When the project is paid for and conducted in the Predator factory in Jax, did it not occur to you that the entire study was them compromized. If you did it at a independent University Lab then you caught my full attention. Jewie, there is an old corporate saying, figures lie and liars figure. I can take any thing and twist it, spin it and have it come out any old way I want it to and make it sound official. What in the hell did you get out of this?
Bob Jewett wrote:> I have wrapped three articles about the Jacksonville Project> (high speed videos of stick/balls/rails done in 1998) on the> SFBA website:>
"...De Jager had a theory that the most English can be imparted if the cue tip is actually accelerating at the moment of contact. Jewett doubted that a human being can accomplish that. Years of debate ended in about an hour when we tried the experiment. 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."
This is suprising and, frankly, hard to believe were it not for the fact that you observed this.
It seems to suggest that at some point in the pendular motion of the forearm you cannot produce any more force on the stick. Can this be true?
It also suggests that there is a maximum bridge length beyond which you can't produce any more cueball speed, even if you could still manage to hit it accurately. Assuming you were using normal bridge lengths (8.5" was mentioned at one point), this maximum length would be fairly short.
On Thu, 3 Mar 2005 03:05:37 +0000 (UTC), Bob Jewett <jewett@sfbilliards.com> wrote:
When the stick hits the cue>ball, the stick slows to 50% of the speed it had before impact.
Is it known to reduce 50% for a cue of any given weight, or is that a measurement for just one cue? It would make sense that a heavier cue would reduce less, but some things don't seem to make sense.
When the stick hits the cue>>ball, the stick slows to 50% of the speed it had before impact.
Is it known to reduce 50% for a cue of any given weight, or is> that a measurement for just one cue? It would make sense that> a heavier cue would reduce less, but some things don't seem to> make sense.
For a good tip, the stick slows to a fraction of its starting speed given by:
(S-B)/(S+B)
where S is the mass of the stick, and B is the mass of the ball.
For an 18-ounce stick and a 6-ounce ball, that's 12/24 or 50% of the initial speed. For a 24-ounce stick and a 6-ounce ball, that's 18/30 or 60% of the initial speed. Note that if the mass of B is very large, like the Earth, the factor is -1 which means the stick bounces back from the "ball" with the same speed it went in at. There is a small correction if the tip is "dead" (technically, inelasitic).
At the same time, the ball speed will be 2S/(S+B) and you can see that typically the cue ball will be moving faster than the stick was.
Byrne covers at least this last equation in his "Advanced" book, and it's probably all in Ron Shepard's APAPP paper, although I haven't looked recently.
Mad Max Mar 2, 10:04 am show options Newsgroups: rec.sport.billiard From: "Mad Max" <madmaxtheone2...@yahoo.com> - Find messages by this author Date: 2 Mar 2005 10:04:10 -0800 Local: Wed, Mar 2 2005 10:04 am Subject: Re: Jacksonville Project articles on-line Reply | Reply to Author | Forward | Print | Individual Message | Show original | Remove | Report Abuse
When the project is paid for and conducted in the Predator factory in Jax, did it not occur to you that the entire study was them compromized. If you did it at a independent University Lab then you caught my full attention. Jewie, there is an old corporate saying, figures lie and liars figure. I can take any thing and twist it, spin it and have it come out any old way I want it to and make it sound official. What in the hell did you get out of this?
When the project is paid for and conducted in the Predator factory in Jax, did it not occur to you that the entire study was them compromized. If you did it at a independent University Lab then you caught my full attention. Jewie, there is an old corporate saying, figures lie and liars figure. I can take any thing and twist it, spin it and have it come out any old way I want it to and make it sound official. What in the hell did you get out of this
I tend to jerk the stick at the cueball when I have a tough longer
shot> (because I feel the long shot takes more ooommppphh behind it and I> jerk to get that oommmphh started). How to stop jerking in this> situation is the "art" part of pool.
It's not necessarily a jerk if you accelerate the cue quickly. But I suppose you should consider it a jerk if you accelerate for only a small fraction of your stroke and then coast the rest of the way.
And more so if you try to stop the cue abruptly after the hit.
Apparently what they found via the Jacksonville experiments is that experienced players tend to accelerate until the tip is pretty close to the cueball. I think this corresponds to our intuitive understanding of what a smooth stroke is.
Bob Jewett mentioned that they never, ever continue applying force right up to the time of contact. The emphatic way he put it caused me to wonder "What's so bad about that?" After all, you get a little more oompa for your trouble, right?
Well, I think the point is that if you continue applying a force after contact, it's a complete waste of energy, and since it would take exquisite timing to relax it during the brief contact period, efficiency demands that you generally do this before the collision.
I guess this is fairly obvious, but since I was momemtarily perplexed, I thought I'd mention it.
I know what he means by consistency: peak speed is where little> differences in stroke speed make the least difference in the shot.
I don't think he means this. I think he's using peak speed to mean the speed of the stick just after the cessation of any force applied to it, by the definition of force.
It's not clear what you mean by "little differences in stroke speed make the least difference in the shot". The speed of the cueball is directly proportional to the speed of the cue stick just before the moment of impact. Any differencs in the cueball's speed due to minor variations in the stick's speed is thus the same throughout the range of possible stick velocities. There is no 'optimal' speed for minimizing this, unless maybe you take into account variations in the elasticity of the tip at different compressions.
I don't mean to put words in his mouth, but my interpretation is that by consistency he means that part of it is achieved by using a fairly uniform acceleration throughout the range of the stroke. The amount of energy supplied to the cue stick is the product of the force applied to it and the distance the force acts upon it. From the physics point of view, it doesn't matter whether you employ a big force over a small distance, or a small force over a big distance, the amount of energy gained by the stick is the same if the product "FxD" is the same.
But from a physiological point of view, as we all sadly know, things aren't the same. The bigger the force we try to apply, the more likely disaster will occur. So it's better to spread the force over as much of the stroke distance as possible, to minimize it. Ideally then, peak speed will be achieved just before impact.
At least, that's what I think he's refering to.
But I don't really know what he means by efficiency.
I really do think he means not wasting energy by continuing to do work (applying force) after the hit has taken place. Yes, as the the article shows, there is a re-acceleration after impact, but this is due to a build up of momemntum of the arm before impact, and not due to any additional work being done.
Well, I think the point is that if you continue applying a force> > after contact, it's a complete waste of energy>
That by itself isn't a bad thing unless it affects the shot itself.
Other than a waste...
and since it would take> > exquisite timing to relax it during the brief contact period,> > efficiency demands that you generally do this before the collision.>
I don't think you "relax" before the collision - I think that point
your stroke is just where maximum speed is "naturally" attained
(because> of the physics of moving your arm in an arc using your muscles).
Can you expand on this? My feeling is that you can continue accelerating your arm throughout the pendular swing (except at the very end of course).
If the ball is struck while the stick is still accelerating, for example half way up the bell-shaped curve that pretty much everybody's speed/time stroke profile follows, the exact timing of the hit will determine the speed of the stick at impact and the ball's speed. On the other hand, if you hit the ball at the peak, the peak is rounded and "flat" at the top, and it makes little difference whether you hit just at the peak or a little bit off -- the speed will be nearly the same. This principle of a smooth maximum is also seen in the half-ball follow angle.
As far as efficiency, suppose you hit at other than the peak. If early, it means that you have really wound up on the shot and are still serious acclerating the stick. You have put lots of unnecessary energy into the shot (and have only achieved a situation where timing is critical). On the other hand, suppose you hit the ball after the peak of speed, when you have started to slow the stick down. I hope it's totally obvious to everyone that this is an inefficient way to hit the ball.
For those of you with back issues of Billiards Digest, this is all covered with diagrams in the November 1998 issue.
Patrick Johnson <patrick.johnsonREMOVE@thiscomcast.net> wrote:
Me:>> I really do think he means not wasting energy
I see from reading his reply that he does mean that, and I'm> surprised that he considers that worth mentioning. ...
Maybe it makes no difference at the low end of the speed range, but as soon as you need power on the ball, you don't want to burn 20 joules to get 5 joules into the ball. Your form will fall apart at the higher arm speed. But it's also a general principle that the best way to do something is with the least effort.
Bob Jewett wrote:> If the ball is struck while the stick is still accelerating, for> example half way up the bell-shaped curve that pretty much everybody's> speed/time stroke profile follows, the exact timing of the hit will> determine the speed of the stick at impact and the ball's speed.
Bob: A slip stroke should change the timing of the hit. If your grip hand moves back two inches during the final backstroke, the stick will contact the ball two inches sooner than your arm anticipated.
I've watched Wayne Norcross at Danny K's use a slip stroke. It seems that he uses it when he needs to add a little extra draw on a long shot, though it's doubtful that an old pro like him would do this to keep from hitting the cue ball late.
When I'm not stroking well, I know that I unintentionally decelerate the stick before impact. On the rare occasions that I get into stroke and draw the ball well, I find that my backhand moves closer to the butt of the cue with each practice stroke. Don't know if I actually execute a slip stroke, but my grip gets very light.
Bob: A slip stroke should change the timing of the hit.> If your grip hand moves back two inches during the final> backstroke, the stick will contact the ball two inches sooner> than your arm anticipated.
I'd agree except that if you have practiced the slip stroke a lot, your arm will know what's going on. I think there are two major benefits of the slip stroke. The first is that if you slip back on the stick, it may be easier to feel sideways movement and avoid it. The second is that the less you bring the stick back, the less chance you have to bring the stick off-line (check out Hopkins, for example).
`There are no advantages to the slip stoke, nobody of merit has used it since the 70's. Join the new century jewie and stop teaching the past. Stop wearing bell bottoms also.
