dwelltime

Fatt, want to put it to a vote?

I'm out of here.  Bye.

see PM

AgentHEX wrote: ???? wrote:   Also, how can we tell that a setup is hard or soft? tt4me wrote: The dwell time will be longer with softer blades and more sponge.  We all know that. "More" sponge or softer sponge?

Tassie52 wrote: My teeny, tiny brain is telling me that a reaction by definition is a response to an action. Without some kind of stimulus there can be no reaction. When playing a shot in table tennis, there are three different kinds of stimulus that a player can react to: what she sees, what she hears, or what she feels. (Listed in that order because, when our opponent plays their shot, that is the order we get the stimulii in.) Our reaction times are entirely dependent upon how long it takes us to receive the stimulus, transmit it to our brains, process it and then relay the necessary reaction to the parts of the body we want to involve in our response. My teeny, tiny, non-medical brain tells me that what we see is always going to be the primary stimulus for our reaction, because it is processed faster than either of the other two. Light travels faster than sound; our eyes see what is happening on the other side of the table long before we feel the ball hitting anything; and the distance from our eyes to our brain is considerably shorter than from our hand (no matter what the speed of the nerve impulse conduction). To suggest that any of this takes places without the brain being involved is, at best, to confuse reflexes (when the doctor hits our knee with his little hammer) and playing a stroke in table tennis. At worst, it suggests to my teeny, tiny non-engineering brain that someone is trolling. And, no, there is not a snowball's chance in Hades of us ever reacting to the ball hitting the blade in time to change what we have already decided to do. The ball is long, long gone.

As mentioned by super-expert Baal himself, the shortest reflexes are not those processed by the brain such as vision, but rather directly by the nervous system. There's no reason to believe that repeated training of the same reactions affect these reflexes, as generally visible in high level athletes. The limit here is not the speed of light/sound but rather 1. the must slower propagation in cells. 2. thinking is even slower. Even the exact speed for the simpler former effect is generally non-trivial in the small: http://en.wikipedia.org/wiki/Action_potential; the diff can be quite significant.

Baal's statement that a "reaction" needs relatively slow brain-thinking is simply misleading. He knows this and is rather transparently trying to manipulate the mods (and other members apparently) to ban me. Let's hope they're not so easily played off.

I wrote exactly:  "Nobody can react fast enough to do anything to change the shot by feel before the ball is already well on its way to the other side".  This is based on the idea that actual time the ball is in contact with blade is around 1 millisecond.  Also some people have thought that long dwell-time equipment would let you do that.  

AgentHEX says I am wrong because of "reflexes" --- or something --- and then says there are all kinds of things about the nervous system I "should" know and somehow didn't consider when I made that remark.  If he is saying the statement is wrong, then I suppose it means that he thinks that somehow the nervous system can make a response that leads to a contraction of muscles in response to some stimulus in less than 1 ms. 

On the other hand, if he thinks that the statement is actually correct (and later he seems to saying it is obvious) but he just wants to dispute something for the sake of stirring things up, (based on something surrounding the word reaction?)--- well that would be trolling, defined in Wikipedia as: "a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory, extraneous, or off-topic messages in an online community (such as a forum, chat room, or blog).... with the deliberate intent of provoking readers into an emotional response."

Now just for the sake of argument, based on all of the threads in which AgentHEX has contributed here, what is the likelihood that the intent of his comments is exactly the thing defined above?  So yes, I would prefer that he was banned (again) if he keeps on doing this kind of thing.  But I have no say in the matter. 

One last thing.  Eventually the sensory stimulus from your hands may tell you, "oh crap, that doesn't feel good, I just mis-hit the ball".  You will also see where the ball is headed, and also maybe what your opponent is getting ready to do to punish your error.  You also probably notice that it sounded wrong.  You will have time to decide to maybe begin to get into a defensive posture or whatever, you probably even have time to think about where you should be moving to minimize the disaster.  But about the shot you just hit??  There is no Jedi trick you can do to undo the bad contact you just made or somehow turn it into a better shot.

Except call a let if a ball came onto the court.  And you can say sorry if the shot that just came off your finger caused your opponent to miss.

"At 100-200 meters/second, a nerve impulse moving up your arm would travel 10-20 cm in that time, far short of your brain (unless your arms are very very short ).

Of course I wrote that!  It is true.  What in the name of god is misleading about it?  Skeletal muscles don't move themselves.  Even a monosynaptic reflex requires nerve impulses to propagate towards the CNS, then make a synapse, and then the impulse has to come back out to the muscles, and the sum of that would be an order of magnitude longer than time ball is still in physical contact with blade. 

Also I never claimed that visual processing is faster than a reflex.  Where did I say that?  Nowhere.  Did I imply it?  No.  Did I meant to imply it?  Absolutely not.  Is the term reflex even relevant to the discussion?  Not really, except for postural reflexes that keep you from falling over.  I said you have time to make all sorts of decisions based on visual, auditory, tactile stimuli after you hit your shot and before you have to make the next one.  Otherwise you wouldn't be able to play.  You even have time for a thought about what you are going to do.  But the one thing you can't do is affect the ball itself after that 1 ms time it spent on your blade, not until you hit it again.  Is this misleading? 


Edited by Baal - 09/13/2013 at 4:49pm

yogi_bear wrote: within a split second a response can be initiated the moment you felt the ball through your reflex that has become an automatic response through repetitive training of stroke and footwork.

And where is the evidence for this claim? Show us the data which demonstrates that the body can initiate and complete a response in <1ms.

A "split second" could mean something like a few hundred milliseconds.  That's a really short time.  It's the kind of thing that lets a good player react to often (but not always) adjust for really fast shots that had the trajectory changed slightly because it grazed the net. Really fast.  But not compared to 1 millisecond.  By the way, it takes a mammalian fast-twitch skeletal muscle at least a couple of milliseconds to generate any real contraction at all, and about 20 milliseconds to achieve peak tension.  So even a muscle by itself cannot contract fast enough, and training all you want cannot change this.     

I wish this thread could be separated into two threads.  One about contact time and the other about how we perceive it.  Is anybody going to wade through all these posts?

tt4me, it is actually worse than that. Now there is third issue of how people rapidly can make a movement in response to a stimulus.  I suspect this distraction from actual dwell time drives you nuts, so I apologize.  Anyway I don't have much to add to any of this. 

JacekGM wrote: tt4me wrote: JacekGM wrote: Has anyone actually calculated the Newton force impact on a 2,7 mm ball with the assumed decellerations and acellerations and 1 msec dwell ? Yes,  this is basic stuff.  The AVERAGE force is the change in momentum of the ball divide by the dwell time.  The peak force is roughly twice that. I have told you how to calculate the average force and the peak force.  Do some home work and assume the ball is moving in at 5 m/s and away at 15m/s and the dwell time is 1 millisecond.  What is the average force?  What is the peak force approximately? Gotcha... you did not tell this to me... the post you quoted is not mine, we are working on correcting that mistake, sorry.

@JacekGM
You stole my words posted on a public forum .

@TT4me,

Your response is highly inconsistent with the idea that dwelltime is more or less constant..  Balldeformation as a meassure for medium and max force combined (or energy) would have to be the same for all equipment with a given change of momentum.

When this deformation is the same then dwelltime must be different for the same accelleration or vice versa. Can,t have both the same (for same momentum).

And more basic (if such would exist) is that momentum doesn,t change.  Momentum is (partly) continued from player to bat to ball for a stroke that  accellerates a ball (with additional energy) or compensate the momentum loss (the part that,s not continued as kinetic momentum ) from a cor <1.

A collision doesn,t accellerate things from additional momentum as long as cor < 1 or equal. It also doesn,t because speed is all relative.
To the table a ball may accellerate from a standard collision that,s not the relative speed for the collision but to a table ; another relative speed thus.
A ball (between the two) then looses relative speed (relative to the bat) just the same as the bat to the ball and even exactly the same. That,s a cor loss of kinetic momentum to the bounce (not one part to other part). For relative speed between the parts (bat and ball) this always has a decelleration for both parts.except with additional energy or relative to the table but then it would skip away to another relative system. Otherwise what would addition of relative mean when speed is always relative anyway ? Speed without the addition relative would say relative to everything in rest such as the table and players. With the addition it means relative between two moving objekts before and after a collision (during dwell thus) stay to that relativity and not midst of dwell skip tp another relative speed (to the table).
Cor is the (current) naming for rel speed out/rel speed in. So for the dwell period  it,s all between bat and ball not either one to the table.  The relative speeds before and after can be calculated by adding the (relative) speeds to the table as Vbat+ Vball (or Vbat - (-Vball)).

But not during dwelltime only before and after. And then it has a loss of (kinetic) momentum for the ball relative to the bat  and thus a speedloss.
To players and table the ball just made a turn with some speedloss or it has more additional energy then what compensates the cor loss.

offcourse there will be a further accelleration with an aktiv enough stroke  but to compensate cor lpss allready needs a certain amount of additional energy and momemtum just to keep the cor = 1 (or rel speed out/rel speed in = 1).




Edited by mercuur - 09/14/2013 at 7:09am

@ mercuur

Most decent players can easily adjust to a ball on the long edge. Not sure on the time frame involved there but it would be only fractions of a second between when you noticed the odd bounce to changing the swing to suit

yogi_bear wrote: not in table tennis, i dont have the data but im gonna give you an example which is very common. supposing you have been pricked by a needle on a part of your body, does it take you about more than a second to respond to it with your reflexes to withdraw your finger from the needle? the smaller the muscle is the faster the response especially the fast twitched muscles. in table tennis, i would like to point the example of high level players. not necessarily top 100 level that i have seen. there are players who can do these in which using their peripheral version they can altogether see the visual and to some extent auditory clues of what their opponent will do and in response change the placement of the ball. waldner is known to do this. the sudden change in placement of the ball is a response that can be done in less done in a a second. i would like also to point out the example in serving with varying spins, haven't you have the experience of doing a serve that the moment you contact the ball, you change some angle in the blade, lessen or increase the contact on the ball in order to initiate a change or variation in the service? when liu gouliang was interviewed on how to make a good serve, he said make the serve look identical on the way you do it but at the moment of contact change the serve through minute movement of the hand and wrist. this can be done in less than a second. if this doesnt support my opinion, i dont know what does. it may not be directly measurable but it does occur.

Yogi, this kind of damage reflex that you mentioned is more typically illustrated by using a burn rather than a needle prick since you need a pretty strong stimulus to evoke it.  There is just one synapse made in the spinal cord.  So the time it takes is approximately conduction time for impulse from (say) your finger to the spinal cord through the sensory neuron at about 75 m/s + the synaptic delay of about 1 ms + propagation time of the nerve impulse back to your arm through the motoneuron, this time closer to 200 m/s because those cells are faster, + another synaptic delay of about 1 ms + length of time it takes for muscle contractile apparatus to engage, another 1-2 ms.  And this is the fastest reflex known in mammals.  Any adjustments ping pong players make to things that happen in a game are much slower than this, as a lot more processing is involved.  There are what you might call hardware limitations.

Sorry tt4m4, he was asking the question!

Actually since you mention it Bluebucket, there are thought to be (at least) two distinct pain pathways and sensations.  One is called "epicritic".  It is very fast because the sensory fibers are heavily myelinated, also the resulting sensation is very well localized and kind of like a pin-prick -- very "sharp", but usually not too severe.  The second is called "protopathic".  It is carried by unmyelinated fibers which conduct very slowly (only about 2-5 m/s), so it is slower in onset, less well localized, generally more severe once it kicks in, and is usually described as a "dull throbbing" pain.  Requires more tissue damage to turn on, also.  So if you burn yourself, you may instantly feel a prick of pain and withdraw your hand quickly (the reflex).  After a discernible time passes, then you feel the really serious protopathic pain, it almost feels like it comes on like a "wave".  The two kinds of pain have different processing pathways all throughout your central nervous system.  People with chronic pain syndromes are usually suffering from protopathic pain, and it is not easy for them to localize it precisely but it is really terrible for them. 

The reflex that causes you to jerk your hand back is pretty fast, it is complete before you really can tell from the pain how badly you burned yourself (which people usually can tell from the protopathic pain).  But still a lot longer than 1 ms.

The sensations we get playing table tennis are hopefully not painful!!

I agree with you, for me there is very little as satisfying in TT as making an adjustment to a fast net ball correctly.  I'm not sure why.  I guess it lets me know that the nervous system is still working pretty well.


Edited by Baal - 09/14/2013 at 12:51pm