PDA

View Full Version : Squirt Measurements



Jal
08-26-2007, 01:11 PM
Dr. Dave has recently posted an article on this here (see entry #2):

http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html

His results back up the oft questioned numbers given by Platinum Billiards and Predator in two areas:

1. Squirt changes very little with shot speed. A possible exception might be at small tip offsets (but unlikely, imo).

2. The reduction in squirt by low squirt cues is significant, say 25-35%, but probably nothing like 50-75%, as some believe.

An interesting side note: his tests indicate that the amount of squirt is not quite a linear function of tip offset.

With regard to point (1), although it may be too early to draw any conclusions, apparently some confuse the combined effects of squirt and swerve with a cue's intrinsic squirt characteristic. To help eliminate this confusion, JoeyA of the AZ Biliiards forum has proposed a new term, "squerve" (although Patrick Johnson of RSB and AZB has used "squirve" prior to this). I think it's a good idea and prefer "squerve", for what it's worth.

Thanks to Dr. Dave and Dave Gross for the time and effort and expense that went into this. For those of us interested in the technical aspects, it really is wonderful that you make these things so available.

Jim

cushioncrawler
08-26-2007, 05:32 PM
Jim -- I still reckon that (pure) squirt dekreecez az qtip hardness inkreecez -- and dekreecez az speed inkreecez.

I will be doing some of my own tests later this year, uzing a qball on a pendulum. But i will be the robot. I know that its very difficult to shoot a consistent "line" at different speedz -- this will be a problem.

One other little problem. To test the effect of qtip softness u would of course havta uze the same cue, ie remoov/change tips, no big deal there. The problem iz that the center of the qtip chalk-mark will indicate a greater offset (for a soft tip) even tho the cue center-line had the same offset. This iz one reezon behind my statement that squirt iz larger for a soft tip.

U could uze the above factoid to predikt that squirt iz greater with greater speed, ie koz the (hard) qtip sqeezez more, and hence the center of the qtip chalk-mark will have a larger offset. But, no, i say that despite this effekt a softish hit will give more squirt. In fact a few little (pendulum) tests that i did in the garage have supported this.

It iz not obvious from Dr Dave'z tests how he accounted for this effekt, it would/could give a graph an incline.

It just occurred to me. When i do (re-do) my pendulum test, i will do some squirt tests for when i hit (try to hit) the qball dead center and dead straight. This will establish "base-lines" for each of the (3) different speedz. Koz, i know that i cue differently at different speedz, its unavoidable -- but thats ok, az long az its repeatable, the base-lines will fix any problem here. I wonder if Dr Dave did a similar calibration for Dave (robot) Gross. I am thinking that one would allso need the same calibration for a real robot too. madMac.

Jal
08-26-2007, 10:33 PM
Hi Mac,

I'll be looking forward to your results if you decide to share them. But I think it will be hard to compete, accuracy-wise, with Dr. Dave's stroke machine and video equipment.

I don't really understand why a soft tip should produce a greater offset?

I think there are two major variables at work as far as squirt and shot speed are concerned. One, which you've pointed out, is contact time and how much endmass is brought into play as a consequence. The other is the added offset from ball rotation. The latter, I believe, is fairly easy to arrive at to a reasonable degree of accuracy since it seems to be relatively independent of the details of the force/time curve. The former, though, is extremely difficult. It may be that contact time is not much affected by speed. For instance, the larger bending of the stick at higher speed may cancel (increase contact time), or more than cancel any "Hertz Law" (reduction in contact time) type of effect?

Jim

cushioncrawler
08-27-2007, 12:21 AM
Jim -- Yes, i think i see what u are saying, and it appearz reezonable.

Re the soft tip sqeezing more (at any one speed), here i am thinking of a tip with a shoulder (either a sharp shoulder or at least only slightly rounded), the shoulder limits the size of the chalkmark in that direction, but the sqeez inkreecez the size of the chalkmark in the other direction, ie measured away from the qball, ie the center of the chalkmark will indicate a wider effektiv offset even tho the cue's centerline woz no different (at first).

Perhaps then the size (a bit) and shape (a lot) affekts the rezults for tip softness, ie a flatish, or nickel, or dime (which iz smaller???) might give different rezults.

And, i am thinking that the cue taper will (might) give different rezults. For instance, with a conical taper the robot will havta shoot down a bit for the qtip to go throo dead level. If the surface iz friktionless then it shoodnt matter, but then again. And, for a conical taper, i am doubly worryd about the need for a "center-hit base-line" sort of calibration (my own natural Vee-Bridge leans to the right).

And, i reckon that every cue haz a natural buck'n'bend. If u (accidentally) buck the buck then this will give different rezults to when u hold the cue to help the buck. This would of course apply doubly to a cue with a bend. In fact, i think that a cue with a big bend might have little squirt or a lot of squirt, depending on how u hold the bend. madMac.

Jal
08-27-2007, 04:36 PM
And I now see what you're saying about the chalk mark being a little misleading because of the truncated edge. For relatively flat tips (eg, quarter radius), the initial point of contact is actually pretty close to the edge of the tip/shaft, if the shaft is 1/2" in diameter, and even more so for a smaller diameter. By the way, a dime radius is 11/32" (8.73 mm), a nickel is 13/32" (10.32 mm), and a quarter 15/32" (11.91 mm).

I wouldn't doubt that you're right about bucking the buck vs going with it, which is a pretty safe statement (on my part) since something should change. /ccboard/images/graemlins/smile.gif But getting a quantitative estimate is another matter. I think what you mean is that the impact time is different, and thus probably endmass?

Jim

cushioncrawler
08-27-2007, 05:05 PM
Jim -- Re "buck". I think that if we put statik axial compression loads on cues then we would find that most cues flexed in one particular direction every time, due to something in the wood, and/or due to being slightly bent to begin with. For squirt tests, a cue might be held (accidentally or intentionally) such that the natural compression-flex (if any) helps (or hurts) the natural squirt-flex.

Me, myself, i have a cue that i modyfyd so that it had a large natural buck (compression flex). I sanded off one side of the shaft (to about 1/3rd depth) for about half the shaft length. Thusly, when i want say skrewback, i hold the "scallop" down -- ie the qtip bucks downwardz, helping the skrew action. The cue iz stiffish one way (across), but flexish the other (up or down). I can get a good skrew action holding the scallop "up" or "down", but "down" definitely givz more skrew. And i think that that direction would allso give less squirt.

Anyhow, it wouldnt hurt to repeat any squirt tests with the cue held at varyus hours of the clock, to see if the natural buck woz a faktor. And, if it woz, then one could do a statik compression test to see if the compression-flex (buck) correlated to the skewed squirt rezults. madMac.

wolfdancer
08-27-2007, 05:48 PM
Mac, what you doing up here, annoying folks?
Get back down to the npr, where we can try to make some sense from this gibberish.....

cushioncrawler
08-27-2007, 06:10 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr>Mac, what you doing up here, annoying folks? Get back down to the npr, where we can try to make some sense from this gibberish.....<hr /></blockquote>I annoy, therefore i am. Right now i am wearing my billiardz (shooting) glasses, with 2 new lenzez, to try to break my eyes-in. The table looks like a rolling plain, and the ballz are like eggz. Left lens iz ok -- but the right iz "too near", it iz meant to be "intermediate" distance, but i think it iz closer to "near", might havta spend $70 to get another new lenz, dunno. I will see how i go in my match in geelong tonite. When i get back i will go looking for non-anti-Global'Warming disbeleeverz. madMac.

wolfdancer
08-27-2007, 06:29 PM
Good luck in your match...it's tough to break in new glasses, esp for old eyes.....
(you won't have to look far when you visit the basement section)

dr_dave
08-28-2007, 09:44 AM
<blockquote><font class="small">Quote Jal:</font><hr>Dr. Dave has recently posted an article on this here (see entry #2):
http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html<hr /></blockquote>Jim,

Thanks for mentioning my article. I've written three articles in the squirt series, and I have four or five more articles planned. Stay tuned. BTW, I have a new URL for my website: billiards.colostate.edu (http://billiards.colostate.edu/). The old URL still works, but the new one is a lot easier to type.

<blockquote><font class="small">Quote Jal:</font><hr>His results back up the oft questioned numbers given by Platinum Billiards and Predator in two areas:

1. Squirt changes very little with shot speed. A possible exception might be at small tip offsets (but unlikely, imo).<hr /></blockquote>As I mention in the article, I also doubt any variation in squirt with speed. I hope to have my cue-testing machine ready soon. The cue will be perfectly horizontal, so the results won't be corrupted by swerve, at any speed.

<blockquote><font class="small">Quote Jal:</font><hr>2. The reduction in squirt by low squirt cues is significant, say 25-35%, but probably nothing like 50-75%, as some believe.<hr /></blockquote>I must admit that, like others, I thought the percentage reduction might be greater; but as you point out, 25% is still significant.

<blockquote><font class="small">Quote Jal:</font><hr>An interesting side note: his tests indicate that the amount of squirt is not quite a linear function of tip offset.<hr /></blockquote>Although, it is very close to linear. This also depends on how you measure tip offset. People who use "tips of English" generally measure offset to the center of the cue stick, and not to the actually contact point on the ball. I use the contact point on the ball. FYI, my July '06 article (http://billiards.colostate.edu/bd_articles/2006/july06.pdf) has some good illustrations of this stuff.

If you plot squirt vs. offset from the data in my article (unfortuantley, only three points of data plus the origin are available), squirt seems to increase a little faster than linearly with tip offset. However, TP A.31 (http://billiards.colostate.edu/technical_proofs/new/TP_A-31.pdf) predicts squirt should increase a little less than linearly with tip offset (see the plot at the bottom of the analysis). Again, I reserve judgment until I can get some good data with my cue test machine.

<blockquote><font class="small">Quote Jal:</font><hr>With regard to point (1), although it may be too early to draw any conclusions, apparently some confuse the combined effects of squirt and swerve with a cue's intrinsic squirt characteristic. To help eliminate this confusion, JoeyA of the AZ Biliiards forum has proposed a new term, "squerve" (although Patrick Johnson of RSB and AZB has used "squirve" prior to this). I think it's a good idea and prefer "squerve", for what it's worth.<hr /></blockquote>Thanks for posting this. I wish I had seen this before I started the series. If I had, I probably would have used "squerve" instead of "effective squirt" (see Diagram 4 in my August '07 article (http://billiards.colostate.edu/bd_articles/2007/aug07.pdf)). Maybe I'll use "squerve" later in the series. I've already added it to my expanded, online glossary (http://billiards.colostate.edu/resources/glossary.pdf).

<blockquote><font class="small">Quote Jal:</font><hr>Thanks to Dr. Dave and Dave Gross for the time and effort and expense that went into this. For those of us interested in the technical aspects, it really is wonderful that you make these things so available.<hr /></blockquote>You're very welcome. Thanks to you also for your frequent contributions and estute observations.

It was a pleasure working with Dave Gross, who is a top regional player. I was very impressed by his desire to better understand the physics of the game.

Regards,
Dave

dr_dave
08-28-2007, 10:12 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I still reckon that (pure) squirt dekreecez az qtip hardness inkreecez<hr /></blockquote>I agree with you here; although, I haven't tested this theory yet. But it makes sense. There is data to suggest that a softer tip stays in contact with the cue ball a little longer (see previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=201666&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1)). This would cause the cue stick to deflect sideways more during contact, as the ball rotates (see Diagram 2 in my August '07 article (http://billiards.colostate.edu/bd_articles/2007/aug07.pdf)), resulting in greater sideways forces (see TP A.31 (http://billiards.colostate.edu/technical_proofs/new/TP_A-31.pdf)).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>and dekreecez az speed inkreecez.<hr /></blockquote>So far, my data does not support this claim.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>I will be doing some of my own tests later this year, uzing a qball on a pendulum. But i will be the robot. I know that its very difficult to shoot a consistent "line" at different speedz -- this will be a problem.<hr /></blockquote>Do you know Rod Cross? He's at Sydney University. He's also been doing a lot of squirt experiments recently, using a ball on a string. You should look him up.

Please share your results after your experiments.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>One other little problem. To test the effect of qtip softness u would of course havta uze the same cue, ie remoov/change tips, no big deal there. The problem iz that the center of the qtip chalk-mark will indicate a greater offset (for a soft tip) even tho the cue center-line had the same offset. This iz one reezon behind my statement that squirt iz larger for a soft tip.<hr /></blockquote>Again, I think the main effect here is contact time, but I'm not sure. HSV A.76a (http://billiards.colostate.edu/high_speed_videos/new/HSVA-76a.htm) is about the best view I've seen of what the tip does during impact. I've probably watched this clip a hundred times, and it still seems to provide more insight every time I see it.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>U could uze the above factoid to predikt that squirt iz greater with greater speed, ie koz the (hard) qtip sqeezez more, and hence the center of the qtip chalk-mark will have a larger offset. But, no, i say that despite this effekt a softish hit will give more squirt. In fact a few little (pendulum) tests that i did in the garage have supported this.

It iz not obvious from Dr Dave'z tests how he accounted for this effekt, it would/could give a graph an incline.<hr /></blockquote>My tip-offset numbers are based on chalk mark measurements. Unfortunately, I have not done tests with various hardness tips on the same cue yet. Again, I think the main issue here is contact time, but this might be difficult to separate out from the deformation issue.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>It just occurred to me. When i do (re-do) my pendulum test, i will do some squirt tests for when i hit (try to hit) the qball dead center and dead straight. This will establish "base-lines" for each of the (3) different speedz. Koz, i know that i cue differently at different speedz, its unavoidable -- but thats ok, az long az its repeatable, the base-lines will fix any problem here. I wonder if Dr Dave did a similar calibration for Dave (robot) Gross. I am thinking that one would allso need the same calibration for a real robot too. madMac.<hr /></blockquote>Good idea. I did do this with Dave Gross. His stroke is extremely repeatable and accurate. I will also be careful to do this with my cue-testing machine.

Regards,
Dave

dr_dave
08-28-2007, 10:26 AM
<blockquote><font class="small">Quote Jal:</font><hr>I think there are two major variables at work as far as squirt and shot speed are concerned. One, which you've pointed out, is contact time and how much endmass is brought into play as a consequence. The other is the added offset from ball rotation. The latter, I believe, is fairly easy to arrive at to a reasonable degree of accuracy since it seems to be relatively independent of the details of the force/time curve. The former, though, is extremely difficult. It may be that contact time is not much affected by speed.<hr /></blockquote>Good summary, Jim. It is interesting that a longer contact time increases squirt due to both effects. More endmass comes into to play, and the end moves more due to ball rotation.

Concerning how contact time varies with shot speed. I did some tests recently that seemed to imply that the contact time does not vary significantly (if at all) with shot speed (for the tips and cues I tested anyway).

Regards,
Dave

wolfdancer
08-28-2007, 12:01 PM
....just when I thought it was safe to "test the waters" up here again....now I know that while I knew,I didn't know everything...it turns out there's more that I didn't know, I didn't know...
I got me a headache...and will have to go to the local pharmacy ...Joe's bar, for some much needed medications.

dr_dave
08-28-2007, 02:13 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> ....just when I thought it was safe to "test the waters" up here again....now I know that while I knew,I didn't know everything...it turns out there's more that I didn't know, I didn't know...
I got me a headache...and will have to go to the local pharmacy ...Joe's bar, for some much needed medications. <hr /></blockquote>There are side benefits to self medication. For example, it becomes more fun to use words like "squerve."

Cheers,
Dave

Jal
08-28-2007, 03:59 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- Re "buck". I think that if we put statik axial compression loads on cues then we would find that most cues flexed in one particular direction every time, due to something in the wood, and/or due to being slightly bent to begin with. For squirt tests, a cue might be held (accidentally or intentionally) such that the natural compression-flex (if any) helps (or hurts) the natural squirt-flex.<hr /></blockquote>Mac, I had contact time on the brain since it's a crucial variable in what I'm working on now (the same thing we discussed via e-mail...yes, still working on it, which is why I haven't given the material you sent proper attention yet). But I think you're mainly refering to stiffness.

Mike Page, a professor and poster on AZB, has repeatedly asserted that stiffness has little or nothing to do with squirt. Patrick Johnson has also done tests (good ones it appears), that support this. On the face of it though, stiffness should be involved in the amount of mass that gets "coupled in" to the endmass. Whether the difference is significant amongst variations in normal cues, from whippy to stiff, is something else. And, a more flexible cue may increase contact time enough to essentially offset any of this potential reduced coupling.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Me, myself, i have a cue that i modyfyd so that it had a large natural buck (compression flex). I sanded off one side of the shaft (to about 1/3rd depth) for about half the shaft length. Thusly, when i want say skrewback, i hold the "scallop" down -- ie the qtip bucks downwardz, helping the skrew action. The cue iz stiffish one way (across), but flexish the other (up or down). I can get a good skrew action holding the scallop "up" or "down", but "down" definitely givz more skrew. And i think that that direction would allso give less squirt.<hr /></blockquote>Interesting. Others report differences based on orientation (normal cues), and that's the reason I think for the laminations of the Predator shaft: to increase consistency. So, what to make of it all?

I would have thought though that more squirt might help with screw, so as to help reduce that first bounce where I think more spin gets rubbed off than if the cueball slides uniformly on the surface. Apparently, you've found this isn't so.

Jim

SKennedy
08-28-2007, 04:11 PM
Hey Woldancer...I'm with you...lets' go back to arguing about global warming and solving world problems. It's much easier to deal with. I don't even have to think this hard to argue with Gayle. While I think it's nice to understand the physics behind something to help explain why things happen or why we need to do certain things, my personal philosophy is K.I.S.S. - Keep It Simple Stupid. Works for me... must make me stupid (thought I would add that part before someone else did).

dr_dave
08-28-2007, 04:29 PM
I agree that a detailed understanding of underlying physics isn't for everybody. However, I think a basic understanding of the fundamentals of squirt, swerve, and throw (and how they vary with the type of shot and with conditions) can help a lot of people. Often, misconceptions and misunderstandings can result in missed shots or missed opportunities.

Dave

<blockquote><font class="small">Quote SKennedy:</font><hr> Hey Woldancer...I'm with you...lets' go back to arguing about global warming and solving world problems. It's much easier to deal with. I don't even have to think this hard to argue with Gayle. While I think it's nice to understand the physics behind something to help explain why things happen or why we need to do certain things, my personal philosophy is K.I.S.S. - Keep It Simple Stupid. Works for me... must make me stupid (thought I would add that part before someone else did). <hr /></blockquote>

Jal
08-28-2007, 04:40 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>I think there are two major variables at work as far as squirt and shot speed are concerned. One, which you've pointed out, is contact time and how much endmass is brought into play as a consequence. The other is the added offset from ball rotation. The latter, I believe, is fairly easy to arrive at to a reasonable degree of accuracy since it seems to be relatively independent of the details of the force/time curve. The former, though, is extremely difficult. It may be that contact time is not much affected by speed.<hr /></blockquote>Good summary, Jim. It is interesting that a longer contact time increases squirt due to both effects. More endmass comes into to play, and the end moves more due to ball rotation.

Concerning how contact time varies with shot speed. I did some tests recently that seemed to imply that the contact time does not vary significantly (if at all) with shot speed (for the tips and cues I tested anyway).

Regards,
Dave <hr /></blockquote>Thanks for the kind remarks Dr. Dave, and again for sharing your work.

I spoke a little loosely. What I meant to say was that given some rotation of the ball during impact, it appears, looking at different force-time curves, that the percentage of this that goes into increasing the effective offset ranges over only a small set of values. But I'm still looking at different curves.

It depends a little bit on amount of skewing of the curve (departure from a symmetrical form), and a little on the symmetric form itself. I have stated previously that the curve gets severely skewed at large tip offsets, but I ignored the differential distance the stick moves forward compared to the cueball. This is important and tends to "de-skew" it. But even with very unsymmetric curves, the percentages mentioned above don't appear to change much. Obviously, you could give this a more sophisticated treatment should you ever turn your attention to it.

You mentioned the contact time as a function (non-funtion actually) of speed. If now or in the future you would like share how you arrived at this, tentatively of course, you'll certainly have my attention.

Sorry, but I haven't given your technical article on squirt a good read yet.

Jim

cushioncrawler
08-28-2007, 06:12 PM
Hi Dr Dave.
Calibration...... Hitting a ball dead center and dead straight iz of course very difficult. Few players would have equalled my hours at a (12') table trying (experimenting etc) to hit the ball straight up and back, at all speedz. I found (lately) that i uzually have a consistent error, hitting the top cushion say 1/4 ball off-line (right). And, i uzually have an inconsistent error, often hitting up to a 1/4 ball left or right of that 1/4-ball-right point. And, i wont even mention the bad dayz.

Grain...... Uzually i will test my stroke by making sure that i hold the arrows up, or down. The arrows are the markings on the cue shaft due to the grain of the ash (all of my cues are ash nowadayz). Uzually, the arrows on one side point away from u, and on the other they point towardz u. Az we all know, an ash cue is stiffer parallel to the plane of the grain. Hencely, my cue will tend to buck up or down rather than left or right. Left or right would both affekt my (straight) stroke -- up or down are ok.

Warp....... Allso, ash cues will uzually warp (with age) at 90dg to the plane of the grain, so, holding the arrows up or down uzually minimizes both problems (ie nonintentional squirt due to grain and warp), but we need to check the warp properly (occasionally it iz in-plane).

Chalk...... I find that the amount of chalk affekts my straight hitting. Hit up and down without chalking, and, in a short time, the ball will have a mind of its own. So, one hazta chalk up consistently, and, best to uze very little chalk.

Left Side...... Getting away from center hitting, i have no trouble putting on lots of left side (english) on the qball, i find it eezy, natural, too natural. But right-hand-side iz diffikult for me, i can never get az much. I wonder if David (robot) Gross uzes the same cue action for center-ball hits and for left english and right english. Only one player that i have ever checked (i havnt checked many) stroked dead straight for every hit, ie whether uzing skrew or left english or ????, and that woz Peter Gilchrist. I think that most players have a natural hoik. For instance, what would the squirt test rezults look like if David uzed rhs (i assume that David uzed lhs for all the tests).

Rod Cross....... I will havta catch up with hiz work -- i wonder how he stops hiz qball (pendulum) from spinning (damned cotton). For sure i will get back here with my own rezults. Looking foreward to more of this stuff. madMac.

cushioncrawler
08-28-2007, 06:41 PM
Hi Jim.
Stiffness...... I feel sure that a stiff cue squirts more. I know that last night in geelong i uzed my stiff cue all nite. I remember one short-range run-throo-jenny (an in-off with pocket-side) where i had to aim towards the scoreboard to get the dezired contact on the objektball. In fact, nowadayz, i am happy to uze back-hand pivot when uzing my stiff cue, and front-hand pivot when uzing my flexy cue. Here i can thank Colin Colenso's articles -- where iz Colin -- i thort that i would be playing against him last week, but they said that he iz too bizzy with hiz new bizness. Anyhow, i take Mike Page's point, that to properly compare a stiffy and a flexy u would havta uze cues with the same tip-wt, my stiff cue iz of course very tip-heavy. But, i have an old hollow steel cue, very very stiff, it weighs 15-1/2oz, ie very very light, and (i think) very tip-light, and the squirt iz terrible. In addition, u karnt get much spin or skrew, just too stiff, stiffest cue i have ever held by far.

Laminations...... I like the idea of being able to hold the cue any old how, without worrying about grain etc, the qtip would last longer for starters.

Skrew...... I think that a flexy cue would be better for short-range or for "soft skrew", and medium stiff best for long-range miracles. Stiff cues would be best if u want consistency, but no good for records.

Bounce....... I find that initial bounce, and any other bounce allso, helps acheev miracle skrew. With a flexy cue the qball often duznt leev the table, but glides along very smoothly, and slows down and loozez backspin az if it haz disc brakes.

Patrick seems to have hiz head skrewed on ok nowadayz, good thing hiz spaceship iz broken down. madMac.

cushioncrawler
08-28-2007, 07:04 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> ....just when I thought it was safe to "test the waters" up here again....now I know that while I knew, I didn't know everything... it turns out there's more that I didn't know, I didn't know... I got me a headache... and will have to go to the local pharmacy ... Joe's bar, for some much needed medications.<hr /></blockquote>Woolfy -- Only a square would be squeamish about a squabble about squerve, stop your squealing. madMac.

dr_dave
08-29-2007, 09:07 AM
<blockquote><font class="small">Quote Jal:</font><hr>You mentioned the contact time as a function (non-funtion actually) of speed. If now or in the future you would like share how you arrived at this, tentatively of course, you'll certainly have my attention.<hr /></blockquote>Actually, I think I spoke a little loosely here. I have not studied this very carefully. I have shot several high-speed video sequences (HSV A.77-A.81 and A.147-A.151 (http://billiards.colostate.edu/high_speed_videos/index.html)) to help quantify this, but I'm not so confident with the results. My camera is really not fast enough, or high-resolution enough to get great data on this topic. The shadows and chalk cloud force one to "interpret" what one is seeing in the clips. After further study of the clips, it appears that contact time is a little longer at slower speeds, but I can't be sure. What I am sure of at this point is that it appears that squirt does not change significantly with speed. Now, if the contact time is longer for a softer shot, one might think the effective mass and squirt would be correspondingly larger. Maybe some of the other factors you and Mac have discussed might come into play here. But again, I think it is all conjecture until we get video with a faster and better camera.

Regards,
Dave

dr_dave
08-29-2007, 09:13 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Rod Cross....... I will havta catch up with hiz work -- i wonder how he stops hiz qball (pendulum) from spinning (damned cotton). For sure i will get back here with my own rezults. Looking foreward to more of this stuff.<hr /></blockquote>Here's a link to Rod Cross' website (http://www.physics.usyd.edu.au/~cross/Collisions.htm). For a while, he has thought that the tip slips on the cue ball during contact, but he has recently come around to believe that there is practically no slip whatsoever (except for a miscue). TP A.31 (http://billiards.colostate.edu/technical_proofs/new/TP_A-31.pdf), experimental data, and video evidence seem to support the no-slip assumption fairly well.

Regards,
Dave