Contact time with the rubber and hitting area

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The study you are linking states very clearly that it is only measuring contact time on a stationary, standstill paddle not taking into account acceleration, which would obviously extend the contact time. At least read and understand what you are linking man.
What does acceleration do? It just increases (or decreases) the racket velocity over time and therefore the impact velocity.
Do any of these studies show that contact time increases with higher impact velocities? No, they all show that contact time decreases with higher impact velocities.
 
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I think your studies are missing a key factor which is sponge. Just shooting a ball at a paddle only gives insight into how much energy it absorbs from the impact. However, it doesn't give any insight into the lateral support it gives once the ball sinks in and creates a well in the rubber. This is most notably seen once you compare hard bat to modern table tennis. This lateral support enables players to offensively drag/attack the ball once it drops below the table instead of being forced to hit lower on the ball like chopping or lobbing. You can see this when a player used to inverted rubbers tries to topspin with other rubbers. The ball just falls down since they tend to hit higher up on the ball but lost the lateral support of sponge. A good example of the offensive capabilities of inverted rubber would be the recent match between Tomokazu Harimoto and Chen Yuanyu. Once you take into account this lateral support, you will then understand how rotational mechanics come into play, that is pronation and supination of the forearm for forehand and backhands respectively. The divot in the sponge/rubber sandwich created during impact allows for it to act like the cup seen in the water cup demonstration when learning about rotational mechanics. While you wouldn't be able keep the ball the full 360 degrees since the forearm can only rotate so much, you'll still be able to have the ball enter at one racket angle and leave at another as long as the racket follows the ball.
 
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If I think logically and use my knowledge of physics acceleration increases dwell time a bit as you use sponge more. Thus point of contact doesn't matter.

On the other side if you hit with a wrong part it means that likely you missed the highest acceleration point already. Also we should take into account blade properties and that sweet spot size is finite. So from empirical point of view it does make sense to hit with certain area.
 
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What does acceleration do? It just increases (or decreases) the racket velocity over time and therefore the impact velocity.
Do any of these studies show that contact time increases with higher impact velocities? No, they all show that contact time decreases with higher impact velocities.
Because it's not a simple instantaneous elastic collision. You're taking advantage of the friction and deformation properties of the rubber to maintain contact and control the ball's path. Just imagine the physics of a slow and controlled forehand flick.
 
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If I think logically and use my knowledge of physics acceleration increases dwell time a bit as you use sponge more. Thus point of contact doesn't matter.

On the other side if you hit with a wrong part it means that likely you missed the highest acceleration point already. Also we should take into account blade properties and that sweet spot size is finite. So from empirical point of view it does make sense to hit with certain area.
I'm a bit confused, are you replying to me? I never talked about parts of the blade. My point was that the sponge allows players to play more on top of the ball rather than below the ball, even when the ball is below net/table height.
Edit: Never mind, I reread the thread. My fault.
 
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says Pimples Schmimples
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It doesn't matter if the racket is stationary or not (we are not talking about relativistic velocities ;)). What matters is the impact velocity either this is only the ball or it is v_ball + v_racket.
It does matter because the ball and racket making perpendicular contact, as in flat smash, is not the same as the racket and rubber rolling over the top (or bottom) of the ball.
Imagine it like those spin trainers they have where the ball spins on a roller.
Then it's clear that you can have longer and shorter contact as your racket follows (and grips) the ball.


As interesting and all as this subject is, I have to say that after this I'm out and just happy to respect other differing (even incorrect😉) opinions because there's no merit to debating this with physics, equations and nerd theory when anyone playing knows when they are getting more and less dwell time and spin based on different shots, different rubbers and different technique... 🤷
 
says Pimples Schmimples
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“You are entitled to your opinion. But you are not entitled to your own facts.” (DP Moynihan) It's well established that contact time is on the order of 1 millisecond. Easy enough to check with Google or ChatGPT, so I'll leave that to you. Then a few simple calculations will give you a clear idea of rolling distance (ChatGPT o1 can even lay this out for you step by step).
You don't understand, or have chosen to ignore, where people have offered the concept of a moving racket at a closed angle rolling over the top of the ball (as in a forehand topspin properly executed with GOOD technique) will give much more contact time than a ball simply bouncing on a rubber.
Choosing to ignore this is just choosing perpetual ignorance and arguing a tangential straw man rather than what the OP actually asked.
 
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You don't understand, or have chosen to ignore, where people have offered the concept of a moving racket at a closed angle rolling over the top of the ball (as in a forehand topspin properly executed with GOOD technique) will give much more contact time than a ball simply bouncing on a rubber.
Choosing to ignore this is just choosing perpetual ignorance and arguing a tangential straw man rather than what the OP actually asked.

Unfortunately it is you who is ignoring the facts. There is NO ROLLING.

What you/we feel is something else.

Yes, we might do something what varies the angle, but this gives us the illusion of rolling, and in reality, we hit at certain angle, which doesn't have time to change and thus - NO ROLLING.
 
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says Pimples Schmimples
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Unfortunately it is you who is ignoring the facts.
There is NO ROLLING.
Where is this a fact?
Dwell time and bite etc is all a myth then?
What you/we feel is something else.

Yes, we might do something what varies the angle, but this gives us the illusion of rolling, and in reality, we hit at certain angle, which doesn't have time to change and thus - NO ROLLING.
So you don't believe the ball rolls any distance on the rubber of a very fast moving racket with a tacky rubber?
Then tell me why my FH doesn't hit the table in front of me when I play a topspin shot with a very closed racket angle.
The ball is digging in, gripping and rolling.
I'm not telling you the ball is there for 2 seconds and rolling the entire length of the rubber but it IS rolling on the rubber.
And don't tell me the answer is because of the incoming topspin either because everyone knows you can play shots with more lift and less lift all based on technique, angle, rubber sponge etc and you either get the bite and the grip (increased dwell) or you don't and you dump it into the net.
Play soft with 09c and see what happens or play hard with it. The difference isn't time spent in contact with the rubber and activation of the sponge?
 
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I think your studies are missing a key factor which is sponge. Just shooting a ball at a paddle only gives insight into how much energy it absorbs from the impact. However, it doesn't give any insight into the lateral support it gives once the ball sinks in and creates a well in the rubber.

This is something Tiefenbacher and Durey (The Impact of the Table Tennis Ball on the Racket) already did in 1994 but I haven't looked through all the other studies' references and searched for it.
T&D keep the well known coefficient of restitution (which they call E_par) and introduce T_par the tangential parameter ("responsible for the ability to produce spin and tangential velocity"). Both parameters decrease with increasing impact velocity.

...While you wouldn't be able keep the ball the full 360 degrees since the forearm can only rotate so much, you'll still be able to have the ball enter at one racket angle and leave at another as long as the racket follows the ball.

As already said: this might be the case if the ball already rotating in the same direction (loop against backspin) as the racket moves or if the ball is more less fixed like with these spin trainers.

It does matter because the ball and racket making perpendicular contact, as in flat smash, is not the same as the racket and rubber rolling over the top (or bottom) of the ball.
Imagine it like those spin trainers they have where the ball spins on a roller.
Then it's clear that you can have longer and shorter contact as your racket follows (and grips) the ball...

Some additional videos:
MASSIVE spin on table tennis serve (shot with 4436 fps)

Table Tennis: Backhand Loop of underspin ball - 1500 fps

Forgot Xu Xin (shot at 3000 fps, loop against backspin, resulting spin = 176.65 rps or 10599 rpm)
 
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says Open t o play :)
I appreciate the discussion and all the maths! :D At the end of day, I would just like to know whether contacting at the rear actually creates no spin.
Velocity shouldnt be a thing here since we're not talking about the tip of the blade and the contact point at the front part (of the tip) has the same distance to the wrist as the rear part (of the tip).
And I don't think people necessarily mean "rolling" when they talk about dwell time, or rather the time in which the ball "digs" into the rubber and stretches it.
 
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OP posted a video (how to) READ THE SPIN ON A SERVE INSTANTLY

Personally i changed my approach to this and receiving a few months ago. I kinda give up on reading the spin on the serve INSTANTLY.

Instead I focus on how to make a good receive EVEN IF IM NOT SURE OF THE SPIN and ON TRYING TO GET AS MUCH INFO EVEN IF LATE.

Of course i watch the opponent serving and try to see the impact but ill be honest, more than 50% of the time, especially against the better players who have good serves, i don't see the impact, because the motion is too fast, i can't always see clearly if the racket angle is below the ball or above, and some servers are masters in disguise.
Instead i try to get partial info: if the impact was NOT FAST then there must not be a LOT of spin. If it is fast, higher chance of heavy backspin. Also i look if the ball has sidespin or reverse sidespin. Many opponents don't disguise the sidespin and we can tell already from the grip and think of which receive we can do and on which side to contact the ball.

Then i try to switch very quickly my attention from the opponents racket to the incoming ball, try to see where is the first bounce (don't always see it), and i must have totally be focused on the ball by the time its in my half where i MUST see the top of the bounce and trajectory to have the timing right, if the serve is short i have also a chance sometimes to pay attention at the ("Nittaku") mark on the ball to see whether the serve is spinny or no-spin/float.

---
this is perhaps the most fundamental change and improvement in my game in the last months (/years ?).

I've removed the frustration of not being able to read the spin immediately
I've removed the urge to receive the ball too early without knowing whats coming to me.

One advice from a previous coach was to "stop-receive" on short serves by taking the ball early on the bounce. but you can't do that if you're not able to know if the serve was float / backspin (or topspin !)
I think it may be a good advice for those advanced players or at least those with high spin reading skills.

But I found out that having a more patient timing works out better for me, its safer, yes its demanding a different touch to play with a different timing. I would still do an aggressive-by the bounce- stop-receive only once in a while but would absolutely refrain from it in game1 or in deuce.

when the ball is long, no hesitation, i know i have to open the game with a loop. if its half long, im also trying most of the time to open with a chiquita (2/3 of table) or with FH. If i feel unsure or hesitant about my position or footwork, then i decide to have a reaction shot like a last split second push or fishing ball.

TLDR
don't try to READ THE SPIN INSTANTLY. Try to get as much information on the serve at all stages, from seeing the grip, to the last split second before you hit the ball. missing the information on the impact is forgivable.
 
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Where is this a fact?
Dwell time and bite etc is all a myth then?
So you don't believe the ball rolls any distance on the rubber of a very fast moving racket with a tacky rubber?
Then tell me why my FH doesn't hit the table in front of me when I play a topspin shot with a very closed racket angle.
The ball is digging in, gripping and rolling.
I'm not telling you the ball is there for 2 seconds and rolling the entire length of the rubber but it IS rolling on the rubber.
And don't tell me the answer is because of the incoming topspin either because everyone knows you can play shots with more lift and less lift all based on technique, angle, rubber sponge etc and you either get the bite and the grip (increased dwell) or you don't and you dump it into the net.
Play soft with 09c and see what happens or play hard with it. The difference isn't time spent in contact with the rubber and activation of the sponge?

Honestly I think I'm able to feel the varying dwell and bite not only on my hits, but also on the hits of the opponents - I mean different opponents give different feeling of dwell and bite. And also, people sometimes complain that when I play with chinese rubbers on the FH, that the ball doesn't fly, and it's like it freezes and then gets released, etc., etc. All that I believe we all can feel. And yet, I believe there is no rolling. Perhaps in my earlier post I have formulated it a bit more aggressively than necessary. It's just that I believe that all these differences essentially come down to these physical points:
- the angle of the incoming ball
- the angle of the blade
- the angle at which the whole system then moves (which is not the angle of the blade)
- the speed of the impact (either you take 2 speeds (ball, blade) or 1 sum speed)
- the hardness of the rubber, and also blade (simplified)

These, imho, are enough to get all we see and are able to produce and the impact time is still in all cases more or less the same (and I'd add here that when the blade angle is changing during stroke - only the angle at contact matters, not the change during contact). And yet we get all those differing results. But when we try to describe, we are describing what we feel, and not necessarily what is really physically happening. There is actually not much need for controversy here... You're free to decide to believe whatever you prefer... And also, often when TT couches/teachers describe something to players/students, they use words which are not physically true, but they are still the most helpful words for development... I'd however at least stand on my point that there is no rolling, except of ROFL ;-) And I'd add that all these have been discussed here extensively already, this feels more like repetition, and that is perhaps why some TTD "heavyweights" (ROFL) are not engaging anymore... Cheers.
 
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I appreciate the discussion and all the maths! :D At the end of day, I would just like to know whether contacting at the rear actually creates no spin.
Velocity shouldnt be a thing here since we're not talking about the tip of the blade and the contact point at the front part (of the tip) has the same distance to the wrist as the rear part (of the tip).
And I don't think people necessarily mean "rolling" when they talk about dwell time, or rather the time in which the ball "digs" into the rubber and stretches it.
from my experience contacting at rear does reduce the spin somewhat but it will still have at least moderate backspin on it if the racket speed is similarly high, it's not gonna be no spin. If you push it assuming it has heavy backspin it will pop up a bit but it's not gonna be an easy kill regardless. As a receiver it is better to risk having it pop up a bit rather than risk making a direct net mistake (for e.g. if you assume there's less backspin but it is in fact strong backspin) as they still have to prove that they can punish the pop-up, and you still have a chance if you retreat a bit and block their attack.

For my heavy underspin/no-spin serves (which have been very effective for me so far), I use a method which I think yields superior results. The difference is whether I brush the ball then pronate, or pronate during the serve (which kills the backspin and can even produce a bit of topspin). This is the method that Ma Lin uses too, and with high toss you can make this difference really subtle. With this, the "nospin" variant is actually mild topspin (not even mild backspin) so an opponent who assumes that it is heavy backspin, when they push it it will result in gigantic pop-ups or direct mistakes out of the table. So you can serve heavy backspin, light backspin and mild topspin with the same serve movement. This method is super unreadable because the serve action can be very fast. Also super easy to keep short - this is my goto serve when I face very strong players who punish long/half-long serves like crazy.

The only players I know who can read this serve, are those who rely on reading the serve trajectory and not the service movement.
 
Incorrect

Incorrect.
A millisecond? Seriously. A millisecond. If this were true then nobody would ever put spin on a ball.

Incorrect.
Unless you want to define 'tiny fraction'. If tiny fraction is 1/50th you are incorrect. If tiny fraction is 1/8th then you are correct. Ever driven your FH topspin forward, contacting the top of the ball with high racket speed and a tacky rubber? You can actually feel the ball (dwell time) on the rubber and it's a lot longer

Correct

Really?
So the constant talk about rubber hardness/softness, pimple structures, sponge density, sponge softness or lack thereof, blade stiffness and/or hardness, all impacting the Dwell time, has nothing to do with how much spin a player can get???
So, with a top spin ball where the point of contact on your racket is at the top (as an example), there is more spin in it than if you made the same stroke (at the same angle) with the lower part of the racket.
So with a push ball, just the opposite at the bottom more spin than if you hit the same ball at the top....ga away guys!
That it's better to hit a ball at the sweetspot (between the lower and upper area) seems logical to me, that's true.
It was about the hitting point on your racket, bottom or top and that really makes no difference in my eyes, I never felt that way anyway, in fact you hit the ball wrong then.
The rest of what you write is true of course, but then it's about the point of contact on the ball, big difference!
 
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