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dwelltime |
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mercuur
Super Member Joined: 01/06/2004 Status: Offline Points: 384 |
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Inquisition on suspicion : http://en.wikipedia.org/wiki/Inquisition Edited by mercuur - 10/02/2013 at 6:29pm |
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larrytt
Silver Member Joined: 04/04/2005 Location: United States Status: Offline Points: 971 |
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AgentHEX believes that if he says something over and Over and OVER it makes it true simply because the other person tires of arguing. That's how trolls think. Hopefully the moderators will eventually tire of this. I wonder how many other threads he's destroyed this way and how many posters he's driven away? The funny thing he probably really believes the stuff he's posting, and there's no way of ever getting reality through to him.
-Larry Hodges
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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I don't think that was "established" at all. Your claim was that given a certain deflection, the speed in the equation denominator shows it's an inverse relationship. See if this make sense: if speed X and deflection Y are related by unknown (but deterministic) equation Y=F(X) and dwell=G(X,Y), you cannot simply used a fixed Y and claim anything insightful from dwell=G(X, 2mm), because the actual equation is necessarily dwell=G(X, F(X)), where F(X) is generally not 2mm.
Have you looked into this? |
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smackman
Assistant Moderator Joined: 07/20/2009 Location: New Zealand Status: Offline Points: 3264 |
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I want a apple ................... hmmm nah orange
sorry too much dwelltime
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Ulmo Duality,Donic BlueGrip C2 red max ,Yinhe Super Kim Ox Black
NZ table tennis selector, third in the World (plate Doubles)I'm Listed on the ITTF website |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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Larry, if this is the case, why do you write far more verbose excuses than answer the rather simple clarifications requested which would at the very least call what you claim is a bluff? It's hardly unjust to explain a relationship you proposed, or why some minor semantic you're arguing matters. The mods should consider how it reflects on this forum before jumping at the bit to ignore context to pretend this is OT or whatever. Edited by AgentHEX - 10/02/2013 at 6:51pm |
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wturber
Premier Member Joined: 10/28/2008 Location: United States Status: Offline Points: 3899 |
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I think our intuition on this may be overly influenced by the cartoons we watched as kids that exaggerate and distort Newtonian physics and the ways that materials react. While we know that what cartoons depict is not correct, it does kinda feel right in some ways. I think this make it easy for us to imbue things that we experience with characteristics that just aren't there.
I'm reminded of a story in Matthew Syed's book, Bounce where top level players were convinced that a player well know for his lightning fast close to the table play took it as obvious that this person had super-fast reflexes. But actual measurements showed his reflexes were actually quite ordinary. They had confused a fantastic anticipation with fast reflexes. As we go about living our lives, we constantly fill in missing information. We are largely unaware that we are doing this filling in. For instance, it isn't immediately obvious to us that everything we see is blurry except for a spot of about 1degree. Our experience is that (assuming good or well corrected vision) that our vision is generally sharp while the vast majority of it is very much out of focus. We also manage to look past the fact that we constantly see two images, not one and even use that to our advantaged (stereoscopic depth perception). And somehow we manage to "fill in" the blind spot that each of our eyes has without noticing it. In fact, we have to take special steps to bring the blind spot to our attentions. Human perception - as versatile and wonderful as it is - has severe limitations. So we should be careful about what we infer from it if our desire is to be accurate. Just because something seems to be a certain way doesn't mean that it is reasonable to assume that this impression is correct. It might be. But depending on the nature of what is being observed, it very well might not. Things that occur very quickly certainly fall into the area where we should be careful about how much we trust our impressions. And this is without even considering how we use back-figuring to build narratives to make sense to what we've only partially observed. The building of these narratives is one of the ways that honest people simply get stuff wrong when giving eye witness accounts of their observations. And there are other sub-conscious things besides back-figuring that influence the narratives that we build to explain our world as well. If you really want to know about a lot of this stuff, you should probably shoot some high speed video (or maybe stills) and directly observe what's going on - and be prepared to be surprised. Edited by wturber - 10/02/2013 at 7:05pm |
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Jay Turberville
www.jayandwanda.com Hardbat: Nittaku Resist w/ Dr. Evil or Friendship 802-40 OX |
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ZApenholder
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Thread destroyed: I can think of about 5 or 6 (but i'm sure there are many many more), which went to simple threads to many many many pages of unreadible posts Posters driven away: Me for sure. And I sure have the same feeling that he really believes in his stuff. I guess he should show us results and get other people (students) to show his creditblity, than oppose to hiding being a computer and act like he has a phd in table tennis as well as other specialities too. |
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larrytt
Silver Member Joined: 04/04/2005 Location: United States Status: Offline Points: 971 |
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Because when I did multiple times, each time you'd change what I wrote and posted it as if it were my words, and then attacked those words as if they were mine - just as you do with so many others. Plus why would I spend time with a troll, which just takes away the time I should be spending in my real profession as a full-time professional table tennis coach and writer? (Yes, while you spend your time theorizing about things you have little experience in, I'm actually living the dream. You could learn a lot if you opened your mind and closed your mouth. And I'm not talking just about the dwell time stuff where you keep changing my words and taking them out of context. My questioning of something about dwell time does not mean I'm asserting something, but you don't seem to make the distinction.) The goal of a troll is to irritate and get a response out of others, so I salute you for your skill at doing so. Hopefully the moderators will catch on to how many threads you hijack and people you drive away. Have a good day; I'm not wasting any more time with you here. -Larry Hodges Edited by larrytt - 10/02/2013 at 6:58pm |
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larrytt
Silver Member Joined: 04/04/2005 Location: United States Status: Offline Points: 971 |
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Yes, I'm one of those posters this troll has driven away. I may respond to some of the stuff he posts about me (with short answers), but I have little confidence in having any serious discussion that he won't hijack. So I'm gone. -Larry Hodges
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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I'm sure it'll somehow be blamed on me that those multiple explanations were mysteriously stricken from the record above.
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larrytt
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You are no doubt correct. Often people mistake questioning something with asserting it is not true. I think there's a lot here that's not quite understood, which explains why people versed in physics often disagree on this stuff (I've seen many of these debates for years), and what they tend to believe often isn't what we seem to see in practice - though of course some of that could be illusory. Anyway, the informative to trolling ratio right now (due to one person) is too high for me. But I thought I owed my National Champion Doubles Partner a response!!! -Larry Hodges
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Professional Table Tennis Coach & Writer
Member, USATT Hall of Fame USATT National & ITTF Certified Coach Former Chair, USATT Coaching Committee www.TableTennisCoaching.com www.MDTTC.com |
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larrytt
Silver Member Joined: 04/04/2005 Location: United States Status: Offline Points: 971 |
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No and no.
Edited by larrytt - 10/02/2013 at 7:09pm |
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Professional Table Tennis Coach & Writer
Member, USATT Hall of Fame USATT National & ITTF Certified Coach Former Chair, USATT Coaching Committee www.TableTennisCoaching.com www.MDTTC.com |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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> which explains why people versed in physics often disagree on this stuff (I've seen many of these debates for years),
The people who appeal to their authority are generally least capable of appealing to merit, so I hope you didn't take their word for it. This is literally intro newtonian physics; there are correct answers here. |
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pingpongpaddy
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I think this is timely. I cant give an informed critique of all the calculations and analysis that has gone on, but my gut feeling as to whether the ball compresses the sponge to the extent that seems to be claimed is doubtful. In my opinion the bat brushing the ball at a very fine angle is not going to cause the ball to sink into the sponge very much. The other thing i note is that there is a perceptible recognisable and measurable sound from a fine brush contact. Now when I hear this sound it seems likely to be longer than expected. But anyway why not get a decent microphone and measure it with software? |
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inactive dotec carbokev
yin he galaxy 1 p ly FH moristo sp AX MAX bh moristo sp ax max |
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larrytt
Silver Member Joined: 04/04/2005 Location: United States Status: Offline Points: 971 |
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False, no, false, and perhaps.
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Professional Table Tennis Coach & Writer
Member, USATT Hall of Fame USATT National & ITTF Certified Coach Former Chair, USATT Coaching Committee www.TableTennisCoaching.com www.MDTTC.com |
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AgentHEX
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That's akin to what they did on that german forum. JRSDallas posted some freq domain transforms of this here and people were apparently impressed because it had numbers or something. It doesn't tell much about the contact per se because most of the sound is residual vibrations. |
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tt4me
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I don't see how you guys have the time for this. I would rather be searching for the truth.
Jay's point about the limitations of perception is valid. I often have customers tell me what they think they see but when I get high speed data it turns out to be something completely different. This is why I am not interested in the perception but in what is actually happening. AgentHex, I never claimed the compression distance was constant. It will obviously vary as a function of the impact speed.
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AgentHEX
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Sure, but your claim of an obvious inverse relation was predicated on keeping it fixed while still allowing speed to vary. The two are not independent vars even though some liberty was taken for that napkin estimate.
Rhetorical, I take it? Edited by AgentHEX - 10/02/2013 at 7:48pm |
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wturber
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You could give it a try. But I think you may need to control room acoustics so room reflections don't muddy things up. And even then, I'm not sure what you can conclude since the racket may be generating sound after the ball is long gone. |
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Jay Turberville
www.jayandwanda.com Hardbat: Nittaku Resist w/ Dr. Evil or Friendship 802-40 OX |
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pingpongpaddy
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I agree it requres a lab But on those very fine contacts I would guess the rubber/sponge sheet insulates the blade from the ball contact thus minimising resonance from the wood. A bigger Problem might be noise from the joints of the human arm making the swing But perhaps I am not cut out for science...... |
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inactive dotec carbokev
yin he galaxy 1 p ly FH moristo sp AX MAX bh moristo sp ax max |
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mercuur
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Flexibillity for blades makes no distinction between stiffer from a more rigid construktion and stiffer from higher elastic strength. Many stiff blades have a strong elastic strength and are stiff for low impact but behave more flexible on a powerloop as blades with less elastic strength but more rigid build. Catalogue values give the stiffness on a norm impact while it has no norm in play with al different impacts. For bladebehaviour (in play) it needs a variety of impacts/strokes and then the flexibillity on these impacts/strokes makes it a more dynamic graph. For a rigid blade it sees the graph flatten then where the blade progressively stiffens for increased impact. (torque). Trying to make it flex more then that (with two hands) would break it, At medium impact the graphlines for different blades can cross each other for same flex on that impact. The more rigid blade will be more flexible with lower impact but stiffer for higher impact. Rigidity has an effect that the ball will impact a blade that stiffened more in the neckzone from the players stroke towards the ball before the contact with the ball is made. A blade with strong enough elasticity equally stiff but less rigid stays softer for the ball when the ball increases the impact more. This makes the contact for the ball softer and gives the experience (which is more then just feeling) that the ball stays longer on the paddle with the sponge eventually compressing to same extend when the blade rebounce is quick and strong enough. Strong but not quick énough or quick but not strong enough wont do this. It needs a certain balance for this and some rigidness improves the quickness. A one ply limbablade of 90 gr for a lamina could be strong enough but lacks the abillity to use the flex from lack of quickness and rigidness. That has to do with the large distance to the neckzone with most torque impact but least resistance for torqueflex from bladeshape and handle construktion. Edited by mercuur - 10/03/2013 at 3:55am |
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tt4me
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I wouldn't use sound. The sound may persist even after contact. I would use acceleration. From the speed after impact formulas used to compute the speed after impact the paddle may slow down a half a meter per second over a period of the dwell time of about 1 millisecond. That is average deceleration rate of 500 m/s or roughly 50g. Even if the speed of impact was much less the rate at which the paddle slows down is still very high. At this point the designer needs to make a decision about what is to be measured. A person will swing the paddle and accelerate it at about 20g at the fastest. The impact with the ball can be easily seen as the paddle decelerates over the contact. The trick will be to record the acceleration at a high sample rate then count how many samples the contact lasts. My 'lab' None of us really know what we were doing. The guys that usually use the camera are mechanical guys. I am holding the paddle and trying to move it around so it is in the field of view. The camera operator is trying to find the best settings. Later I/we added two more lights so we could get to 2000 FPS. It takes some setup time to make a good video. The guy operating the camera can design just about anything electrical. |
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mercuur
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500 m/sec ^2 ?
For a 200 gr racquet the mediate force would be F = 0,2 * 50= 10 (N) . That,s a mediated weight 1 (kg) as equivalent. For maximum compressed sponge it will be much higher. I would think that,s too high. And to the ball from action is reaction 10 N = 0,0027 * a Fills in as a = 3700 M/sec^2. But seconds don,t fit in a millisec. It needs to do likewise then as you did for the batdecelleration. :
This increased numeric decelleration from 0,5 (m/sec^2) to 500 (M/sec) / 1 (millisec). to fit to the short period of dwell. Accelleration for the ball increases the same then for numeric value with a faktor 1000. Otherwise it discriminates between accelleration and decelleration. Consekwently that's 3.700 (m/sec^2) * 1000 = 3700.000 (m/sec) / (millisec). Millisec between brackets because it,s a unitconversion for this part. The next following 0,999 millisec has no contact with the ball. No accelleration no decelleration. So delta V for the ball would be 3700.000 (m/sec). How do you explain that ? Edited by mercuur - 10/03/2013 at 7:50am |
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tt4me
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See above. You need to multiply the 3700m/s by the dwell time. It is so easy. Just keep the units straight. |
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mercuur
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What,s straight ? When you myltiply 3700 (m/sec)* 0,001 (sec) it makes 3,7 (Msec/sec). Your sponge is too thick. ------------------- Edited by mercuur - 10/03/2013 at 1:41pm |
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wturber
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Straight is so that the terms are multiplied or divided as well as the numbers. 3700 m/sec * 0.001 sec - 3.7 meters ( the "sec/sec" term drops out and need not be shown because it is equal to 1). I think, perhaps, that's what he meant by "straight." I'm not sure where the 3700 m/sec came from, but I don't think anything in table tennis is moving that fast. 37 m/sec seem more in line with reality and that yields 3.7 cm of movement in 0.001 seconds. |
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Jay Turberville
www.jayandwanda.com Hardbat: Nittaku Resist w/ Dr. Evil or Friendship 802-40 OX |
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mercuur
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The faktor 1000 is from 1000 (msec) / 1 (sec).
That makes it a unitconversion for n. Similar as switching between inches and cm except much easier because it corresponds with decimal system that we are used to. With a ruler that has inches on one side and cm on the other it,s also easy to switch for a carpenter. On purpose or by accident. Switchung such a ruler unnoticed to sawcut a length of wood can be catastrophical for a produkt to make. 100 (cm) makes a length 100/2,54 (inch) = 39 (inch). It needs a faktor 2,54 to correkt. But this must be done before cutting the length of wood or afterward it,s suddenly a faktor 1/2,54 =0,39 too short. When this is for one of four chair legs it won,t be a chair to sit on. It,s handier then to use a cm ruler or an inch ruler or use the first leg as a meassuring length for the other three. Reading 23,237 sec on a clock it,s easy done to read this as 23237 (millisec). Just ignore the komma. Even easier as switching the ruler for a carpenter. On purpose or coincidental. Edited by mercuur - 10/05/2013 at 6:11am |
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