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dr_dave
05-18-2007, 12:38 PM
Last year, I was asked by Scientific American magazine to write a full-length article dealing with the physics of billiards. Needless to say, I was very excited and I worked hard on the article. Unfortunately, after many months of work and re-work (based on their input), the editorial staff decided to not publish the article after all. Needless to say, I was very disappointed (crushed, actually).

So the article wouldn't go totally to waste, I decided to post it online and share it with you guys. Feel free to print, copy, or link to it. Here it is: The Amazing World of Billiards Physics (http://www.engr.colostate.edu/~dga/pool/physics/Alciatore_SCIAM_article_posted_version.pdf).

I hope some of you guys find it interesting and worth reading. It was written for a typical Scientific American audience (educated and interested in science and technology, but not necessarily pool players).

Regards,
Dave

cushioncrawler
05-18-2007, 05:02 PM
Dr Dave -- Thanks for the article, i will have a read later. Didnt Bob Byrne or someone do a small article, perhaps in the "Amateur" section, i have it here somewhere (couldnt find it). Theze amateur articles had lots of shakey scratchy little pencil diagrams n drawings, very effektiv. Funny, i had vizions of doing (submitting) a billiards type article to scientific american myself, in about 1988 -- but i karnt remember exactly which aspect of ball moovments and collisions that i might have had in mind. Actually, yes, it might have been on the effect of the bedcloth nap with respect to sidespin and curve. I have a copy of that article somewhere, but i doubt that anyone iz going to be asking me for a copy. Anyhow, not to worry, with a little tweaking i can convert it to describe the effekt of the grain of the grass on the path of a golf putt, and i might be famous yet. madMac.

ceebee
05-18-2007, 05:09 PM
Nice article Dr. Dave & thanks for sharing your knowledge. Someday, you & I should get together. I would enjoy spending a day sharing knowledge about this chosen Sport of mine & I suppose your's too.

Bob_Jewett
05-18-2007, 07:08 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> ... Didnt Bob Byrne or someone do a small article, perhaps in the "Amateur" section, i have it here somewhere (couldnt find it). ... <hr /></blockquote>
I think the article you are thinking of was by Jearl Walker, the editor of the "Amateur Scientist" columns, and it was republished in: "Roundabout - The Physics of Rotation in the Everyday World : A Scientific American Reader"

Sadly, although he used some of Byrne's info, he got some important things wrong. For example, he said that for a fixed stick speed, the ball speed is independent of the eccentricity of the hit. That's foolishness.

cushioncrawler
05-18-2007, 09:24 PM
Bob -- Yes, that sounds like the article. Looks like Bob Byrne in the drawings i think. I have it somewhere here. My stuff is mostly all packed up, koz i am shifting house, when the new joint is finished. Karnt wait to get my 12' table and billiard room up and running. I only had a 6' table in my old joint. madMac.

dr_dave
05-19-2007, 12:08 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> ... Didnt Bob Byrne or someone do a small article, perhaps in the "Amateur" section, i have it here somewhere (couldnt find it). ... <hr /></blockquote>
I think the article you are thinking of was by Jearl Walker, the editor of the "Amateur Scientist" columns, and it was republished in: "Roundabout - The Physics of Rotation in the Everyday World : A Scientific American Reader"

Sadly, although he used some of Byrne's info, he got some important things wrong. For example, he said that for a fixed stick speed, the ball speed is independent of the eccentricity of the hit. That's foolishness.<hr /></blockquote>
Bob and Mac,

FYI, Jearl Walker's article can be found here (http://www.engr.colostate.edu/~dga/pool/physics/index.html) under "general interest articles." After reading that article, I thought the Scientific American editors would be thrilled with my article. I guess I was wrong.

Regards,
Dave

dr_dave
05-19-2007, 12:17 PM
<blockquote><font class="small">Quote ceebee:</font><hr>Nice article Dr. Dave &amp; thanks for sharing your knowledge.<hr /></blockquote>You're welcome, and thank you.

<blockquote><font class="small">Quote ceebee:</font><hr>Someday, you &amp; I should get together. I would enjoy spending a day sharing knowledge about this chosen Sport of mine &amp; I suppose your's too.<hr /></blockquote>I would like that. I hope to meet a lot more of the CCB'ers out there. I plan to attend Derby City and maybe the BCA expo next year, so maybe I'll be able to meet more of you guys. My demanding schedule in recent years has made it tough for me to travel for fun.

Catch you later, and good luck with your BreakRak product,
Dave

bradb
05-19-2007, 03:30 PM
Great article Dave. Very enlightning to have a concise, technical reason for all the shots I've learned over the years but was'nt totally aware of how they worked. I probably could have progressed much easier had there been something like this available when I first started out.

Did they give you any reason as to why they declined the article? Its seems right up their alley. I would have loved to have done the graphics.

Brad

cushioncrawler
05-19-2007, 06:18 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> ....I think the article you are thinking of was by Jearl Walker, the editor of the "Amateur Scientist" columns, and it was republished in: "Roundabout - The Physics of Rotation in the Everyday World : A Scientific American Reader". Sadly, although he used some of Byrne's info, he got some important things wrong. For example, he said that for a fixed stick speed, the ball speed is independent of the eccentricity of the hit. That's foolishness. <hr /></blockquote>Bob -- Just read Dr Dave's link to that article. It is beautifully written, great drawings, nice and simple etc. But, even tho it iznt very tecky, it still manages to have lots of errors, or at least over-simplifikations. I remember that on my copy i scribbled lots of notes re mistakes etc, az i allways do with any such tecky article -- eg "very little friction between colliding balls" (no, there can be lots of friction), "qball initially stops dead when fullball collision" (no, e iz never 1.000), etc.

Possibly Dr Dave's article is too lengthy etc. For instance, the article that i had in mind (that i wrote) woz simply to try to answer a very historic arguement about why (and how much) a spinning-rolling ball uzually kurves on a napped cloth. This affekts snooker and billiards.

I reckon that i could do an article about stun-throo, ie about e for a balltoball collision, and how e varys for the different types of balls made over the years. This duznt affect any game much at all (duzzenmadder), alltho it duz have an effekt on the qball's deflexion angle, ie it mainly affekts (affekted) english billiards over the years.

Anyhow, perhaps a very detailed look into one simple aspect of ball stuff would be more digestable. For example, an article on balltoball friction would be an eye-opener. madMac.

bradb
05-19-2007, 06:44 PM
I think given the rather starchy nature of this Magazine they backed off when terms like Balls, stroke and squirt popped up in the copy.

cushioncrawler
05-19-2007, 07:04 PM
<blockquote><font class="small">Quote bradb:</font><hr> I think given the rather starchy nature of this Magazine they backed off when terms like Balls, stroke and squirt popped up in the copy. <hr /></blockquote>Ok -- Penthouse Magazine then. Centerfold ??? -- perhaps Dr Dave laying (nude) in a big pile of poolballs. One could sex the wordage up a bit more by inklooding -- screw, leather, drag, cushion-angle, bed-friktion etc. madMac.

DickLeonard
05-20-2007, 11:00 AM
Cushioncrawler when I was playing golf and sank a 40 footer or chipped in from off the green I was supposed too. I was a poolplayer. I never received any accolades as being a good putter or short iron player I was a poolplayer.

I quit playing golf at 14 I was 4ft 7 and 70 lbs my brain was telling me where are you going with this game. I was shooting in the mid 90s at the private cc I caddied at playing only Mondays [caddies day]. When I graduated high school at 5ft 2 and 86 lbs, I knew I had made the rght decision even tho I was still caddying.

I always maintained that in pool the ability to shoot away from the pocket to pocket the object ball was important in putting. Once you learned to have your putt cross the break line it was on its way to the hole. Most golfer would turn their putter inside or outside at the moment of truth.####

wolfdancer
05-20-2007, 11:19 AM
Your book sounds great!!!!
Will you be writing it in (the Queen's)English.....or using the almost unreadable Aussie dialect?

cushioncrawler
05-20-2007, 02:47 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Your book sounds great!!!!
Will you be writing it in (the Queen's)English.....or using the almost unreadable Aussie dialect? <hr /></blockquote>Woolfy -- Anything i write for one of my 3 books (mostly finished now) would have lots of semi-fonetik stuff, i avoid any unnecessary english. But for a magazine etc i daresay english is mandatory. I will havta email u a chapter or two from the three books, The Cushion Crawlerz Bible, Billiards Arithmetikally Treated, and Billiardz for Loozerz. madMac.

cushioncrawler
05-20-2007, 02:58 PM
<blockquote><font class="small">Quote DickLeonard:</font><hr> Cushioncrawler when I was playing golf and sank a 40 footer or chipped in from off the green I was supposed too. I was a poolplayer. I never received any accolades as being a good putter or short iron player I was a poolplayer. I quit playing golf at 14 I was 4ft 7 and 70 lbs my brain was telling me where are you going with this game. I was shooting in the mid 90s at the private cc I caddied at playing only Mondays [caddies day]. When I graduated high school at 5ft 2 and 86 lbs, I knew I had made the rght decision even tho I was still caddying. I always maintained that in pool the ability to shoot away from the pocket to pocket the object ball was important in putting. Once you learned to have your putt cross the break line it was on its way to the hole. Most golfer would turn their putter inside or outside at the moment of truth.#### <hr /></blockquote>Dick -- I gave golf away 3 years ago, koz i got sick of 4'-7" skoolkidz chipping in from off the green all the time. When i first met one of them he couldnt hit the ball more than 100yds, then a year later he woz playing off 5. I never got down to less than 9 -- i missed a 3' putt one saturday which would have dropped me to 8.4, ie to 8, and i missed -- i turned my putter inside at the moment of truth (gulp). Now, every billiards tournament that i enter, u can bet that i get to play the smallest kid in the tournament, and, after our game, the dad iz allwayz seen hugging the kid and throwing the kid up in the air and yelling "i dont beleev it" and "son of a gun". The pool bit -- on a napped snooker cloth u allwayz havta allow for the break(s). sadMac.

dr_dave
05-21-2007, 01:55 PM
<blockquote><font class="small">Quote bradb:</font><hr>Great article Dave. Very enlightning to have a concise, technical reason for all the shots I've learned over the years but was'nt totally aware of how they worked. I probably could have progressed much easier had there been something like this available when I first started out.<hr /></blockquote>Thank you for the positive feedback. I appreciate it.

<blockquote><font class="small">Quote bradb:</font><hr>Did they give you any reason as to why they declined the article? Its seems right up their alley. I would have loved to have done the graphics.<hr /></blockquote>The best I can do to paraphrase their final feedback is:

They just didn't like it. They also thought my writing style was a little too colloquial. Also, it seems they just decided they didn't want to publish a billiards physics article after all.

Catch you later,
Dave

billiardgrue
05-21-2007, 01:57 PM
[ QUOTE ]
Obviously, the farther you hit the CB of center, the more sidespin you impart..<hr /></blockquote>

My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!

What does monotonically increase with increasing tip offset is the maximum sidespin/speed *ratio* Rr/Wi (the important thing when interested in cue ball behavior off of cushions). This is because, although the ball doesn't spin as fast as for a 1/2-ball tip contact, the linear speed is diminished as tip offset increases to make the overall ratio bigger. I found the counterintuitive result surprising and the distinction very interesting when what he described/calculated finally sunk in.


[ QUOTE ]
With a massť shot, the final path of the CB will be...<hr /></blockquote>

Coriolis had an additional caveat to that method which can be found at the very end of chapter VIII. He breaks down massť shots into separate cue/ball and ball/table impacts to make his friction-independent figure 34 construction that you describe, but there is a region of elevation/offset where he mentions that because the cue and ball do not separate after impact, the elements of motion depend on friction and therefore outside the scope of that construction. He doesn't attempt to describe the details beyond mentioning that good players still find a way to control the ball even in that regime.

dr_dave
05-21-2007, 02:26 PM
<blockquote><font class="small">Quote billiardgrue:</font><hr>[ QUOTE ]
Obviously, the farther you hit the CB of center, the more sidespin you impart..<hr /></blockquote>

My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Good point. One should be careful when quantifying the amount of sidespin, and when discussing offset limits. Coriolis is a little unclear with the maximum offset numbers (e.g., see pages 7 and 8 in his book). Also, see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf) for more details and information. You are right about him reporting the maximum spin rate, for a given stick speed, corresponding to an offset of 0.5R. The generally accepted safe miscue limit in the pool world is 0.5R.

<blockquote><font class="small">Quote billiardgrue:</font><hr>What does monotonically increase with increasing tip offset is the maximum sidespin/speed *ratio* Rr/Wi (the important thing when interested in cue ball behavior off of cushions). This is because, although the ball doesn't spin as fast as for a 1/2-ball tip contact, the linear speed is diminished as tip offset increases to make the overall ratio bigger. I found the counterintuitive result surprising and the distinction very interesting when what he described/calculated finally sunk in.<hr /></blockquote>I also prefer using what I call the "spin rate factor (SRF)" to quantify the amount of English (see the article mentioned above, and see TP A.12, TP A.22, and TP A.25 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/index.html)). As you have pointed out, SRF is what really matters for most shots with English.

Regards,
Dave

dr_dave
05-21-2007, 02:38 PM
<blockquote><font class="small">Quote billiardgrue:</font><hr>[ QUOTE ]
With a massť shot, the final path of the CB will be...<hr /></blockquote>

Coriolis had an additional caveat to that method which can be found at the very end of chapter VIII. He breaks down massť shots into separate cue/ball and ball/table impacts to make his friction-independent figure 34 construction that you describe, but there is a region of elevation/offset where he mentions that because the cue and ball do not separate after impact, the elements of motion depend on friction and therefore outside the scope of that construction. He doesn't attempt to describe the details beyond mentioning that good players still find a way to control the ball even in that regime.<hr /></blockquote>Good point. Cloth friction during impact is a small "practically matter" that the math and graphical method doesn't address. Speed is also another very important "practical matter" that requires feel. FYI, I have more information on these topic in my November '05 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/nov05.pdf).

Regards,
Dave

MrLucky
05-21-2007, 03:24 PM
Thanks Dave as always a well presented methodology posed in a way that makes a very difficult subject much easier to consume! this will be added to my repertoire !
Phil /ccboard/images/graemlins/grin.gif

dr_dave
05-21-2007, 03:41 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Possibly Dr Dave's article is too lengthy<hr /></blockquote>I thought that at first also; but after SCIAM received my first draft (which was much shorter), they asked for more and told me to not worry about the length ... they would edit it if necessary later. Unfortunately, "later" never came.

Dave

dr_dave
05-21-2007, 03:43 PM
<blockquote><font class="small">Quote MrLucky:</font><hr> Thanks Dave as always a well presented methodology posed in a way that makes a very difficult subject much easier to consume! this will be added to my repertoire !
Phil /ccboard/images/graemlins/grin.gif <hr /></blockquote>Thank you. I'm glad at least a few people have seen and liked the article. That way, all of my efforts didn't go totally to waste.

Regards,
Dave

dr_dave
05-21-2007, 03:50 PM
<blockquote><font class="small">Quote dr_dave:</font><hr><blockquote><font class="small">Quote billiardgrue:</font><hr>What does monotonically increase with increasing tip offset is the maximum sidespin/speed *ratio* Rr/Wi (the important thing when interested in cue ball behavior off of cushions). This is because, although the ball doesn't spin as fast as for a 1/2-ball tip contact, the linear speed is diminished as tip offset increases to make the overall ratio bigger. I found the counterintuitive result surprising and the distinction very interesting when what he described/calculated finally sunk in.<hr /></blockquote>I also prefer using what I call the "spin rate factor (SRF)" to quantify the amount of English (see the article mentioned above, and see TP A.12, TP A.22, and TP A.25 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/index.html)). As you have pointed out, SRF is what really matters for most shots with English.<hr /></blockquote>Therefore, you do get a higher SRF (and more relative spin) with more tip offset. To get a faster absolute spin-rate at larger offsets, you must also use a faster stroke. I thought this was too much detail for the summary article for SCIAM.

Regards,
Dave

wolfdancer
05-21-2007, 04:29 PM
For a practical demonstration of Masse:
web page (http://video.google.com/videoplay?docid=-1789371924005542099)
Did I say practical?....these are practically impossible !!!

Coriolis would have been proud........

cushioncrawler
05-21-2007, 04:35 PM
Gruey -- Perhaps someone could do the tests re R/r and max absolute sidespin. If a small notch were cut into the qball, this would prevent misscues, hencely one could acheev an R/r of say 0.99. An iron-willie (robotik cue) would help allso -- alltho it would be good if the cue-to-ball mass-ratio could be varyd to check that bit of the theory. Plus slo-mo video. Az Dr Dave infers, any rezults might be useless in actual play where R/r karnt really exceed 0.5 koz of misscues. Me, myself, i will have a bit eech way -- i reckon that this Coriolis Effekt duznt exist -- but, if it duz exist, then i reckon that the max would be nearer to 0.4 than 0.5 -- in which case perhaps it might have praktical application. greenMac.

cushioncrawler
05-21-2007, 04:57 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Possibly Dr Dave's article is too lengthy<hr /></blockquote>I thought that at first also; but after SCIAM received my first draft (which was much shorter), they asked for more and told me to not worry about the length ... they would edit it if necessary later. Unfortunately, "later" never came. Dave <hr /></blockquote>Dr Dave -- Just thinking some more. Perhaps a billiards article would be of more interest to sciam if it had more physics, rather than mainly maths. I have a feeling that more measurements (RealWorld) would be very very interesting if they in fact contradicted MathLand. MathLand is probably boring to most, everyone (and skoolkids) think that they know it all when it comes to math theory, especially when it is Theory, ie "assuming no losses", or "for an infinitely hard sphere", or "ignoring friction" etc. Not saying that any of your articles suffer here at all, but i have a feeling that RealWorld billiard paradoxes and counter-intuitive stuff would be sexy.

There are lots of "problems" that interest me. For example -- why duz an ivory ball collizion sound sharper and harder than the collision of any other modern or historic billiard ball, when an ivory ball is the softest ball ever uzed (i think), and haz the longest impakt time, and haz the lowest COR (e = say 0.80). And why duz the krapamith sound like the softest ball ever made/uzed, when it has nearnuff the largest e (e = say 0.95) of any/all balls. madMac.

dr_dave
05-21-2007, 05:00 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> For a practical demonstration of Masse:
web page (http://video.google.com/videoplay?docid=-1789371924005542099)
Did I say practical?....these are practically impossible !!!

Coriolis would have been proud........ <hr /></blockquote>I think Coriolis would have been inspired to write another book.

That's pretty amazing stuff.

Dave

Bob_Jewett
05-21-2007, 05:25 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>... I think Coriolis would have been inspired to write another book.

That's pretty amazing stuff.

Dave <hr /></blockquote>
I think he would have concluded that the cloth/ball coefficient of friction was about 0.05.

cushioncrawler
05-21-2007, 08:17 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>... I think Coriolis would have been inspired to write another book. That's pretty amazing stuff. Dave <hr /></blockquote> I think he would have concluded that the cloth/ball coefficient of friction was about 0.05.<hr /></blockquote>Bob -- Has anyone measured balltobed friction for various cloths and various conditions, eg silicone spray, polished ball (mu = 0.05 ???). I think woollen bedcloths might go from say 0.15 new (havnt measured it) to 0.25 oldish, not counting rolling rezistance which might add say 0.01. madMac.

Jal
05-21-2007, 11:43 PM
<blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.

Jim

dr_dave
05-22-2007, 09:08 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>... I think Coriolis would have been inspired to write another book.

That's pretty amazing stuff.

Dave <hr /></blockquote>
I think he would have concluded that the cloth/ball coefficient of friction was about 0.05. <hr /></blockquote>Do you know what kind of spray or polish he uses on the cue ball to help enable such amazing feats of magic?

Dave

bradb
05-22-2007, 10:41 AM
--/quote Dave]
They just didn't like it. They also thought my writing style was a little too colloquial. Also, it seems they just decided they didn't want to publish a billiards physics article after all.---

Dave, I think their shirts are a little too stuffed... pool is just a little too politically incorrect. The guy who asked you to do it was probably very keen on it then some purist upstairs got wind of it and put the kybosh on it. I would'nt give up on it, I think you could probably find some other main stream publisher out there who would love to run it. -Brad

SpiderMan
05-22-2007, 01:42 PM
Dave,

Did they actually specify an issue that your article was to have run in?

I have always suspected that editors "overbook" authors, and then make final decisions after the materials actually appear. Too many writers start out enthusiastic and then never produce a final manuscript. It works out great for the publication, to pick and choose, but it's very unfair to diligent authors such as yourself who are not told that it's actually a "science fair".

Years ago I wrote a 3-part series for a trade journal, "RF Design". I believe that the issue my first installment went into was postponed several times, but they finally put it in about 4 or 5 months later than we originally discussed. I don't remember for certain, but it seems like the reasons given were something to the effect that "we have more advertisers in tune with that particular subject material for such-and-such month". That may have been true, but they also may have liked other simultaneous submissions better at the time.

Anyway, don't be shocked if they call you back sometime in the near future and want to run your article.

I'm a regular conspiracy theorist, aren't I?

SpiderMan

Bob_Jewett
05-22-2007, 02:01 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... Do you know what kind of spray or polish he uses on the cue ball to help enable such amazing feats of magic? ... <hr /></blockquote>
Silicone spray is the standard, I think. It's applied either to a small towel or to the player's glove. The latter is less obtrusive.

dr_dave
05-22-2007, 02:38 PM
<blockquote><font class="small">Quote bradb:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>They just didn't like it. They also thought my writing style was a little too colloquial. Also, it seems they just decided they didn't want to publish a billiards physics article after all.<hr /></blockquote>
Dave, I think their shirts are a little too stuffed... pool is just a little too politically incorrect. The guy who asked you to do it was probably very keen on it then some purist upstairs got wind of it and put the kybosh on it. I would'nt give up on it, I think you could probably find some other main stream publisher out there who would love to run it.<hr /></blockquote>Brad,

Thank you for your thoughts and support. After SCIAM pulled the plug, I did try Discover magazine, but they weren't interested. I'm happy to just have the article (http://www.engr.colostate.edu/~dga/pool/physics/Alciatore_SCIAM_article_posted_version.pdf) live in Cyberspace. I think the people interested in such a thing will find it and share it with others.

Regards,
Dave

dr_dave
05-22-2007, 02:44 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr>Did they actually specify an issue that your article was to have run in?<hr /></blockquote>I had a deadline. I was a month early with the final draft. (Maybe that was part of the problem ... I gave them too much time to "consider" it.)

<blockquote><font class="small">Quote SpiderMan:</font><hr>I have always suspected that editors "overbook" authors, and then make final decisions after the materials actually appear. Too many writers start out enthusiastic and then never produce a final manuscript. It works out great for the publication, to pick and choose, but it's very unfair to diligent authors such as yourself who are not told that it's actually a "science fair".

Years ago I wrote a 3-part series for a trade journal, "RF Design". I believe that the issue my first installment went into was postponed several times, but they finally put it in about 4 or 5 months later than we originally discussed. I don't remember for certain, but it seems like the reasons given were something to the effect that "we have more advertisers in tune with that particular subject material for such-and-such month". That may have been true, but they also may have liked other simultaneous submissions better at the time.

Anyway, don't be shocked if they call you back sometime in the near future and want to run your article.<hr /></blockquote>I won't hold my breath, but thank you for sharing your thoughts and story.

<blockquote><font class="small">Quote SpiderMan:</font><hr>I'm a regular conspiracy theorist, aren't I?<hr /></blockquote>I guess I was a little naive, but I was still shocked by how they handled the situation.

Watch out for those black helicopters.

Regards,
Dave

dr_dave
05-23-2007, 11:36 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.<hr /></blockquote>Jim,

Coriolis takes energy loss into consideration. Your equations and numbers above assume energy is conserved (i.e., the collision is perfectly elastic). Coriolis assumes an energy loss percentage of 13-14%, and he assumes this is constant with stick speed (backed up by limited experiments) and tip offset (not backed up by experiments). I will refer to page numbers in David Nadler's English translation of Coriolis' book. If you don't have a copy, you should get one. The energy loss stuff is discussed on page 63. As you mention above, if energy is assumed to be conserved, the maximum absolute spin (assuming constant stick speed) occurs at an offset of 0.5R, and the tip and ball surface do not separate under those conditions. On page 65, Coriolis derives 0.6R for the offset resulting in no post-impact separation, assuming the loss of energy. At offsets greater than this, the tip would theoretically stay in contact with the ball after impact and rob the ball of some of its spin. Obviously, this analysis neglects cue stick deflection and vibration and ball squirt. His equation agrees with yours above if you throw out the energy loss terms. On page 69, he derives 0.5R for the maximum-absolute-spin offset, also assuming the loss of energy.

Interestingly, on page 60, he reports that experience has taught players that offsets up to 0.7R are possible without miscue. Were tips better in the early 1800's, or was he mistaken? More recent experience (and high-speed video) has shown that offsets in the 0.5R range more typically represent the miscue limit (see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf)).

Bottom line at the table: None of this really matters that much. If you want to safely avoid miscues, you should not use offsets beyond about 0.5R. Also, if you want to achieve more spin, and you are already at the limit of safe tip offset, just hit the ball harder.

Regards,
Dave

wolfdancer
05-23-2007, 12:04 PM
Interesting article...AND even readable for a non-tech type, like me.
My guess as to why they didn't publish, was that while it had the requisite physics/math concepts.....they may have felt it would not be interesting enough for the non-pool playing readership?
I'd shop it around a bit...maybe "New Scientist" mag, would like it..
The bright side is that you have been published...I've got some 60 years of rejection slips, laying around....but nobody took Grandma Moses seriously as a painter until she hit her 80's....so there's still hope!!

dr_dave
05-23-2007, 12:12 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Interesting article...AND even readable for a non-tech type, like me.
My guess as to why they didn't publish, was that while it had the requisite physics/math concepts.....they may have felt it would not be interesting enough for the non-pool playing readership?<hr /></blockquote>I also thought that, but when I learned they had done a shorter billiards physics article previously, I thought my article (which I thought was better and more interesting) would be attractive to the editorial board. That shows you how much I know.

<blockquote><font class="small">Quote wolfdancer:</font><hr>I'd shop it around a bit...maybe "New Scientist" mag, would like it..<hr /></blockquote>I've already moved on to other things, but if you or anybody else want to pursue this, I would be happy to split the payment 50/50. But don't expect to get rich ... magazine don't pay much for this sort of thing.

<blockquote><font class="small">Quote wolfdancer:</font><hr>The bright side is that you have been published...I've got some 60 years of rejection slips, laying around....but nobody took Grandma Moses seriously as a painter until she hit her 80's....so there's still hope!! <hr /></blockquote>Hang in there!

Regards,
Dave

Jal
05-23-2007, 10:10 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.<hr /></blockquote>Jim,

Coriolis takes energy loss into consideration. Your equations and numbers above assume energy is conserved (i.e., the collision is perfectly elastic). Coriolis assumes an energy loss percentage of 13-14%, and he assumes this is constant with stick speed (backed up by limited experiments) and tip offset (not backed up by experiments). I will refer to page numbers in David Nadler's English translation of Coriolis' book. If you don't have a copy, you should get one. The energy loss stuff is discussed on page 63. As you mention above, if energy is assumed to be conserved, the maximum absolute spin (assuming constant stick speed) occurs at an offset of 0.5R, and the tip and ball surface do not separate under those conditions. On page 65, Coriolis derives 0.6R for the offset resulting in no post-impact separation, assuming the loss of energy. At offsets greater than this, the tip would theoretically stay in contact with the ball after impact and rob the ball of some of its spin. Obviously, this analysis neglects cue stick deflection and vibration and ball squirt. His equation agrees with yours above if you throw out the energy loss terms. On page 69, he derives 0.5R for the maximum-absolute-spin offset, also assuming the loss of energy.

Interestingly, on page 60, he reports that experience has taught players that offsets up to 0.7R are possible without miscue. Were tips better in the early 1800's, or was he mistaken? More recent experience (and high-speed video) has shown that offsets in the 0.5R range more typically represent the miscue limit (see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf)).

Bottom line at the table: None of this really matters that much. If you want to safely avoid miscues, you should not use offsets beyond about 0.5R. Also, if you want to achieve more spin, and you are already at the limit of safe tip offset, just hit the ball harder.

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

Thanks for the feedback. I appreciate you taking the time to look this up. Without seeing page 65, I'm still skeptical because of the following argument. (Sorry about the long winded stuff, but if you want to check the logic behind the graph below, here it is.)

In the ideal elastic case (ignoring squirt, double hits...), the cueball's speed is:

Vb' = 2Vs/(S + Mb/Ms)

where Vs is the pre-impact stick speed, and S = (5/2)(b/R)^2 +1.

The stick's post impact speed is:

Vs' = Vs(S - Mb/Ms)/(S + Mb/Ms)

For an inelastic collision, the cueball's speed is some number K times the above expression for Vb':

Vb' = 2KVs/(S + Mb/Ms)

Conservation of momentum then requires that the stick's post-impact speed is:

Vs' = Vs(S + (1-2K)Mb/Ms)/(S + Mb/Ms)

which can be verified of course by adding MsVs' + MbVb', which equals MsVs.

The separation speed in the elastic case is:

Vsep = Vs(2- S + Mb/Ms)/(S + Mb/Ms)

In the inelastic case, it's some number e times this. Equating Vb' - Vs' to this:

Vs[2K - (S + (1-2K)Mb/Ms)]/(S + Mb/Ms) = eVs(2- S + Mb/Ms)/(S + Mb/Ms)

and solving for K:

K = (1/2)[(2 - S + Mb/Ms)e + S + Mb/Ms]/(1 + Mb/Ms)

For a center ball hit (b/R = 0, S = 1), K is the familiar (1 + e)/2. But there are two cases when K = 1: when e=1 or:

b/R = Sqrt[(2/5)(1 + Mb/Ms)]

and it doesn't matter what the value of e is:

Here is a plot of the separation speed for various values of e and tip offset:

http://ww2.netnitco.net/users/gtech/SeparationSpeed.jpg

The parameter e, which represents an intrinsic energy loss (unlike K), most likely changes with tip offset, but there is always a positive separation speed up to .73R whenever e is greater than zero (and a mass ratio of 1/3).

The above logic, which originates from momentum conservation, seems very persuasive. However, I'll naturally be interested to see what you think.

Jim

billiardgrue
05-24-2007, 12:34 AM
If you read French, the complete Coriolis text is available via Google Books here (http://books.google.com/books?id=a2USAAAAIAAJ). The relevant part is Chapter 2 (Nadler's p.65 is pp. 93-94 in the French). You can even download it as a pdf. Unfortunately, all of the beautiful graphical constructions in the back have been mangled in the Google version due to a poor scanning job.

dr_dave
05-24-2007, 10:49 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.<hr /></blockquote>Jim,

Coriolis takes energy loss into consideration. Your equations and numbers above assume energy is conserved (i.e., the collision is perfectly elastic). Coriolis assumes an energy loss percentage of 13-14%, and he assumes this is constant with stick speed (backed up by limited experiments) and tip offset (not backed up by experiments). I will refer to page numbers in David Nadler's English translation of Coriolis' book. If you don't have a copy, you should get one. The energy loss stuff is discussed on page 63. As you mention above, if energy is assumed to be conserved, the maximum absolute spin (assuming constant stick speed) occurs at an offset of 0.5R, and the tip and ball surface do not separate under those conditions. On page 65, Coriolis derives 0.6R for the offset resulting in no post-impact separation, assuming the loss of energy. At offsets greater than this, the tip would theoretically stay in contact with the ball after impact and rob the ball of some of its spin. Obviously, this analysis neglects cue stick deflection and vibration and ball squirt. His equation agrees with yours above if you throw out the energy loss terms. On page 69, he derives 0.5R for the maximum-absolute-spin offset, also assuming the loss of energy.

Interestingly, on page 60, he reports that experience has taught players that offsets up to 0.7R are possible without miscue. Were tips better in the early 1800's, or was he mistaken? More recent experience (and high-speed video) has shown that offsets in the 0.5R range more typically represent the miscue limit (see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf)).

Bottom line at the table: None of this really matters that much. If you want to safely avoid miscues, you should not use offsets beyond about 0.5R. Also, if you want to achieve more spin, and you are already at the limit of safe tip offset, just hit the ball harder.

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

Thanks for the feedback. I appreciate you taking the time to look this up. Without seeing page 65, I'm still skeptical because of the following argument. (Sorry about the long winded stuff, but if you want to check the logic behind the graph below, here it is.)

In the ideal elastic case (ignoring squirt, double hits...), the cueball's speed is:

Vb' = 2Vs/(S + Mb/Ms)

where Vs is the pre-impact stick speed, and S = (5/2)(b/R)^2 +1.

The stick's post impact speed is:

Vs' = Vs(S - Mb/Ms)/(S + Mb/Ms)<hr /></blockquote>
Agreed. But both of these results assume that energy is conserved. In other words, they assume a perfectly elastic collision between the cue tip and cue ball (i.e., e = COR = 1).

<blockquote><font class="small">Quote Jal:</font><hr>For an inelastic collision<hr /></blockquote>Here's the problem!!! The equations above don't apply anymore. Please check out Coriolis' book. He covers the case above, and the case on the inelastic collision. Although, as I have mentioned, he still ignores:
- how the COR varies with offset and speed
- the effects of cue stick deflection and vibration
- the effects of cue ball squirt


Again, the remainder of your message below assumes both that energy is conserved and that the collision is inelastic. This is not legal (or physically possible).

Regards,
Dave

<blockquote><font class="small">Quote Jal:</font><hr>, the cueball's speed is some number K times the above expression for Vb':

Vb' = 2KVs/(S + Mb/Ms)

Conservation of momentum then requires that the stick's post-impact speed is:

Vs' = Vs(S + (1-2K)Mb/Ms)/(S + Mb/Ms)

which can be verified of course by adding MsVs' + MbVb', which equals MsVs.

The separation speed in the elastic case is:

Vsep = Vs(2- S + Mb/Ms)/(S + Mb/Ms)

In the inelastic case, it's some number e times this. Equating Vb' - Vs' to this:

Vs[2K - (S + (1-2K)Mb/Ms)]/(S + Mb/Ms) = eVs(2- S + Mb/Ms)/(S + Mb/Ms)

and solving for K:

K = (1/2)[(2 - S + Mb/Ms)e + S + Mb/Ms]/(1 + Mb/Ms)

For a center ball hit (b/R = 0, S = 1), K is the familiar (1 + e)/2. But there are two cases when K = 1: when e=1 or:

b/R = Sqrt[(2/5)(1 + Mb/Ms)]

and it doesn't matter what the value of e is:

Here is a plot of the separation speed for various values of e and tip offset:

http://ww2.netnitco.net/users/gtech/SeparationSpeed.jpg

The parameter e, which represents an intrinsic energy loss (unlike K), most likely changes with tip offset, but there is always a positive separation speed up to .73R whenever e is greater than zero (and a mass ratio of 1/3).

The above logic, which originates from momentum conservation, seems very persuasive. However, I'll naturally be interested to see what you think.

Jim <hr /></blockquote>

dr_dave
05-24-2007, 11:26 AM
See the correction in <font color="red">red</font color> below. Sorry for the confusion.

Dave
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.<hr /></blockquote>Jim,

Coriolis takes energy loss into consideration. Your equations and numbers above assume energy is conserved (i.e., the collision is perfectly elastic). Coriolis assumes an energy loss percentage of 13-14%, and he assumes this is constant with stick speed (backed up by limited experiments) and tip offset (not backed up by experiments). I will refer to page numbers in David Nadler's English translation of Coriolis' book. If you don't have a copy, you should get one. The energy loss stuff is discussed on page 63. As you mention above, if energy is assumed to be conserved, the maximum absolute spin (assuming constant stick speed) occurs at an offset of <font color="red">0.73R</font color>, and the tip and ball surface do not separate under those conditions. On page 65, Coriolis derives 0.6R for the offset resulting in no post-impact separation, assuming the loss of energy. At offsets greater than this, the tip would theoretically stay in contact with the ball after impact and rob the ball of some of its spin. Obviously, this analysis neglects cue stick deflection and vibration and ball squirt. His equation agrees with yours above if you throw out the energy loss terms. On page 69, he derives 0.5R for the maximum-absolute-spin offset, also assuming the loss of energy.

Interestingly, on page 60, he reports that experience has taught players that offsets up to 0.7R are possible without miscue. Were tips better in the early 1800's, or was he mistaken? More recent experience (and high-speed video) has shown that offsets in the 0.5R range more typically represent the miscue limit (see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf)).

Bottom line at the table: None of this really matters that much. If you want to safely avoid miscues, you should not use offsets beyond about 0.5R. Also, if you want to achieve more spin, and you are already at the limit of safe tip offset, just hit the ball harder.

Regards,
Dave <hr /></blockquote>

Jal
05-24-2007, 12:18 PM
<blockquote><font class="small">Quote billiardgrue:</font><hr> If you read French, the complete Coriolis text is available via Google Books here (http://books.google.com/books?id=a2USAAAAIAAJ). The relevant part is Chapter 2 (Nadler's p.65 is pp. 93-94 in the French). You can even download it as a pdf. Unfortunately, all of the beautiful graphical constructions in the back have been mangled in the Google version due to a poor scanning job. <hr /></blockquote>Thank you Billiardgrue. I have downloaded it and will see if I can make any sense of it.

Jim

dr_dave
05-24-2007, 12:50 PM
Jim and others,

FYI, if anybody wants to see an illustration and the details, I just posted a complete analysis and discussion for the elastic-collision case. It shows the derivation of Jal's equations and result below. See TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf).

Regards,
Dave
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote billiardgrue:</font><hr>My reading of Coriolis is that he concludes that maximum possible *absolute* sidespin Rr is imparted at a 1/2-ball radius off center due to collision inelasticity and a 3:1 cue/ball mass ratio. It was not a practical suggestion because of miscue danger (although they are related), but an absolute rpm maximum. It is *not* true (according to him) that you get more spin the farther from center you hit the CB!<hr /></blockquote>Can you give me some idea why he came to this conclusion?

I ask because simple theory says that maximum absolute spin should occur at an offset ratio:

(b/R) = .73 = Sqrt[(2/5)(1+Mb/Ms)], where Mb/Ms = 1/3

Moreover, this is independent of the elasticity of the collision - it can be perfectly elastic or perfectly inelastic (the ball and stick have zero separation speed regardless).

One consequence is that the amount of spin and speed move toward their predicted ideal elastic values as you go from zero offset toward the miscue limit. It's hard to see then why considerations of elasticity limit the spin.

(The above ignores squirt and stick re-acceleration after impact, ie, double hits.)

I would appreciate any clarification.<hr /></blockquote>Jim,

Coriolis takes energy loss into consideration. Your equations and numbers above assume energy is conserved (i.e., the collision is perfectly elastic). Coriolis assumes an energy loss percentage of 13-14%, and he assumes this is constant with stick speed (backed up by limited experiments) and tip offset (not backed up by experiments). I will refer to page numbers in David Nadler's English translation of Coriolis' book. If you don't have a copy, you should get one. The energy loss stuff is discussed on page 63. As you mention above, if energy is assumed to be conserved, the maximum absolute spin (assuming constant stick speed) occurs at an offset of 0.73R, and the tip and ball surface do not separate under those conditions. On page 65, Coriolis derives 0.6R for the offset resulting in no post-impact separation, assuming the loss of energy. At offsets greater than this, the tip would theoretically stay in contact with the ball after impact and rob the ball of some of its spin. Obviously, this analysis neglects cue stick deflection and vibration and ball squirt. His equation agrees with yours above if you throw out the energy loss terms. On page 69, he derives 0.5R for the maximum-absolute-spin offset, also assuming the loss of energy.

Interestingly, on page 60, he reports that experience has taught players that offsets up to 0.7R are possible without miscue. Were tips better in the early 1800's, or was he mistaken? More recent experience (and high-speed video) has shown that offsets in the 0.5R range more typically represent the miscue limit (see my October '05 BD article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2005/oct05.pdf)).

Bottom line at the table: None of this really matters that much. If you want to safely avoid miscues, you should not use offsets beyond about 0.5R. Also, if you want to achieve more spin, and you are already at the limit of safe tip offset, just hit the ball harder.

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

cushioncrawler
05-24-2007, 03:56 PM
Dr Dave'n'Jim -- What is the effect of a heavier cue, ie 4:1 ??? madMac.

Jal
05-24-2007, 07:15 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Jim and others,

FYI, if anybody wants to see an illustration and the details, I just posted a complete analysis and discussion for the elastic-collision case. It shows the derivation of Jal's equations and result below. See TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf).

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

Your critique helped. At first, it wasn't clear why you were characterizing the treatment as only applying to the elastic situation. In fact, the parameters K and e were introduced for the inelastic case. I still think the equations are valid (up to a point), but they are misleading (to myself included).

I added curves for the after/before energy ratio (E'/E) to the graph, and now see that indeed you would have to have a perfectly elastic collision to achieve a tip offset of .73R, with a non-negative separation speed. If it's true that you'll always get something like a 10-20% energy loss, then the curve for E'/E (e=0) puts the limiting tip offset for zero separation speed somewhere between .4R and .6R.

Thanks to you, Coriolis, Mac (who stated that it might be as low as .4R earlier), and Billiardgrue for the prompting. I'll look forward to reading your treatment later and will answer Mac's question if you or someone doesn't beat me to it.

Jim

cushioncrawler
05-24-2007, 09:23 PM
<blockquote><font class="small">Quote Jal:</font><hr> ....Thanks to you, Coriolis, Mac (who stated that it might be as low as .4R earlier), and Billiardgrue for the prompting. I'll look forward to reading your treatment later and will answer Mac's question if you or someone doesn't beat me to it... <hr /></blockquote>Jim -- I dont know why i thort 0.4 -- i probably had some silly notion that i karnt even remember now.

But, i still think that it would be possible to make a small tip-sized hole in a ball to allow spin measurements up to say 0.9r (without miscueing), to see what a real cue can do (albeit in an unreal situation). But this would need slo-mo i guess. I probably wont do any such tests myself koz i karnt think of how i might meazure spin-rate at home, anyhow the tests would need accurate (or at least fixed) cue-speed (ie a robot).

The best that i could do would be to uze screw, hitting the qball into an OB so that the qball stops dead (nearnuff), then, the distance (mm) that the qball screws back would tell me the amount of bottom-spin that it had (or at least which shot had more). Regarding pace, if i hit each "shot" as hard as i could, and compared the best results (mm) for varous R/r's, then this might proov something i think.

Actually, a cue on a pendulum might "work". On 2 cotton pendulums actually, each pendulum made up of 2 legs so that the cue swung accurately (i have done this sort of thing before). But, i would havta find a way of stopping the cue from following throo and fouling. I'll be back. madMac.

Jal
05-25-2007, 01:16 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave'n'Jim -- What is the effect of a heavier cue, ie 4:1 ??? madMac. <hr /></blockquote>Hi Mac,

Here is a graph of the separation speed vs, well, you can read the heading. It covers mass ratios of 1/3 (black curves) and 1/4 (blue curves). Although each individual curve represents a fixed constant energy loss ratio at all tip offsets, no such supposition is intended. As Dr. Dave pointed out earlier, this may or may not be true.

http://ww2.netnitco.net/users/gtech/SeparationSpeedvsE.jpg

I suppose the moral is that if you have a choice between a light inefficient tip/stick and a heavy inefficient tip/stick, go with the light one.

If this isn't what you were looking for, let me know. Now I'm going to read his treatment and prepare any necessary further retractions.

Jim

cushioncrawler
05-25-2007, 06:29 PM
<blockquote><font class="small">Quote Jal:</font><hr> .....I suppose the moral is that if you have a choice between a light inefficient tip/stick and a heavy inefficient tip/stick, go with the light one. If this isn't what you were looking for, let me know. Now I'm going to read his treatment and prepare any necessary further retractions....<hr /></blockquote>Jim -- I think that the absolute spin might be larger for a heavyr cue, koz the yy axis is i think a ratio only. But, it could allso be said that the lighter the cue then the faster the stroke (Shepard had a stab at a possible relationship i think).

Re "e" for cue'to'ball impacts, it would be possible to do some cue'on'pendulum-into-ball'on'pendulum tests, at least for fullball (central) impacts. However, i reckon that a fair approximation for "e" might be gained by simply dropping the cue vertically onto a heavy steel anvil, and measuring the rebound. I think that such a test might suggest that e (fullball) woz less than 0.85 -- in which case e for an offset shot would be even less (due to slippage and bending). Dont be tempted to simply drop the cue onto a concrete garage floor, no matter how thick, concrete (on ground) is a disaster for rebound tests.

But, i reckon that less-stiff cues would give more spin than more-stiff cues. Coriolis duznt factor-in stiffness. A cue naturally wants to bend when in compression, and this bending can (duz) put extra spin on the ball. And here i am not talking about the momentum and energy robbed by the cue "twirling" during impact, which is another factor favoring less-stiff cues.

All in all, a cue might acheev zero "Coriolis" separation (in "Coriolis" theory) with the ball at an R/r of only say 0.50. But, would this mean that the max spin would then be found at say 0.40 ?? And, if one then factored in the compression-induced-bend (for a less-stiff cue), then we might be looking at 0.35 for max spin (and max back-spin). And, if one then factored in the fact that back-spin evaporates at a fixed rate (per second), and that the qball shood get to the OB sooner rather than later, then the best R/r for (long-range) screw might be say 0.30.

Somewhere along the line, i think a graph(s) showing peak (optimum) values would help vizualize some of this stuff. And i am sure that i have kum completely off the rails with my understanding of some of this stuff. madMac.

dr_dave
05-25-2007, 11:49 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave'n'Jim -- What is the effect of a heavier cue, ie 4:1 ??? madMac. <hr /></blockquote>Mac,

See Equations 9 and 10 in TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf). A heavier cue stick (i.e., larger m.s) would create slightly more spin at a given offset, and maximum spin would be predicted at a slightly smaller offset (.70 for 4:1 instead of .73 for 3:1, assuming energy conservation).

Regards,
Dave

Jal
05-26-2007, 02:37 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> .....I suppose the moral is that if you have a choice between a light inefficient tip/stick and a heavy inefficient tip/stick, go with the light one. If this isn't what you were looking for, let me know. Now I'm going to read his treatment and prepare any necessary further retractions....<hr /></blockquote>Jim -- I think that the absolute spin might be larger for a heavyr cue, koz the yy axis is i think a ratio only. But, it could allso be said that the lighter the cue then the faster the stroke (Shepard had a stab at a possible relationship i think).<hr /></blockquote>Mac, the second part is just about impossible to predict from theory, ie, what is is the optimum cue weight for a particular individual? You would have to know the momemnt of inertia of the person's arm about his elbow and it's hard to see how this could be determined. Of course, just trying out different cues should do it if you had reasonably identical tips on all of them. That makes answering the first part (absolute spin vs cue mass) also impossible to answer. You could take a stab at it, however, by considering the following:

For some energy loss ratio E'/E (which is less than 1), the tip offset which results in zero separation speed is:

b/R = Sqrt[(2/5)(1 + Mb/Ms)[1 - (1 + Ms/Mb)(1 - E'/E)]]

This yields the "x"-axis intercepts in the graph above, and puts an upper limit on b/R. Given the relatively modest values for this when E'/E is something like .85, one wonders if exceeding this limit is involved in miscues. At any rate, let's assume that you could cue up to this offset.

The amount of spin is related to the cueball's speed by:

RW' = (5/2)(b/R)Vb'

and

Vb' = 2KVs/(S + Mb/Ms)

where

S = (5/2)(b/R)^2 + 1

K = (1/2)[1 + Sqrt[1 - (S + Mb/Ms)(1 - E'/E)(Ms/Mb)]]

You can compare RW' for different mass ratios and their associated maximum b/R's, for some fixed E'/E. The problem is deciding on the initial stick speed, Vs, for the different cue weights. If I had some good rationale I would plot this out, but it doesn't seem worth it at the moment.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Re "e" for cue'to'ball impacts, it would be possible to do some cue'on'pendulum-into-ball'on'pendulum tests, at least for fullball (central) impacts. However, i reckon that a fair approximation for "e" might be gained by simply dropping the cue vertically onto a heavy steel anvil, and measuring the rebound. I think that such a test might suggest that e (fullball) woz less than 0.85 -- in which case e for an offset shot would be even less (due to slippage and bending).<hr /></blockquote>For a fullball hit, I think Bob Jewett has measured the cueball's speed at 1.3X the stick's speed (rather than the ideal 1.5 at a mass ratio of 1/3). As you surmised, this corresponds to an e of about .73. The problem is that we'd need to know how this changes with offset and I think it would be hard (as you've indicated), to get an accurate measurement of the tip offset. It can be taken off the high-speed videos rather easily, from the spin/speed ratio. But to see how well the reality conforms to the theory, you would need to know the particular mass ratios involved.

You're idea of observing how much the cueball draws back struck me as promising, but then you would need to know the cueball's pre-impact speed, as well as the stick's, via some direct measurement I think.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>... A cue naturally wants to bend when in compression, and this bending can (duz) put extra spin on the ball. And here i am not talking about the momentum and energy robbed by the cue "twirling" during impact, which is another factor favoring less-stiff cues.<hr /></blockquote>I don't see how the bending does anything but impart sideways velocity (squirt), which robs it of some spin (the force is more centrally directed), but...?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>...And, if one then factored in the fact that back-spin evaporates at a fixed rate (per second), and that the qball shood get to the OB sooner rather than later, then the best R/r for (long-range) screw might be say 0.30.<hr /></blockquote>I agree that max draw can sometimes be achieved with less than max offset for the reasons you state Mac. But it all depends on how much cue speed you're willing to generate and simultaneously maintain accuracy. This has been discussed before amongst our little group, and I did do the math for the ideal elastic case (Ron Shepard probably did it too and it looks like Dr. Dave as well.) According to my results, if there is essentially no limit to the cue speed (within reason), you do get max draw by hitting as low as possible. With limits, though, hitting a little higher does the trick (depending on the limits). But the difference in tip offset for table distances and reasonable cue speeds was, if I recall, not much. I'll have to look this up, or better yet, read Dr. Dave's analysis.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Somewhere along the line, i think a graph(s) showing peak (optimum) values would help vizualize some of this stuff. And i am sure that i have kum completely off the rails with my understanding of some of this stuff. madMac.<hr /></blockquote>It takes a bit of effort for me to generate graphs (lots of cutting and pasting), but I would be quite willing if I thought it might yield reliable results. We don't know much about real world values for E'/E, especially as it varies with offset, and there's that nasty problem of stick speed vs cue weight for different individuals. But, something to ponder. If you're really interested in a particular graph, speculative issues aside, I'll give it a go, but I could use some more specifics as to exactly what you want.

Jim

cushioncrawler
05-26-2007, 06:53 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave'n'Jim -- What is the effect of a heavier cue, ie 4:1 ??? madMac. <hr /></blockquote>Mac, See Equations 9 and 10 in TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf). A heavier cue stick (i.e., larger m.s) would create slightly more spin at a given offset, and maximum spin would be predicted at a slightly smaller offset (.70 for 4:1 instead of .73 for 3:1, assuming energy conservation).Regards, Dave<hr /></blockquote>Yes, thanks for that -- i had a look , eq (11) is certainly simple enuff -- and i am determined to try to come to grips with that whole "proof" later this year, and i might do some tests allso. I might try to add some peripheral thorts when i get around to answering Jim's new posting in a few minutes, and u might be able to clear some of them/thoze up allso as usual. madMac.

cushioncrawler
05-26-2007, 07:42 PM
<blockquote><font class="small">Quote Jal:</font><hr>.... You're idea of observing how much the cueball draws back struck me as promising, but then you would need to know the cueball's pre-impact speed, as well as the stick's, via some direct measurement I think.<hr /></blockquote>Jim -- Thanks for that posting -- I will havta look more closely at the/your equations etc later this year. The notion of getting max absolute spin (or screw) at less than max tip offset is fascinating, and i dont recall it being raised in similar threads perhaps 1 year ago. Even if, as everyone sez, the theory is oversimplified, and probably redundant anyhow koz of real-world limits for max tip offset.

Getting back to your above comments -- My thinking is/woz that hitting the qball (with screw) into an OB woz actually meant to obviate the need to know the qball's speed, koz the qball would stop "dead" (nearnuff) for all speeds (alltho, as u know, i am allways pointing out that the qball never stops dead, it allways stuns-throo at a small speed, up to 4% of initial V at high speeds, 1% or 2% of V at low speeds). But u might allready be aware of that, and perhaps u wanted to keep tabs on V for some other reason.

<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>... A cue naturally wants to bend when in compression, and this bending can (duz) put extra spin on the ball. And here i am not talking about the momentum and energy robbed by the cue "twirling" during impact, which is another factor favoring less-stiff cues.<hr /></blockquote>I don't see how the bending does anything but impart sideways velocity (squirt), which robs it of some spin (the force is more centrally directed), but...?<hr /></blockquote>I think slo-mo of a cue hitting a slippery plate would show that the qtip wants to "buck" sideways during impakts, due to buckling of the cue. This effekt could have a strong influence on sidespin and screw. A less-stiff cue would buckle more-so -- hence more sidespin for the same effort (compared to a stiffy), but only up to a point, ie a cue could be too "soft" (i wont uze the word too "whippy" koz as Dr Dave points out this term haz better usage elsewhere).

Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin (screw).

<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>Somewhere along the line, i think a graph(s) showing peak (optimum) values would help vizualize some of this stuff. And i am sure that i have kum completely off the rails with my understanding of some of this stuff...<hr /></blockquote>It takes a bit of effort for me to generate graphs (lots of cutting and pasting), but I would be quite willing if I thought it might yield reliable results. We don't know much about real world values for E'/E, especially as it varies with offset, and there's that nasty problem of stick speed vs cue weight for different individuals. But, something to ponder. If you're really interested in a particular graph, speculative issues aside, I'll give it a go, but I could use some more specifics as to exactly what you want...<hr /></blockquote>Jim -- I think i will have to look/think more closely about this stuff later in the year, and i will get back to you on all of this. But, of course if u guys want to pursue this right now then i will do my best to keep up. madMac.

Jal
05-27-2007, 02:20 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> ...The notion of getting max absolute spin (or screw) at less than max tip offset is fascinating, and i dont recall it being raised in similar threads perhaps 1 year ago.<hr /></blockquote>Mac, I think it's interesting and useful to know too. I remember the discussion (http://www.billiardsdigest.com/ccboard/showflat.php?Cat=&amp;Board=ccb&amp;Number=223552&amp;Forum=cc b&amp;Words=Jim%20%20jal%20maximum%20draw%20distance&amp;M atch=And&amp;Searchpage=0&amp;Limit=25&amp;Old=allposts&amp;Main=2 23341&amp;Search=true#Post223552) because Dr. Dave asked for a justification for some of the things I was saying, and I stiffed him (was distracted by another problem).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Getting back to your above comments -- My thinking is/woz that hitting the qball (with screw) into an OB woz actually meant to obviate the need to know the qball's speed, koz the qball would stop "dead" (nearnuff) for all speeds (alltho, as u know, i am allways pointing out that the qball never stops dead, it allways stuns-throo at a small speed, up to 4% of initial V at high speeds, 1% or 2% of V at low speeds). But u might allready be aware of that, and perhaps u wanted to keep tabs on V for some other reason.<hr /></blockquote>You're right Mac. I re-read your post and see that the purpose is to get the spin, not spin/speed ratio.

<blockquote><font class="small">Quote cushioncrawler:</font><hr><blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>... A cue naturally wants to bend when in compression, and this bending can (duz) put extra spin on the ball. And here i am not talking about the momentum and energy robbed by the cue "twirling" during impact, which is another factor favoring less-stiff cues.<hr /></blockquote>I don't see how the bending does anything but impart sideways velocity (squirt), which robs it of some spin (the force is more centrally directed), but...?<hr /></blockquote>I think slo-mo of a cue hitting a slippery plate would show that the qtip wants to "buck" sideways during impakts, due to buckling of the cue. This effekt could have a strong influence on sidespin and screw. A less-stiff cue would buckle more-so -- hence more sidespin for the same effort (compared to a stiffy), but only up to a point, ie a cue could be too "soft" (i wont uze the word too "whippy" koz as Dr Dave points out this term haz better usage elsewhere).<hr /></blockquote>I'm still wondering what you mean. I think you're refering to a kind of "S" shaped curve that develops (or maybe with more humps/nodes)? If so, it's not obvious that this produces more spin. Why do you think it does?

I don't know anything about it and therefore am not saying it doesn't. But on the face of it, it seems to me that this is just another "compression" mode of sorts, and there will be energy losses associated with this too. It's not clear to me that the energy losses here would be less than with straight longitudinal compression, which would be "relieved" by this snaking somewhat Maybe you're seeing this in a completely different way.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin (screw).<hr /></blockquote>I think it's pretty clear that squirt reduces spin/speed ratios, and less clear but true that it reduces absolute spin itself, ie, the cueball's speed is also diminished. Do you agree?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- I think i will have to look/think more closely about this stuff later in the year, and i will get back to you on all of this. But, of course if u guys want to pursue this right now then i will do my best to keep up. madMac. <hr /></blockquote>The problem is keeping up with you. You offer up a number of provocative ideas and trying to resolve them in a quantitative way usually isn't easy, if doable at all, by me anyway. (But keep em coming.)

Jim

cushioncrawler
05-27-2007, 06:16 PM
<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>... A cue naturally wants to bend when in compression, and this bending can (duz) put extra spin on the ball. And here i am not talking about the momentum and energy robbed by the cue "twirling" during impact, which is another factor favoring less-stiff cues.<hr /></blockquote>I don't see how the bending does anything but impart sideways velocity (squirt), which robs it of some spin (the force is more centrally directed), but...?<hr /></blockquote><blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>... I think slo-mo of a cue hitting a slippery plate would show that the qtip wants to "buck" sideways during impakts, due to buckling of the cue. This effekt could have a strong influence on sidespin and screw. A less-stiff cue would buckle more-so -- hence more sidespin for the same effort (compared to a stiffy), but only up to a point, ie a cue could be too "soft" (i wont uze the word too "whippy" koz as Dr Dave points out this term haz better usage elsewhere).<hr /></blockquote>I'm still wondering what you mean. I think you're refering to a kind of "S" shaped curve that develops (or maybe with more humps/nodes)? If so, it's not obvious that this produces more spin. Why do you think it does? I don't know anything about it and therefore am not saying it doesn't. But on the face of it, it seems to me that this is just another "compression" mode of sorts, and there will be energy losses associated with this too. It's not clear to me that the energy losses here would be less than with straight longitudinal compression, which would be "relieved" by this snaking somewhat Maybe you're seeing this in a completely different way.<hr /></blockquote>Jim -- In effect i reckon that a qball hit dead center will allways have a little (or a lot) of unwanted spin (or screw) -- especially for a less-stiff cue. The contact point on the qball, at the instant of separation, will allways (if zero slippage) have the same velocity as the qtip. The qtip will allways have some sort of sideways velocity at separation. Another reason perhaps to uze a bent cue, koz here u can hold the cue such that the "buck" helps the action, koz the buck will for sure be (or want to be) in the direction of the bend. This stuff mightnt be a worry for a stiff cue, but i am sure that it raizes (can raize) its ugly head for non-stiff cues. For example, if u find a google link to the hi-speed photos of a projectile hitting a teflon tube end-on, u can see that the tube end moovs sideways a long way during impakt, while the rest of the tube is trying its best to mimic a snake.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin (screw).<hr /></blockquote>I think it's pretty clear that squirt reduces spin/speed ratios, and less clear but true that it reduces absolute spin itself, ie, the cueball's speed is also diminished. Do you agree?<hr /></blockquote>Jim -- Its difficult to imagine a very very very stiff'n'heavy cue hitting a qball. No matter how small the cue moovment it will none the less have a shared velocity at the mutual qtip'ball contact. So, i go one step further, and imaging a truely solid cue, zero sideways moovment. Now, if zero slippage, the only possible sidespin would be on account of internal flexing within the ball itself, helped a bit allso by the ball's temporary flatspot. Here then the ball's spin would be due mainly to the relationship of the balls rotational flexing relative to the balls compression flexing. I reckon that, depending on where things fell along the (sinusoidal?) graph, a qball could even have reverse spin at separation (but this might only be possible for a rubber ball). What do u think?? madMac.

Jal
05-27-2007, 10:05 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- In effect i reckon that a qball hit dead center will allways have a little (or a lot) of unwanted spin (or screw) -- especially for a less-stiff cue. The contact point on the qball, at the instant of separation, will allways (if zero slippage) have the same velocity as the qtip. The qtip will allways have some sort of sideways velocity at separation. Another reason perhaps to uze a bent cue, koz here u can hold the cue such that the "buck" helps the action, koz the buck will for sure be (or want to be) in the direction of the bend. This stuff mightnt be a worry for a stiff cue, but i am sure that it raizes (can raize) its ugly head for non-stiff cues. For example, if u find a google link to the hi-speed photos of a projectile hitting a teflon tube end-on, u can see that the tube end moovs sideways a long way during impakt, while the rest of the tube is trying its best to mimic a snake.<hr /></blockquote>Mac, I think that bending increases spin in the sense that it reduces endmass, and therefore squirt, but the difference is pretty small (though the effect probably increases at small offsets). Given the slow propogation of the transverse forces, it doesn't seem likely that you'll see much in the way of additional bending modes, but...?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Its difficult to imagine a very very very stiff'n'heavy cue hitting a qball. No matter how small the cue moovment it will none the less have a shared velocity at the mutual qtip'ball contact. So, i go one step further, and imaging a truely solid cue, zero sideways moovment. Now, if zero slippage, the only possible sidespin would be on account of internal flexing within the ball itself, helped a bit allso by the ball's temporary flatspot. Here then the ball's spin would be due mainly to the relationship of the balls rotational flexing relative to the balls compression flexing. I reckon that, depending on where things fell along the (sinusoidal?) graph, a qball could even have reverse spin at separation (but this might only be possible for a rubber ball). What do u think?? madMac. <hr /></blockquote>Mac, this was also discussed by us a while ago. I offered a formula for the squirt angle here (http://www.billiardsdigest.com/ccboard/showflat.php?Cat=&amp;Board=ccb&amp;Number=242570&amp;Forum=cc b&amp;Words=rigid%20squirt%20mass%20train&amp;Match=And&amp;Se archpage=0&amp;Limit=25&amp;Old=allposts&amp;Main=242235&amp;Searc h=true#Post242570).

If you don't want to look (and who would?), as a cue gets extremely rigid and heavy, and assuming the collision is virtually elastic, at a tip offfset of (2/5)R, for instance, you should see about 16.5 degrees of squirt. The assumption is that the point of contact on the ball will move in the same direction as the cue (no sideways component by our assumption of rigidity, great weight and no slippage). But, in general (normal cues), the contact point moves forward faster than the tip and this gives it a rotational component about the center of the ball, in addition to its sideways motion. With the extreme cue, the fact that the contact point is at least moving forward (and only moving forward by our assumptions), this by itself should give it a rotational component. The spin/speed ratio (Rw/v) works out to about 0.31 for the (2/5)R offset.

But then there's the question of separation speed. I haven't worked this out, but intuition suggests that there should be plenty of it (a very heavy object colliding with a light one results in the light one moving at twice the heavy one's speed.) Not much is lost, I think, if the "true" collision direction is 16.5 degrees off the original cue direction.

Over to you.

Jim

bradb
05-28-2007, 10:17 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin )) end of quote.

Max, Is there anything in here that can provide a neophyte some practical application to advancement of their game? I've tried to dive into the murky depths of the dialogue here, but it appears (from my perch that is lower than even a layman) that this is an exercise in theory for mathemeticians. I ask this because you and others in here are also players and can bridge the gap between abstract and application. I do know that better cues are strenghtened to reduce deflection, is there an inference suggested in these formulas that is a guide to the different aspects of a cues construction and its impact on play? -Brad

Jal
05-28-2007, 05:24 PM
<blockquote><font class="small">Quote bradb:</font><hr>
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin )) end of quote.

Max, Is there anything in here that can provide a neophyte some practical application to advancement of their game? I've tried to dive into the murky depths of the dialogue here, but it appears (from my perch that is lower than even a layman) that this is an exercise in theory for mathemeticians. I ask this because you and others in here are also players and can bridge the gap between abstract and application. I do know that better cues are strenghtened to reduce deflection, is there an inference suggested in these formulas that is a guide to the different aspects of a cues construction and its impact on play? -Brad

<hr /></blockquote>Brad, as far as I know, what Mac and I have been discussing almost certainly cannot help one's game. Maybe he feels differently, which I think is pretty clearly so as far as a bent cue is concerned.

So, to the extent that the math was opaque, you didn't really miss anything.

Jim

dr_dave
05-28-2007, 05:24 PM
<blockquote><font class="small">Quote bradb:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>Then there is the bizness of squirt. I reckon that a stiff cue will give more squirt (ok), but, more than that, i say that an infinitely stiff (and infinitely heavy) cue gives max squirt and zero spin (or very very little). Any ordinary qtip must be mooving in sympathy with that part of the qball, or at least the qtip must be mooving no slower. Hencely the stiffer the cue the more the effect of the cue's inertia on not just the qball's squirt angle but on the qball's spin ))<hr /></blockquote>Max, Is there anything in here that can provide a neophyte some practical application to advancement of their game? I've tried to dive into the murky depths of the dialogue here, but it appears (from my perch that is lower than even a layman) that this is an exercise in theory for mathemeticians. I ask this because you and others in here are also players and can bridge the gap between abstract and application. I do know that better cues are strenghtened to reduce deflection, is there an inference suggested in these formulas that is a guide to the different aspects of a cues construction and its impact on play?<hr /></blockquote>Brad, in TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf), I tried to give conclusions after all of the math and physics. Here's the bottom line: If you want more spin, use more stick speed (up to the point where your accuracy might suffer). As far as how much tip offset to use, it doesn't help that much increasing the tip offset as you get closer to the miscue limit (which is at about half the ball radius from the center). Here's a good summary of useful advice:<ul type="square"> shape the tip well (e.g., dime radius). use chalk when hitting off-center. when hitting off-center, more speed gives you more spin. when getting close to the miscue limit, adding more tip offset doesn't create much extra spin, so it is not advisable to totally max out the tip offset. It is better (safer, with very little loss in spin) to back off a little from the miscue limit.[/list]This list is probably fairly obvious to most people (with the possible exception of the last bullet), but I thought I would summarize it anyway.

Regards,
Dave

cushioncrawler
05-28-2007, 06:36 PM
<blockquote><font class="small">Quote bradb:</font><hr> ...Max, Is there anything in here that can provide a neophyte some practical application to advancement of their game? I've tried to dive into the murky depths of the dialogue here, but it appears (from my perch that is lower than even a layman) that this is an exercise in theory for mathemeticians. I ask this because you and others in here are also players and can bridge the gap between abstract and application. I do know that better cues are strenghtened to reduce deflection, is there an inference suggested in these formulas that is a guide to the different aspects of a cues construction and its impact on play? -Brad<hr /></blockquote>Brad -- I bet that u could teach/show me heaps -- i am a very average player. I reckon that no player can get very far very fast unless they get lessons or at least someone to check them out. I have never had payed lessons, but i have rubbed shoulders with lots of champs, and discussed (or at least overheard) lots of coaching stuff.

Whenever i check out a team mate, i am sure that i look at things that few coaches look at, or at least i look at things differently, or at least i give advice that no one else would ever give. Invariably we are all human (except for Patrick), and how well we play depends on how well we get around our faults. Lots of praktis helps, but ultimately it is the eyesight (aim-error) that holds us back.

I think that most of what u see/hear about cues is rubbish. However, i think that ultimately the key to better play, ie to help overkum aim-error, is in your cue(s). Most of us shood be uzing a bent cue, and probably a conical taper. Otherwize be prepared to spend (waste) hours and hours and years and years finding and then loozing that "eureka" feeling, again and again, untill u wize up that "it" is allways a phantom. Now u (i dont mean u) are ready to really wize-up, but, who are u going to call ??? U (Brad) were lucky, u ran into an instructor who put u onto bent cues.

Another "cue" thing. I am really impressed with "low deflection" and "pivot point" and "bridge length" theories. These theories are mostly brort up to help some players to use english with more confidence, but i see it all as being of more use for when u are simply trying to hit a qball without english (i am not saying that i thort of this first). Having firstly wized-up that he/she needs a bent cue, u shood then find a bent cue with a squirt that suits your favorite bridge length. Alternatively, perhaps u can alter your bridge length to suit your favorit cue. I will try this myself next billiards season.

All of this reminds me of the new "wonder" cue that Burroughs &amp; Watts brort out in about 1910(?). It had a 12" steel pin in the tip, to keep the cue dead straight. Here they erred both ways, they failed to see that a bent cue can be "medicinal", and they failed to see that a big squirt can be "poizon". They patented-made-promoted this heap of junk, so, were they stupid?? -- No -- they discarded the worthless K55 and K66 style cushion profiles back in about 1890(?), so they were actually smart. madMac.

bradb
05-29-2007, 09:56 AM
Thanks Dave, Max, Jim and others for your replies.

Myself, and I'm sure others are who follow these technical threads are appreciative because we wonder if we are missing out on something.

I never saw much use in the expensive cues until I became a more advanced player and then realized what non deflection can do. The mechanics of what happens when a cue strikes a Q ball is still something that has always been "feel," but over the years I've come to learn that a deeper knowledge of the game is something I can benefit from.

- Brad

dr_dave
06-06-2007, 06:20 PM
Jal and others,

FYI, I just added the derivation of cue ball speed and spin, taking into effect energy loss (and coefficient of restitution) of the tip-ball collision. It starts in the middle of page 3 of TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf).

I also added some summarizing statements at the end, so the people out there who don't like math and physics can just jump to the bottom of half of the last page.

Please take a look when you get a chance and let me know if you disagree with anything.

Thanks,
Dave

<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Jim and others,

FYI, if anybody wants to see an illustration and the details, I just posted a complete analysis and discussion for the elastic-collision case. It shows the derivation of Jal's equations and result below. See TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf).

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

Your critique helped. At first, it wasn't clear why you were characterizing the treatment as only applying to the elastic situation. In fact, the parameters K and e were introduced for the inelastic case. I still think the equations are valid (up to a point), but they are misleading (to myself included).

I added curves for the after/before energy ratio (E'/E) to the graph, and now see that indeed you would have to have a perfectly elastic collision to achieve a tip offset of .73R, with a non-negative separation speed. If it's true that you'll always get something like a 10-20% energy loss, then the curve for E'/E (e=0) puts the limiting tip offset for zero separation speed somewhere between .4R and .6R.

Thanks to you, Coriolis, Mac (who stated that it might be as low as .4R earlier), and Billiardgrue for the prompting. I'll look forward to reading your treatment later and will answer Mac's question if you or someone doesn't beat me to it.<hr /></blockquote>

Deeman3
06-07-2007, 08:07 AM
<blockquote><font class="small">Quote bradb:</font><hr> Thanks Dave, Max, Jim and others for your replies.

Myself, and I'm sure others are who follow these technical threads are appreciative because we wonder if we are missing out on something. <font color="blue"> I read them so I can nod off at night. /ccboard/images/graemlins/grin.gif </font color>

I never saw much use in the expensive cues until I became a more advanced player and then realized what non deflection can do. <font color="blue"> Brad, I am happy you have advanced your game so far. However, I don't beleive in "non-deflection" no matter what scientific guise it is under. Reduced deflection may have value but I even argue that on occasion. </font color> The mechanics of what happens when a cue strikes a Q ball is still something that has always been "feel," but over the years I've come to learn that a deeper knowledge of the game is something I can benefit from. <font color="blue"> Sadely, I wish this same accumulation of knowledge made my game leap forward but I continue to struggle to find a more than a dozen or so games where advanced knowledge, that beyond the "feel" and "aim" intuitive part of the game got me out. I do love to follow the threads and especially like the discussions between Doc, Max, Jim and Bob but I miss the sanity of Cornerman who I feel has a great understanding of what matters and what does not. Unfortunately, while I know he has the education and knowledge to contribute, I believe he sort of drops out when the discussion becomes what some of us dummies would consider arcaine and non-practical knowledge. Doesn't anyone else miss his and a couple of others ability to cut through all the crap to the part that helps win games? </font color>








<hr /></blockquote>

dr_dave
06-07-2007, 09:24 AM
<blockquote><font class="small">Quote Deeman3:</font><hr>I miss the sanity of Cornerman who I feel has a great understanding of what matters and what does not. Unfortunately, while I know he has the education and knowledge to contribute, I believe he sort of drops out when the discussion becomes what some of us dummies would consider arcaine and non-practical knowledge. Doesn't anyone else miss his and a couple of others ability to cut through all the crap to the part that helps win games?<hr /></blockquote>I certainly agree that Fred adds a lot to this forum, and I wish he were more active.

Here's my stab at cutting through all of the physics "crap" in this thread: If you want more spin on the cue ball, hit it further from the center and harder (no surprise here). For maximum spin, it is best to use more speed rather than more offset as you approach the miscue limit (which occurs at about 1/2 the ball's radius from center). This assumes you can still maintain good control and accuracy at the higher speed. A lighter cue stick and a low-squirt shaft might also help create a little extra spin at large offsets, but these are small effects.

Regards,
Dave

PS: Most of the physics and math behind the observations above can be found in TP A.30 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-30.pdf).

Deeman3
06-07-2007, 10:37 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Deeman3:</font><hr>I miss the sanity of Cornerman who I feel has a great understanding of what matters and what does not. Unfortunately, while I know he has the education and knowledge to contribute, I believe he sort of drops out when the discussion becomes what some of us dummies would consider arcaine and non-practical knowledge. Doesn't anyone else miss his and a couple of others ability to cut through all the crap to the part that helps win games?<hr /></blockquote>I certainly agree that Fred adds a lot to this forum, and I wish he were more active.

Here's my stab at cutting through all of the physics "crap" in this thread: If you want more spin on the cue ball, hit it further from the center and harder (no surprise here). For maximum spin, it is best to use more speed rather than more offset as you approach the miscue limit (which occurs at about 1/2 the ball's radius from center). This assumes you can still maintain good control and accuracy at the higher speed. A lighter cue stick and a low-squirt shaft might also help create a little extra spin at large offsets, but these are small effects.

Regards,
Dave <hr /></blockquote>

<font color="blue"> Dave,

Nice and concise summary even a Caveman can understand... /ccboard/images/graemlins/smirk.gif</font color>

dr_dave
06-07-2007, 11:22 AM
<blockquote><font class="small">Quote Deeman3:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Deeman3:</font><hr>I miss the sanity of Cornerman who I feel has a great understanding of what matters and what does not. Unfortunately, while I know he has the education and knowledge to contribute, I believe he sort of drops out when the discussion becomes what some of us dummies would consider arcaine and non-practical knowledge. Doesn't anyone else miss his and a couple of others ability to cut through all the crap to the part that helps win games?<hr /></blockquote>I certainly agree that Fred adds a lot to this forum, and I wish he were more active.

Here's my stab at cutting through all of the physics "crap" in this thread: If you want more spin on the cue ball, hit it further from the center and harder (no surprise here). For maximum spin, it is best to use more speed rather than more offset as you approach the miscue limit (which occurs at about 1/2 the ball's radius from center). This assumes you can still maintain good control and accuracy at the higher speed. A lighter cue stick and a low-squirt shaft might also help create a little extra spin at large offsets, but these are small effects.

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

Nice and concise summary even a Caveman can understand... /ccboard/images/graemlins/smirk.gif<hr /></blockquote>Thank you.

Your discussion about Fred reminded me of Fran. I wish she were also back and active again. She seemed to provide a unique perspective as an intuition-and-feel, non-technical-type instructor and past pro player with lots of good insight and experience.

Some people probably think I'm crazy expressing a desire for Fred and Fran to be active again, given how much they both seemed to like to go after me in the past. Actually, I kind of miss that. I think the only other user from which I have received more abuse was "Popcorn." I miss him too.

Regards,
Dave

wolfdancer
06-07-2007, 12:49 PM
"....Some people probably think I'm crazy expressing a desire for Fred and Fran to be active again, given how much they both seemed to like to go after me in the past. Actually, I kind of miss that"
A glutton for punishment.....try wearing a hair shirt instead;
you can always get that off your back, when it gets too bothersome...but you may never get....lol
I agree, both Fred and Fran have a lot of good input to offer ....."intuition and feel"....to me that's what playing in the zone would be all about...and maybe someday, if I can just remove, temporarily, all this technical clutter from my brain....I'll get here???
Sudden thought...is Dr. Dave preventing me from reaching the next level????????

dr_dave
06-07-2007, 01:09 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>....Some people probably think I'm crazy expressing a desire for Fred and Fran to be active again, given how much they both seemed to like to go after me in the past. Actually, I kind of miss that<hr /></blockquote>
A glutton for punishment.....try wearing a hair shirt instead; you can always get that off your back, when it gets too bothersome...but you may never get....lol
I agree, both Fred and Fran have a lot of good input to offer ....."intuition and feel"....to me that's what playing in the zone would be all about...and maybe someday, if I can just remove, temporarily, all this technical clutter from my brain....I'll get here???
Sudden thought...is Dr. Dave preventing me from reaching the next level???????? <hr /></blockquote>You finally exposed my devious nature. The true purpose of all of the work I do is to prevent people from learning the true secrets of the game. I will never disclose my true "snake-oil" formulas. /ccboard/images/graemlins/grin.gif

Regards,
Dave

Jal
06-07-2007, 03:48 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just added the derivation of cue ball speed and spin, taking into effect energy loss (and coefficient of restitution) of the tip-ball collision. ....

Please take a look when you get a chance and let me know if you disagree with anything.<hr /></blockquote>Dr. Dave,

No disagreement here (and I did do the algebra). It may not be much comfort, and perhaps even a little distressing, but your results are the same ones I got above (in the second graph where K is expressed as a function of E'/E), but in a slightly differnt form. /ccboard/images/graemlins/smile.gif

I particulary liked eq.'s 21 and 22, which shows how e intrudes itself, replacing what was once a factor or term of 1 in the elastic case. Very nice!

An argument can be made that, ignoring squirt, eta increases a little with tip offset. This would be true if K (in my version) remains fairly constant or possibly increases with offset. (K is a measure of the reduction of the impulse the cue delivers from the ideal elastic case.) But with squirt included, K probably does diminish and therefore likely eta (E'/E) too.

As far as getting more spin with more offset vs more speed, I agree, for what it's worth, that using more speed is safer if you're already out there near the miscue limit. But just to note that when more english is required, it's usually the spin/speed ratio which is important, I think, and which can ony be increased with more tip offset (I know you know!)

I also noticed that you simplified the final result for Vb (in the radical) a bit. It's been kind of surprising that the expression is so neat and elegant. Thanks again for yet another well-presented analysis.

Jim

dr_dave
06-07-2007, 04:09 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just added the derivation of cue ball speed and spin, taking into effect energy loss (and coefficient of restitution) of the tip-ball collision. ....

Please take a look when you get a chance and let me know if you disagree with anything.<hr /></blockquote>Dr. Dave,

No disagreement here (and I did do the algebra). It may not be much comfort, and perhaps even a little distressing, but your results are the same ones I got above (in the second graph where K is expressed as a function of E'/E), but in a slightly differnt form. /ccboard/images/graemlins/smile.gif<hr /></blockquote>I'm glad we seem to totally agree on the entire analysis. Now, I can sleep at night. /ccboard/images/graemlins/wink.gif

<blockquote><font class="small">Quote Jal:</font><hr>I particulary liked eq.'s 21 and 22, which shows how e intrudes itself, replacing what was once a factor or term of 1 in the elastic case. Very nice!<hr /></blockquote>I was actually a little surprised at the complexity of the relationship between COR and collision efficiency.

<blockquote><font class="small">Quote Jal:</font><hr>An argument can be made that, ignoring squirt, eta increases a little with tip offset. This would be true if K (in my version) remains fairly constant or possibly increases with offset. (K is a measure of the reduction of the impulse the cue delivers from the ideal elastic case.) But with squirt included, K probably does diminish and therefore likely eta (E'/E) too.<hr /></blockquote>I haven't thought about these details yet. It would be nice to have some data for this.

<blockquote><font class="small">Quote Jal:</font><hr>As far as getting more spin with more offset vs more speed, I agree, for what it's worth, that using more speed is safer if you're already out there near the miscue limit. But just to note that when more english is required, it's usually the spin/speed ratio which is important, I think, and which can ony be increased with more tip offset (I know you know!)<hr /></blockquote>Good points. An example (I think) where absolute spin is more important than spin/speed ratio is a power-draw shot with no cut angle. The action of the CB depends only on the amount of spin, since all of the speed is lost in the collision.

<blockquote><font class="small">Quote Jal:</font><hr>I also noticed that you simplified the final result for Vb (in the radical) a bit. It's been kind of surprising that the expression is so neat and elegant. Thanks again for yet another well-presented analysis.<hr /></blockquote>I was also a little surprised by how neat some of the results are.

Regards and thanks,
Dave

cushioncrawler
06-07-2007, 04:34 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ....Here's my stab at cutting through all of the physics "crap" in this thread: If you want more spin on the cue ball, hit it further from the center and harder (no surprise here). For maximum spin, it is best to use more speed rather than more offset as you approach the miscue limit (which occurs at about 1/2 the ball's radius from center). This assumes you can still maintain good control and accuracy at the higher speed. A lighter cue stick and a low-squirt shaft might also help create a little extra spin at large offsets, but these are small effects....<hr /></blockquote>Dr Dave -- Without going back and reading all of the earlyr postings, i think i shood add 2 comments which arize from earlyr similar threads.

1... It would be rare for a player to want to hit a shot very hard to get extra sidespin. Uzually a player wants extra sidespin/speed ratio. Hencely, the shot iz more likely to need qtip'to'qball contact at 8 o'clock or 4 o'clock.

2.... Hitting very hard would uzually be the answer for getting more screw. Here a cue can be too-stiff or not stiff enuff, especially when the range to the OB is large. And, dont forget to get the qball bouncing on the way to the OB (for long range screw shots). madMac.

wolfdancer
06-07-2007, 04:50 PM
Dr. Dave, I see many beginning players hit the ball "hard" instead of adding speed, as you recommend. Might just be semantics but there's a big difference to me...hard is usually a punch shot, that ends up as a stun shot, and since most of the energy is transferred to the o.b.....not much "magic" is left in the c.b.
I upped my game a bit by thinking "speed" and adding follow through...( that's also the extent of my tech know-how as regards to pool )

cushioncrawler
06-07-2007, 05:07 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Dr. Dave, I see many beginning players hit the ball "hard" instead of adding speed, as you recommend. Might just be semantics but there's a big difference to me... hard is usually a punch shot, that ends up as a stun shot, and since most of the energy is transferred to the o.b..... not much "magic" is left in the c.b. I upped my game a bit by thinking "speed" and adding follow through... (that's also the extent of my tech know-how as regards to pool)<hr /></blockquote>Woolfy.
"semantics" -- u shoodnt bring religion into this.
"hard" -- karnt u modify one of yor golf-training-fans to fit onto a cue, to develop strength.
"magic" -- this belongs on the Russian website.
"thinking" -- thinking a ball into the hole, or whatever, iz all covered in that old book "pyscho cybernetics" (i have one). madMac.

wolfdancer
06-07-2007, 09:31 PM
I had one,and from memory....Maxwell Maltz ???
I can look it up, but just checking out the "retrieval system" today.
I can't remember though, what the book was all about....
Can i still become a Republican, with half a memory...or do i need to forget everything?

wolfdancer
06-07-2007, 09:40 PM
Mac, i just googled Maltz...and found this:
(Matt Furey is carrying on the good Doctor's work...but doubt if Max would appreciate what has become of his research)
Those who have seen Furey speak LIVE are astounded at how he can walk into a room and hold large audiences spell-bound for hours upon end. Time ceases to exist as an awe-inspiring presence permeates the room. Nothing Furey has to say is "canned" or "scripted." He speaks stream-of-consciousness, fearlessly trusting in the Universe to give him the very words he needs to uplift and inspire. Oftentimes an audience will witness Furey go on a roller-coaster ride of emotional highs - from laughter to tears to a feeling of profound love and bliss. No one leaves a Matt Furey event unchanged.
http://www.psycho-cybernetics.com/images/matt_furey_speaks.jpg

It sounds suspiciously like EST, and Werner Erhard (real name..John Paul Rosenberg)

cushioncrawler
06-07-2007, 09:51 PM
My books are stored, but google sez that u are correct, maxwell maltz, 1960. Karnt remember what woz in it. My billiards mate gave me a copy, he had about 10 -- loves it. He sez that he can now moov a ball with hiz mind. It iz particulary deadly in getting your opponent's ball to jaw out. madMac.

Deeman3
06-08-2007, 07:29 AM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Dr. Dave, I see many beginning players hit the ball "hard" instead of adding speed, as you recommend. <font color="blue"> Wolfdancer, this is one of the truest utterances I have ever heard a secular progressive make! Hard is completely different from "speed" or "pace" especially in applying draw and spin. </font color> Might just be semantics but there's a big difference to me...hard is usually a punch shot, that ends up as a stun shot, and since most of the energy is transferred to the o.b.....not much "magic" is left in the c.b. <font color="blue"> This is where me and most PHD's part company as I know I can drag/induce spin by playing in the "that's way too far off center land" of the cue ball and get reactions off the rail most of these guys just dream about. Max is right, it's maybe not magic but it's something "extra" in applying spin a formula just won't accomplish for you. O.K. back to my remedial hut for a while.... /ccboard/images/graemlins/smirk.gif </font color>
I upped my game a bit by thinking "speed" and adding follow through...( that's also the extent of my tech know-how as regards to pool ) <font color="blue"> I'd prefer (you have my book) that you think "pace" rather than speed. It delivers a more thoughful message than speed. Speed belongs to that Saint Dale Earnhart.... No, I never had a "3" on my truck nor on my shoulder holster.</font color> <hr /></blockquote>

dr_dave
06-08-2007, 08:52 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ....Here's my stab at cutting through all of the physics "crap" in this thread: If you want more spin on the cue ball, hit it further from the center and harder (no surprise here). For maximum spin, it is best to use more speed rather than more offset as you approach the miscue limit (which occurs at about 1/2 the ball's radius from center). This assumes you can still maintain good control and accuracy at the higher speed. A lighter cue stick and a low-squirt shaft might also help create a little extra spin at large offsets, but these are small effects....<hr /></blockquote>Dr Dave -- Without going back and reading all of the earlyr postings, i think i shood add 2 comments which arize from earlyr similar threads.

1... It would be rare for a player to want to hit a shot very hard to get extra sidespin. Uzually a player wants extra sidespin/speed ratio. Hencely, the shot iz more likely to need qtip'to'qball contact at 8 o'clock or 4 o'clock.

2.... Hitting very hard would uzually be the answer for getting more screw. Here a cue can be too-stiff or not stiff enuff, especially when the range to the OB is large. And, dont forget to get the qball bouncing on the way to the OB (for long range screw shots). madMac. <hr /></blockquote>Good points. No disagreements here; although, I'm not so sure about the importance of cue stiffness.

Regards,
Dave

wolfdancer
06-08-2007, 11:17 AM
Dee, I understand how an engineer, would cringe at speed and pace being used interchangeably...but to a small town, country boy like myself, we use whatever word pops up first.
And....your book...
I'm between travel plans...visitors have left.....I've performed my ablutions, in preparation for my reading.....
So far I have only read the opening line
"It was a dark and stormy night..."
Didn't you steal that from Bulwer-Lytton?

dr_dave
06-08-2007, 11:33 AM
<blockquote><font class="small">Quote Deeman3:</font><hr>... I wish this same accumulation of knowledge made my game leap forward but I continue to struggle to find a more than a dozen or so games where advanced knowledge, that beyond the "feel" and "aim" intuitive part of the game got me out. ...<hr /></blockquote>Dee,

The purpose of the physics analyses and discussions isn't always just to help make your game better. Often, it is just to help develop a better understanding of what is going on with the physics. Now, sometimes that improved understanding can help lead to insight and technique advice that can help at the table. I think two good examples are the 30-degree rule (http://www.engr.colostate.edu/~dga/pool/threads.html) and my recent series of articles dealing with throw (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html). I think in both of these cases, the insight gained from the physics can go a long way to helping people develop and improve faster. Also, for some people (e.g., me), understanding can help improve confidence. Anytime I can back up my intuition with understanding, I usually have more confidence. That way, when I get down in my stance, I can better focus on confidently executing the shot, without having to subconsciously doubt my intuition.

Now, top players who have perfect intuition don't need to "understand" the 30-degree rule peace-sign technique, or how to achieve maximum throw, or the effects of inside vs. outside English, or rail cut-shot physics, because they instinctively know all of this stuff based on intuition and confidence built from years and years of successful practice and play. They "just know" where the balls will go on every shot. However, for everybody else, I think a little knowledge, understanding, and insight can help one improve faster and have more confidence.

Others and I have debated these issues many times in the past. If people are interested in reading the highlights, they can visit the pertinent links under "mental aspects" here (http://www.engr.colostate.edu/~dga/pool/threads.html).

Regards,
Dave

"I like to play better too ... and the physics understanding and insight sometimes helps me with this."

Deeman3
06-08-2007, 12:20 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Dee, I understand how an engineer, would cringe at speed and pace being used interchangeably...but to a small town, country boy like myself, we use whatever word pops up first.
And....your book...
I'm between travel plans...visitors have left.....I've performed my ablutions, in preparation for my reading.....
So far I have only read the opening line
"It was a dark and stormy night..."
Didn't you steal that from Bulwer-Lytton? <hr /></blockquote>

<font color="blue">You inadvertently opened the wrong book. The Truth starts, "he needed Killin' but I never had kilt a Democrat before, at least an admitted one but, of course, it was a dark and stormy night!" /ccboard/images/graemlins/grin.gif </font color>

Deeman3
06-08-2007, 12:28 PM
Dave,

I agree with you that knowledge is a good thing and does contribute to a perceptive person's play, especially knowing the functional limitations of a shot or reaction of balls, cushion and sticky substances. I see many players shooting shots that are absolutely impossible and their lack of knowledge hurts them. I also agree technical knowledge, to some degree, can add confidence to a person learning the game as well. As long as too much misunderstanding or overestimation of it's ability to improve your overall play is not assigned to it, I see little harm.

Just last night I was working with DeeWoman on the 31.425 degree rule when "peace" broke out. /ccboard/images/graemlins/smirk.gif

dr_dave
06-08-2007, 01:25 PM
<blockquote><font class="small">Quote Deeman3:</font><hr>I agree with you that knowledge is a good thing and does contribute to a perceptive person's play, especially knowing the functional limitations of a shot or reaction of balls, cushion and sticky substances. I see many players shooting shots that are absolutely impossible and their lack of knowledge hurts them. I also agree technical knowledge, to some degree, can add confidence to a person learning the game as well. As long as too much misunderstanding or overestimation of it's ability to improve your overall play is not assigned to it, I see little harm.<hr /></blockquote>Thanks for the reply. Nice summary. I agree.

<blockquote><font class="small">Quote Deeman3:</font><hr>Just last night I was working with DeeWoman on the 31.425 degree rule when "peace" broke out. /ccboard/images/graemlins/smirk.gif <hr /></blockquote>Now I feel honored.

Catch you later,
Dave

wolfdancer
06-08-2007, 01:25 PM
I think Dr. Dave has made a good point there, about understanding the "why" of a shot...and like you note, I often see newer players attempt a shot that just can't be made...the one that comes to mind is the impossible frozen ball bank that they try.
luckily, I don't need to know any physics to play golf...i know instinctively if i hit a ball with hi-low left....it will go under the nearby branches, then over the next tree, before curving towards the dogleg left green.
This "physics" of pool reminded me of some old baseball "physics" ...well, it is baseball season...and my Red sox are on their way to another WS win!!!
In the Sept. 15, 1941 issue of Life Magazine"


http://img.timeinc.net/Life/covers/1941/cv091541.jpg

There was an article "proving" that a thrown baseball does not curve:
HE HEAD GAME
Baseball Seen From the Pitcher's Mound
By Roger Kahn

"THE HELL IT DON'T CURVE"


Ask them hitters about the curve. They'll tell you.
It's Public Enemy Number One.
-CHARLIE DRESSEN


Before considering pitching as history, and pitching as combat and indeed, pitching as life, it makes some sense to review a controversy that has spilled into baseball's modern times. On September 15, 1941 Life magazine, then the most popular weekly in the United States, published a dramatic photo essay which suggested that a baseball could not be made to curve. That year Lefty Gomez, a droll Californian who pitched for the New York Yankees, was fighting back from arm trouble and hooking his way across a season in which he would lead all American League pitchers with a winning percentage of .750. "Damn," Gomez said, as he stuffed a copy of Life into his locker in the catacombs under the grandstands at Yankee Stadium. "Here I am, trying to make a comeback and what do they tell me? My best pitch is an optical illusion."


The old Life, a contentious, sexy, influential, self-important publication, was not above firecracker journalism, printing stories charged with more shock value than substance.* But the curve-ball piece, a copiously illustrated photo essay, appeared to be serious business. Life engaged a renowned photographer named Gjon Mili and hired two pitchers, including the Hall of Fame lefthander Carl Hubbell, who had been a twenty-game winner five times for the New York Giants. Both pitchers threw what were supposed to be breaking balls "under the scrutiny of three high-speed cameras." The magazine published eleven pictures and reported: "Mili's evidence fails to show the existence of a curve, raises once more the possibility that this stand-by of baseball is after all only an illusion." Details of Mili's methodology were left vague, but Life's collective mind brooked no argument with its conclusion: Thrown baseballs always follow a straight path. The hop of Bobby Feller's fast ball did not exist, either, Life added. Feller had won twenty-seven games the year before, mostly with hopping fast balls. Like the curve, Life maintained, Feller's hopping hard stuff was "a batter's optical illusion." Honed to an edge, Life's charge came down to this: Big-league pitching in America was a fraud.

Three months later the Japanese attacked Pearl Harbor.

Gjon Mili went on to other things. He induced Pablo Picasso to stand in a pitch-black room, holding a baton tipped with a light bulb. Mili set the time exposure on his Leica and said, "Draw." The subsequent photographs of Picasso's sketches in light were a wonder.

"But wait a minute, Mr. Mili," I said some years afterward, during an all-night Christmas party at his studio loft. "How do you think it's possible for people with just about the best vision in the world, major-league hitters, to be so consistently fooled by optical illusions? And why do some pitchers have better optical illusions than others?"

Mili shrugged. He was famous. His Christmas parties were famous. He held a wineglass in one hand. A dazzling Eurasian model clutched his arm. Salvador Dali, in cape and mustache, was entering. A Broadway actress, standing on a platform, announced that she was going to strip naked. Baseball must have seemed far away. "Please," Mili said. "Go get yourself a drink. We'll talk about curve balls some other time." We never did. Dali embraced Mili. I failed to catch the Eurasian model's name or eye. The Broadway actress stopped her striptease early when Walter Winchell arrived, talking loudly. She would undress for a wine-dark Soho party, but not for the hundred and fifty newspapers and all the ships and clippers at sea that were Winchell's glaring and prodigious syndicate.

People and publications are sure of one thing when they advance the hypothesis that a curve ball doesn't curve-or that a fast ball doesn't hop, or that a slider doesn't slide, or that an inshoot doesn't shoot in, or that a knuckleball doesn't "knuck." Putting this in Newtonian terms, they know that their action will produce a reaction. (When certain publications need attention, they move toward fireworks journalism. The old Saturday Evening Post, wanting to show special verve, once published an article entitled: "I Hate Dogs." Grrrr. Outrage arrived in a rush of mail sacks burdened with missives defending poodles, Chihuahuas, and wolfhounds and threatening to loose hungry Dobermans on the author.)

After about five decades of intermittent research, I have to conclude that articles in Life and elsewhere that deny the existence of a curve belong to the hoary I-Hate-Dogs genus, which does not mean that they will go away. Look magazine hired a photographer named Frank Bauman in 1953. This time, according to an anonymous Look writer, the pictures indicated that "Yes, a ball does curve, but in a gentle arc. No, a curve ball does not break." Different cameras. Different conclusion.

Within the past decade a scholarly batting coach, Ben Hines, who has worked for the Los Angeles Dodgers and the Houston Astros, undertook baseball studies from a different angle. Working with various ophthalmologists, Hines tried to find out precisely how a batter perceives a pitch. For example, which eye dominates the batter's vision at various points in the flight of the ball. One conclusion Hines reached was that sometimes a pitched ball moves faster than the ability of human eyes to focus. Calling a pitch a blur can be literally correct. This blur, Hines and his attending physicians decided, has the ophthalmological effect of slightly exaggerating the baseball's motion. A hop seems higher. A curve ball, in the baseball phrase, "falls off the table." The vanquished batter then shakes his head and swears, "That last damn pitch musta broke three feet."

Hines' work suggested, no, that last curve didn't really break that much, any more than Babe Ruth could clout home runs "a country mile." But for either exaggeration to have a starting point, movement of the baseball-the hop, the curve, the long home run- first has to be there. As we shall see, scholarly physical studies of the 1990s prove that a hop, a curve, a slider and a "knuck" are as real as the old Life's phenomenal newsstand sales. Put simply, a spinning baseball does veer in flight and sometimes sharply. That is physical fact. In addition, human vision, wondrous and imperfect, exaggerates the movement of the baseball. Voil-! Reality and illusion at the same instant, the stuff of magic, love affairs and curve balls.*

Fun, games and gainful employment have taken me from the very lowest levels of baseball to the very highest and the curve ball, the curve ball that breaks, is a wholly consistent element in that experience. When I was no more than six years old, my father, once a strong-armed college third baseman, threw gentle wwrinkles at me down the long upstairs hallway of the large whitestone house where we lived in Brooklyn. I remember the house on St. Mark's Avenue. I remember my father. I remember the curves. We played catch with a gray rubber ball that cost five cents at Horowitz Candy &amp; Stationery around the corner on Kingston Avenue. Mr. Horowitz's Baby Ruth candy bars sold three for a dime. Our family always lived in corner houses. That way my grandfather could install small black-and-white signs, A. Rockow, DDS, on two streets, possibly increasing his dental practice during the Depression, when more people suffered from toothaches than could afford the drillings and fillings required to eliminate them.

In the long white upstairs hallway, I reached toward the spinning
gray rubber ball. It drifted past my right hand. I said, "Dad, what was that?"

"Let's try again."

He threw three more three-quarter overhand wrinkles. Then he said, "Curve ball."

"How do you throw that?" I said.

He showed me a quick wrist snap; he was rolling his right wrist sharply clockwise at the moment he released the rubber ball over his index finger.

"Let me try." I had seen the glorious windup of Van Lingle Mungo, who kicked phenomenally high and struck out just about one major league batter an inning when he pitched for the Dodgers at Ebbets Field during the 1930s. I kicked back, a ridiculous mini-Mungo in the long-ago white hall, kept my footing and rolled my wrist as I released the gray rubber ball. The ball I thought I was hurling toward my father, my first curve, jumped out of my hand as I snapped my wrist, sailed sideways into the wall on my left with a certain amount of force. It caromed into the wall on the right. Then back to the wall on the left. Boom blap. Boom. Blap. Oh, nuts.

My mother, who had been reading Melville or Whitman on the blue crushed-velvet sofa in the living room, called out what would become a war cry: "No ball playing in the house!"

Deeman3
06-08-2007, 02:07 PM
I believe, about the time the above picture of Lord Mountbatten was taken and decades before he was murdered, I remember a black and white film short perhaps by Nesbit about the curve ball where a pitcher, although probably not Bullet Bob Feller, was set up with three posts that had their edges tangent with each other over a measured distance while the aforementioned hurler stood and threw his best curve balls that would go inside the first pole, clear the outer tangent edge of the middle pole and curve around the last pole. Now, unless some Flat Earth Society Member is still out there claiming that transits and straightedges are an optical illusion, I believe this urban legend has been firmly tucked into bed. I still have several small lumps on my scalp where I misjudged a few optical illusions sailed at me by Alvin Roser back in 1970.....

I believe in God, a curve ball and low pressure created by differential relative speeds on opposite sides of the spinning ball.... so I must be a loon....or recovering democrat....

dr_dave
06-08-2007, 02:24 PM
<blockquote><font class="small">Quote Deeman3:</font><hr>I believe in God, a curve ball and low pressure created by differential relative speeds on opposite sides of the spinning ball.... so I must be a loon....or recovering democrat....<hr /></blockquote>Dee,

Be careful ... somebody might accuse you of being a "techie" (or even worse: a "religious, republican techie"). You wouldn't want that. /ccboard/images/graemlins/tongue.gif

Dave

cushioncrawler
06-08-2007, 05:49 PM
Woolfy -- In golf the dimples are there to get extra distance, without them a golf ball would kum to ground more quickly than a lead wt (reverse Magnus). In baseball i guess that left'hand'spin makes the ball curve to the right. In cricket a bowler shines one side of the ball (the ball haz a single seam) and the ball curves towards the shiney side (ball is bowled with seam vertical and in line with trajectory). But, sometimes, for a very fast ball, the ball might curve to the right, but then after it hits the ground (ie after it loozez speed) it curves the other way (the seam iz vertical throo-out). Anyhow, i doubt that this sort of aerodynamic effect kums into play in any billiards shot or billiards theory, alltho, i myself do uze (have uzed) other sorts of aerodynamic effects to help explain a few age-old billiards puzzles and arguements. The first line of a book -- i have allready got one for my first fiction effort, az follows....
"In the last days of hiz life, Dick Seaman, Olympic Silver medallist, one-time contender for the boxing championship, and former Vice President of the USA, commited suicide." madMac.

wolfdancer
06-08-2007, 08:02 PM
Dee, you're right about the pitcher that proved a ball did curve...there was also another "urban legend" that was proved wrong with hi speed photography...the one about a race horse, not having all four legs off the ground at the same time.
I forgot to add in my original post...that maybe like the amount of curve in a baseball....Dr. Dave's peace sign rule...is an optical illusion....

Deeman3
06-09-2007, 07:54 AM
Yes, If memorex serves me right, the horse/legs off ground at gallop thingy was a series of cameras set up with independent trip wires so it was actually a movie made like those old flip books. I once fanticized about if Bo Derek's legs were off the ground while her breasts were in mid stride in that running scene in "10" but my then wife woke me up.....or maybe it was if her legs were off the ground when...never mind...