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dr_dave
12-04-2004, 02:08 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> I have had many questions and comments from readers concerning the 30-degree rule. In this discussion thread, I will post Q&amp;A's that might be of interest to others. <hr /></blockquote>

dr_dave
12-04-2004, 02:11 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
How can a train my hand to take the 30 degree shape you show in your videos?

A (from me):
I used a plastic 30-60-90 triangle (see NV 3.8 on my website) to practice to the point where I can form a 30 degree "V" sign with my hand very consistently. For most people, a firm "V" ("peace") sign is very close to 30 degrees, but it is still good to practice. You can purchase a drafting triangle at any arts supplies store or college bookstore. You can also make your own by cutting one out of cardboard or paper (see Figure 3.24 on p. 54 of "The Illustrated Principles of Pool and Billiards"). To cut one out, use the following dimensions:

triangle width = 1 foot (alternatively: 30 cm)
triangle height = 7 inches (alternatively: 17 cm)

Those dimensions result in a triangle with a 30 degree angle (or close enough for application of the 30 degree rule, which is not perfectly exact anyway). <hr /></blockquote>

dr_dave
12-04-2004, 02:12 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
Physicist that I have talked to say the 90 degree rule applies on every shot. In other words, the cue ball always leaves along the tangent line, perpendicular to the direction of the object ball. I think your 30 degree rule violates the laws of physics.

A (from me):
Your physicist friends are partly correct. The cue ball does start out in the tangent line direction after impact with the object ball. However, topspin (e.g., from forward roll or a follow shot) or bottom spin (e.g., from a draw shot) start taking effect immediately. For high speed shots, the cue ball persists along the tangent line longer before the path curves. However, for slow to medium speed shots, the cue ball curves away from the tangent line very quickly. If you're not convinced, see the video demonstrations of the 30 degree rule (NV 3.8, 3.9, 3.10, and 7.4) on my website.

Concerning the 30 degree rule violating the laws of physics, I know of two physics professors that would take offense at that statement. They prove the basis of the rule mathematically with valid physical principles (see TP 3.3 and the supporting paper on my website for more information). They also back up their claims with photographic evidence.
<hr /></blockquote>

dr_dave
12-04-2004, 02:13 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
I was noticing that if you look at the 90 degree rule in the same way as the 30 degree rule, -- that is, measuring from the aim line to the deflected path...the 90 degree rule could actually be called a 45 degree rule. (I realize the traditional "tangent line" discussion is the 90 degree rule.)

The 90 degree rule looks at deflection path vs Object path but if you look at it as aim line vs deflection it is 45 degrees (for that 1/4 to 3/4 ball cuts range...)

Just thought I would mention that. Seems to me if both rules are presented with the same "point of reference"...the aim line, they might be easier to remember......

A (from me):
Thank you for your message and for your insights. I wish what you propose would work in every case, but unfortunately it does not. The 90 degree rule predicts a 45 degree cue ball deflection only for a cut angle close to 45 degrees (for a ball-hit fraction close to 0.3). For a very small cut-angle (a near full hit) stun shot, the deflected angle is close to 90 degrees. And for a very thin cut (near zero ball-hit fraction), the deflected angle is close to zero (i.e., the cue ball path deflects very little). In fact, for every cut angle, including those in the 1/4 and 3/4 ball-hit range, the deflected cue ball angle is different; but the angle between the deflected cue ball and object ball paths is always 90 degrees (for a stun shot only). I hope that makes sense.

For more information, see my January-July, 2004 articles at www.engr.colostate.edu/pool/bd_articles (http://www.engr.colostate.edu/pool/bd_articles) and pages 41-56 in "The Illustrated Principles of Pool and Billiards," especially Figure 3.10 on p. 42 and Figure 3.17 on p. 50. <hr /></blockquote>

dr_dave
12-04-2004, 02:19 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>Q (from a BD reader):
What is the effect of speed on the 30 degree rule?

A (from me):
First, remember that the 30 degree rule applies only when the cue ball is rolling at object ball impact. For example, it does not apply for a stun shot (where the 90 degree rule applies) or for a draw shot (where the final deflected angle of the cue ball depends significantly on the amount of bottom spin).

Concerning speed, the harder you hit the cue ball, the longer it persists along the tangent line (in the 90 degree direction), before it turns to the 30 degree direction. However, the final deflected angle is still very close to 30 degrees. For slow to medium speed shots, the cue ball deflects away from the tangent line in the 30 degree direction almost immediately.

For more information, see Section 4.07 ("Controlling the Cue Ball Path") in "The Illustrated Principles of Pool and Billiards" (pp. 115-123), especially Figure 4.41 on p. 120. Also, I will be writing a series of follow-up articles on the 30 and 90 degree rules in Billiards Digest. They should appear in the magazine starting in February, 2005. <hr /></blockquote>

dr_dave
12-04-2004, 02:23 PM
When does the 30 degree rule apply?

A (from me):
The 30 degree rule applies for any shot where the cue ball is rolling (i.e., not sliding) at object ball impact. Figure 3.21 on p. 52 of "The Illustrated Principles of Pool and Billiards" shows the most common cases. When the cue ball is very close to the object ball, rolling can occur only with a follow shot. For a medium distance between the cue ball and object ball, slow speed or a follow shot results in rolling. For a large distance shot, the cue ball will be rolling at object ball impact for almost any stroke, except a power draw. In other words, the 30 degree rule applies for many types of shots.

For a good player executing good position control, leaving natural angles on all shots, the 30 degree rule applies for almost every shot!

dr_dave
12-04-2004, 02:27 PM
Is the 30-degree rule exact? In other words, does the cue ball deflect at exactly 30 degrees?

A (from me):
No, the 30-degree rule is not exact. For a half-ball hit, the deflected angle is actually about 34 degrees, and for 1/4- and 3/4-ball hits, the deflected angle is about 26 degrees. But the reason why the rule is so useful is that the deflected angle is still very close to 30 degrees over this very large range of cut angles from a fairly thin hit to a fairly full hit. Because of this, the rule applies to many (even most) shots and can be used to plan and predict cue ball motion for:
<ul type="square"> position play.
safeties
carom and billiard shots
break-up shots
avoidance shots
etc![/list]
For more information, refer to my articles, videos, and technical proofs concerning the 30-degree rule on my website and pages 48-56 in "The Illustrated Principles of Pool and Billiards."

dr_dave
12-04-2004, 02:28 PM
<blockquote><font class="small">Quote silverbullet:</font><hr>
If your information is accurate, then it would be very useful. However, it does not exactly match up with what I read in the 'Science of pocket billiards' by jack koehler.But then jack talks about the 30 degree hit including variations depending on cb speed and distance between the balls. Oh geez. How am I supposed to know who is right???

There is a guy on az with phd in physics who is into this stuff, so guess I will have to ask him. /ccboard/images/graemlins/frown.gif

Laura<hr /></blockquote>

The 30-degree rule is based on an analysis performed by two professors with PhDs in physics. If you want to see the detailed analysis, see TP 3.3 and the supporting technical paper on my website (www.engr.colostate.edu/pool (http://www.engr.colostate.edu/pool)).

Now, the exact path of the cue ball depends on shot speed. I will post a detailed discussion on this soon. Basically, the harder you hit the cue ball, the longer it persists along the tangent line (in the 90 degree direction), before it turns to the 30 degree direction, but the final deflected angle is still very close to 30 degrees for all rolling shots. For slow to medium speed shots, the cue ball deflects away from the tangent line in the 30 degree direction almost immediately. See my NV videos for demonstrations.

PS: At the risk of sounding defensive or conceited, FYI, I have a PhD in mechanical engineering and teach courses in advanced dynamics analysis, so I know a little about physics. I also back up most of the claims in my book and in my articles with video demonstrations, high-speed video, technical proofs, and intuition from experience. I hope you don't take offense at these statements ... that is not my intent.

dr_dave
12-04-2004, 02:29 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> The 30-degree rule is based on an analysis performed by two professors with PhDs in physics. If you want to see the detailed analysis, see TP 3.3 and the supporting technical paper on my website (www.engr.colostate.edu/pool (http://www.engr.colostate.edu/pool)).
<hr /></blockquote>

How do your answers compare to the graphs and analysis on APAPP?

Fred <hr /></blockquote>

I'm not sure to what pages, problems, or sections you are referring; but if Ron Shepard includes similar analyses in his document, I would expect them to be valid and agree with the work I cited. All of Ron's work is thorough, with all I's dotted and all T's crossed.

dr_dave
12-04-2004, 02:33 PM
Does the 30-degree rule apply only for a half-ball hit?

A (from me):
No. The whole point of the 30-degree rule, and the reason why it is so useful, is that it applies over a very large range of cut angles. As long as the cue ball is rolling (i.e., not sliding) at object ball impact, the cue ball's direction will be deflected by very close to 30 degrees for cut angles ranging from a 1/4-ball hit to a 3/4 ball hit.

<ul type="square"> my April-June, 2004 articles posted at:
http://www.engr.colostate.edu/pool/bd_articles
pages 48-56 in my book "The Illustrated Principles of Pool and Billiards"
videos 3.9, 3.10, and 7.4 at http://www.engr.colostate.edu/pool/normal_videos[/list]

Ross
12-04-2004, 03:57 PM
<blockquote><font class="small">Quote silverbullet:</font><hr>
If your information is accurate, then it would be very useful. However, it does not exactly match up with what I read in the 'Science of pocket billiards' by jack koehler.But then jack talks about the 30 degree hit including variations depending on cb speed and distance between the balls. Oh geez. How am I supposed to know who is right???

There is a guy on az with phd in physics who is into this stuff, so guess I will have to ask him. /ccboard/images/graemlins/frown.gif

Laura<hr /></blockquote>

Laura - Dave and Koehler agree completely. The 30 degree rule only applies to a cb with natural roll. If you hit the cb with top english you will have natural roll right away for all shots, so the 30 degree rule will apply no matter the speed and length of the shot.

But if you hit center ball or below center, the cb slides (or backspins) for a while and then because of friction with the cloth it starts to pick up forward roll until it finally reaches a naturally rolling state. So for any shot where you are not using top english, it is true that the speed of the shot and the distance to the ob determine whether or not you have natural roll at impact and hence whether the 30 degree rule applies. That is all Koehler was pointing out.

Bob_Jewett
12-06-2004, 07:05 PM
<blockquote><font class="small">Quote Ross:</font><hr> ... Laura - Dave and Koehler agree completely. ... <hr /></blockquote>
With one important exception, as I recall Koehler's section on follow-shot angles. His plot of cue-ball angle versus fullness of hit is not correct. The real curve has a particular shape, that shape is important, and it is not what Koehler presented.

recoveryjones
12-06-2004, 08:31 PM
<blockquote><font class="small">Quote Ross:</font><hr> <blockquote><font class="small">Quote silverbullet:</font><hr>
If your information is accurate, then it would be very useful. However, it does not exactly match up with what I read in the 'Science of pocket billiards' by jack koehler.But then jack talks about the 30 degree hit including variations depending on cb speed and distance between the balls. Oh geez. How am I supposed to know who is right???

There is a guy on az with phd in physics who is into this stuff, so guess I will have to ask him. /ccboard/images/graemlins/frown.gif

Laura<hr /></blockquote>

Laura - Dave and Koehler agree completely. The 30 degree rule only applies to a cb with natural roll. If you hit the cb with top english you will have natural roll right away for all shots, so the 30 degree rule will apply no matter the speed and length of the shot.

Speed doesn't matter...hmmmmm, I'm not so sure.I just saw a Eddie Parker instructional video where he set up the EXACT SAME SHOT(see wei table illustration below) into the side pocket.He then proceeded to cut the ball in three different times using the EXACT SAME TOP-CENTER ENGLISH at various speeds including slow,medium and fast.Each time the cue ball hit on different diamonds on the rail as it bounced off the object ball after it was potted.The difference of where the cue ball ended up(hitting the rail) between slow and fast speed was quite substancial.After seeing him do the demonstration on that video, I can definitly say that SPEED IS A FACTOR influencing angle.

He also set up the same cut in the side using center ball and bottoms hits with the three various speeds and each time with those experimental shots the cue ball found a different FIRST rail location as well.Conclusion: Speed influences angle no matter where you strike the cue ball.RJ

Below is the approximate shot(as I visulized it from the video) that Eddie Parker set up in his video to illustrate his point.I need glasses...LOL, but I think it's close.

START(
%AZ4U9%BB8\2%CB7[6%DB6\0%EC1\3%FB6[9%GB5[8%HB4[5%IB6[4%JB6[4
%KB7\0%LB2[4%MB3\2%NB3\1%OB3[9%PU4I5%eB4`6
)END

On the soft shot WITH STRAIGHT TOPS the cue ball almost contacts(comes up short due to slow speed) the rail on the second diamond to the right of the side pocket.

On the meduim speed shot(STRAIGHT TOPS) the cue ball strikes the diamond third to the right of the lower side pocket.

On the fast speed shot(STRAIGHT TOPS) the cue ball strikes two inches from scratching in the corner pocket.

All three shots were done with TOP CENTER english at different indicated speeds.

Conclusion: Speed influences angle.IF the cue ball heads for completely different rail locations, how can they all be 30 degree angles?

Having posted all this maybe there is something I didn't understand about Dave's teaching or other posters explanations. If so, I stand corrected.RJ

Ross
12-06-2004, 09:24 PM
RJ, I thought twice about saying that speed doesn't matter without clarifying what I meant. I hoped it would slide, but of course you caught it!

Here is the detail I left out. When you hit with follow the angle that the cb FINALLY ends up going is not speed dependent. However, after impact the cb doesn't start out at its final angle. First it goes off on the tangent line first (90 degrees to the ob path) and then as the top spin starts to take effect on the cloth it bends to its final angle. So for a soft shot, the cb goes down the tangent maybe an inch and then curves to, say, 30 degrees. For a very hard shot the cb may slide over a foot before curving off at an angle of 30 degrees to the original path. So you can end up with very different strike points on the cushion like the example you gave.

I think the reason that rules of thumb like the "30 degree rule" are still useful is that for slow to medium shots the the slide is not too much so you can reasonably APPROXIMATE your results with a 30 or maybe a 35 degree rule (35 to account for the slide). However as you hit the ball more and more firmly, the slide down the tangent line factor becomes more and more significant and must be taken into account.

Sorry if my original post was misleading.

dr_dave
12-06-2004, 09:30 PM
<blockquote><font class="small">Quote Ross:</font><hr>When you hit with follow the angle that the cb FINALLY ends up going is not speed dependent. However, after impact the cb doesn't start out at its final angle. First it goes off on the tangent line first (90 degrees to the ob path) and then as the top spin starts to take effect on the cloth it bends to its final angle. So for a soft shot, the cb goes down the tangent maybe an inch and then curves to, say, 30 degrees. For a very hard shot the cb may slide over a foot before curving off at an angle of 30 degrees to the original path. So you can end up with very different strike points on the cushion like the example you gave.

I think the reason that rules of thumb like the "30 degree rule" are still useful is that for slow to medium shots the the slide is not too much so you can reasonably APPROXIMATE your results with a 30 or maybe a 35 degree rule (35 to account for the slide). However as you hit the ball more and more firmly, the slide down the tangent line factor becomes more and more significant and must be taken into account.<hr /></blockquote>

Very well stated.

Again, for good players playing good position, leaving an anlge for each subsequent shot, the 30 degree rule applies on almost every shot!

dr_dave
12-06-2004, 09:34 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>With one important exception, as I recall Koehler's section on follow-shot angles. His plot of cue-ball angle versus fullness of hit is not correct. The real curve has a particular shape, that shape is important, and it is not what Koehler presented.<hr /></blockquote>

The exact plot is shown in TP 3.3 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-3.pdf). Also, the cue ball deflection angle for a 1/2-ball hit is shown to be 33.7 degrees, and the angle for a 1/4- or 3/4-ball hit fraction is shown to be 27.6 degrees.

recoveryjones
12-07-2004, 02:04 AM
<blockquote><font class="small">Quote Ross:</font><hr> RJ, I thought twice about saying that speed doesn't matter without clarifying what I meant. I hoped it would slide, but of course you caught it!

Here is the detail I left out. When you hit with follow the angle that the cb FINALLY ends up going is not speed dependent. However, after impact the cb doesn't start out at its final angle. First it goes off on the tangent line first (90 degrees to the ob path) and then as the top spin starts to take effect on the cloth it bends to its final angle. So for a soft shot, the cb goes down the tangent maybe an inch and then curves to, say, 30 degrees. For a very hard shot the cb may slide over a foot before curving off at an angle of 30 degrees to the original path. So you can end up with very different strike points on the cushion like the example you gave.

I think the reason that rules of thumb like the "30 degree rule" are still useful is that for slow to medium shots the the slide is not too much so you can reasonably APPROXIMATE your results with a 30 or maybe a 35 degree rule (35 to account for the slide). However as you hit the ball more and more firmly, the slide down the tangent line factor becomes more and more significant and must be taken into account.

Sorry if my original post was misleading. <hr /></blockquote>

Thanks Ross, That makes much more sense.RJ

dr_dave
12-07-2004, 11:45 AM
FYI, I have just posted a pre-print version of an instructional article (Feb, 2005) (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html) summarizing some of the questions and answers discussed in this thread. The article contains illustrations. This is the first in a series of articles I plan to post on this topic.

dr_dave
02-02-2005, 02:06 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr>With one important exception, as I recall Koehler's section on follow-shot angles. His plot of cue-ball angle versus fullness of hit is not correct. The real curve has a particular shape, that shape is important, and it is not what Koehler presented.<hr /></blockquote>

The exact plot is shown in TP 3.3 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-3.pdf). Also, the cue ball deflection angle for a 1/2-ball hit is shown to be 33.7 degrees, and the angle for a 1/4- or 3/4-ball hit fraction is shown to be 27.6 degrees. <hr /></blockquote>
FYI, I just added some stuff to TP 3.3 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-3.pdf). It probably won't be of interest to most of you out there, but I thought I'd share it anyway (for the physics geeks in the crowd).

The most interesting addition concerns the maximum cue ball deflected angle (see the bottom of TP 3.3 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-3.pdf)). It turns out that the maximum deflected angle does not occur exactly at a half-ball hit. I think many people (including myself in the past) often assume this. The maximum angle (33.75 degrees) actually occurs at a cut angle of about 28 degrees, which corresponds to a 0.53 ball-hit fraction. For most people, these numbers are close enough to 30 degrees and a 1/2-ball hit, but I thought others might be interested in knowing the exact numbers.

Bob_Jewett
02-02-2005, 03:22 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>... It turns out that the maximum deflected angle does not occur exactly at a half-ball hit. I think many people (including myself in the past) often assume this. ... <hr /></blockquote>
This was discussed some time ago in rec.sport.billiard (and I'm sure appears in Ron Shepard's paper, APAPP). Two of many exact expressions for the cut angle that gives maximum cue ball deflection angle are (1/2)*arccos(5/9) and arctan(sqrt(2/7)). Which one you get depends on how you analyze the problem. A search on 28.1255 in Google Usenet groups at http://groups.google.com/advanced_group_search will find some references.

dr_dave
02-02-2005, 04:09 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>... It turns out that the maximum deflected angle does not occur exactly at a half-ball hit. I think many people (including myself in the past) often assume this. ... <hr /></blockquote>
This was discussed some time ago in rec.sport.billiard (and I'm sure appears in Ron Shepard's paper, APAPP). Two of many exact expressions for the cut angle that gives maximum cue ball deflection angle are (1/2)*arccos(5/9) and arctan(sqrt(2/7)). Which one you get depends on how you analyze the problem. A search on 28.1255 in Google Usenet groups at http://groups.google.com/advanced_group_search will find some references.<hr /></blockquote>
Bob,

Thanks for pointing to the RSB thread. I look forward to reading it.

You are correct, the 28.125 degree result does also appear in Ron Sheppard's paper. I just checked and found it on page 54 (Problem 4.15). It is derived in a different way, and the answer is in a different form, but the results agree.

superstroke
02-04-2005, 04:58 AM
All I have to say is that I thank you for the article in BD
learning the 30 degree rule using my fingers as the peace sign is just an added brick to my wall, it's very strong info for exact precision pool. Thanks again.
P.S. I even use it to demonstrate for people I am teaching.

02-04-2005, 05:13 AM
Dr. Dave,

I enjoyed your article in BD this month. I am fairly new to the game and have been playing mostly by "feel". I am looking forward to putting the information from your article to use and improving the consistancy in my shotmaking. Thanks

dr_dave
02-04-2005, 09:42 AM
<blockquote><font class="small">Quote superstroke:</font><hr> All I have to say is that I thank you for the article in BD
learning the 30 degree rule using my fingers as the peace sign is just an added brick to my wall, it's very strong info for exact precision pool. Thanks again.
P.S. I even use it to demonstrate for people I am teaching. <hr /></blockquote>
You are very welcome. I also think that the "30-degree-rule brick" is critically important and should be in everybody's toolbox. I am very proud of my hand trick (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168250&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) - I don't think anybody has suggested this before. I use the "peace sign" quite a lot when I play to detect a possible scratch, plan position play, or aim carom shots. One day, I hope to see somebody using it on TV during a match. That would make me very proud.

dr_dave
02-04-2005, 09:59 AM

I enjoyed your article in BD this month. I am fairly new to the game and have been playing mostly by "feel". I am looking forward to putting the information from your article to use and improving the consistancy in my shotmaking. Thanks <hr /></blockquote>
I'm glad you are finding my articles useful in your game. If you have not seen my previous articles dealing with the 90 and 30 degree rules, you might want to also refer to them online (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html).

02-04-2005, 11:28 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote loofnicnad:</font><hr> Dr. Dave,

I enjoyed your article in BD this month. I am fairly new to the game and have been playing mostly by "feel". I am looking forward to putting the information from your article to use and improving the consistancy in my shotmaking. Thanks <hr /></blockquote>
I'm glad you are finding my articles useful in your game. If you have not seen my previous articles dealing with the 90 and 30 degree rules, you might want to also refer to them online (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html). <hr /></blockquote>

That's a lot of good, grounding information. Thanks again!

dr_dave
02-07-2005, 03:02 PM
FYI, I just posted a new instructional article presenting the effects of ball inelasticity and friction on the 90 and 30 degree rules. Check it out. Please let me know if you have any comments, constructive criticism, or differences in opinion. The article doesn't go to the BD printer for another month.

The physics geeks out there might also be interested in my two new technical analyses (TP A.5 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-5.pdf) and TP A.6 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-6.pdf)) that support the conclusions in the article.

cushioncrawler
10-23-2005, 09:27 PM
In English Billiardz on a 12ft table most of the old-timerz said that a half-ball contact gave the widest Qball deflexion angle, forcerz etc excluded. They weren't quite correct --- but it dependz on definition.
If the deflexion angle iz mezured from the original line joining the centerz of the stationary ballz, then the hallowed 0.53 contact duznt deliver the goodz, 0.50 duz.
I should hav said, 0.50 might, koz, most shots are at close range. Az the Qball to Objektball separation gets smaller, the maximum deflexion iz obtained by a 0.40 contact, then 0.30, then 0.20 etc.
At nursery cannon range, my speciality, the max deflexion iz often got with a 1/8th ball contact. Az i said, it dependz on definition.

HALHOULE
10-24-2005, 03:22 AM
AND I SUPPOSE YOUR STUDENTS GET AN ACCURATE AND CONSISTENT AIMING SYSTEM? WHAT AIMING SYSTEM MIGHT THAT BE?

dr_dave
10-24-2005, 07:24 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> In English Billiardz on a 12ft table most of the old-timerz said that a half-ball contact gave the widest Qball deflexion angle, forcerz etc excluded. They weren't quite correct --- but it dependz on definition.
If the deflexion angle iz mezured from the original line joining the centerz of the stationary ballz, then the hallowed 0.53 contact duznt deliver the goodz, 0.50 duz.<hr /></blockquote>If you are just talking about angle, the reference line you describe is no different than that shown in TP A.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-4.pdf). The deflected "angle" is maximum for a 0.53 ball-hit fraction (see this posting (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=178482&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=&amp;vc=&amp;PHPSESSID=) for more information).

Also, if you are talking about cue ball "displacement" instead of deflection angle, speed is also a consideration (see my June '05 instructional article (http://http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html) for more information).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>I should hav said, 0.50 might, koz, most shots are at close range. Az the Qball to Objektball separation gets smaller, the maximum deflexion iz obtained by a 0.40 contact, then 0.30, then 0.20 etc.
At nursery cannon range, my speciality, the max deflexion iz often got with a 1/8th ball contact. Az i said, it dependz on definition.<hr /></blockquote>
The 30 degree rule assumes that the cue ball is rolling at object ball impact. At closer range, you must use follow to ensure a rolling cue ball (for more info, see my April '04 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html)).

I'm sorry if I misinterpreted anything you wrote. If I did, please let me know.

Regards,
Dave

PS: What is a "nursery cannon range?"

Stretch
10-24-2005, 10:38 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> In English Billiardz on a 12ft table most of the old-timerz said that a half-ball contact gave the widest Qball deflexion angle, forcerz etc excluded. They weren't quite correct --- but it dependz on definition.
If the deflexion angle iz mezured from the original line joining the centerz of the stationary ballz, then the hallowed 0.53 contact duznt deliver the goodz, 0.50 duz.<hr /></blockquote>If you are just talking about angle, the reference line you describe is no different than that shown in TP A.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-4.pdf). The deflected "angle" is maximum for a 0.53 ball-hit fraction (see this posting (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=178482&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=&amp;vc=&amp;PHPSESSID=) for more information).

Also, if you are talking about cue ball "displacement" instead of deflection angle, speed is also a consideration (see my June '05 instructional article (http://http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html) for more information).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>I should hav said, 0.50 might, koz, most shots are at close range. Az the Qball to Objektball separation gets smaller, the maximum deflexion iz obtained by a 0.40 contact, then 0.30, then 0.20 etc.
At nursery cannon range, my speciality, the max deflexion iz often got with a 1/8th ball contact. Az i said, it dependz on definition.<hr /></blockquote>
The 30 degree rule assumes that the cue ball is rolling at object ball impact. At closer range, you must use follow to ensure a rolling cue ball (for more info, see my April '04 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html)).

I'm sorry if I misinterpreted anything you wrote. If I did, please let me know.

Regards,
Dave

PS: What is a "nursery cannon range?" <hr /></blockquote>

Hi Dave, just a few thoughts. I don't know a lot about the physics of it, but i do know that a half ball hit from 1 ft away is different than a half ball hit from 6 ft away. That asside, i find it a great tool. One of the nice things about it is control. A naturally rolling half ball hit will send the ob approx. the same distance as the cue ball. controll the cue ball and u control the ob as well. Great for planning safety leaves, gives u a great edge target and predictable cue ball path after contact. Full ball, 3/4 ball, 1/2 ball, 1/4 ball, thin........learn the secrets of all 6 and you can't miss. When i started to see the angles, i knew which catagory my contact point fell into as far as aiming ob up. You can tailor every angle with the cue ball run out too. When i'm feelin it i'm just planning my cue ball. When u get the shape right the ob pockets as a side note. /ccboard/images/graemlins/smile.gif St.

dr_dave
10-24-2005, 11:15 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>If the deflexion angle iz mezured from the original line joining the centerz of the stationary ballz, then the hallowed 0.53 contact duznt deliver the goodz, 0.50 duz.<hr /></blockquote>
Just to be clear, for the 30 degree rule and the results in TP 3.3 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-3.pdf) and TP A.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-4.pdf), the deflection angle is measured relative to the original direction of the cue ball (not the original line of centers).

Regards,
Dave

dr_dave
10-24-2005, 11:27 AM
<blockquote><font class="small">Quote Stretch:</font><hr>Hi Dave, just a few thoughts. I don't know a lot about the physics of it, but i do know that a half ball hit from 1 ft away is different than a half ball hit from 6 ft away.<hr /></blockquote>Agreed. But the cue ball deflection angle is the same regardless of the shot distance if the deflection angle is measured relative to the original cue ball direction (i.e., the aiming line). (For more info, see the angle reference message (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=208365&amp;page =0&amp;view=&amp;sb=&amp;o=&amp;fpart=&amp;vc=).) The 30 degree rule and peace-sign aiming technique (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=186845&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=1) are based on this reference. Please let me know if I am still missing your point.

<blockquote><font class="small">Quote Stretch:</font><hr>That asside, i find it a great tool. One of the nice things about it is control. A naturally rolling half ball hit will send the ob approx. the same distance as the cue ball. controll the cue ball and u control the ob as well. Great for planning safety leaves, gives u a great edge target and predictable cue ball path after contact.<hr /></blockquote>
Excellent point! For those that are interested in the precise numbers, I have a complete analysis at TP A.16 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-16.pdf).

Regards,
Dave