StarTalk Radio - #ICYMI: Cosmic Queries: Tennis Special Edition

Episode Date: September 7, 2017

Are you ready for a deep dive into hardcore tennis physics? This week, Gary O’Reilly and Chuck Nice welcome back sports physicist John Eric Goff to answer fan-submitted questions about tennis, from the silly to the serious.Don’t miss an episode of Playing with Science. Subscribe to our channels on:Apple Podcasts: https://itunes.apple.com/us/podcast/playing-with-science/id1198280360?mt=2GooglePlay Music: https://play.google.com/music/listen?u=0#/ps/Iimke5bwpoh2nb25swchmw6kzjqSoundCloud: https://soundcloud.com/startalk_playing-with-scienceStitcher: http://www.stitcher.com/podcast/startalk/playing-with-scienceTuneIn: http://www.tunein.com/playingwithscienceNOTE: StarTalk All-Access subscribers can watch/listen to this entire episode commercial-free. Find out more at https://www.startalkradio.net/startalk-all-access/ Subscribe to SiriusXM Podcasts+ on Apple Podcasts to listen to new episodes ad-free and a whole week early.

I'm Gary O'Reilly. And I'm Chuck Nice. And this is Playing With Science. Yes, today is a Cosmic Queries tennis show where we open the floor to our StarTalk Playing With Science family and let them pose the questions. So if you ever wondered why your balls spin and why you must always keep them fuzzy... Yeah, I knew you'd like that.

Come on now, you know I can't do... I'm just going to go with it. I'm not going to do it. I'm just going to continue. And if you have any interest in a new spin on a never-ending string theory, you are in the right place because our good friend, Professor Eric Goff from Lynchburg College, Virginia, and author of Gold Medal Physics, is the man to unlock the answers to your questions. Now, let's get back to some fuzzy balls that spin. So, Eric, good to have you back.

How have you been, sir? I'm doing great. It's good to be back. How are you, Gary and Chuck? We are fabulous, yes. Good to hear you. So what have you been up to? Well, our classes begin in a week, so I've got about three more days before I need to start preparing for them. It's good to see that those kids are getting a quality education as you last minute their curriculum, professor. Well, I get all the research done before the classes start. Hey, by the way, now that the Tour de France is over, for those who know that you are the person who does the modeling, how did you end up ultimately? Oh, we did a really fabulous job this year. Our last stage, we missed by just 11 seconds. So we had a fantastic prediction set. 15 of our stages, we did better than 4%. 11 of them, we did better than 2%. Wow. So we had good predictions this year.

And you nailed Chris Froome from the start anyway. We had, yeah, I mean, I kind of figured Chris Froome was going to be the guy to beat, and no one could beat him, so he got in fourth. Can't touch this. And by the way, before we go any further, so how many does that make for Chris Froome, guys? Three in four. That's three in four? Yeah.

Well, it's his fourth total, but third in a row, right? Third in a row, but fourth total. Okay, cool. And how many more before we say he's better than Lance Armstrong, just as a point of interest? Well, Lance has officially won zero, right? Damn, that hurt. Ooh, professor.

Below the belt blow from the professor. I love it. Hey, well, let's get into our question. All right, let's get our first question. Mark Miller from Halifax, Nova Scotia on Patreon. This is how you pose a question to get it on Playing With Science. Love the show, says Mark. So I read that the fuzz on the felt cover of a tennis ball helps control its speed and bounce.

Would the fuzz itself have an effect on the effects of spin? We see more amazing curved shots. So, Professor, I'm going to knock that over the net. It's all yours. So the fuzz actually increases the cross-sectional area of the ball going through the air. So you get a little bit more area than if it didn't have fuzz. You get a little bit more air drag on it. So it will slow the ball down a little bit. As for the spin, the fuzz actually does help with the spin, but mostly

for low spin balls. When you start getting up to high speeds and high spin, the fuzz tends to lay down on the ball's surface a little bit more, and you don't notice it quite as much when you get really high spins and really high speeds. So let's say you take the fuzz off of the ball. How much would it change the game? Well, you're going to notice that more for the low spin, low speed shots, you're going to get a little bit less of a curve. You're also going to get a little bit less of a bounce off the ground if you have the fuzz on there because you get a little bit more friction. So you get less of a bounce with the f the fuzz with the fuzz gotcha and

if you take the fuzz off you're going to reduce the air drag a little bit so the balls are going to be moving a little bit faster gotcha this touches on a question from james arnold from facebook uh he says why is tennis played with fuzz fuzzy bouncy balls which you've already addressed is the fuzz important yet we've touched on that one. Or could it be shaved down? Now, Chuck, I thought you'd be all over this because this is in your ballpark, as it were. No, I mean, seriously. First of all, I am not about shaving the fuzz from the balls because the way I feel is though it gives the balls a juvenile look.

And I, for one, like mature looking balls. Well, that does add an extra wrinkle to the problem, doesn't it? It certainly does. Do not encourage him, Professor, please. We've got a long way to go in this show. What's the sort of coefficient of drag and all the rest of it that this fuzziness brings to a tennis ball? When you put fuzz on a tennis ball, what it's actually doing is it kind of thickens the boundary layer of air that's around the ball. And the flow of the air around the ball looks a little bit more what we call laminar than it does turbulent.

Say that again now. Can you explain those two things? I missed that. So for low speeds, the air separates behind the ball kind of at a big wake. When you go a lot faster, the air gets wrapped around the ball a little bit tighter, and the so-called drag coefficient drops. That was the drag crisis we've talked about on an earlier show.

Yes! You've started again, Professor. So the fuzz actually will thicken that boundary layer and move that drag crisis to a higher speed. So you actually get a little bit more on the drag coefficient, a little bit more area. So there's actually considerably more drag on the ball with the fuzz than if you didn't have any of it on there. So it's just kind of the opposite of like a boat in a lake. Like the faster the boat goes, the bigger the wake is. So you're saying the faster this ball

spins and goes through the air with the fuzz, the smaller the wake behind it. Well, with the fuzz, you actually get a bigger wake. Oh, I see what you're saying. When you cross that drag crisis into the turbulent regime, the wake would actually kind of wrap more around the back of the boat into like a narrower wake. Gotcha. What's interesting is we've seen this type of tennis ball for, I can't remember how long. And are you just wondering, the people who introduced this type of tennis ball into the sport,

do you think they would have been all over the physics of it and thinking, right, this is how we progress the game? I don't know the actual history. I mean, I know with golf balls, they started with smooth balls. And then the aristocracy noticed that when the bourgeoisie were playing with the used balls that they were discarding, they were going farther. So now we dimple the ball. So I imagine there was some trial and error involved. I mean, if you remove the fuzz, I mean, how fast do you want the game to be? I mean, how few hits do you need in a volley for it to be good tennis? How fast a serve would you have on a completely clean surface? Well, that's funny because 33 Kyleford from Instagram asked this question.

How fast does the ball have to spin for the spin to affect the trajectory? So at what point does the ball have to speed up so that the spin can create a different or create movement? spin can create a different or create movement? Well, so the, I mean, any type of spin is going to give it a little bit of a sideways movement. You're always going to have a little bit of this magnus force for even small spin. The typical angular speed you see on a tennis ball tend to be somewhere between about 16 revolutions per second and 80 revolutions per second. about 16 revolutions per second and 80 revolutions per second. If you like thinking about RPMs, that's somewhere between 1,000 and 5,000 revolutions per minute. Wow, not bad.

When you're getting a serve well in excess of 120 miles an hour with a lot of topspin, these things are really spinning. And what the spin actually does, the topspin for a serve, it'll increase the available range to something like two and a half to four degrees. And that gives the player a little bit more room for error when you're aiming for like the sideline or the center line or the back corner for a serve. Go ahead, Professor. Keep going, Professor. So, keep going, Professor. Well, another nice thing about the spin is that when it hits the ground, the ball is spinning. And if I could show you, I would. But when the ball is turning and it hits the ground, the ground imparts a significant amount of friction on it, and it can actually kick the spin up.

It can double the spin. So you get a lot more spin off the bounce, and that can play havoc with some inexperienced players. Absolutely. Now, can you just, I mean, because now that you've opened this up, I really just am asking for myself, can you explain, because that seems counterintuitive, the fact that the ball hits the ground, you would think that that would slow the spin down. That, in fact, you use the term friction. Normally, whenever we think of friction, we think of something being slowed down. It goes into retro. It goes into retro.

So how exactly does it kick the spin up? It's very interesting. Well, try to imagine a ball coming into a surface at an angle and it has no spin. When it hits the surface, the ball and the surface are going to rub against each other, and you're going to have a frictional force in the opposite direction the way the ball's moving. So the ball will actually leave the surface with spin. And you can do this with, if you ever have a super ball, just take it and spin it and drop it straight down. And you'll watch it kind of walk. It'll look like it's walking back and forth with each new bounce

as the spin changes direction. You're right. You're absolutely. Oh, that's great. Okay. So we've got, I love how I just told him he's right. Like he's not a professor of physics. You know, I'm just, I saw it more as an agreement. Yeah. I'm like, Hey, you know what? You're right. Like I approve. So if you can imagine, uh, adal serve that comes in at the sort of pace we're talking about 100 mile an hour plus but because he imparts so much top spin it dives once it clears the net and then when it sort of hits the hits the court surface and then kicks up i've now got to return that, but I want to return the favor, as it were, with my own top spin. So how and what forces am I going to need to use to return that serve from Nadal at that sort of speed? And how do we go about that? So the ball will be spinning in the opposite direction you

want it to spin if you want to return it with topspin. So you're going to have to slice your racket up the back of the ball to arrest the spin that Nadal gave it and then give it your own topspin on the way back. So I've got to impart more force and topspin than what he has served up for me. Well, keep in mind the speed of the ball when it hits the court on the opponent's side, it's about three quarters of the speed from which it when it hits the court on the opponent's side, it's about three quarters of the speed from which it was hit off the racket. The interaction with the ground is going to take another quarter of that speed off. So it's only going about half as fast when it reaches the player from the serve. So you have gotten a little bit of a benefit from the the air resistance slowing the ball down the impact with the court

so you're not exactly hitting 120 mile an hour ball when it when it gets to you from the dolls racket all right so that's interesting there's hope for me yet when i play him i got my money on you oh you're all hot yes but they will be pesos or rubles. Just keep him off of clay and you may have a chance. Sure. All right, so official Sam Karani wants to know this from Instagram. Hey, it's Sam from Chicago. Hi, Sam. Hey, Sam.

How much torque is applied to a tennis ball when it is hit with slice? tennis ball when it is hit with slice. So slice can actually, you know, get the, I mean, you see Roger Federer doing this a lot. You can get up to 4,000 RPMs or so with a really good slice shot. The collision time the ball spins on the racket, it's only in the four to five millisecond range. Wow. So if we're just calculating an average torque, you're getting about two and a half foot pounds of torque, which may not sound a lot when you think about exerting two and a half pounds at a foot's distance. But keep in mind, the ball is a lot smaller and the time at which that's acting is small. So you've got a much smaller lever arm, a much larger force on the ball. is small. So you've got a much smaller lever arm,

a much larger force on the ball. Generally, when you slice, you take an awful lot of pace out of that ball and it just, just floats over. And a lot of times the slices, because, um,

it's like you're recovering. It's a recovery shot. You know, sometimes it's, if you're closer than that, it's a really smart killer shot. That's true. Cause, uh, it, it takes than that, it's a really smart killer shot. That's true, because it takes the...

Does the slice slow the ball down? Because that's what it looks like when these guys are playing. It looks like the slice slows the ball down, and a lot of times it ends up looking like a drop shot, and you see the other player rushing towards the net to try and pick up the shot. Let's ask the professor. Yeah, does it slow it down?

So if you serve it with topspin, you can get an added bounce on, say, a hard court or clay, grass, it'll not have that quite as good a jump off the court. But if you've got backspin on it, then you're really going to deaden the ball when it hits the court.

The friction's going to really deaden the jump off the court. the court the friction's going to really deaden the jump off the court gotcha all right next question i think it's tyler mena if not it's tyler men on facebook and this is kind of like the the bar room question how fast must a tennis ball be traveling at minimum to go through a racket oh wow okay so. Okay, so it's one of those, who's going to get there at the end, Michael Phelps or the shark? Right.

It's one of those kind of questions. Like, so if you're playing with a cyborg and he hits, first of all, if he hits the ball to you hard enough to go through your racket, that means it should have gone through his racket. Well, of course, it depends on if you're swinging your racket when the ball comes. I mean, if he's hitting a stationary ball hard enough to get it up to the speed to break your racket,

are you going to hold your racket still or are you going to try to hit the ball? So if you try to hit the ball, the effect is going to be even greater and you don't need quite the speed. So I don't know if the questioner means, Tyler means that the racket is stationary. All right, let's go with playing a shot. Okay, so here's the thing. Let's go with a regular human being serves like a Rafael Nadal, okay? Serves the ball. I'm not sure Rafael's going to be happy with you calling him regular. I got to tell you, you know what? He may not be, but it's cool.

He'll get over it. I'm sure. But let's say that Nadal serves, right? And then our cyborg comes and hits the ball in a regular swinging motion. How hard would that ball have to, how hard would he have to swing to get the ball to go through the actual strings or even to get stuck in the strings? Now, let's go through. Just blast through. Yeah. If you put the ball on the net, you're getting something like, let's say about seven strings in each direction

that are going to be really in contact with the ball. And if you look up some of the tensile strengths for the strings that are used, they might be around 140 pounds or something. So in other words, you could hang that much weight from a string before it starts to stretch and break. Now, if you take those 14 strings and assume they all had 140 pounds, you're getting near a ton of force, nearly 2,000 pounds. But of course, that's not quite how it works because the center strings are going to assume a lot more of that force than the ones near the side of the ball. I think you're going to need something in the 150 to 200 mile an hour range for the ball

before you're actually going to snap the string. Gotcha. We're on our way to that. Yeah, I got to tell you something. The way the game is going, who knows? So you would have to get up somewhere around 200 miles an hour. What would it take for the ball itself to not be able to withstand that? Do you have any information on that?

I think the ball can take a lot more force. I mean, I've seen videos of people putting balls in various compression devices where you get 10,000 pounds or some crazy amount of force on the ball before they break. That's called marriage. That's called marriage. Yeah. Yeah. But I mean, it's not something you're going to easily be able to do by putting it in your hand and breaking it uh despite what you see in some movies all right here's a question i like uh matt moose on facebook why do tennis balls come in a vacuum sealed can interesting question To keep them fresh? What is this? That's why they're so delicious.

Yeah, you get about, what, three of these balls in a can, kind of like a Pringle-sized can. And you open the top, and you got this pull tab. And the reason is, is the rubber that's making the outside of this tennis ball is very, very slightly permeable to air. And what that means is that the air inside the ball under normal atmospheric conditions is going to start leaking out. And if you were to just leave these balls in an unpressurized can like that sitting on a short store shelf for months, you open up the can and the balls are going to have lost a lot of their internal pressure, basically getting too atmospheric.

So you have a dead ball at that case. Matt Moose, you just got us taken to school. Yeah, man. Because I never knew that. That's a cool question. And of course, the professor gave us the most fabulous answer. We will take our first break. When we come back, more of your Cosmic Query questions about tennis,

balls fuzzy, balls spinning, and Chuck's marriage breakup. Hopefully not. We'll be back shortly. Balls got to breathe. Welcome back. I'm Gary O'Reilly. And I'm Chuck Nice. And this is Playing With Science. We've already looked at the balls, the spin, and the freshness of a three-pack.

Yeah. Yeah. And now it's time to take a look at the rackets themselves, which have plenty of interest, particularly when it comes to friction. I'm going to stick on this point, and it's going to milk it, and of course the power they impart to a tennis ball. So, Chuck, our next question, but first, reintroduce our guest today. Yes, of course. He is Professor Eric Goff from Lynchburg College in Virginia

and the author of Gold Medal Physics. The Science of Sports, which I can recommend is a fabulous, fabulous read. Oh, I've just seen our next question. Chris Ryu from the Atom Club in Sturminster Newton in the United Kingdom. Do you know where that is? Yes, it's in the county. It's in Dorset, isn't it? You see? Oh, wow. Look at you guys. This is why he is a professor, because he knows stuff like that. So where's Dorset? Okay, Dorset is southwest England. So you go, if you think on the south of England, so you go Kent, Sussex, Hampshire, Dorset, Devon, Cornwall.

So that's way, so Dorset's pretty far south. I mean, Dorset is one of the most prettiest places in England, or Britain for that matter. However, the Atom Club, I'm just thinking there's a nearby town called Blanford Forum. And I'm just wondering if there's a rival club called the Up and Atom Club, because this just creates this little rivalry. But anyway, enough of my ramblings about teary eyed England. Is there any evidence that grunting, like you're giving birth to a pineapple, helps generate extra power in your swing? Why on earth you went to pineapple, I suppose I know really.

Professor, all yours. Wow, giving birth to a pineapple. That really takes me back to a South Park episode with Paris Hilton. That's maybe where it generates from. But that's maybe where it generates from. What I'm thinking now is the grunting. You think of, you know, like Monica Salas and other players who've done that. Right.

The coaches, some of the coaches will teach that grunting is a way to kind of time the release of the energy within the body with when you hit. The analogy I like is that, you know, in karate, we use kia, you know, and in Krav Maga class, Krav Maga physics is the subject of my next book. We use oish. Good plug, good plug, Professor, well done. When you punch something and you say oish, there's a negative to this, of course, although it could be positive from the point of view of the person who's grunting, which is it messes with your opponent. They don't like to hear the grunting. It's a distraction.

Especially the opponent as the fans themselves. I have to tell you, too, that when you sit in the stadium, it's a distraction as a fan. I'm sorry. Because it's a little much when you listen to some of these players get into it. It's just like, you know, it's very...

That's actually quite accurate. Yeah, I got to tell you, it can be a little, like, if you let your mind wander, I'm just saying. Which obviously you have. Yeah, you might forget that you're at a tennis match. So you chewed out the tennis and you went somewhere. He went to birthing a pineapple. Yeah, you might forget that you're at a tennis match. So you chewed out the tennis and you went somewhere. He went to birthing a pineapple. He did, yeah. It's a little, it can be disturbing and distracting.

It's like a really bad allergy you've got there. Okay, we've lost Chuck for a couple of minutes. I'll continue and sail on my own. All right, here we go, Professor. Give him his full name. Mark Eric Svensson. And it's questions from Facebook. For obvious reasons, tennis serves and hits are faster with longer rackets.

But at what point would the racket be too long and the extra torque required would provide diminishing returns? So we've already had the larger head rackets. So now you're going to turn up with a Monty Python-esque giant tennis racket. Yeah, where you play the game from the stands. Yeah. So what's the limit? Just how far shouldn't we go? Yeah. Well, the ITF, the International Tennis Federation rules set the limit at 29 inches. Typically, players are in the 27 to 27 and a half inch range.

So these rackets are about 9 to 14 ounces, so nearly a pound. I mean, the problem is, of course, if you were to make it too long, now you're making the racket heavier. If you were to make it too long, now you're making the racket heavier. So you are going to be able to get more torque on it, but it's also going to cost you more energy to swing your racket. So you're going to get tired faster. So someone like John Isner, who's what, 6'8", 6'9"? Holy crap. Could you imagine giving him a regular-sized tennis racket?

It would look like a table tennis paddle. So he is going to have a naturally longer racket because he's got these naturally longer levers. So there must be some room for the bigger, taller players to be able to have longer rackets. Randy Johnson throwing off of a pitching mound. You know, I mean, basketball players, obviously. So, you know, that added ability to increase torque with your just natural height or arm length is just one of your gifts. And you cover more of the court just because you're a natural taller. It's like a basketball player. You've got that wingspan.

Right. So, you know, you're not having to shuttle across the baseline so much to get to a shot that's in the corner. You just reach out that wing and pop. There it goes back again. Just arm strength. So is there a place where it can be too long? Because he talks about diminishing returns here. Is there a point where the length of the racket actually is a detriment? Well, again, it depends on the player. I mean, if you're an amateur, you don't want to be using the piece of equipment that's a little too big for you. If you're swinging something with more mass because it's longer, there's an energy cost to that.

You know, every time you swing that racket, it's going to consume calories in your body. So you're going to have to take that into account. You know, if you're going to be playing a five set match over several hours that's interesting that's a whole nother different type of science then because it's conditioning fitness and muscle strength all right um moving on to our next question samet sina from facebook in barrington illinois many players choose to use shock absorber on their strings. They range in the size and shape, but all seem to function similarly. How are these small rubber-esque pieces able to reduce the shock felt while hitting the ball? And it goes on to ask, are there any performance benefits to using one aside from mere player preference?

So first of all, you're going to have to explain what is a shock absorber? Is that the little rubber grommets that actually house the string at the rim of the racket? So on a racket, on the racket head, you will have a sweet spot. Then you'll have a point of percussion and somewhere along the line and then sort of the balance and everything. But let the professor explain rather than me because he is the professor and obviously i am not so if you put some mass on the racket you know just little bead or anything just any kind of mass on a string if it's vibrating and you've put mass on it then the vibration is going to dampen much faster there's more inertia. There's more mass.

You're trying to swing back and forth. But what the shock absorbers or those little grommets really do is they get rid of the ping. So when you hit the tennis ball with the racket, the string vibrations are kind of in the 500 to 600 hertz range. So we can hear those as like a ping. of in the 500 to 600 hertz range so we can hear those as like a ping if you put the little grommet on there the little shock absorber that tends to deaden the hit and it sounds more like a thud but it's not going to help you with the vibrational energy in the racket because most of that's actually in the frame and the reason is the frame is about 20 times more massive than the strings so what's really dampening out the energy in the racket is your hand it's not the the little grommets are more for the sound than anything else it's not really going to save your hand much will those little uh shock absorbers

affect the sweet spot i know the size of the racket head has increased the size of the sweet spot and players love that but does it have any effect in that sense or is it just that much yeah almost you don't get a real change in where the sweet spot is so then really the uh to to dampen the uh vibration of the racket during uh these you know high intensity collisions with the ball, you really would have to have some kind of material, like a tempered foam or something like that, on the grip. Or what would you do to reduce that is really what I'm asking. So if you hit it in the – I mean, there are technically two sweet spots. I mean, there's a vibrational node,

and then a little bit closer to the throat is the center of percussion. Now, one of the vibration node is where if you hit the ball there, you don't get any vibrations. You get a little bit of a shock in the hand if you hit it the center of percussion, and they're not too far apart, so these spots are very close together, but you get a small vibration if you hit it the center of percussion, but you don't get any shock in the hand. So that big spot in the middle, the racket where you're trying to hit the ball, is going to keep the vibrations low on the hand. Now, the power point is much closer to the throat, more the center of the racket. So it's kind of down on the strings, away from the tip in the throat of the string bed. Now

that'll have significant vibrations. You're really going to feel that even if you get a lot more power from your shot. Wow. And so are players cognizant of this when you're a professional player? Are you actually looking at a ball and making the mental calculation, even though this ball may be coming at you at 100 plus miles per hour, are you actually making a hand-eye assessment where you're trying to get this ball directly in the middle of this racket so that you can get this sweet spot? Oh, I'm sure they have an intuitive physics of where they want to hit the ball on that racket i mean this is a piece of equipment that's in their hand for you know hours a day practicing for years and years so and they have a very very good feel for where that ball is going

to hit the racket when they're swinging if i relate that to my playing days in soccer you know that to execute a certain pass a certain shot requires a certain skill now if it's a cross-court volley if it's a slice if it's a top spin return and I need to place that ball directly in the tram lines on that far side if I'm playing doubles or just in that corner because now two shots later I'm going to kill my. I have to be able to dial up a certain series of shots. And the techniques that are in there, that I will have, as the professor says, I have had this racket in my hand hour after hour after hour,

week, month, year after year. I'll just be thinking, this one, pop. And I won't be thinking about it. The calculation through my brain, to my body, through history is there. And that's what you're seeing. These guys are so practiced. It's a programmed reaction is what it is through experience.

Then I get to the point where my opponent knows I'm going to dial up this shot. Right. So I just throw the eyes. Right. So I'm now looking at that far corner and then I'll just cut it to the other side and he will follow my eyes.

Right, because he's anticipating what you're anticipating. Absolutely. So now you get to the real genius. These guys are calculating that you're calculating and calculating against your calculation, and it just gets better and better and better. And you know what? What you just said there is such a fascinating part

of so many professional sports, and that is when you talk about watching the eyes. And so in tennis, it's like when you see a cross-court shot, and then you see the return, which should be back across the court, but it goes straight down the line. And you see the guy who made the cross-court is just like, damn, he got me. He totally got me. And the same thing in football where you hear linebackers talk about watching the quarterback's eyes. Oh, yeah.

Like, how good do you have to be to be on a level where you're playing this sport and reading somebody's eyes at the same time? I mean, it's incredible. They won't just read the eyes. eyes at the same i mean it's it's incredible they won't just read the eyes they will now read the body language because if they're really that sharply in tune mentally they will know the potential is to go down the line right or across so now they'll the eyes are one read that's one tell the other one is body language because i have to put my body in a certain shape to play a certain shot. So therefore they immediately calculate what's wrong with this picture.

And it's, that's how I said the levels get better and better. And as a spectator, when you see Nadal, when you see federal, when you see Murray, when you see Djokovic, you are watching guys that are so good at every single category.

Absolutely. Well, and two quick points, the, the, even the best of the best, you're going to see faults, unforced errors, so good at every single category. Absolutely. Well, and two quick points. Even the best of the best, you're going to see faults, unforced errors. I mean, you know, they're not going to be able to hit it exactly the way they want it every single time. And the second point is there's research that's shown the eyes cannot follow a pitched

baseball, you know, that four tenths of a second that it's traveling. So it's the same thing with a fast moving tennis ball. I mean, they're not able to actually track the ball every little millimeter of its trajectory. I mean, there's enough intuitive physics, you know, the biomechanics that they've trained themselves for years to know where to be, where to, you know, react to a certain, you know, even sound of the ball coming off the racket. That's a fabulous point, Professor, because now it becomes a sensual thing. You're looking and you're hearing and you're looking at eyes, you're looking at body shape, you're looking at noises and all sorts of different things.

And also when the noise of the racket is another tell, it's like, remember you said, you're off again. It's very sensual. the noise of the racket is another tell it's like remember you said you're off again very you know that that thud on a home run right where you just go head up this one's leaving the park yeah you know that you know that the same with the tennis and that's how that's how high level these players are it's fabulous yeah well it's a game of inches and grunting and balls. And gosh, it is very, very sensual. We are going to take another break. If we didn't get, I think just mainly for Chuck's benefit, I'm going to shower. If we haven't got to your questions, I do apologize.

We are limited in the time because once again, big thanks to everybody. We got so many questions in. We do our best to cover as many as possible. We are going to take that break. The good professor, Professor Eric Goff, author of Gold Medal of Physics, will be staying with us.

So will you. I hope that break now. We'll be back very, very shortly where we'll touch on quartz and surfaces. So if your question was in that category, stick around, you're up next. We're back, yes, playing with science. Cosmic Queries, the tennis special built by our own listeners.

So we have a big thank you to every single one of you who threw your questions in. Hopefully we've pulled them out of the hat. So we've got the professor, Eric Goff, with us still. So we will have him unlock the answers in all of your questions. So, right, courts, surfaces, and more. So, Chuck, next question, please. Yeah, this is Joe Gassior from Facebook, and he's from Barrington, Illinois.

Oh, second from Barrington, Illinois. Yeah, number two. Yeah, Joe wants to know this. How do players slide on different surfaces? Clay, grass, hard courts. Is there a different technique used or is there just more force put into the slide to overcome a greater coefficient of friction

between the shoe and the surface? Thanks. Also, too, are they using different footwear for these different surfaces? I mean, that sounds about right. I would say yes, but I'm going to go with the professor's answer. Go ahead, professor. Well, so grass is certainly the fastest surface.

The grass is a little slicker. You get a little less friction on the ball. The bounces aren't quite as high. When you're seeing a match on grass, the players tend to be using a lot more speed and power the rallies don't last quite as long if you're a big powerful server you're going to love grass the hard courts usually have some kind of synthetic or acrylic layer sitting on a asphalt or concrete base those are kind of in the middle between clay and grass. Clay is certainly the slowest. You have a lot of court friction on the ball that you get these high bounces,

and the players use a lot of topspin and sliding on clay. You have all the particulates down on the surface, so the shoes are able to slide a lot better on the clay. Although a facet of my new research that was just published is we've now got a pretty good explanation for why you're seeing sliding more on hard courts. Which it is. Come on then. Drum roll. New research.

This was work I did a year spin at the University of Sheffield. So any of our UK listeners, check out Matt spin at the University of Sheffield. So any of our UK listeners, check out Matt Curry at the University of Sheffield. And anyone in the US who's looking to do some sports science, check me out here at Lynchburg College. And what we're doing right now is we're looking into shoe treads. And what we found by studying some rubber with holes in it is if you make these little dimpled holes, there's a critical area, a critical ratio of the area of the holes to the total contact area. And if you go past it, the static friction drops by more than 11% on a hard court. So what that means is if you put your shoe down and it's not quite sliding, the static friction is what you feel. Once it starts to slide, we call that kinetic friction.

But if you can reduce that static friction, you can initiate sliding much faster. So basically like a race car tire. So you have different grades grades so you go from slicks to medium to wet weather tires and as accordingly but it's interesting with the the holes in the rubber what size of holes are we talking about here because so if you can get something of order 25 percent of a contact area the shoe to have kind of a dimple or a hold area, you're going to get a reduction in this slide friction, you know, to initiate the slide quicker. If you look at Roger Federer, he uses a Nike court zoom. You'll see exaggerated and deeper cut herringbone

on the outside of the shoe. Novak Jokovic, who's really one of the pros that makes a lot of use of sliding. Yeah, he's an incredibly athletic player. Absolutely. I mean, he's got an Adidas Novak Pro named after him. You'll see a deep, grooved, circular section on the outside of his shoe. Andy Murray, you know, from Gary's neck of the woods.

I mean, he's going to have a… Well, he's left Adidas and gone to Under Armour, hasn't he? He's got an Under armor charged ultimate and you'll notice it's got like four cutout sections on the outside edge so again the gaps are going to help him slide uh even younger players like diego schwartzman uses a fila cage delirium and it's quite different from the that's actually a shoe right because that's yeah because it actually sounds like a very dangerous dog yeah the phila cage delirium yeah very it sounds slightly cyborg yeah it's interesting when you talked about holes in the soles of the shoe because adidas made a shoe for soccer but a a flat shoe not a studded or cleated shoe back in the 60s and it had sort of

suction cups throughout the sole and and you when you sort of talked about hold but you're not talking about that sort of thing it's actually the opposite yeah these are i mean we're talking about like dimples yeah yeah so you're talking about grooves or some kind of depressions into the rubber, into the sole of the shoe. And the idea is that it will start sliding if you have enough hole area to initiate this slide. You can go out and buy a Wilson glide shoe, and it's got these two slide plates in each of the shoes and you can kind of get practiced on sliding with that. But all of these shoes that the pros are using on the hard courts, the ones that are taking advantage of sliding, you're going to notice some gaps in the tread that get a little wider than some of the traditional herringbone. So it's really shoe technology that's bought this

about. Oh yeah. I mean, it's changing the game on hard courts because sliding used to be really the purview of clay and to some extent on grass too. But I mean, really clay was the sliding surface. But once you start adding in something new like sliding on hard court, I mean, you're changing the shots that the the elite are going to be able to reach this will have been driven by the players because the players style has said look i need i can't have an aggressive tread on the sole of my shoe because it's impeding the style of game that i bring so they'll have gone back to their manufacturer and said can you construct something that allows me to do this?

The only thing I'm thinking now is if you start to slide on a hard court, that sole better be fire retardant because you're going to get really, really hot shoes. And that's another thing because all of a sudden feet burn and you will get the destruction on your skin. I mean, from playing on hard surfaces as a soccer player you will get a lot of friction and that gets that energy gets transmitted up through the shoe into the foot okay well in that case i'm all for it because nothing would make me happier than to be at a professional tennis match and see somebody's that's right see somebody's

feet burst into flame oh god i'm you think think that's why they also swap shoes out sometimes. It's a whole new meaning to this player's on fire. Hot foot, baby. All right. Okay, so now Julian Janz from Facebook wants to know this. If we make a tennis field with moon dust, will it have the effect than that will it have the effect than roland garros tennis field uh will the bounce be better or worse compared to other surfaces uh what's a

roland garros tennis field roland garros was a famous french tennis player and roland garros is the number one tennis court and complex in France, in Paris, and it is where the French Open is. It's where the French Open is. Okay. And so if you made it out of Moondust, will you get the same consistency as a clay court? Well, I think someone's going to sort of come in late at night and steal it because we know how valuable Moondust is.

But there's only one person to answer that. Professor, Moond Professor, moon dust, tennis court, where do we go from there? The majority of moon dust is a silicon dioxide glass, and it's come about from a bunch of these meteorite collisions with the surface of the moon, but it's actually pretty nasty stuff. It's very abrasive. Some of the astronauts complained about it starting to get through their suits. It also sticks to stuff. It'll stick to the balls you're playing with, the shoes, the clothes, and the players wouldn't really want to breathe it in. It's got some iron in it. I mean, it's not something you'd want to be playing tennis on.

I mean, it's not something you'd want to be playing tennis on. Okay. So it's a punishment. So if you're being punished, you've been sent to the Moondust Court to play tennis. Sure, yeah. And if you're on the moon and the gravitational pull is about a sixth what it is here, you're going to get some pretty long shots. You're going to need a big court too. Oh, Professor, good segue.

Well done, sir. Joe McKillop on Facebook. need a big court too. Yeah. Oh, professor. Good segue. Well done, sir. Joe McKillop on Facebook. He tied straight into this, right? What's the biggest thing in the solar system from which a ball hit by the best tennis pro could achieve escape velocity? Love the show, Joe. Thank you so much. And we love your question, professor. But now what's he mean by what's the biggest thing? We don't know who he or she. I love your question, Professor. But now what's he mean by what's the biggest thing? We don't know who he or she is.

Well, I think I can answer that. So, you know, if you're going to escape Earth, I mean, not even accounting for air resistance. I mean, just to get off the gravitational tug of the Earth, you're going to need about a 25,000 mile per hour launch. You're going to need something a little more just to get past the atmosphere. So the idea is can you find something small enough in the solar system that you could hit a nice, strong tennis serve and it could actually leave the object without ever coming back? And I had to check what the world record is on a tennis serve, and it's Australia's Sam Growth. This is 163.4 miles an hour in 2012. Wow. Say that again.

That's incredible. 163 miles per hour on a tennis serve? Wow. Yeah. So let's just say we're not quite at that point. We're going to hit 150 miles an hour. quite that point. We're going to hit 150 miles an hour. The escape speed actually scales with the square root of the mass of the object divided by its radius. So you need to find something out there that is going to fit what you need. The Earth is about 28,000 times, that ratio is about

28,000 times too big. So I actually found a moon of Saturn, Hyperion, that'll do the trick. If you serve a tennis ball 150 miles an hour, it will escape Hyperion. You know, Hyperion is one of these little chaotic tumbling moons of Saturn that it's only a couple hundred miles wide in one direction, maybe 120-some-odd miles in another direction. And you can actually get the ball to leave that little moon of Saturn. So really, the answer is the smallest thing in the solar system where you can achieve escape velocity is Hyperion. So let's pack our bags and head to the Hyperion Country Club.

There you go. Racket and Balls Club. We've lost another ball again. Well, you might be able to find it. Down that escape velocity. Saturn will hold it. Yeah, all of a sudden you'll find a whole lot of tennis balls in orbit around Saturn. Another lovely day

here at the Hyperion Tennis Club where we're out of balls because we keep losing them to escape velocity. Oh, well. Anyway. We'll have to put the membership up. All right, let's move on.

All right, next question. That was actually a very fascinating question, Joe. Thank you, Joe McKillop. This is Mr. G, and he comes to us through Twitter, at DiatomicSciNerd. And he wants to know this. If we put players into suits on a court inside of a vacuum dome, what happens to the flight dynamics of the ball? Next gen tennis, anyone?

Oh, Mr. G, you're so terribly clever. That's actually a really fun little thought experiment. Let's get some guys into spacesuits. Let's put them in a vacuum. And then let's play some tennis. What are we going to look at? What kind of game are we looking at at that point? We do know now from our first segment that there's a lot of dynamics that we'll lose when it comes to the fuzziness of the ball.

But what are we looking at professor well you're also going to lose sound because you're not going to have sound propagating in a vacuum oh man so that means i can't listen to all those wonderful grunts of people birthing pineapples unless you've got like a you know a microphone inside the helmet and and you know, speakers or something in there that you can hear the other player. We'll bring in the sound effects and we'll make it work. So air resistance is obviously gone. So the balls are going to be moving a lot faster. You're not going to be able to get any effect from spin. You're not going to have any air to whip around that ball and have that nice Magnus effect help curve the ball. So forget all those nice curves on your shots.

So the result will be a really boring game of tennis is basically what we're saying here. I mean, if you could serve 150 miles an hour, I mean, the drag force is like nine times the weight of the ball. I mean, it's a huge effect on the ball. So you take out the air. I mean, it's a much, much different game. Do you think vacuum-dumb tennis is going to catch on? Well, think about the ball moving a lot faster and your ability to get to it wearing a big suit.

Yeah, like I said, it's a really boring game of tennis. You serve, and basically everybody game of tennis. You serve. Basically, everybody just holds serve. You serve, and the other person watches the ball go by. That's the way the game is played. Hit, walk, hit, walk. Hit, walk, hit, walk, hit, walk, hit, walk. Okay. All right.

Time for one more question. Just one more. Just the one more. Kevin Moynihan, go on then, Chuck. Kevin Moynihan wants to know this, coming to us from Facebook. And you have to answer this, professor. Scientifically. Scientifically. Scientifically.

Kevin says this. How come I can't stop laughing at that picture of Trump playing tennis? Probably because it's as funny as a picture of Trump playing president. Oh! Snap! I didn't need two days to come up with that conclusion. And I live an hour from Charlottesville. Oh my God.

You were, I got to tell you, kudos. That was, that was excellent. My friend has got, professors got the answers as proven once again, man,

professor Eric golf, the author of gold medal physics. Thank you so much for your time. Thank you for bringing us the answers to so many of our listeners' questions. Thank you to our listeners. This show does not exist without you, and your questions

have been brilliant, and hopefully the answers have been fulfilling. Chuck? What another great show. That's all I can say. A lot of fun. Professor, thank you. It's always informative and entertaining when you are on. Yeah, glad to can say. A lot of fun. Professor, thank you. It's always informative and entertaining when you are on. Yeah, glad to be on.

I can't wait to hook up with you at the Hyperion Tennis Club. Oh, dear. It's going to be a long, long, long trip to get there. I was going to say, yeah, that's quite a ways, isn't it? Yeah, it's just not quite around the corner. Right, that's it for today's show. Hope you've enjoyed it.

Hope you tune in to Playing With Science in the future. We do look forward to your company. Until then, bye-bye.