All about dwell time, maybe, but only if there are enough people interested.

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Dwell time seems to be a hot topic among TT players but honestly I bet NO ONE really anything about it. All they know is the myths perpetuated by the TT forums.

Let me start by saying dwell time can be infinite. If your paddle is horizontal to the ground and you place a ball on it it will stay there indefinitely until you tilt the paddle. The dwell time is infinite. This is an extreme case but it is a simple case. If the ball is stationary that means there is no net force acting on it. The force of the sponge pushing up on the ball is equal to force downwards due to gravity. This is a fundamental concept that the stupid physics PhDs and moderators on other forums don't seem to be able to grasp.

You can see that in this case having infinite dwell time really doesn't help with generating speed or spin.

If anybody wants to learn more I will explain more and try to keep it simple.
 
I held my stiffest blade up the other day, and forced a ball against it so hard the ball nearly broke, yet I couldn't cause a relative deflection of the tip of the blade by even a micrometre! But I generated no spin or speed.

If you'd like to know more about my experiments, I'll upload a paper onto the arXiv in the morning. Just give me the word. But I can tell you that the conclusion I reached: no one on this forum can grasp stiffness.

Since you want to act like a smartass, if we take dwell time to be the total time the ball spends on the surface of the rubber, then it's a product of the effective area of the bat young's modulus and its reaction to the stress. Both of which are a result of the impact of a ball flying at high speeds against a bat that's meeting it at speed too. Why high speed? Because we need enough force to deform effective surface we're working with. The force of gravity you've chosen here is essentially an arbitrary and small force incapable of producing significant deformation, and so plays no part in our two step model of dwell time: the deformation due to the impact with the incoming ball, and the reaction from the blade to the stress caused by deformation (which shoots the ball back out).

If you had any insight at all, instead of leaving the ball lying on your bat and marvelling at infinities, you would have pressed the ball down to various depths into the rubber and taken measurements of how soon it takes the leave the rubber's surface when you release your finger. You'd have gained some information into the rubber's reaction to stress.

But no, you gave us that pointless post.
 
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"Stupid physics PhD"
 
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"Stupid physics PhD"
The problem is most PhDs forget what they have learned after taking the class and getting their degree. I am in a unique position where I get challenged almost once a week. Real life is not a pass fail exam. There is only being right with the optimal solution.
 
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I held my stiffest blade up the other day, and forced a ball against it so hard the ball nearly broke, yet I couldn't cause a relative deflection of the tip of the blade by even a micrometre! But I generated no spin or speed.
This is a good point. If the paddle didn't deflect then it wouldn't add anything to speed because it wouldn't spring back and add to the speed or spin of the ball. So?

If you'd like to know more about my experiments, I'll upload a paper onto the arXiv in the morning. Just give me the word. But I can tell you that the conclusion I reached: no one on this forum can grasp stiffness.
I can. I know all about natural frequency, damping factors etc. It is what I do.

Since you want to act like a smartass,
I just seem to have an intuitive grasp of how things work. Not just in TT but in industry. I have made a lot of money there. I realize that not everyone can grasp what is obvious to me but those that disagree should do some studying first.
You didn't say you disagreed with what I wrote.

if we take dwell time to be the total time the ball spends on the surface of the rubber, then it's a product of the effective area of the bat young's modulus and its reaction to the stress. Both of which are a result of the impact of a ball flying at high speeds against a bat that's meeting it at speed too. Why high speed? Because we need enough force to deform effective surface we're working with. The force of gravity you've chosen here is essentially an arbitrary and small force incapable of producing significant deformation, and so plays no part in our two step model of dwell time:
but it does in the simple case. If the ball is to remain in contact with the rubber the rubber/paddle can not exert a higher force on the ball than the force due to acceleration. The force of acceleration is only the force due to gravity in my example above. The upwards force is due to the rubber pushing up. Since they are equal the ball stays on the rubber. In all cases the force of the rubber on the ball must be roughly equal to the force of acceleration if the ball is going to stay in contact with the rubber.

the deformation due to the impact with the incoming ball, and the reaction from the blade to the stress caused by deformation (which shoots the ball back out).
Yes, but that is because the force due to deformation is greater than the force due to acceleration. Simply put, if the the ball is embedded in the rubber to the point that a 100 N force is being applied then to keep the ball depressed an acceleration is required that is so high a 100N force is applied to the ball. Good luck with even a pro being able to accelerate a ball at 100N/0.0027Kg=37037.03703703704m/s^2. No one can accelerate a paddle at that speed but if they could the ball would remain in contact with the rubber and embedded so that the rubber was exerting 100N on the ball.


If you had any insight at all, instead of leaving the ball lying on your bat and marvelling at infinities, you would have pressed the ball down to various depths into the rubber and taken measurements of how soon it takes the leave the rubber's surface when you release your finger. You'd have gained some information into the rubber's reaction to stress.
[/quote]
You have no insight. The condition for dwell time is simple. If the ball is to stay in contact with the rubber the force the rubber exerts on the ball must be equal to the force of acceleration. If the force due to acceleration is higher than the force from the rubber the ball will embed itself deep into the rubber. If the force from the rubber is higher than the force from the ball the ball will start to move away from the paddle. It is simple Newtonian laws of physics. One just needs to apply them.

But no, you gave us that pointless post.
It is pointless to you only because you are like the PhDs or worse on the other forums.

It really would be best if you looked up who I am before calling me a smartass. A lot of people have paid me a lot of money for my "smartass" calculations in all sorts of industries and fields. This makes you look pretty stupid for not doing some research before being so critical. You have not pointed out to anything that I said is wrong.
 
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This thread could be interesting, but all I see here is name calling and insecurity.

I could make this interesting by commenting on the terribly dualistic, western idea of "right and wrong" and "only one optimal solution" and why it's faulty in the real world, but that'd be even more off topic. :rolleyes:
 
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A blade does not deflect, spring back, and add speed to the ball. Adding speed to the ball, as in having it come back off a stationary bat faster than it came in, would imply that energy has come from somewhere. Bats do not have a mechanism by which they have some energy store which adds energy to the ball on every stroke and depletes the energy store. If they did, they'd either have limited lifetimes depending on how long the energy store holds up, or we'd need to replace the energy store every once in a while. Wood does not work like this. The best you can hope for is a perfectly rigid bat and a perfectly elastic collision, which obviously doesn't happen. So no blade of the type we play with can add speed to the ball, otherwise we'd have had perpetual motion systems long ago. It can merely hope to lose as little of that speed as possible. Low stiffness blades along the axis perpendicular to the blade face work by a more involved mechanism than just conservation of energy. Interestingly, I think a flexible blade could increase or decrease dwell time depending on its relative oscillating frequency compared with the properties of the rubber.

My friend, your credentials mean nothing here. Only your ideas are of value. Certainly how much money you've made in industry is not a sign of your mastery of nonlinear bodies. Your original post just made some irrelevant remark about equilibrium (irrelevant because we're dealing with non-equilibrium mechanics), claimed that the stupid moderators and physics phds don't understand it (even though I've tutored not-especially-bright 15 year olds who have a good grasp of the concept). But you were right, I didn't disagree with your first post. It was so trivial there was no need for disagreement. It was only irrelevant. Your second post, however, was very misguided. I disagree with much of it.

For your own future reference, there is no "force due to acceleration". Acceleration is the result of force, not the cause of it.

I wish you the best luck in your studies, but remember that ego will not get you far in academia. Work hard, be humble, work with knowledge for the sake of knowledge, and you'll do well.

All the best.
 
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Dwell time seems to be a hot topic among TT players but honestly I bet NO ONE really anything about it. All they know is the myths perpetuated by the TT forums.

Let me start by saying dwell time can be infinite. If your paddle is horizontal to the ground and you place a ball on it it will stay there indefinitely until you tilt the paddle. The dwell time is infinite. This is an extreme case but it is a simple case. If the ball is stationary that means there is no net force acting on it. The force of the sponge pushing up on the ball is equal to force downwards due to gravity. This is a fundamental concept that the stupid physics PhDs and moderators on other forums don't seem to be able to grasp.

You can see that in this case having infinite dwell time really doesn't help with generating speed or spin.

If anybody wants to learn more I will explain more and try to keep it simple.

The problem is that your assumptions and definitions are totaly wrong and you are obviously as you told before in other threads to narrow minded to accept reality.
--> "stupid physics PhDs" That's why i will not even try to explain you how you have to interpret it right.
 
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Okay guys. First off, RUN. Second off, run faster. Stay away. This is a trap. Nobody wants to be caught arguing with a menstruating woman; especially when she is trapped in the body of the planters mascot.

Pnachtwey, you have been so good for the last few months. You haven't called anyone an idiot in so long. Don't let the autism get the better of you. And let us all know when you are off the estrogen therapy.

If you didn't already know here is Pnachtwey's specially developed technique for creating as little dwell time as possible.


Sent from Deep Space by Abacus
 
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Pnachtwey, you have been so good for the last few months. You haven't called anyone an idiot in so long. Don't let the autism get the better of you. And let us all know when you are off the estrogen therapy.

Sent from Deep Space by Abacus

Peter, i had the same kind of impression as carl.
And not only the tone of your posts became better.
So, please don't fall back.

@Carl: :D
 
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sure, i'll bite. tell us more about dwell time. although i don't really see what wonders you can shed light on, except that it's a lot shorter than people generally think.

i find the main reason for so many disagreements between pnachtway and everyone else is that he takes everything literally but also lacks the subjective dimension of someone with more insight. when talking about dwell time he will talk about ACTUAL dwell time and ONLY about actual dwell time, without taking into the account that people with a lot more skill than he has have developed a feeling for the effect that the bat has on the hand when hitting the ball at different angles. because of this pnacht may have the edge when it comes to numbers but in practical terms and how this effects the game he will be completely lost. on the other hand, a pro may have no idea about the physics going on in the shots that he makes but he can still perform stuff that pnacht isn't even remotely aware of.
 
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sure, i'll bite. tell us more about dwell time. although i don't really see what wonders you can shed light on, except that it's a lot shorter than people generally think.

i find the main reason for so many disagreements between pnachtway and everyone else is that he takes everything literally but also lacks the subjective dimension of someone with more insight. when talking about dwell time he will talk about ACTUAL dwell time and ONLY about actual dwell time, without taking into the account that people with a lot more skill than he has have developed a feeling for the effect that the bat has on the hand when hitting the ball at different angles. because of this pnacht may have the edge when it comes to numbers but in practical terms and how this effects the game he will be completely lost. on the other hand, a pro may have no idea about the physics going on in the shots that he makes but he can still perform stuff that pnacht isn't even remotely aware of.

You make a good point. These discussions on the scientific side are of limited use to a player, but can be very important in designing equipment.

However, don't be misled. The guy who started this thread is posing as if he has information, but the knowledge and calculations he has presented so far are the kind of thing that a 16 year old school physics student with a poor grasp of the material would say. He says that for the duration that the ball is on the rubber, the force from sponge onto the ball and the ball onto the sponge must be roughly equal. This is untrue. When a ball strikes a bat, for most of the duration of the contact there is a varying difference between the force of the ball onto the sponge and the sponge onto the ball.at first the ball exerts more force, and increasingly the force of sponge on ball gets bigger. That's a very crude and simple explanation, but it's the kind of thing any good A-level student can explain. Our friend has only a rudimentary and half correct view of the simple physics.
I don't want to throw credentials around, because if you're wrong you're wrong, whoever you are, but I'll be starting a full time program of research into condensed matter and materials physics in a few months. I have some real background in the subject, and my impression is that our friend is making his experience with physics to be more than it really is.
 
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I got zero problem with Pnchy trying to explain the different aspects of impact dynamics. We have all had our shots at this topic. Pnchy appears to have a desire to specifically categorize and quantify it all. That is a noble objective, however, there are too many changing variables to achieve a coherent "numbers" explanation.

Pnchy is infinitely more experienced and qualified to go into that territory, but I think it is also a trap for him as well. One cannot completely apply all that stuff to a set and defined number of variables, when there are more at play... and those are darned difficult to measure and quantify.

It might be best served to explain some foundations and principles of how things work and interact. Even some of that is not an easy task to simplify and show relations.

One example is how the same model of table plays differently given different top layer and bottom layer floor materials (Straight concrete, wood over concrete, red mat over concrete, etc)

One joker in the deck I have always made known is hand pressure at impact. Control over this is known as "Touch" and many coaches advocate it, some can explain and show how to adjust and what happens given a different grip and pressure... but no ONE coach or player has assembled a complete coherent explanation covering most situations.

Grip pressure at impact has a lot to do with the result and it is likely the most under-rated and least discussed thing in Table Tennis stroke and impact dynamics. Out of anyone on this forum to my small knowledge, Next Level gets it and appreciates it to use it for his advantage in matches.
 
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A few concepts of things affecting the dwell to get the result you want.

We all seek maximum dwell, and in most cases, you need max dwell for max spin, however, we are not trying for max spin on all our shots. Sometimes we are going for max or near max peed with enough spin to control it, or we go for a simple control shot, etc. So, there is no ONE set way to hit ever every ball. There will unique changes in the factors and how we apply them to get the result, which is different for different players given the same or different ball.

We assume we are in close enough to optimal position, are on balance, and impact the ball within our hitting zones.

The incoming speed, spin, height (where we choose to impact it), and vertical direction of travel are factors. There is a different impact required to get the same desired result, or the same kind of impact will make a different result.

The bat speed at impact, as well as the acceleration during dwell are huge factors in determining how long or short the dwell is and the result of the ball.

Bat angle is important as you are using more or less sponge and sponge/topsheet pips rebound... or more or less of the blade's properties.

EDIT: Your Bio-mechanics greatly affect your efficient acceleration (and bat speed) and how you make impact.

Grip pressure at impact is a huge factor that determines both rebound pace, how the ball stays in dwell, and how it will come out.

Another under-discussed thing is how one gets the ball to have the topsheet wrap around it, as well as how to engage the sponge. These are really critical things affecting the dwell, and more importantly, the result of the ball.

I have zero academic credentials to back up anything I say in this matter. I do, however, have practical experience as an amature player as many of us have, in knowing what/how/why things affect our result. Long dwell is real important for heavy spin, and anyone facing me as an opponent knows I make heavier spin on my openers and some of my finishing shots than they ever experienced.

At teh end of the day, some good amature players and just about ALL of the elite amature players how a very strong understanding of these things and do not consciously think about them in a match. They know how to adjust for a given ball to make the result what they are trying to accomplish - all without any math/physics background. For these, it is a matter of first-hand learning, knowledge of what does what given an input, and thousands of hours of training and practice.

On the ground, we call this PRACTICAL EXPERIENCE and there is no substitute for this. If one is confident in this, he or she will waste no time in decision making, all that stuff will be sped up for them to allow them to use the time to read opponent and the ball, then quickly select and execute an effective response.
 
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A blade does not deflect, spring back, and add speed to the ball. Adding speed to the ball, as in having it come back off a stationary bat faster than it came in, would imply that energy has come from somewhere.
I never said the ball will come off the bat fast than it came in. That would imply a COR > 1.

Bats do not have a mechanism by which they have some energy store which adds energy to the ball on every stroke and depletes the energy store.
When a blade deflects the kinetic energy is being converted to potential energy as they flex. Faster blades will return a higher percentage of the energy. During this time they have some energy like a stiff spring. Hard stiff blades don't absorb much energy so the don't lose much. Tell us on another thread what make one blade faster than another. You are trying to derail dwell time discussion.

If they did, they'd either have limited lifetimes depending on how long the energy store holds up, or we'd need to replace the energy store every once in a while. Wood does not work like this. The best you can hope for is a perfectly rigid bat and a perfectly elastic collision, which obviously doesn't happen.
Blades do flex but some flex more than others and my Firewall Plus doesn't appear to flex at all but that is only a visual observation.

So no blade of the type we play with can add speed to the ball, otherwise we'd have had perpetual motion systems long ago.
The energy isn't generated by the paddle it is generated by the player.
So what makes one blade faster than another?

It can merely hope to lose as little of that speed as possible.
True for a stationary paddle.

Low stiffness blades along the axis perpendicular to the blade face work by a more involved mechanism than just conservation of energy. Interestingly, I think a flexible blade could increase or decrease dwell time depending on its relative oscillating frequency compared with the properties of the rubber.
We agree here. So where is the energy being conserved?

My friend, your credentials mean nothing here. Only your ideas are of value. Certainly how much money you've made in industry is not a sign of your mastery of nonlinear bodies. Your original post just made some irrelevant remark about equilibrium (irrelevant because we're dealing with non-equilibrium mechanics), claimed that the stupid moderators and physics phds don't understand it (even though I've tutored not-especially-bright 15 year olds who have a good grasp of the concept). But you were right, I didn't disagree with your first post. It was so trivial there was no need for disagreement. It was only irrelevant. Your second post, however, was very misguided. I disagree with much of it.
The debate about dwell time went on for a long time on TT forums. NO ONE did the simple math except me. Years later Baal finally did his "napkin" math approximation.

For your own future reference, there is no "force due to acceleration". Acceleration is the result of force, not the cause of it.
???????!!!!!!! You seem to think that only a=F/m applies. All those books that have F=ma must be wrong then.

So if put a ball on a horizontal blade the ball exerts 0.0027Kg*9.807m/s^2=0.0265N on the paddle and the paddle exerts the same force on the ball. Now if I accelerated this paddle upwards at 9.807m/s^2, 1g, won't the force between the ball and paddle be doubled? Gatcha! The force between the ball and paddle will change by how the paddle is accelerated and this is a key point to understanding dwell time.

Grandpa, you are only trying to get some notches in your belt and it won't happen so start you own thread on blades, flex, energy and speed. Now go away and start your own thread about the speed of blades.
 
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Pnchy said:
The force between the ball and paddle will change by how the paddle is accelerated and this is a key point to understanding dwell time.

I believe this to be a true and very central concept to understanding and applying inputs to achieve the desired result. I believe there is a lot more in play, but this is a very important thing.
 
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The problem is that your assumptions and definitions are totaly wrong and you are obviously as you told before in other threads to narrow minded to accept reality.
--> "stupid physics PhDs" That's why i will not even try to explain you how you have to interpret it right.
How does one argue with that? What assumptions and definitions are wrong? Be specific.
The case where the ball is resting on the blade seemed to be simple enough that Grandpa accepted it.
This is why I get pissed and call people idiots. They throw stones without making a good counter argument. The problem is that few can.

You have wasted my time and bandwidth. I should have added to the title to this thread to "and they aren't idiots"

Be smart guys and back up you claims with facts. Grandpa is at least trying.
 
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