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View Full Version : The 30 degree rule is not just for "techies"



dr_dave
12-28-2004, 08:35 AM
<blockquote><font class="small">Quote anonymous:</font><hr>
dr. dave...Not to take anything away from your 'technical expertise', I believe that knowing simple physics, that show definitively that topspin causes the CB to curve across the tangent line, and backspin causes the CB to curve away from the tangent, are much more significant than applying a '30 degree rule'...which can be ruled out by how high or low you stroke the CB, and how much speed you shoot. Keep it simple! However, for the techies out there, your explanations are excellent and well illustrated.<hr /></blockquote>
The 30 degree rule is not just for "techies." The derivation and physics behind it IS just for "techies," but knowing where the cue ball will go for basic shots is important to and attainable by ALL. For a stun shot, the cue ball heads directly in the tangent line direction. For a roll shot, the cue ball heads very close to the 30 degree direction, which is easy to visualize with your hand (see NV 3.8 (http://www.engr.colostate.edu/~dga/pool/normal_videos/index.html)). I think that's fairly simple.

To me, being able to judge where the cue ball will go with various draw and follow shots at different speeds is not simple. That ability, even if you know all of the principles, requires lots of intuition that can come only with years of practice and experience.

For more information on how to "keep it simple," see my January-July, '04 and February-March, '05 instructional articles online (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html). See also: the 30 degree rule discussion thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168248).

ras314
12-28-2004, 04:00 PM
Two things make the "30 deg rule" worth while for me. No. 1 is the relatively large error in hit possible for a near 30 deg deflection. No. 2 is the relative ease of the half ball aim point. It doesn't hurt that a cb will normally have natural roll on any long shot when a lot of draw or follow is not used.

Every now and then it is quite useful for a carom on the 9 when there is no easy run on the table. /ccboard/images/graemlins/grin.gif

Cane
12-28-2004, 04:28 PM
<blockquote><font class="small">Quote anonymous:</font><hr>
I believe that knowing simple physics, that show definitively that topspin causes the CB to curve across the tangent line, and backspin causes the CB to curve away from the tangent, are much more significant than applying a '30 degree rule'...which can be ruled out by how high or low you stroke the CB, and how much speed you shoot. Keep it simple! However, for the techies out there, your explanations are excellent and well illustrated.<hr /></blockquote>


Anonymous: Well, I can't keep it simple, because there are some technical things that happen when two spheres collide (CB and OB) that every pool player who wants to be proficent at this game must understand. They don't have to understand them on a highly technical level, but they do need to understand them.

1. ANY time two balls collide, they will seperate at a 90 angle, the tangent line as we call it.

2. When the CB is skidding as in a stop shot, the CB will leave and remain on that tangent line (assuming like mass of cue ball and OB. Magnetic balls and oversized balls react a bit differently because of difference in weight).

3. When the CB has "natural roll" it will leave the OB along the tangent line then travel forward of it, and on the hit's Dave is describing, it will leave on a line somewhere between 30 and 34.

4. When a CB has top spin on it, it STILL leaves the OB along the tangent line, then travels forward of it.

5. When the CB has backspin, it will still travel momentarily along the tangent line before it curves behind the tangent line.

6. MOST IMPORTANT!!! The speed of the CB determines how far the CB will travel after it leaves the OB at 90 before it deviates from that line. The higher the speed, the longer the CB remains on the tangent line, the slower the speed, the quicker the CB leaves the tangent line in whatever direction you want it to go because of the spin.

Dave could definitely explain the physics involved in spheres on a technical level better than I can, even though I am an BSME, but the plain simple fact is that there are laws of physics that must be considered in pool to play at a high level. We won't all think of them as "collision of spheres" or "tangent lines" or whatever, but we will all think of them on some level if we want good cue ball control.

Later,
Bob

PQQLK9
12-28-2004, 06:23 PM
Hey Cane Dr. Dave hijacked this quote from another thread /ccboard/images/graemlins/confused.gif that was made by Scott Lee. Dr. Dave was the one who used the term anonymous.

Stretch
12-28-2004, 07:08 PM
<blockquote><font class="small">Quote PQQLK9:</font><hr> Hey Cane Dr. Dave hijacked this quote from another thread /ccboard/images/graemlins/confused.gif that was made by Scott Lee. Dr. Dave was the one who used the term anonymous. <hr /></blockquote>

My sentiments too. Bad form to "quote" someone then not even use his name, or worse call him "anonimus". On a different thread to? Hmmmmmm. I know Dave lifted a post of mine and put it on another thread (where it died). But at least he was gracious enough to introduce what i said as from me. Scott more than deserves a mention for his post, if it's to be used eslewhere as well. St.~~great post Scott!~~

dr_dave
12-28-2004, 09:03 PM
<blockquote><font class="small">Quote Stretch:</font><hr> <blockquote><font class="small">Quote PQQLK9:</font><hr> Hey Cane Dr. Dave hijacked this quote from another thread /ccboard/images/graemlins/confused.gif that was made by Scott Lee. Dr. Dave was the one who used the term anonymous. <hr /></blockquote>

My sentiments too. Bad form to "quote" someone then not even use his name, or worse call him "anonimus". On a different thread to? Hmmmmmm. I know Dave lifted a post of mine and put it on another thread (where it died). But at least he was gracious enough to introduce what i said as from me. Scott more than deserves a mention for his post, if it's to be used eslewhere as well. St.~~great post Scott!~~<hr /></blockquote>
Sorry about that. I meant no offense to Scott or anybody else. I just wasn't sure if Scott would have wanted to be labeled by name when I started the new thread. I thought it was safer to just list the quote as from "anonymous." I should have just asked him ... I will next time. I guess I don't know all of the CCB etiquette yet. I started the new thread because people have complained in the past that my other thread was too large. Again, I apologize if I have caused any confusion or offense.

Rod
12-28-2004, 09:18 PM
[ QUOTE ]
To me, being able to judge where the cue ball will go with various draw and follow shots at different speeds is not simple. That ability, even if you know all of the principles, requires lots of intuition that can come only with years of practice and experience.
<hr /></blockquote>

That's what separates the players from the novice. Even good players most times don't know when. I expect the c/b ball to bend at a certain point to play position. All very good players rely on this talent. Speed has the most effect but spin and even angle need to be factored in a shot as well. Knowing when and how much is critical to play at a high level. Lets not forget about conditions, some difficult shots are plain easy and others are just plain tough. You need to know what the table will give you for a certain situation. I'll pass on knowing all the techie stuff, I'm just fine right where I am!

Wally_in_Cincy
12-29-2004, 07:21 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>
... I guess I don't know all of the CCB etiquette yet. ...<hr /></blockquote>

You're doing fine.

Bob_Jewett
12-29-2004, 01:04 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ...
To me, being able to judge where the cue ball will go with various draw and follow shots at different speeds is not simple. That ability, even if you know all of the principles, requires lots of intuition that can come only with years of practice and experience....<hr /></blockquote>
However, if the cue ball is rolling smoothly on the cloth when it hits the object ball, there is a fairly simple way to judge the final angle of the cue ball for a given cut angle of the object ball. The rule is simple, but it's based on physics. Similarly, if you have "full draw" on the cue ball, by which I mean that there is as much draw as you have follow for a smoothly rolling cue ball, there is a similar system that gives the final angle of the cue ball.

And there are what you might call "mileposts" such as the right-angle rule for "full draw" and a half-ball hit.

dr_dave
12-29-2004, 10:37 PM
<blockquote><font class="small">Quote Rod:</font><hr> &lt;/font&gt;&lt;blockquote&gt;&lt;font class="small"&gt;Quote:&lt;/font&gt;&lt;hr /&gt;
To me, being able to judge where the cue ball will go with various draw and follow shots at different speeds is not simple. That ability, even if you know all of the principles, requires lots of intuition that can come only with years of practice and experience.
<hr /></blockquote>

That's what separates the players from the novice. Even good players most times don't know when. I expect the c/b ball to bend at a certain point to play position. All very good players rely on this talent. Speed has the most effect but spin and even angle need to be factored in a shot as well. Knowing when and how much is critical to play at a high level. Lets not forget about conditions, some difficult shots are plain easy and others are just plain tough. You need to know what the table will give you for a certain situation. I'll pass on knowing all the techie stuff, I'm just fine right where I am! <hr /></blockquote>
Rod,
As usual, well put!
Dave

dr_dave
12-29-2004, 10:49 PM
<blockquote><font class="small">Quote Wally_in_Cincy:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>
... I guess I don't know all of the CCB etiquette yet. ...<hr /></blockquote>

You're doing fine. <hr /></blockquote>

Thanks Wally. I'm glad somebody thinks I'm OK.

Regards,
Dave

dr_dave
12-29-2004, 10:56 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ...
To me, being able to judge where the cue ball will go with various draw and follow shots at different speeds is not simple. That ability, even if you know all of the principles, requires lots of intuition that can come only with years of practice and experience....<hr /></blockquote>
However, if the cue ball is rolling smoothly on the cloth when it hits the object ball, there is a fairly simple way to judge the final angle of the cue ball for a given cut angle of the object ball. The rule is simple, but it's based on physics. Similarly, if you have "full draw" on the cue ball, by which I mean that there is as much draw as you have follow for a smoothly rolling cue ball, there is a similar system that gives the final angle of the cue ball.

And there are what you might call "mileposts" such as the right-angle rule for "full draw" and a half-ball hit. <hr /></blockquote>

Thanks Bob. Your contributions are appreciated.

Regards from New Orleans (where I am visiting my family),
Dave