This is the tip of a bullwhip and that crack you hear is this breaking the sound barrier. My question is why or how? Like, if you think about it, your arm’s never leaving your body and something’s going faster than the speed of sound in just a few hundred milliseconds and over several feet. That’s a big deal. So April is an engineer first and foremost. I think all this whip business is just a reason for you to explore– – Fluid dynamics?- Fluid dynamics. (cackling)I really do.
So April on the internet, you may have seen her, Guinness Book of World Records whip stuff, she’s good with whips. But what’s really interesting in April, is your brain. – There’s something in fluid dynamics known as the no-slip boundary condition. And so, its pulling that air with it. – It depends on whether or not you’re using a Lagrangian framework, which centers on here, or a Eulerian framework that centers on the overall mesh.
That’s what I was thinking. I was wondering if it was a Lagrangian or Eulerian framework, but I wasn’t going to say anything. The first thing we did was create a news tip for the bullwhip and attach it to the whip and after that, we set up the camera system. The way we’re getting this shot is using the schlieren technique, and this is what took us so long to coordinate. Basically, we have a point-light source right here and that light is coming out, it’s spreading out, it’s hitting this mirror, this parabolic mirror, and as it comes back, what it’s doing is it’s converging to this point right here. You can see there’s the light coming through at the focal point. And then we’ve got red and green gels right there and (whip cracks). (laughing) That’s scary.
Go watch Derek’s video on schlieren, it’s better than this one. That is unnerving. After everything was set up, we literally got crackin’. (whip cracks) OK, that triggered. Let’s see what it did. We learned two major things in my buddy’s garage. First a question, though. Growing up, I used to play Castlevania a lot, so for me, it made sense that the crack of the whip would happen at full extension of the whip ’cause that’s what you want to do with the bad guys, right? You want to keep them as far away from you as possible. When we set up a high-speed camera expecting the whip to crack as it does in Castlevania, the shockwave would always enter the field of view before the whip did. So it’s cracking way back there. – It’s cracking before we think.
I learned something. I didn’t know that.- Yeah. I didn’t know that either. – It actually happens as the whip unrolls, not at the end as I thought. And in order to visualize what’s happening, we switched from the overhand strike to the sidearm strike. What you’re about to see here are two engineers that have researched this stuff and were totally blown away because the experiment worked and we’re starting to see things for the first time that we totally didn’t expect. OK. We are getting somewhere. (laughing) (whooshing) (thundering) (snapping) The second thing that we learned in the garage is there may be a mechanism that’s causing it to accelerate just before breaking the sound barrier. (whip cracks)
Those strands right there are not in tension. Do you see that? – Yeah, they’re just, it’s chaos. – [Destin] And then there’s this moment– – [April] Where they all come together. – [Destin] Where they all come together and when it starts to pull, that’s when the initial shockwave starts. – [April] So it’s the collapse. – [Destin] The collapse is when it happens. – [April] And the drag coefficients going down. – The fact that we’reseeing a new mechanism is a really big deal. So obviously, we have to take this more seriously. We just figured out how whips work. We should totally publish this. – Yeah. -The Ernst-Mott Institutepaper, by the way, freakin’ amazing.
There’s a dude in it that looks like a moose wearing bells and a clown suit. (laughing) I don’t know what’s happening. It’s actually a great paper. You should totally read it. They talk about wishing they had a faster high-speed camera so they could see what happens at the tip. Also, the paper at theUniversity of Arizona, they try to measure with math the entire length of the whip as it unrolls. They try to describe that movement. Like all of it at the same time. It would measure the three-dimensional position of the wave as it goes down the whip. What if we could do that?
And that’s exactly what we’re about to do. Under the guidance of my doctoral advisor, Dr. Kavan Hazeli at the University of Alabama in Huntsville, we’ve assembled the team and we’re about to figure this junk out. We designed the experiment and gathered together in what’s called the atom lab. It uses an array of cameras to track anything with reflective tape on it. The way it works is essentially this. We also put reflectors on her arm so we could better understand the mechanical input to the whip.
The image from one camera would essentially be an array of white dots 500 frames per second, but if you coupled this data with the data from other cameras, you can triangulate each individual segment of the whip at 500 frames per second giving you true three-dimensional data. OK, here we go. [Man] Three, two, one, go. – You can that the Viconcameras up on the wall are taking data at 500 hertz, which means they’reflashing every 10 frames on the high-speed camera here. You’ll notice that the whip unrolls normally, very similar to how the paper from the University of Arizona described it mathematically. Let’s make a few observations here.
First, there seems to be a wave that moves down on the whip. As the hand moves forward and then stops, it transfers momentum into the whip itself. Then, one segment of the whip, as it unrolls and straightens out, seems to transfer all of its momenta into the next segment, and then the next segment and so on and so forth. As indicated by this red line moving along the bottom here, you can see the velocity of that straightening out of the whip moves forward.
We can then look at the atom lab data and measure the input momentum in three dimensions and use that information as a tool to help us build a model. So the whips coming up towards the mirror. (muffled mumbling) That’s awesome. Is that awesome? – Yes. – Another thing to look at is what’s happening onthe top of the whip. The velocity is speeding up. Most researchers think this has to do with the conservation of momentum.
The whip is tapered so each smaller section on the way down has to speed up to maintain the same amount of momentum. This is the exact reason we took so much time upfront to measure the mass and dimensional properties of the whip all the way down. This is where it gets most interesting for me. If you look closely at the atom lab data you’ll notice that right the tip of the whip the markers seem to disappear right when the whip accelerates.
ven if the atom lab didn’t lose the track, you can tell that the frame rate of the atom lab isn’t sufficient to determine the acceleration through the most interesting part of the wave, which, of course, is the shock formation. This is exactly why we set up the schlieren camera. (light guitar music) (whooshing) I’m not gonna explain any of our preliminary conclusions but at this point, we’redoing two types of analysis, obviously how that wave propagates, but also the tip velocity of the whip.
If you watch closely, it looks like the tip’s getting pulled along behind that shockwave. (whooshing) (smacking) What we do know is that the popper isn’t necessary. – There you go. There you go. There you go. – So it’s like this. I know this sounds crazy, but I’m already changing my habits in everyday life because I understand whip dynamics better. Have you ever done this? You’re in your car, you reach for your charging cable and you pull it towards you real quick and it whips you really hard? That hurts like a mother. The reason that happens is whip mechanics. I cannot be the only person in the world that’s ever done that.
You don’t want to just pull it quickly because that conservation momentum builds up and you get lashed in the face. So bullwhip was probably the first manmade invention to break the speed of sound. This is not an SR-71, this is the A-12, the predecessor to the SR-71. There are 13 of these built. Ready, watch. That was fast wasn’t it, OK? (laughing) I’ll go back and do it slower and tell you about the aircraft on the way. OK, we’re back at the front. So, I want to tell you about Audible. Audible is sponsoring this video.
There’s a book called Skunk Works. You can get a free audiobook of your choice by going to audible.com/smarter or texting the word smarter to 500500 to get any audiobook of your choice. In this case, your choice is Skunk Works. I’ve already made your choice for you. You have to listen to this book. It’s about the development of the SR-71 and the F1-17 stealth fighter. I’m sorry, I just passed the hot naughty bits. Look at this. So think about the shockwave. But you had to get air inside the cowling there. It’s amazing.
Anyway. Go to audible.com/smarter,download Skunk Works, listen to it with your ear holes. You’re gonna love it. This thing would heat up in flight. They had to make it out of titanium. All kinds of cool stuff in the book. I just want you to go to audible.com/smarter, download Skunk Works, or text the word smarter to 500500. You’re gonna learn stuff, it’s gonna make you smarter and you’re gonna know more about breaking the sound barrier.
Um, I have two blasters, and if I fire the one that you’ rethinking about right now, feel free to subscribe. Or not, whatever. Ready? (sirens blare)(chuckling) They’re on the same thing. That’s a, they cycle… (sirens blare) See, but now they’re not. The gap in my data is spacial. I’m not gonna get any of that. And the gap in your data is temporal.