## Subtitles section Play video

• 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.

• [music]

• 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?

• [music]

• 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.

• 3..2..

• 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..

• [music]

• 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.

• [music]

• 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.

• 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