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hanisch
03-30-2007, 03:54 PM
[i posted this on azbilliards, but was informed that this forum might be even more suitable for this type of discussion. so here it is.]

i apologize for the length of this post, but i'm trying to exposit, as clearly as i can, a significant point which, as far as i know, has been severely mistreated in the pool world.

i have heard too many times from pool players, and i have read too many times in the pool literature, that you can achieve all the cue ball action you need with merely one stroke. so i've heard, and so i've read, it does not matter whether i use a long stroke or a short stroke, whether i have lots of follow-through or none at all, my cue ball will react in the same way. all i can do with my stroke is provide a linear speed and a contact point for my tip on the ball. and in doing so, i can achieve all possible combinations of linear and angular velocities. i don't believe this.

the justification of this "one stroke is all you need" thesis is usually made with two arguments. the first goes something like this: after the ball leaves your tip, the ball does not care if your tip follows through or not. no doubt, any reasonable person will agree with this. the problem with this argument, however, is that it implicitly assumes that there is no significant difference between the event of your tip first contacting the ball and the separate event of the ball leaving your tip. this brings us to the second argument usually made: the jacksonville experiments "demonstrated" that there is no significant difference between these two events. let's explore this a little deeper.

what the jacksonville experiments actually demonstrated (in relation to this discussion) was this: for the limited strokes tested, the time between these two events--let's call this the dwell time--was very small, about a millisecond. (i should mention that the jacksonville experiments were a great milestone in advancing our understanding. however, no experiment should yield conclusions thought to be definitive; advancement in any science involves constant constructive criticism of previous experiments leading to ever new, better experiments.) first, let's consider the first clause. the strokes tested must have been very limited. in "billiards digest" shamos wrote, "no matter how anyone stroked, the best we could do was to have the cue stick move at constant speed for the last few inches before it hits the ball. in fact, unless a very good stroke is used, the stick actually decelerates on the way in." why couldn't anyone produce a stroke that was accelerating at contact? there's no reason to think that this is physically impossible. in fact, i contend that top three-cushion players do this all the time. perhaps during the experiments, only perfect pendulum strokes were used. (for what it's worth, three-cushion players employ such pendulum strokes for only a minority of shots.) note that no elite players were used to produce the strokes tested.

let's now explore the second clause, namely that the dwell time is very small. this finding has been used to dismiss many hypotheses concerning what contributes to ball action (e.g. grip, follow-through, etc.). since only non-accelerating (or decelerating) strokes were tested, such dismissals are at best premature. to see why, we need to understand what happens during this very small dwell time.

if the tip is not accelerating at contact, we can view the contact between the tip and ball as a collision between two objects. when a non-accelerating object hits a stationary object, energy is transferred from the former to the latter. (if the kinetic energy is conserved, such a collision is said to be elastic. see http://en.wikipedia.org/wiki/Elastic_collision for a nice explanation.) what happens during the collision is very, very complicated. we need to know how the objects deform under stress, how the stress propagates, etc. to simplify all this, physicists use the concept of an impulse. an impulse is defined as the change in momentum of an object when a large force is applied over a very brief period of time. we can now say that, at best, the jacksonville experiments showed what the dwell time was for "impulsive strokes" (i.e. non-accelerating strokes). but what happens when the tip accelerates as it hits the ball? surely this is possible.

acceleration implies a force. when a force acts upon an object over a distance, a transfer of energy takes place. physicists refer to this transfer of energy as work. (see http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html for a good explanation.) i am contending that when a player produces an accelerating stroke, work is being done to the ball. if this is indeed happening, there should be a measurable dwell distance--the distance over which the ball travels while still in contact with the tip. (note that referring to the jacksonville experiments here is useless as no accelerating strokes were tested.) for these "working strokes" (i.e. accelerating strokes) it is the dwell distance, not the dwell time, that is relevant. in fact, the dwell time for working strokes may indeed be roughly the same as the dwell time for impulsive strokes. however, the dwell distance will be significantly greater for working strokes. in a working stroke, the tip is pushing the ball over a longer distance, but since the tip is accelerating, more distance will be covered in the same time interval. moreover, the deformations of the tip and ball is different for working strokes than it is for impulsive strokes. for working strokes, since the tip is accelerating, such compressions and decompressions may occur more quickly than for impulsive strokes. this is widely known for the collision between the strings of a tennis racket and a tennis ball. the dwell time is roughly five milliseconds for nearly all types of tennis strokes. but the dwell distance is much greater for those strokes where the racket accelerates through the ball.

if i am correct, that is, if top players routinely employ working strokes, then what has passed as conventional wisdom in poolrooms and in the pool literature must be reconsidered. it is my belief that a significant factor as to why top pool players are far more consistent than amateurs is that they "work" the cue ball a lot more; that is an accelerating stroke is more consistent than a non-accelerating one. furthermore, top three-cushion players are able to achieve the wide range of spin-to-speed ratios (at many varying speeds) that they do since they employ many different strokes, each with differing amounts of work, and some with only impulse.

i look forward to reading other thoughts on this.

william hanisch

dr_dave
03-30-2007, 04:12 PM
<blockquote><font class="small">Quote hanisch:</font><hr>... i apologize for the length of this post, but i'm trying to exposit, as clearly as i can, a significant point which, as far as i know, has been severely mistreated in the pool world.

i have heard too many times from pool players, and i have read too many times in the pool literature, that you can achieve all the cue ball action you need with merely one stroke. so i've heard, and so i've read, it does not matter whether i use a long stroke or a short stroke, whether i have lots of follow-through or none at all, my cue ball will react in the same way. all i can do with my stroke is provide a linear speed and a contact point for my tip on the ball. and in doing so, i can achieve all possible combinations of linear and angular velocities. i don't believe this. ...<hr /></blockquote>From a physics perspective, all that matters is cue stick speed, cue stick elevation, and offsets (left/right and up/down) from center at impact. It doesn't matter how you get there or what you do after. Also, any dynamic forces due to acceleration or deceleration during the brief tip contact times are insignificant as compared to the extremely large momentum transfer impact forces (except maybe for really slow push-type strokes).

Now, some people can achieve better slow-speed control or better power by modifying their normal stroke some. Also, many types of shots require different types of strokes because a normal stroke won't be comfortable or possible in all situations.

For more information, see my stroke "best practices" document (http://www.engr.colostate.edu/~dga/pool/resources/stroke_best_practices.pdf), especially item 5, and my May '06 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/may06.pdf). Also, you might be interested in some past thread highlights under "stroke" in the threads summary section of my website (http://www.engr.colostate.edu/~dga/pool/threads.html).

Regards,
Dave

Bob_Jewett
03-30-2007, 04:54 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... the strokes tested must have been very limited. in "billiards digest" shamos wrote, "no matter how anyone stroked, the best we could do was to have the cue stick move at constant speed for the last few inches before it hits the ball. in fact, unless a very good stroke is used, the stick actually decelerates on the way in." why couldn't anyone produce a stroke that was accelerating at contact? there's no reason to think that this is physically impossible. in fact, i contend that top three-cushion players do this all the time. ... <hr /></blockquote>
Any lack of stroke variation was not for want of trying. One of the shooters had set the record for most points in the European Artistic Billiards championship, so there was more than a little physical expertise present. He was also a big exponent of an accelerating stroke being required on major spin shots until he saw what he actually did.

I'm convinced that players learn very early in their careers that the best -- easiest, most accurate, most efficient -- way to hit the cue ball is at the peak of the stroke speed.

One problem with trying to shoot a stroke that is still accelerating when it hits the cue ball is the chance of a double hit.

As for the second item -- increased dwell time -- I covered this some in a couple of articles in BD. (I never used an impulse model for the interactions, and in fact I constructed a finite-element-analysis model that could include such factors as tip hardness, stick taper and weight at the joint.) The hand/stick/tip/ball system can be viewed as three masses with the middle mass (tip/stick) connected to the others by springs. The spring constants are important. The tip/ball spring constant is about 100 times higher than the hand/stick spring constant. One thing this implies is that the hand can have almost no effect on the tip/ball collision. (The grip in golf can have no direct effect on club-head/ball interaction, but for other reasons.)

If you are going to propose an effect, I think it is not unreasonable to ask you to offer at least a sketch of the physical mechanism you propose along with some estimates of the parameters, such as spring constants and masses involved. It would also be nice to have a specific shot that demonstrates the usefulness of a non-peak-speed-at-contact stroke. I think there is none except perhaps for fouette shots.

cushioncrawler
03-30-2007, 05:47 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> ....One problem with trying to shoot a stroke that is still accelerating when it hits the cue ball is the chance of a double hit..... <hr /></blockquote>Bob -- I agree. A foul will soon rear its ugly head. But, and this might sound contradictory to my "foul" remark, but acceleration throo the qball iz futile.

All the same, 2 things are certain. A short poke, or a large flourish, or ??????, will give best rezults for a player, and, then, later, it wont. madMac.

iralee
03-30-2007, 05:47 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> From a physics perspective, all that matters is cue stick speed, cue stick elevation, and offsets (left/right and up/down) from center at impact. It doesn't matter how you get there or what you do after. Also, any dynamic forces due to acceleration or deceleration during the brief tip contact times are insignificant as compared to the extremely large momentum transfer impact forces (except maybe for really slow push-type strokes).

Now, some people can achieve better slow-speed control or better power by modifying their normal stroke some. Also, many types of shots require different types of strokes because a normal stroke won't be comfortable or possible in all situations.

For more information, see my stroke "best practices" document (http://www.engr.colostate.edu/~dga/pool/resources/stroke_best_practices.pdf), especially item 5, and my May '06 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/may06.pdf). Also, you might be interested in some past thread highlights under "stroke" in the threads summary section of my website (http://www.engr.colostate.edu/~dga/pool/threads.html).

Regards,
Dave <hr /></blockquote>

I think something very important is being missed here. Clearly it doesn't matter "how you get there and what you do after" your tip touches the cueball, but hanisch is suggesting that the "work" a player does DURING the contact-time (dwell time), however small, IS significant - precisely from a physics perspective. "Relatively brief" tip-ball contact times in the millisecond range may seem insignificant to most people - but in many fields (particularly in my own line of work) a single millisecond is an eon. In the Jacksonville Experiments, Jewett measured dwell distances of approximately 3mm with a non-accelerating stroke. At this point, no one should reasonably jump to conclude that cue-stick acceleration has NO effect on contact-time, contact-distance, or cue-ball forces based on these experiments alone. On the tables, top players always talk about having "good timing" in their stroke and good instruction usually includes advice to accelerate through the ball (or at least to try). Players spend their entire lifetimes honing their "stroke"; could it be so simple as merely speed, elevation, and tip-offset?

I am certain that I don't stand alone (with most 3-cushion players) to wholeheartedly disagree with you in discounting the value (and effect) of an accelerating stroke as an effective technique to increase the distance that the tip "dwells" on the cue-ball. There are many shots in carom billiards where the relative ball-speeds must be carefully moderated - where one's ability to control the acceleration in their "stroke" is a huge factor in successful play (position in straight-rail or delicate multi-rail kiss-passing in 3-cushion) as we try to select and create the perfect "mix" of spin/speed to solve each problem at the table.

I realize that for games like nine-ball, where the exact speed of the object ball (into the pocket) is not usually paramount, these forces are much less of a factor. One-pocket is a different story, of course.

As an instructor of beginner students, I could understand why one intentionally might omit the introduction of complicated strokes from the first lessons. In this context, I could see how "keeping it simple" - at least until the student's coordination and mechanics became better developed - would be a recommended teaching strategy.

As a more advanced player, I am motivated by a very practical perspective (how do I avoid thousands of kiss problems on the table? should I ignore the recommendations of every top professional 3-cushion player on this topic? etc), and ESPECIALLY from a physics perspective - cue-stick acceleration (or "stroke") counts greatly. I am greatly convinced that it is NOT merely about speed, elevation and tip-offset as you suggest. Every fiber in my being disagrees with your simple characterization.

A controlled experiment could be done (using high-speed video) to show that different tip accelerations DURING impact can affect the dwell-distances and hence the effective forces involved.

If it is in the future shown that dwell distances can be manipulated by employing different degrees of acceleration in one's stroke - then I hope you would be willing to modify your stance on this topic or your opinion of its significance.

Perhaps these "brief" tip contact times are not as insignificant as you think they are.

-Ira

Cornerman
03-30-2007, 06:02 PM
<blockquote><font class="small">Quote hanisch:</font><hr> in fact, i contend that top three-cushion players do this (accelerate) all the time. <hr /></blockquote>One of the strokers that Shamos was talking about in the Jacksonville Experiment was a three cushion artistic champion.

Fred

Jal
03-30-2007, 06:07 PM
A very well stated set of propositions. If it's any consolation, I agree with some of what you said in a round-about kind of way.

First, for the reasons both Dr. Dave and Bob Jewett stated, having a tight grip and attempting to accelerate the stick during contact just doesn't get you anything. The butt only moves a very small distance relative to the grip hand during impact, and to make a difference, a large force, something on the order of 100 lbs, would have to develop between your stick and hand over this tiny distance (roughly 1/64" - 1/100"). The hand's inherent softness won't come anywhere close. Try pressing the butt of your cue down on a bathroom scale and observing how much force is generated per unit distance of movement of your hand relative to the butt.

But, accelerating up to impact should, in principle, provide some gain in cue speed. It has to do with the shape of the force vs time curve. And I think common sense suggests strongly that this is true. I've tried moving my grip hand back to effect this, and have been able to produce more draw as a result.

Once the tip contacts the ball though, the compression forces quickly overwhelm the relatively meager force applied by your hand/arm. Maybe for a small fraction of the contact period accelerating does make a difference, but it rapidly pales into insignificance. And note that any force that's being applied gets distributed between the mass of the stick and ball, so the cueball only sees about one part in four.

But if you could prove the party line wrong, that would be, well, nice.

Jim

hanisch
03-30-2007, 06:20 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> Any lack of stroke variation was not for want of trying. One of the shooters had set the record for most points in the European Artistic Billiards championship, so there was more than a little physical expertise present. He was also a big exponent of an accelerating stroke being required on major spin shots until he saw what he actually did. <hr /></blockquote>

i don't want to give the impression that i am belittling what you did. quite the opposite. i am grateful to you for what you did, and i hope it leads to more experiments.

still, can you explain why nobody was able to produce a stroke that was accelerating throughout? perhaps it was being conscious of being filmed, they very bright lights, etc. but it can't be too difficult. according to the diagram in your article "don't grip it and rip it," there was increasing acceleration for the first 10 centimeters of the forward stroke. for the next 10, there was still positive acceleration, though it was decreasing. the acceleration stopped only in the last 2 or 3 centimeters. if the ball was about 5 centimeters closer, you would have had an accelerating stroke.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> I'm convinced that players learn very early in their careers that the best -- easiest, most accurate, most efficient -- way to hit the cue ball is at the peak of the stroke speed. <hr /></blockquote>

i don't understand what you mean by "peak of the stroke speed." for an accelerating stroke, there is no peak. a peak only occurs when acceleration drops to zero. i don't see why a stroke where acceleration drops to zero at contact is the "best -- easiest, most accurate, most efficient -- way to hit the cue ball."

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> One problem with trying to shoot a stroke that is still accelerating when it hits the cue ball is the chance of a double hit. <hr /></blockquote>

quite the contrary. a double hit can only occur if the stroke stops accelerating, then starts accelerating again. such a stroke is not a smooth accelerating stroke.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> As for the second item -- increased dwell time -- I covered this some in a couple of articles in BD. (I never used an impulse model for the interactions, and in fact I constructed a finite-element-analysis model that could include such factors as tip hardness, stick taper and weight at the joint.) The hand/stick/tip/ball system can be viewed as three masses with the middle mass (tip/stick) connected to the others by springs. The spring constants are important. The tip/ball spring constant is about 100 times higher than the hand/stick spring constant. One thing this implies is that the hand can have almost no effect on the tip/ball collision. (The grip in golf can have no direct effect on club-head/ball interaction, but for other reasons.) <hr /></blockquote>

i never said the dwell time will increase. however, i did say the dwell distance will increase for accelerating strokes.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> If you are going to propose an effect, I think it is not unreasonable to ask you to offer at least a sketch of the physical mechanism you propose along with some estimates of the parameters, such as spring constants and masses involved. It would also be nice to have a specific shot that demonstrates the usefulness of a non-peak-speed-at-contact stroke. I think there is none except perhaps for fouette shots. <hr /></blockquote>

i don't know what you mean by "propose an effect." i am not trying to model the very complex interactions between the tip and ball during their collision. rather, i am treating them as an impulse. however, what i am adding is that for accelerating strokes, there is more going on than the interactions during collision (i.e. the impulse). there is work (in the physicists sense of the word) being done on the ball by the cue stick. this work cannot be ignored.

i assume that you mean by "non-peak-speed-at-contact stroke" a stroke that is accelerating at contact. to avoid certain kisses in three-cushion, you must be able to achieve certain spin-to-speed ratios at various given speeds (i.e. you must be able to to achieve many combinations of linear and angular velocities). what i am asserting is that by restricting yourself to only impulsive (i.e. non-accelerating) strokes, you are restricting yourself to a much smaller range of combinations of linear and angular velocities.

william

Bob_Jewett
03-30-2007, 06:37 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ...
still, can you explain why nobody was able to produce a stroke that was accelerating throughout? perhaps it was being conscious of being filmed, they very bright lights, etc. but it can't be too difficult. ...
<hr /></blockquote>
No, it is immensely difficult. It goes against every bit of billiard learning that any decent player has acquired over years of practice and perfecting the stroke. I urge you to try shooting shots in which the acceleration of the stick can be measured and to shoot shots in which the ball is struck at peak acceleration. It's too bad that the needed equipment is not more readily available, but I really do think that if more people could actually see the mechanics of their strokes, and the strokes of champions, they would stop worrying about developing a million strokes for a jillion shots.

Bob_Jewett
03-30-2007, 06:47 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... i don't understand what you mean by "peak of the stroke speed." for an accelerating stroke, there is no peak. a peak only occurs when acceleration drops to zero. i don't see why a stroke where acceleration drops to zero at contact is the "best -- easiest, most accurate, most efficient -- way to hit the cue ball."
... <hr /></blockquote>
The "most efficient" part is fairly simple to explain. For any particular acceleration profile of the shot, what placement of the cue ball will result in the highest speed of the cue ball? That is, if you look at the speed versus time or the speed versus position of the stick, and imagine that the cue ball can be magically moved without the player's knowledge, where do you want to place the cue ball so that the cue ball will be moving fastest after the shot. The answer according to physics is very, very simple: when the stick has peak speed. That is when the acceleration is zero.

"Easiest" is sort of addressed in my post above. It is really, really hard to actually hit the cue ball when you are still accelerating. It is totally unnatural. Maybe that's a learned distaste, but as far as I can see, it is common to all good players.

As far as the most accurate, I think this is covered in the article where I plot out the speed of the stick versus time. If you try to hit the ball during the part of the speed/time curve that is still rising, your timing will have a large effect on the speed of the ball. If you hit the ball when the stick has reached its peak speed, the timing of the shot is not so important. A lot of different timings will produce nearly the same ball speed.

Sid_Vicious
03-30-2007, 06:55 PM
"but I really do think that if more people could actually see the mechanics of their strokes, and the strokes of champions, they would stop worrying about developing a million strokes for a jillion shots."

Then where would we find the "fish" to hook Bob /ccboard/images/graemlins/grin.gif You are absolutely right, and I am probably the world's worst to be talking, really...sid

Bob_Jewett
03-30-2007, 07:00 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... i never said the dwell time will increase. however, i did say the dwell distance will increase for accelerating strokes.... <hr /></blockquote>
Well, the distance tip and ball travel together depend primarily on the speed of the shot or rather the amount the tip is compressed. The two will travel together over a distance on the table of roughly three times the compression of the tip (and ferrule and shaft and joint, if they compress). The amount of compression (for a given tip) is almost entirely determined by how fast the stick is moving and is only very, very slightly affected by what your hand is doing at that instant.

The main point here is that any force that the hand can apply during tip/ball contact is very, very small compared to the force between the tip and the ball. With a firm grip, you might increase the tip/ball force during the tip/ball contact by 1%. That is not enough to give any significant help to the shot.

Let's compare two ways to hit the ball: If you hit the shot at peak acceleration you are necessarily hitting at less speed than if you simply waited for the acceleration to finish and the speed to peak. You will waste roughly 50% of the speed. If you wait for the peak speed, you will get roughly twice the speed in the shot, which is 4 times the energy. There is a small correction to add to the first case and that is due to the force on the stick from your hand at the instant of tip/ball contact. That is the 1% increase I mentioned before. That's to be compared with a 100% increase if you simply time the shot differently.

Bob_Jewett
03-30-2007, 07:26 PM
<blockquote><font class="small">Quote hanisch:</font><hr>... quite the contrary. a double hit can only occur if the stroke stops accelerating, then starts accelerating again. ... <hr /></blockquote>

In one sense this is true. On an accelerated stroke, when the tip hits the ball, the speed of the stick is suddenly reduced to half the speed it had at the instant just before contact. (This is also true for non-accelerated shots.) But as far as the hand is concerned, it need not stop pushing forward during this time, and the force and acceleration could actually continue to increase until the cue ball was struck a second time.

Here is an accelerated shot for you to try. Put the cue ball on the spot so you can shoot it up the centerline of the table. Bring the tip to within half an inch of the cue ball. <font color="red">WITH NO BACKSTROKE</font color> bring the stick forward with a 12-inch-long continuously accelerating stroke. I think you will hit the cue ball twice. Note the emphasis. Most experienced players will find it nearly impossible to shoot the shot without a backstroke the first time.

Bob_Jewett
03-30-2007, 07:37 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... to avoid certain kisses in three-cushion, you must be able to achieve certain spin-to-speed ratios at various given speeds (i.e. you must be able to to achieve many combinations of linear and angular velocities). what i am asserting is that by restricting yourself to only impulsive (i.e. non-accelerating) strokes, you are restricting yourself to a much smaller range of combinations of linear and angular velocities.

william
<hr /></blockquote>
And I believe that physics says that the spin-speed ratio for a particular hit is determined almost entirely by the lever arm of the shot -- that is, how far from center you hit the cue ball. To the best of my knowledge, there has never been any demonstration that other factors are important in determining the spin/speed ratio.

Also, I think you are wrong in assuming that an accelerated stroke is significantly more or less "impulsive" than an orthodox "peak speed" stroke. Further, there is good reason to believe that for maximum spin/speed ratio, you want to minimize tip/ball contact time.

hanisch
03-30-2007, 08:00 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ... i don't understand what you mean by "peak of the stroke speed." for an accelerating stroke, there is no peak. a peak only occurs when acceleration drops to zero. i don't see why a stroke where acceleration drops to zero at contact is the "best -- easiest, most accurate, most efficient -- way to hit the cue ball."
... <hr /></blockquote>
The "most efficient" part is fairly simple to explain. For any particular acceleration profile of the shot, what placement of the cue ball will result in the highest speed of the cue ball? That is, if you look at the speed versus time or the speed versus position of the stick, and imagine that the cue ball can be magically moved without the player's knowledge, where do you want to place the cue ball so that the cue ball will be moving fastest after the shot. The answer according to physics is very, very simple: when the stick has peak speed. That is when the acceleration is zero.

"Easiest" is sort of addressed in my post above. It is really, really hard to actually hit the cue ball when you are still accelerating. It is totally unnatural. Maybe that's a learned distaste, but as far as I can see, it is common to all good players.

As far as the most accurate, I think this is covered in the article where I plot out the speed of the stick versus time. If you try to hit the ball during the part of the speed/time curve that is still rising, your timing will have a large effect on the speed of the ball. If you hit the ball when the stick has reached its peak speed, the timing of the shot is not so important. A lot of different timings will produce nearly the same ball speed. <hr /></blockquote>


bob,

you are missing something significant here. you are assuming that an accelerating stroke does not do work to the ball. that is, you are assuming that the distance over which the tip remains in contact with the ball--the dwell distance--is insignificant. indeed, for non-accelerating strokes, it may be insignificant. but for accelerating strokes you are pushing the ball over a not insignificant distance.

this work has at least two positive effects. one is that it contributes to increasing the balls velocity. see http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html for a nice demonstration. you say that "when the stick has peak speed...is when the acceleration is zero." yes, but if the stick is applying work to the ball (i.e. if employing an accelerating stroke), more than just stick speed contributes to the balls velocity. the work being done contributes.

the other effect is that is helps the ball move more consistently. when a basketball player dribbles a ball, he doesn't slap at it. rather he pushes the ball down and absorbs it on the way up. by maintaing a force over a distance, inaccuracies at contact are corrected. top players massage the cue ball, they don't whack at it.

william

dr_dave
03-30-2007, 08:20 PM
<blockquote><font class="small">Quote iralee:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> From a physics perspective, all that matters is cue stick speed, cue stick elevation, and offsets (left/right and up/down) from center at impact. It doesn't matter how you get there or what you do after. Also, any dynamic forces due to acceleration or deceleration during the brief tip contact times are insignificant as compared to the extremely large momentum transfer impact forces (except maybe for really slow push-type strokes).

Now, some people can achieve better slow-speed control or better power by modifying their normal stroke some. Also, many types of shots require different types of strokes because a normal stroke won't be comfortable or possible in all situations.

For more information, see my stroke "best practices" document (http://www.engr.colostate.edu/~dga/pool/resources/stroke_best_practices.pdf), especially item 5, and my May '06 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/may06.pdf). Also, you might be interested in some past thread highlights under "stroke" in the threads summary section of my website (http://www.engr.colostate.edu/~dga/pool/threads.html).

Regards,
Dave <hr /></blockquote>

I think something very important is being missing here. Clearly it doesn't matter "how you get there and what you do after" your tip touches the cueball, but hanisch is suggesting that the "work" a player does DURING the contact-time (dwell time), however small, IS significant - precisely from a physics perspective.<hr /></blockquote>Well, I guess I disagree with his physics perspectives, based on the physics perspectives I provided. Here is more detail:

ball mass = 6 oz
typical ball speed = 5 mph
typical tip contact time = 0.001 sec

Given this information, the peak force generated between the cue tip and cue ball during impact is over 100 pounds (I will post the details of the analysis if people are interested). The only way the grip hand could have a significant affect during the 0.001 sec contact time is if the skin and flesh of the grip hand could generate forces that are significant, as compared to the impact forces. As Bob has pointed out, a human grip (regardless of how tight it might be) is not stiff and responsive enough to generate such forces in such a short amount of time.

<blockquote><font class="small">Quote iralee:</font><hr>"Relatively brief" tip-ball contact times in the millisecond range may seem insignificant to most people - but in many fields (particularly in my own line of work) a single millisecond is an eon.<hr /></blockquote>Agreed. In my main line of work (i.e., in my "day job"), dealing with control electronics and high-speed machinery, a millisecond can also be an eternity.

<blockquote><font class="small">Quote iralee:</font><hr>In the Jacksonville Experiments, Jewett measured dwell distances of approximately 3mm with a non-accelerating stroke. At this point, no one should reasonably jump to conclude that cue-stick acceleration has NO effect on contact-time, contact-distance, or cue-ball forces based on these experiments alone.<hr /></blockquote>I have also done extensive high-speed-video experiments (see the high-speed video section of my website (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html)), and I agree that one must be careful when trying to jump to conclusions. I have tested tip contact times for all ranges of speeds, tip hardnesses, and with people of different stroke types, and the contact times are always very close to 0.001 sec (see the links under "cue tip contact times" in the threads summary section of my website (http://www.engr.colostate.edu/~dga/pool/threads.html) for more information).

<blockquote><font class="small">Quote iralee:</font><hr>On the tables, top players always talk about having "good timing" in their stroke and good instruction usually includes advice to accelerate through the ball (or at least to try). Players spend their entire lifetimes honing their "stroke"; could it be so simple as merely speed, elevation, and tip-offset?<hr /></blockquote>Yes; but developing a consistent, well-controlled, and accurate stroke is still a major challenge that requires natural ability and lots of hard work.

<blockquote><font class="small">Quote iralee:</font><hr>I am certain that I don't stand alone (with most 3-cushion players) to wholeheartedly disagree with you in discounting the value (and effect) of an accelerating stroke as an effective technique to increase the distance that the tip "dwells" on the cue-ball. There are many shots in carom billiards where the relative ball-speeds must be carefully moderated - where one's ability to control the acceleration in their "stroke" is a huge factor in successful play (position in straight-rail or delicate multi-rail kiss-passing in 3-cushion) as we try to select and create the perfect "mix" of spin/speed to solve each problem at the table.

I realize that for games like nine-ball, where the exact speed of the object ball (into the pocket) is not usually paramount, these forces are much less of a factor. One-pocket is a different story, of course.

As an instructor of beginner students, I could understand why one intentionally might omit the introduction of complicated strokes from the first lessons. In this context, I could see how "keeping it simple" - at least until the student's coordination and mechanics became better developed - would be a recommended teaching strategy.

As a more advanced player, I am motivated by a very practical perspective (how do I avoid thousands of kiss problems on the table? should I ignore the recommendations of every top professional 3-cushion player on this topic? etc), and ESPECIALLY from a physics perspective - cue-stick acceleration (or "stroke") counts greatly. I am greatly convinced that it is NOT merely about speed, elevation and tip-offset as you suggest. Every fiber in my being disagrees with your simple characterization.

A controlled experiment could be done (using high-speed video) to show that different tip accelerations DURING impact can affect the dwell-distances and hence the effective forces involved.

If it is in the future shown that dwell distances can be manipulated by employing different degrees of acceleration in one's stroke - then I hope you would be willing to modify your stance on this topic or your opinion of its significance.

Perhaps these "brief" tip contact times are not as insignificant as you think they are.<hr /></blockquote>Maybe, but I still haven't seen physical reasoning, theoretical development, or experimental results yet that would help me embrace your perspective. Concerning stroke acceleration and follow-through, see item 5 in my stroke "best practices" document (http://www.engr.colostate.edu/~dga/pool/resources/stroke_best_practices.pdf) and item b on page 2 of my May '06 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/may06.pdf).

Regards,
Dave

Bob_Jewett
03-30-2007, 09:12 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... you are missing something significant here. you are assuming that an accelerating stroke does not do work to the ball. that is, you are assuming that the distance over which the tip remains in contact with the ball--the dwell distance--is insignificant. ... <hr /></blockquote>
No, I'm not assuming it. I am calculating it within a reasonable model of the stick-hand-tip system. That model seems to explain all of the major phenomena that have been observed. Unfortunately, it seems we cannot agree on that model.

In the golf example that you found, I think there is a point to consider: In golf, what the hands are doing on the club at the instant of club head-ball contact is not important. A laser could cut the club off at the end of the grip just before the club hits the ball and the shot would be unchanged. That's because the mechanism of energy transfer from the hands to the head is pretty slow and the ball is on the club head for a relatively short time. Something similar keeps your hands from influencing the shot at the instant of contact at pool.

Do you have any shot that you feel requires an accelerating stroke that cannot be made with a "peak speed" stroke?

Jal
03-30-2007, 10:02 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ... i don't understand what you mean by "peak of the stroke speed." for an accelerating stroke, there is no peak. a peak only occurs when acceleration drops to zero. i don't see why a stroke where acceleration drops to zero at contact is the "best -- easiest, most accurate, most efficient -- way to hit the cue ball."
... <hr /></blockquote>
The "most efficient" part is fairly simple to explain. For any particular acceleration profile of the shot, what placement of the cue ball will result in the highest speed of the cue ball? That is, if you look at the speed versus time or the speed versus position of the stick, and imagine that the cue ball can be magically moved without the player's knowledge, where do you want to place the cue ball so that the cue ball will be moving fastest after the shot. The answer according to physics is very, very simple: when the stick has peak speed. That is when the acceleration is zero.<hr /></blockquote>But the converse is not true. Given a particular bridge length, maximum speed is not obtained if zero acceleration occurs just at impact, although this does yield the best energy efficiency.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>...As far as the most accurate, I think this is covered in the article where I plot out the speed of the stick versus time. If you try to hit the ball during the part of the speed/time curve that is still rising, your timing will have a large effect on the speed of the ball. If you hit the ball when the stick has reached its peak speed, the timing of the shot is not so important. A lot of different timings will produce nearly the same ball speed. <hr /></blockquote>Not necessarily so. Timing errors are less with an accelerated stroke, assuming one has some control over the timing. By timing, I mean timing, ie, a change in the shape of the force/time curve. A non-accelerated stroke at impact is more accurate over small variations in bridge length, again assuming that one doesn't/can't make a timing change to adjust to it. An accelerated stroke is more accurate for a larger increase in bridge length.

I know I'm blowing in the wind here, but I've done about twenty pages of math on this topic and have a program which produces numbers in accord with the above assertions. You can't be certain of any of this, however, without having accelerometer graphs of actual players that show how the force/time curves change in response to deliberate variations in the stroke.

JohnnyP has posted some examples of his normal stroke, which I have modeled with a set of harmonics. In the model, altering the timing so that acceleration takes place at impact produces results in agreement with the above statements. But the caveat is that I don't know how well the model reflects the biomechanical realities of a significant change in timing.

I am not arguing for an accelerated stroke here, but just trying to presents some facts about it that may very well hold true for a real-life player.

Jim

Bob_Jewett
03-30-2007, 10:30 PM
<blockquote><font class="small">Quote Jal:</font><hr> ... Not necessarily so. Timing errors are less with an accelerated stroke, assuming one has some control over the timing. ... <hr /></blockquote>
Yes and no. It depends on what you assume is kept constant. For a given speed/time profile of the stroke, if you assume some error in the location of the cue ball (or the player's perception of the location of the cue ball), I think my claim is correct.

What we don't know, as you pointed out, is what sort of errors real players have for a particular fixed shot. Maybe they are very good at achieving a fixed total momentum transfer in a certain distance perhaps with little sensitivity to variations in the acceleration profile. I doubt that they are very good at achieving exactly 70% of a final peak speed in a fixed distance. But we don't know.

One acceleration profile I've seen suggested that the forward force is nearly constant over a significant fraction of the travel to impact.

Jal
03-30-2007, 10:43 PM
<blockquote><font class="small">Quote hanisch:</font><hr>you are missing something significant here. you are assuming that an accelerating stroke does not do work to the ball. that is, you are assuming that the distance over which the tip remains in contact with the ball--the dwell distance--is insignificant. indeed, for non-accelerating strokes, it may be insignificant. but for accelerating strokes you are pushing the ball over a not insignificant distance.

this work has at least two positive effects. one is that it contributes to increasing the balls velocity. see http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html for a nice demonstration. you say that "when the stick has peak speed...is when the acceleration is zero." yes, but if the stick is applying work to the ball (i.e. if employing an accelerating stroke), more than just stick speed contributes to the balls velocity. the work being done contributes.<hr /></blockquote>Work is being done by the compressive forces on the cueball regardeless of whether or not a force is being applied by the hand at impact. The question is whether you can increase this force/work significantly. For that you need to know the numbers, some of which Dr. Dave indicated above.

Along with these is the fact that the peak force applied by your hand/arm on a high speed shot is in the range of about 15 - 20 lbs. By the time the tip gets to the ball, a lot of this will have dropped off, and indeed, if you could hit while at peak force, this would not yield the most stick speed on the way to the ball (if the math model truely represents the real situation). And what force is left is reduced by its distribution amongst the stick and ball.

It's the form of the force/time curve before the tip ever makes contact with the ball that can produce some measurable gains (in theory).

Jim

hanisch
03-30-2007, 11:22 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ... you are missing something significant here. you are assuming that an accelerating stroke does not do work to the ball. that is, you are assuming that the distance over which the tip remains in contact with the ball--the dwell distance--is insignificant. ... <hr /></blockquote>
No, I'm not assuming it. I am calculating it within a reasonable model of the stick-hand-tip system. That model seems to explain all of the major phenomena that have been observed. Unfortunately, it seems we cannot agree on that model.

In the golf example that you found, I think there is a point to consider: In golf, what the hands are doing on the club at the instant of club head-ball contact is not important. A laser could cut the club off at the end of the grip just before the club hits the ball and the shot would be unchanged. That's because the mechanism of energy transfer from the hands to the head is pretty slow and the ball is on the club head for a relatively short time. Something similar keeps your hands from influencing the shot at the instant of contact at pool.

Do you have any shot that you feel requires an accelerating stroke that cannot be made with a "peak speed" stroke? <hr /></blockquote>

bob,

if i push an object across the floor (assume no or negligible friction) for a certain distance, i am applying a force on the object for the entire distance. by definition i am doing work on the object. the object will keep increasing its velocity (i.e. it will accelerate) over the entire distance.

once i let go of the object there is no longer any force acting on the object. therefore no more work is done on the object, and the object will no longer accelerate. it will continue on at a constant velocity.

if we are so far in agreement, let's consider your example of a laser cutting off the golf club at the grip just before it contacts the ball.

before the laser cut the club, the player was applying a force on the club, and thus doing work to the club, thereby accelerating it. but once the club is severed, no longer is there any force acting on the club. therefore the club cannot do work on the ball. the force is gone. but if the club was not severed, the force would still be present and the club would be doing work on the ball, accelerating it for the distance the club remained in contact with the ball.

you see, the shot would be changed dramatically. in one case (club intact) work is being done on the ball, accelerating it, and in the other case (club severed by a laser just before impact) no work is being done on the ball.

do you really thing that if a batter let go of the bat just before the bat hit the ball it would be same as if the batter held on and swung through it? in the latter case there is a force. in the former, there isn't.

william

Jal
03-31-2007, 12:34 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> ... Not necessarily so. Timing errors are less with an accelerated stroke, assuming one has some control over the timing. ... <hr /></blockquote>
Yes and no. It depends on what you assume is kept constant. For a given speed/time profile of the stroke, if you assume some error in the location of the cue ball (or the player's perception of the location of the cue ball), I think my claim is correct.<hr /></blockquote>I would agree. It's almost a philosophical problem (at least a psychological one) to determine if a speed error was the result of a stroke not well matched to a bridge length, or a bridge length not well matched to a stroke. Our disagreements, I think, have sort of hinged on this.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>One acceleration profile I've seen suggested that the forward force is nearly constant over a significant fraction of the travel to impact. <hr /></blockquote>Is this supposed to be a desirable or actual profle? The few accelerometer graphs we've been privy to don't come close to being constant over any time interval (except at the peak), if I remember correcty.

Jim

dr_dave
03-31-2007, 07:58 AM
<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote Bob_Jewett:</font><hr>One acceleration profile I've seen suggested that the forward force is nearly constant over a significant fraction of the travel to impact. <hr /></blockquote>Is this supposed to be a desirable or actual profle? The few accelerometer graphs we've been privy to don't come close to being constant over any time interval (except at the peak), if I remember correcty.<hr /></blockquote>I have actual acceleration plots from two sources in TP A.9 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-9.pdf), along with some qualitative analysis. All of the plots show dynamically changing acceleration during the forward stroke.

Regards,
Dave

dr_dave
03-31-2007, 08:18 AM
<blockquote><font class="small">Quote hanisch:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ... you are missing something significant here. you are assuming that an accelerating stroke does not do work to the ball. that is, you are assuming that the distance over which the tip remains in contact with the ball--the dwell distance--is insignificant. ... <hr /></blockquote>
No, I'm not assuming it. I am calculating it within a reasonable model of the stick-hand-tip system. That model seems to explain all of the major phenomena that have been observed. Unfortunately, it seems we cannot agree on that model.

In the golf example that you found, I think there is a point to consider: In golf, what the hands are doing on the club at the instant of club head-ball contact is not important. A laser could cut the club off at the end of the grip just before the club hits the ball and the shot would be unchanged. That's because the mechanism of energy transfer from the hands to the head is pretty slow and the ball is on the club head for a relatively short time. Something similar keeps your hands from influencing the shot at the instant of contact at pool.

Do you have any shot that you feel requires an accelerating stroke that cannot be made with a "peak speed" stroke? <hr /></blockquote>

bob,

if i push an object across the floor (assume no or negligible friction) for a certain distance, i am applying a force on the object for the entire distance. by definition i am doing work on the object. the object will keep increasing its velocity (i.e. it will accelerate) over the entire distance.

once i let go of the object there is no longer any force acting on the object. therefore no more work is done on the object, and the object will no longer accelerate. it will continue on at a constant velocity.

if we are so far in agreement, let's consider your example of a laser cutting off the golf club at the grip just before it contacts the ball.

before the laser cut the club, the player was applying a force on the club, and thus doing work to the club, thereby accelerating it. but once the club is severed, no longer is there any force acting on the club. therefore the club cannot do work on the ball. the force is gone. but if the club was not severed, the force would still be present and the club would be doing work on the ball, accelerating it for the distance the club remained in contact with the ball.

you see, the shot would be changed dramatically. in one case (club intact) work is being done on the ball, accelerating it, and in the other case (club severed by a laser just before impact) no work is being done on the ball.

do you really thing that if a batter let go of the bat just before the bat hit the ball it would be same as if the batter held on and swung through it? in the latter case there is a force. in the former, there isn't.<hr /></blockquote>William,

With a golf swing, baseball swing, or powerful pool stroke, most of the work is done well before impact, and very little work (practically none) is during the brief impact period. The work done before impact creates momentum (of the club, bat, or cue). This momentum is what creates the extremely large impulse forces that occur during the brief impact period. The final ball-speed is all about club-head, bat, and cue stick speed at impact. Tiger Woods generates tremendous club-head speed before impact, and Babe Ruth generated tremendous bat-speed before impact (... it also helped that he used a heavy bat ... momentum is about speed and mass, so the more of each, the better). No human can generate much energy (i.e., do much work) during the incredibly brief contact times (because our power is limited ... energy = power * time); although, they can generate incredible energy over a long swing or stroke. Think about the amount of time spent on the swing/stroke vs. the impact time interval. The athlete spends more than 100x as much time on the swing/stroke as compared to the impact interval. So, in simple terms, you can generate more than 100x as much energy during the swing/stroke as you can during impact.

Regards,
Dave

Jal
03-31-2007, 12:53 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote Bob_Jewett:</font><hr>One acceleration profile I've seen suggested that the forward force is nearly constant over a significant fraction of the travel to impact. <hr /></blockquote>Is this supposed to be a desirable or actual profle? The few accelerometer graphs we've been privy to don't come close to being constant over any time interval (except at the peak), if I remember correcty.<hr /></blockquote>I have actual acceleration plots from two sources in TP A.9 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-9.pdf), along with some qualitative analysis. All of the plots show dynamically changing acceleration during the forward stroke.

Regards,
Dave <hr /></blockquote>Dr. Dave,

Looking at Andreas Efler's stroke, the first and third, but especially the third, do show a period of almost constant velocity, then a surge toward the end. His second one looks very similar to John Pizzuto's except for a very sharp spike just before impact. Is he exerting fine control with a flick of his wrist perhaps?

Although they don't show much in the way of acceleration at impact, all three are quite different from each other and certainly seem to qualify as "different strokes", the subject of this thread.

Jim

Jal
03-31-2007, 01:16 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>With a golf swing, baseball swing, or powerful pool stroke, most of the work is done well before impact, and very little work (practically none) is during the brief impact period. The work done before impact creates momentum (of the club, bat, or cue). This momentum is what creates the extremely large impulse forces that occur during the brief impact period. The final ball-speed is all about club-head, bat, and cue stick speed at impact. Tiger Woods generates tremendous club-head speed before impact, and Babe Ruth generated tremendous bat-speed before impact (... it also helped that he used a heavy bat ... momentum is about speed and mass, so the more of each, the better). No human can generate much energy (i.e., do much work) during the incredibly brief contact times (because our power is limited ... energy = power * time); although, they can generate incredible energy over a long swing or stroke. Think about the amount of time spent on the swing/stroke vs. the impact time interval. The athlete spends more than 100x as much time on the swing/stroke as compared to the impact interval. So, in simple terms, you can generate more than 100x as much energy during the swing/stroke as you can during impact. <hr /></blockquote>I think that this is the clearest and most convincing explanation of why what goes on during contact is negligible.

Jim

dr_dave
03-31-2007, 03:24 PM
<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>I have actual acceleration plots from two sources in TP A.9 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-9.pdf), along with some qualitative analysis. All of the plots show dynamically changing acceleration during the forward stroke.<hr /></blockquote>Dr. Dave,

Looking at Andreas Efler's stroke, the first and third, but especially the third, do show a period of almost constant velocity, then a surge toward the end.<hr /></blockquote>
The blue curves in the top three plots (red curves in the bottom two plots) represent forward acceleration. A positive acceleration implies slowing in the backward direction (e.g., at the end of the back swing) and/or speeding up in the forward direction (e.g., during most of the pre-impact portion of the forward stroke). A negative acceleration implies slowing in the forward direction (e.g., in the later part of the forward warm up strokes) and/or speeding up in the backward direction (e.g., at the beginning of the backstroke).

I think the relatively flat portion of Andreas' curve, before impact, corresponds to the second half of his back-swing. Notice how it is nearly identical to the shapes in the warm-up strokes (which I think are fairly firm). I think the entire forward stroke, before impact, is represented by the tall peak. The final forward stroke is much faster and more forceful than the warm-up strokes. After the peak, and before impact, the acceleration appears to go negative a little, implying he was actually decelerating a little before impact (if you trust the sensor, its calibration, and the data acquisition). At impact, the signals go wild due to shock waves and vibration.

In the first two plots (softer strokes), the acceleration is still positive at impact, implying that the cue stick is speeding up during the entire forward stroke (e.g., he is accelerating into the ball). Both of Pizutto's plots show slight slowing (negative acceleration) just before impact.

Andreas does not appear to have a distinct pause at the transition between the back and forward stroke because the acceleration curve would be flat (at zero) if there were a deliberate pause.

<blockquote><font class="small">Quote Jal:</font><hr>His second one looks very similar to John Pizzuto's except for a very sharp spike just before impact. Is he exerting fine control with a flick of his wrist perhaps?<hr /></blockquote>Again, the spike represents the entire forward stroke, not any weird wrist action. Note that the time scales are very different between the two sets of plots. Pizutto's plots are just showing the final forward stroke and the resulting shock and vibration immediately after impact. Andreas' plots show a much large time interval, including warm-up strokes.

Regards,
Dave

Jal
03-31-2007, 03:59 PM
Thank you Dr. Dave. Your interpretation makes much more sense.

I meant constant acceleration above, not velocity (well, maybe), but definitely didn't appreciate the different time scale compared to Pizzuto's.

Jim

dr_dave
03-31-2007, 04:52 PM
<blockquote><font class="small">Quote Jal:</font><hr> Thank you Dr. Dave. Your interpretation makes much more sense.

I meant constant acceleration above, not velocity (well, maybe), but definitely didn't appreciate the different time scale compared to Pizzuto's.<hr /></blockquote>Jim,

You're welcome. And thank you for prompting me to think about these plots more than I had done so before.

Catch you later,
Dave

DickLeonard
04-02-2007, 08:44 AM
Iralee as a straight pool player who learned the secret of playing 14.1 was controlling the object balls just as a straight rail billiard player learns to controll the billiard balls. It is by controlling your stroke and follow thru,draw,follow and english all play a difference on the outcome of how the balls react. Always playing position for out balls meant you are never without a shot.

I learned that by playing an angled cutshot into the corner pocket and having the object ball just make the pocket with a 2 inch follow my cueball would reach x on the table now hitting the same shot with a three inch follow thru it would hit x+1 and four inch follow would hit x+2 and a five inch follow would hit x+4. So it is possible by controlling the length of your follow thru to play without the appearance of hitting the balls hard.

I have watched tapes of three cushion played on heated tables with fast cloth, I could see that playing positon on long rail/short rail/long rail shots it would be possible by hitting the balls with a soft stroke to walk the balls up the table and then turn around and walk them them down the table. Of course maybe some player has develop this system of running points in three cushion. ####

hanisch
04-02-2007, 06:18 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ...
still, can you explain why nobody was able to produce a stroke that was accelerating throughout? perhaps it was being conscious of being filmed, they very bright lights, etc. but it can't be too difficult. ...
<hr /></blockquote>
No, it is immensely difficult. It goes against every bit of billiard learning that any decent player has acquired over years of practice and perfecting the stroke. I urge you to try shooting shots in which the acceleration of the stick can be measured and to shoot shots in which the ball is struck at peak acceleration. It's too bad that the needed equipment is not more readily available, but I really do think that if more people could actually see the mechanics of their strokes, and the strokes of champions, they would stop worrying about developing a million strokes for a jillion shots. <hr /></blockquote>

bob,

there is something really bothering me about the diagram in your "don't grip it and rip it" article. (see http://www.sfbilliards.com/jax_bd150.pdf and go to the last page.) the diagram shows a stroke such that the tip has no (or perhaps even negative) acceleration from when the tip is about 2 or 3 centimeters from the ball, all the way up to when the tip contacts the ball. then, after contact--after the tip is no longer in contact with the ball--the tip begins to accelerate again. this seems to me to be a badly flawed stroke. do you see why?

for the tip to stop accelerating before contact (well before contact--2 or 3 centimeters before contact), the force that got the tip moving during the forward stroke must have ceased (or even went in the opposite direction, if the tip decelerated before contact). but for the tip to accelerate again after contact, there must have been a force acting on it.

so, we have these events:

1. force acts to accelerate the tip (provided by the stroke)
2. force ceases to act, so that the tip has constant velocity, or
2a. force acts in the opposite direction, slowing down the tip (provided by the perhaps faulty stroke)
3. force acts in the opposite direction, slowing down the tip (provided by the impact with the ball)
4. force acts to accelerate the tip once again (provided by the perhaps faulty stroke)

if i understand you correctly, you maintain that the "best -- easiest, most accurate, most efficient -- way to hit the cue ball" is "when the stick has peak speed. that is when the acceleration is zero." but for this to happen, whatever force got the tip accelerating in the first place (i'm referring to the force generated from the stroke) must fully stop from acting before contact, otherwise you wouldn't have zero acceleration. but if the force fully stops, how does the tip start accelerating again after contact? there must be a force causing this acceleration.

it seems to me that the stroke in the diagram has a significant jerkiness to it. if the stroke was smooth, there would be no acceleration after contact. the tip would continue at the speed it had after contact, then decelerate due to the force in the opposite direction from the hand and arm not letting the stick go.

however, contrary to your ideal stroke, if the stroke was maintaining a force throughout contact (that is, accelerating through the ball--i.e. the absence of event 2. or 2a. above), then there would be an increase in acceleration after contact. but this would be due to the fact that the force from the start of the forward stroke never ceased, but was momentarily, partially offset by the force of impact with the ball.

it is this accelerating through contact stroke that i see all the top three-cushion players use for a good deal of shots. (that's not to say that all shots are taken with this type of stroke. i've also seen top players use short decelerating strokes for certain shot, which require certain combinations of spin and speed. also, they vary how much they accelerate through, again, depending on what's needed.) moreover, all else being equal, i would say that accelerating through (that is, maintaining the force of the stroke throughout the shot), provides for a more consistent shot.

william

Bob_Jewett
04-02-2007, 07:03 PM
<blockquote><font class="small">Quote hanisch:</font><hr> ... there is something really bothering me about the diagram in your "don't grip it and rip it" article. (see http://www.sfbilliards.com/jax_bd150.pdf and go to the last page.) the diagram shows a stroke such that the tip has no (or perhaps even negative) acceleration from when the tip is about 2 or 3 centimeters from the ball, all the way up to when the tip contacts the ball. then, after contact--after the tip is no longer in contact with the ball--the tip begins to accelerate again. this seems to me to be a badly flawed stroke. do you see why? <hr /></blockquote>

It is important to realize that the hand is much softer than the tip. Your skin acts like a very limp spring when compared to the springiness of the tip. As I explained (or tried to) in the article, when the stick hits the ball, its speed is reduced by 50% during the 1 millisecond or so that the tip is on the ball. This is absolutely standard and expected. What was not expected (at least by me) is the increase after contact. In retrospect, it should have been expected. When the stick suddenly slows, the hand cannot and does not slow down as much. It keeps moving forward and gradually the spring action of the flesh pulls forward on the stick and back on the hand to make their speeds equal again.

In fact from the difference in times that the two interactions take (stick-ball and hand-stick) it is possible to estimate the "spring constant" of your hand.

The softness of the hand-stick connection is a point that is very important to understand. You seem to be assuming, very falsely, that the hand and stick are very stiffly bound together. If you make that false assumption, false conclusions are sure to follow.

[ QUOTE ]
for the tip to stop accelerating before contact (well before contact--2 or 3 centimeters before contact), the force that got the tip moving during the forward stroke must have ceased (or even went in the opposite direction, if the tip decelerated before contact). but for the tip to accelerate again after contact, there must have been a force acting on it.<hr /></blockquote>
Yes, and that is the hand and its stored kinetic energy.

dr_dave
04-03-2007, 10:34 AM
William,

I agree with Bob's answers (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=248642&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) 100%. See also a previous post (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=176991&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=1) that helps back up his arguments. The high-speed video clip (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-34.htm) mentioned helps illustrate the grip-hand spring back. It is easiest to visualize in the FWD30 portion of the video.

Regards,
Dave

<blockquote><font class="small">Quote hanisch:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote hanisch:</font><hr> ...
still, can you explain why nobody was able to produce a stroke that was accelerating throughout? perhaps it was being conscious of being filmed, they very bright lights, etc. but it can't be too difficult. ...
<hr /></blockquote>
No, it is immensely difficult. It goes against every bit of billiard learning that any decent player has acquired over years of practice and perfecting the stroke. I urge you to try shooting shots in which the acceleration of the stick can be measured and to shoot shots in which the ball is struck at peak acceleration. It's too bad that the needed equipment is not more readily available, but I really do think that if more people could actually see the mechanics of their strokes, and the strokes of champions, they would stop worrying about developing a million strokes for a jillion shots. <hr /></blockquote>

bob,

there is something really bothering me about the diagram in your "don't grip it and rip it" article. (see http://www.sfbilliards.com/jax_bd150.pdf and go to the last page.) the diagram shows a stroke such that the tip has no (or perhaps even negative) acceleration from when the tip is about 2 or 3 centimeters from the ball, all the way up to when the tip contacts the ball. then, after contact--after the tip is no longer in contact with the ball--the tip begins to accelerate again. this seems to me to be a badly flawed stroke. do you see why?

for the tip to stop accelerating before contact (well before contact--2 or 3 centimeters before contact), the force that got the tip moving during the forward stroke must have ceased (or even went in the opposite direction, if the tip decelerated before contact). but for the tip to accelerate again after contact, there must have been a force acting on it.

so, we have these events:

1. force acts to accelerate the tip (provided by the stroke)
2. force ceases to act, so that the tip has constant velocity, or
2a. force acts in the opposite direction, slowing down the tip (provided by the perhaps faulty stroke)
3. force acts in the opposite direction, slowing down the tip (provided by the impact with the ball)
4. force acts to accelerate the tip once again (provided by the perhaps faulty stroke)

if i understand you correctly, you maintain that the "best -- easiest, most accurate, most efficient -- way to hit the cue ball" is "when the stick has peak speed. that is when the acceleration is zero." but for this to happen, whatever force got the tip accelerating in the first place (i'm referring to the force generated from the stroke) must fully stop from acting before contact, otherwise you wouldn't have zero acceleration. but if the force fully stops, how does the tip start accelerating again after contact? there must be a force causing this acceleration.

it seems to me that the stroke in the diagram has a significant jerkiness to it. if the stroke was smooth, there would be no acceleration after contact. the tip would continue at the speed it had after contact, then decelerate due to the force in the opposite direction from the hand and arm not letting the stick go.

however, contrary to your ideal stroke, if the stroke was maintaining a force throughout contact (that is, accelerating through the ball--i.e. the absence of event 2. or 2a. above), then there would be an increase in acceleration after contact. but this would be due to the fact that the force from the start of the forward stroke never ceased, but was momentarily, partially offset by the force of impact with the ball.

it is this accelerating through contact stroke that i see all the top three-cushion players use for a good deal of shots. (that's not to say that all shots are taken with this type of stroke. i've also seen top players use short decelerating strokes for certain shot, which require certain combinations of spin and speed. also, they vary how much they accelerate through, again, depending on what's needed.) moreover, all else being equal, i would say that accelerating through (that is, maintaining the force of the stroke throughout the shot), provides for a more consistent shot.<hr /></blockquote>

iralee
04-03-2007, 02:36 PM
<blockquote><font class="small">Quote DickLeonard:</font><hr> Iralee as a straight pool player who learned the secret of playing 14.1 was controlling the object balls just as a straight rail billiard player learns to controll the billiard balls. It is by controlling your stroke and follow thru,draw,follow and english all play a difference on the outcome of how the balls react. Always playing position for out balls meant you are never without a shot.
<hr /></blockquote>

It's been almost 20 years since I had the pleasure of having DickLeonard run hundreds of balls on me in straight pool at the RPI student union. I still have vivid images of the wide variety of strokes that he used to use as he ran rack after rack after rack...etched in my mind. I may have been "green" at the time, but I payed very close attention during my lessons - watching how he would "pop" the ball on certain shots and "massage" the ball on others - depending on the exact given situation.


A different stroke tailored to every shot; that's what is needed in order to perform beyond a certain level. The notion of reducing and simplifying the complexity of what is involved can be tempting (to find the time to "specialize" on a smaller subset of techniques); but I conclude that if one starts to eliminate from the spectrum of strokes available to them (accelerations/varying degrees of follow-through), they inadvertently deprive themselves from the depth and richness in the game - limiting their own potential.

I feel like it would be a mistake to discount our body's capabilities or our mind's ability to sense and produce even the most subtle effects on the billiard table. My experience is that the human being handles slight nuances better than we ever give them credit for. One one-thousandth of a second of tip-ball contact time is a mere blink of an eye, but to a sensitive billiard player, this entire span of time is very precious. During this seeming instant, the work done is far from "insignificant"! It actually represents a full and precise transfer of all of the energy/information the ball requires to make even the most complicated 3-cushion billard pattern.

Contrary to what some have suggested here, there exist many shots in billards that are difficult, if not impossible, to make by sticking with a single non-accelerating stroking strategy. We've all heard comments about top-players' eccentricities (Efren's roller coaster arm or Sang Lee's swiping stroke) that seem to suggest that these players were great DESPITE their departures from the classically taught ideals (one correct stance, pendulum stroke, etc.) - makes me wonder.

Before we all blindly (and naively) embrace these trivial characterizations on technique, I think it pays for us to revisit the rigidity of textbook approaches vigorously against real science to make sure that the scientists don't accidentally render significant things nil while dumbing things down within the equations.

At this time, I think it is still premature for anyone to say that we have scientifically proven that acceleration through the cue-ball is a useless stroking strategy. From what I see, insufficient evidence has been presented to make this assertion. People on this board trust and look to the technical expertise of the engineers, mathematicians and physicists for answers that might help them play better. Especially if in a position of technical authority, to present premature theories and partial "findings" as de fact o truth is, at best, careless. Many billiard students starve for an analytical explanation, doling out hasty science is irresponsible - if the scientists jump to conclusions without enough evidence to back them up.

I enjoy reviewing and thinking through all of the current theories regarding the topic of different strokes. Andreas Efler's work and the Jacksonville experiment studies are indeed milestones - and only the beginning. But, for me, the "jury's still out" regarding any theory that dismisses the effective uselessness of accelerating strokes through the cue ball.


(after 20 years, I still have flashbacks of 150 to -2),
-Ira /ccboard/images/graemlins/wink.gif

Bob_Jewett
04-03-2007, 03:03 PM
<blockquote><font class="small">Quote iralee:</font><hr> ... A different stroke tailored to every shot; that's what is needed in order to perform beyond a certain level. The notion of reducing and simplifying the complexity of what is involved can be tempting (to find the time to "specialize" on a smaller subset of techniques); but I conclude that if one starts to eliminate from the spectrum of strokes available to them (accelerations/varying degrees of follow-through), they inadvertently deprive themselves from the depth and richness in the game - limiting their own potential.
... <hr /></blockquote>
OK. But it is up to you to propose a particular shot as an example. Is there any shot that can demonstrate the utility of a special stroke technique? (In this case, we are clearly not talking about masses or fouettes.) That is, does any shot require a swooping motion? Or stick acceleration at impact? Or a tight grip?

It's simple to refute those concrete-minded scientists: give a specific example.

Jal
04-03-2007, 04:18 PM
<blockquote><font class="small">Quote iralee:</font><hr> ...
A different stroke tailored to every shot; that's what is needed in order to perform beyond a certain level. The notion of reducing and simplifying the complexity of what is involved can be tempting (to find the time to "specialize" on a smaller subset of techniques); but I conclude that if one starts to eliminate from the spectrum of strokes available to them (accelerations/varying degrees of follow-through), they inadvertently deprive themselves from the depth and richness in the game - limiting their own potential.... <hr /></blockquote>Extremely well stated if I may be a judge. It was a pleasure to read. But we can separate out the psycho-motor requirements of a particular player, or maybe players in general, from the physics of the stick/ball interaction itself. While it may not be true that what has been said about the latter has been proven beyond any possible doubt, the arguments are pretty persuasive.

As far as acceleration, just to say it again, "accelerating through" may give you some measurable gain in cueball speed/spin (probably, in my opinion), but not because you're applying force during impact, but up to impact. Since you can't turn it off at the moment of impact, it's not immediately obvious as to which of these is producing the gain. But physics points a finger at one and not the other.

Jim

iralee
04-04-2007, 12:36 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote iralee:</font><hr> ... A different stroke tailored to every shot; that's what is needed in order to perform beyond a certain level. The notion of reducing and simplifying the complexity of what is involved can be tempting (to find the time to "specialize" on a smaller subset of techniques); but I conclude that if one starts to eliminate from the spectrum of strokes available to them (accelerations/varying degrees of follow-through), they inadvertently deprive themselves from the depth and richness in the game - limiting their own potential.
... <hr /></blockquote>
OK. But it is up to you to propose a particular shot as an example. Is there any shot that can demonstrate the utility of a special stroke technique? (In this case, we are clearly not talking about masses or fouettes.) That is, does any shot require a swooping motion? Or stick acceleration at impact? Or a tight grip?

It's simple to refute those concrete-minded scientists: give a specific example. <hr /></blockquote>

I do have specific examples to illustrate the utility of acceleration techniques and I intend to share them later.

However, before getting to them, I wish to address my original point without distraction - which is that as (scientifically/technically-minded billiard players) it would be a mistake to assume that we have already answered the question concerning acceleration strokes having no physical effect on the cue ball.

I wouldn't dare jump to refute a scientific explanation purely on my intuition as is suggested. I have only a bachelor's background knowlege in physics - but I am familiar enough with scientific method to recognize when premature conclusions are being drawn. We have seen some (very) nice acceleration graphs and vivid high-speed videos that, for me, raise many questions (which I hope to see answered during my lifetime) and cause further speculation as we search for a more complete (and applicable) model.

Will you agree that there are still gaps and unchecked assumptions that being made or are you of the opinion that all sufficient evidence has been presented? I find that we have a limited number of studies to date, many without controls. I'd like to help and come up with more revealing material as a result of these discussions if we have the opportunity to here.

I agree that science often shows us that we cannot trust our intuition alone - especially when it comes to matters of physics. Many illusions lurk to fool our limited senses and therefore we need tools and constructions to prove things one way or another. In science, I have found that it is often tempting and appealing to assume that the unobvious is true and stop there. But sometimes, iff we keep on digging, we can resolve concepts for which we have a strong intuition about - with sound and scientific explanations within a new paradigm (new model, etc). I am actually a member of neither camp - findings that agree or disagree with my intuition do not matter. The only thing that matters is illumination: that I see proofs are well founded and that hold their ground on their own. Then, and only then, I can have the courage to modify my intuition on a topic. Afterwards, we can hope to find utility for the newfound facts and feel resolute about our basis for them.

I admire that you have delved into hand dynamics (dampening, resiliency,etc) within your model - older impulse-based models for stick/ball interaction pale in comparison. Could this dampening effect of a "working" (accelerating) hand actually increase the dwell distance as it decreases the impulse effect of the tip material on the ball? (like a volleyball player "sets" up a shot for the spiker)

As I said, I do have very interesting examples of kiss avoidance solutions in 3-cushion where the best strategy for success is enhanced by the utility of an accelerating stroke (shown to me by Sang Lee). Describing them will require exacting diagrams and careful explanations to make them clear - and as soon as I have time to do this, I will post them here in this thread in response. I also want to avoid subjectively based arguements concerning specific shots and their optimal playing strategies within this response - as tempting as your invitation sounds to me. (I love to discuss shots - it is one of my favorite hobbies)

The question of whether or not specific examples of utility exist is a separate issue from whether or not we (as a group) have proved scientifically that there is (or is not) an effect of an accelerating stroke on the cue ball.

I am probably as convinced about the real benefits of different strokes, you are convinced of the insignificance of the existence of differing effects of accelerating strokes. If it is scientifically proven that there is no effect of acceleration on the ball action, then I will must reconsider my position about what is actually happening during certain problem shots I have in mind. In other words, I welcome the possibility of proving my intuition wrong.

On the other hand, if the scientists on this board are less interested in proofs and simply doubt the practicality of the strategy (of accelerating through) in game play (due to the lack of useful examples on hand) I may be able to help by pointing out scenarios. I am versed on specific 3-cushion shots that contain multiple-kiss problems where the solution sets are narrow enough to illustrate good examples of the usefulness of the technique (usually the cue ball gets manipulated to either "race ahead" to pass a hazardous intersection with a moving ball or "puts on the brakes" to avoid getting kissed out.)

Bear in mind that even if I isolate a good shot example to illustrate the benefits of employing an accelerating stroke, and someone else shows that another kind of (zero-acceleration) stroke can be used to make the shot - does not automatically remove the validity of the accelerating stroke as the best strategy to use (i.e. the balls can be shown to behave differently). But, I will keep this in mind and try my best to choose examples that will visually weed out these subtle differences by exaggerating the nuances in relative ball speeds with, and without, an accelerating stroke.

Respectfully,
-Ira

iralee
04-04-2007, 02:05 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>
And I believe that physics says that the spin-speed ratio for a particular hit is determined almost entirely by the lever arm of the shot -- that is, how far from center you hit the cue ball. To the best of my knowledge, there has never been any demonstration that other factors are important in determining the spin/speed ratio.
<hr /></blockquote>

Suppose I had a bowling ball in front of me and I wished to get it into a spinning roll into the pins without throwing it with the traditional bowling grip:

I could strike it sharply off center (with a rubber-tipped object) towards the direction of my target (lever arm approach) - try my best to judge the deflection...

Another approach could be to take hold of one of the finger holes and fling my hand in the shape of an arc (around the center of the ball) while pushing gently forward in the direction of the target.

I know billiard balls and bowling balls are quite different things. But, I still imagine that certain spin/speed ratios might be easier to achieve using one approach vs the other. I don't dismiss the possibility that all spin/speed ratios can be achieved using two different approaches, but I remain skeptical (try spinning it in place). Still, practically speaking, one approach for arriving at a particular spin/speed ratio might prove itself to be easier to duplicate (repeatable) than the other. I would consider this a better stragegy to use.

Forgive the strange example - somehow, it has always helped me to "magnify" objects when I think of them.

-Ira

Bob_Jewett
04-04-2007, 03:10 PM
<blockquote><font class="small">Quote iralee:</font><hr>... Will you agree that there are still gaps and unchecked assumptions that being made or are you of the opinion that all sufficient evidence has been presented? I find that we have a limited number of studies to date, many without controls. ... <hr /></blockquote>
Well, speaking as a scientist, all theories are eternally provisional and are waiting for data to refute them. That's the way science works. Science can prove nothing, more or less by the way it is defined. The law of gravitation seems pretty convincing, but it's not really a law -- it's just a theory that hasn't been disproven yet. It allows predictions to be made, and as long as everything goes according to plan, it continues to be accepted for the time being.

I think a point that you might want to consider while you're preparing possible shots that demonstrate the utility of different strokes is that according to pretty solid theories, at the instant the cue ball leaves the tip, eleven numbers completely describe its state: three for location, three for spin, three for velocity and two for orientation. (Usually the ball is assumed to be uniform, and the last pair is not considered. And, if you consider the ball to be vibrating, then a lot more numbers are required.) A stroke can only affect the outcome of the shot by changing one or more of those numbers. If a stroke is somehow special, scientists probably will ask which of those numbers has particular importance.

Bob_Jewett
04-04-2007, 03:16 PM
<blockquote><font class="small">Quote iralee:</font><hr> ... Still, practically speaking, one approach for arriving at a particular spin/speed ratio might prove itself to be easier to duplicate (repeatable) than the other. I would consider this a better stragegy to use. ... <hr /></blockquote>
I agree completely with this. The difficulty in showing one technique is more consistent than another is to find an appropriate test. I think if humans are involved, this is very hard.

cushioncrawler
04-04-2007, 05:33 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> ......And I believe that physics says that the spin-speed ratio for a particular hit is determined almost entirely by the lever arm of the shot -- that is, how far from center you hit the cue ball. To the best of my knowledge, there has never been any demonstration that other factors are important in determining the spin/speed ratio.....<hr /></blockquote>Bob -- I disagree here. The ball can only ever do what the cue (or cushion) allows. A bit of the ball iz in contact with a bit of the cue (or cushion), and these can only ever be doing the same thing at the instant of seperation (if zero slippage). Thusly, spin etc depends on things other than lever arm. For instance, how much spin could one get with a one ton steel rod ??

Yesterday i woz going throo my stuff, and i found a program that i wrote/crunched years ago to find the "best" friktion for a cushion, if u wanted to minimize "jump". I found that for a cushion ht of 0.70D, the "best" balltocushion friktion woz 0.44. Any less than 0.44, or any more, and the ball jumped more (for 90dg attack here). I reckon that it iz all more complicated than just looking at the lever arm. And, 0.70 aint best either, but that iz another story. madMac.

iralee
04-05-2007, 11:08 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote iralee:</font><hr>... Will you agree that there are still gaps and unchecked assumptions that being made or are you of the opinion that all sufficient evidence has been presented? I find that we have a limited number of studies to date, many without controls. ... <hr /></blockquote>
Well, speaking as a scientist, all theories are eternally provisional and are waiting for data to refute them. That's the way science works. Science can prove nothing, more or less by the way it is defined. The law of gravitation seems pretty convincing, but it's not really a law -- it's just a theory that hasn't been disproven yet. It allows predictions to be made, and as long as everything goes according to plan, it continues to be accepted for the time being.
<hr /></blockquote>

Yes. Thomas Kuhn described the period (when everything goes according to plan) in the cycle of scientific revolutions as "normal science". As science advances and anomolies emerge, a revolution eventually occurs and a paradigm shift is needed before science may return to "normal" again. In the context of this thread, today's "normal billiard science" states that the tip-ball interaction is too brief and therefore insignificant to effect any work on the ball. From my perspective, there are many anomolies to this theory being observed in the art - enough that should motivate us to dig deeper.

Detailed experimentation and theoretical work using physics and math has been applied to separately model two distinct events: the motion of the cue stick before contact and the behavior of the cue ball after it leaves the tip. A lot seems to revolve around the assumption of insignificance based on the duration (.001 sec) while the tip interacts with the ball and the forces involved. Following this, many explanations have been drafted around this to justify the non-existance of a "working stroke": difficulty for humans to actually accelerate through the ball, large eclipsing tip forces (100x hand), human inability to conciously/physically manipulate such great forces in such short time, etc.

With no real answers, we search to find real-world examples to observe. In this vein, identifying applications and examples of perceived usage may give us added motivation to continue the search for an experiment that validates the existance of a working stroke. Skeptical people I've discussed this with in the past actually believe that if they can discount the merit of specific examples, this somehow helps to support the non-existance theory. I find this to be a very confused way of looking at these important questions.

In an attempt to address these concerns appropriately, your improved concept (hand/stick/tip/cue springs/levers) represents a breakthrough and seems a much better model to pursue in more detail. Exactly what goes on during this impulse-full, force-full, dampened hand? - This is surely complex and needs to be better understood.

I propose that we should devise a way to observe the dwell distances against varying degrees of acceleration to see if there are measurable difference. Such findings would answer many questions. If there are no observable differences in dwell distance between strokes of varying accelerations, then we can more readily dismiss claims that any appreciable work is actually being performed during the brief moment. Until then, how can any of us know for sure?


<blockquote><font class="small">Quote Bob_Jewett:</font><hr>
I think a point that you might want to consider while you're preparing possible shots that demonstrate the utility of different strokes is that according to pretty solid theories, at the instant the cue ball leaves the tip, eleven numbers completely describe its state: three for location, three for spin, three for velocity and two for orientation. (Usually the ball is assumed to be uniform, and the last pair is not considered. And, if you consider the ball to be vibrating, then a lot more numbers are required.) A stroke can only affect the outcome of the shot by changing one or more of those numbers. If a stroke is somehow special, scientists probably will ask which of those numbers has particular importance. <hr /></blockquote>

After the cue ball leaves the tip, perhaps only eleven numbers tells us all about state the cue-ball, but this wasn't a point in question. Clearly, there is no magical property in any stroke that affects the cue-ball after the tip has left the ball. I think we are looking for numbers to help us model what happens during the all-important tip-ball-dwelling event - the time during which the tip is in contact with the cue ball. Some of the most important numbers I would like to see are figures for actual dwell distances (not just times), the acceleration curve during the period in question, attempts to measure energy stored in the shaft wood while it buckles (as well as the hand), etc.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote iralee:</font><hr> ... Still, practically speaking, one approach for arriving at a particular spin/speed ratio might prove itself to be easier to duplicate (repeatable) than the other. I would consider this a better stragegy to use. ... <hr /></blockquote>
I agree completely with this. The difficulty in showing one technique is more consistent than another is to find an appropriate test. I think if humans are involved, this is very hard. <hr /></blockquote>

I think we can agree that this is a real challenge. Still, using human subjects combined with fine measuring equipment and/or cleverly constructed experiments, we may yet find the answers we seek.

Naturally, all of these ideas will be propagated through the pool "classrooms" and instructional literature. Practical concerns aside, I think we should keep digging for the next revolution to explain what occurs on every stroke. If we can describe with greater certainty what happens deep down in the mechanics of a stroke, then I am confident that the real-world will find ways to benefit from the facts.

The question about whether accelerating strokes can produce a working effect and the debate about whether or not using them in practice is an effective strategy should be seen as two completely separate issues.


-Ira

Jal
04-05-2007, 01:25 PM
<blockquote><font class="small">Quote iralee:</font><hr> ...A lot seems to revolve around the assumption of insignificance based on the duration (.001 sec) while the tip interacts with the ball and the forces involved. Following this, many explanations have been drafted around this to justify the non-existance of a "working stroke":<hr /></blockquote>You make it sound as if someone, on a whim perhaps, made the decision that the work done is insignificant, and then everbody got in line to offer their rationals for this.

<blockquote><font class="small">Quote iralee:</font><hr>...difficulty for humans to actually accelerate through the ball<hr /></blockquote>Probably immpossible except maybe at a very, very slow cue speed (if you mean actually having the cue increase forward speed during impact, as opposed to applying force to retard its deceleration.)

<blockquote><font class="small">Quote iralee:</font><hr>I propose that we should devise a way to observe the dwell distances against varying degrees of acceleration to see if there are measurable difference. Such findings would answer many questions. If there are no observable differences in dwell distance between strokes of varying accelerations, then we can more readily dismiss claims that any appreciable work is actually being performed during the brief moment. Until then, how can any of us know for sure?<hr /></blockquote>As motivation, it would help if you or somebody offered some reason that it might be important. Several arguments have been raised against it, but none in favor, at least in a quasi-quantitative manner.

A simple experiment though (if you have a fairly high speed camera), is to measure the cueball's speed after applying a stroke which has the stick measurably accelerating at impact. If its speed is measurably greater than the stick's speed (and mass) alone would dictate, then you would have your demonstration. Non-accelerating shots would also need to be filmed to get the effective mass ratio of the particular cue and ball, as well as associated energy losses. Both non-accelerating and accelerating shots should have the cue moving at roughly the same speed just before impact.

A couple of additional (but vague) considerations work against the additional dwell distance notion.

First, if the dwell time is increased as well, then the extra hand force that the cueball experiences is reduced to less than the one part in four mentioned earlier. (But, to be fair, if the dwell time is reduced, then this is increased to greater than one part in four.)

Second, as tip offset is increased, the compression force should become asymmetric over its time interval, and very highly asymmetric at large tip offsets. Instead of a gradually increasing force reaching a peak at about T/2, then falling off in a mirror-like fashion, it should peak early on during impact, and then probably drop off rather quickly. This is a necessary consequence, I think, of putting spin on the ball and is derived from the reduced separation velocity of the ball and stick. So even if you observed increased dwell distance, the force acting over that "extra" distance should be, I think, reduced to a low level by then.

But this is a little speculative, admittedly.

Jim

dr_dave
04-06-2007, 09:29 AM
Jim,

Nice summary!

But, putting the physics aside for a moment, all that really matters is what works for different players. If a player can achieve more cue tip speed by thinking: "accelerate through the ball," then that is a good practice. In fact, this is what I do when I need power (e.g., with a power draw or power break) ... I imagine "smoothly accelerating through the ball" and I try to exaggerate a straight and long follow-through. Both mental images help me generate more tip speed at impact and help me keep my stroke straight. Different people will modify their strokes in various ways for various types of shots to achieve better control and repeatability of impact speed and placement. Stroke biomechanics and control, and personal differences, and how one thinks, is much more complicated and important than the physics of the cue tip and cue ball. See also: my previous posting on follow-through (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=223913&amp;page =0&amp;view=&amp;sb=&amp;o=&amp;fpart=&amp;vc=).

To us (you, me, Bob, Fred, others?), it is clear that the grip hand can have little effect during impact, and that tip speed (and offset, and angle) is all that really matters. But different people will need to do different things to achieve different tip speeds in different situations and for different types of shots.

Regards,
Dave

<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote iralee:</font><hr> ...A lot seems to revolve around the assumption of insignificance based on the duration (.001 sec) while the tip interacts with the ball and the forces involved. Following this, many explanations have been drafted around this to justify the non-existance of a "working stroke":<hr /></blockquote>You make it sound as if someone, on a whim perhaps, made the decision that the work done is insignificant, and then everbody got in line to offer their rationals for this.

<blockquote><font class="small">Quote iralee:</font><hr>...difficulty for humans to actually accelerate through the ball<hr /></blockquote>Probably immpossible except maybe at a very, very slow cue speed (if you mean actually having the cue increase forward speed during impact, as opposed to applying force to retard its deceleration.)

<blockquote><font class="small">Quote iralee:</font><hr>I propose that we should devise a way to observe the dwell distances against varying degrees of acceleration to see if there are measurable difference. Such findings would answer many questions. If there are no observable differences in dwell distance between strokes of varying accelerations, then we can more readily dismiss claims that any appreciable work is actually being performed during the brief moment. Until then, how can any of us know for sure?<hr /></blockquote>As motivation, it would help if you or somebody offered some reason that it might be important. Several arguments have been raised against it, but none in favor, at least in a quasi-quantitative manner.

A simple experiment though (if you have a fairly high speed camera), is to measure the cueball's speed after applying a stroke which has the stick measurably accelerating at impact. If its speed is measurably greater than the stick's speed (and mass) alone would dictate, then you would have your demonstration. Non-accelerating shots would also need to be filmed to get the effective mass ratio of the particular cue and ball, as well as associated energy losses. Both non-accelerating and accelerating shots should have the cue moving at roughly the same speed just before impact.

A couple of additional (but vague) considerations work against the additional dwell distance notion.

First, if the dwell time is increased as well, then the extra hand force that the cueball experiences is reduced to less than the one part in four mentioned earlier. (But, to be fair, if the dwell time is reduced, then this is increased to greater than one part in four.)

Second, as tip offset is increased, the compression force should become asymmetric over its time interval, and very highly asymmetric at large tip offsets. Instead of a gradually increasing force reaching a peak at about T/2, then falling off in a mirror-like fashion, it should peak early on during impact, and then probably drop off rather quickly. This is a necessary consequence, I think, of putting spin on the ball and is derived from the reduced separation velocity of the ball and stick. So even if you observed increased dwell distance, the force acting over that "extra" distance should be, I think, reduced to a low level by then.

But this is a little speculative, admittedly.

Jim <hr /></blockquote>

dr_dave
04-06-2007, 11:27 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>With a golf swing, baseball swing, or powerful pool stroke, most of the work is done well before impact, and very little work (practically none) is during the brief impact period. The work done before impact creates momentum (of the club, bat, or cue). This momentum is what creates the extremely large impulse forces that occur during the brief impact period. The final ball-speed is all about club-head, bat, and cue stick speed at impact. Tiger Woods generates tremendous club-head speed before impact, and Babe Ruth generated tremendous bat-speed before impact (... it also helped that he used a heavy bat ... momentum is about speed and mass, so the more of each, the better). No human can generate much energy (i.e., do much work) during the incredibly brief contact times (because our power is limited ... energy = power * time); although, they can generate incredible energy over a long swing or stroke. Think about the amount of time spent on the swing/stroke vs. the impact time interval. The athlete spends more than 100x as much time on the swing/stroke as compared to the impact interval. So, in simple terms, you can generate more than 100x as much energy during the swing/stroke as you can during impact. <hr /></blockquote>I think that this is the clearest and most convincing explanation of why what goes on during contact is negligible.<hr /></blockquote>Thanks Jim. I thought it was pretty convincing also, but apparently not convincing enough for all.

Dave

DickLeonard
04-06-2007, 12:56 PM
IraLee I have always thought after watching Mike Zuglan run 148 on Ray Martin that I should show Mike the finesse he is missing in his game. Then my brain says if he alters his game to finessing he probably would lose his ability to make the long shots. Once your used to shooting short shots it makes coming with the long shots much harder.

I had played my pool with Joe Canton, who I considered the absolute best at shot selection and controlling both the cueball and the object balls. Controlling the object balls you need all the strokes that straight rail and balkline players use.

You need to see the outcome of what happens when the cueball collides with the object ball in relationship to your next shot and creating your breakshot.
Most shots are played in the rack half of the table with only a very small percentage of the balls being shot in the far two corners.

I had an old room owner show me the game of balkline that helped me see how the players would walk the balls around the table just by using english to controll the balls with a delicate stroke. That aided me in seeing when balls collide it is better to make the next shot easy than to hit it with out thought and create a problem.

RPI has changed, the Union is now run by the manager of the book dept and the billiard room is run by the students. Its schedule varies so that I find it like gambling whether it is open. I still have that disk for you, I just need your address or should I send it to Carom Cafe. Best Dick