Daniel and Kelly’s Extraordinary Universe - What is the physics behind skipping stones?

Episode Date: September 12, 2019

Find out how skipping stones works today with Daniel and Jorge Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Listen to the new season of Dacius Come Again on the IHeartRadio app, Apple Podcast, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to

choose an adaptive strategy, which is more effortful to use, unless you think there's a good outcome. Weddance is easier. Ignoring is easier. Denials easier. Complex problem solving takes effort. Listen to the psychology podcast on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Hey, Daniel, what did you like to look at the world through the eyes of a physicist? Oh, it's amazing. There's red, there's green, and then there's blue. It's really quite beautiful.

I mean, like, are you always trying to analyze and understand everything? Like, is the world just a giant mess of puzzles and interesting phenomenon? Pretty much, it's hard to turn that part of your brain off once you've turned it on. I mean, don't you ever want to just sit back, relax, and just live in the moment and experience things? Yeah, every time I do that, I think, how does that work living in the moment? What is relaxation anyway? Hi, I'm Horam, a cartoonist, and the creator of PhD comics. Hi, I'm Daniel Whiteson. I'm a particle physicist, and I'm incapable of fully relaxing.

Do you think that's a personal trade, or is that just comes with a job of being a physicist? Yeah, I can't tell about the cause and effect there. Am I that way because I became a physicist, or did I become a physicist because I am that way? Causation versus correlation. That's right. But, you know, sometimes you can do both. Sometimes you can enjoy looking at the world and unraveling its mysteries, you know.

Some people do puzzles for fun. And for me, the universe is my puzzle. Well, hopefully that's why people are listening in to this. Welcome to our podcast, Daniel and Jorge, Explain the Universe, a production of iHeard radio. In which we look at the universe like a big puzzle, and we try to take it apart for you and hopefully entertain you along the way

with our terrible dad jokes. Entertain you and also maybe ruin your vacations or your relaxation times. Or enhance your relaxation by showing you a whole other dimension behind the simple plane of reality that everybody else experiences. Do you feel like sometimes you are like a Neo in the Matrix where you can see the code behind everything around you?

No, but I can totally do that kick move. You can dodge bullets and look like Keanu Reeves. Hey, I've never been shocked. Okay, I can say that. You successfully dodge every bullet that's been fired at you. Every single bullet fired at anybody I successfully dodged. Oh, wow. That's a lot of bullets.

That's a lot of bullets. Yeah, so today on the podcast we'll be tackling a phenomenon that maybe, hopefully, a lot of people have done or tried to do or look at and think, hey, that's pretty cool. Yeah, I think a lot more people have tried to do it than successfully done it. Something you might do when you're out for a relaxing stroll or maybe out on vacation or just killing time or having some thoughts to yourselves. So today on the program, we'll be talking about physics of skipping stones. That's right. Why is that even possible? Why is it that you can bounce a rock on water? I mean, it seems sort of crazy. If you had never seen it, but somebody described it to you, you would be pretty skeptical. Yeah, it's pretty cool.

And this is, you know, when you're walking by a lake or a pond or maybe just even like a fountain, you might have seen people or try to do it yourself as you pick up a little stone and you throw it and it skips along the surface of the water, sometimes a lot. Yeah, what's your personal record, Jorge? Probably made like 10 skips in a stone, maybe 10, 12. It's kind of hard to count, right? Isn't it? Isn't it hard to count at some point?

Yeah, especially at the end there, they get faster and faster. My son really likes to skip stones. I think his record is eight, and mine is something more like five or six. Is this a profession some people have? Like, are there professional stone skippers? There certainly are competitions where people fight voraciously for the championship. I don't know if they get paid for it, but they do pretty well. The current world record for most number of skips is 88.

88 skips. So you throw a rock at some water, a body of water, and it skips 88 times. It's unbelievable. Like, how do they even see those? They must have like a camera, like the kind of. they use the really fancy tennis matches. How far is that, like, when you throw it? Yeah, what's actually interesting, in the U.S., they have stone skipping competitions,

and there they count the number of skips, whereas if you go to sort of international world championships stone skipping, they don't care about the number of skips. They care about the distance. And the furthest stone anybody's ever thrown via skipping is 121 meters. That's a lot. That's really, it's longer than a soccer field. It's like a seventh of a kilometer. Yeah, it's huge. It's unbelievable.

So somebody has really figured out how to do this thing. And, you know, when you're out there and you're skipping stones, you sort of get a feeling for it. You're like, okay, I need this kind of stone. I've got to swing it this kind of way. It's sort of like throwing a frisbee a little bit. You sort of feel it out with your mind. It's like it's it in your wrist. Is it in your, you know, arm movement?

Yeah. Is it about the water? Yeah. And about the perfect stone. And most people just sort of figure it out intuitively, right? They try this. They try that. And eventually they sort of get the hang of it and they perfect it, right?

And that's how most people approach the world, right? You learn how to walk, not by like thinking about the physics of walking. You learn how to ride a bike just by sort of trying it out. Your brain gets trained to sort of learn the physics intuitively. You don't like write down equations. But it is possible also to take this really fun vacation activity and sort of ruin it by, you know, turning into an equation. No, doesn't it make you want to appreciate it more? you know, wants you to understand the physics behind it?

Depends on what the answer is, right? If the answer is something, ho-hum, then, you know, maybe you've ruined the magic. But if the answer is, there's some crazy surprising physics in there, then, yeah. Then, you know, doing the physics has revealed something fascinating about the universe. So we're in for some crazy surprising physics. Turns out that the way most people think skipping stones works is not the way it actually works. Well, I think I've got the trick of it, but maybe we'll see. We'll see if what I'm doing

corresponds to the physics of it. All right, I'll give you a physics grade at the end of it. All right, well, it is kind of complicated, and we were wondering how many people out there knew what it takes or how it works or what's actually happening when you skip a stone. So I walked around the streets of Aspen, Colorado, a beautiful town in the mountains with lots of stones and lots of little lakes and ponds

so people could have plenty of chance to practice their skipping. And I asked folks, do you know why it's possible to skip a stone? Did most people respond? Oh, I don't skip stones. I just throw gold bullion. It's Aspen. So they said, I don't skip stones. I get stoned. That's a different physics episode. Probably somewhere in Aspen, you can buy like a $97 gold-plated perfect skipping stone. So you went out there and you asked people on the street if they knew why is it possible to skip stones on a lake? So think about it for a second and then listen to what people had to say.

Distance, tension, speed, friction. Gravity. Because it's hydroplining. Water has surface tension. It's like tight tension. It hurts if you fall on it wrong. But if you put a rock on the water, the surface tension won't hold it out. It's moving at high velocity.

It has a flat surface. And so it's going to spin across the flat. If it had jagged edges, it would catch and get pulled into the water. Gravity. Okay, but gravity would pull it down. Yeah, okay. I don't know. All right.

A lot of great answers here. A lot of your favorite answers, right? Gravity. Yeah, gravity. Yes, always works. You can also say the Big Bang or physics. And that's usually how things work. Yeah, usually.

Physics is the way everything works. So, yeah, that's a solid answer. I know we've got lots of people saying things like surface tension, right? Or hydroplaining or just, geez, I have no idea. Some people had really never thought about it before. That's one of my favorite moments is when I spark in their minds this moment of curiosity. Because then they always turn around and they ask me. They're like, well, tell me the answer.

Now you asked me, I have to know. Yeah, a lot of answers like surface tension, the speed, the shape of the rock, what's going on? Yeah, so based just on those answers, you might guess that the answer is pretty complicated. There might be a lot of things going on, right? Some physics magic. Some physics, not magic. And it turns out it is pretty complicated. We should dig-

Magical physics. Can I say magical physics? Physics, ruining magic for hundreds of years. Magic-adjacent physics, maybe. That's right. The most popular answer that you heard there is surface tension, and that makes some sense, right? Is it the surface tension? Turns out it's not surface tension, right?

That's a tempting answer because you think, oh, the water is sort of holding the surface together. There is some resistance there, and you may have even seen, like, bugs skimming on the surface of water, or you could put a paper clip down on water and it can sit on the surface tension, right? So there's a sense that the water is doing something there to hold something up, right? But it turns out surface tension is nothing to do with skipping stones. Maybe step us through a little bit. What is surface tension? Yeah, surface tension happens when you have a liquid and that liquid is attracted to itself, right?

And so it wants to clump it together. So, for example, if you put a drop of water on a table, it doesn't just run totally flat, which is what you would expect from a smoothly flowing liquid under gravity, right? Gravity, any... It doesn't spread out, you know, out to cover the whole table. Exactly. It stays together as a drop. one molecule thick cover coating, but it stays as a droplet, right?

That's right. It stays as a droplet. And the reason is that the molecules are attracted to each other. There's some small force pulling the molecules to each other. And we've talked on another episode about how water is a dielectric. And so it's neutral, right? The positive and negative charges balance overall, but the positive negative charges aren't on the same side of the water molecule.

And so they can line up in this way where the positive end of one water molecule tracks the minus end of another one. They can tug on each other a little bit. So they like to stay together. They're like a little scared crowd of children or something. They clump together in fear. It's like having a handful of magnets. At a distance, maybe they are neutral to each other.

But if you get them closed, they'll start to clump together. Yeah, maybe a handful of magnets was a better analogy than a clump of scared children. Probably. Or are they scared because you're coming at them with a clump of magnets? Because I'm holding a rock, right? No, yeah, so it clumps together. That's what surface tension is, is the water clumping together. And so it, and that happens also on the surface, right?

Not just inside, but also on the surface. It's kind of like why in space, if you see a blob of water, it doesn't just spread out like a gas. It stays as a blob of water. Yeah, exactly, because it's attracted to itself. So that causes surface tension, right? That's what surface tension is. And then, wait, wait, why is it called surface tension?

Like, what's happening at the surface? It's called surface tension, because, at the surface, if you poke it, it sort of holds together, like it creates this sort of sheet at the surface that resists being torn apart or penetrated. It's the same way that, like, the wall holds itself together, right? You have bonds between the molecules that are holding the wall together. These bonds are much, much weaker, which is why water, in this case, is a fluid, right? It's just a weaker version of those same bonds that hold them all matter together.

Right, right. But there's something special about the surface, isn't it? like the, isn't it, or maybe I'm wrong, is that the molecules on the surface are sort of holding on a little bit tighter to each other than the ones like inside of the water. Could be.

You tell me you're the engineer. Then we're completely lost. No, but the key thing when it comes to understanding skipping stones is, you know, could you use surface tension to skip a stone? Because you can use it to float a bug, right? Like some bugs stand on water because the water refuses

to sort of be broken apart. That's right. Yeah, the water holds itself together and creates a surface, right? But that only really works for very, very low weight objects because the surface tension is not very strong. I mean, you touch a drop of water

and it clings to you instead, right? It's very easy to break surface tension. And if it was just surface tension, then you could be able to take a rock and put it on water and it would float there, right? But a rock that you could easily skip, if you put it on the surface of the water,

it would just sink through. Some people might be wondering, is it the surface tension that's creating some kind of trampoline on the water that's maybe causing the stone to skip? Exactly. That was kind of the scenario

we're trying to debunk. Yeah, that's definitely not happening because if you put a stone on a trampoline, right, it doesn't fall through the trampoline, right? So you know the trampoline is strong enough to bounce the stone back up. But if you put a stone,

just lay it sort of gently on the surface of the water, you know what's going to happen. It's not going to sit there. It's going to sink unless your stone weighs the same as a paperclip, right? in which case you probably can't skip it anyway. But a stone that you could skip won't sit gently on the water.

So surface tension is not enough to provide sort of a trampoline effect there. Even if it's going fast, I could maybe imagine somebody thinking you throw a stone so fast at a body of water that it actually kind of bounces back from hitting that surface tension. It does bounce back, but not because of the surface tension, right? And you can see this because you can skip stones or skip objects on things without as much surface tension. For example, you can even skip things off like the atmosphere. You know, sometimes when spacecraft are trying to reenter the atmosphere, there's an angle they have to enter it where if they go too steep, then they heat up too much.

But if they go too shallow, then they skip off the atmosphere back into space. Oh, you can skip spaceships. Yeah, you can skip spaceships. I don't think it's a good idea. I don't think anybody's ever done it on purpose. I think it's a... Is there a world record for that one or competition? Yeah, one.

And the guy bounced out into space and nobody's ever seen him before. He won. They sent him the diploma, but they didn't get it. You can also skip on surfaces that have no tension at all. Like you can skip rocks on sand dunes, right? And sand doesn't have any attraction to itself. There's no surface tension on sand dunes. You don't get drops of sand, right?

So you see this skipping effect in places with more or less surface tension. And the bottom line, though, is that surface tension is just super weak and it can't contribute at all. All right, so it's not surface tension that's helpful. helping you or helping us skip stones, so there must be other things. So let's get into it, but first, let's take a quick break. Imagine that you're on an airplane, and all of a sudden you hear this. Attention passengers, the pilot is having an emergency, and we need someone, anyone, to land this plane.

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Listen to the new season of Grasas Has Come Again as part of My Cultura Podcast Network on the IHartRadio app, Apple Podcasts, or wherever you get your podcast. All right, we're talking about why is it possible to skip stones? on a lake. Like, what's the physics of it? And so we talked about how it's not surface tension, which is what a lot of people guessed. And so maybe it might be something else. So I would guess it maybe has something to do with the spin that you put into the stone. Is that kind of what's happening? It feels like a good answer, right? Because when you're skipping stones, you notice that if you spin them really fast, they skip better, right? We will talk about it in a moment how the stone's spinning actually does help it skip, but it's not actually necessary.

I mean, the spin, what it does is it helps make it fly straight sort of like a frisbee so that it like hits the water at a good angle and a good direction and all that stuff. But it's not actually necessary. You can skip a stone without spinning it, it's possible. I always thought that it was something to do with like conservation of angular momentum, you know? Like if you spin it, it wants to keep spinning and that keeps it kind of level, which then kind of makes it graze the surface of the water. Yeah, I mean, you're getting there.

It's not actually necessary. for spinning but you're right it keeps it sort of flat right um just the way a frisbee flies better when it's spinning for the same reason as you say angular momentum it doesn't like to tip over or it takes more of a force to tip it over um and it turns out that you skip best when you hit the water at just the right angle and so spinning the stone does help it hit at that right at that angle that the good angle for skipping but it's not actually necessary you can skip a stone without spinning it it is possible wow you're blowing my mind here you can skip stone you can skip stone on sand, and you can do it without spinning.

Yeah, yeah, exactly. Skipping turns out to be quite the fascinating physics topic. All right, so then if it's not surface tension or spinning, what's happening when we skip stones? Well, this is actually really interesting, and it turns out there's a physicist about 20 years ago whose son asked him, hey, dad, how is it that you can skip stones? What's the physics of it?

And he was like, oh, I'm sure it's pretty simple. And he started digging into it, and turns out it's pretty complicated, and he spent months studying this and doing experiments, and he finally came up with an equation, an equation that predicts how many skips you'll get from a stone as a function of the angle of the stone, the velocity of the stone, the speed of skipping, the weight of the stone, all this stuff. And so he was able to isolate sort of what are the important factors in getting a stone to skip. So wait, his son asked him a question, like, hey, dad, and then three years later, he's like, here it is.

Here's a 10-page paper full of equations. That's what you wanted, right? I just wanted a yes or no answer, dad. The kid probably totally forgot about it. He's like, oh, I don't care, whatever. That's what it's like to have visits for a parent. No, the kid is still waiting by the lake with the stone in the same. Dad, show me how.

Wait, I just got to finish this equation. Did he figure this out from, like, equations? Or was this all experimental? Like, I'm going to try different stone sizes. and different angles and different velocities or a little bit of both? It was a little bit of both. He started out theoretically.

He was like, can I understand the forces involved? And what we do all the time in physics, which is critical, is he simplified the problem. He's like, okay, let me assume the stone is perfectly flat. Let me assume it's a perfect circle. Let me assume it hits the water at this angle or whatever. He made some assumptions to simplify the problem. And then he was able to write down equations

that he thought would describe the forces involved. and that let him make predictions. He's like, okay, if these are the forces involved, right? And he knows how the forces change as a function of the angle you throw it in the speed, then I can make predictions for how many times a stone will skip. Then he went out and checked it.

And he actually did some experiments to see if his equations were valid. And was it working because he got the paper published. Yeah, exactly. I want to see what that peer review process was like. Did somebody go out there with a bunch of stones and his paper and try this thing out? I'm not quite sure.

But he published the paper. it's a guy from the University of Leone in France, and in his paper, he suggests that the critical variables are, of course, the flatness of the stone, the viscosity of the fluid, right? The viscosity of the liquid, which is not the same thing as surface tension,

the angle of the stone and its speed. Wow, so none of those things involve surface tension or spinning. Yeah, and spinning again helps because it helps you get the right angle, right? And it's also easier to throw a rock really fast if you're spinning it sort of out the tip of your finger as you throw it. So spinning is sort of like a supplemental thing. It's not necessary, but it's helpful.

I'm waiting for the twist in the story where you say, and then he became the world record holder. So in the end, it's not really surface tension. It's much more about like the viscosity of the water, right? Because, you know, think about like... Meaning like the thickness of it or how goofy it is. Yeah, how goopy it is, right? Water, not only is it attracted to itself, which causes surface tension,

and it's a fairly small force, but it's also kind of viscous, right? It's like, you know, there's a bit of goopiness to it. Like, honey is goopier, of course, than water, right? And this comes from how the molecules would rub by each other, like the friction, the molecule to molecule friction. So it's a different physics, right?

Surface tension is about attraction of the molecules. This is about how the molecules flow past each other. If something's really viscous, like tar or like a giant vat of honey, like I would imagine if I throw a skipping stone on top, it would just kind of blurb, kind of, you know, it wouldn't skip, or would it? I don't know. Oh, no, that's a good question. I think, I mean, obviously, if it's really viscous, then it's a flat surface, then it will skip, right? So there's probably some point in there. Like super duper. Yeah. Super duper viscous, but not sticky.

Yeah, exactly. And, you know, you can come up with examples of liquids that are really viscous, but don't have a lot of surface tension or the other way around. So there's a complicated relationship between surface tension and viscosity. But in the end, what you need is viscosity, and the reason is that when the stone hits the water, you want the water to not be able to sort of flow out of the way fast enough, right? Like, you want the water to push back. Yes, exactly. You need the water to push back. And so, like, when you jump off a diving board and you land totally flat on the water, right?

If you've done that, you know that water can feel like concrete, right? Like belly flop, like a belly flop. Yeah, a belly flop, exactly. If you fall off a bridge, for example, from high enough, you can die landing in water. right, because water just can't get out of the way fast enough. And so it pushes back on you, just sort of the way the ground does, right, when you land on it. It doesn't get out of the way fast enough.

Yeah. Like if you're falling through air, air is much, much less viscous than water and it gets out of the way, right? It just moves out of the way up. I mean, there's still some friction there, which is why you have a terminal velocity, but it gets out of the way fast enough for you to pass through it, right? But water is much, much more viscous, so it provides much, much more drag. And if you hit the water flat, then you're going to get a big force the

other direction, which is going to make your belly smart, or make your rock skip. So that's the key, right, is that the water pushes back up on the rock. You can't skip rocks on clouds or air. You can skip rocks on air, actually. I mean, you can skip spaceships on air, but

it takes much, much higher speed, yeah. Well, this is a perfect point to take a break. Imagine that you're on an airplane, and all of a sudden you hear this. The pilot is having an emergency and we need someone, anyone, to land this plane. Think you could do it?

It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, pull that, turn this. It's just, I can do it my eyes close. I'm Manny. I'm Noah. This is Devon. And on our new show, no such thing. We get to the bottom of questions like these.

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I hope you'll join me and my extraordinary guests for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. So it's about the viscosity of the liquid. So the more viscous it is, the easier it is to bounce it. Yes, you need a flat object and a viscous liquid. And that's a... Oh, a flat object. What if it's not flat?

Well, if it's not flat, like, I mean, the most extreme thing is if you drop, like, you know, drop something really thin and sharp into the water, it's just going to separate the water and sink down to the bottom, right? So you need to drop something flat so that it... And so the water can't move out of the way. You need to belly flop. Yes, exactly. Skipping stones should be called belly flopping stones. Don't they have funny names for this in other countries?

Like, what do they call it in England? In England, they call it ducks and drakes, which makes absolutely no sense to me. Like, are you shooting ducks? Like, what's going on? Wait, like, if you're throwing stones at a lake to skip, to create those ripples and skips, that's called ducks and drakes? Ducks and drakes, yep. Somebody out there in England, explain that to us. In France, they have a clever name for it.

They call it ricochet, which makes some sense, right? Your rock is ricocheting off the surface of the water. What are some other funny words? Well, these are words that don't even make sense to me. Like, in Ireland, they call it stone scuffing, the way you would scuff your shoes and get marks on them or something. You can't say it with an Irish accent, Danny. I can't do an Irish accent, not at all.

No, but every language has a word for it. And the funniest one is that according to the Oxford English Dictionary, right? So according to the Brits, the way Americans say it is they say it's called Dapper And that's not a word I've ever heard. So, like, what are the Brits doing over there telling us what we call skipping stones? And they're getting it totally wrong. Well, it's all just ducks and drinks to them.

That's right. They got no credibility over there. Is that where the dab comes from? Where am I thinking of the dab? I am not culturally relevant enough to answer that question. But it's more than just the viscosity, right? And more than just having silly name. Okay, so it's more than just having substance

to the thing you're trying to skip on, which water does. It has enough viscosity to skip stones. That's right, because you know when you jump off a diving board and belly flop, you don't skip, right? So there's a difference between belly flopping and skipping. And then what else is going on here? So another key is the angle, right? When you throw the stone, you want it the front edge of the stone to be higher than the back edge of the stone.

So you want the stone when it hits the water for the trailing edge to hit first. All right. And the reason is that you're pushing down on the water. And if you have that angle... Kind of like a wheelie, like you're tilted back. Yes, exactly, exactly. Though I do not recommend trying to do this with your motorcycle or your mountain bike. I mean...

Or do it and send us a video. That would be awesome. I think that's called geeses and gooses in England. I think you're probably right. And what happens when you do that is then you push down the water at an angle and the water creates kind of a ramp, right? because you've pushed it down so the back end is further down than the front end and so you have a ramp that slopes up, okay?

And here's where the speed comes out. You've got to be moving fast. So you push down on the water to create a ramp and then that ramp launches you back up into the air at the same angle. You're not really bouncing then? It's more like you're going into the water and then creating a ramp for you to take off of.

Yeah, well, you're doing both at the same time. One of my favorite things about sort of projectile motion in physics is how you can break things up into two dimensions that are totally independent, right? Motion in one dimension is independent from motion and the other dimension. Somebody in the question-answer section said that the reason that you can skip a rock is because it's moving really fast in one direction and so it doesn't fall down, which is totally not true, right? Like if you shoot a bullet, you know, it is moving really, really fast parallel to the surface of the earth,

but it's also at the same time falling. And falling towards the surface of the earth is not affected by your motion parallel to the surface. And so you've got two things going on here. One is you're bouncing perpendicular to the surface of the water, right? But you're also moving parallel. So you've got the belly flop in the perpendicular direction, and you've got this little ramp action in the parallel direction. Well, what happens if you don't hit the water at a good angle?

Like, let's say you hit the water kind of leaning forward instead of leaning back. Then you end up the front edge of your rock will dig into the water, and it'll slow it down and it'll flip. And then you don't get any more skips. You don't create this little ramp. Yeah. Because remember, the key to getting a lot of skips is doing the same thing over and over again. So you want that when you leave the water, you're at the same angle as when you hit the water, right?

So that you can hit the water again at that same angle. So anything that flips you over or starts you spinning, you're losing your energy and you're not going to hit the water at the right angle of the next skip. Well, I would have thought the spin was really important because without the spin, wouldn't you lose that angle really quickly with all the water. slushing around. Yeah, spinning is important and nobody wins the stone skipping world championship without a really good spin. But it's not technically necessary. But yeah, it's really important to maintaining the angle and to maintaining your speed. So there's a lot of different things going on when just one simple rock hits the water. All right. And then so viscosity angle and then what's the last

critical ingredient? Last critical ingredient is speed, right? If you are not moving fast enough, then you sink when you hit the water because the ramp sort of dissolves, right? That's the last. The ramp does not, doesn't stick around for very long. You hit the water, right? And you bounce back because the water doesn't have a lot of time to move out of the way. But you want to get off of that ramp as soon as you can. Because just past the ramp is a little divot, right? And so you want to get off of that ramp and so you need enough speed.

You need to be moving faster than the water is, of course. Moving faster horizontally. Or does it help to go fast a little bit, you know, into the water? Or do you get that? You need both. You need, if you're not moving fast enough perpendicular to the water, then you won't get the bounce, right? You need to be hitting the water with enough speed that the water can't get out of the way

and pushes back at you. You also need horizontal velocity, so you can get off that ramp before it dissolves. But if you're going to slow, then, you know, you push the water into a ramp, but then you don't take off. You just kind of blew into the water. That's exactly the sound it makes. Wow, you must have done these experiments. That's what it sounds like in every slow-motion video clip I've seen on YouTube.

Yeah, but every time you bounce, you also do lose energy. It's impossible not to because there's friction. And so you hit the water and it slows you down a little bit. So every bounce is, in the best case scenario, like 80 to 90% of the previous bounce. And so that's why, you know, they get faster and faster. The time between bounces gets smaller and smaller because you're not going as fast. You're not going as far up, so it doesn't take as much time to come back down. So that's pretty good.

Like you only lose 20% in each skip, or is that like a, you know, is that what the pros do? Or is that what happens when anyone skips don't? Is that it's always 80%. No, that's the like top level performance, like 80 or 90%. Yeah, and that's the key to getting a lot of skips is losing the smallest amount of energy every skip, which means hitting the water at just the right angle. And it's one of these things where it's very sensitive. You're slightly off of the optimal angle.

You're going to lose a lot more energy in the first skip. And then you're going to be off on the next angle and the next angle. And pretty soon you know you're sinking to the bottom of the lake. That's pretty impressive, 80%. So that's how they get to like 100 meters. Yeah, exactly. We're 88 skips, which still blows my mind. It feels like that would take like an hour.

You know, like you throw the rock and then just like 10 minutes later, you're still counting skips or something. Well, towards the end, it's not like skip, skip, skip, skip. It's like Yeah, exactly. It's like stuttering skiffs at the end, which is what tells me these really like

massively competitive events, they must have some sort of camera that's taking pictures to count these skips. They can't have like a super spotter or something just using their eyeballs. You think it's at that high tech?

You think they have like corporate sponsors and pro athletes? Probably some Swiss watch company is sponsoring it, et cetera. Yeah, I bet the top guys have groupies and travel around in fancy buses and all sorts of stuff. All right.

So then, Have you tried this since learning the secrets here? Have you tried and does it help? Did it help you skip stones better? No, and that's the thing about physics. It tells you how the universe works. It gives you insight, but it doesn't help you actually navigate the situation.

You know, for example, we did that whole podcast episode about how to ride a bike, right? That doesn't make me ride bikes any better, especially because we learned that physics doesn't know why bicycles balance, right? But you can still ride a bike. So there's this disconnect between understanding something and being able to do it. Well, you know, it did help me. I mean, after learning all of this, I did try it. And it does help.

Like, if you know that you have to throw it at the water, kind of at a little bit of an angle leaning back, that's a huge help. Because, you know, before you would, I would try to, like, throw it at the water. So it's perfectly parallel to the water. I thought that was the secret, you know. But, like, once you know, you have to, like, kind of lean it back a little bit, it does help you skip it. All right, well, there you go. I mean, not 88 skips, but, you know. Physics has improved your life, Jorge, for the first time.

It ruined my vacation, but it increased my standing in the world rankings of... It's amazing to me that the universe is mathematical, that we can understand it at all, that it seems to follow these rules that we can write down on paper and manipulate with our minds. It's amazing that that works, and it's a joy to see what it happens, you know, that we can actually isolate the critical elements and understand something. So the next time you see something weird, the next time you see something you don't understand, you know, think about the physics of it. What's making that happen? What's going on inside? Is there some microscopic explanation that can help you understand why those ducks are

chasing that funny bird or, you know, why those clouds form in that weird way. There's physics all around us. And if you don't understand, just send the question to Daniel and we'll answer it on the podcast. That's right. Before, after I do a bunch of experiments at Jorge's house. Skipping gold coins on my... That's right. Hey, can I borrow a few of those gold coins, please? I got do some experiments. Oops, they sank to the

bottom of the lake. Sorry about that. All right, well, we hope you enjoyed that. And as Neo

says, whoa. Thanks for tuning in. See you next time. If you still have a question after

listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook,

Twitter, and Instagram at Daniel and Jorge, that's one word, or email us at Feedback at danielandhorpe.com. Thanks for listening and remember that Daniel and Jorge

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