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Billy_Bob
01-13-2006, 12:45 PM
Where *exactly* will the cue ball go after various shots?

I'm getting to be fairly good at figuring out where the cue ball will go after various shots, that is the "general direction" the cue ball will go.

But I need to know how to tell *exactly* where the cue ball will go after various shots if possible.

I don't know how to look at a shot and figure out, say where the cue ball will hit the object ball, then where it will hit the cushion *exactly*, then where it will go from there *exactly*. (Especially with cut shots where the object ball is varying short distances from the cushion - an inch further out from the cushion changes things a lot!)

So say I have a cut shot, then want the cue ball to come off the cushion after the shot and roll between two balls rather than hitting one of them. Right now I might hit either ball or maybe the cue ball will roll between them. I can't tell *exactly* where it will go.

So what is the best way to go about learning this? Or is this just an experience thing?

Cane
01-13-2006, 01:47 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Where *exactly* will the cue ball go after various shots?<hr /></blockquote>

To be frank, while the physics are there to "estimate" cue ball path, it's just not an exact science. There are too many variables from table to table, and even from one part of the table to the other, and then you throw in cushions...

A good example would be a discussion we had recently (don't know if it was here or AZB) where I said the Tangent line was 90° and Fred, rightfully, pointed out that while it was theoritically 90° that it was actually approx 86°. Now, get on a different table, with a different cue ball and it might be more or less than that, depending on any of a number of factors, including CB and OB mass, condition of cloth, kind of cloth, etc. Then there are the cushions... what kind are they, how old are they, what kind of profile are they, were they installed properly, too high, too low, different cloth tension on different sections of the same table, etc, etc, etc.

What I'm saying is that you can get a very good approximation of CB path, but I don't know anyone that can EXACTLY predict it every time. I wish I could... that would mean I'd always play absolutely perfect position and I'd never miss my shots. While there are some great players out there that can get the cue ball, on the average, VERY close to where they want it most of the time, there is nobody that knows EXACTLY where the CB is going every time... not Bustamante, not Reyes, no Archer, not Owen, NOBODY. If they did, they'd never miss because they'd NEVER be out of line.

All you can do is to gain ACCURATE knowledge, whether it's taught to you, or learned through experience (what I call "walking 5000 miles around the table"), to more accurately approximate CB paths, especially if you're going to a cushsion after a shot. The game is usually won by the player that can approximate those paths most consistently.

Later,
Bob

Bumps
01-13-2006, 02:10 PM
I pretty much agree with Cane, would add that your stroke has a lot to do with it. Developing a consistant stroke is something we all strive for but few, if any, will achieve one. if your stroke is a bit too hard, not enough follow through, hit on the cue ball is off a hair, etc. AWFUL lot of variables in anyone's stroke, even the pros' to calculate that accurately.

Jal
01-13-2006, 03:45 PM
<blockquote><font class="small">Quote Cane:</font><hr>...A good example would be a discussion we had recently (don't know if it was here or AZB) where I said the Tangent line was 90° and Fred, rightfully, pointed out that while it was theoritically 90° that it was actually approx 86°. Now, get on a different table, with a different cue ball and it might be more or less than that, depending on any of a number of factors, including CB and OB mass, condition of cloth, kind of cloth, etc.... <hr /></blockquote>I think your assessment of the overall difficulty of making precise predictions is right on the mark, but a small point with regard to this 86 degree thing. I believe it's far more variable than your statement might indicate, even for the same balls, same table, etc., although it's not too bad an average. Throw and cut angle alter it considerably. And I don't think that cloth conditions affect it any noticeable way.

Jim

randyg
01-13-2006, 04:21 PM
We can only control three things in pool, Angle-Speed-Spin.

Everything else is a condition that we have to deal with. If we cover our A.S.S. we can control our cueball on every shot....SPF-randyg

SpiderMan
01-13-2006, 04:22 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Where *exactly* will the cue ball go after various shots?<hr /></blockquote>

Always where we send it, not always where we wish it.

SpiderMan

Cane
01-13-2006, 04:37 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> Always where we send it, not always where we wish it.

SpiderMan <hr /></blockquote>

Marty, there was an older gentleman that used to hang out in my pool room every day and just watch the players. One day, I made a shot and tried to get in a little position window and missed the position. I jumped back and said "Dammit Whitey, that wasn't what I wanted you to do!". Mr Moore, jumped out of his chair, got behind me and said "Bob, it must be what you wanted, because you put it there! Ole whitey won't go where you don't make it roll." Like you said... not always where we wish it... /ccboard/images/graemlins/smile.gif

Later,
Bob

Scott Lee
01-13-2006, 07:03 PM
<blockquote><font class="small">Quote randyg:</font><hr> We can only control three things in pool, Angle-Speed-Spin.<hr /></blockquote>

Randy...I thought the only WE can control...is the cuestick! LOL You use the cuestick to control A.S.S.! /ccboard/images/graemlins/grin.gif

Scott

Billy_Bob
01-14-2006, 11:45 AM
That is kind of what I thought.

I guess this will be a "do-it-yourself" thing then. I suppose I can set up various shots near the cushion, then try to figure out in advance where the cue ball will hit the cushion exactly, maybe mark the spot in advance.

Then see how well I do each time. When I am off on my "guessing", figure out what happened and why, etc.

Then when I get good at predicting this, figure out where cue ball will go from there. Maybe draw line on table in advance of shot. Then see how well my "psychic" abilities are!

I know from practicing certain shots that I get better at them. And this is because I only shoot those shots and pay 100% attention to those specific shots for a few months.

So I suppose I can do the same with position play. But as I have learned with some impossible shots, they are low percentage. So if nothing else, I will learn which position shots are low percentage (in your dreams), and which are high percentage - easy. Then if given a choice in the future, go for the sure thing.

Make any sense? Suggestions?

pooltchr
01-14-2006, 12:32 PM
Bob,
The 8 balls on the rail tangent line drill in the expert class.....you know you can predict the path of the cue ball...I've seen you do it!
Steve

Billy_Bob
01-14-2006, 12:54 PM
Well I know the human brain is an amazing thing. When I was in college, I worked at a picture framing store. The picture frames would have dings and cuts in them and they needed to be touched up with paint. Well I did this, but the boss pointed out to me that my touch up colors did not match. They looked like they matched to me...

Anyway after doing this for a year, my "sense of color" became highly developed. I got to be quite good at matching colors exactly. So it was something which can be developed and learned.

And same thing with pool. I play with a guy who is a surveyer during the day. I would imagine that he uses angles and so forth constantly for his work. Well he is quite good at prediciting where the cue ball will go.

So I think this is something which can be developed. Just need to find the right drills/exercises which will help to develop this skill is all.

Maybe set up exact shot and draw line where cue ball goes after hit. Then get cue ball to go 1mm to left side of line, then 1mm to right side of line, right on line, 1/2 inch to left, 1/2 inch to right, etc. - Just burn it into my brain...

RonMont
01-14-2006, 01:04 PM
Start by using a center ball hit more often. In fact, practice a stop shot until you can stop the cue ball without any movement. I know this sounds basic but the problem is a basic one. The natural tangent angle that the cue ball takes after hitting a ball only occurs with a center ball hit. Many players cheat themselves by using spin on every shot and as a result never see the correct (natural) deflection path.
Be very deliberate with your stroke, the cue ball should slide to the contact point. If it picks up follow the angle off the object ball will not be correct. Of course in normal play any shot more than few inches will have follow on it but slide the cue ball in practice and get used to seeing the natural path. I think you will then become able to predict the angle with draw or follow.

Billy_Bob
01-14-2006, 10:45 PM
Update on my little experiment...

This morning, I set an object ball about 1/2 inch off the cushion and near a corner pocket and placed a "3 ring binder - hole reinforcement sticker" there to mark the exact spot, same with cue ball.

Then I first shot the same shot many times to be sure I could get the cue ball to come off the rail at the same angle each time. Then with chalk, I marked the line where the cue ball was going each time.

Then I hit the CB about 1 mm to right of center, and darned if I did not get the CB to come back about 2 mm to one side of the line. I never realized how critical a center hit was and how just a tad (1 mm) off center can impart a little spin.

So anyway it is possible to get the cb to come off a hit with very slight differences. Anyway I kept playing with this...

*But* the difference with this practice was that I was concentrating and looking at where the CB went *exactly*, not on making the object ball.

Anyway tonight when I was playing, similar shots came up. And I knew exactly where the CB would go with a center hit. I did not know where it would go with various tips of english, but I had that center hit ingrained into my head. And as it turned out, that was where I needed the CB to be each time tonight. So then I just needed to use the correct speed was all.

Anyway I think this system will work (To help me learn better where the CB will go exactly). There are of course too many zillions of different shots to practice them all. But I think I can remember a particular shot I have trouble with on a particular night, diagram it, then practice that specific shot for an hour or so.

Sort of like if you miss a shot, shoot the same exact shot 100 times. Same thing, except this would be setting up the same shot, but paying attention to where the cue ball goes after the shot instead of where the object ball goes. Then trying different english, follow, stun, draw.

Maybe over time (like a year) I will learn many common shots.

Scott Lee
01-15-2006, 12:13 PM
Billy_Bob...Sidespin (english) has NO effect on directional path of the CB (tangent line), after collison with the OB, unless top or bottom are added. While you may have thought you hit horizontal center, and 1mm off-center...if the CB came back off the tangent line, you were adding unintentional topspin or draw. You're correct in your assumption that even 1mm above or below true center, will cause the CB to deviate a little.
Right or left spin alone will not...

Scott Lee

Billy_Bob
01-15-2006, 12:18 PM
The shot I was shooting, the CB hit the OB, then the cushion, then came back. So the different direction(s) was caused by spin on the CB and its hitting the cushion.

Scott Lee
01-15-2006, 12:24 PM
My mistake...hitting the cushion would definitely have an effect on the path of the CB. /ccboard/images/graemlins/blush.gif

Scott Lee

Billy_Bob
01-15-2006, 12:36 PM
Below is the practice shot I was shooting.

The specific shot does not matter so far as learning exact position. I was just using this for testing. There are zillions of of different shots which could be set up of course.

Anyway when shooting the following shot with center, the CB would go to A. If using just a tad of left english (like 1 mm), the CB would come back to B. And right, C. So I was amazed at how you could use just a little english and get the CB to diviate just a little. Of course using 2 tips of right/left english would make it deviate quite radically.

http://endeavor.med.nyu.edu/%7Ewei/pool/pooltable2.html

START(
%AF9D5%PN8O6%QH1X0%RG4Y9%SH8Y9%WH3E0%XN3N8%]I1Z1%^H7C4

)END

RonMont
01-15-2006, 03:30 PM
Sounds like you are learning fast. I would like to add a couple of points. Keep in mind that hitting off center will cause deflection. Sometimes this can cause you to under hit the object ball reducing the apparent angle of the cue ball after it hits the object ball. Deflection and spin cause opposite effects. If your spin contains below/above center left or right hit the cue ball can curve opposite to the direction caused by deflection. It is possible with say, high left spin to see the cue ball to curve to the left of a center hit. With a more firm stroke deflection can cause it to veer to the right. And yes, just the right touch can cause one to cancel the other! Have fun, Ron

Billy_Bob
01-15-2006, 09:07 PM
So far as using english and cue ball deflection goes, I fixed that a long time ago. I use a Predator 314 shaft and apply english using the "pivot point" for my cue, so I can shoot a long shot using english and the cue ball will go to the same spot as a center ball hit.

Of course I can't shoot a cut shot when using english, aiming the same as I would with a center hit. The spinning cue ball will change where the object ball goes.

But the bottom line is that I have been able to use english for quite some time now and make my shots. And I have been able to get the cue ball to go the "general direction" I want after a hit.

And I'm beginning to be able to break out clusters with the cue ball after a shot. Maybe 25% of the time. (Miss breakouts the other 75% of the time, but getting better.)

My problem now is determining in advance *exactly* where the cue ball will go before I shoot. I can make the object ball go exactly where I want, but there might be a few inches this way or that where the cue ball goes.

So my project for now is to "try" to see if I can get more accurate on *predicting* in advance exactly where the cue ball will go.

If I can have some method of determining this, and say I wanted to break up a cluster and the CB will be a little off, then I could apply a tad left english or a tad right english (if cb was coming off cushion) and get it to hit the target instead of missing.

Fran Crimi
01-16-2006, 10:30 AM
I can't tell you how to learn where the cb will go because it's about forming associations between observation, assessment and then feel. We all approach it differently. Your friend, who you say can predict the path of the cb well, has probably been able to make those associations within himself.

However, I can tell you that the end result is always going to be your performance. And performance is feel. What's different about different people is that some can do a quick observation and then shift straight to feel. Others need to spend more time in consciously assessing their observation before they can make an association with feel.

The 'natural' or prodigy, looks at a shot and then makes an immediate association with feel.

I think we all have the ability to feel things quicker than we do if we would trust ourselves enough to allow that to happen.

Fran

Drop1
01-17-2006, 12:23 PM
Try playing some 3cushion billards,or what they call carombola where I live. Its a whole new world when it comes to ball control. I don't know how close you are to a 10' table. The other thing I do is cut 2" disks from the plastic used to cover coffee cans,and try to place the cue ball 1" from the disk. I might have as many as seven disks on the table at any one time.

Billy_Bob
01-17-2006, 12:58 PM
Actually I have been playing a modified old english billiards game which uses 3 balls. I got to be quite good at this, but no one will play with me anymore. Here are my modified rules...

Modified Old English Billiard Rules

Balls: Play with 3 balls; yellow ball, red ball, and cue ball.

Baulk-line and Baulk
A straight line drawn along the "head string" (end where break from - 2nd diamond) and is called the Baulk-line, and that line and the intervening space is termed the Baulk.

The "D": The "D" is a semi-circle described in Baulk with its center at the middle of the Baulk-line and with a radius of 11½in.

Spots: Three spots are marked on the center long line of the table:

-The foot spot (where 1 ball is placed for 9-ball rack).
-Center of table
-The middle of the of head string (middle of baulk-line).

Game
A game is the period of play from the opening stroke, until it is completed, by reaching the end of a specified period of time or either player reaching the number of points specified.

Cue Balls
The white ball is the cue ball of one player.
The yellow ball is the cue ball of the other player
The balls other than your cue ball are object balls.

Play
The choice of cue ball and which side is to play first shall be decided by lagging or a coin flip.

The red is placed on the spot other players cue ball on the center spot. The first player plays from in-hand (inside "D").

The players play alternately, or in turn, unless a score is made, in which case the striker continues the playing

Cue ball in-hand: The cue-ball must be struck from within the lines of the "D", and the cue-ball must be played out of Baulk.

The cue-ball must contact a cushion or ball out of Baulk before re-entering and coming to rest in Baulk, or before hitting a ball in Baulk.

The cue-ball may be played against a cushion in Baulk before hitting a ball out of Baulk.

Spotting Object Balls: Balls shall be placed on the spot closest to the ball return unless that spot is occupied in which case the next spot should be used.

Scoring: Points are made by pocketing any ball or by caroms - singly or in combination.

A carom or pocketed cue ball - 2 points.
Pocketed red - 3 points
Carom and pocketed white - 4 points.
Carom and pocketed red - 5 points.

Drop1
01-17-2006, 01:20 PM
Carombola rules, Each play has a white ball,and there is a red ball that belongs to no one. The object is to hit three rail,and a white ball,and then the red ball. It can be any combination,as long as your ball hits three rails before hitting the second ball. Look at Three cushion billard rules, you will get a better understanding. It is really helping my game. I still can't draw,and it is possible to rumble the felt trying, however it didn't tear. /ccboard/images/graemlins/blush.gif

Billy_Bob
01-17-2006, 01:46 PM
<blockquote><font class="small">Quote Drop1:</font><hr>...I still can't draw,and it is possible to rumble the felt trying, however it didn't tear. /ccboard/images/graemlins/blush.gif <hr /></blockquote>

Thanks for the 3 rail info.

You still can't draw? What happens when you draw using a striped ball as the cue ball? Does it spin backwards at first? (Note it took me at least a year of practicing draw shots to get half way decent.)

And what is the condition of the balls? Hopefully not an oversized coin-op ball which is larger than the object balls. A cue ball which has a dull finish and is pitted from years of flying on the floor can be quite difficult to draw as well.

Drop1
01-17-2006, 06:29 PM
These are Bucket of Blood pool halls,in the heart of one of the worst areas of Guadalajara,not for tourist. The balls are as you described,and the tables are warped. I go in the morning,never at night. The thing is, I was drawing pretty good last week:going back tomorrow,and work on the draw a little more. I'm looking at videos of draw shots,and I don't see a common thread among the people I'm watching. It has to be in my stroke.

vaillancourtroch
01-17-2006, 07:04 PM
Scott Lee Wrote:

"Billy_Bob...Sidespin (english) has NO effect on directional path of the CB (tangent line), after collison with the OB, unless top or bottom are added."


English does effect the trajectory of the CB after hitting the OB. But it is usually negligible.

pooltchr
01-17-2006, 07:36 PM
<blockquote><font class="small">Quote vaillancourtroch:</font><hr> Scott Lee Wrote:

"Billy_Bob...Sidespin (english) has NO effect on directional path of the CB (tangent line), after collison with the OB, unless top or bottom are added."


English does effect the trajectory of the CB after hitting the OB. But it is usually negligible. <hr /></blockquote>

Possibly with minute unintended top or bottom spin. Otherwise, I have to agree with Scott. With pure sidespin, the CB will take the 90 degree path while spinning like a top. Try shooting straight into an object ball using just side spin. With no forward or backward roll, the cue ball will stop dead and just spin and spin.
Side spin only has an impact when a ball hits a rail...not when it hits another ball.
Steve
Steve

Billy_Bob
01-18-2006, 01:00 PM
<blockquote><font class="small">Quote Drop1:</font><hr> These are Bucket of Blood pool halls,in the heart of one of the worst areas of Guadalajara,not for tourist. The balls are as you described,and the tables are warped...<hr /></blockquote>

Well I would not suggest learning how to draw with old dull looking pitted all over balls. And if the cue ball is oversized, it is not going to draw well.

I would suggest getting your own cue ball. A new cue ball will make a world of difference. If these are coin-op tables with a magnetic cue ball, get an Arimith tournament magnetic cue ball. Or otherwise an Arimith "measles" cue ball with the red dots on it. Then you can see the spin when the cue ball is at the far end of the table.

I'm pretty good at drawing. But I have run across some really nasty looking cue balls which don't draw well at all. And it is not just me. I have put two cue balls side by side, and have had several players draw both. All players had trouble drawing the nasty cue ball, but could draw the new cue ball quite well.

I think it is something to do with all the little pitts on the cue ball instead of it having a smooth surface. And an oversized cue ball is heavier and very hard to draw.

Anyway get various cue ball here...
http://www.poolndarts.com/index.cfm/fuseaction/Catalog.Category/categoryID/80.cfm?CFID=1550405&amp;CFTOKEN=1de306337e6f2c10-4D7739B0-D61C-4F06-BC47C3401E62078D

Drop1
01-18-2006, 02:05 PM
I like the idea of the spotted cue ball. The cue is a Tad one of two I have had for twenty years. I think its the pitted balls, and my inconsistant stroke. Sheldon Lebow is going to be making my next cue. I think we will start end of March.

vaillancourtroch
01-18-2006, 05:26 PM
Quote from pooltchr:

"I have to agree with Scott. With pure sidespin, the CB will take the 90 degree path while spinning like a top."

Sorry. After some thought, I do realize I was wrong. The friction force would be along the tangent therefore it cannot alter the trajectory of the CB.

Although your example of a straight on shot is the only shot where it should theoretically be possible to see a slight drifting of the CB after contact due to sidespin/friction force. I hope I don't have to appoligize later for this one. I believe I have seen this happen. Although it would be hard to tell if the CB movement is due to friction or if it was not dead straight.

cushioncrawler
01-19-2006, 05:49 AM
Further to komments from Vaillancourtroch &amp; Pooltchr &amp; RonMart &amp; Scott Lee -- i might add a few thorts.

.......A stunned qball followz throo at below 2% of its impakt speed at low speed impakts -- &amp; abov 4% of its impakt speed at very hi speed impakts -- for full-ball impakts. In other wordz e goze from say 0.94 to 0.89 here.

.......If friktion kan throw the objekt ball between say 3dg left &amp; 3dg ryht -- then friktion kan make a difference of 6dg in the objekt ball'z trajektory.

.......The 90dg rule sez that the (split) angle between the qball'z trajektory &amp; the objekt ball'z trajektory iz nearnuff 90dg.
.......But my kalkulationz &amp; mezurements indikate that the split iz 00dg for a full-ball kontakt, 88.0dg for a halfball kontakt, &amp; 89.3dg for an eighth kontakt. This iz for zero friktion, ie zero throw (eg if the qball haz a little bit of running side, ie korresponding rotation). Stunned qball here --- &amp; medium speed impakt.
.......For zero sidespin on the qball, the abov figurez bekum -- 00dg, &amp; 84.3dg, &amp; 84.6dg. (Friktion exists here for thin kontakts -- reducing to zero for fullball kontakts).
.......I havnt dunn the kalkulationz, but for check side the abov figurez might bekum 50dg, &amp; 84.3dg, &amp; 84.6dg.
.......I havnt dunn the kalkulationz (yet), but if the qball haz running side to spare, the abov figurez might bekum -- 50dg, &amp; 88dg, &amp; 92dg. (Beleev it or not).

.......If the split for zero friktion were 90dg, then running side kood make it 93dg, &amp; check side kood make it 87dg -- by virtue of the difference in the objekt ball'z angle. This kontradikts what haz been sed by otherz -- mainly koz otherz forgot about the objektball'z throw.
.......Otherz were of kourse talking about the qball'z angle only, when they sed that running &amp; check dont affekt the angle -- they werent talking about the split. But here again, otherz were wrong.
.......Az the split iz less than 90dg, then running inkreecez the split (a little), &amp; check dekreecez the split (a lot) -- here i am now talking about a halfball kontakt, &amp; stun.
.......The komponent of the qball'z speed along the initial ball-to-ball kontakt line dependz on e only.
.......The sidewayz komponent (V) iz modyfyd by friktion (v) -- hence the angle iz modyfyd allso. V-v iz a bigger modyfykation than V+v, hence check side haz a bigger effekt than running.
.......Aktually, i am now pretty sure that i did do the aforementioned kalkulationz -- but i karnt find them -- I'll do them again one day.

vaillancourtroch
01-19-2006, 05:15 PM
The proof from Dr. Dave @ 30dg impact angle:

http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf


The 90 degree rule is more like 86.7 degree (theta +theta1).

It would appear that with left or right english, theta1 would become smaller or bigger, due to the friction force component in the normal direction. I would expect this change to be small.

cushioncrawler
01-20-2006, 05:44 AM
G'day vaillancourtroch...
.......U were right when u sed that the qball'z angle woznt much affekted by check nor running -- i kalkulate that check takes 0.22dg off the angle, &amp; running addz only 0.18dg -- a total of only 0.40dg -- much less than i thort.

.......Thanks for the info re Dr Dave'z stuff. I see that Dr Dave kalkulates that a typikal split iz 83.259dg -- my kalkulationz giv 84.19dg -- mine (&amp; i assume Dr Dave'z) are for pure stun -- i uze a smaller e, but a larger friktion %. So far so good.

.......For zero friktion my split iz 88.53dg.

.......When i rekrunch the numberz for check side i get 84.19dg again (no surprize here).

.......When i rekrunch for running side i get 93.68dg -- i woz expekting say 92dg. My first worry iz whether it iz possible to put enuff running side on the qball to liv up to the theory -- i think it iz, at least it iz for a halfball kontakt. I reckon that this stuff will not go unchallenged.

.......The difference tween check &amp; zero friktion iz 4.34dg. The difference tween zero &amp; running iz 5.15dg. Total diff iz 9.49dg.
.......Here i woz surprized that running woz so powerfull -- but this woz partly koz i inklood flatspot sqeez in my kalkulationz, this makes a difference of 0.61dg in favor of running, not much, so i am a bit puzzled (i hope i havnt goofed somwhere here).

dr_dave
01-20-2006, 09:21 AM
FYI to all,

In my February-June, 2005 instructional articles (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html), I explain and illustrate the finer points of the 90 and 30 degree rules (e.g., when and why they apply and when they don't, and by how much).

Regards,
Dave

<blockquote><font class="small">Quote vaillancourtroch:</font><hr> The proof from Dr. Dave @ 30dg impact angle:

http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf


The 90 degree rule is more like 86.7 degree (theta +theta1).

It would appear that with left or right english, theta1 would become smaller or bigger, due to the friction force component in the normal direction. I would expect this change to be small.<hr /></blockquote>

vaillancourtroch
01-20-2006, 02:41 PM
Dr Dave,

I don't believe you have a proof of the above calculation on your website? I, and probably others, would be interested to see the theoretical effect of english on the 86.7 degree angle.

Should one consider this effect in the game? If cushioncrawler's calculation are correct, probably not.

Also, how can one obtain properties of the billard ball (coefficient of restitution and friciton)?

dr_dave
01-20-2006, 03:16 PM
<blockquote><font class="small">Quote vaillancourtroch:</font><hr>I don't believe you have a proof of the above calculation on your website? I, and probably others, would be interested to see the theoretical effect of english on the 86.7 degree angle.<hr /></blockquote>

Diagram 1 in my April '05 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/april05.pdf) illustrates the effects of inelasticity (i.e., the coefficient of restitution) and ball friction (i.e., throw) on the 90 degree rule. TP A.5 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf) shows the detailed analysis along with example numbers.

Diagram 1 in my May '05 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/may05.pdf) shows the effects of English. The details for that are in TP A.7 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-7.pdf).

I illustrate the effects on both the cue ball and object ball for all cases. If you have a specific question that you think is still unresolved, let me know.

Only inelasticity affects the cue ball direction. Friction, from collision-induced throw and/or English, theoretically (and I think practically) has no affect on the cue ball direction for a stun shot (for which the 90 degree rule applies).

Regards,
Dave

dr_dave
01-20-2006, 03:24 PM
<blockquote><font class="small">Quote vaillancourtroch:</font><hr>I, and probably others, would be interested to see the theoretical effect of english on the 86.7 degree angle.

Should one consider this effect in the game? If cushioncrawler's calculation are correct, probably not.<hr /></blockquote>
Well, the 90 degree rule is used mostly to predict the cue ball direction for a stun shot. Since English and throw don't affect the cue ball direction, the effects don't need to be considered when applying the 90 degree rule.

Now, object ball throw is a whole separate issue. For everything you ever wanted to know about throw (for all types of shots), see TP A.14 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-14.pdf) and the links under "throw" in the threads summary area of my website (http://www.engr.colostate.edu/~dga/pool/threads.html).

I hope this answers your question. If not, let me know.

Regards,
Dave

dr_dave
01-20-2006, 03:38 PM
<blockquote><font class="small">Quote vaillancourtroch:</font><hr>how can one obtain properties of the billard ball (coefficient of restitution and friciton)? <hr /></blockquote>
Here are some example property values from various sources and from basic experiments I've done:

coefficient of restitution (inelasticity): 0.90 to 0.94

coefficient of sliding friction between balls and table cloth: 0.15 to 0.3

coefficient of friction between balls: 0.01 to 0.15 (but highly dependant on shot speed)

coefficient of friction between cue tip and cue ball: 0.6

ball-rail coefficient of restitution (for zero angle kick): 0.7

ball rolling resistance: 0.01-0.03

FYI, good sources for technical information like this can be found in the physics resources section of my website (http://www.engr.colostate.edu/~dga/pool/physics.html).

Regards,
Dave

wolfdancer
01-20-2006, 05:25 PM
I hope that you won't mind my posting about your latest research project before the results can be tabulated.
Anyway, here's Dr. Dave and students, at his top secret lab, deep within the bowels of colostate
trying to determine the COR of anvil against stone
http://www.physics.ucla.edu/demoweb/demomanual/mechanics/hamblocs.jpg

vaillancourtroch
01-21-2006, 02:36 AM
Quote form Dr. Dave:

"Since English and throw don't affect the cue ball direction, the effects don't need to be considered when applying the 90 degree rule."

I am either disagreeing or not understanding.

If the balls were perfectly elastic (e=1), english would have no effect.

Since e &lt; 1, english should have some effect.

For this example problem

http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf

Theta + theta2 = 86.693 (this is the cue ball direction with respect to the normal at contact)

Wouldn't (theta + theta2) vary if you applied english on this shot? If so, then english does affect the path of the cue ball.

dr_dave
01-21-2006, 03:11 PM
Very funny. /ccboard/images/graemlins/tongue.gif

I just have one question: Whom am I ... the guy with the sledge hammer or the guy holding the stone? Or am I the distinguished-looking gentleman by the window?

Dave

<blockquote><font class="small">Quote wolfdancer:</font><hr> I hope that you won't mind my posting about your latest research project before the results can be tabulated.
Anyway, here's Dr. Dave and students, at his top secret lab, deep within the bowels of colostate
trying to determine the COR of anvil against stone
http://www.physics.ucla.edu/demoweb/demomanual/mechanics/hamblocs.jpg <hr /></blockquote>

wolfdancer
01-21-2006, 03:27 PM
you, of course, being in the league of distinguished gentlemen...would be standing by the window overseeing the project.lol
I was doing my own research on COR....Being a non- scientist non-engineer...I'd only seen limited examples of the term.
The cartoon is from a UCLA site web page (http://www.physics.ucla.edu/demoweb/demomanual/matter_and_thermodynamics/matter/coefficient_of_restitution_balls.html) which turned out to be an interesting read.
The USGA, by the way, has limited the COR of the thin walled metal drivers to .87....to limit the "springboard effect"

dr_dave
01-21-2006, 03:41 PM
<blockquote><font class="small">Quote vaillancourtroch:</font><hr> Quote form Dr. Dave:

"Since English and throw don't affect the cue ball direction, the effects don't need to be considered when applying the 90 degree rule."

I am either disagreeing or not understanding.

If the balls were perfectly elastic (e=1), english would have no effect.

For this example problem

http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf

Theta + theta2 = 86.693 (this is the cue ball direction with respect to the normal at contact)

Wouldn't (theta + theta2) vary if you applied english on this shot? If so, then english does affect the path of the cue ball.<hr /></blockquote>
In TP A.5, theta1 is the angle that the CB path diverges from the tangent line. It depends on the post-impact normal (impact line) and tangential (tangent line) speed components. The amount of friction and the type and amount of English affect only the tangential component, and e (the COR) affects only the normal component. If e=1, the normal component is 0, and regardless of the English, the CB will head in the tangent line direction. If e&lt;1 (as it is in real life), then the CB will retain a small amount of "normal" speed. In this case, if the tangential speed changes (e.g., with English), then the CB direction will be affected by the amount and type (outside vs. inside) of English. Therefore, I am agreeing with you. Sorry if I caused confusion earlier. When I get some time, I'll combine the analyses from TP A.5 through TP A.8 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/index.html) so all effects can be seen working together for various types of shots. Maybe I'll also write another follow-on article.

Thank you for pointing this out. Good job!
Dave

enso55
01-22-2006, 05:13 PM
Dr. Dave,

Those are, from what I read, some interesting calculations you've made. Your last statement was right on of course. Although I don't even bother telling this to beginning and even intermediate players (which, as I see it, is probably why there is so much confusion on this matter), YES, english does in fact affect the direction of the cueball, and much more importantly, the speed. The only way the direction and speed would not be affected is if there was no friction between pool balls. Any good one pocket player either knows this, or knows this subconciously anyway.

These forums sure are a good way to kill some time, aren't they?

dr_dave
01-23-2006, 09:19 AM
enso55,

I agree with you on all points, especially the point about these forums being excellent outlets to chew up valuable time.

I also agree that for all players that can benefit from the 90 and 30 degree rules, the small effects due to inelasticity, friction, and English should be of little concern. Most people accurate and experienced enough to detect these effects probably already have an excellent understanding or intuitive feel for these principles and subtleties.

Regards,
Dave

<blockquote><font class="small">Quote enso55:</font><hr> Dr. Dave,

Those are, from what I read, some interesting calculations you've made. Your last statement was right on of course. Although I don't even bother telling this to beginning and even intermediate players (which, as I see it, is probably why there is so much confusion on this matter), YES, english does in fact affect the direction of the cueball, and much more importantly, the speed. The only way the direction and speed would not be affected is if there was no friction between pool balls. Any good one pocket player either knows this, or knows this subconciously anyway.

These forums sure are a good way to kill some time, aren't they? <hr /></blockquote>