How can a harder rubber be slower than a soft one?

brokenball said:

Zeio's post is shows a graph. I can draw lines too. The question is were does the data come from to draw lines.
Call me suborn. I am mostly skeptical. I have made a lot of money being skeptical. Generalizations like hard rubbers are faster than soft rubbers is not right. I said this before, I have a sheet of Giant Dragon Guard Anti that has hard but very dead rubber. If you press on it an let go you can still see where you pressed on the rubber. Obviously this rubber is not springing back quickly and is slow. So not all hard rubbers are faster than soft rubbers. Why not? There is more to being fast than just being hard or slow.

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the missing factor you are looking for is 'elasticity'
hard without elasticity = slow
hard with elasticity = fast

I find this a very interesting thread.
I can remember in the 1970's comparing Sriver and Mark V and concluding that Mark V was slightly more responsive than Sriver. My method of testing rubbers was to bounce a ball from a few inches above the rubber surface and apply spin. I never thought to compare the effect of full power strokes with each rubber as possibly having a different performance ranking with the bouncing from hand test.

If I understand what's being expressed here, however some of the rubbers with harder sponges will perform with good control in a pushing situation, but provide super power in a topspin drive situation.
Now one of the issues in the heyday of Mark V was that it was a rubber that was not for beginners because beginners couldn't control it in pushing and serve return situations, even though they obviously enjoyed looping away with it.
But it seems that these new hard sponges should provide control in push and serve return, while still supplying power for the big shots.
Is this analysis correct?

Also it seems that the manufacturers should be providing not just sponge thickness and hardness numbers but also elasticity (or degree of damping?) as a separate number.
what would be really nice if the ITTF
certified the Hardnesss and Elasticity factors for all rubbers rather than have manufacturers providing their in house figures

Zeen said:

the missing factor you are looking for is 'elasticity'
hard without elasticity = slow
hard with elasticity = fast

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Yes, yes, yes, yes.
Likewise, soft rubbers low elasticity = slow
soft rubbers with high elasticity = fast

To paraphrase James Carville, "it is the elasticity stupid"

It is the elasticity or coefficient of restitution that really makes a difference.
There are no equations for computing the speed after impact using hardness or durometer readings. There are equations that using elasticity or the coefficient of restitution.

The coefficient of restitution can vary from 0 to 1 but most TT rubbers are probably in the 0.6 to 0.7 range. The TT companies keep making more and more rubbers and hyping them as if they were the next great thing when they are actually not much, if any different, from what has been made before.

There is too much talking about equipment on these forums as if going to make them play better.
I am a "Goldilocks" person. There is too fast, too slow and just right. I shake my head when I see people asking about rubbers that really aren't that much different.

I think it is better to spend money on coaches, fitness or good practice time. You really need to do both because trying to fix just one thing will not help much because a lack of fitness will prevent you from doing what the coach is trying to do.
Also, good coaches are hard to find. Too many believe in the TT myths or want to do drills that can be done with a robot.

brokenball said:

Yes, yes, yes, yes.
Likewise, soft rubbers low elasticity = slow
soft rubbers with high elasticity = fast

To paraphrase James Carville, "it is the elasticity stupid"

It is the elasticity or coefficient of restitution that really makes a difference.
There are no equations for computing the speed after impact using hardness or durometer readings. There are equations that using elasticity or the coefficient of restitution.

The coefficient of restitution can vary from 0 to 1 but most TT rubbers are probably in the 0.6 to 0.7 range. The TT companies keep making more and more rubbers and hyping them as if they were the next great thing when they are actually not much, if any different, from what has been made before.

There is too much talking about equipment on these forums as if going to make them play better.
I am a "Goldilocks" person. There is too fast, too slow and just right. I shake my head when I see people asking about rubbers that really aren't that much different.

I think it is better to spend money on coaches, fitness or good practice time. You really need to do both because trying to fix just one thing will not help much because a lack of fitness will prevent you from doing what the coach is trying to do.
Also, good coaches are hard to find. Too many believe in the TT myths or want to do drills that can be done with a robot.

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exactly. not so many factors are actually important when choosing rubbers. Once you know your preferred hardness, throw angle and elasticity, you can lay back and shrug your shoulders over irrelevant discussions.

"Also, good coaches are hard to find. Too many believe in the TT myths or want to do drills that can be done with a robot. "

If you do not understand why a robot cannot replace drills done by a human coach then it shows your level of knowledge in tt. I bet ypu have not even produced decent good players.

yogi_bear said:

"Also, good coaches are hard to find. Too many believe in the TT myths or want to do drills that can be done with a robot. "

If you do not understand why a robot cannot replace drills done by a human coach then it shows your level of knowledge in tt. I bet ypu have not even produced decent good players.

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I understand why. I didn't say robots can replace coaches but the can do some things as well as coaches can.
Robots can't analyze weaknesses. Robots can't play games.

I am not a coach. Never claimed to be but I can analyze things very well. I have made lots of money analyzing things and solving/correcting problems. That is what hard headed engineers do!

brokenball said:

I understand why. I didn't say robots can replace coaches but the can do some things as well as coaches can.
Robots can't analyze weaknesses. Robots can't play games.

I am not a coach. Never claimed to be but I can analyze things very well. I have made lots of money analyzing things and solving/correcting problems. That is what hard headed engineers do!

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You cannot fully analyze if you are not deep into the game. It goes beyond physics. There are other areas such as body mechanics, physical fitness, mental training and touchy feel.

The Coach is doing coaching things, the robot is doing robotish things. Both have their specific place in the training process. We have coaches, and we have robots. Trainees have coaching sessions and they have robot sessions too. Experienced players may have robot sessions on their own, youngsters are Always assisted by a coach during a robot session. In general the robot sessions are no more than 20% of the total training process.
Thats how it is in our club.

yogi_bear said:

You cannot fully analyze if you are not deep into the game.

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That is vague. What does 'deep into the game' mean? I have analyzed many things I knew little about before meeting with the customer or the customer telling me what he wants to do.

It goes beyond physics.

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Physics provides knowing what needs to be done.

There are other areas such as body mechanics, physical fitness, mental training and touchy feel.

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Yes, if it only came down to physics I would be damn good.
Doing what needs to be done is the challenge.
I am aware of the body mechanics.
It is the physical fitness part that gets me because I am 66.

Meanwhile, people read my posts and zeen's post.

Indicating or including elasticity won't really help. Hard-headed engineer should've known better before throwing that term around when he kept beating the dead horse for years with that oddball anti rubber.

Butterfly Super Anti has the softest sponge at 20 degrees, of all rubbers on offer. Nittaku Best Anti has the softest sponge at 20 degrees as well, of all rubbers on offer. Yet hard-headed engineer wouldn't quote them because they don't fit into his worldview.

Elasticity doesn't explain the poor bounce despite a hard topsheet/sponge because that oddball rubber is exploiting the viscoelastic property known as hysteresis. Hardness doesn't matter at that point because it doesn't behave elastically like typical rubbers would.

https://ooakforum.com/viewtopic.php?f=17&t=18582

The Guard should have the same top-sheet as the Guard special, but it seemed less tacky to me. With the 0.8 mm sponge it is also about twice as heavy as the 1.8 mm Guard Special. The top-sheet is very inelastic which, on bal contact, results in the same shallow dents as happens with the Special. The dents are even more shallow with the Guard, almost invisible, but they are obviously there to stay.

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https://ooakforum.com/viewtopic.php?f=17&t=18429

I tested the Giant Dragon Guard [Special; edit], 1.8mm, black on a Stiga Tube Defensive blade (FH LKT Pro XT 1.5). First of all this rubber should be renamed - it should be Dark Side of the Moon, as that is how it looks after a few minutes of play: full of impact-dents that don't go away (not even when I am writing this, an hour later). I wonder if this is legal...

The topsheet is very thick, with flat thick pips in, and enough tack to collect dust. It is also brilliant black, shiny. The sponge is pink, porous, and similar to that of Dawei Grass 20: press a fingernail in it and the indenture won't go away anymore. Quality seems fine to me, this rubber may be very durable (apart from the dents).

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zeio said:

Indicating or including elasticity won't really help. Hard-headed engineer should've known better before throwing that term around when he kept beating the dead horse for years with that oddball anti rubber. Butterfly Super Anti has the softest sponge at 20 degrees, of all rubbers on offer. Nittaku Best Anti has the softest sponge at 20 degrees as well, of all rubbers on offer. Yet hard-headed engineer wouldn't quote them because they don't fit into his worldview.

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How does these rubbers not fit into what I say? They are slow. They are not like Giant Dragon's Guard. I have multiple cheats of of Super Anti, Anti Power, and Best Anti and one sheet each of Buffalo and Mega Block. I know what they are like.

Elasticity doesn't explain the poor bounce despite a hard topsheet/sponge because that oddball rubber is exploiting the viscoelastic property known as hysteresis. Hardness doesn't matter at that point because it doesn't behave elastically like typical rubbers would.

https://ooakforum.com/viewtopic.php?f=17&t=18582


https://ooakforum.com/viewtopic.php?f=17&t=18429

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There is nothing in the ooakforum that disagrees with what I said.

How can you refute the speed after impact formula? The coefficient of restitution is a measure of the elasticity. The speed after impact formula does not include hardness.
https://en.wikipedia.org/wiki/Coefficient_of_restitution
It is amazing how you can hold on to your false ideas for so many years.
Tell us where the formula in the Wikipedia article is wrong.
Show us a formula that can be used to calculate the speed after impact using hardness.

Argh! Not this crap again. COR, speed after impact(my bad, velocity after collision, I insist), ratio of tangential COR to normal COR(throw angle, FFS), paddles don't generate energy unless you burn 'em and on and on. *bleep* me. This is disappointing. Hard-headed engineer has shown little if any growth in 10 friggin' years...

Here's the deal. "COR is an index that describes the relative elasticity of an impact." It's a mathematical description of "given this initial condition and this final condition, this is what happens". It doesn't explain why it happens this way or what causes it to happen this way.

Hard-headed engineer could work out the CORs from the real-world data that yours truly quoted above and argue until he's blue in the face and it still won't answer the OP's question.

To answer that one has to look further, in this case elasticity of the material, or elastic modulus.

To keep things simple, the stress-strain curve of a vulcanized rubber would look something like the figure below. Stress and strain here mean the force taken to displace(stretch/compress) the material. The elastic modulus, AKA Young's modulus in this case, is the linear region of the plot.



The steeper the slope, the higher the stress required for the respective strain, and the higher the Young's modulus. In the real world, rubber acts viscoelastically, so the storage modulus, loss modulus and tan delta(a measure of hysteresis that leads to damping) come into play as well.

Remind yourself that vulcanization adds elasticity to rubber because crosslinks are formed during the process and the higher the crosslink density the harder it gets, until a certain point. This is why harder rubber takes more force to stretch and if the force is not enough to reach the sponge, much of the energy is lost in the topsheet, according to data from Butterfly. Think of the force required to draw a heavy bow vs a light bow.

Now, what hard-headed engineer doesn't realize is that oddball anti rubber behaves beyond the elastic region, into the plastic region(permanent deformation). What high performance rubber would do that? Who'd be dumb enough to make that comparison?

Note the "craters" all over the topsheet that don't "recover".

http://www.game-changer.net/2019/05/10/why-experts-suck-at-predicting-the-future/

Tetlock and Mellers found that not only were the best forecasters foxy as individuals, but they tended to have qualities that made them particularly effective collaborators. They were “curious about, well, really everything,” as one of the top forecasters told me. They crossed disciplines, and viewed their teammates as sources for learning, rather than peers to be convinced. When those foxes were later grouped into much smaller teams—12 members each—they became even more accurate. They outperformed—by a lot—a group of experienced intelligence analysts with access to classified data.

So, what’s the difference?

In Tetlock’s 20-year study, both the broad foxes and the narrow hedgehogs were quick to let a successful prediction reinforce their beliefs. But when an outcome took them by surprise, foxes were much more likely to adjust their ideas. Hedgehogs barely budged. Some made authoritative predictions that turned out to be wildly wrong—then updated their theories in the wrong direction. They became even more convinced of the original beliefs that had led them astray. The best forecasters, by contrast, view their own ideas as hypotheses in need of testing. If they make a bet and lose, they embrace the logic of a loss just as they would the reinforcement of a win. This is called, in a word, learning.

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Zeio, why antispin rubbers only? Shouldn't that be applicable to all rubbers?

Note the extra word "oddball", typical anti rubber from Butterfly and Nittaku should behave more like high performance rubber.

zeio said:

Argh! Not this crap again. COR, speed after impact(my bad, velocity after collision, I insist), ratio of tangential COR to normal COR(throw angle, FFS), paddles don't generate energy unless you burn 'em and on and on. *bleep* me. This is disappointing. Hard-headed engineer has shown little if any growth in 10 friggin' years...

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That is because Newtonian physics hasn't changed in 10 years and you have failed to learn it.

Here's the deal. "COR is an index that describes the relative elasticity of an impact." It's a mathematical description of "given this initial condition and this final condition, this is what happens". It doesn't explain why it happens this way or what causes it to happen this way.

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No it doesn't but it would be a much better way of explaining the speed of a rubber than just arbitrary numbers that the fraudulent TT manufacturers give.

Hard-headed engineer could work out the CORs from the real-world data that yours truly quoted above and argue until he's blue in the face and it still won't answer the OP's question.

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But we have answered the OP question. It is the elasticity, not the hardness or softness of the rubber.

To answer that one has to look further, in this case elasticity of the material, or elastic modulus.

You avoid my questions.
What is your source?
What is the amount of stress that is applied to a top sheet?
Does it go outside the linear region?
Obviously it does for the GD Guard. My GD Guard would look like that for a while but it eventually flattened out.

To keep things simple, the stress-strain curve of a vulcanized rubber would look something like the figure below. Stress and strain here mean the force taken to displace(stretch/compress) the material. The elastic modulus, AKA Young's modulus in this case, is the linear region of the plot.

The steeper the slope, the higher the stress required for the respective strain, and the higher the Young's modulus. In the real world, rubber acts viscoelastically, so the storage modulus, loss modulus and tan delta(a measure of hysteresis that leads to damping) come into play as well.

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Do you even know how to use Young's modulus? Shell Oil uses our controllers for testing rock samples. They apply force until the rock sample fractions and record a curve similar to what you show. We can record the forces and positions every 0.25 ms.

The linear part will indicate how the material will compress with a given force but it DOES NOT INDICATE HOW FAST which is important to elasticity.

Now, what hard-headed engineer doesn't realize is that oddball anti rubber behaves beyond the elastic region,

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What elastic region? There is a linear region but again, your chart does no indicate how fast the rubber will restore itself.

into the plastic region(permanent deformation). What high performance rubber would do that? Who'd be dumb enough to make that comparison?

Note the "craters" all over the topsheet that don't "recover".

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Yep, my GD Guard would like like that after pressing on the rubber or after striking a ball but it would restore itself eventually. I think the video shows a poor glue job.

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