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dr_dave
01-07-2008, 05:27 PM
In response to debate and discussion in several threads, I decided to post some videos relating to the effect sidespin has on the path of a ball. To be clear, I am referring to sidespin only, not masse spin. CB swerve is well understood. Also, a slight amount of "OB swerve" is possible with masse spin transferred to the OB from follow or draw on the CB (see the end of TP A.24 (http://billiards.colostate.edu/technical_proofs/new/TP_A-24.pdf)). Here, I am just looking at the effect of pure sidespin as a ball is rolling. I call this effect "OB turn."

Here are the videos:

NV B.7 - Ball "turn" caused by sidespin (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm)

NV B.8 - Straight throw of a second object ball (http://billiards.colostate.edu/normal_videos/new/NVB-8.htm)

Check them out and let me know if your experiences and/or explanations are different.

Regards,
Dave

Ralph_Kramden
01-07-2008, 06:35 PM
Dr. Dave - Clicking on NV B.8 shows a decent drawshot with no elbow drop.
Just FYI it links to video NV B.9 instead of the intended video.

dr_dave
01-07-2008, 08:21 PM
<blockquote><font class="small">Quote Ralph_Kramden:</font><hr> Dr. Dave - Clicking on NV B.8 shows a decent drawshot with no elbow drop.
Just FYI it links to video NV B.9 instead of the intended video.<hr /></blockquote>Thank you for pointing this out. The link is fixed now. Here it is for convenience:

NV B.8 - Straight throw of a second object ball (http://billiards.colostate.edu/normal_videos/new/NVB-8.htm)

Enjoy,
Dave

cushioncrawler
01-08-2008, 05:24 AM
Dr Dave -- I think that the sidespin videos showed a hint of reverse kurv for some of the qballz (slow speeds here) and sometimes lots of reverse kurv for the handball (very slow speeds here) but sometimes non-reverse kurv. I am certain that a slowing ball (with lots of spin) shood have a bit of reverse kurv, and a lot of reverse kurv just before stopping (but still spinning).

This woz the effekt(s) seen on 12' tables when (cotton napless) Janus Cloth woz uzed -- production stopped during WW2. Unfortunately, the stupid looking nappy woollen cloths are now used for all billiards and snooker. In fakt, Walter Lindrum made hiz record 4137 on Janus -- a little known fakt.

About 3 years ago i played a match (English billiardz) on a completely worn out (napless) woollen cloth. Actually, once u got used to it, it woz ok. But, one guy played a short-jenny, and, the ball went "the other way" (ie it had reverse kurv). He couldnt beleev it. Twernt a surprize to me.

I think that the same sort of kurv(s) might one day be seen for an OB, albeit very little compared to a spinning slow handball. madMac.

Bambu
01-09-2008, 01:22 AM
Very interesting, Dave. Thanks for taking the time to shoot both of those videos. I enjoyed both of them, yet I am still only feeling half satisfied so far. Starting with the “ball turn caused by sidespin” video, I like the way you explained the reason for the slight curve, and I agree with that. You hit on the key point, which was that at very slow speeds, the ball may curve slightly. And I agree, its hard to reproduce the curve effect with just sidespin alone. Also, at the very end of the shot (or any shot), I also agree that the table takes over the roll of the ball. Overall, very well done, no complaints, point well taken. Sidespin can cause a small amount of curve, depending on the shot. My friend on the other hand, got a different impression. He seems to think you are chalking the curve up to table roll and dirt alone. We would also like to know the table size and the cloth you have.
One thing you said in the first video which seemed a tad unfair though, as well as unexpected....was the way you hit the ball with English and said how english itself has very little effect on the path of the cueball. I do see you say you are first adjusting for squirt and English by hitting high on the cueball. But does that mean you are trying to make the ball go straight despite the English? Or do you mean to say that when you aim with English, you aim the same way you would with no English because the ball is going to go straight anyway? Or is it that you think the ball will go straight, but the squirt makes you adjust your straight line of aim slightly? I mean, there are many adjustments required for aiming with English. I can’t see how you would say that a ball hit with English travels straight. Don’t you need to factor in cue speed, amount of English, and cue angle when saying balls hit with English go straight?
I see the squirt of the left English at 0:47 causing a hit of the straight edge, just before the ball hits the rail. You can even hear the sound of the ball clipping the wood. The very next shot at 0:53 shows the opposite effect, as the English carries the ball slightly away from the straight edge. Also at 1:17 in the video using right English, I can see the ball curving away from the straight edge slightly.
I also notice that at times you use words like “relatively” and “very little” when referring to curve on a ball hit with English. Other times you use the word perfectly to describe the straightness. I really don’t mean to nitpick, but it cant be both, especially when its only a slight curve were looking for to begin with. Other than the English issue though, I am happy with the sidespin explanation. Thanks very much, Dave.
As for the second video, straight throw of a second object ball, I get different results. Once again, this video begins with the term “very close to a straight line path” when referring to the thrown ball. No disrespect I assure you, but in my opinion that’s an unfair statement. A path can’t be straight and close to straight at the same time. Another thing that comes to mind is that while you do acknowledge that spin transfer at slow speeds can cause curve in the first video, the second video should be no different. They are both spinning balls that have received spin transfer, so why should they react any differently? If anything, the reaction in the second video should curve more because it has the added benefit of the extra friction from the kissing ball. This should increase the throw effect.
Aside from that, there are some very important differences in the way you did your test as compared to mine. Firstly, I question the angle of the object ball in relation to the pocket. This is in the very beginning, at 0:20 or so. You indicate where the object ball is destined for on the short rail, but that angle looks slightly off. It could be just the video, or even my player, but a better view of the angle toward the bottom rail would have been nice. You say its 3/4ths to the diamond, but it looks like a bit less as compared to the angle of your cue as you reference the spot on the rail. Though it may not be practical, I still think snapping a chalk line to show the line of centers, as well as the path to the pocket would be more accurate. Perhaps some sewing thread would work as well.
My next disagreement regards the width of the channel you allowed. There is no specification on that measurement in the video, but it is very important to honor that number for this test to work fairly. My tests show that any bigger than 3 inches allows too much room for the ball to move off of its original path, and still curve back towards the pocket. Three inches seems to be my limit in pocketing the ball without hitting any cues. Even a quarter inch less is a no go, for me and 2 others. I can’t say for sure, but the gap looks like a bit more than 3 inches in the video. It’s nothing personal, I don’t doubt your integrity, Dave. It’s just that unless it’s specified, it’s hard to tell 3 inches from 3 and a half in a video.
The last bone I have to pick about the way this test was run, is the distance used. My shot called for using the rack spot as the place to set up the balls, while you appear to have moved the shot somewhat closer, perhaps 2 diamonds worth from the looks of it. Maybe your table is an 8 footer? If so, whats the diamond distance on on an 8? This shot calls for about 77 inches from the head spot to the pocket. In my opinion, distance is directly responsible for why it’s so hard to make a 9 foot straight line, as opposed to creating a 1 foot straight path. Less distance means less curve to me, so I would have to insist on the balls being frozen on the head spot, or at least the full 77 inches.
The last lag of the object ball, the point where the ball gets beyond the cues...appears to be the point where the ball rolls slow enough to be “taken by the table(table roll).” Depending on speed, I see the curve or slight change in angle towards the pocket, occurring somewhere around the midpoint of the 2 cues(if the shot was set up right).
How about testing to see how narrow you can make the gap, while still making the ball? A test like that would really tell a lot. Testing at different speeds and using different spins would also help. Another good test would be to check the original shot for table roll. Set up another similar frozen ball shot, but facing the opposite way in relation to the same pocket. So, the new “check” shot would be aimed a few inches up the long rail. Doing the opposite of what was just done would show that if the original results were due to table roll, the ball should roll the same way for both shots.
As far as I am concerned, there is a reason average pockets are twice the size of the balls, to allow for the slight curve of throw. Pool is much harder than just hitting where the right contact points are, or identifying where the supposed straight path to a pocket is. This is also part of the reason why long shots are so much harder than short ones.
Thanks again, Dr. Dave. I know you spent a lot of time on this. But no matter the result, I don’t think this topic has been a waste of time. I certainly find all this very interesting. I hope I am not asking too much by requesting a re-test with a few adjustments? If not, I understand you have done your part. Either way, you have inspired me to make a video of my own. I hope to have that ready very soon.

Bambu
01-10-2008, 08:54 AM
Dunno what a short jenny is, but I am with you mac. A spinning ball with left or right spin, combined with a forward roll....can curve if it has time to grab the cloth as it slows down.

dr_dave
01-10-2008, 11:56 AM
<blockquote><font class="small">Quote Bambu:</font><hr> Very interesting, Dave. Thanks for taking the time to shoot both of those videos. I enjoyed both of them, yet I am still only feeling half satisfied so far. Starting with the “ball turn caused by sidespin” video, I like the way you explained the reason for the slight curve, and I agree with that. You hit on the key point, which was that at very slow speeds, the ball may curve slightly.<hr /></blockquote>... but not predicatably or consistently.

<blockquote><font class="small">Quote Bambu:</font><hr>And I agree, its hard to reproduce the curve effect with just sidespin alone. Also, at the very end of the shot (or any shot), I also agree that the table takes over the roll of the ball. Overall, very well done, no complaints, point well taken. Sidespin can cause a small amount of curve, depending on the shot.<hr /></blockquote> Agreed, but again this is not an effect I think can be used to one's benefit in pool game situations. I think there would always be better (less risky and easier) alternatives than trying to rely on "ball turn."

<blockquote><font class="small">Quote Bambu:</font><hr>My friend on the other hand, got a different impression. He seems to think you are chalking the curve up to table roll and dirt alone.<hr /></blockquote>Table roll, dirt, and cloth imperfections can certainly be more significant than the "ball turn" effect. I was not able to consistently demonstrate "ball turn" because it is such a tiny effect, and it only takes a tiny disturbance to change the direction of a rolling ball (especially at slow speed). I think both you and your friend are correct. "OB turn" does exist, but "OB turn" is probably not an important effect (IMO).

<blockquote><font class="small">Quote Bambu:</font><hr>We would also like to know the table size and the cloth you have.<hr /></blockquote>I have an 8' Conneley with the original cloth. I don't know the brand, but I think it has average speed and slickness. It's certainly not as fast or slick as Simonis.

... to be continued

Regards,
Dave

dr_dave
01-10-2008, 12:27 PM
<blockquote><font class="small">Quote Bambu:</font><hr>One thing you said in the first video which seemed a tad unfair though, as well as unexpected....was the way you hit the ball with English and said how english itself has very little effect on the path of the cueball.<hr /></blockquote>The main point I am making here is I am not considering "ball swerve" due to masse spin. With all of the examples in the video, I was careful to apply as little masse spin as possible. Also, due to the low speed of the shots, any "ball swerve" would occur within the first few inches of slide anyway. Once the ball is rolling, only "ball turn" (due to sidespin) can alter the path of the ball (in addition to table roll, dirt, and cloth imperfections).

... to be continued

Regards,
Dave

dr_dave
01-10-2008, 01:36 PM
<blockquote><font class="small">Quote Bambu:</font><hr>I do see you say you are first adjusting for squirt and English by hitting high on the cueball. But does that mean you are trying to make the ball go straight despite the English?<hr /></blockquote>When one uses English, one must adjust for squirt, swerve, and throw (either consciously or intuitively). Diagram 3 (and the supporting explanation) in my August '07 article (http://billiards.colostate.edu/bd_articles/2007/aug07.pdf) does a pretty good job summarizing the effects. Squirt occurs only while the cue tip is in contact with the CB. When the CB leaves the tip, it tries to head in a straight line. If the CB has any masse spin (e.g., caused by any cue elevation), the CB will curve only during the sliding phase of the motion (e.g., the first couple of inches for a slow shot). Once sliding ceases and rolling begins, the CB heads in a straight line (for all practical purposes). This is the motion I am illustrating in the video. To have the CB head straight down the tape measure, I did need to adjust my aim slightly for squirt (and a very small amount of swerve).

<blockquote><font class="small">Quote Bambu:</font><hr>Or do you mean to say that when you aim with English, you aim the same way you would with no English because the ball is going to go straight anyway?<hr /></blockquote>No. I do aim differently, but the CB still goes straight after it begins to roll (which happens very early in the shots in the video).

<blockquote><font class="small">Quote Bambu:</font><hr>Or is it that you think the ball will go straight, but the squirt makes you adjust your straight line of aim slightly?<hr /></blockquote>These and many more related questions are answered and illustrated in my recent series of articles on squirt (http://billiards.colostate.edu/bd_articles/index.html). Please check them out.

<blockquote><font class="small">Quote Bambu:</font><hr>I mean, there are many adjustments required for aiming with English.<hr /></blockquote>Agreed. That's why I have written so many articles on these topics.

<blockquote><font class="small">Quote Bambu:</font><hr>I can’t see how you would say that a ball hit with English travels straight.<hr /></blockquote>Again, in the video, the CB squirts a little in one direction off the cue tip and it swerves back a little (due to slight cue elevation) during the first few inches of sliding, but then the CB is rolling with sidespin and travels straight. Again, my articles cover all of this in great detail. Please check them out.

<blockquote><font class="small">Quote Bambu:</font><hr>Don’t you need to factor in cue speed, amount of English, and cue angle when saying balls hit with English go straight?<hr /></blockquote>Absolutely. These are the topics of several of my articles.

... to be continued

Regards,
Dave

dr_dave
01-10-2008, 01:51 PM
<blockquote><font class="small">Quote Bambu:</font><hr>I see the squirt of the left English at 0:47 causing a hit of the straight edge, just before the ball hits the rail. You can even hear the sound of the ball clipping the wood. The very next shot at 0:53 shows the opposite effect, as the English carries the ball slightly away from the straight edge.<hr /></blockquote>That's because my aim (and aim compensation) and stroke was not perfect on every shot. I'm sorry I wasn't better at this.

<blockquote><font class="small">Quote Bambu:</font><hr>Also at 1:17 in the video using right English, I can see the ball curving away from the straight edge slightly.<hr /></blockquote>The ball is not curving ... it is heading in a straight line at a slight angle (i.e., my squirt/swerve aim compensation was not perfect).

<blockquote><font class="small">Quote Bambu:</font><hr>I also notice that at times you use words like “relatively” and “very little” when referring to curve on a ball hit with English.<hr /></blockquote>When there appeared to be a slight curve, I used these terms.
<blockquote><font class="small">Quote Bambu:</font><hr>Other times you use the word perfectly to describe the straightness.<hr /></blockquote>I said this only when the ball appeared to go in a straight line, with no perceptible curve. I should probably never use a word like "perfectly," because nothing is ever perfect in the real world.

<blockquote><font class="small">Quote Bambu:</font><hr>I really don’t mean to nitpick, but it cant be both<hr /></blockquote>You are right. The ball often went straight, but sometimes there was a slight curve. There is a theoretical "tendency" for the ball to curve slightly one way, but sometimes it curves the other way slightly (with the same speed and spin). Again, the effect is too tiny to be used practically in game situations.

Regards,
Dave

Bambu
01-10-2008, 02:55 PM
Thanks for clearing that up for us, Dave. I am glad that we can agree that it exists. I said "at very slow speeds, the ball may curve slightly(and you added)but not predicatably or consistently." And I agree with what you amended my statement with. Indeed, it is hard to control or use to your advantage.
This also makes me wonder about the actual number I have heard regarding this effect. That being .07 or 1/10th of a degree, 1/thousandth of an inch, or a quarter inch per 9 feet. While the actual difference may not matter, I think its only an estimate of what can occur, not the maximum possible effect. I also think that the results of that test which arrived at .07 (or any remotely close number)would vary somewhat from player to player. So if the average change is say a .07 degree change per 9 feet, some players may acheive more than .07, while others less or even none.
I also think that there is a reason it is so hard to predict or control this effect, nobody practices it. Most people dont even think it exists. The way I see it, at slow speeds you are at the mercy of the table to begin with. The right spin may help the shot, it may not. Sometimes you have no safety available, no better alternatives, so why not carry an extra tool in your bag? Sometimes you can try to take advantage of the spin, and play a safety at the same time.
I sort of look at it like a jump shot. Unless you practice it, and learn how to execute, its almost impossible. There are also often better alternatives to a jump shot, yet its a shot. I'm not saying this is "the new jump shot" by any stretch, just something that pops up once in a blue moon. But, something to try is better than nothing. You cant practice table roll, but you can develop cue speed to get more consistent spin transfer. People can either ignore this information and the correct spin which certain shots seem to want, and have guesswork and table roll determine their fate. Or, they can try something probably never before considered, attempted or practiced. Something very hard to do, but something real. And though a very small effect, it is as controllable as any particular player/table combination can make it.
However, I still respect your opinion that this small amount of curve is impractical. And in a general sense I agree. For most players....it is insignificant, uncontrollable, unpredictable. Once again many thanks for everything, Dave.

Bambu
01-10-2008, 02:59 PM
Sorry I wasnt clear on that, Dave. Yes, now I understand, thanks.

Bambu
01-10-2008, 03:59 PM
I really did read all of your articles, Dave. And I am sorry I was not clear on the explanation in the video. I really dont mean to make you repeat your explanations. We are in agreement on this. Sorry that took so long.

Bambu
01-10-2008, 04:26 PM
I dont mean to question your understanding of english. It just seemed weird when you said english and straight in the same breath. But I understand what you mean, balancing squirt and swerve perfectly is tough to do.
As far as your explanation, I agree. I like the way you said "There is a theoretical "tendency" for the ball to curve slightly one way, but sometimes it curves the other way slightly (with the same speed and spin).
The more I think about this, the more I am starting to think that certain tables will show this effect more than others. Perhaps the roll on a simonis cloth is a bit more true, and not at the mercy of the table quite as much as say, regular cloth would be. On a regular cloth, all bets are pretty much off at slow speeds, because the table just takes over the shot. That would explain why I see a bit more curve at slow speeds than you seem to, and have a bit easier time in reproducing it.

dr_dave
01-10-2008, 05:26 PM
<blockquote><font class="small">Quote Bambu:</font><hr>... For most players....it is insignificant, uncontrollable, unpredictable.<hr /></blockquote>On my table, I think "ball turn" is insignificant, uncontrollable, and unpredictable for all players.

<blockquote><font class="small">Quote Bambu:</font><hr>Once again many thanks for everything, Dave. <hr /></blockquote>You're welcome.

Regards,
Dave

dr_dave
01-10-2008, 05:33 PM
<blockquote><font class="small">Quote Bambu:</font><hr> I really did read all of your articles, Dave. And I am sorry I was not clear on the explanation in the video. I really dont mean to make you repeat your explanations. We are in agreement on this. Sorry that took so long.<hr /></blockquote>I'm sorry if I seemed a little frustrated or impatient. I'm glad it seems clear to you now.

Regards,
Dave

dr_dave
01-10-2008, 05:38 PM
<blockquote><font class="small">Quote Bambu:</font><hr> I dont mean to question your understanding of english. It just seemed weird when you said english and straight in the same breath. But I understand what you mean, balancing squirt and swerve perfectly is tough to do.
As far as your explanation, I agree. I like the way you said "There is a theoretical "tendency" for the ball to curve slightly one way, but sometimes it curves the other way slightly (with the same speed and spin).
The more I think about this, the more I am starting to think that certain tables will show this effect more than others. Perhaps the roll on a simonis cloth is a bit more true, and not at the mercy of the table quite as much as say, regular cloth would be. On a regular cloth, all bets are pretty much off at slow speeds, because the table just takes over the shot. That would explain why I see a bit more curve at slow speeds than you seem to, and have a bit easier time in reproducing it. <hr /></blockquote>I intend to try the experiments out on various tables with different cloths (e.g., fast and slick vs. slow and sticky) and conditions (e.g., dry vs. humid, clean vs. dirty, new vs. old). Maybe "ball turn" could be significant, consistent, and useful under certain conditions. It certainly isn't on my table.

Regards,
Dave

Bambu
01-10-2008, 05:59 PM
You are right, Dr. Dave. I really did not mean to suggest that I could do something you could not, especially on your own table. I should have realized earlier, that a slower cloth might not react to the spin as true, or even at all at slow speeds.

Bambu
01-10-2008, 06:04 PM
Thats ok, Dave, no problem. And I am glad you have cleared alot up for me as well. Thanks for weathering the storm on this. I know I can be forgetful sometimes. And great idea trying testing under different conditions, too. I look forward to reading about that.

Ralph_Kramden
01-11-2008, 09:24 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> In response to debate and discussion in several threads, I decided to post some videos relating to the effect sidespin has on the path of a ball. To be clear, I am referring to sidespin only, not masse spin. CB swerve is well understood. Also, a slight amount of "OB swerve" is possible with masse spin transferred to the OB from follow or draw on the CB (see the end of TP A.24 (http://billiards.colostate.edu/technical_proofs/new/TP_A-24.pdf)). Here, I am just looking at the effect of pure sidespin as a ball is rolling. I call this effect "OB turn."

Here are the videos:

NV B.7 - Ball "turn" caused by sidespin (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm)

NV B.8 - Straight throw of a second object ball (http://billiards.colostate.edu/normal_videos/new/NVB-8.htm)

Check them out and let me know if your experiences and/or explanations are different.

Regards,
Dave <hr /></blockquote>
In the video NV B.7 is it possible to get this spinning action on the cueball just by hitting it with a cue?

Unless the cueball hits an object ball with stun and kills most of the forward motion, the sidespin would terminate long before it stops rolling forward because of cloth friction.

Spinning the cueball with fingers can only simulate the 'OB Turn' if the forward motion is limited. To spin at that rate after being hit with a cue, the ball would also be moving forward quickly unless stopped abruptly by hitting another ball.

dr_dave
01-12-2008, 12:49 PM
<blockquote><font class="small">Quote Ralph_Kramden:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>...NV B.7 - Ball "turn" caused by sidespin (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm)...<hr /></blockquote>
In the video NV B.7 is it possible to get this spinning action on the cueball just by hitting it with a cue?<hr /></blockquote>... only if the CB hits another ball (to lose most of its speed), as you suggest below.

<blockquote><font class="small">Quote Ralph_Kramden:</font><hr>Unless the cueball hits an object ball with stun and kills most of the forward motion, the sidespin would terminate long before it stops rolling forward because of cloth friction.<hr /></blockquote>Actually, the CB retains its sidespin quite well while rolling. Even the soft cue shots in the video retained English over the full table length.

<blockquote><font class="small">Quote Ralph_Kramden:</font><hr>Spinning the cueball with fingers can only simulate the 'OB Turn' if the forward motion is limited. To spin at that rate after being hit with a cue, the ball would also be moving forward quickly unless stopped abruptly by hitting another ball.<hr /></blockquote>I did this to try to exaggerate the effect. You are correct ... this amount of spin is not likely during a typical pool game.

Regards,
Dave

dr_dave
01-14-2008, 10:15 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- I think that the sidespin videos showed a hint of reverse kurv for some of the qballz (slow speeds here) and sometimes lots of reverse kurv for the handball (very slow speeds here) but sometimes non-reverse kurv. I am certain that a slowing ball (with lots of spin) shood have a bit of reverse kurv, and a lot of reverse kurv just before stopping (but still spinning).<hr /></blockquote>Mac,

How would you explain the physics of why a rolling ball with sidespin should have reverse curve (e.g., left English causing curve to the right)?

You are right about reverse curve in the video. Sometimes a slow rolling/spinning ball curves as my physics reasoning suggest (e.g., left spin causing curve to the left), and other times it curves the other way (e.g., left spin causing curve to the right, aka "reverse curve"). On a pool table, I think the direction of turn is mostly due to local properties of the table and cloth (levelness, cloth imperfections, cloth directional properties, little pieces of dirt) where the ball is slowing to a stop. It doesn't take much to make a slow-rolling ball change direction.

Having said that, I still think there is a tiny physics effect that tends to turn the ball in the "natural" ("non-reverse") direction. Jal and I have been trying to come up with a solid physics/mathematical proof, but no conclusive results yet.

Regards,
Dave

dr_dave
01-14-2008, 01:48 PM
Mac,

FYI, I have an analysis posted in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf). Let me know if you have any comments or disagreements. I think the results are reasonable; although, the numbers are a little larger than I expected based on observations (e.g., NV B.7 (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm)).

Regards,
Dave
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- I think that the sidespin videos showed a hint of reverse kurv for some of the qballz (slow speeds here) and sometimes lots of reverse kurv for the handball (very slow speeds here) but sometimes non-reverse kurv. I am certain that a slowing ball (with lots of spin) shood have a bit of reverse kurv, and a lot of reverse kurv just before stopping (but still spinning).

This woz the effekt(s) seen on 12' tables when (cotton napless) Janus Cloth woz uzed -- production stopped during WW2. Unfortunately, the stupid looking nappy woollen cloths are now used for all billiards and snooker. In fakt, Walter Lindrum made hiz record 4137 on Janus -- a little known fakt.

About 3 years ago i played a match (English billiardz) on a completely worn out (napless) woollen cloth. Actually, once u got used to it, it woz ok. But, one guy played a short-jenny, and, the ball went "the other way" (ie it had reverse kurv). He couldnt beleev it. Twernt a surprize to me.

I think that the same sort of kurv(s) might one day be seen for an OB, albeit very little compared to a spinning slow handball. madMac. <hr /></blockquote>

wolfdancer
01-14-2008, 01:54 PM
I see Mac is still using that dvorak keyboard, but touch typing with the qwerty system....

wolfdancer
01-14-2008, 02:11 PM
There may be other forces acting upon the ball. As you know in
Walter Russell's 1926 book "The Universal One"...he contends that opposing forces are really one source which has separated. In layman's terms (excuse me for talking "down" to you)an analogy would be that any force divides and creates a resisting, or balancing force.
Consider Mr. Russell's theories that:
"I contend that electricity and gravitation are one, also that magnetism and radiation are one, and that both of these forces make up the two opposing forces evident in every effect of motion. I also contend that these two opposing forces are unity, or one, expressing themselves as opposing separate forces only as they travel in opposite directions, the centripetal direction of a closing spiral, in which all attributes are endothermic, and the centrifugal direction of an opening spiral, in which all attributes are exothermic.

I also contend that the electric force attracts, or contracts, or compresses, or condenses, or generates energy into solids of visible matter, while the magnetic force repels, or expands, or disintegrates, or rarifies, or degenerates energy into tenuous, invisible matter. This belief of unity of force, expressed in a continuous cycle of integration following disintegration, of generation succeeding degeneration, of the visible lifting itself out of the invisible in forever repeative cyclic intervals"
Again, in layman's terms....while you are putting left English on the ball, this force splits off and sets up a resisting force.......
Thus the universe remains in balance....
Hope this helps.....you have my permission to use this in a future lecture....

Ralph_Kramden
01-14-2008, 02:31 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> In response to debate and discussion in several threads, I decided to post some videos relating to the effect sidespin has on the path of a ball. To be clear, I am referring to sidespin only, not masse spin. CB swerve is well understood. Also, a slight amount of "OB swerve" is possible with masse spin transferred to the OB from follow or draw on the CB (see the end of TP A.24 (http://billiards.colostate.edu/technical_proofs/new/TP_A-24.pdf)). Here, I am just looking at the effect of pure sidespin as a ball is rolling. I call this effect "OB turn."

Here are the videos:

NV B.7 - Ball "turn" caused by sidespin (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm)

NV B.8 - Straight throw of a second object ball (http://billiards.colostate.edu/normal_videos/new/NVB-8.htm)

Check them out and let me know if your experiences and/or explanations are different.

Regards,
Dave <hr /></blockquote>
When you talk about 'OB turn' at slower speeds as in video NV B.7 are you considering the angle of the spinning axis?

The spinning axis must be somewhat off perpendicular in order for the ball to move forward as it spins. It would be like a spinning top as the spin starts to slow. The top remains in place until it loses momentum and begins to yaw. The axis tilts and then the top starts to move until it tobbles over.

Placing the striped ball with the stripe leaning in the same way as it is at .018 in your video and hitting low on the stripe will show a complete "OB turn" at a higher rate of speed. You may not see the ball move but it will 'turn over' as soon as the spin axis comes up to the perpendicular position.

Hitting low ON the tilted stripe (off center) will put angled backspin on the ball. This will cause the stripe to rise horizontally when the ball spins as it rolls. As soon as the spinning stripe becomes horizontal with pure sidespin it will 'Turn Over' and continue rolling.

To prove the 'OB turn' you could try hitting the red/white practice ball low on the divided color line placed at a tilted angle. If the red side is to the right when hit, it will roll to the end of the table with the red side on the left. You can see it 'turn over' as the spinning axis comes to perpendicular. The ball may run straight but there is a definate 'OB turn'.

Edited: I guess in this case it would actually be 'CB turn'.

dr_dave
01-14-2008, 04:33 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> I see Mac is still using that dvorak keyboard, but touch typing with the qwerty system.... <hr /></blockquote>I think Mac has gotten better with using the "Queen's English," but he still can't seem to completely part with his radical Aussie phonetic puzzlers. Sometimes I think it is cute, but most of the time it is an annoyance. I think more people would read and appreciate his posts more if he would use the accepted language.

Regards,
Dave

dr_dave
01-14-2008, 04:35 PM
Thank you for your help. /ccboard/images/graemlins/crazy.gif

Now I understand. /ccboard/images/graemlins/tongue.gif

Dave

<blockquote><font class="small">Quote wolfdancer:</font><hr> There may be other forces acting upon the ball. As you know in
Walter Russell's 1926 book "The Universal One"...he contends that opposing forces are really one source which has separated. In layman's terms (excuse me for talking "down" to you)an analogy would be that any force divides and creates a resisting, or balancing force.
Consider Mr. Russell's theories that:
"I contend that electricity and gravitation are one, also that magnetism and radiation are one, and that both of these forces make up the two opposing forces evident in every effect of motion. I also contend that these two opposing forces are unity, or one, expressing themselves as opposing separate forces only as they travel in opposite directions, the centripetal direction of a closing spiral, in which all attributes are endothermic, and the centrifugal direction of an opening spiral, in which all attributes are exothermic.

I also contend that the electric force attracts, or contracts, or compresses, or condenses, or generates energy into solids of visible matter, while the magnetic force repels, or expands, or disintegrates, or rarifies, or degenerates energy into tenuous, invisible matter. This belief of unity of force, expressed in a continuous cycle of integration following disintegration, of generation succeeding degeneration, of the visible lifting itself out of the invisible in forever repeative cyclic intervals"
Again, in layman's terms....while you are putting left English on the ball, this force splits off and sets up a resisting force.......
Thus the universe remains in balance....
Hope this helps.....you have my permission to use this in a future lecture.... <hr /></blockquote>

dr_dave
01-14-2008, 04:52 PM
When a ball has sidespin only, the ball's spin axis is vertical. When a ball is rolling, the ball's spin axis is horizontal. When a ball is rolling with sidespin, the ball's spin axis is somewhere in between (but in the same vertical plane). As the sidespin wears off, the spin axis gradually tilts closer and closer to the horizontal direction.

You have to be careful with how you interpret spin with a striped ball, because it is easy to get misleading info. For example, if the stripe happens to be aligned with the spin direction, it will look like the ball isn't spinning at all (as with a well-hit center-ball hit drill shot with the stripe vertical). As another example, a striped ball starting with stripe tilted and hit on the centerline will appear to have complicated spin and wobble, even though it is just rolling. A striped ball is good for visualizing a centerball hit when the stripe is vertical, because any "wobble" in the stripe indicates an off-center hit; but in general, an Aramith "measles" ball is much better for visualizing the spin axis of a ball.

Regards,
Dave

<blockquote><font class="small">Quote Ralph_Kramden:</font><hr>When you talk about 'OB turn' at slower speeds as in video NV B.7 are you considering the angle of the spinning axis?

The spinning axis must be somewhat off perpendicular in order for the ball to move forward as it spins. It would be like a spinning top as the spin starts to slow. The top remains in place until it loses momentum and begins to yaw. The axis tilts and then the top starts to move until it tobbles over.

Placing the striped ball with the stripe leaning in the same way as it is at .018 in your video and hitting low on the stripe will show a complete "OB turn" at a higher rate of speed. You may not see the ball move but it will 'turn over' as soon as the spin axis comes up to the perpendicular position.

Hitting low ON the tilted stripe (off center) will put angled backspin on the ball. This will cause the stripe to rise horizontally when the ball spins as it rolls. As soon as the spinning stripe becomes horizontal with pure sidespin it will 'Turn Over' and continue rolling.

To prove the 'OB turn' you could try hitting the red/white practice ball low on the divided color line placed at a tilted angle. If the red side is to the right when hit, it will roll to the end of the table with the red side on the left. You can see it 'turn over' as the spinning axis comes to perpendicular. The ball may run straight but there is a definate 'OB turn'.

Edited: I guess in this case it would actually be 'CB turn'. <hr /></blockquote>

Jal
01-14-2008, 06:38 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> There may be other forces acting upon the ball. As you know in
Walter Russell's 1926 book "The Universal One"...he contends that opposing forces are really one source which has separated. In layman's terms (excuse me for talking "down" to you)an analogy would be that any force divides and creates a resisting, or balancing force.
Consider Mr. Russell's theories that:
"I contend that electricity and gravitation are one, also that magnetism and radiation are one, and that both of these forces make up the two opposing forces evident in every effect of motion. I also contend that these two opposing forces are unity, or one, expressing themselves as opposing separate forces only as they travel in opposite directions, the centripetal direction of a closing spiral, in which all attributes are endothermic, and the centrifugal direction of an opening spiral, in which all attributes are exothermic.

I also contend that the electric force attracts, or contracts, or compresses, or condenses, or generates energy into solids of visible matter, while the magnetic force repels, or expands, or disintegrates, or rarifies, or degenerates energy into tenuous, invisible matter. This belief of unity of force, expressed in a continuous cycle of integration following disintegration, of generation succeeding degeneration, of the visible lifting itself out of the invisible in forever repeative cyclic intervals"
Again, in layman's terms....while you are putting left English on the ball, this force splits off and sets up a resisting force.......
Thus the universe remains in balance....
Hope this helps.....you have my permission to use this in a future lecture.... <hr /></blockquote>Wolfdancer, his thesis sounds like gobbledygook, but that is, more-or-less, the road that physics has traveled. They've succeeded in showing that several of the fundamental forces are in fact different aspects of an underlying unity. And the work of Emily Noether, a relatively unheralded mathemetician, though much appreciated by Einstein, has proven that the conservation laws (momentum, energy) are related to abstract symmetries of space and time.

This is all above me. And it will certainly be a while before its applicability to pool becomes apparent (especially if I'm the one to do it), but you've definitely hit on something important. I had no idea you delved this deeply into things.

Jim

Bambu
01-15-2008, 02:32 PM
Dave, I read the paper but because of the math involved its tough for me to understand how the equation works out. I would like to know if the rpm's of the ball are being factored in(not just the speed the ball is traveling).

dr_dave
01-15-2008, 02:39 PM
<blockquote><font class="small">Quote Bambu:</font><hr> Dave, I read the paper but because of the math involved its tough for me to understand how the equation works out. I would like to know if the rpm's of the ball are being factored in(not just the speed the ball is traveling).<hr /></blockquote>Both the forward roll of the ball and the sidespin are accounted for. It turns out the spin-down friction torque is fairly constant with sidespin rate (rpm's), but as the ball travels more slowly, the force can turn the ball a little more. I hope that's clear. Let me know if it ain't.

Regards,
Dave

Bambu
01-15-2008, 02:44 PM
I think so, thanks Dave. Does that mean the cue speed(the rpm's) will have a direct effect at slow speeds, effecting the amount of slight curve? Also, if you increase the number 8 to 9 for a larger table in the equation, would the final variable also increase slightly?

dr_dave
01-15-2008, 03:21 PM
<blockquote><font class="small">Quote Bambu:</font><hr> I think so, thanks Dave. Does that mean the cue speed(the rpm's) will have a direct effect at slow speeds, effecting the amount of slight curve?<hr /></blockquote>Sorry, I'm not sure I follow you, but I'll try to answer anyway.

The physics in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf) predicts the cue ball will tend to "turn" more at slow speed (where the "roll" rpm is less). The amount of "turn" doesn't seem to depend on the amount of English (sidespin rpm).

But again, the effect is extremely small and can get "lost in the noise" of other slow-roll effects (levelness, dirt, cloth irregularities, etc.). I've rolled many balls at slow speeds on different parts of my table with different amounts of sidespin. Sometimes the ball curve one way, and sometimes it curves the other, but it usually goes pretty darn straight. But the physics does suggest there might be a small tendency for the ball to curve in the direction of the spin (e.g., left spin is predicted to create a slight curve to the left).

If you are observing consistent ball "turn" on your table, and can make it turn in either direction with left and right English (along the same line of the table with the same speed), please post a video. Until I see such evidence, I will remain skeptical of the value of ball turn. I was not able to produce consistent and solid evidence when I filmed NV B.7 (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm).

Regards,
Dave

Bambu
01-15-2008, 03:46 PM
I regret that this will be my first time making a video, and it will take some time. And I do not doubt your results or explanation at all. I do suspect that a table that is more sensitive to curve would react to the rpm's at low speeds a bit more(simonis). I also think the consistency is directly related to the ability to generate rpm's on the object ball. Thats why I am asking about the rpm's of the ball, as opposed to the speed. I still cant call this effect consistent to my own ability, but I think there is room for improvement, and that others would have varying results.

dr_dave
01-15-2008, 03:56 PM
<blockquote><font class="small">Quote Bambu:</font><hr>I regret that this will be my first time making a video, and it will take some time. And I do not doubt your results or explanation at all. I do suspect that a table that is more sensitive to curve would react to the rpm's at low speeds a bit more(simonis). I also think the consistency is directly related to the ability to generate rpm's on the object ball. Thats why I am asking about the rpm's of the ball, as opposed to the speed. I still cant call this effect consistent to my own ability, but I think there is room for improvement, and that others would have varying results.<hr /></blockquote>Forget about the OB experiment for now ... it is too difficult (too many variables).

Just hit a CB with English at slow speeds such that, after squirt and swerve, it heads along a straight line (e.g. a tape measure). That's not too hard to do. See if you can make the ball turn consistently in either direction, based on the type of spin. If a CB rolling with sidespin can turn, then so can an OB with a small amount of transferred English.

Regards,
Dave

Bob_Jewett
01-15-2008, 05:36 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> .... Just hit a CB with English at slow speeds such that, after squirt and swerve, it heads along a straight line (e.g. a tape measure). That's not too hard to do. See if you can make the ball turn consistently in either direction, based on the type of spin. ... <hr /></blockquote>
Or use Byrne's suggestion for this test which is to set a cue ball spinning like a top by shooting a stop shot with side. Then tap the cue ball in the wanted direction with another ball. Some people, like Mike Massey, can make the ball spin in place by snapping it with their fingers.

dr_dave
01-15-2008, 05:45 PM
Bob,

Thanks for the idea. Aim still needs to be adjusted for "reverse throw." But this is much easier than trying to adjust for squirt and swerve with a CB-only test, and you can obviously create much more spin with the pre-spin OB.

Regards,
Dave

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> .... Just hit a CB with English at slow speeds such that, after squirt and swerve, it heads along a straight line (e.g. a tape measure). That's not too hard to do. See if you can make the ball turn consistently in either direction, based on the type of spin. ... <hr /></blockquote>
Or use Byrne's suggestion for this test which is to set a cue ball spinning like a top by shooting a stop shot with side. Then tap the cue ball in the wanted direction with another ball. Some people, like Mike Massey, can make the ball spin in place by snapping it with their fingers. <hr /></blockquote>

Bambu
01-15-2008, 07:39 PM
I agree, If a CB rolling with sidespin can turn, then so can an OB with a small amount of transferred English.
But on a slow shot, after the swerve is gone and the ball is rolling straight, there is not enough spin left on the ball for it to curve. But did it curve before the swerve wore off? Yes. The combination of speed and power will dictate the amount of max curve, based on cloth resistance. There are other factors of course, like cue angle and how close to the eddge of the ball you hit.

cushioncrawler
01-16-2008, 04:48 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- I think that the sidespin videos showed a hint of reverse kurv for some of the qballz (slow speeds here) and sometimes lots of reverse kurv for the handball (very slow speeds here) but sometimes non-reverse kurv. I am certain that a slowing ball (with lots of spin) shood have a bit of reverse kurv, and a lot of reverse kurv just before stopping (but still spinning).<hr /></blockquote>Mac, How would you explain the physics of why a rolling ball with sidespin should have reverse curve (e.g., left English causing curve to the right)? You are right about reverse curve in the video. Sometimes a slow rolling/spinning ball curves as my physics reasoning suggest (e.g., left spin causing curve to the left), and other times it curves the other way (e.g., left spin causing curve to the right, aka "reverse curve"). On a pool table, I think the direction of turn is mostly due to local properties of the table and cloth (levelness, cloth imperfections, cloth directional properties, little pieces of dirt) where the ball is slowing to a stop. It doesn't take much to make a slow-rolling ball change direction. Having said that, I still think there is a tiny physics effect that tends to turn the ball in the "natural" ("non-reverse") direction. Jal and I have been trying to come up with a solid physics/mathematical proof, but no conclusive results yet. Regards, Dave<hr /></blockquote>Dr Dave -- I think that early on a spinning OB or spinning QB are in a skidding phase -- later they enter a rolling phase. At the start of the rolling phase i reckon that the ball'z spin axis iz in a plane leaning back a bit, ie not vertical -- the lean of the plane iz (nearnuff) the effektiv hill slowing the ball.

Say the ball haz clockwize spin. Here the leftwards forces in the leading area of the footprint are nearnuff balanced by the rightwards forces in the rear (here we are still talking about the situation at the end of the skidding phase, ie the start of rolling). Now, az the ball slowz, any unbalancing of the leftwards and rightwards forces must rezult in the ball veering. If the rear area of the footprint supports more and more of the ball's wt az the ball slowz (clockwize spin here) then the ball must veer to the right.

So, the arguement bekumz, duz the spin axis (plane) bekum more vertical az the ball slowz, ie duz the area in the rear of the footprint support more and more of the wt. If the answer iz yes, then left english leads to veer (kurv) to the right.

During the skidding phase we can (uzually) expekt veer to the left.

Allso, aerodynamic effekts in the leading edge of the footprint kan be expekted to create (trap) more air pressure on the left side of the (leading edge of the) footprint than on the right side. This iz a major effekt for a napped woollen cloth, but must be a faktor for a non-direktional napped pool cloth allso.

When i did my tests for spin and kurv, for direktional napped cloths, i repeated theze tests on top of the cotton table-covers. Theze tests showed that clockwize spin made the ball kurv to the right az it slowz (handspin here).

But i am still thinking about all of this stuff. madMac.

cushioncrawler
01-16-2008, 04:56 AM
<blockquote><font class="small">Quote Bambu:</font><hr> Dunno what a short jenny is, but I am with you mac. A spinning ball with left or right spin, combined with a forward roll....can curve if it has time to grab the cloth as it slows down.<hr /></blockquote>A short jenny iz an in-off played from in-hand (ie from in the Dee), played into a middle pocket, the OB being near the cushion between the baulkline and the pocket. Players allwayz uze a lot of inside english here (check side), the spin makes the ball kurv into the pocket, but mainly the spin acts az "pocket side", ie making the pocket "bigger". With zero nap, the qball will kurv away from the pocket rather than into it, az my team-mate found out. madMac.

dr_dave
01-16-2008, 09:45 AM
<blockquote><font class="small">Quote Bambu:</font><hr>I agree, If a CB rolling with sidespin can turn, then so can an OB with a small amount of transferred English.
But on a slow shot, after the swerve is gone and the ball is rolling straight, there is not enough spin left on the ball for it to curve. But did it curve before the swerve wore off? Yes. The combination of speed and power will dictate the amount of max curve, based on cloth resistance. There are other factors of course, like cue angle and how close to the eddge of the ball you hit.<hr /></blockquote>Excellent summary. "Ball turn" is not a strong or consistent enough effect to use to your advantage at a pool table. "OB swerve" is a small effect that can possibly be used to your advantage with your original shot example, but the shot would need to be hit nearly perfectly: with enough speed to delay the OB swerve effect, but not too much to reduce the spin-transfer effect, and with perfect OB direction, after accounting perfectly for CB squirt, swerve, throw. Wow! I think the easy safety is a much better play, for any skill level.

Regards,
Dave

dr_dave
01-16-2008, 10:48 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I think that early on a spinning OB or spinning QB are in a skidding phase<hr /></blockquote>
Agreed. This is when swerve occurs.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>later they enter a rolling phase. At the start of the rolling phase i reckon that the ball'z spin axis iz in a plane leaning back a bit, ie not vertical<hr /></blockquote>When a ball is rolling with sidespin, the ball's spin axis has two components: a vertical component due to sidespin and a horizontal component due to roll. So for a rolling ball with spin, the ball's spin axis is always in a vertical plane (e.g., up and to the left for right spin). The ball's spin axis never tilts back. I'm not sure what you mean by "spin axis." Are you referring to the axis of the resultant normal? Feel free to refer to the diagrams in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf).

Regards,
Dave

Bambu
01-16-2008, 10:49 AM
Lol Dave, thanks. Yes exactly, thats what makes the shot so tough, even tough to describe. And I agree, the safety is almost always a better choice than object ball curve. I really did not mean to try to justify its usefulness, only its existence. I only tried to create a game situation out of the shot because I was asked to. Originally, the shot was only designed to demonstrate the slight curve, nothing more. Thanks again for being so open minded about this.

dr_dave
01-16-2008, 10:53 AM
<blockquote><font class="small">Quote Bambu:</font><hr>LOl Dave, thanks. Yes exactly, thats what makes the shot so tough, even tough to describe. And I agree, the safety is almost always a better choice than object ball curve. I really did not mean to try to justify its usefulness, only its existence. I only tried to create a game situation out of the shot because I was asked to. Originally, the shot was only designed to demonstrate the slight curve, nothing more. Thanks again for being so open minded about this.<hr /></blockquote>You are very welcome. Thank you for making me think about this more than I ever have (and probably ever will again). I'm glad you seem more at peace now. Did you win or lose your bet with your friend, or did you even have a bet?

Regards,
Dave

cushioncrawler
01-17-2008, 04:57 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I think that early on a spinning OB or spinning QB are in a skidding phase<hr /></blockquote>
Agreed. This is when swerve occurs.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>later they enter a rolling phase. At the start of the rolling phase i reckon that the ball'z spin axis iz in a plane leaning back a bit, ie not vertical<hr /></blockquote>When a ball is rolling with sidespin, the ball's spin axis has two components: a vertical component due to sidespin and a horizontal component due to roll. So for a rolling ball with spin, the ball's spin axis is always in a vertical plane (e.g., up and to the left for right spin). The ball's spin axis never tilts back. I'm not sure what you mean by "spin axis." Are you referring to the axis of the resultant normal? Feel free to refer to the diagrams in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf).

Regards,
Dave <hr /></blockquote>Dr Dave -- Of course any moovment can allwayz be analyzed in an X Y Z system, but that duznt mean that the (equilibrium) spin axiz iz (allwayz) in a vertical plane. In fakt, answering one of your earlyr questionz, the math here must in fakt be one of the most exquizit examples of math that can ever be imagined. If momentum iz some sort of new math language, then rotational momentum iz some sort of math poetry. The "right hand rule" dictates that (once skidding endz) the spin axis must be nearnuff in the plane of the "effektiv supporting force". This iz math at its most subtle. Right now i have had too many redz, but, in years gone bye (since 1987), i have spent countless hours imagining all of the torqs and forces etc kumming into play here. Any out of balance sidewayz (etc) forces will (must) moov the spin axis towardz equilibrium. This equilibrium must be nearnuff normal to the plane of "the hill" (rolling rezistance) slowing the ball (az u say, this hill might be about 1%). If the forces in the leading edge etc are very great then this can only help my arguement. If theze forcez were ten times greater then it would only help my arguement even moreso. Koz, theze and other forces "sort themselves out" during skidding. Afterwards, after equilibrium iz reeched, what happenz happenz, and what happenz determinez what the final kurv iz during the later stages of slowing. Sure, there might be a giant kurve "with" the spin early on, but i am only concerned with the kurv during the late stages, and this must be "reverse kurv" (but might be something else on a nappy cloth). madMac.

dr_dave
01-17-2008, 10:44 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I think that early on a spinning OB or spinning QB are in a skidding phase<hr /></blockquote>
Agreed. This is when swerve occurs.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>later they enter a rolling phase. At the start of the rolling phase i reckon that the ball'z spin axis iz in a plane leaning back a bit, ie not vertical<hr /></blockquote>When a ball is rolling with sidespin, the ball's spin axis has two components: a vertical component due to sidespin and a horizontal component due to roll. So for a rolling ball with spin, the ball's spin axis is always in a vertical plane (e.g., up and to the left for right spin). The ball's spin axis never tilts back. I'm not sure what you mean by "spin axis." Are you referring to the axis of the resultant normal? Feel free to refer to the diagrams in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf).

Regards,
Dave <hr /></blockquote>Dr Dave -- Of course any moovment can allwayz be analyzed in an X Y Z system, but that duznt mean that the (equilibrium) spin axiz iz (allwayz) in a vertical plane.<hr /></blockquote>It doens't matter which frame of reference you use as long as you include all spin, force, and torque components. Do you think I have left something out? As long as a ball has some sidespin, it will always have a spin component about the vertical axis.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>The "right hand rule" dictates that (once skidding endz) the spin axis must be nearnuff in the plane of the "effektiv supporting force".<hr /></blockquote>For that to be true, the ball would need to also have masse spin (spin about the x axis in my diagrams), because with only sidespin and roll, the total spin axis is in the vertical plane. Do you think a rolling ball with sidespin develops slight masse spin?

Regards,
Dave

Bambu
01-18-2008, 04:33 PM
Well Dave, I myself in my own small way, am certainly glad to have taken part in the creation of your latest paper on ball turn. My reason for seeking you out did come from my own gut feeling and curiosity.
But I must admit, you are right. Though there was no money at stake, there was indeed something else going on behind the scenes. As much as a part of me wants to, I cannot bring myself to publicly cry out his name in victory. But at least for me, this topic stems from a previous debate about object ball curve which I was having with another well known physicist.
Though he is stubborn, and still will not concede, I am more than at peace with myself on account of you and your hard work. I no longer need to convince myself of my sanity. And, I owe it all to my outstanding and extremely open minded experience on Billiards Digest. Thanks again Dave, you rock!

dr_dave
01-18-2008, 04:36 PM
<blockquote><font class="small">Quote Bambu:</font><hr> Well Dave, I myself in my own small way, am certainly glad to have taken part in the creation of your latest paper on ball turn. My reason for seeking you out did come from my own gut feeling and curiosity.
But I must admit, you are right. Though there was no money at stake, there was indeed something else going on behind the scenes. As much as a part of me wants to, I cannot bring myself to publicly cry out his name in victory. But at least for me, this topic stems from a previous debate about object ball curve which I was having with another well known physicist.
Though he is stubborn, and still will not concede, I am more than at peace with myself on account of you and your hard work. I no longer need to convince myself of my sanity. And, I owe it all to my outstanding and extremely open minded experience on Billiards Digest. Thanks again Dave, you rock! <hr /></blockquote>You are very welcome. I'm glad your experience with the CCB is good. Thank you for the kind words.

Regards,
Dave

Bambu
01-19-2008, 08:05 AM
Sorry for the delayed reply mac. I am sorry, but its very hard for me to understand your terms. In off, in-hand, the dee, baulkline. No disrespect mac, but these words are not what I am familiar with. Thanks anyway.

cushioncrawler
01-20-2008, 04:06 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>later they enter a rolling phase. At the start of the rolling phase i reckon that the ball'z spin axis iz in a plane leaning back a bit, ie not vertical<hr /></blockquote>When a ball is rolling with sidespin, the ball's spin axis has two components: a vertical component due to sidespin and a horizontal component due to roll. So for a rolling ball with spin, the ball's spin axis is always in a vertical plane (e.g., up and to the left for right spin). The ball's spin axis never tilts back. I'm not sure what you mean by "spin axis." Are you referring to the axis of the resultant normal? Feel free to refer to the diagrams in TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf). Regards, Dave<hr /></blockquote>Dr Dave -- No ball iz ever rollin/spinning along a horizontal surface. The surface, from the ball's point of view, iz a hill. The grade of the hill iz what slowz the (rolling) ball. So, it iz eezyr to think of the whole thing az (not a ball rolling along a yielding horiz surface but) a ball rolling up a hill (1% say), the hill being a solid (non-yielding) surface. Thusly, it iz now eezyr to see that the vertical (ie the z axis) shood be considered to be normal to that hill (and hencely that yielding hill).

Nextly, we can see that the actual (total) spin axis will lay in a plane which cuts the horizontal at 90dg to the direction of travel, and allso that the plane will be nearnuff perpindicular to the hill.

The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long). The tilting iz not critical to my explanation. The sidewayz friktional forces (in the footprint) trailing the axis will push (the ball) one way and the sidewayz forces ahead of the axis will push the other way. Az the rolling ball slowz, if the trailing forces are (bekum) greater than the leading forces, then the ball must acquire reverse kurv.

Dr Dave -- How is all of this so far??? madMac.

Jal
01-20-2008, 08:29 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- No ball iz ever rollin/spinning along a horizontal surface. The surface, from the ball's point of view, iz a hill. The grade of the hill iz what slowz the (rolling) ball. So, it iz eezyr to think of the whole thing az (not a ball rolling along a yielding horiz surface but) a ball rolling up a hill (1% say), the hill being a solid (non-yielding) surface. Thusly, it iz now eezyr to see that the vertical (ie the z axis) shood be considered to be normal to that hill (and hencely that yielding hill).

Nextly, we can see that the actual (total) spin axis will lay in a plane which cuts the horizontal at 90dg to the direction of travel, and allso that the plane will be nearnuff perpindicular to the hill.

The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long). The tilting iz not critical to my explanation. The sidewayz friktional forces (in the footprint) trailing the axis will push (the ball) one way and the sidewayz forces ahead of the axis will push the other way. Az the rolling ball slowz, if the trailing forces are (bekum) greater than the leading forces, then the ball must acquire reverse kurv.

Dr Dave -- How is all of this so far??? madMac. <hr /></blockquote>Mac, I agree with just about everything you said, including reverse curve. It's taken me a week (or has it been a month?) but it finally sunk in. Very nice Mac, very nice!

You didn't say this explicitly, so I may be arguing with myself, but I don't think a cessation of curving, however transitory, is necessarily achieved when the plane of the spin axis is normal to the "hill". When and if this happens, the normal force acting on the front half does not have to be equal to the normal force acting on the rear half - the spin axis being the dividing line between front and back. Any number of combinations of the two can add up vectorally to the tilted total normal force, which defines the hill's grade. Or do you see it differently?

Jim

dr_dave
01-20-2008, 01:45 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long).<hr /></blockquote>I don't think I buy his (e.g., I don't understand your definition of "equilibrium" in this context), but I will try to think about it some more.

FYI, my analysis does take into account the tilted normal force due to rolling resistance.

Dave

Jal
01-21-2008, 08:39 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long).<hr /></blockquote>I don't think I buy his (e.g., I don't understand your definition of "equilibrium" in this context), but I will try to think about it some more.

FYI, my analysis does take into account the tilted normal force due to rolling resistance.

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

The only thing we know for sure is that the net force normal to the surface of a rolling ball is tilted back by about 0.8 deg. We also know that it is comprised of two net normal forces, Nf and Nb, acting on the front and back halves, respectively. The vertical component spin (axis) is the dividing line between front and back. I really can't see that much can be gleaned from this.

Beyond that we have to assume a few things, some likely true, others iffy, and some completely unjustified, imo, though possibly true.

In the first category (likely true), is that Nf is initially larger than Nb. The reason that this is probably true has to do with the mechanism of rolling resistance: the cloth does not decompress fast enough on the back half of the dimple to balance Nb and Nf. (We know that it's not any kind of friction that slows the ball since the circumferential forces do their meager part to speed up a rolling ball.)

We can also assume that the normal forces are approximately the same for a sliding ball (iffy, but probably true enough).

During the sliding phase, we might assume the coefficient of friction is independent of surface speed. This is not such a good assumptiom at very low surface speeds, but probably is about right during the bulk of the sliding phase. From this and a touch of math we can figure that the magnitude of the front and back net friction forces are (mu)Nf and (mu)Nb. But we have no idea of the comparative sizes of Nf and Nb, and therefore know nothing about the net lateral friction, (mu)(Nf-Nb), much less the torques generated by them. And even if we did know the size and directions of Nb and Nf, we still wouldn't know the net torques acting on either half. If you know that this could be deduced, please explain further.

I agree with Mac that the torque produced by the cloth during the sliding phase should degrade the wiping action of the initially vertical spin, until Nb closely approaches Nf in magnitude (assuming they're unequal to begin with). That's what friction does. And I'm pretty sure this is what he means by "equilibrium". It causes a tilting of the vertical spin axis axis component as the friction torque degrades the "masse" component of z-spin. (Note the quotes.) And it also seems reasonable that once this is achieved, further slowing will keep things slightly out of balance, with the friction generated by Nb winning. The spin axis is already tilted, which more or less equalizes Nb and Nf, by awarding Nb more surface area. But as the ball slows, the cloth fibers now have more time to react and increase Nb. So now the vertical spin axis component has to retrace its steps, more or less. Reverse curve may not in fact take place, but it does seem very plausible by this line of reasoning (Mac's).

Nevertheless, I don't see how we know enough to make any predictions about sidespin curve. If you could demonstrate that more can be said about it, or that any of the above is absolutely or likely wrong, I'm of course all ears. Your treatment in TP B-2 is pretty sophisticated (I've been catching up on some of the math). But I think it skirts around some of the critical unknowns, and the very same ones that my less sophisticated math tried to avoid. (Still, in trying to keep up, I learned some great stuff. Thank you!)

Jim

cushioncrawler
01-22-2008, 04:09 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- No ball iz ever rollin/spinning along a horizontal surface. The surface, from the ball's point of view, iz a hill. The grade of the hill iz what slowz the (rolling) ball. So, it iz eezyr to think of the whole thing az (not a ball rolling along a yielding horiz surface but) a ball rolling up a hill (1% say), the hill being a solid (non-yielding) surface. Thusly, it iz now eezyr to see that the vertical (ie the z axis) shood be considered to be normal to that hill (and hencely that yielding hill).

Nextly, we can see that the actual (total) spin axis will lay in a plane which cuts the horizontal at 90dg to the direction of travel, and allso that the plane will be nearnuff perpindicular to the hill.

The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long). The tilting iz not critical to my explanation. The sidewayz friktional forces (in the footprint) trailing the axis will push (the ball) one way and the sidewayz forces ahead of the axis will push the other way. Az the rolling ball slowz, if the trailing forces are (bekum) greater than the leading forces, then the ball must acquire reverse kurv.

Dr Dave -- How is all of this so far??? madMac. <hr /></blockquote>Mac, I agree with just about everything you said, including reverse curve. It's taken me a week (or has it been a month?) but it finally sunk in. Very nice Mac, very nice!

You didn't say this explicitly, so I may be arguing with myself, but I don't think a cessation of curving, however transitory, is necessarily achieved when the plane of the spin axis is normal to the "hill". When and if this happens, the normal force acting on the front half does not have to be equal to the normal force acting on the rear half - the spin axis being the dividing line between front and back. Any number of combinations of the two can add up vectorally to the tilted total normal force, which defines the hill's grade. Or do you see it differently?<hr /></blockquote>Jim -- Yes i agree. If the spin axis plane iz ever exaktly normal to the "hill" then equilibrium will allmost certainly still be a long wayz away. And, dont forget, if the hill iz 7/5ths% then the slowing will be reduced to 5/5ths due to the YY rotational momentum coming to the rescue. So, when we say that the hill iz 1% i am never sure whether we mean that it iz 7/5% or 5/5th%.

I have identyfyd about 11 effekts etc that might make a spinning (or rolling) ball kurv (12 if u inklood masse type effekts). One effekt iz air pressure in the footprint. Logically for clockwize spin the left-hand area of the front of the footprint must trap air moreso than the right-hand area. It wont be a big effekt, but if u worked out the grade of the sidewayz hill (i havnt) that would cause the ball to roll off say 2" in say 7 seconds then that side-grade might be only say 1% of 1%. madMac.

cushioncrawler
01-22-2008, 04:46 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long).<hr /></blockquote>I don't think I buy his (e.g., I don't understand your definition of "equilibrium" in this context), but I will try to think about it some more.

FYI, my analysis does take into account the tilted normal force due to rolling resistance. Dave<hr /></blockquote>Dr Dave -- I think Jim explained ok what i mean by equilibrium. But i am having trouble trying to think all of this throo again (after all theze yearz). U might help me out here. Lets say that "the" plane of the spin axis (i know that there are an infinite number of theze spin axis planes but) iz "leaning backwards" a bit (ie nearly normal to the hill). Now, if the sidewayz force(s) in the trailing area of footprint iz larger than the sidewayz force in the leading edge (clockwize spin here, and ball iz rolling), would this "out of balance" force (torq) make the ball "turn" left a bit or would it tend to make it turn right?? Real question here. If the ball iz to look for my "equilibrium" (while slowing) then the ball here shood be looking to turn right???? Or, shood it??? Hmmm - still thinking. madMac.

dr_dave
01-22-2008, 02:52 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long).<hr /></blockquote>I don't think I buy his (e.g., I don't understand your definition of "equilibrium" in this context), but I will try to think about it some more.

FYI, my analysis does take into account the tilted normal force due to rolling resistance.

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

The only thing we know for sure is that the net force normal to the surface of a rolling ball is tilted back by about 0.8 deg. We also know that it is comprised of two net normal forces, Nf and Nb, acting on the front and back halves, respectively. The vertical component spin (axis) is the dividing line between front and back. I really can't see that much can be gleaned from this.

Beyond that we have to assume a few things, some likely true, others iffy, and some completely unjustified, imo, though possibly true.

In the first category (likely true), is that Nf is initially larger than Nb. The reason that this is probably true has to do with the mechanism of rolling resistance: the cloth does not decompress fast enough on the back half of the dimple to balance Nb and Nf. (We know that it's not any kind of friction that slows the ball since the circumferential forces do their meager part to speed up a rolling ball.)

We can also assume that the normal forces are approximately the same for a sliding ball (iffy, but probably true enough).

During the sliding phase, we might assume the coefficient of friction is independent of surface speed. This is not such a good assumptiom at very low surface speeds, but probably is about right during the bulk of the sliding phase. From this and a touch of math we can figure that the magnitude of the front and back net friction forces are (mu)Nf and (mu)Nb. But we have no idea of the comparative sizes of Nf and Nb, and therefore know nothing about the net lateral friction, (mu)(Nf-Nb), much less the torques generated by them. And even if we did know the size and directions of Nb and Nf, we still wouldn't know the net torques acting on either half. If you know that this could be deduced, please explain further.

I agree with Mac that the torque produced by the cloth during the sliding phase should degrade the wiping action of the initially vertical spin, until Nb closely approaches Nf in magnitude (assuming they're unequal to begin with). That's what friction does. And I'm pretty sure this is what he means by "equilibrium". It causes a tilting of the vertical spin axis axis component as the friction torque degrades the "masse" component of z-spin. (Note the quotes.) And it also seems reasonable that once this is achieved, further slowing will keep things slightly out of balance, with the friction generated by Nb winning. The spin axis is already tilted, which more or less equalizes Nb and Nf, by awarding Nb more surface area. But as the ball slows, the cloth fibers now have more time to react and increase Nb. So now the vertical spin axis component has to retrace its steps, more or less. Reverse curve may not in fact take place, but it does seem very plausible by this line of reasoning (Mac's).

Nevertheless, I don't see how we know enough to make any predictions about sidespin curve. If you could demonstrate that more can be said about it, or that any of the above is absolutely or likely wrong, I'm of course all ears. Your treatment in TP B-2 is pretty sophisticated (I've been catching up on some of the math). But I think it skirts around some of the critical unknowns, and the very same ones that my less sophisticated math tried to avoid. (Still, in trying to keep up, I learned some great stuff. Thank you!)<hr /></blockquote>Jim,

Excellent post!!! Thank you for summarizing everything so well. Based on our conversations, I've been thinking some more about my TP B.2 analysis (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf), and I have some new ideas to try out. I'll let you know if they lead to any useful info. I agree with you that the current version of my analysis does have some holes (including masse spin, however slight it might be).

Again, excellent post! Thank you again for your ideas and for trying to keep me honest.

Regards,
Dave

dr_dave
01-22-2008, 02:54 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>The right-hand-rule dictates that the spin axis (and hencely the plane of the axis) will allwayz be tilting (towards or away from vertical), searching for (torque) equilibrium (but never finding it for long).<hr /></blockquote>I don't think I buy his (e.g., I don't understand your definition of "equilibrium" in this context), but I will try to think about it some more.

FYI, my analysis does take into account the tilted normal force due to rolling resistance. Dave<hr /></blockquote>Dr Dave -- I think Jim explained ok what i mean by equilibrium. But i am having trouble trying to think all of this throo again (after all theze yearz). U might help me out here. Lets say that "the" plane of the spin axis (i know that there are an infinite number of theze spin axis planes but) iz "leaning backwards" a bit (ie nearly normal to the hill). Now, if the sidewayz force(s) in the trailing area of footprint iz larger than the sidewayz force in the leading edge (clockwize spin here, and ball iz rolling), would this "out of balance" force (torq) make the ball "turn" left a bit or would it tend to make it turn right?? Real question here. If the ball iz to look for my "equilibrium" (while slowing) then the ball here shood be looking to turn right???? Or, shood it??? Hmmm - still thinking. madMac. <hr /></blockquote>I also have some more thinking (and analysis re-work) to do. Jal did an excellent job summarizing his (and your) concerns and ideas.

Regards,
Dave

Jal
01-22-2008, 04:21 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>...Lets say that "the" plane of the spin axis (i know that there are an infinite number of theze spin axis planes but) iz "leaning backwards" a bit (ie nearly normal to the hill). Now, if the sidewayz force(s) in the trailing area of footprint iz larger than the sidewayz force in the leading edge (clockwize spin here, and ball iz rolling), would this "out of balance" force (torq) make the ball "turn" left a bit or would it tend to make it turn right?? Real question here. If the ball iz to look for my "equilibrium" (while slowing) then the ball here shood be looking to turn right???? Or, shood it??? Hmmm - still thinking. madMac. <hr /></blockquote>Mac, as you say, it should turn to the right with clockwise spin (english). Your premise is that the lateral friction force is greater on the trailing edge. It might not necessarily veer right if your premise was just that the net force acting normal to the surface on the trailing half (Nb) was larger. It might be that Nb is not seeing as much surface speed overall as Nf and that the coefficient of friction is accordingly reduced. (With a particular ball/cloth combination that was tested, an experiment found that mu tends to drop off at low surface speeds.) We don't have to worry about the torque here.

But of course I am worrying that you're seeing something I'm not. If so, send me a bottle of Red so that we can both take a look at it. /ccboard/images/graemlins/smile.gif

Jim

Jal
01-22-2008, 04:33 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>...Based on our conversations, I've been thinking some more about my TP B.2 analysis (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf), and I have some new ideas to try out. I'll let you know if they lead to any useful info. I agree with you that the current version of my analysis does have some holes (including masse spin, however slight it might be).<hr /></blockquote>Dr. Dave, I was worried that it might appear that I was ignoring some of things you pointed out to me. I'm relieved that you haven't taken any offense. Looking forward to the next round and whatever math might need to be absorbed to understand it.

You are very gracious and it is appreciated.

Jim

cushioncrawler
01-25-2008, 02:58 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>...Lets say that "the" plane of the spin axis (i know that there are an infinite number of theze spin axis planes but) iz "leaning backwards" a bit (ie nearly normal to the hill). Now, if the sidewayz force(s) in the trailing area of footprint iz larger than the sidewayz force in the leading edge (clockwize spin here, and ball iz rolling), would this "out of balance" force (torq) make the ball "turn" left a bit or would it tend to make it turn right?? Real question here. If the ball iz to look for my "equilibrium" (while slowing) then the ball here shood be looking to turn right???? Or, shood it??? Hmmm - still thinking. madMac. <hr /></blockquote>Mac, as you say, it should turn to the right with clockwise spin (english). Your premise is that the lateral friction force is greater on the trailing edge. It might not necessarily veer right if your premise was just that the net force acting normal to the surface on the trailing half (Nb) was larger. It might be that Nb is not seeing as much surface speed overall as Nf and that the coefficient of friction is accordingly reduced. (With a particular ball/cloth combination that was tested, an experiment found that mu tends to drop off at low surface speeds.) We don't have to worry about the torque here.

But of course I am worrying that you're seeing something I'm not. If so, send me a bottle of Red so that we can both take a look at it. Jim<hr /></blockquote>Jim -- I'm struggling a bit. My right hand rule sez that, due to the trailing force pushing the clockwize spinning ball to the right, the rezulting torq "turns" the rolling ball to the left. So, which one wins -- the "turn" or the "push". If the turn wins then my equilibrium karnt i think exist. Hmmmm.

Getting back to a microskopik look at the footprint. In the leading edge the ball brushes the (if any) nap to the right, then, when the trailing edge passes, it hazta brush "against" the nap, ie the mu here iz larger. But, larger or not, diss dont madder, the question iz -- which mu etc falls or rizes most az rolling falls to zero.

Likewize re the mu(s) falling with speed. It iz diffikult to see how this might come into all of this, ie whether it would favor the leading or trailing edge. madMac.

Jal
01-25-2008, 02:05 PM
Mac, with the latest version of FireFox and automatic spellchecking, there are all kinds of red lines under your text. I wonder why though, it all looks perfectly good to me.

<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I'm struggling a bit. My right hand rule sez that, due to the trailing force pushing the clockwize spinning ball to the right, the rezulting torq "turns" the rolling ball to the left. So, which one wins -- the "turn" or the "push". If the turn wins then my equilibrium karnt i think exist. Hmmmm.<hr /></blockquote>I don't know if this will help, but I think the short answer is that the torque doesn't affect its translational motion. It will only work to reduce/alter the spin.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Getting back to a microskopik look at the footprint. In the leading edge the ball brushes the (if any) nap to the right, then, when the trailing edge passes, it hazta brush "against" the nap, ie the mu here iz larger. But, larger or not, diss dont madder, the question iz -- which mu etc falls or rizes most az rolling falls to zero.<hr /></blockquote>We're kind of piling on assumptions and guesses as we go, but I would think that mu would diminish on the trailing edge and increase on the front edge. As some of the surface area granted to Nb (in the process of equalizing Nb and Nf during an earlier phase) is now taken away, Nb should also see less average surface speed, and that might (should?) mean a smaller mu. In other words, there might be two mechanisms at play that bring the lateral friction forces into balance. One is changing the relative surface areas alloted to Nb and Nf by the tilting of the vertical spin component at various angles, since it is the dividing line between front and back (by our definition). And concomitant with that, mu could be changed since they see more or less surface speed as the pole moves away from or approaches them. But I think the limb we're on is beginning to make some ominous noises.

Jim

cushioncrawler
01-26-2008, 07:44 PM
<blockquote><font class="small">Quote Jal:</font><hr>...I don't know if this will help, but I think the short answer is that the torque doesn't affect its translational motion. It will only work to reduce/alter the spin...

...We're kind of piling on assumptions and guesses as we go, but I would think that mu would diminish on the trailing edge and increase on the front edge. As some of the surface area granted to Nb (in the process of equalizing Nb and Nf during an earlier phase) is now taken away, Nb should also see less average surface speed, and that might (should?) mean a smaller mu. In other words, there might be two mechanisms at play that bring the lateral friction forces into balance. One is changing the relative surface areas alloted to Nb and Nf by the tilting of the vertical spin component at various angles, since it is the dividing line between front and back (by our definition). And concomitant with that, mu could be changed since they see more or less surface speed as the pole moves away from or approaches them. But I think the limb we're on is beginning to make some ominous noises....<hr /></blockquote>Jim -- I reckon that a torq (akting on the ball) will (allwayz) inkreec or dekreec the spin-rate, and, unless akting direktly in line with the spin-axis, will korze the axis to "turn" (ie swing around to a different angle). If the ball turns (faces) left (say) then this (the ball's roll) creates forces in the footprint pushing the ball to the left. Theze leftwardz forces tend to cancel the (say) rightwardz forces (in the trailing area). It all gets too diffikult to think about.

And, i reckon that if the Nb and Nf torqs were in balance (torqwize), then they wouldnt necessaryly be in balance forcewize, ie there might (would) be a sidewayz force nonetheless. And, a small sidewayz force would certainly korze the ball to veer. For instance, if u pushed lightly on the side of a brick it might not moov, but, if someone pushed (skidded) that brick forewards, that small side-push of yours would make the brick "track" on a small angle (az u of course know very well). For our ball, that small angle would of course bekum a kurve (whereaz the brick wouldnt kurv).

I might come across my old notes. If theze help solve my thinking etc, i will send a PM. madMac.

dr_dave
01-31-2008, 11:27 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>...Based on our conversations, I've been thinking some more about my TP B.2 analysis (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf), and I have some new ideas to try out. I'll let you know if they lead to any useful info. I agree with you that the current version of my analysis does have some holes (including masse spin, however slight it might be).<hr /></blockquote>Dr. Dave, I was worried that it might appear that I was ignoring some of things you pointed out to me. I'm relieved that you haven't taken any offense. Looking forward to the next round and whatever math might need to be absorbed to understand it.

You are very gracious and it is appreciated.<hr /></blockquote>Jim,

I finally found time to take another stab at the analysis and the justifications for my assumptions. I still think masse spin will not develop as the ball rolls with English, but I could be wrong. Take a look at the latest version (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf), and let me know what you think of my assumptions and new explanations. I've also included a look at what effect masse spin could have on the results.

Thanks again for your keen and discerning eye.

Regards,
Dave

Bambu
01-31-2008, 08:54 PM
As long as I am allowed to skip to the end, I am liking that conclusion very much. Awesome, thanks Dave!

dr_dave
02-01-2008, 10:26 AM
<blockquote><font class="small">Quote Bambu:</font><hr> As long as I am allowed to skip to the end, I am liking that conclusion very much. Awesome, thanks Dave! <hr /></blockquote>I'm glad you like it, but I think TP B.2 (http://billiards.colostate.edu/technical_proofs/new/TP_B-2.pdf) and NV B.7 (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm) support both sides of the argument. A ball rolling with sidespin goes straight for all practical purposes, and cloth irregularities can create a much bigger effect, especially at slow speeds. Sometimes the ball will go straight as it slows with right spin, sometimes it will curve right as it slows with right spin, and sometimes it will curve left as it slows with right spin. Having said that, the physics does seem to suggest that there might be a small tendency for the ball to curve in the spin direction (e.g., right curve for right spin), but due to the assumptions in the analysis and the results of the video demonstrations, the value of this information is questionable.

Regards,
Dave

Bob_Jewett
02-01-2008, 02:05 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... Having said that, the physics does seem to suggest that there might be a small tendency for the ball to curve in the spin direction (e.g., right curve for right spin), but due to the assumptions in the analysis and the results of the video demonstrations, the value of this information is questionable. ... <hr /></blockquote>
Some snooker books have sizable sections that discuss the various curves that you might see according to whether the ball is going with or against the nap, or has left or right spin against the nap, or is swerving, or is going quickly or slowly. Some of those books illustrate S-curves for some combination of spin, speed and elevation. That is for cloth with a strong, directional nap. In the old days, carom cloth also had nap, and the tables were said to have a "long" end and a "short" end according to the direction of the nap on the cloth.

I have never seen a convincing demonstration of such curving due to the nap. I suppose it's possible that I've seen curve caused by nap, but I have never seen it clearly distinguished from slate that was not level. Perhaps Max has a suitable experiment to suggest -- I have a napped 12x6 billiards table available.

dr_dave
02-01-2008, 02:17 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... Having said that, the physics does seem to suggest that there might be a small tendency for the ball to curve in the spin direction (e.g., right curve for right spin), but due to the assumptions in the analysis and the results of the video demonstrations, the value of this information is questionable. ... <hr /></blockquote>
Some snooker books have sizable sections that discuss the various curves that you might see according to whether the ball is going with or against the nap, or has left or right spin against the nap, or is swerving, or is going quickly or slowly. Some of those books illustrate S-curves for some combination of spin, speed and elevation. That is for cloth with a strong, directional nap. In the old days, carom cloth also had nap, and the tables were said to have a "long" end and a "short" end according to the direction of the nap on the cloth.<hr /></blockquote>I don't have much experience with napped cloths. My experiments, videos, analysis, and conclusions apply to a level and clean pool table with napless cloth.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>I have never seen a convincing demonstration of such curving due to the nap. I suppose it's possible that I've seen curve caused by nap, but I have never seen it clearly distinguished from slate that was not level. Perhaps Max has a suitable experiment to suggest -- I have a napped 12x6 billiards table available.<hr /></blockquote>I have also read many claims of significant "ball turn" on a napped cloth. Like you, I would also be curious to see a convincing demonstration. Maybe somebody can post or find some well-done YouTube videos for us.

Thanks,
Dave

Bambu
02-01-2008, 03:40 PM
I am in full agreement with that, Dave. If I implied it, I did not mean to say a ball with right spin ALWAYS curves right. I do realize the table can take over any shot, (especially at slow speeds)and I also agree that the effect is not very significant.
On a simonis cloth there will be less dimples, less table roll. That should result in a "truer" curve, in the direction of the spin(IMO).
You are graced with a much better way of explaining things than me, and I am thankful for that, as well as all the time you have spent on this.

bradb
02-03-2008, 10:49 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>I have never seen a convincing demonstration of such curving due to the nap. I suppose it's possible that I've seen curve caused by nap, but I have never seen it clearly distinguished from slate that was not level. /quote]




There are many demonstrations. One is the Dennis Taylor video that shows it clearly.

Place the Qball at one end of the table near a corner. Place another ball mid table with a third ball at the opposite corner directly in line behind it. Now shoot diagonally just past the mid ball with table length (or slightly more) roll.

Now go to the other end and shoot in the opposite direction. In Dennis's video (hopefully now its a CD) you can see the curve clearly. One way hits the far ball, the other rolls out.


-brad

/ccboard/images/graemlins/smile.gif

Bambu
02-04-2008, 11:35 AM
Thanks, Brad. I would love to see that taylor video myself. I searched, but came up empty. When you say many demonstrations I dont doubt you, but do you know of anything in particular??

bradb
02-04-2008, 12:31 PM
I have seen it in other snooker videos but Taylor's is the one that came to mind. It was years ago so it may be hard to find.

I did find these, I googled Dennis Taylor snooker, Master the game, and found a few new and used. -brad

dr_dave
02-04-2008, 02:03 PM
I've seen lots of instructional snooker stuff on Youtube, but nothing showing "ball turn." Has anybody seen this on Youtube? It would be nice to have something to link to that everybody can view and discuss.

Dave

<blockquote><font class="small">Quote bradb:</font><hr> I have seen it in other snooker videos but Taylor's is the one that came to mind. It was years ago so it may be hard to find.

I did find these, I googled Dennis Taylor snooker, Master the game, and found a few new and used. -brad <hr /></blockquote>

bradb
02-04-2008, 04:45 PM
I have seen nothing on youtube Dave. Its something that you would have to tract down by buying the old video and editing the section out.

If you can find a 12' 100% wool snooker table, you could probably make your own. -brad

cushioncrawler
02-11-2008, 05:54 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> I've seen lots of instructional snooker stuff on Youtube, but nothing showing "ball turn." Has anybody seen this on Youtube? It would be nice to have something to link to that everybody can view and discuss.
Dave<blockquote><font class="small">Quote bradb:</font><hr> I have seen it in other snooker videos but Taylor's is the one that came to mind. It was years ago so it may be hard to find. I did find these, I googled Dennis Taylor snooker, Master the game, and found a few new and used. -brad<hr /></blockquote><hr /></blockquote>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac.

dr_dave
02-11-2008, 10:55 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> I've seen lots of instructional snooker stuff on Youtube, but nothing showing "ball turn." Has anybody seen this on Youtube? It would be nice to have something to link to that everybody can view and discuss.
Dave<blockquote><font class="small">Quote bradb:</font><hr> I have seen it in other snooker videos but Taylor's is the one that came to mind. It was years ago so it may be hard to find. I did find these, I googled Dennis Taylor snooker, Master the game, and found a few new and used. -brad<hr /></blockquote><hr /></blockquote>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac. <hr /></blockquote>Mac,

Thanks for the offer, but I would prefer to see a convincing demonstration. To me, what would be convincing would be showing left sidespin, right sidespin, and no sidespin in both directions along the same line of a table, all at the same slow speed (6 shots total). Then the experiment could be repeated along different lines of the table, at different angles to the nap brush direction. If the turn (or lack thereof) is repeatable with multiple attempts of all 6 shots (along various lines), then I would be convinced. I've tried this on a few pool tables and I am not convinced "ball turn" is significant (or even existent) on a napless cloth.

I would do the demonstration myself, but I'm not aware of any directional-napped-cloth tables in my area.

Regards,
Dave

Bambu
02-11-2008, 06:29 PM
I would like to see them, mac. Thanks very much-

Bambu

dmanasseri@nyc.rr.com

cushioncrawler
02-11-2008, 07:05 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> I've seen lots of instructional snooker stuff on Youtube, but nothing showing "ball turn." Has anybody seen this on Youtube? It would be nice to have something to link to that everybody can view and discuss.
Dave<blockquote><font class="small">Quote bradb:</font><hr> I have seen it in other snooker videos but Taylor's is the one that came to mind. It was years ago so it may be hard to find. I did find these, I googled Dennis Taylor snooker, Master the game, and found a few new and used. -brad<hr /></blockquote><hr /></blockquote>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac. <hr /></blockquote>Mac,

Thanks for the offer, but I would prefer to see a convincing demonstration. To me, what would be convincing would be showing left sidespin, right sidespin, and no sidespin in both directions along the same line of a table, all at the same slow speed (6 shots total). Then the experiment could be repeated along different lines of the table, at different angles to the nap brush direction. If the turn (or lack thereof) is repeatable with multiple attempts of all 6 shots (along various lines), then I would be convinced. I've tried this on a few pool tables and I am not convinced "ball turn" is significant (or even existent) on a napless cloth.

I would do the demonstration myself, but I'm not aware of any directional-napped-cloth tables in my area. Regards,
Dave<hr /></blockquote>Dr Dave -- One uzually gets 3 balls of reverse kurv against the nap, and 2.5 balls of kurv with the nap (for spinning ball). And, i have seen cloths where one can get over 2 balls of kurv for a ball with zero spin, in some directions. madMac.

cushioncrawler
02-11-2008, 07:07 PM
<blockquote><font class="small">Quote Bambu:</font><hr> I would like to see them, mac. Thanks very much- Bambu
dmanasseri@nyc.rr.com<hr /></blockquote>Bambu -- I havta shoot throo, but will send some good stuff when i get back later today. madMac.

Bambu
02-12-2008, 11:46 AM
Dave, I agree that a demo would be better. But I am surprised that an open minded individual such as yourself, would not at least want to take a look at macs work.

dr_dave
02-12-2008, 12:05 PM
<blockquote><font class="small">Quote Bambu:</font><hr> Dave, I agree that a demo would be better. But I am surprised that an open minded individual such as yourself, would not at least want to take a look at macs work. <hr /></blockquote>I would be happy to look at his work if he wants me to, but I honestly don't have much interest in napped-cloth physics, because I've never played on napped cloths (that I can remember), and I probably never will. The only Snooker table I've ever played on had Simonis. Also, honestly, I'm a little tired of looking at "ball turn" physics. I spent far too much time on this topic already. Although, I would still be interested in seeing convincing napped-cloth ball-turn demos (just for fun and general interest).

Regards,
Dave

bradb
02-12-2008, 08:18 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Bambu:</font><hr> Dave, I agree that a demo would be better. But I am surprised that an open minded individual such as yourself, would not at least want to take a look at macs work. <hr /></blockquote>I would be happy to look at his work if he wants me to, but I honestly don't have much interest in napped-cloth physics, because I've never played on napped cloths (that I can remember), and I probably never will. The only Snooker table I've ever played on had Simonis. Also, honestly, I'm a little tired of looking at "ball turn" physics. I spent far too much time on this topic already. Although, I would still be interested in seeing convincing napped-cloth ball-turn demos (just for fun and general interest).

Regards,
Dave <hr /></blockquote>

Dave, are you sure you played on a snooker table with Simonis, I was told you can't put a shaved cloth on a snooker table. As far as I know all snooker tables (unless you were playing on a some sort of hybred) all use napped cloth. -brad

Bambu
02-12-2008, 08:29 PM
I hear you Dave. I am pretty "ball turned out" myself. And yeah, the nap puts an additional strain on things. I can only speculate, since I have never played snooker. But I would think there would be at least a small amount of common ground between the two, at least in one direction of the nap. Perhaps down the road sometime, you might want to have a look. Skimming through it, I get a strong impression that mac has spent quite a bit of time on this. Many Thanks-

Bambu

dr_dave
02-13-2008, 10:30 AM
<blockquote><font class="small">Quote bradb:</font><hr>Dave, are you sure you played on a snooker table with Simonis, I was told you can't put a shaved cloth on a snooker table. As far as I know all snooker tables (unless you were playing on a some sort of hybred) all use napped cloth.<hr /></blockquote>The person I played with said it was Simonis, but he could have been wrong. The cloth was certainly fast and seemed to play like Simonis. Maybe others with more US snooker experience can give us the scoop.

Regards,
Dave

dr_dave
02-13-2008, 10:35 AM
<blockquote><font class="small">Quote Bambu:</font><hr> I hear you Dave. I am pretty "ball turned out" myself. And yeah, the nap puts an additional strain on things. I can only speculate, since I have never played snooker. But I would think there would be at least a small amount of common ground between the two, at least in one direction of the nap. Perhaps down the road sometime, you might want to have a look. Skimming through it, I get a strong impression that mac has spent quite a bit of time on this.<hr /></blockquote>OK. You've convinced me to ask Mac for his stuff so I can have a look. However, I still want to see an actual and convincing demonstration. If these effects are important, there must be a demonstration available on YouTube somewhere. If not, somebody with a snooker table and digital camera (or camera phone or camcorder) can easily post one.

Regards,
Dave

dr_dave
02-13-2008, 10:38 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac. <hr /></blockquote>Mac,

Please e-mail me what you have (preferably in "The Queen's English"). I would like to have a look at it and maybe post it for you (if you are interested) so others can see and refer to it.

Thanks,
Dave

bradb
02-14-2008, 12:19 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> The person I played with said it was Simonis, but he could have been wrong. The cloth was certainly fast and seemed to play like Simonis. Maybe others with more US snooker experience can give us the scoop.
Regards,
Dave <hr /></blockquote>

My dealer (pool that is) told me that they can't put Simonis 860 on a snooker table because of the rounded pocket openings. Don't know if this is true but it makes sense. The shaved cloth really stretches as compared to the napped wool.

There is a mixture of wool and synthetic fiber for Snooker tables, maybe Simonis makes a Snooker cloth also. -brad

Bambu
02-14-2008, 05:12 PM
Thanks Dave. As my jewish great grandmother used to say, "vy not take a look, it vouldnt hoit."

cushioncrawler
02-15-2008, 02:01 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac.<hr /></blockquote>Mac, Please e-mail me what you have (preferably in "The Queen's English"). I would like to have a look at it and maybe post it for you (if you are interested) so others can see and refer to it. Thanks, Dave<hr /></blockquote>Dr Dave -- I have just sent u pdfs of 8 chapters from The Cushion Crawler'z Bible, which i put together about 3 or 4 yrs ago (and i have other similar stuff allso). Theze 8 chapters have my uzual miss-spelling, but i can email the Word verzions if ever u want to upgrade the spelling for posting (posting would be good). Az uzual, all of my stuff iz free to anyone to uze etc any old way they want. I would be pleezed to get feedback re any of my ideas. Some of this stuff woz rushed, and i have now changed my mind in places (having now learnt from your articles), hencely bits might need a re-write. madMac.

dr_dave
02-15-2008, 10:11 AM
<blockquote><font class="small">Quote Bambu:</font><hr> Thanks Dave. As my jewish great grandmother used to say, "vy not take a look, it vouldnt hoit."<hr /></blockquote>But ... if we spend too much time looking under every pebble, we might not have time to see the mountain. /ccboard/images/graemlins/tongue.gif

I just made that up, but I'm sure it must have been said by some grandmother (or martial arts instructor) before. /ccboard/images/graemlins/wink.gif

Regards,
Dave

dr_dave
02-15-2008, 10:52 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I suspekt that i am the world authority on SpinKurv and NapDrift on a woollen (direktional) napped cloth. I have identyfyd at least 12 reasons (effekts) (forces) that contribute. I have written a few articles on this. I can email this stuff to anyone interested. madMac.<hr /></blockquote>Mac, Please e-mail me what you have (preferably in "The Queen's English"). I would like to have a look at it and maybe post it for you (if you are interested) so others can see and refer to it. Thanks, Dave<hr /></blockquote>Dr Dave -- I have just sent u pdfs of 8 chapters from The Cushion Crawler'z Bible, which i put together about 3 or 4 yrs ago (and i have other similar stuff allso). Theze 8 chapters have my uzual miss-spelling, but i can email the Word verzions if ever u want to upgrade the spelling for posting (posting would be good). Az uzual, all of my stuff iz free to anyone to uze etc any old way they want. I would be pleezed to get feedback re any of my ideas. Some of this stuff woz rushed, and i have now changed my mind in places (having now learnt from your articles), hencely bits might need a re-write. madMac.<hr /></blockquote>Thanks Mac. I look forward to looking through your stuff (despite the lack of "Queen's English"). I've posted your "DriftKurv" chapter under "general interest articles" in the physics resources page of my website (http://billiards.colostate.edu/physics/index.html). The direct link to your article is:

billiards.colostate.edu/physics/mac_drift_curve_chapter.pdf (http://billiards.colostate.edu/physics/mac_drift_curve_chapter.pdf)

Thanks again for being willing to share your stuff. I'll let you know if I have any feedback; although, I don't have any experience with napped woolen cloths.

Regards,
Dave

Bob_Jewett
02-15-2008, 06:21 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... The direct link to your article is:... <hr /></blockquote>
I'm afraid that my early schooling has not enabled me to read the article. If anyone has been able to read it, is an actual test described, or is this just hypothesizing? I have four snooker tables with napped cloth available for tests.

Note that it is necessary to distinguish between nap-induced curve and a non-level table. If the test cannot do that, it is not worth attempting.

dr_dave
02-15-2008, 07:21 PM
I also wish Mac would use "English" (or "American") and have more scientific rigor, but I thought his write-up was interesting anyway.

Regards,
Dave

<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... The direct link to your article is:... <hr /></blockquote>
I'm afraid that my early schooling has not enabled me to read the article. If anyone has been able to read it, is an actual test described, or is this just hypothesizing? I have four snooker tables with napped cloth available for tests.

Note that it is necessary to distinguish between nap-induced curve and a non-level table. If the test cannot do that, it is not worth attempting. <hr /></blockquote>

Bob_Jewett
02-15-2008, 07:43 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... I thought his write-up was interesting anyway.... <hr /></blockquote>
Was any practical test for nap-induced curve described in it?

cushioncrawler
02-16-2008, 02:31 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... I thought his write-up was interesting anyway.... <hr /></blockquote>Was any practical test for nap-induced curve described in it?<hr /></blockquote>Bob -- Az luck would have it, the two 12' tables that i did the kurv tests on were each the worst tables in the house. One, at Frankston RSL Club, woz Alcock No 550 or thereabouts, made in perhaps 1864, which means that the (4) slates in 1989 were no longer flat -- certainly it had bad rolls, but mainly along near the cushionz, which my tests kept away from anyhow. And, the No2 (12') table at Cheltenham Club, on which i did some of the tests, woznt very old, but i have since found that this table too iz the worst in the house, for bad rolls, but once again mainly near the cushions, which my tests kept away from anyhow.

My own personal (home) table iz Alcock No 981, made in perhaps 1870 (which i bort 4 years ago), and i notice that the original slates have been replaced by new (flatter??) slates, probably from a table made in perhaps say 1905.

Bob -- Regarding my methodology, i recall that i uzed finger spin for the SpinKurv tests, uzing a wooden "straight edge" to give accurate initial alignment (trajektory). For the DriftKurv tests (zero spin here), i think i uzed one of my ball-ramps.

For the "Janus Cloth" tests, i think i rolled (with finger spin) a ball along the top of a cotton (no nap) table protector. madMac.

dr_dave
02-16-2008, 09:24 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... I thought his write-up was interesting anyway.... <hr /></blockquote>
Was any practical test for nap-induced curve described in it? <hr /></blockquote>Like you, I will remain skeptical until I see a convincing video demonstration (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=275251&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1).

Regards,
Dave

Bambu
02-17-2008, 08:00 AM
I suppose that for every great proverb, there is also an an equal, opposite reaction.
Tell me Dave, if I had a video of shot #1, (which was only accepted as a "proposition shot") would you consider that a "convincing demonstration?"

dr_dave
02-17-2008, 09:22 AM
<blockquote><font class="small">Quote Bambu:</font><hr>Tell me Dave, if I had a video of shot #1, (which was only accepted as a "proposition shot") would you consider that a "convincing demonstration?"<hr /></blockquote>... I don't think so. There are too many ways to cheat that shot (intentionally or not), and a video probably wouldn't be convincing. Please don't start the debate on that shot again. This was already beaten to death in the previous thread.

I described what I think would be a convincing demonstration here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=275251&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). Also, I would prefer to see this on a pool table with standard (napless) cloth.

Regards,
Dave

Bambu
02-17-2008, 01:43 PM
With all due respect, Dave, if you didnt think the effect was real: Why would you coin a phrase like "ball turn" and take the time to create a proof on it?

dr_dave
02-18-2008, 10:19 AM
<blockquote><font class="small">Quote Bambu:</font><hr> With all due respect, Dave, if you didnt think the effect was real: Why would you coin a phrase like "ball turn" and take the time to create a proof on it? <hr /></blockquote>Honestly, when I started the analysis, I thought the effect was too small to be useful, but I still wanted to see whether or not the physics would suggest a possible explanation. I had to make several assumptions in the analysis (which might not be perfectly sound), but I think the results are in line with observations. I coined the term "ball turn" to distinguish it from "squirt," "swerve," and "throw." These are all different effects, with "ball turn" being the smallest and least predictable.

Regards,
Dave

Bambu
02-19-2008, 08:35 PM
Because you said you remain skeptical,(and wanted a demo) I just wasnt sure you believed the effect was genuine. Thanks for clearing that up for me, Dave.