dwelltime

Imagine seeing a blade all in action "flexed" (which is a too simple term but so common that it,s hard to explain not using it). Midst between tensioning and relaxationphase.
I don.t wonder that this has the maximum load.
But I do wonder what maximum load for physics ?
What term in Physics represents this apart from pressure forces (action and reaction).

Is it represented by elastic energy, elastic power or both ?
I was thinking energy but now I tend to the idea of both even when the units wouldn,t immediately fit for that moment. (in the end it does)

Idea is that "loading" upto where relaxationphase starts has  E*T=> P (elastic power thus).
Dwellperiod overlaps with this T from beginning  of contact to where the sponge is maximum compressed but this T starts before dwell starts from the hands of players.
Loading the sponge nd ball contributing for this can be added to this for a total elastic Power in between the technical  tensiningphase and relaxationphase for all springs involved.
Then the relaxation period starts and follows as  P/T => Ek. "Breaking down" P elastic into kinetic energy.
But other T now. Much shorter as it,s only last part of the dwellperiod where the first part of the dwellperiod was only a small part for the total T for loading the paddle.

Hence an enormous increase of kinetic energy Ek. Large part of the energy that the player brought in was immediately connected to the blade (so not with a kinetic in between). This part of energy waits to come out until the relaxationphase starts.

The standard collision idea fails completely then for this part because it assumes preservation of kinetic energy (instead of generating it).
There is no physics law that says kinetic energy must be conserved.
Energy must be conserved is an existent physics law (no increase or decrease) but not for kinetic energy in particular.

The blade is just an extension of the hand for this offcourse. Hand muscles and fat is softer then wood even tensioned muscles. So that allows deformation also and also adds to the elasticity.
Looping with a stiff blade is still possible but needs a good hand for it.
But when bladehandling makes a flexible blade resonate to this it doesn,t cost energy for a stroke.
Except when dwell is too short for making this happen. A thicker sponge can do the trick then and Looping instead of flathitting.
 







Edited by mercuur - 10/02/2013 at 5:08pm

A sponge is compressed between the ball and blade. Between the actionforces and reactionforces (both from both sides). Better avoid the long story telling about how a ball compresses a sponge or penetrates into a rubber.  TT balls don,t penetrate rubbers. At least not that I have seen.

The paddle contact's the ball with elastic energy in the blade not equal to zero for a powerloop or flathit. .

P=E/sec  is not a physics equation. It,s as if it has a standard dwell of one second to compare every other dwell period to.
The physics equation is P=E/T (unit/unit) whatever units used. Not energy per second. All units belong between brackets for ratio's or equations. Not one of the two between the brackets and other in the equation or ratio.

It all depends then what you can or want to set for the equation. E and T as a standard period or P or nothing set ?
In general I would say nothing as it all depends from different strokes, different paddles, rubbers, blades, players. Same stroke with a different blade or rubber or player all makes it a different stroke from one variable.
W=F*S.  P=E/T.
F depends on spongepressure. But S/T can be different with same amplitude or same dwell. Depends on resilience, Same as between  soft and slow for a rubber or equally soft and quick.




Edited by mercuur - 10/02/2013 at 3:09pm

Larry, you haven't been around here a lot lately to experience our man AgentHEX. 

You have a good night too, AgentHEX. 

AgentHEX wrote: Larry, why resort like this? Everyone can see your dwell time logic is not going to work out, so there's no need to pretend otherwise with some unconvincing excuse that there's some meaningful difference between "tennis" and "tennis example" which you btw can't be bothered to explain.

hi folks esp tt4me
i would suggest the following for measuring dwell;
When we brush the ball finely, a 'zzz' sound is clearly made. it has perceptible length.
If you record and play this back you can display the result with sound wave analysis software. You can also record the shotmakers comment immediately after the shot is made as to whether the dwell he perceived was longer or not
this might shed more light than the video evidence in some ways
What do you think?

AgentHEX wrote: Ah ok, so you can't be bothered to explain what you mean when it's inconvenient. I hope those students don't ask too many question, too.

AgentHEX wrote: larrytt wrote: Sorry, AgentHEX, not interested in continuing or playing math games. Is this some kind of joke? You claimed I didn't understand you, so I'm literally asking you what you mean. Using numbers (or charts or whatever) is generally how quantitative things are expressed in this world.  Even when I point out my exact words - "The tennis example is apples and oranges" - you insist on changing my words, and say, "Apples and oranges means that tennis and TT cannot be compared." I didn't say that. I said "The tennis EXAMPLE" (CAPS added for emphasis) cannot be compared. That means the specific EXAMPLE you gave, not tennis in general. But I've already explained this, and you've chosen to continue to misquote me. Can you explain why you keep changing my words ("The tennis example") to tennis in general?  -Larry Hodges How exactly is the tennis example apples and oranges anyway? I can't find any reason other than maybe you say so, but that's not a very good reason.

larrytt wrote: Sorry, AgentHEX, not interested in continuing or playing math games.

Is this some kind of joke? You claimed I didn't understand you, so I'm literally asking you what you mean. Using numbers (or charts or whatever) is generally how quantitative things are expressed in this world.

Even when I point out my exact words - "The tennis example is apples and oranges" - you insist on changing my words, and say, "Apples and oranges means that tennis and TT cannot be compared." I didn't say that. I said "The tennis EXAMPLE" (CAPS added for emphasis) cannot be compared. That means the specific EXAMPLE you gave, not tennis in general. But I've already explained this, and you've chosen to continue to misquote me. Can you explain why you keep changing my words ("The tennis example") to tennis in general?  -Larry Hodges

How exactly is the tennis example apples and oranges anyway? I can't find any reason other than maybe you say so, but that's not a very good reason.

I thought I could let this thread die, die, die but no.
Larry, did you look back through the thread to find my high speed videos shot at 2000 FPS?

1.  I don't like the term dwell time.  Dwell implies being stationary and the ball isn't stationary on the rubber.  I prefer the term contact time.
2.  I thought that Baal confirmed that we couldn't detect short differences in contact time.  By short I mean a few hundred micro seconds.
3.  Larry,  you are wrong and AgentHex is right about this accelerating through the ball stuff.  By definition, if the paddle is still accelerating then it hasn't reached maximum speed and if you want to hit the ball fast you want as much paddle speed as possible.  Also,  AgentHex is right in that the amount of speed increase during the contact time is very small and makes little difference.
4.  I have repeatably ask people to tell us how to increase the dwell time.   Hitting the ball softly will not do it.  So here is a quick calculation.   Earlier mercuur asked me about how much force is applied to hit the ball.  For a typical hit the peak force is about 100N.  At that point the ball is embedded in the rubber and compressed as far as it will go.   If the paddle is accelerated so that the paddle continues to apply 100N the ball will stay compressed and actually be stopped or dwell relative to the paddle.  Now I ask everyone and anyone.  What does the acceleration need to be so that the paddle continues to apply 100N on the ball?  I figure that that a person might be able to accelerate a paddle at most 20G but probably much lower.  That isn't near high enough if the rubber, ball, and wood are pushing the ball away at 100N.  Sure,  I agree that accelerating through the ball increases dwell time but it is microseconds and Baal said we couldn't make that distinction.  Long ago I posted a thread about a trampoline on a spaceship.  I am sure that most that I was nuts at the time but the problem is exactly the same.
5. If you want to maximize paddle swing then one should do similar exercises as martial artists.
6. Given that the student is not a martial artist then it is best to find where in the student's swing the paddle speed is the greatest and make a point to hit the ball at that point.   Now everyone can see the futility.  That would require super foot work so that the ball could always be hit at the optimal point.    The real goal should be to make the optimal point as big as possible because no matter how good you are there will be times when the foot work is not good enough.

AgentHEX wrote: What? Did you not clearly state above that dwell time is longer for soft shots AND power strokes?

larrytt wrote:

Larry H calling you a troll - Priceless. It's so funny that you don't know that you don't know.
[/QUOTE]

AgentHEX wrote: larrytt wrote: AgentHEX wrote: larrytt wrote: AgentHEX wrote: The feeling of dwell is not really a real thing but rather something that exists in someone's head so it's kind of hard to comment on. I don't mean that in any disparaging sense, that's just how it is. What is your evidence for this? -Larry Hodges 1. Tennis players describe the same feeling of more dwell for harder shots, yet we know harder tennis shots actually dwell less. It might not be the same for TT, but it illustrates the principle. 2. You can check the physiology of whether humans can meaningfully differentiate sub-millisec sensations. I'm quite sure not. 3. Feelings are very much a matter of the mind. Things without minds similar to ours do not have feelings. This is just how reality/language works. The tennis example is apples and oranges. How so? There are distinct differences but I wouldn't necessarily claim the TT player is so much smarter as to not make the same misjudgement. If you want to maximize dwell time, of course you hit the ball softly. You probably get the most dwell time of all when pushing or serving with spin. The dwell time we are talking about is when you are using power and sinking the ball into the sponge. So you believe that dwell is simultaneously longer on softer AND harder shots, and that this is unique to TT amount racketsports. Interesting. You used the example of "harder" shots when that's not what we're talking about in terms of table tennis power, which is speed AND spin. As I've posted, increasing the apparent dwell time affects spin even more; in fact, it gives so much spin that you can loop with more speed, using the extra spin to control the speed.  Can you see the problem when you tautologically equate longer "apparent dwell time", which is a feeling not physically measurable, to some real physical phenomenon, and question anyone who claims the former may not be accurate? Note the burden of proof here isn't on me. As to the millisec differences, how do you know they can't differentiate this? Have you cited a study? A person might not be able to react to something in a millisecond, but he might be able to feel it. There's a huge difference there.  A millisecond is a very short period of time, so short that any "feeling" needs to be more akin its frequency rather than duration because we really have nothing to reference for events in human spans that short, except this is nonrepeating so no such luck. Member Baal here is supposed a pro at this so maybe has something to offer. Your third example isn't evidence.  -Larry Hodges My third point is definitionally true.

Edited by larrytt - 10/02/2013 at 2:12am

AgentHEX wrote: larrytt wrote: AgentHEX wrote: The feeling of dwell is not really a real thing but rather something that exists in someone's head so it's kind of hard to comment on. I don't mean that in any disparaging sense, that's just how it is. What is your evidence for this? -Larry Hodges 1. Tennis players describe the same feeling of more dwell for harder shots, yet we know harder tennis shots actually dwell less. It might not be the same for TT, but it illustrates the principle. 2. You can check the physiology of whether humans can meaningfully differentiate sub-millisec sensations. I'm quite sure not. 3. Feelings are very much a matter of the mind. Things without minds similar to ours do not have feelings. This is just how reality/language works.

fatt wrote: if it's a comparison between 2 rubbers it does not matter how much dwell they have; the only interesting factor is which has more or less depending what the person wants.

Sure, but which has more or less? I've certainly demonstrated where "experienced" or "respected" reviewers' accounts differ (might be for throw, but same difference that it's not worth checking).