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

[yogi_bear]

If hard headed engineer is smart in mathematics and physics then hard headed engineer should even have the simple logic in the use of terms and languages for common people that not every term used should be equated to engineering and mathematics but as a metaphor or other representations. Does that mean that if we talk politics, the term "power" should be called power =work/time???

 

[brokenball]

If hard headed engineer is smart in mathematics and physics then hard headed engineer should even have the simple logic in the use of terms and languages for common people that not every term used should be equated to engineering and mathematics but as a metaphor or other representations. Does that mean that if we talk politics, the term "power" should be called power =work/time???

Why not use the proper terms? However, you know the proper definition. Use it.
People generate power, not paddles.
People have control, not paddles.
Equipment will not not help you play better although I do think it can make you play worse.
I would think Yogi would be supporting this as he is a coach that is interested in making people better players.

Getting back to the original question. If the rubber is like a spring. Then if the ball hits a soft spring or a hard spring the ball will come back at the same speed given the springs are linear, weigh the same, and don't bottom out. What make a difference is the damping and the weight of the spring. This is a basic engineering problem.
https://en.wikipedia.org/wiki/Mass-spring-damper_model
The damping ratio makes a big difference on the return speed.
Also, the weight of the spring makes a little difference because when the spring start to expand or rebound it must not only accelerate the mass of the ball but also the mass of the spring. Actually the effective mass of the spring is 1/3 of its actual mass. There is a data base of uncut rubbers where one can get good estimates of the mass of 1 sq cm of rubber.
1 sq cm is a good estimate for the contact area between the ball and rubber.

 

[yogi_bear]

Why not use the proper terms? However, you know the proper definition. Use it.
People generate power, not paddles.
People have control, not paddles.
Equipment will not not help you play better although I do think it can make you play worse.
I would think Yogi would be supporting this as he is a coach that is interested in making people better players.

Getting back to the original question. If the rubber is like a spring. Then if the ball hits a soft spring or a hard spring the ball will come back at the same speed given the springs are linear, weigh the same, and don't bottom out. What make a difference is the damping and the weight of the spring. This is a basic engineering problem.
https://en.wikipedia.org/wiki/Mass-spring-damper_model
The damping ratio makes a big difference on the return speed.
Also, the weight of the spring makes a little difference because when the spring start to expand or rebound it must not only accelerate the mass of the ball but also the mass of the spring. Actually the effective mass of the spring is 1/3 of its actual mass. There is a data base of uncut rubbers where one can get good estimates of the mass of 1 sq cm of rubber.
1 sq cm is a good estimate for the contact area between the ball and rubber.

Oh i know the terms but i do not dwell on nor force it on people since unlike hard headed engineers I have engineer friends of various fields who for heaven's sake are varsity level platers or at least 2000 us rating all of whom do not force physics or mathematical dedinitions on common terms yet they know how to apply and separate the meaning of such terms.

 

[langel]

XIOM knows what they are talking about. Here is a quote from XIOM's Europe website (read the part regarding sponge hardness:

3. Understand how the catapult affects your game:

In general the softer the rubber, the more bouncy it is at slow arm movement. The harder rubbers of VEGA series are the ones that can produce the highest amount of spin and speed, when the player is able to activate their full potential. Due to different sponge and topsheet structures rubbers with the same sponge hardness can have different catapult effects.

On the one hand springy rubbers take away work from the player and can produce spin and speed easily also with softer strokes like slowly played topspins. On the other hand less bouncy rubbers can be helpful in short short game over the table.

Exactly.

Here is my statement posted 08/22/2019

"Well, while speed and spin feeling may always vary personally, due to different style and stroke implementation, and may not correspond strictly to the producer statements, the "catapult" is alway as it is intended by the producer.
Something else - the max speed of the rubber is not linked lineary to the catapult. In Xiom rubbers most of the softer tensors have stronger catapult, which for some players is better, but have slower max speed than the harder ones."

If interested you may read the discussion in the thread:

https://www.tabletennisdaily.com/forum/showthread.php?21696-Xiom-Rubbers

I've had similar thoughts in many other threads regarding catapult and springiness, I prefer harder and less bouncy rubber and feel them much better over the table and with softer touches, though they have much greater speed potential. And I'm glad that I feel the rubbers of Xiom the same way as they are intended to perform by Xiom.

 

[zeio]

All right, time to get back on track. How about a he-did-the-math answer?

A student named 佐藤 秀祐(SATO Shuusuke?) of Keio University did a paper on this topic in 2014.

Basically, it involves dropping a ball onto the racket with soft and hard rubbers from different heights and the rebounds are measured. Skipping the formulas, he concludes that the free-fall velocities at those heights are not high enough to make a significant difference but players will be able to since their swings are so much faster. 13m/s vs 30m/s, not enough momentum to activate(dig into) the hard sponge.

Blue dot: Soft
Orange square: Hard
Y-axis: Rebound height in cm±SD
X-axis: Drop height in cm±SD

ここで,今回はラバーの硬さの違いによる跳ね返りの違いを考えているので,(11)式はEのみの関数となる.さらに,ラバーには厚みがあるので最大縮みには限りがあると考える.軟らかいラバーが限界縮みに達するときの高さをℎ1とするとℎ<ℎ1のときは(11)式から縦弾性係数が小さいほど最大縮みは大きくなるので,軟らかいラバーのほうが最大縮みは大きくなり,弾みも大きくなると考えられる。ℎ>ℎ1のとき軟らかいラバーは限界縮みに達しているので高さが大きくなっても最大縮みは大きくならず,弾みも変わらないが,硬いラバーはまだ限界縮みに達していないため最大縮みは大きくなっていき,硬いラバーの限界縮みに達したときは縦弾性係数が大きい硬いラバーの方がより弾むと考えられる.このような現象は自由落下の速度では起こらないが,卓球の速度だと起こると考えられる.今回はラバーに生じる衝撃力は一定であるとして考えたが,実際はラバーとボールの接触する面積はラバーの面積と比べて小さいため,さらに深く議論するためにはこのようなことも考慮にいれなければならない.

５．結論
自由落下による跳ね返り実験ではラバーの硬さによる跳ね返りの違いを観察することはできなかったが,卓球の速度で実験を行えば、ラバーの硬さの違いによる跳ね返りの違いを観察できると考えられる.

Here, since we are considering the difference in bounce due to the difference in rubber hardness, Eq. (11) is a function of only E. Furthermore, since the rubber has a certain thickness, the maximum shrinkage is considered to be limited. Assuming that the height at which the soft rubber reaches the limit shrinkage is ℎ1, when ℎ <ℎ1, the maximum shrinkage increases as the normal modulus decreases from Eq. (11), so the maximum shrinkage increases with the soft rubber. It is thought that the momentum also increases. When ℎ> ℎ1, the soft rubber has reached the limit shrinkage, so the maximum shrinkage does not increase even if the height increases, and the momentum does not change, but the hard rubber has not yet reached the limit shrinkage, so the maximum shrinkage is larger when the rubber reaches the critical shrinkage, it is considered that the hard rubber with higher normal elasticity rebounds more. This phenomenon does not occur at the speed of free fall, but occurs at the speed of table tennis. In this study, we assumed that the impact force generated by the rubber was constant, but in fact, the area where the rubber and the ball contacted was smaller than the area of the rubber, so this should be taken into account for further discussion.

5. Conclusion
In the rebound experiment by free fall, it was not possible to observe the difference in the rebound due to the hardness of the rubber, but if the experiment was performed at table tennis speed, it would be possible to observe the difference in the rebound due to the difference in the hardness of the rubber.

 

[zeio]

A netizen named 桂花田(sweet olive field) from Taiwan did a similar experiment for glued/unglued Sriver series, Bryce series, Plasma series and many others over a decade ago and came to a similar conclusion.

 

[yogi_bear]

That is the thing i have been trying to explain in the simplest of terms. That is why harder rubbers have a higher max speed when you reach a certain amount force applied to the rubber but when lesser amount of force is applied it is also slow.

 

[Haito]

Other way of the explaining thing is to think of the sponge as compression spring. The softer the spring the less force you have to use to compress it, but also the lower energy it will release. The harder the spring, the more energy it can store, but the harder it is to compress it. If you won't compress the spring, then you would not expect it to repress, right?

(I was just trying to use analogy in layman terms, i think there is a bit more to this when it comes to sponges)

 

[Zeen]

that study is nice to have, but it's overkill for explaining the obvious. As Xiom stated, harder rubbers can produce more quality, but need faster arm / more impact force to do so. And that's all one needs to know. Just as with jumping on a trampolin that has low tension vs one that has high tension. It depends on the weight of the person jumping on it. Overcomplicating things doesn't put anything back on track.

 

[zeio]

If hard headed engineer is smart in mathematics and physics then hard headed engineer should even have the simple logic in the use of terms and languages for common people that not every term used should be equated to engineering and mathematics but as a metaphor or other representations. Does that mean that if we talk politics, the term "power" should be called power =work/time???

Oh, hard-headed engineer enforces a zero-tolerance policy on ambiguity and contradictions due to his line of work.

https://hbr.org/2012/06/all-hail-the-generalist

Finally, there appears to be reasonable and robust data suggesting that generalists are better at navigating uncertainty. Professor Phillip Tetlock conducted a 20+ year study of 284 professional forecasters. He asked them to predict the probability of various occurrences both within and outside of their areas of expertise. Analysis of the 80,000+ forecasts found that experts are less accurate predictors than non-experts in their area of expertise. Tetlock’s conclusion: when seeking accuracy of predictions, it is better to turn to those like “Berlin’s prototypical fox, those who know many little things, draw from an eclectic array of traditions, and accept ambiguity and contradictions.” Ideological reliance on a single perspective appears detrimental to one’s ability to successfully navigate vague or poorly-defined situations (which are more prevalent today than ever before).

 

[zeio]

Other way of the explaining thing is to think of the sponge as compression spring. The softer the spring the less force you have to use to compress it, but also the lower energy it will release. The harder the spring, the more energy it can store, but the harder it is to compress it. If you won't compress the spring, then you would not expect it to repress, right?

(I was just trying to use analogy in layman terms, i think there is a bit more to this when it comes to sponges)

The analogy I think of is motor unit recruitment, where muscle fibers are activated in order of size from smallest to largest depending upon the intensity, known as the size principle. As the force output increases, you start losing fine motor control as larger motor units take over, making it harder to use a harder rubber.

Baal has written on that extensively for threads about heavy/light setups. Look it up if you're interested.

 

[zeio]

that study is nice to have, but it's overkill for explaining the obvious. As Xiom stated, harder rubbers can produce more quality, but need faster arm / more impact force to do so. And that's all one needs to know. Just as with jumping on a trampolin that has low tension vs one that has high tension. It depends on the weight of the person jumping on it. Overcomplicating things doesn't put anything back on track.

Fresh off the boat. Here, to get you up to speed. Be sure check out the chart for Xtend series, which answers the OP's question.

The funny thing is pnachtwey used the term in his own response(surprisingly reasonable) for roughly the first year, before all of a sudden becoming self-aware like an AI and decided to go on a personal crusade to destroy any dialogue at every mention of the term.

It's been 7 years and I honestly think it's high time we got past the argument over nomenclature. It's getting nowhere. Any normal person would simply treat you like a cuckoo when you tell them "throw angle? I'm offended by that." Nobody cares if that term is not your cup of tea. Just move on.



With all that said, below is for those interested(ripped from Yasaka Catalog 2018 and TSP Catalog 2018)

Rakza X & Soft - Max grip
Rakza 7 & Soft - Spin-oriented
Rakza 9 & Soft - Speed-oriented

Power transfer chart, X-axis = Input(how hard you hit), Y-axis = Output(how strong your shot)

Same thing but for Xtend series
The range each model performs the best
The softer one is more bouncy at low impact
The harder one shows it power at strong impact

Who says a blade doesn't have throw angle?

Left chart, strong/weak impact for rubbers w/ ORC and those w/o
Right chart, swing speed(the higher, the stronger the impact), how Super/Speed/Spin/Soft compare with normal rubbers at the same sponge hardness

 

[Dr Evil]

An easy way to think about it is how much energy is wasted/dissipated by the rubber. Hard rubber tends to waste more energy at low impact speeds, whereas soft rubber wastes more energy at high impact speeds.

 

[zeio]

An easy way to think about it is how much energy is wasted/dissipated by the rubber. Hard rubber tends to waste more energy at low impact speeds, whereas soft rubber wastes more energy at high impact speeds.

Please stick to the rules. Avoid staying the obvious in physics terms but try to obfuscate your explanation with technical jargon.

 

[Zeen]

Very nice of you to spend the time and post more data that backs up all the claims made in XIOM's description, so we can all refer to it now instead of obfuscating the obvious with superflous graphics and technical terms

 

[zeio]

In the 2011 Yasaka Catalog, there's this passage for the Pryde series.

Difference in performance due to rubber hardness
The softer the rubber, the higher the acceleration when hitting lightly, but the lower the power limit. Conversely, the harder the rubber, the higher the acceleration when hitting hard than hitting lightly, and the higher the power limit.
For beginners to intermediate players and those who don't hit hard as often, soft rubbers would feel more bouncy. Conversely, top players with power tend to prefer hard rubbers in their search for rubbers that can balance both speed and spin when hitting hard.

 

[brokenball]

Some many statements made without justification or proof! Show me where the hardness of rubber fits into the speed after impact.
I agree with Dr Evil that rubbers dissipate energy but I would like to see the evidence that hard rubbers waste more energy at low speeds and soft rubber wastes more energy at high speed.

BTW, dropping the ball on a paddle is not a good way of testing rubbers. The speed of the ball will be low.
Even if you drop the ball from very high the speed is quickly limited by air resistance.

 

[Dr Evil]

I agree with Dr Evil that rubbers dissipate energy but I would like to see the evidence that hard rubbers waste more energy at low speeds and soft rubber wastes more energy at high speed.

See for example zeio's post directly above yours.

 

[zeio]

A netizen named 桂花田(sweet olive field) from Taiwan did a similar experiment for glued/unglued Sriver series, Bryce series, Plasma series and many others over a decade ago and came to a similar conclusion.

                       Speed70    Speed90      KTS      Cypress 9mm   Senkoh-A.  
 -------------------- ---------- ---------- ---------- ------------- ----------- 
  Plasma 470 max       50----71   50----69   50----70   50----67      50----67.  
  Plasma 470 2.0       54----76   53----75   53----77   53----75      52----74.  
  Bryce 2.1            53----72   53----72   52----72   52----70      50----70.  
  Bryce Hard           48----70   49----70   48----70   47----68      46----67.  
  JO Gold max          50----70   50----69   51----69   50----67      50----65.  
  F1 Hard max          49----70   49----68   50----68   50----67      48----66.  
  Moristo 2000 2.0     50----67   50----67   50----70   50----69      50----65.  
  Plasma 430 max       52----72   52----73   52----73   51----70      50----69.  
  Plasma 430 2.0       52----72   54----72   52----73   52----72      52----71.  
  Sriver max           44----63   45----66   45----66   45----63      43----62.  
  Sriver EL max        48----67   48----67   48----67   47----67      46----66.  
  Gallardo Speed max   52----70   51----71   51----71   50----70      50----68.  

Drop height: 100----150cm

 

[brokenball]

See for example zeio's post directly above yours.

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.