Slow Motion Flipping Cat Physics | Smarter Every Day 58

Hey, it's me Destin. Welcome back to SmarterEveryDay! 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 reword 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. Once I get my angular rotation started in one direction, I can't stop it.

Today, we're going to use a high-speed camera. We're not going to use Alley because this is my daughter's cat; I don't want to hurt it. We're going to use a stunt cat. Let me introduce you to Gi-Gi, the stunt cat. (music) I'll just flip the, uh, the video vertical and then motion track the cat. It's just going to take a lot more effort in post. We're going to try to do it in a way that doesn't make anybody mad. That's pretty hard to do.

You gotta drop the cat. Ready, Gi-Gi? Good kitty! Checking out the high-speed data there, Gi-Gi? Okay, the first thing a cat does when it's falling is try to figure out which way is up. It does this either with the gyro in the ear or with its eyes. Ready to talk cat physics? Alright.

So check out this footage I captured with the Phantom Miro while Gi-Gi goes to get a drink of water. So here's what's interesting about this, to me. You'll notice that at the beginning of the drop, the cat is not rotating; halfway through the drop, the cat is rotating, and at the very end, Gi-Gi somehow stopped rotating. Newton's law says 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. O.K., so in order to really get the right data, we're going to have to drop her 90 degrees out of phase. Atta girl! This time watch her tail. 3, 2, 1!