BALL BOUNCE ON DIFFERENT SURFACES – what it means for THIEM

Just had a kind of discussion  about the subject. Because of having found a Federer-related context, I have started to post about this on  PeRFect-tennis blog. This does not went well, because many readers there thought, I was attacking Federer. They called me idiot, troll, whatever. Well, not the first time.  But I got then an excellent hint from wilfried, one of most involved readers of my blog – why not to compile this all and post here as an article for readers, who are eventually interested in such general tennis issues (every one of them applies of course somehow to Thiem) and will not feel attacked even if it will lead to some criticism on Thiem. Thiem does not feel a God and his fans (thanks God) don’t feel priests or bishops in his church 😉 So, let’s start.


When watching tennis matches we have sometimes impression, the ball is accelerating after bounce. Is this an impression only? Or can the ball under some conditions really accelerate? If it can, how can the player influence this behavior? What’s the difference in potential acceleration between different court surfaces? Can a player make it an effective weapon to  more easily win points?

All those questions have obviously to do with some aspects of playing skills. Speed and power of hitting the ball. Spin.  Body movement before hitting. Racket frame and strings and  stringing tension.  The rest are laws of physics (different kinds of energy, velocity, gravity, friction, energy saving and transformation), and  player-independent conditions. Court surface. Material, inner pressure and elasticity  of the ball.


How can we find out if the impression is reality? Ask physicists? Find a reliable measuring technology? Maybe both, because the physicist must found the investigation on laws of physics, and eventually find some factors, which are not represented in existing laws but can have/have an influence. And measuring, (for instance videography using slow-motion, where you can even count manually, for instance rotations of the ball per time unit to say exactly, how big is the spin of the observed ball) if a proper method and equipment found, can tell as about “facts”, no matter, what physicists say.

So first I have tried to find some theoretical evidence. Here are the “results”?


Let’s first describe the ball bounce in simple terms. The ball is hit by a player with a racket strings. If we don’t think about serve, the ball comes with some velocity, direction, spin, at some angle and height, at which it will be hit. While hitting all those parameters are changed: the direction is reversed (to the other side of the court), but of course it gets new intended direction (the player is not acting as a wall), new angle, velocity and spin. If the ball came with backspin (slice), from the point of view of the player who will just hit it,  it’s just initial topspin. If he  wants to hit with topspin, must only add some topspin. but must not produce it from zero. If the ball comes with topspin (=initial backspin for the “now”-hitter)  and the player wants to hit the ball with topspin, must add more topspin, because must first compensate to zero the backspin of the coming topspin ball. Well, a bit complex, but if you hit yourself, you will see after some tries, how it reacts and feels.

Now the ball is hit with new initial parameters and flies over the net to land on the part of the court of the opponent. While flying, the ball loses velocity and spin because of air friction and eventually wind. Then the ball lands on the court and bounces. The time of the bounce are some milliseconds.

What happens, during those few milliseconds.

The ball hits the ground with some velocity, at some angle and with some spin. Hitting the ground, the ball is deformed and flattened (because the ball is elastic), the air in the interior of the ball (the pressure of this air it’s somewhat higher than the atmospheric pressure around the ball, when the ball doesn’t move) is compressed. Part of energy i s transformed into heat and lost, so principally  the ball moves high and forwards after the bounce with less energy than before the bounce. If the ball was hit with topspin, it is still rotating forwards (side spin component is transformed into forwards movement too) and using the energy accumulated in the ball during the bounce, the ball regains the spin with no change of spin direction – if it was hit with topspin, it continues to fly with topspin, which can be even doubled, compared with the spin the ball had just before the bounce. This may make the ball to rise it’s velocity after the bounce.  Not compared to the initial velocity when the ball was hit with the racket, but to the rest velocity existing before landing on court. So theoretically the ball can accelerate after the bounce if hit with extreme topspin.

In terms of the game this means, such ball can go faster and/or higher after the bounce, stealing the returner the time for reaction.

This works differently on different surfaces and create preconditions of how to return (the ball bring back into play).


Right now we have 3 top players, able to use extreme topspin. It’s Nadal, Federer and … Thiem.

You may have read my article about topspin game on hard courts as it’s often misunderstood as something specific for clay (well – the biggest tospin-producer, Rafael Nadal, may be “guilty” ;)) – if not, look here.


Here are some links, where you can find more about laws of physics governing the case of tennis ball bouncing:

http://nessis.org/nessis13/kovalchik.pdf

http://www.tennisindustrymag.com/articles/2004/04/follow_the_bouncing_ball.html

VISUAL EXPLANATION – no physics knowledge needed 😉

https://www.quora.com/Can-a-ball-accelerate-after-hitting-the-ground

https://physics.stackexchange.com/questions/117091/why-does-a-ball-bounce-lower

https://www.scientificamerican.com/article/experts-tennis-topspin-ball/#


Now about differences between different surfaces, which may be the most interesting in terms of  the real game

Federer has 20 slam crowns: 1 on clay, 8 on grass, 11 on hard (55% of all).
Nadal has 16: 10 on clay, 2 on grass, 4 on hard.
Federer’s overall titles: 11 on clay, 17 on grass, 66 on hard (70% of all)
Nadal’s overall titles: 53 on clay, 4 on grass, 18 on hard
Federer-Nadal H2H record 15:23, 11 of 15 Federer’s wins on hard, 2 on grass, 3 on clay
Grass is special for small number of tournaments. It’s Wimbledon (for an old tradition) and some pre-Wimbledon preparation tournaments. So, grass is not comparable with clay. But grass is comparable with hard. So, on one end of the spectrum is clay, another is hard+grass.
Matches on grass are in average 10 minutes longer than on clay. Rallies on clay are by 7 seconds longer than on grass, but only 2 seconds longer than on hard. Rallies on grass were/are always longer than on other surfaces.
So in average you need more endurance on grass than on clay.
Have you ever tried to play tennis on grass? If not, try to imagine, watching football. On clay you can slide, thus saving your joints and avoiding injuries. To play on grass (after some matches, it’s no more grass but soil) is the most dangerous for joints and tendons. The most healthy surface is obviously clay. Hard surface is a killer and should be banned from tennis. Grass is rewarding big serve and dropshot. And the ability (inborn or learned) to move well on grass. Good preparation for tennis on ice.

Just read Jonathan’s post https://www.perfect-tennis.com/court-speed-2017/.
It was about trends, not about comparison, but the data, you quoted there are also good for comparison. While we must take into account, such comparison could give different results every year.
But let’s take only your table and CPI as maybe best measure.
Wimbledon was just 2017 not the fastest court among slams and Masters. But it was still about 1,5x faster than the fastest clay event (Monte Carlo).
The table from the article shows, one extreme was Madrid and Roland Garros and the other – Australian Open, Shanghai and London.
I’m still convinced, grass gives the biggest acceleration after the bounce (if we compare the same shot, with same speed, spin, same ball, same weather a.s.o.). Simply because the friction on grass is lower than on other surfaces (they say grass is more “slippery”, causing the ball to bounce lower and be faster.
This is all to add to my impression (also coming from playing tennis myself), the ball can accelerate after the bounce, of course losing energy and not able to jump back to the height from which it was hit.

There is of course the spin.
I don’t know, how to explain the spin’s (in fact topspin) role in eventual acceleration of the ball after bouncing. But for my experience and logic topspin (advancing rotation) can be a factor in accelerating the ball after the bounce. Once more – probably on every surface, but the most on the most slippery grass (lowest friction).

Simple logic explanation of the ball accelerating more after the bounce on grass. For whatever physical reason bounces are lower on grass/hard than on clay, but the ball has the same energy when hitting the court after an equal serve/shot. This energy unloads in two main components: bouncing in the height and advancing. The less energy used for the bounce (vertical component), the more energy left for advancing.
Of course, this acceleration is relative not to the speed of the ball when hit by the racket but to the speed when the ball is landing on court. I think, it’s all about topspin and other factors (like surface, mainly friction, the ball itself) is the cause of difference in the amount of acceleration (still topspin = advancing rotation assumed) for ceteris paribus. Of course, not every player will be able to produce such a big topspin to cause the effect, but some can. It’s first of all Federer and Nadal. Now maybe also Thiem.
Back to science – this https://www.scientificamerican.com/article/experts-tennis-topspin-ball/#seems to be quite simple and scientific explanation of the ball increasing speed (accelerating) after the bounce (depending on spin).

So let’s stay with the statement, the ball slows down on every surface, but it slows down more in clay then on grass/hard, while hard is not equal hard.
I don’t know, how the real spin is measured (I mean numbers which are displayed to spectators) and how accurate is this measurement. But what is crucial for my way of thinking, is not the absolute speed of the ball after bounce, but the difference between surfaces.

Spin is first diminishing during the flight of the ball because of air friction, but can even double after the bounce, (partly because side spin is then converted by the impact and friction into forward spin), so it’s theoretically possible the ball hit at 5000 RPM to reach 7200 RPM or more after the bounce. This could explain the possible ball acceleration of the ball after bounce.


What does it all mean for Thiem in terms of his game , results and prospects on different surfaces?

Thiem has one of heaviest topspins in the game.  How can he use it and where?

I think, he can use it well on every surface, because heavy topspin makes shots difficult to return. On every surface. On clay with high bounce.  On hard and grass with flat, fast bounce. Both good as preparation for the attack.

Against the best such topspins are hard but they can answer with long slices,, mostly to the backhand, after which  the ball is “dead” after bounce – no velocity, no spin. To hit another big topspin after receiving such a ball is risky and needs mor own energy to be used. Long cross-court exchanges should be avoided (even if Thiem’s slice is quite good and still better. Good example would be Federer or Delpo, both defending big shots to their backhand wing just this way. And waiting for opportunity to overrun and hit forehand with extreme angle. Or attack the net, if one of such topspin shots is a bit too short.

If this happens, Thiem should try to be the first to  change direction of the ball exchange to forehand and try to hit forehand down-the-line. It’s a chess – who changes first, has both bigger chance and bigger risk.

So, as always, the best thing is to mix-up shots. While everyone expects, Thiem will hit hard topspin (but cannot reach the same spin with single-handed backhand) one after other, it’s a chance for him to win points with dropshots, unexpected flat slices with side rotation a.s.o.

Well, it may sound trivial, but you should use every good shot you have. And never too long the same 🙂


8.01.2018 Update 13:41

Just found an interesting article about convergence of surfaces. Not directly related to the title of the article, but yes – to it’s part about differences between surfaces.

http://www.tennisabstract.com/blog/2013/04/08/the-mirage-of-surface-speed-convergence/

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