Dwell Time .....

[brokenball]

This is one of the unfortunate things about this subject is that, it really appears to be rehashed arguments from a decade ago.

That is because others talk about feelings and not facts.
Notice that zeio makes his claim about rubber oscillating on the paddle without evidence.
Show us the evidence!

It is easy to see the whole paddle oscillating in the Toxic 5 video but it is also easy to see that the whole paddle does not keep up with the ball during the rebound. That is one of the reasons Toxic 5's are slow.

Boll's and Mitzutani's opinions do not change reality. If you hand the same paddle to each player does the paddle magically change? I have asked this same kind of question before.
I bet there will only be crickets on this one.

They would still be arguing about how many milliseconds dwell time last without my videos.
What is more is that NO one is willing to do that math except Baal's crude approximation.
At least his approximation reduced the dwell time to a millisecond or two, not the many millisecond everyone was talking about before.
The problem with Baal's attempt is that it assume constant deceleration. It isn't because as the ball goes into the sponge the resistance gets stronger. The other assumption is that the rubber stay in contact with the ball through out the rebound. It doesn't. At least Baal was curious enough to try.

My recommendation is to stop posting. Think about it. If people are mentioning a thread from MyTT from a decade ago and still trying to re-litigate arguments from back then, then something is a bit off with what is going on.

This is a good idea if one only has opinions.

There is a reason I made the post below when someone woke this thread up a month ago:

and re-woke it up again a few days ago. This happens because no one facts or are willing to do the math. They just have opinions and myths that get perpetuated on the TT forums. It was stated above, no one talks about this at the clubs. Just on TT forums of misinformation and myths.

Frankie has still not made another post and people are still arguing about ancient history

Yes, and some people should be embarrassed.

without being willing figure out what kind of variables are really in play.

I know the variables that are in play.

 

[Der_Echte]

An example is the player grip. It's difficult to model in experiments. Changes in grip pressure affect how the racket behaves and this alone affects how different players perceive the feel and stiffness of the same racket. It's always wise to appreciate the player experience as something tangible and valuable, rather than dismissing it as illusory and disposable.

I have frequently noted this very thing in showing why it is a mission impossible to represent result of ball with a formula. The grip and change have a huge effect on hte result and is damned difficult to get a machine to do that and quantify it.

With players who struggle with blocking or countering long a heavy topspin incoming ball, I say to them to use a loose grip, less power and compact swing... and magically, the player is no longer shooting ball out long, makes some of his or her own spin, and is consistent enough to trheaten in the point.

 

[igorponger]

"The Centipede's Dilemma".

A centipede was happy – quite!
Until a Guney Toad in fun
Said, "Pray, which leg moves after which?"
This raised her doubts to such a pitch,
She fell exhausted in the ditch
Not knowing how to run.

From science of psychology we know of "effect of cintipede" as follows
-- if we have learnt certain movements so that they have sunk below the level of conscious control, then if we try to follow them consciously we very often interfere with them so badly that we stop them.
As the best famous example prodigy violinist Adolf Busch being asked by fellow-violinist Bronisław Huberman how he played a certain passage of Beethoven's violin concerto. Busch answered smilingly that it was quite simple—and then found to his utter horror that he could no longer play the passage.

[size=+2]Once you have imprudently sunk into the physics of table tennis you can*t play the game any longer.[/size] So pity for you.

 

[Baal]

This says it all about this thread.

https://youtu.be/I_e-RQZVwxg

 

[UpSideDownCarl]

That is because.....

The problem is actually that you can't let things go that really just don't seem to matter that much to anyone but you.

So, guys, why bother with this.

Or:

Will it go round circles?
Will it fly high like a bird up in the sky?



I am tempted to lock the thread. But I won't. Not as long as people still seem to be acting somewhat civilly. But what is the actually point of either side of this discussion. I personally see none. Sometimes it is okay to agree to disagree.

Jane, stop this crazy thing!

 

[Der_Echte]

It this thread Mary teaming up with Jane?

 

[Llamalland]

Baal did some "napkin" calculations many years ago on the MYTT forum that were pretty good.
Before that I had posted a similar calculation in "Anton's obscure question" thread. I posted a link to a view of Tacshow123 "catching" the ball and dropping it on the other side of the table. That is the video UpsideDownCarl was looking for. It is hard to find even if you know what you are looking for.

First we will make some crude estimates. With a little thought is is possible to estimate very closely. Too many think that because they can't solve a problem exactly that they shouldn't try solving the problem.

Assume the contact speed with the paddle is 10 m/s or 10mm/ms. That is the combined speed of the ball coming at the paddle and the paddle coming at the ball. The speed is measured relative to the paddle.

During the contact time the ball will slow down to 0 then speed up again in the opposite direction.

Lets assume the total contact time is 1 ms so the ball spends 0.5ms slowing down and 0.5ms speeding up.
How far will the ball go in 0.5 ms? During the time the ball is slowing down from 10mm/ms to 0mm/ms we will assume the ball decelerates at a constant rate. ( this is not right, the ball slows down slowly at first but slows down faster as the ball compresses the rubber, but we are making a crude estimate, look up Hooke's law ) Therefore the average speed during the 0.5ms of slow down time is 5mm/ms.

If the average speed is 5mm/s for 0.5ms, how far did the ball push into the paddle?
5mm/ms*0.5ms=2.5mm

Is this distance reasonable? I think we are in the ball park. I think the 2.5mm is a little too much. I think if I did some calculus and assumed the deceleration rate was not linear but was parabolic as described by Hooke's law, the deceleration distance would be shorter.
The ball will compress some so the center of mass of the ball may travel another 1-2mm closer to the paddle.
A 2mm rubber may compress 1mm. The blade may flex some but I doubt most paddles people buy will have visible or measureable flex but we know the blade flexes a little bit due the the sound.

This distance can be made shorter by decreasing the contact speed or by reducing the contact time.

A teaser for you problem solvers out there that like to strain your brain.
How can you tell how much of the ball makes contact with the top sheet?
How can you uses this to determine how far the ball's center of mass still moves after contact?
Are there any calculus wizards out there that can figure out the how the ball will decelerate if Hooke's law applies so that the deceleration rate is not constant.
How what is the peak force applied to the ball? Why do we care?

I know people will have mixed feelings about me reigniting this thread, but whatever, it's an interesting question and this is the only thread anywhere I've looked where people at least try to talk about this objectively.
For background, I'm a sensory neuroscientist, and at least as a sensory phenomenon, humans would not be able to distinguish a long and a short contact on the scales of table tennis contact times. We simply don't have the tactile equipment. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4893195/ for details - the thresholds discussed here are well beyond the known contact times for the ball. To our sensory system, it's indistinguishable from one instantaneous contact (if we ignore vibration afterwards)

Of course, it's a useful fiction and you can be the best player in the world while harbouring whatever myths help you play better and rationalise your technique. Knowing the physics somewhat hasn't helped me play much better! And we CAN tell some things from tactile feedback : vibration probably gives us some information about the quality or style of shot (though I think this is exaggerated and conflated with audition).

But I also wanted to better answer brokenball's question about the non-linear dynamics of the ball pressing into the rubbers. The hint to solving this is in what you already mentioned - Hooke's law. It is usually used to describe the forces involved in springs, but it is reasonable to apply it here too. But the motion of springs is very commonly sinusoidal, and for good reason, and the same applies here!

So the force (and therefore acceleration) on the ball is (negatively) proportional to the depth of penetration into the rubber, as you correctly point out. For every further mm of depth pushing into the rubber, there will be some rough corresponding increase in acceleration out of the rubber (ignoring the possibility to bottom out, let's assume reasonable rubber thickness). So some simple calculus: a=acceleration, v=velocity, s=displacement. Differentiating with respect to time, s'=v, v'=a, so s''=a, but s is proportional to negative a! Something is only proportional to its negative double derivative when we're dealing with sin waves, and that is why we see sin waves in spring motion. The portion of the sin wave we have is where acceleration is only positive. s is the same at the start of contact to the end of contact (that being the undeformed, equilibrium surface of the rubber) and (negative) max in the middle, v is reversed (assuming ideal simple energy transfer, of course it's never that simple but it's a useful assumption here) from the start to the end and zero in the middle, and acceleration starts off zero, ends off zero and is maximum in the middle. So this fits equations of the form s = -cosx, v=sinx and a = cosx over a range of -pi/2 to pi/2, where -pi/2 is start of contact, pi/2 is end of contact and 0 is the point of deepest penetration where the ball is still and experiencing maximum acceleration. (of course there will be constants and this assumes a period etc. etc.)

So it is not a parabolic acceleration dynamic but a sinusoidal one that Hooke's law describes. And the correction is reasonably easy to make. I knocked this up in desmos to show - the red line represents displacement/ball position, the blue line represents velocity and the green line represents acceleration. The black line represents the linear model you described. By working out the average speed and giving the length of contact, you were essentially integrating the first half of the black line (from -pi/2 to 0). In my graph that has an area of pi/4 (b*h/2). The equivalent part of the integration of the green line is 1 (since we've conveniently used a sinusoid with 2pi period which plays nicely with calculus rules) - the integral of the green line is actually the blue line, so take the blue line at t=0 and subtract the blue line at t=-pi/2 and you get 1). So there is a correction factor of 4/pi.

So in fact you are incorrect - the ball will penetrate further than in a linear model. And this makes sense, as there is more speed into the bat at all stages of the actual dynamics than there would be in a linear model.
So the answer would be that given your conditions of 10 m/s and 1ms, the ball penetrates not 2.5 mm but 2.5*4/pi mm = 3.18 mm in this highly idealised (but slightly more realistic than linear) scenario

Anyway, sorry to those of you who wanted this to stay buried, you're welcome to anyone who appreciates this information.
Edit : I made a mistake here and compared the black linear model to the green acceleration, where the proper comparison is with the blue velocity line in a similar way. But the same shape and same logic and same conclusions apply, so I'm not going to bother correcting it all the way.

 

[brokenball]

Great! Someone intelligent to cover this topic!
You backed up what Baal, a PhD that does medical research somewhere in SE Houston, said years ago about being able to tell the difference between long and short dwell times. This blows away Dan's, a very good TT player that owns this site. And USDC, MichaelJ still doesn't know anything about dwell time.

Long ago Baal made what he called a "napkin" calculation for dwell time. He got close but he assumed a linear deceleration and acceleration. This basically debunked the crap that was being said by the clowns on MYTT. Also, I made high speed videos take in 2010 of impacts between the ball and paddle.

You are right about the motion being sinusoidal if the rubber/sponge is modelled as a spring and the ball is the mass. Your model would have the TT ball oscillate back and forth on a spring. This is a something that mechanical engineers learn. However, there is internal friction in the sponge and rubber, so energy is lost.
m*x''+d*x'+k*x=f(x) the damping "d' can't be ignored. Most rubbers have a coefficient of restitution of about 0.6 to 0.7 despite the fraudulent claims that each rubber is faster than the next.

Another thing you have overlooked is that when the rubber starts to push the ball forward, it not only moving the mass of the ball but also the mass of the rubber. In the mass and spring example, the effective mass of the spring must also be accelerated because it can't push the ball if it doesn't maintain contact with the ball.

This is yet another problem. The rubber doesn't maintain contact with the ball for as long as you think. If the position where the ball just touches the ball is called 0, the rubber does not maintain contact with the ball all the way to 0. This means any motion that the rubber makes after the contact with the ball is lost energy. So the resulting motion is not a sine wave.

Another thing I showed a few months ago was that the ball compresses too. So, if the ball compresses the center of gravity of the ball can move forward without the ball actually needing to penetrate the rubber. I have a press where I compressed a TT ball by closing the press in 0.001 increments and graphing the force.

So what now? No one seems to be interested in the physics of TT. They rather boost or talk about the next harder or faster rubber. I think it is best to just start a new thread and tell people their brain will hurt if the view it. Better yet is to get a thread where only you and I can post because the clowns on this forum will distract, and ruin, any thread they don't understand. If you want we can do this by private message. I have a motion control forum where we can' hash this out in peace. I hope you are good at calculus and differential equations. Your move.

 

[Llamalland]

Great! Someone intelligent to cover this topic!
You backed up what Baal, a PhD that does medical research somewhere in SE Houston, said years ago about being able to tell the difference between long and short dwell times. This blows away Dan's, a very good TT player that owns this site. And USDC, MichaelJ still doesn't know anything about dwell time.

Long ago Baal made what he called a "napkin" calculation for dwell time. He got close but he assumed a linear deceleration and acceleration. This basically debunked the crap that was being said by the clowns on MYTT. Also, I made high speed videos take in 2010 of impacts between the ball and paddle.

You are right about the motion being sinusoidal if the rubber/sponge is modelled as a spring and the ball is the mass. Your model would have the TT ball oscillate back and forth on a spring. This is a something that mechanical engineers learn. However, there is internal friction in the sponge and rubber, so energy is lost.
m*x''+d*x'+k*x=f(x) the damping "d' can't be ignored. Most rubbers have a coefficient of restitution of about 0.6 to 0.7 despite the fraudulent claims that each rubber is faster than the next.

Another thing you have overlooked is that when the rubber starts to push the ball forward, it not only moving the mass of the ball but also the mass of the rubber. In the mass and spring example, the effective mass of the spring must also be accelerated because it can't push the ball if it doesn't maintain contact with the ball.

This is yet another problem. The rubber doesn't maintain contact with the ball for as long as you think. If the position where the ball just touches the ball is called 0, the rubber does not maintain contact with the ball all the way to 0. This means any motion that the rubber makes after the contact with the ball is lost energy. So the resulting motion is not a sine wave.

Another thing I showed a few months ago was that the ball compresses too. So, if the ball compresses the center of gravity of the ball can move forward without the ball actually needing to penetrate the rubber. I have a press where I compressed a TT ball by closing the press in 0.001 increments and graphing the force.

So what now? No one seems to be interested in the physics of TT. They rather boost or talk about the next harder or faster rubber. I think it is best to just start a new thread and tell people their brain will hurt if the view it. Better yet is to get a thread where only you and I can post because the clowns on this forum will distract, and ruin, any thread they don't understand. If you want we can do this by private message. I have a motion control forum where we can' hash this out in peace. I hope you are good at calculus and differential equations. Your move.

Yeah obviously harmonic motion is a gross oversimplification of what is actually going on, but it's at least a refinement over a linear or parabolic model. I'm definitely not going to try to model anything beyond that, I'm not really much of a physicist, just a biologist who enjoys working with maths. Each of the issues you mention isn't really something I overlooked (I was aware of all of them as possibilities) but just factored out of this calculation because I lack the data and correct values to model them.

I would be interested in being part of a further conversation about it (by PM or other forums, whatever), but I'm probably not going to drive anything. I'm decent at calculus but not at a level beyond undergrad.

p.s. I actually forgot about this conversation (partly because it took over a week for my post to pass review or something, partly because I had a significant trip overseas for a (successful!) job interview at about the same time) but was reminded about it by a conversation about what would happen if you dropped a ball through a vacuum hole through the earth (let's say through the poles so the trajectory is not affected by earth's rotation), which is much better modelled by simple harmonic motion (though the inconsistent density of the earth means it isn't perfect), and some pretty simple calculus assuming uniform density can show you that the fastest velocity achieved is sqrt(g*r) = sqrt(9.8*6371000) = 7900 m/s (right in the earth's centre), and the period is 84 minutes. And I realised the last time I'd done such calculus was for this little exercise!

 

[superbackhand]

The problem with posting on this site is that people "distract" the thread with their ignorant comments. Look at how long this thread is already but nothing is learned.

it is called “Reel World”.

 

[superbackhand]

Yes, but you mean real world.
There are other ways/places to post information than this forum.
This forum is hostile to knowledge, and it prefers myths.

its the internet - filters are what you need

 

[igorponger]

Mechanoreceptor - Wikipedia

en.wikipedia.org

Dwell time is a specific sense innate to a human, varies by far for different individuals.
_____________
Be happy.

 

[Llamalland]

There might be a way to measure the opposing force as a function of distance actually - it usually requires somewhat complicated equipment, but you can use a 3D printer (or anything capable of moving in small steps) and a small scale. I've used a similar technique to measure force-curves for mechanical keys of various sorts and actions.

It wouldn't be super accurate and wouldn't have great resolution, but it might be enough to establish linearity or (presumably) non-linearity. Ideally you'd lay a blade with only one side covered on top of scales (or just a regular bat, but you'd confound the force of the other side compressing), and that on top of the print bed, then manually tell the stepper to go small steps (preferably with some kind of blunt surface, maybe a cut-in-half ball) until you register a change in weight on the scales, and then keep going down to see how that changes.

One might argue you can't compare the dynamics of a system with a static test like this, but usually that works out pretty ok.

 

[Atas Newton]

I do get a feeling the argument has totally ran its course, but out of curiousity, @brokenball could you resurrect those videos with the vibrating blade? The links are dead.

 

[Tony's Table Tennis]

Over so many years, I wonder how much of table tennis (actual game play) has every one improved by

 

[Llamalland]

You are looking at it wrong. If you avoid the myths then you don't waste time doing what doesn't work.
Also, I steer people from TT scams. Too hard rubber, boosters etc. Those the listen save money.
The TT manufactures provide false information. Think about it, there is so many different rubbers. How different can they be? The coefficient of restitution only goes from 0 to 1 for TT rubbers and most are around 0.5 to 0.7.
That is a very small range but every few months someone comes out with a "new" rubber same as the "old" rubber.
There is a lot of bad advice like on concave or convex strokes. Accelerating through the ball.
And then there is a lot of non-sense about dwell time. Too much worrying about dwell time which is something that know one really knows anything about. People can't even agree if it is what you feel or true contact time.

Largely I agree. But at least one benefit I've seen from quite hard rubbers (which the physics I think backs up, but I'm open to being corrected) is you can make better closed face shots with them. A soft rubber topsheet will deform more even within the very short contact, changing the angle of the actual contact slightly away from rubbers' resting state, meaning your shot will be more normal to the bat's surface, and a hard rubber will result in a more lateral shot. A lot of the language around that is very misleading, but at least that aspect of it I believe - I have a much softer rubber on my backhand because I'm not as good at closing the angle with my backhand, but my forehand rubber is harder and I'm able to close my bat angle more and get spinnier loops out of it.

Typically that gets wrapped up in "throw angle" which is abused almost as badly as dwell time. But 95% of people aren't really after a scientifically accurate description of what's going on or ready to hear terms like lateral restitution or elastic deformation, they just want something they can easily wrap up.

Also I think a lot of "bad advice" is good advice based on bad explanations, and most people don't get good by caring about the accuracy of the physics of their thought process, but by finding techniques that work for them. Dwell time as a thing people can perceive and use is total BS, but a useful myth for many, if only because it makes them focus on the tiny instant of contact in a better way. I'll happily correct people about it, but if conceptualising something in terms of a myth is what leads people to a better technique, good on them.

I think people are better off knowing what the science is, though. I mean, if I wanted to be a better player, I'd want to keep my mentality, technique and thoughts while playing very very separate from my scientific knowledge, keep a very focused mind on "if I do A, that gets result B" and try not to care about what is going on between A and B except in my free time as a curiosity. But what I want is not just to be a better player. It's to enjoy table tennis. Part of enjoying it for me is understanding how the physics work. I'm never going to be a pro or even a particularly high level amateur even, but I really enjoy understanding the world and little quirks of it work like this.

So I guess my point is this:
1. If people want to understand the physics of the game they play, don't try to knock them by bringing it back to table tennis skill development.
2. If you want to be good, think about the game however is helpful to you. Don't let reality get in the way of a useful fiction you tell yourself.

The best athletes visualise their own success, trying to will it into existence. On some level they know it's not the way the world works (ok maybe some of them buy into things like "the secret" and think they can influence the world with positive thinking, but not really that many) but imagining that they can create their own reality through the power of meditation or whatever really helps them do what they do.

 

[NextLevel]

You are looking at it wrong. If you avoid the myths then you don't waste time doing what doesn't work.
Also, I steer people from TT scams. Too hard rubber, boosters etc. Those the listen save money.
The TT manufactures provide false information. Think about it, there is so many different rubbers. How different can they be? The coefficient of restitution only goes from 0 to 1 for TT rubbers and most are around 0.5 to 0.7.
That is a very small range but every few months someone comes out with a "new" rubber same as the "old" rubber.
There is a lot of bad advice like on concave or convex strokes. Accelerating through the ball.
And then there is a lot of non-sense about dwell time. Too much worrying about dwell time which is something that know one really knows anything about. People can't even agree if it is what you feel or true contact time.

That's the issue: a 1600 player at best (with a tail wind making up 200 of those points) telling a 2200+ player with confidence what improves table tennis play and what is and isn't bad advice without any reservations about his limitations. You can't make this stuff up. Baal was not delusional and at least worked to reconcile traditional TT instruction with his understanding of neuroscience and physics and he played at a strong amateur level.

 

[NextLevel]

Typically that gets wrapped up in "throw angle" which is abused almost as badly as dwell time. But 95% of people aren't really after a scientifically accurate description of what's going on or ready to hear terms like lateral restitution or elastic deformation, they just want something they can easily wrap up.

Also I think a lot of "bad advice" is good advice based on bad explanations, and most people don't get good by caring about the accuracy of the physics of their thought process, but by finding techniques that work for them. Dwell time as a thing people can perceive and use is total BS, but a useful myth for many, if only because it makes them focus on the tiny instant of contact in a better way. I'll happily correct people about it, but if conceptualising something in terms of a myth is what leads people to a better technique, good on them.

I think people are better off knowing what the science is, though. I mean, if I wanted to be a better player, I'd want to keep my mentality, technique and thoughts while playing very very separate from my scientific knowledge, keep a very focused mind on "if I do A, that gets result B" and try not to care about what is going on between A and B except in my free time as a curiosity. But what I want is not just to be a better player. It's to enjoy table tennis. Part of enjoying it for me is understanding how the physics work. I'm never going to be a pro or even a particularly high level amateur even, but I really enjoy understanding the world and little quirks of it work like this.

So I guess my point is this:
1. If people want to understand the physics of the game they play, don't try to knock them by bringing it back to table tennis skill development.
2. If you want to be good, think about the game however is helpful to you. Don't let reality get in the way of a useful fiction you tell yourself.

The best athletes visualise their own success, trying to will it into existence. On some level they know it's not the way the world works (ok maybe some of them buy into things like "the secret" and think they can influence the world with positive thinking, but not really that many) but imagining that they can create their own reality through the power of meditation or whatever really helps them do what they do.

It's a bit self-serving to argue that one can understand the physics of the game at a significant level and not play or coach or even design TT equipment well enough to show such understanding has utility. It would be similar to claiming to be a brilliant civil engineer but being unable to design or build actual structures.

I have no problem with the idea that traditional TT instruction is based on physics that is not rigorous. What I have a problem with is when people who claim this then make statements that can actually harm your table tennis play if taken literally, then claim based on models they have never applied to coach or build a good player that they should be taken seriously and that others are idiots.

I honestly can't remember what the dwell time discussion was per se, but if we can agree that since you already added this disclaimer:

To our sensory system, it's indistinguishable from one instantaneous contact (if we ignore vibration afterwards)

Then most of what you are writing has little or any practical value to a table tennis player since no one I know of just uses tactile sensations to improve their attempts to increase dwell time and they definitely use things like the vibrations of the blade and repeated practice using a lot of senses, including visual feedback.

 

[Llamalland]

It's a bit self-serving to argue that one can understand the physics of the game at a significant level and not play or coach or even design TT equipment well enough to show such understanding has utility. It would be similar to claiming to be a brilliant civil engineer but being unable to design or build actual structures.

If that's directed at me, I never claimed my (poor, idealised and basic) understanding of (a very small part of) the physics had any practical application. It isn't even at the stage of any possible practical application, I just figured out what the forces at play would look like if we made a lot of simplifying assumptions a little better than a previous post had done. There could be practical applications to this, but they would be many steps away from application. If anything in that analogy, I'd be a low-level physicist who just started doing their modelling of an element of, say, building strain, being told it's self-serving because it hasn't resulted in any practical change to civil engineering yet.

I honestly can't remember what the dwell time discussion was per se, but if we can agree that since you already added this disclaimer:

To our sensory system, it's indistinguishable from one instantaneous contact (if we ignore vibration afterwards)

Then most of what you are writing has little or any practical value to a table tennis player since no one I know of just uses tactile sensations to improve their attempts to increase dwell time and they definitely use things like the vibrations of the blade and repeated practice using a lot of senses, including visual feedback.

Yes. I never claimed otherwise, in fact I explicitly have said more than once that you can improve play better by just doing what works instead of worrying about the physics. Why so combative? I've never claimed to be helping people improve, I haven't even said anything that someone could even try to use to improve based on the physics.

 

[zeio]

Chances are hardheaded engineer has been doing all of them all along, as indicated by experimental data on various players, yet he just won't accept facts.

https://www.tabletennisdaily.com/forum/topics/wrapping-the-ball.31447/post-413739

More and more recent studies show that all those "mental constructs" are not that far off from the scientific measurements. It comes down to the details (voids, unknowns) that people had to fill in by guessing to the best of their experience and knowledge (intuition again?) because they just didn't know for sure as they didn't have the tools to peek beyond "the event horizon".