 3.. 2.. 1..
OK so you think you've figured it out? Check this out.
You probably noticed that when the cat was falling, her tail was rotating in the
direction opposite of where her body was rotating. What's interesting about that
is that that's not how it works. In fact even Bobtail cats
can do this. It's called the cat righting reflex. I'll prove it to you.
I came across some video from the 60s when the air force was researching micro gravity for
future astronauts. Turns out they took some cats up on parabolic flights.
He tries to rotate his tail to flip over but it doesn't work. He just ends up
nutating wildly. Then he does something interesting. He takes his back
and he bends it, and when he bends his back and then creates motion, something interesting happens.
Aah. Now we're getting somewhere. So let me
show you one more cat flip with the Miro and we'll figure this out.
OK the arched back ends up being pretty
important. What he does is he divides his body up into two separate rotational
axes that are tilted from one another. When he's released he pulls his front paws in
and does the ice skater trick. He decreases his moment of inertia in the front so he can spin
fast up there, but in the back he pushes his legs away from him, increasing his moment
of inertia, so a really large twist in the front equals a really small
twist in the back in the opposite direction and the torques equal out. 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 that moment of intertia and stop the front twist, and extend his back
legs along that rear axis. That allows him to twist those around
really fast, and then all he has to do is pull them back in under his body and then extend
all four legs and brace for impact.
So thank you for your attention. I hope you learned something
pretty cool about cats. If you don't mind.. [Angry meowing] Ooh! OK OK I'm done!
If you would, go check out your other cat videos after trying
to catch Gigi. Wooh! A little too rowdy. If you'd like to, click Gigi
the cat to subscribe, we'd appreciate it. I hope you had a good one. And aah
Get the ball! You gotta catch her first. I got it, you want it?
Look... Very cool cat.
She let us drop her hundreds of times. Or, you know, maybe just 5.
Want your ball? Go get it!
Click her if you want to subscribe, but right now we're playing fetch.
Ready? Go get it!
I'm Destin. You're getting Smarter Every Day. Have a good one.
[Whispered] There you go.
You earned it.
Let me explain why cats are
wizards at physics. First of all they have physiology working for them. They have no working clavicle
like I do, and secondly they have very flexible back bones.
The talent needs a break.
30 centimeters or higher. Anything below that is unsafe.
Not that we condone dropping cats. C'mere!
C'mere.. There you go. Go get in the catapult.
3.. 2.. 1.. Oh man.
[ Captions by Andrew Jackson ] captionsbyandrew.wordpress.com
Captioning in different languages welcome. Please contact Destin if you can help.


慢速解析從天而降的貓如何翻轉（High Speed Video of Flipping Cats | Smarter Every Day 58 (Cute Cat vs Physics)）

6609 分類 收藏
VoiceTube 發佈於 2012 年 12 月 12 日
  1. 1. 單字查詢


  2. 2. 單句重複播放


  3. 3. 使用快速鍵


  4. 4. 關閉語言字幕


  5. 5. 內嵌播放器


  6. 6. 展開播放器


  1. 英文聽力測驗


