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[00:00:02]

This is the InFocus podcast from The Hindu. Hello and welcome to the Hindus InFocus podcast. My name is Jan Shriram and I'm your host for today. This is a rare episode in which we're discussing sports, but we are taking a slightly different tack today. We're going to look at the science behind why a cricket ball swings and use this opportunity to highlight some really interesting research work that's been happening in this area. Our immediate motivation, of course, is the DNA test match currently underway between India and Australia that's being played with the pink ball, not the pink ball is, of course, relatively novel in cricket.

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And there's still a lot of curiosity and attempt to understand how it behaves differently to the red and white ball. So while we address the ball in the course of this conversation today, we do not restrict ourselves to it. We talk overall about the general mechanics of swing and the various factors that affect it. Now, that might sound a little complex, but what is really special about this episode, as I mentioned earlier, is that we look at an aspect of cricket from a science perspective rather than a sports reporting one.

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And that's possible thanks to the work being done by my guest today. Professor Sanjay Gupta teaches at the Department of Aerospace Engineering at IATA Kanpur. And for the past several years, he has been leading a team of researchers conducting experiments to understand the physics governing the swing of a cricket ball. I won't say more. I let him explain further. But as I said, I don't it motivation for doing this podcast is the test currently underway between India and Australia.

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But the insights that Professor Matute provides goes much beyond that and will stand the test of time. Professor Mattos, thank you so much for joining us on the Hindus InFocus podcast today and for making time for having this conversation.

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Thank you for having me here. Right. So, of course, the kind of immediate motivation in terms of the news point to have this conversation is the in Australia Test match that's starting today. And it's it's a DNA test match being played with the pink ball. So we will get to speaking about the ping pong. But I thought a good way to start this generally is to talk about the research that you've been doing on cricket ball, on the cricket board, and talk about aspects of, you know, the swing of the cricket board and how you brought science into the study of this.

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So please tell us a little bit about how this project started, this this project of looking at the science of the swing of cricket.

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Sure. So I am a professor in aerospace engineering and we do a lot of fluid mechanics. I'm interested in many things. And one of the important things I like to look at is turbulence. One of the basic things that we do is look at canonical flows like spheres and cylinders and which have very little geometry complexity, but have all the richness of the flows. So when students approach us for projects and would like to do some work related to fluid dynamics, maybe either for their Batchelor's projects or for their master's thesis, then they get very excited and they find it very glamorous that if they can relate it to something in real life.

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So. So what we did is we the problem remains the same. It is turbulence. But then if you put in it the glamour of a cricket ball or a golf ball or a hockey ball, then the students get super excited and the physics remains exactly the same. So that's how this all began about 10 years ago. We've been working on this.

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When you're talking about the swing of a cricket ball, basically you're saying that in in what you study, it's basically studying turbulence and slow decline. And could you tell me a little bit about how I mean, what is the kind of experimentation and the kind of study method that you used?

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So so so you imagine there is a sphere with with a seam on it, like a cricket ball, and we want to understand the fluid mechanics of it. So primarily, there are three ways that one can look at it. One is, you know, in a very theoretical sense, you know, you you look at some equations and do some, you know, make some notes using the equations. The other is you can actually do this numerically.

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So you take the same equations, make a computer model and solve these equations and get something meaningful out of it. The third one would be actually you do experiments. So so we've we've tried actually two of these techniques. We've we've done a numerical model. And then we have also made models of of cricket ball and we have taken actual cricket balls and then experiments on them in a wind tunnel. So just to give you an idea of what a wind tunnel is, you know, imagine a bowler delivers a ball and the ball moves towards the batsman.

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Now, I could do a change of frame of reference and I could imagine that I am sitting on the cricket ball as an observer and the ad is coming at me. So I placed this ball inside a room, as you call it. And then there is a breeze which is generated by a fan, of course, in a more complex way. And that goes, let's say, from left to right and the ball is stationary. Then one could measure the forces that act on the ball and then, you know, do more analysis.

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So these are the essentially two approaches that we have taken. Right. So you have a wind tunnel and then you simulate various situations in which a cricket ball is moving through that wind tunnel.

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That's right. That's right. That's right. So so in a in a cricket ball, you know, the parameters that a bowler would typically have is so if I'm a bowler, you know, a fast bowler, maybe like Boomerang or some other fast bowler, I could use my pace. So that's the velocity of the ball. Or if I'm sitting on the ball, it is the velocity at which the end is coming at the ball. That's one parameter.

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The other parameter could be the same orientation to the to the floor. So how so? That would be basically my dispute with the disposition when I deliver the ball. And then we could talk about the backspin on the ball. So again, if I am a bowler, I would like if I am a symbol that I would like to stabilise the seam. And that is typically done by imparting a backspin to it. It comes very naturally. And then there are these other effects, like the ambient effects, you know, maybe whether it is day or night, it is hard to call humidity's high or low.

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So typically what we do is we take all these effect. Into account scientifically and then kind of throw the results back into the as if the bullet would be using these parameters, that that sounds really fascinating.

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So and I guess the question to ask then is, you know, what have you discovered about your experiments? What did they discover about what how the ball swings? Because that is a that is the conventional way in which sports writers and aficionados of the sport understand things like swing. But is that a more sort of complex understanding that you can sort of give us?

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Sure, sure. So I'll try to make this as simple as I can. I first tried to tell you about the gospel and come to the cricket ball. So so imagine if I had a smooth sphere and I use that as a golf ball of exactly the same diameter and I try hitting it. What what happens is that because the ball is very smooth, the surface is very smooth, the boundary layer or the flow on this ball would remain luminous.

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And it turns out that it would incur a lot of air resistance, it would incur a lot of drag. So if I hit it, it will not go as far as a dimpled cricket, a dimpled golf ball would go. So by artificially putting a roughness on it, by artificially putting the bulls on it, when I hit a golf ball with the same force as I would hit us football, it turns out, because it becomes double in the air resistance when it is smaller and it can travel a larger distance.

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So that's the that's essentially the difference that a laminar versus a turbulent flow can cause. No, this is the golf ball is dimpled, so that is motor. What does that do to its movement, to the right?

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So so what what happens is that if I had a smooth ball, the boundary layer would be or the flow on it would be laminate. Yeah, but when I make dimples on it, it disturbs the flow, adds a little bit randomness to the flow and makes it double. And what the turbulence does is that the the effect it has on the floor. So there's something called flow separation. OK, how far the floor remains attached to the ball, that kind of increases when the flow becomes turbulent.

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In layman's terms, it would mean that the floor would have the golf ball would have less drag on it or less air resistance on it once I make the boundary layer or the floor turbulent. So it would travel further. If will travel further because there's less air resistance with the same force when I hit the ball and because the floor has become turbulent. So now the ball can travel and farther. And so, so that's that's the situation of a golf ball not come a cricket ball.

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Yeah. So if I had a small sphere again, you know, the floor would be kind of symmetric, the same everywhere. You know, if I, if I, if I look at the ball, but not because of the presence of a seam, the the turbulence can be initiated on the side of the scene. And then there's the neck. The other side, which is which is which we call is the non seam side. And now there's a distinction between the two surfaces of the ball.

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So to make it more clear, suppose I am a batsman and a ball approaches me. Right. The seam is, let's say, pointing towards, let's say, the slip of slip. And what would happen is that as the ball travels towards me of the floor on, it actually is hitting the seam side sooner than it hits the non seam side. And effectively, what that would do is that one part of the ball would have a turbulent flow and the other part would still be a laminar flow.

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So the part which sees the the seam that becomes turbulent and the part which does not see the seam remains laminate. And what that does, it it generates a side force on the ball now. So as a bowler, I cannot control the trajectory of the ball. So instead of just going straight to the batsman, it can actually move literally. And that's what is referred to as swing. And how does how this other externalities like wind and all that affect this show.

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So so it turns out that, you know, if I if if it was the perfect ventral kind of a situation and I have a brand new ball and all these balls are, say, identical, they are spheres, perfect spheres, and they have a perfect seam on them, then everything is ideal. And I can actually be very sure of what happens when. But, you know, life is not like that. It the ball is going to become rough as the match goes on.

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Be not all balls are exactly the same. I mean, they are not perfect spheres. So in fact in manufacturing there would be minor differences between balls. And even as a batsman hits the ball, you know, it loses very city. Then we have these differences of weather. So if I have, let's say, a cold weather versus warm weather, then it turns out it affects the density of air. So if I have, let's say, cold weather, the air is denser.

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And if the if it is warm, then it is lighter.

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And what it does to the to to the to the forces is that if I have the ball traveling at exactly the same speed, everything else being same, then in the cold weather, I would see a larger force because the density of the air is largest and in warmer weather I would see less force.

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So the same bullet at the same speed, if he blows, let's say, in lords at the lower temperature. He would see a swing, but the same boy learning feebles in Eden Gardens at a certain speed beach ball that in Lords he may not see a swing everything as being remaining safe. So those are the external factors, for example.

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Similarly, humidity, you know, if I have more moisture content in the air, then it actually reduces the density of air because as you may be aware, the molecular weight of water is smaller than the molecular weight of air, so actually reduces the density of the air. So therefore, if I have a humid day versus a dry day, it would again affect my the way the ball swings. There could be many other factors. For example, this is not proven, but many people speculate.

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That if I have, let's say, moisture content on beach, then my skin can absorb moisture and it can the protrusions can become larger, so it fills up and therefore it it can make the fluid turbulent more effectively. So once the ball becomes a little bit wet because of moisture. So there are two contrasting effects. One is the Bowl may not be able to get the ball wet, but if he does and he's able to bowl at the regular speed, then actually they can generate more swing force and the ball would swing around a little bit more.

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So there are lots of complexities, both in terms of weather and in terms of external conditions that complicate the swing bowling.

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Right. Yeah, I know it sounds like it. And so, I mean, we will get to the pink ball. But, you know, Leslie, is that what's the comparison that you find between the red and the white boy, for instance?

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OK, so so, you know, I'm sorry to break this news, but color on its own has no effect on swing. So. So if I took a white ball and I magically made it red, the color obviously cannot affect the fluid dynamics or the, you know, the the swing of the ball directly. So my understanding is that, you know, you first take off in your manufacturing when you when you want to put a color on the leather.

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So first you process the leather. So typically the test balls, you know, they are made of four quarters, two halves and then two more quarters on each half. And then you try to stitch them, polished them and put the pigment on them. Now, the process of putting a pigment on the leather would be different on whether I want to put a white pigment or I want to put a red pigment or I want to put, you know, a pink pigment.

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So the lacquer that goes on it or the polish that goes on it is kind of different. So, so. So that's one thing. The second thing is also the the manufacturing process. So if you have, let's say, an AC manufacturer, one manufacturer versus Kookaburra versus maybe Duke, they would all use different processes. And even the red one from the three companies would behave differently because of same height, because of the way they stitched the ball, because of the way they process the pigmentation and the lacquer they put on the ball.

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OK, so so it turns out that, you know, it's not just the color there are. There are many, many factors that affect the ball. So let's not talk about the same manufacture, but two different pigments. And let's say I have the white pigment and I have the red pigment. It turns out that, you know, the same process, the same kind of lacquer may not hold the two kinds of the two kinds of pigments.

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And it may very well happen that I may have to put a stickler for of lacquer, for sustaining a white pigment. And therefore, that surface would be smoother than, let's say, I would have a red color pigment and it may even last longer. So as my ball gets older, it is quite possible that fight global may sustain more scuff marks as compared to a red color ball, and it may therefore retain its newness, if I may say, for a larger number of overs.

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Right. And the tipping point. What about the people in that case?

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So what I read is, you know, I have still not done experiments on the pink ball. You have to lay our hands on a few balls. But my understanding is that a pink pigment is a little bit more tricky to be sustained by leather. So one would have to put a typical coat of the polish or the lacquer or whatever one calls it.

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And therefore it has more shiny, you know, in terms of fluid mechanics. It's a smoother surface. If you look at the roughness, a pink one would be more smoother than a red ball. That's number one. Number two, the same size is all the same. Height is also a little bit different. So I am told that the pink ball has a more prominent scene. So this will do two things if if I have a brand new pink ball and a brand new smoothbore.

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A red ball, then the then the pink ball would be smoother and it would have a more prominent seam, what that would do is that as a bowler, I would see a bigger differential on the floor, on the two surfaces, the seam in the non team side. So I would get more swing with a pink ball as compared to a red ball? No. As the ball gets older, you know, now with the new rule that people cannot use their saliva, they will not be able to maintain the shine of the ball as they used to in in earlier times covid.

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So so if I have a natural lacquer which kind of sustains the Polish a little longer, then for the swing bowler, that's that's, you know, a dream come true. So therefore, a pink ball, I think would be would give a smaller a more advantage compared to a red ball. That's the speculation that I have after going through the processes of how they manufacture these balls. Yeah. So, I mean, so many questions come to mind, just not necessarily related to the pink ball right now, but just one of the one of the things we're talking about swing one of the like one of the sort of mystery elements of cricket is reverse swing.

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Sure. And what what is what are the sort of experiments and studies found about the swing?

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Good. I am so glad you asked this question. So so so let me first clarify what what we mean by reversing in technical terms as far as the fluid mechanics this is concerned. So so, you know, if the seam is oriented, let's say, towards the slip. And the ball moves towards the slip, so it moves in the direction of the seam. That's called a regular swing, the conventional swing. Yeah, but if it moves the other way, the seam is pointing in one particular direction, but the ball has a little movement in the opposite direction.

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Then it is called a reverse swing. And popularly, it's also known as the ball is reversing. So there was a question that can a new ball reversing because you will often hear commentators say that the ball is becoming old and it is reversing now. So I used to have this curiosity that can a new ball reversely. So that was one of the things that we looked at in our experiments and our computational studies and what we found is, yes, it can be a newborn, so support a bowler.

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And, you know, I can bowl, let's say, from zero to, let's say, one kilometers per hour from from 30 kilometers per hour to one hundred forty eight kilometers per hour. And I hold the same same position. I hold the same back spin. Everything else is the same. I just changed my speed of delivery. So what our research shows is that up to a certain speed, let's say maybe something like 60 to 70 kilometers per hour.

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There is no significant little force on the ball, so there would be no swing. And then let's say between 60 to something like 30 or 40 kilometers per hour, I would actually start swinging the ball. So. So it would be a conventional swing. And then when I go beyond one hundred forty or so kilometers per hour, then actually I would start generating the worst swing. OK, so I need a new ball. Can also reversing.

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But of course it is difficult to control the seam when you are bowling at such a rapid pace. I mean the the kinesiology becomes very important. There is movement and the whole body motion. All right. So we've tried to look at in our study that, you know, various parameters. So, for example, the ball speed, then the same orientation. Then even though the condition of the ball so slow as you may be aware, that players, they use something called a contrast swing.

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So what they do is they they keep one side of the ball shiny and the other side, they allow it to become rough as the game progresses. So you must have seen, you know, that when the fielders feel the ball or when the ball that is going towards the bowling mark, they put the light on the ball and rub it on one side. Right. It turns out that's not random so that the side would choose which surface of the which hemisphere of the ball they would polish and which one they would let it remain, you know, rough.

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And this difference, in addition to the seam can actually swing and also cause it was sweet. So this this this term is called contrast swing. Yeah. Yeah.

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Now, the interesting part is that as the ball gets older, there is this very nice roll that the roughness of the ball plays and kind of it is in direct competition with the scene of the ball. So you could have a situation where on one side the the the seam is making the floor taller and on the other side, because it is rough, the roughness is making the floor taller. So if you are a smart bowler and you have a lot of experience, you can actually use the state of the ball, the orientation of the seam, the speed, the playing conditions, you know, like the wind, the temperature, all this to deceive the batsman.

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So it's it's really a bizarre number of parameters. Right.

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And this is something that many smart bowlers discover by intuition. What you're describing to me scientifically. Absolutely. Absolutely. And I think they know a lot more than food. And again, this is what they were. No, there's no doubt in my mind. And you're also saying that theoretically it's possible, even with a new ball bowled at very high speeds to generate reverse swing, but that requires an extraordinary amount of controls.

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That's right. So there are bowlers, you know, who can generate reverse swing on a new ball. So so there was this English bowler, Simon Jones, I think very tall bowler. And I have seen the clips of his bowling video clips where I think he gets to Washington with a brand new cricket ball. So it's very much possible.

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And so, you know, just to just sort of close with running out of time, just to sort of close, you know, you've done all this research about the mechanics of the ball. Does this could this contribute in any way to sort of going into the design of of cricket balls? And where does this research take you?

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You know, you've touched upon something which which is very close to my heart. I also do work on on badminton, shuttlecocks and on cricket balls and gospel. And really, I mean, so there are two aspects to sports. One is, you know, the the athletics itself, the skills and the other is entertainment. I mean, if I'm going to watch a 20 match and I want a really nice entertainment, I would like so much adventure in it that everything should be uncertain.

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That's the beauty of a game. And one can use these these research findings to design balls, which would which would make things more challenging. You know, why should the why should there just be a course? They should also be you know, I should have as a captain, if I am the bowling captain, I should be able to choose out of, let's say, five kinds of balls, which one I would like to use today and maybe have three different balls in a game, one for the spinner, one for the base, one for the seam.

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So there are lots and lots of possibilities. I think the future is bright in sports. That's that's all I can say. Professor. Thank you for joining us for this really fascinating discussion and, of course, good luck for your research ahead and thank you for making time for us on this podcast today.

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Thank you very much. My pleasure. InFocus will be back soon with analysis of the biggest news issues in the meantime, you can find our podcast on Spotify, Apple, podcasts, Stitcher and other platforms. Just Search for InFocus by The Hindu. We'll see you soon.