Hello, and welcome to the Physics World stories podcast. I'm Andrew Gl, and in this episode, we're gonna be asking the question could athletes mimic basil lizards and turn water running into an Olympic sport. It's also the title of a feature on the Physics world website physics world dot com written by Nicole Sharp. The slightly surprising answer will be that yes, shall carry Richardson, the 100 meter world champion could, theoretically do it, but would need the help of a space
agency. That's to come. His Nico Shaw. I am an aerospace engineer and a science communicator. My training is in fluid dynamics. So I studied the physics of fluids. I got a Phd in that, about, 10 years ago, And I have long been fascinated with all the different ways that fluid show up on our lives? Do you have a blow? I do. Which we can't say... We can't say the name of it. The name of it is Fy d. The former name of it, you can't say. Okay. Because it's swearing.
Originally. Yeah. First 1, we can't say, then it's yeah, fluid dynamic. That... That's right. That's that was the original name. Yes. Nowadays, it's just Fy. So what is it that makes you squarely really excited about fluid dynamics? You know, it's it's funny. I went dear into an engineering degree as an undergraduate. I I decided probably in about middle school. So I was maybe 12 or 13 years old when I decided that I wanted to study Aerospace engineering.
Kind of a weird choice because I didn't know any engineers, I did not have any true idea what Aerospace engineers did, but I was like, this is what I'm gonna do. So I go into engineering, I'm taking all the classes, did I'm actually simultaneously taking classes for a German degree. I was I was a double major for most of my undergraduate years. And I'm just kinda putting up with the
engineering classes. Like, I can do them, but they're not really all that engaging to me, and I spend a lot more time being interested. And in my other classes, until we come to a unit on fluid dynamics, and I remember the professor talking about how air moved over an airplane wing and just being completely fascinated. And he came to the end of 1 of the lectures he said, okay. That's as much as we're gonna talk about this. You have to wait to take another course from
this other. Professor, it'll be in a year from now. And I just wanted to stand up and shout. Don't stop now. This is the first interesting thing. Any of you said, So that was kind of my... That was the moment that I think I realized so that I love fluid dynamics. Arguably, I... I had been fascinated with what fluids were doing before that because I can, you know, think back to to various things that I did in my childhood.
But I didn't realize that, you know, this was a subject I could study until that class. And I unfortunately, did have to wait the further year before I got to take the class that was fully dedicated to fluid dynamics. But, that pretty much solidified my love for the subject. And I decided I wanted to do graduate school at it. And I went deep down a hole and spent a lot of time crawling in and out of wind tunnels.
Just wanted to do anything and everything having to do with understanding, particularly in my work how how error moved around things. But then as a a graduate student as a Phd student. I had kind of some downtime. In in my experiments when the facility that I needed got very badly broken. It's we're gonna have to wait for a
while for it to be available again. And I think it was during that that I started the blog, and I I just kinda felt that, here's this awesome subject that I'm constantly learning new and interesting things about? And why doesn't everybody else know about it and get excited about it too? Think there's about... 3600 articles now. Wow. I've been doing it for 14 years Yeah. For most of that time, 5 days a week. So that adds up to a lot. It's it's over half a billion words.
There's presumably been quite a few areas of fluid dynamics that have fascinated you have these years. Can you pick out 1 that wasn't this 1 that we're about to talk about? Scientifically speaking, fluids actually includes air? It includes any gas, liquids, as well as things like plasma. And in some cases, granular materials kinda get get lumped with fluids. So things like sand and snow and the way that they move. So 1 thing that I love
thinking about. And this this in some ways touches on stuff that I studied in in my Phd are the concept of insta instability So a lot of times in fluid dynamics, you'll have a situation where a relatively small disturbance. Sometimes, we'll call them per renovations, are actually able to gain energy and grow and kind of lead from a nice orderly flow into a very chaotic 1. And 1 of the ones that is It's it's probably my favorite instability is called the Kelvin helm halt and stability.
And it's essentially what's responsible for ocean waves. So when air moves over a flat water surface, that adds the energy where if you have any small disturbance, any ripple on the water that makes it bigger and bigger and bigger. And so you ultimately get ocean waves that are, you know, curling over crest and and breaking, you know, like, the big ones that surfers like to ride, So there's this absolutely stunning thing that's happening all the time between the air and the water.
But that's not the only place that the Kelvin helm holds stability shows up. It it'll show up in different layers of the atmosphere. And sometimes you get these amazing clouds that look like... Oh, they look exactly like Ocean waves breaking. And it's because you happen to have 2 layers of air that are moving pass 1 another at different speeds, and it triggers that same.
And the thing that just utterly fa me about this particular 1 is aside from the fact that it's beautiful that you can actually see this happen, so many different places. You see it between the air and water, you see it between different layers of air to get the clouds you also see it between different bands of gases on Jupiter where you get all the beautiful swirl coming together. And I think the largest place that I've seen it is actually in a galactic cluster.
Where we're talking, it's all of a sudden, like, thousands of light years across, you could get the same instability that I can see out my window right now. Amazing. That's amazing. I don't want to swear about. Fluid dynamics? Exactly. See. I've got you. I understand it now. Okay. So why is it? That made you wonder whether humans could mimic lizards and run across water. You know, I think the the idea originally arose because of watching superhero movies. And Tv shows.
So I remember when the incredibles came out that there's a a part where the little boy who can run really fast. Dash is able to... He surprises himself when he's running away from the villains and he suddenly runs across. Cross water, and it's like, oh, cool. I could do this. And there was much later I was watching the C w show the flash, and I think the first season of that. There's an episode.
Where, Barry Allen has to run across the bay with somebody or, like, to get to somebody and take care of things before there's a giant explosion. And his team estimate that he's gonna have to run 650 miles an hour. In order to run on water. And I
remember hearing that in in the episode. And, you know, normally, as a physicist, I have to be relatively good at you know, suspension of disbelief when I'm watching a lot of the kinds of shows that I like to watch, but I I remember reading that and being like, that can't be right. You there's there's no way. Why would he need to go that fast. And so, I think that was part of what motivated me to figure out, like, actually how fast does a human have to go to be able to run on water.
Okay. I mean, I the obvious question though is how fast do you have to go to run on water. Honestly only about as fast as, highway speed in a car. Oh okay. So, I mean, clearly much faster than any of us who aren't superheroes are capable of running, at least assuming that you're doing it here on Earth and that you're not, you know, adding anything to your feet to make them bigger or something like that. You would only have to go about highway
speed. To be able to do it. But it turns out there are ways that you can get around that. So 1 option is that you make your feet really big. And this is something that I didn't touch on in the article, but it was... There were a couple of engineers, at Cornell who essentially did this version of the experiment where they they put meter squared they call them Lily pads, just like, I don't know. Maybe a piece of plywood or something across a swimming pool. And with a little bit of practice, they
were able to run across them. And essentially what that does is is the exact same physics as the bass is closer and everything that's discussed in the article. But it basically gives you a giant foot that you're slapping down onto the water without having to waste the energy of pulling it back up. It's Okay. That's kind of fun. So they have the... These things strapped to their feet or were they on those left of the door? No. They they just had them floating.
And they don't... It's not like, there are these kind of buoyant mats that people will run on. On water. It's not like that because it's not buoyant. It's it's only buoyant enough to hold itself up. If you were to stand still on this lily pad, you would sink. Okay. But if you keep moving the slap, the impulse from that slap is enough that you can actually run across the water. In my head when you said bigger feet. I was thinking so clowns could do it. So it has to be bigger than clown
feet. Right? Yeah. Yeah. At least at least for this version, it would it would have to be bigger than cloud. What what if a cloud was running at 690 miles an hour. Would that Oh, well, that... Then they'd have no problem. They wouldn't be clown shoes for that. Aside from very fast running clowns, as Nicole mentioned, in nature some characters
are able to run on water. 1 of them is the Basil lizard, also known for fairly obvious reasons as the Jesus Christ there's They're mainly found, I think in Central America and South America, Though my understanding is that there are pockets of them in Florida. And they do this for relatively short distances, and they do it primarily to get away from predators. Because you can imagine if something is coming after you and you just take off across the river.
Chances are they're not gonna be able to come after you all that easily. So it's a convenient convenient skill for them. But these lizards are about... I wanna say a hundred grams or so. So they're much too heavy for just surface tension to keep them up. That's that's what would work for, say, a spider or a water strider or most insects can just kind of walk across the water because they're just way so very little. It's not gonna work for the bass lizard. So what the lizard does instead is it
has relatively oversized feet. And it slaps them down hard against the water. And just the same way that you having your foot hit a track causes the track to push you back up. That's the exact same thing that's going on with the water, except the water is squishy and it can move. So there's some extra complications and trying to stay upright when the thing that you're pushing against can move around like that.
But generally speaking, they're getting most of their ability to stay up from slapping the water hard enough to give them. Vertical impulse. So when the lizards are running, it's sort of a circular motion in a way with their leg. A little bit. I mean, they're they're moving forward, they're kind of putting their foot in, and then they pull it out before
the water closes around it. Okay. And the older and bigger they are, the more awkward it looks as they do it because they're having a harder and harder time staying above the water. Yeah. Yeah. I can advertise with that. Totally put something I'm finding or playing football or cycling or anything that the older I get, the heavier I get the role could I look. Some reason? Yeah. Yeah. No. I same. Alright you told me why you're looking at it, But why are
that why are people actually looking? What's the purpose of it? Is there any some is there any real reason why knowing this helps please? Well, so I can tell you that the the biologist who has inspired to look at this was looking at it. In part because she was fascinated by the similarities and the toes of the bass lizard which runs on water. And a different kind of desert lizard that runs on sand.
And so her fascination is in figuring out how it is that these animals are able to run on vastly different surfaces and why it is that there are visual similarities between the limbs of these lizards doing such vastly different things. Is that something we can learn from apart from just knowing that these lizards have different
ways of doing things. Well, I mean, in general, a a lot of the the kind of work that goes on in understanding animal lo comes back into play in engineering through bio mechanics and bio robots. 1 of the things that engineers have discovered is that it's really hard to get robots that can move over
vastly different types of ground. Like, maybe you can get something that works really well on a carpet surface, but struggles on little no n or a tile surface or if you spread gravel on something, all of a sudden, it's really difficult for it to move. Sand is another thing that's that's really tough. And so for a lot of engineers who are wanting to design robot that can get into places like disaster zones after you've had some kind of
natural disaster. You wanna get through this rub, find out if there's anyone there that you need to rescue. You need to be able to build the devices that are capable of moving over many different types of terrain and adapting to them. So being able to understand how particular ways that, you know, how how is that animals are able to do this and and move so well across so many different surfaces. Is really valuable for engineers in that respect.
But, I mean, we're not gonna be inventing shoes to help us run across water, Are we. That's not gonna be in. Not on Earth. Unfortunately, if you want to run across liquid surfaces on Earth. You don't really have too many options. You could run across Oo, which is a mixture of corn starch and water. It is... You can find that all over Youtube. It is possible to run across swimming pools of that. You do need a cement mixer in order to mix that stuff up at that scale. But it is very doable.
It doesn't work quite the same way because there's additional things going on inside the fluid. That kind of enable you to stay up in that situation. If you just wanna run across plain water, the moon turns out to be a pretty good place to do it. Not that the water is there, you'd have to, you know, take it and cope with the lack of air and whatnot. But the gravity on the moon is actually about right, so that people are capable of keeping themselves up on the water that's...
That was actually shown in an Italian experiment that I did discuss in the article, were they essentially put people in a harness that mimics being at lunar gravity or or other reduced gravity situations, and they had them run in place with fins on their feet that made them have proportionately sized feet like a basil. So a little bigger than human feet kinda like your clown shoes.
And they would just run in place over this pool that they were suspended over, and you can see in the footage, which is absolutely amazing to watch. That it is possible for a human to support themselves at least for several seconds at a time. I think at lunar gravity, everyone that they had that they were testing could do it. But as they increased the gravitational the equivalent grab gravity levels, it got harder and harder for people. Just going back to watching Apollo astronauts.
Wish I've done a lot. Oh... There a lot of fun. Absolutely. But they don't do a lot of running. They do a lot of bouncing. Is it is it possible to run on the moon. I think it would probably take some practice to figure out exactly how to do it. It's fair to say that the... There... It's unlikely that your stride is going to look the exact same. That if we're gonna make an Olympic sport out of this, which I... It's the ideal thing. Right? We we're not going to go to the moment to do that.
Can you see an Olympic sport in the swimming pool with these lily pads on it? And I mean, they could. If if they did the Lily pad option, that that is feasible. And it that would be really interesting to see people raising. I think they would have to do it in kind of time trial sort of way because if you had multiple people jumping for the same lily pad at once, everyone's just gonna fall. Apparently, you have to hit the middle of the Lilly pad quite well to get it
to work. Otherwise, you lose your balance and you fall off. This sounds pretty skill, which is what you want from middle olympics. Yeah. Say what worries mean about it though the... Is the end? How do you stop? I think you have to transition from... Just like the lizard do. Right? You transition from being on the water to being on the side of the pool. Yeah. Actually... That's how the lizards do it. They run from, like, ground across the water and back to ground.
As opposed to the g who being water birds, they're happy to do it just from the water to the water. So g are pretty spectacular because they're about 10 times heavier than the lizards. I think they they are, like, 2 2 and a half kilograms these birds. They're black and white. They don't look all that spectacular. They just, you know, look like water birds.
Except they have this behavior that they do when they're mating, they have a display called Rushing, where the 2 mated graves will rise up out of the water, kicking their feet as fast as you can you know, imagine practically. I think it's about 20 steps a second. It's ridiculous compared to anything that you know, a human can do. And when they do this, they rise up out of the water with their wing stationary
behind them. So they're not getting any help from their wings at all, and they just run across the water for 20 meters or so. It's like a synchronized swimming display except running on water. Yeah. It's amazing. Quite apart from the running and water bit, the whole display is an incredible. An incredible thing. Oh, yes. But is that sort of effectively the same as the lizards? The way they're doing. Yeah. The physics The physics is very much the same.
The 1 significant difference I would note between them is that the birds... Pull their feet out of the water differently. And it's a little unclear exactly what goes on during that step because it happens underwater, and you can't get g to do this in the lab. You can only do it when you're out in the field. So it's really hard to see what's happening under the water from cameras that are second on land. Massive boats
float on water. The way that that boats and people float on water is with buoyancy. So it it relies on us displacing a volume of water that is, well, it equal to the weight that we have under the water essentially. So the further submerged you are, and the more you can push water aside, the more of a buoyant force you get. That doesn't really help with the basil and the g because not very much of them is underwater. If they were would that
help? I mean, like, could you sort of run just underneath? I mean at that point you're just swimming. That's it's like the duck. Right? The their feet are going wild underneath the surface, but they look like they're just lighting along other there Olympia who are competing in Paris who could effectively run on water. Yes. There are Olympia in Paris who have the speed that they could run on water, not on earth.
We would we would have to be having the space Olympics. 1 option as as I said before is we could... Have events on the moon and, you know, just transplant a pool up there. Another option, which I think is is a particularly interesting 1 is having instead of water running, having ethane running across the lakes of Titan. That sounds amazing. Titan is 1 of Saturn's moons.
It's a particularly interesting place because it's the only other place in our solar system that has surface level liquid bodies place so lakes and seas, and oceans. Prior to to finding out that Titan has these hydrocarbon lakes. We thought that Earth was the only place that that just had liquid sitting on the surface that you could swim or run in, Why would we be able to run on that un titan? Mostly because titan is smaller than Earth, it has, less gravity.
Which means that, in general, you don't have to have as much vertical impulse, or you don't have to be creating the same amount of force to keep yourself up just because your lighter. But also because of the ethane rather than water. Yeah. There's funny thing about it is that, the density of the ethane is lower, So it actually doesn't help you as much as water. Like, if you could have water there, that would that would make it a little bit easier, but that's not what they have. They have
ethane thing. Oh, okay. So would actually be more helpful if it was water. Little bit more helpful, You would get a little bit more vertical out of it. If they had water, we'd already be there though. Right? Yeah. Well, if what water does exist on titan is frozen because it's extremely cold there. Okay. Okay. So you're gonna have to run in jumpers. Yeah. Yeah. You're you're gonna have to be able to dress very warm and hold your breath. Okay. Yeah. Diaz is not gonna be great. Is it on tight? No.
Okay. As colleague explains in the feature on physics well dot com, it's not just anybody who could run across the likes of Titan. 1 person who could is the Us sprinter, Shi carry Richardson. The fastest woman in the world right now. Running on titan legs, racism and have the advantage of weighing just 45 kilograms, while her Uk size 5 shoes provide a good foot area. According to Nicole calculations, the Us athlete fleet would have to run at about 8.7 meters per second.
That's within her world championship time, which she ran at 9.3 meters per second. For those of us who are, slightly larger and not quite so blistering fast as Richardson. We could, of course just enter the Titan freestyle swim instead. You first. Back to Nicole now, and my 1 last question for her, which is are we really gonna be adding this to the Olympics. Well, I think, you know, it it might be an idea a little before its time still, we're gonna have to get get creative
to to bring it into the Olympics. And I imagine the Io is going to have a lot of questions shenzhen. While we might have to wait some time for the space olympics pixel running on water to be part of the Olympic games. This year's Olympic games in Paris run from the 20 sixth of July to the eleventh of August. And 1 news sport that you can find in there
is breaking or break dancing. And if you want to know about the physics of that and plenty of other sports, sport You can go back to our previous episode of the Physics World stories podcast where we hear from
John Eric Go. The author, of gold medal physics, the science of sports And of course, you can find out much more about the potential and the nature of running on water in the coal shops article on physics world dot com could athletes, mimic basil lizards and turn water running into an Olympic sport. Next month we'll be delving into some of the drama in the recent past of so. The hump for the Higgs boson on that Lhc switch on, and well, how did they end up not destroying the world?
And how could they capture the public's imagination again? That's next month, but for now, Enjoy the Olympics, and thank you very much for listening.