PDA

View Full Version : expanded glossary of pool/billiards terms



dr_dave
03-22-2007, 04:06 PM
FYI, I just posted an 18-page expanded glossary of pool and billiards terms and phrases. It can be found, with links to some other useful collections, under "references" in the instructor and student resources section of my website (http://www.engr.colostate.edu/~dga/pool/resources/index.html). Check it out. Please let me know if you think I left out any obvious or really important terms or phrases.

Thanks,
Dave

dr_dave
03-22-2007, 04:38 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just posted an 18-page expanded glossary of pool and billiards terms and phrases. It can be found, with links to some other useful collections, under "references" in the instructor and student resources section of my website (http://www.engr.colostate.edu/~dga/pool/resources/index.html). Check it out. Please let me know if you think I left out any obvious or really important terms or phrases.<hr /></blockquote>
For convenience, here's the direct link (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) to the expanded glossary.

Bob_Jewett
03-22-2007, 05:34 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... Please let me know if you think I left out any obvious or really important terms or phrases. ... <hr /></blockquote>
You may want to get Shamos's Encyclopedia for a list of over 2000 billiard terms with definitions, origins and illustrations. There are sure to be some obvious terms there that you want to include.

Angle of incidence does not specify the two lines that determine the angle. The ambiguity is often confusing. Are you using the normal or the tangent as the second line?

Jal
03-22-2007, 06:01 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just posted an 18-page expanded glossary of pool and billiards terms and phrases. It can be found, with links to some other useful collections, under "references" in the instructor and student resources section of my website (http://www.engr.colostate.edu/~dga/pool/resources/index.html). Check it out. Please let me know if you think I left out any obvious or really important terms or phrases.<hr /></blockquote>
For convenience, here's the direct link (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) to the expanded glossary. <hr /></blockquote>Thanks again for the resource Dr. Dave. It's a very nice reference. A couple of points:

Does SAM stand for "simple aiming system" or "supplemental aiming system"? I believe I've seen the latter used by some of its teachers.

Commentators, especially in one-pocket, use the term "ducking" as a synonym for a safety/defensive maneuver.

I went through the whole list but can't remember if it had "twisting", as in "twisting in a bank".

Jim

cushioncrawler
03-23-2007, 10:52 PM
Dr Dave -- I think that some terms could be modifyd to reinforce the fact that there is a temporary flatspot at balltoball impact.

For instance, "Contact Point" could say "The (first) point of contact.....".

"Impact Point" and "Impact Line" could reinforce the existance of a temp flatspot allso.

"Flatspot" -- In fact i think that this iznt listed.

"COR" for a rail. I think that the wordage here could be based on how COR is measured (or could be measured), ie V1 and V2, or ????

"Deflection" -- could mention that it is "degrees".

"Cueball angle error" -- Here i think that it iz difficult to define whether it is the actual final error, or whether it is based on actual cue-line, or ???? What about where the player habitually picks the "wrong spot", then aims wrong, and then hits the "correct spot", and the whole time is convinced that he/she is No1. madMac.

dr_dave
03-26-2007, 12:01 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... Please let me know if you think I left out any obvious or really important terms or phrases. ... <hr /></blockquote>
You may want to get Shamos's Encyclopedia for a list of over 2000 billiard terms with definitions, origins and illustrations. There are sure to be some obvious terms there that you want to include.<hr /></blockquote>That is a great reference. I have a copy. I'll brose through it when I manage to find hours of free time. The Shamos book has many more terms than I would want to include. It also includes many obscure and historical terms that many people would never hear or read. After a casual glance, it appears that my list also has many terms and phrases that don't appear in Shamos' book.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>Angle of incidence does not specify the two lines that determine the angle. The ambiguity is often confusing. Are you using the normal or the tangent as the second line?<hr /></blockquote>I use the normal (perpendicular) as the reference line, as with standard optics convention. This convention also makes more sense when using the terms "lengthen the angle" and "shorten the angle." I think my definition is clear (see below). If you still think it is not, please let me know.

approach angle (AKA “angle of incidence”): the angle at which a ball approaches a rail, measured from the rail perpendicular. A ball driven directly into (perpendicular to) a rail has an approach angle of zero.

Thanks,
Dave

Bob_Jewett
03-26-2007, 12:07 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ...
approach angle (AKA “angle of incidence”): the angle at which a ball approaches a rail, measured from the rail perpendicular. A ball driven directly into (perpendicular to) a rail has an approach angle of zero. ... <hr /></blockquote>
I would guess that most pool players would call that an approach angle of 90 degrees. Thus the chance for confusion.

dr_dave
03-26-2007, 01:22 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ...
approach angle (AKA “angle of incidence”): the angle at which a ball approaches a rail, measured from the rail perpendicular. A ball driven directly into (perpendicular to) a rail has an approach angle of zero. ... <hr /></blockquote>
I would guess that most pool players would call that an approach angle of 90 degrees. Thus the chance for confusion. <hr /></blockquote>I agree that many authors (e.g., Byrne) and pool players use 90 degrees to refer to an angle of incidence where there is no "approach angle" into to the rail. I chose to use the more standard convention (from optics, where the "angle of incidence" is defined relative to the normal). Also, with the optics convention, the terms "lengthen the angle" and "shorten the angle" make more sense. For a straight-on bank shot, both the approach angle and rebound angle are 0. As the approach angle is increased, the rebound angle increases (i.e., it "lengthens"). If you add running (natural) English, the rebound angle lengthens (i.e., it increases) even more. I know many books and people use the non-standard convention (what you claim is the "standard" pool convention), in which case the rebound angle gets smaller when it is "lengthened," but I decided to use the more standard convention (according to optics) that also makes sense with other "standard" pool terminology.

Regards,
Dave

dr_dave
03-26-2007, 01:26 PM
FYI, I just posted a new and improved version of my expanded glossary, based on input from several people and my review of several other published glossaries. I also added some links and a reference under "for reference" in the Instructor and Student Resources section of my website (http://www.engr.colostate.edu/~dga/pool/resources/index.html) if you want to research things even further.

Happy reading,
Dave

PS: Again, please let me know if you think any common and/or important terms or phrases are missing.

dr_dave
03-26-2007, 01:30 PM
<blockquote><font class="small">Quote Jal:</font><hr>Does SAM stand for "simple aiming system" or "supplemental aiming system"? I believe I've seen the latter used by some of its teachers.<hr /></blockquote>Thank you for pointing this out. It is "supplemental" (correct in current version).

<blockquote><font class="small">Quote Jal:</font><hr>Commentators, especially in one-pocket, use the term "ducking" as a synonym for a safety/defensive maneuver.<hr /></blockquote>I also added this.

<blockquote><font class="small">Quote Jal:</font><hr>I went through the whole list but can't remember if it had "twisting", as in "twisting in a bank".<hr /></blockquote>I have never heard or read this term, and I couldn't find it in any of the other glossaries I have reviewed, so I would prefer not add it, unless others also think it is a common and/or important term.

Thanks,
Dave

Bob_Jewett
03-26-2007, 01:32 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... I know many books and people use the non-standard convention (what you claim is the "standard" pool convention), in which case the rebound angle gets smaller when it is "lengthened," but I decided to use the more standard convention (according to optics) that also makes sense with other "standard" pool terminology.... <hr /></blockquote>
Actually, I don't think there really is a standard pool convention for this. That's why when discussing angles off cushions, I try not to assume that the reader has any particular convention in mind. I try never to say, "wider angle" for example. Instead I might say, "closer to parallel to the cushion". Life would be a little easier if all pool players knew what "longer" meant in reference to angles off cushions, but they don't.

dr_dave
03-26-2007, 01:39 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... I know many books and people use the non-standard convention (what you claim is the "standard" pool convention), in which case the rebound angle gets smaller when it is "lengthened," but I decided to use the more standard convention (according to optics) that also makes sense with other "standard" pool terminology.... <hr /></blockquote>
Actually, I don't think there really is a standard pool convention for this. That's why when discussing angles off cushions, I try not to assume that the reader has any particular convention in mind. I try never to say, "wider angle" for example. Instead I might say, "closer to parallel to the cushion". Life would be a little easier if all pool players knew what "longer" meant in reference to angles off cushions, but they don't. <hr /></blockquote>I agree that it is always best to avoid confusion where possible by being clear and consistent with definitions and/or by using more descriptive words and phrases and/or by showing illustrations.

Regards,
Dave

dr_dave
03-26-2007, 01:47 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- I think that some terms could be modifyd to reinforce the fact that there is a temporary flatspot at balltoball impact.

For instance, "Contact Point" could say "The (first) point of contact.....".

"Impact Point" and "Impact Line" could reinforce the existance of a temp flatspot allso.

"Flatspot" -- In fact i think that this iznt listed.

"COR" for a rail. I think that the wordage here could be based on how COR is measured (or could be measured), ie V1 and V2, or ????

"Deflection" -- could mention that it is "degrees".

"Cueball angle error" -- Here i think that it iz difficult to define whether it is the actual final error, or whether it is based on actual cue-line, or ???? What about where the player habitually picks the "wrong spot", then aims wrong, and then hits the "correct spot", and the whole time is convinced that he/she is No1. madMac.<hr /></blockquote>Thanks Mac. I made some changes per some of your suggestions. I think some of your suggestions are inapproprate for a glossary (e.g., how something is measured). The glossary is a quick and concise summary. If somebody wants details, examples, and illustrations, a complete introductory pool book is probably more appropriate.

Thanks again,
Dave

Jal
03-26-2007, 02:15 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>Does SAM stand for "simple aiming system" or "supplemental aiming system"? I believe I've seen the latter used by some of its teachers.<hr /></blockquote>Thank you for pointing this out. It is "supplemental" (correct in current version).<hr /></blockquote>Glad you caught my "system" instead of "method" error.

<blockquote><font class="small">Quote dr_dave:</font><hr><blockquote><font class="small">Quote Jal:</font><hr>I went through the whole list but can't remember if it had "twisting", as in "twisting in a bank".<hr /></blockquote>I have never heard or read this term, and I couldn't find it in any of the other glossaries I have reviewed, so I would prefer not add it, unless others also think it is a common and/or important term.<hr /></blockquote>I have heard the term used a couple of times, but can't say how widespread it is.

I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".

Jim

SpiderMan
03-26-2007, 02:30 PM
For what it's worth, I'd normally use perpendicular as a (zero) reference also. A "wide bank" to me is one that has an approach angle more toward the parallel than the perpendicular. But since it may be taken either way, it's probably good to include a diagram or description for this one.

SpiderMan

SpiderMan
03-26-2007, 02:36 PM
<blockquote><font class="small">Quote Jal:</font><hr>
I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".
Jim <hr /></blockquote>

In my mind, "deflection" requires another adjective in order to be concise. In other words, unless you say "cue-ball deflection", many will tend to assume you mean deflection of the shaft.

On the other hand, "squirt" invariably refers to an action of the cueball.

In both written and oral descriptions, I therefore prefer to talk about shaft deflection and ball squirt.

SpiderMan

dr_dave
03-26-2007, 03:17 PM
<blockquote><font class="small">Quote Jal:</font><hr>I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".<hr /></blockquote>I also prefer "squirt" to "deflection" because "cue ball deflection" can be confused with "cue stick deflection." This can be really confusing since "cue stick deflection" (at the tip) is actually larger with cue sticks that have smaller "cue ball deflection." However, I decided to not try to change the world on this one. Predator and others sell "low-deflection" cues even if you and I and others prefer to call them "low-squirt" cues.

Thanks again for your input and corrections,
Dave

dr_dave
03-26-2007, 03:32 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>
I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".
Jim <hr /></blockquote>

In my mind, "deflection" requires another adjective in order to be concise. In other words, unless you say "cue-ball deflection", many will tend to assume you mean deflection of the shaft.

On the other hand, "squirt" invariably refers to an action of the cueball.

In both written and oral descriptions, I therefore prefer to talk about shaft deflection and ball squirt.<hr /></blockquote>I agree with you 100%, but it seems that most people (including the cue industry) still use the word "deflection" instead of "squirt." It seems that most don't care what the cue stick is doing ... only the cue ball. Hence, when I hear or read "low-deflection cue," I assume they mean "low cue-ball-deflection cue." Like you, I wish they would use "low-squirt cue" to avoid the possible confusion.

Regards,
Dave

cushioncrawler
03-26-2007, 03:35 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ...... If you add running (natural) English, the rebound angle lengthens (i.e., it increases) even more..... <hr /></blockquote> Dr Dave -- I reckon that in many cases a little bit of "running" actually inkreecez the rebound angle, and "check" dekreecez the rebound angle -- i think that this is so when the attack-angle is more than 50dg off perpindicular. We see this on a 12' table. It must have to do with the friktion depending on slip-rate.

It probably helps to explain why topspin gives a high kicker in a tennis serve and in a cricket delivery. madMac.

SpiderMan
03-26-2007, 03:44 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>
I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".
Jim <hr /></blockquote>

In my mind, "deflection" requires another adjective in order to be concise. In other words, unless you say "cue-ball deflection", many will tend to assume you mean deflection of the shaft.

On the other hand, "squirt" invariably refers to an action of the cueball.

In both written and oral descriptions, I therefore prefer to talk about shaft deflection and ball squirt.<hr /></blockquote>I agree with you 100%, but it seems that most people (including the cue industry) still use the word "deflection" instead of "squirt." It seems that most don't care what the cue stick is doing ... only the cue ball. Hence, when I hear or read "low-deflection cue," I assume they mean "low cue-ball-deflection cue." Like you, I wish they would use "low-squirt cue" to avoid the possible confusion.

Regards,
Dave <hr /></blockquote>

And when they say their "shaft deflects a lot". Are they saying that their shaft deflects the cueball a lot?? /ccboard/images/graemlins/grin.gif

SpiderMan

dr_dave
03-26-2007, 03:48 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>
I noticed that you chose "deflection" as the "official" term and labeled "squirt" as slang. "Deflection" is more dignified, imo, and it's possible that more people on these forums use it than "squirt".
Jim <hr /></blockquote>

In my mind, "deflection" requires another adjective in order to be concise. In other words, unless you say "cue-ball deflection", many will tend to assume you mean deflection of the shaft.

On the other hand, "squirt" invariably refers to an action of the cueball.

In both written and oral descriptions, I therefore prefer to talk about shaft deflection and ball squirt.<hr /></blockquote>I agree with you 100%, but it seems that most people (including the cue industry) still use the word "deflection" instead of "squirt." It seems that most don't care what the cue stick is doing ... only the cue ball. Hence, when I hear or read "low-deflection cue," I assume they mean "low cue-ball-deflection cue." Like you, I wish they would use "low-squirt cue" to avoid the possible confusion.

Regards,
Dave <hr /></blockquote>

And when they say their "shaft deflects a lot". Are they saying that their shaft deflects the cueball a lot?? /ccboard/images/graemlins/grin.gif<hr /></blockquote>I'm not sure what they mean when they say this, but there is a good product available on the market that might be appropriate: Viagra! /ccboard/images/graemlins/grin.gif

Dave

PS: Be careful where you squirt.

Cornerman
03-27-2007, 07:35 AM
Big list.

Does a fouetté shot necessarily have to be shot with extreme inside? I never thought so.

"Twisting" should be in there, as it's more common than most of the other terms in the list.

As a point of organization, it might be useful to separate technical and/or industry terms from slang/jargon. Also, if terminology not common to US pool is listed, then you'll end up missing a ton of other game/country specific terminology. E.g. fluke and scratch.

Fred

Cornerman
03-27-2007, 08:16 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> Instead I might say, "closer to parallel to the cushion". Life would be a little easier if all pool players knew what "longer" meant in reference to angles off cushions, but they don't. <hr /></blockquote>I'm sure most pool players when they are talking about banking, "longer" means the object ball hit the cushion farther down the table than the hole.

I've never liked referencing the bank angle because of everything that's discussed here.

Fred

dr_dave
03-27-2007, 11:43 AM
<blockquote><font class="small">Quote Cornerman:</font><hr>Does a fouetté shot necessarily have to be shot with extreme inside? I never thought so.<hr /></blockquote>Good point. I've revised the definition to make it more inclusive.

<blockquote><font class="small">Quote Cornerman:</font><hr>"Twisting" should be in there, as it's more common than most of the other terms in the list.<hr /></blockquote>Ok. You and Jal have convinced me to add "twisting in a bank." Now, would you be so kind as to provide me with a definition with which most people would agree. I could not find one anywhere, nor did anybody I ask know what it means.

<blockquote><font class="small">Quote Cornerman:</font><hr>As a point of organization, it might be useful to separate technical and/or industry terms from slang/jargon.<hr /></blockquote>That would require too many judgment calls as to what is technical/industry/slang/jargon. I prefer having one list so people can easily find almost any common term or phrase (or terms used in my book and articles).

<blockquote><font class="small">Quote Cornerman:</font><hr>Also, if terminology not common to US pool is listed, then you'll end up missing a ton of other game/country specific terminology. E.g. fluke and scratch.<hr /></blockquote>I resisted adding the common snooker/British terms, but I thought they were used frequently enough on forums and by pool players to warrant mention. But I agree this is not necessary useful ... adding some, but not all. That's why I added some links and references for other resources.

Thank you for your feedback and recommendations. I appreciate it.

Regards,
Dave

dr_dave
03-27-2007, 03:50 PM
<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr><blockquote><font class="small">Quote Jal:</font><hr>I went through the whole list but can't remember if it had "twisting", as in "twisting in a bank".<hr /></blockquote>I have never heard or read this term, and I couldn't find it in any of the other glossaries I have reviewed, so I would prefer not add it, unless others also think it is a common and/or important term.<hr /></blockquote>I have heard the term used a couple of times, but can't say how widespread it is.<hr /></blockquote>Jim,

You and Fred have convinced me to add "twisting in a bank" to the expanded glossary. Could you please let me know what you think the phrase means? I couldn't find it anywhere, and the few people I asked didn't know. I assume it has something to do with using spin transfer (from cut angle or English). I hope it doesn't have something to do with twisting the cue stick during the stroke.

Thanks,
Dave

dr_dave
03-27-2007, 03:56 PM
<blockquote><font class="small">Quote Cornerman:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr> Instead I might say, "closer to parallel to the cushion". Life would be a little easier if all pool players knew what "longer" meant in reference to angles off cushions, but they don't. <hr /></blockquote>I'm sure most pool players when they are talking about banking, "longer" means the object ball hit the cushion farther down the table than the hole.<hr /></blockquote>Agreed. When you "lengthen the angle" (e.g., with running English), the "rebound angle" (i.e., "angle of reflection") from the normal (perpendicular) increases, and the bank goes "longer."

Dave

Tom_In_Cincy
03-27-2007, 04:36 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Cornerman:</font><hr>Does a fouetté shot necessarily have to be shot with extreme inside? I never thought so.<hr /></blockquote>Good point. I've revised the definition to make it more inclusive.&lt;&lt;much snipped&gt;&gt;
Regards,
Dave <hr /></blockquote>

Dave,
I read your revised def of the fouetté and it is better.

It has been my experience as a player and an official to look for the double hits when the cue ball is very close to the object ball.
The fouetté (close French translaton is 'whip') shot can be used to actually draw the cue ball off the object ball when they are that close.
Mike Shamos did an artilce last year in his BD column that also had a set up for us non-3 cushion players to understand and possibly use during pocket billiard games.
The object ball is on the spot, the cue ball directly behind it and 1/16th of an inch away. With extreme bottom right, a full stroke, and aiming the cue ball just a balls width from the right hand side of the upper left hand corner, with some practice, you can draw the cue ball directly into the bottom left hand corner.
With extreme top right (and using the same aim) you can go 3 rails into the same bottom left pocket.

An impressive shot for all those players that don't believe it is possible with the cue ball that close to the object ball.

dr_dave
03-27-2007, 10:45 PM
<blockquote><font class="small">Quote Tom_In_Cincy:</font><hr>I read your revised def of the fouetté and it is better.<hr /></blockquote>Thanks. I agree.

<blockquote><font class="small">Quote Tom_In_Cincy:</font><hr>It has been my experience as a player and an official to look for the double hits when the cue ball is very close to the object ball.
The fouetté (close French translaton is 'whip') shot can be used to actually draw the cue ball off the object ball when they are that close.
Mike Shamos did an artilce last year in his BD column that also had a set up for us non-3 cushion players to understand and possibly use during pocket billiard games.
The object ball is on the spot, the cue ball directly behind it and 1/16th of an inch away. With extreme bottom right, a full stroke, and aiming the cue ball just a balls width from the right hand side of the upper left hand corner, with some practice, you can draw the cue ball directly into the bottom left hand corner.
With extreme top right (and using the same aim) you can go 3 rails into the same bottom left pocket.

An impressive shot for all those players that don't believe it is possible with the cue ball that close to the object ball.<hr /></blockquote>I do remember Mike's article. In fact, I think the article is the reason I decided to include the term in the glossary. "Whip shot" (same as fouetté) is also included.

Now, I just need to know what "twisting a bank in" means. Do you or others know?

Regards,
Dave

Jal
03-27-2007, 11:37 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>...Now, I just need to know what "twisting a bank in" means. Do you or others know?<hr /></blockquote>In the context in which I heard it (DCC short-rack bank pool), it meant (at least I took it to mean), putting some transfered english on the object ball to alter its rebound angle, as per your spin transfer demonstration not long ago. I can't remember whether it was Danny DiLiberto or Mark Wilson who used the term.

I've also heard it used with regard to a missed cut shot, but I don't think it was clear whether the commentator meant swerve or spin induced throw.

Perhaps Cornerman will nail it down, but the bank shot reference is likely correct.

Jim

Ralph S.
03-28-2007, 01:54 AM
Correct me if I am wrong, but I beleive many players also or generally refer to twisting a bank shot as bending a bank shot. Thus meaning they use english to slightly change the natural path the object ball would normally take, ie: shortening or lengthening the object balls path.

Cornerman
03-28-2007, 08:00 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> Now, I just need to know what "twisting a bank in" means. Do you or others know?

Regards,
Dave <hr /></blockquote>Twisting = spinning. Twisting a bank means to use spin to lengthen the shot. Using spin to shorten the shot is "hold up."

Some players will also say that they "twisted the shot in," simply meaning they used spin to make the ball (a normal cut shot).

Fred

dr_dave
03-28-2007, 09:36 AM
<blockquote><font class="small">Quote Cornerman:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Now, I just need to know what "twisting a bank in" means. Do you or others know?

Regards,
Dave <hr /></blockquote>Twisting = spinning. Twisting a bank means to use spin to lengthen the shot. Using spin to shorten the shot is "hold up."

Some players will also say that they "twisted the shot in," simply meaning they used spin to make the ball (a normal cut shot).<hr /></blockquote>Fred and Jal,

Thanks a bunch. I just added:

twist: use spin to alter a shot (e.g., use spin-transfer to “twist” a bank in, or use SIT to “twist” a shot in).

I already have all of the other terms we've been throwing around: "long," "hold-up," "lengthen," etc.

Regards,
Dave

Bob_Jewett
04-03-2007, 12:12 PM
<blockquote><font class="small">Quote Cornerman:</font><hr> ... Does a fouetté shot necessarily have to be shot with extreme inside? I never thought so. ... <hr /></blockquote>
No, there are at least two fouette shots I can think of that require outside english. It is startling to see them played and made. One of them was on a recent video posting of Massey and Yow practicing for the Artistic Billiards demo event.

Bob_Jewett
04-03-2007, 12:15 PM
<blockquote><font class="small">Quote Cornerman:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Now, I just need to know what "twisting a bank in" means. Do you or others know?

Regards,
Dave <hr /></blockquote>Twisting = spinning. Twisting a bank means to use spin to lengthen the shot. Using spin to shorten the shot is "hold up."

Some players will also say that they "twisted the shot in," simply meaning they used spin to make the ball (a normal cut shot).

Fred <hr /></blockquote>
I think "twisting" also applies to other bank shots, such as: at one pocket, a ball is an inch off the side rail two diamonds from your pocket. Bank the ball one cushion off the head rail back to your pocket.

Jal
04-06-2007, 01:42 PM
Dr. Dave,

Here are a couple of phrases which recently came to mind that you may or may not want to add. I've gone through your entire list a couple of times, but without going through it again I can't be sure if you have any of these in some alternate form.

"Staying in line", as in maintaining proper angles for subsequent positioning of the cueball as a player moves from ball to ball in a shot sequence.

"Getting an angle", as in positioning the cueball for a cut shot when a player needs to move the cueball laterally for the next shot.

"One-stroking", as when a player, because of nerves or over-confidence, dispenses with the usual warmup strokes and proceeds to miss.

"Jumping up" (often accompanied by one-stroking), as when the player himself/herself raises up out of their stance too quickly (ie, midshot).....as distinguished from anything the cueball might do.

"Bending a bank", as RalphS mentioned earlier. I don't know how common this is, but maybe he can verify that it is used often enough.

These are sort of procedural/form references, but used so often that they may warrant inclusion.

I know you don't want to get too "physicy", but since there are phrases like "coefficient of restitution" and "center of percussion", perhaps "coefficient of friction" might be added too.

You have the definition of "cut angle" precisely given. Although it doesn't come up often in general discussion, it would be nice to have some standardized term for the angle between the aiming line and the line between centers of the cueball and object ball in their pre-shot positions. I believe Mac has called this the "attack angle", and I've used "approach angle" (the latter already being used in reference to the cushion). It becomes an important consideration when the balls are close together. (A standard word may already exist and I may have momentarily forgotten whatever one you may use in your technical proofs.)

In the same vein, you might consider some term for the shift in the tangent line due to the finite compression time. It's not completely negligible in that it should, according to my calculations, virtually cancel throw for a rolling cueball at medium speeds (5-10 mph) at all cut angles, and becomes more significant at very large cut angles and speeds.

Just some thoughts.

Jim

BRussell
04-06-2007, 02:14 PM
Here's one I don't get. It's on Dave's list:

back cut: a cut shot where the cue ball is shot away from the target pocket.

I don't understand the language about being shot away from the pocket. The cue ball isn't shot directly toward the pocket unless it's a straight-in shot. If it's a cut shot, it's always shot away from the pocket, right?

dr_dave
04-06-2007, 02:29 PM
<blockquote><font class="small">Quote BRussell:</font><hr> Here's one I don't get. It's on Dave's list:

back cut: a cut shot where the cue ball is shot away from the target pocket.

I don't understand the language about being shot away from the pocket. The cue ball isn't shot directly toward the pocket unless it's a straight-in shot. If it's a cut shot, it's always shot away from the pocket, right? <hr /></blockquote>You are correct. The original definition was not very good.

How's this:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target rail than the object ball).

Thanks,
Dave

dr_dave
04-06-2007, 03:20 PM
<blockquote><font class="small">Quote Jal:</font><hr> Dr. Dave,

Here are a couple of phrases which recently came to mind that you may or may not want to add. I've gone through your entire list a couple of times, but without going through it again I can't be sure if you have any of these in some alternate form.

"Staying in line", as in maintaining proper angles for subsequent positioning of the cueball as a player moves from ball to ball in a shot sequence.

"Getting an angle", as in positioning the cueball for a cut shot when a player needs to move the cueball laterally for the next shot.

"One-stroking", as when a player, because of nerves or over-confidence, dispenses with the usual warmup strokes and proceeds to miss.

"Jumping up" (often accompanied by one-stroking), as when the player himself/herself raises up out of their stance too quickly (ie, midshot).....as distinguished from anything the cueball might do.

"Bending a bank", as RalphS mentioned earlier. I don't know how common this is, but maybe he can verify that it is used often enough.

These are sort of procedural/form references, but used so often that they may warrant inclusion.

I know you don't want to get too "physicy", but since there are phrases like "coefficient of restitution" and "center of percussion", perhaps "coefficient of friction" might be added too.<hr /></blockquote>Thank you for the suggestions. I've added revised entries for each of these.

Thanks,
Dave

dr_dave
04-06-2007, 03:27 PM
<blockquote><font class="small">Quote Jal:</font><hr>... You have the definition of "cut angle" precisely given. Although it doesn't come up often in general discussion, it would be nice to have some standardized term for the angle between the aiming line and the line between centers of the cueball and object ball in their pre-shot positions. I believe Mac has called this the "attack angle", and I've used "approach angle" (the latter already being used in reference to the cushion). It becomes an important consideration when the balls are close together. (A standard word may already exist and I may have momentarily forgotten whatever one you may use in your technical proofs.)<hr /></blockquote>I don't think I have ever used a term for this angle, and I don't think I have ever seen this angle referenced in published material. I think I would probably call it the "ghost-ball angle" because it is the angle between the OB and the GB as seen from the CB. Actually, I would probably avoid calling it anything, and just talk about the cut angle and distance between the CB and OB instead. I will consider adding it if we can come up with a term that doesn't mean something else and is meaning and useful. I think I need more convincing on this one.

Thanks,
Dave

PS: In my book (but not in the glossary), I also use "approach angle" in reference to frozen combos.

dr_dave
04-06-2007, 03:31 PM
<blockquote><font class="small">Quote Jal:</font><hr>... you might consider some term for the shift in the tangent line due to the finite compression time. It's not completely negligible in that it should, according to my calculations, virtually cancel throw for a rolling cueball at medium speeds (5-10 mph) at all cut angles, and becomes more significant at very large cut angles and speeds.<hr /></blockquote>Jim,

Are you referring to the slight compression and flattening between the CB and OB during their incredibly brief contact time? I have not looked at these numbers, but I would expect them to be way too small to have any significant effect on tangent-line angle or shift. However, intuition isn't always right, so I would like to see your data and calculations.

Thanks,
Dave

Bob_Jewett
04-06-2007, 03:54 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... How's this:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target rail than the object ball). ... <hr /></blockquote>
I think that's still ambiguous. How about: "when the butt of the cue stick passes over one of the cushions adjacent to the pocket." It could continue, "The more perpendicular the cue stick is to that cushion, the greater is the back cut."

dr_dave
04-06-2007, 04:09 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... How's this:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target rail than the object ball). ... <hr /></blockquote>
I think that's still ambiguous. How about: "when the butt of the cue stick passes over one of the cushions adjacent to the pocket." It could continue, "The more perpendicular the cue stick is to that cushion, the greater is the back cut." <hr /></blockquote>Ok. Here is what I have posted (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) now:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target pocket rail than the object ball). In other words, the butt of the cue stick passes over one of the cushions adjacent to the target pocket. The more perpendicular the cue stick is to that cushion, the greater the back cut.

Thanks,
Dave

Jal
04-06-2007, 04:31 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>... You have the definition of "cut angle" precisely given. Although it doesn't come up often in general discussion, it would be nice to have some standardized term for the angle between the aiming line and the line between centers of the cueball and object ball in their pre-shot positions. I believe Mac has called this the "attack angle", and I've used "approach angle" (the latter already being used in reference to the cushion). It becomes an important consideration when the balls are close together. (A standard word may already exist and I may have momentarily forgotten whatever one you may use in your technical proofs.)<hr /></blockquote>I don't think I have ever used a term for this angle, and I don't think I have ever seen this angle referenced in published material. I think I would probably call it the "ghost-ball angle" because it is the angle between the OB and the GB as seen from the CB. Actually, I would probably avoid calling it anything, and just talk about the cut angle and distance between the CB and OB instead. I will consider adding it if we can come up with a term that doesn't mean something else and is meaning and useful. I think I need more convincing on this one.

Thanks,
Dave

PS: In my book (but not in the glossary), I also use "approach angle" in reference to frozen combos. <hr /></blockquote>Dr. Dave,

"Ghost-ball angle" sounds great to me. I also like "attack angle", but yours is perhaps more evocative. At any rate, I probably can't make a strong case for inclusion, other than that it is part of the geometry and happens to crop up in the analysis of some shots (lately the "impossible shots" of a recent thread). I defer to your judgement (of course).

Jim

Jal
04-06-2007, 04:42 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>... you might consider some term for the shift in the tangent line due to the finite compression time. It's not completely negligible in that it should, according to my calculations, virtually cancel throw for a rolling cueball at medium speeds (5-10 mph) at all cut angles, and becomes more significant at very large cut angles and speeds.<hr /></blockquote>Jim,

Are you referring to the slight compression and flattening between the CB and OB during their incredibly brief contact time? I have not looked at these numbers, but I would expect them to be way too small to have any significant effect on tangent-line angle or shift. However, intuition isn't always right, so I would like to see your data and calculations.

Thanks,
Dave
<hr /></blockquote>Yes, that is what I'm refering to (aka "flatspot squeeze"). I'll make up a diagram with numbers later tonight for your consideration. From past discussions, Cushioncrawler (Mac) seems to get the same figures as I do, which bolsters my confidence that they are likely right. But it will be nice to have your verdict.

Jim

dr_dave
04-06-2007, 04:50 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>... you might consider some term for the shift in the tangent line due to the finite compression time. It's not completely negligible in that it should, according to my calculations, virtually cancel throw for a rolling cueball at medium speeds (5-10 mph) at all cut angles, and becomes more significant at very large cut angles and speeds.<hr /></blockquote>Jim,

Are you referring to the slight compression and flattening between the CB and OB during their incredibly brief contact time? I have not looked at these numbers, but I would expect them to be way too small to have any significant effect on tangent-line angle or shift. However, intuition isn't always right, so I would like to see your data and calculations.

Thanks,
Dave
<hr /></blockquote>Yes, that is what I'm refering to (aka "flatspot squeeze"). I'll make up a diagram with numbers later tonight for your consideration. From past discussions, Cushioncrawler (Mac) seems to get the same figures as I do, which bolsters my confidence that they are likely right. But it will be nice to have your verdict.

Jim <hr /></blockquote>Jim,

I look forward to seeing your diagram, numbers, and calculations.

Thanks,
Dave

BRussell
04-06-2007, 05:17 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Ok. Here is what I have posted (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) now:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target pocket rail than the object ball). In other words, the butt of the cue stick passes over one of the cushions adjacent to the target pocket. The more perpendicular the cue stick is to that cushion, the greater the back cut.

Thanks,
Dave <hr /></blockquote> Hmm, maybe it's me, but I still don't get it. Is there some cut angle that's always a back cut, say 45º or more? From your definition it seems like maybe it's a matter of degree rather than one discrete point where it becomes a back cut?

I don't mean to be picking on this, but it's just a term I've often heard people use when playing, and I've never understood it, and I've never asked for fear of looking stupid. /ccboard/images/graemlins/grin.gif

dr_dave
04-06-2007, 05:29 PM
<blockquote><font class="small">Quote BRussell:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Ok. Here is what I have posted (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) now:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target pocket rail than the object ball). In other words, the butt of the cue stick passes over one of the cushions adjacent to the target pocket. The more perpendicular the cue stick is to that cushion, the greater the back cut.

Thanks,
Dave <hr /></blockquote> Hmm, maybe it's me, but I still don't get it. Is there some cut angle that's always a back cut, say 45º or more? From your definition it seems like maybe it's a matter of degree rather than one discrete point where it becomes a back cut?

I don't mean to be picking on this, but it's just a term I've often heard people use when playing, and I've never understood it, and I've never asked for fear of looking stupid. /ccboard/images/graemlins/grin.gif <hr /></blockquote>I think any cut shot, where the cue stick points away from the near target-pocket rail is a "back cut." For larger cut angles, it is a tougher back cut, but even a small cut angle shot can be a "back cut" (e.g., if the OB is close to a long rail and the CB is even closer, and you are cutting the OB into the corner pocket at the end of the long rail).

Regards,
Dave

Jal
04-07-2007, 01:59 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>
I look forward to seeing your diagram, numbers, and calculations.<hr /></blockquote>Dr. Dave, for better or worse, here they are. The angle delta is the one we seek, which is of course greatly exaggerated in the diagram for the sake of clarity. The length x (see object ball) is half the distance the cueball will traverse along the new tangent line during impact.

http://ww2.netnitco.net/users/gtech/CompressionAngle.jpg

The second derivation, which adds a throw adjustment for x, assumes the compression force is symmetric about T/2, which is only approximately true (e is not 1). This allows us to figure the average throw velocity as 1/2 the final throw velocity u. But this is a very, very small effect so I'll use the first and simpler formula to calculate delta.

With an initial cueball speed of 3 mph, delta is as follows for the indicated cut angles:

15: 0.07 deg
30: 0.13
60: 0.23
80: 0.27

With an initial speed of 7 mph:

15: 0.16 deg
30: 0.32
60: 0.55
80: 0.62

And with an initial speed of 12 mph:

15: 0.28 deg
30: 0.54
60: 0.94
80: 1.06

I assumed an impact time (T) of 0.0002 sec in all of the calculations, which of course is not likely to be exactly true.

Do you think the logic is correct?

Jim

Cornerman
04-07-2007, 08:17 AM
<blockquote><font class="small">Quote BRussell:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Ok. Here is what I have posted (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) now:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target pocket rail than the object ball). In other words, the butt of the cue stick passes over one of the cushions adjacent to the target pocket. The more perpendicular the cue stick is to that cushion, the greater the back cut.

Thanks,
Dave <hr /></blockquote> Hmm, maybe it's me, but I still don't get it. Is there some cut angle that's always a back cut, say 45º or more? From your definition it seems like maybe it's a matter of degree rather than one discrete point where it becomes a back cut?

I don't mean to be picking on this, but it's just a term I've often heard people use when playing, and I've never understood it, and I've never asked for fear of looking stupid. /ccboard/images/graemlins/grin.gif <hr /></blockquote>If you don't know what a back cut is, then the progression of the glossary definition attempt is only going to confuse you, I'm afraid.

None of my explanation will help either...

These are all examples of back cuts. Notice that one of them, there is no adjcacent rail.

http://CueTable.com/P/?@2ABDB1PNDj2UBDB2UcIq1kNDj1kBSv2kIrF@

http://CueTable.com/P/?@4AUuU4PXnG4UUuU4UUmX4UdGt4kXnG4kTgF4kDQj3kaBh3kM qD@

http://CueTable.com/P/?@3ABXQ1PRWH3UBXQ2UdII1kRWH4kBHU3kQni3kaRV@

So, it's really where the object ball is in relation to the cueball and the pocket.

You might just say, "that's a normal cut shot." It is, but it's backward cut shot (back cut) as opposed to any normal cut shot:

http://CueTable.com/P/?@3AEqR4PJiQ3UEqR3UcbH4kJiQ3kCeX2kAeF@

http://CueTable.com/P/?@3AFah2PCNI3UFah3UcAh2kCNI3kDuU4kSKk4kbBW4kDKm@

I guess the definition could have something to do with drawing lines parallel to the rail and seeing where the cueball and object ball lines land. THe cueball parallel line will be inside the object ball line.

The standard Mosconi break shot in 14.1 is usually a backcut, and he would advise to follow off the stack. If it's less than a back cut, Mizerak would advise to draw off the stack.

Fred

Stretch
04-07-2007, 09:28 AM
<blockquote><font class="small">Quote Cornerman:</font><hr> <blockquote><font class="small">Quote BRussell:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Ok. Here is what I have posted (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf) now:

back cut: a cut shot where the cue ball is shot well away from the target pocket (e.g., when the cue ball is much closer to the target pocket rail than the object ball). In other words, the butt of the cue stick passes over one of the cushions adjacent to the target pocket. The more perpendicular the cue stick is to that cushion, the greater the back cut.

Thanks,
Dave <hr /></blockquote> Hmm, maybe it's me, but I still don't get it. Is there some cut angle that's always a back cut, say 45º or more? From your definition it seems like maybe it's a matter of degree rather than one discrete point where it becomes a back cut?

I don't mean to be picking on this, but it's just a term I've often heard people use when playing, and I've never understood it, and I've never asked for fear of looking stupid. /ccboard/images/graemlins/grin.gif <hr /></blockquote>If you don't know what a back cut is, then the progression of the glossary definition attempt is only going to confuse you, I'm afraid.

None of my explanation will help either...

These are all examples of back cuts. Notice that one of them, there is no adjcacent rail.

http://CueTable.com/P/?@2ABDB1PNDj2UBDB2UcIq1kNDj1kBSv2kIrF@

http://CueTable.com/P/?@4AUuU4PXnG4UUuU4UUmX4UdGt4kXnG4kTgF4kDQj3kaBh3kM qD@

http://CueTable.com/P/?@3ABXQ1PRWH3UBXQ2UdII1kRWH4kBHU3kQni3kaRV@

So, it's really where the object ball is in relation to the cueball and the pocket.

You might just say, "that's a normal cut shot." It is, but it's backward cut shot (back cut) as opposed to any normal cut shot:

http://CueTable.com/P/?@3AEqR4PJiQ3UEqR3UcbH4kJiQ3kCeX2kAeF@

http://CueTable.com/P/?@3AFah2PCNI3UFah3UcAh2kCNI3kDuU4kSKk4kbBW4kDKm@

I guess the definition could have something to do with drawing lines parallel to the rail and seeing where the cueball and object ball lines land. THe cueball parallel line will be inside the object ball line.

The standard Mosconi break shot in 14.1 is usually a backcut, and he would advise to follow off the stack. If it's less than a back cut, Mizerak would advise to draw off the stack.

Fred <hr /></blockquote>

I'm confused by this term as well. For me a cut shot is a cut shot regardless of where it's going. I have used the term cut back or back-cut to describe a particular shot but only when describing a bank shot as in cutback bank shot. This is where your banking a ball backwards against itself. These are notoriously hard to judge because they keep wanting to come back short of the pocket. You really have to OVERCUT them a bit to bring them back on line to the pocket. Other than that, i just go with calling a cut shot just that if it's going straight to a pocket. St.

Bob_Jewett
04-09-2007, 10:45 AM
<blockquote><font class="small">Quote Cornerman:</font><hr> ... If you don't know what a back cut is, then the progression of the glossary definition attempt is only going to confuse you, I'm afraid. ... <hr /></blockquote>
My suggestion for a definition -- the butt of the cue stick passes over one of the two cushions adjacent to the pocket -- doesn't work for the side pocket shot in your examples. It can be patched up if a cushion is added (imaginarily) between the "far" points of the two side pockets.

When I was first learning to play, the guys in the pool hall planted the nasty little mind worm in my brain that "back cuts" were somehow special and more difficult than normal shots. I think the main problem with them for corner pockets is that you can't actually see the target on the cloth that you are shooting the ball towards, if you are well down on the shot. One technique for dealing with them is to construct a temporary "non-back cut" rail with your cue stick.

dr_dave
04-09-2007, 04:38 PM
Jim,

Thanks for the illustration and equations. I looked through it and still have a few concerns. When I get some time, I'll try to look at this in more detail.

Here are my concerns:

- I don't think you can assume the CB and/or CB velocities are constant during the impact.

- The ball contact times probably vary tremendously with speed and cut angle. The only data I've seen is Marlow's data for full-ball (zero cut angle) hits at various speeds. Here is his data for contact times for three different speeds (from the corrected page 45 of his book):

0.559 ms @ 0.1 m/s
0.284 ms @ 1 m/s
0.144 ms @ 10 m/s

And again, this is for full-ball hits only. I would expect the contact times to decrease with cut angle, but I could be wrong.

- Whatever you do, total momentum must be conserved after impact ... that's the only thing we know for sure. If you also assume e=1, then energy should also be conserved.

I have to admit that I'm still a little skeptical that the tiny ball deformations can have any significant affect on the tangent line offset or direction, but I'm still open to the possibility.

Regards,
Dave


<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>
I look forward to seeing your diagram, numbers, and calculations.<hr /></blockquote>Dr. Dave, for better or worse, here they are. The angle delta is the one we seek, which is of course greatly exaggerated in the diagram for the sake of clarity. The length x (see object ball) is half the distance the cueball will traverse along the new tangent line during impact.

http://ww2.netnitco.net/users/gtech/CompressionAngle.jpg

The second derivation, which adds a throw adjustment for x, assumes the compression force is symmetric about T/2, which is only approximately true (e is not 1). This allows us to figure the average throw velocity as 1/2 the final throw velocity u. But this is a very, very small effect so I'll use the first and simpler formula to calculate delta.

With an initial cueball speed of 3 mph, delta is as follows for the indicated cut angles:

15: 0.07 deg
30: 0.13
60: 0.23
80: 0.27

With an initial speed of 7 mph:

15: 0.16 deg
30: 0.32
60: 0.55
80: 0.62

And with an initial speed of 12 mph:

15: 0.28 deg
30: 0.54
60: 0.94
80: 1.06

I assumed an impact time (T) of 0.0002 sec in all of the calculations, which of course is not likely to be exactly true.

Do you think the logic is correct?

Jim
<hr /></blockquote>

Jal
04-09-2007, 05:52 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ..Thanks for the illustration and equations. I looked through it and still have a few concerns. When I get some time, I'll try to look at this in more detail.<hr /></blockquote>Dr. Dave,

Of course it's best if you think it through independently, but I'd just like to respond to a few points for the record.

<blockquote><font class="small">Quote dr_dave:</font><hr>- I don't think you can assume the CB and/or CB velocities are constant during the impact.<hr /></blockquote>I agree. My derivation is not exact and assumes (for the non-friction/non-throw case) that the cueball's velocity along the chord (x-direction) is vsin(alpha). As you're indicating (I think), the object ball will be given some momentum in this direction during the first half of impact. As I see it, it will have this momentum quelched during the second half (arguing from symmetry and taking e=1).

In turn the cueball will slow during the first half and then regain its original speed vsin(alpha) during the second. So its time averaged velocity will in fact be a little less than vsin(alpha) in this direction. I've mulled over how to calculate this, and I don't think it would be too hard assuming a Hertz force/compression relation F = Ky^(3/2) where y is the total "penetration" of the balls. An adjustment to the OB's final velocity would similarly need to be made.

But my thoughts were that these are likely small corrections to an already fairly small effect (along with inelasticity and throw), so I didn't pursue it any further.

<blockquote><font class="small">Quote dr_dave:</font><hr>- The ball contact times probably vary tremendously with speed and cut angle. The only data I've seen is Marlow's data for full-ball (zero cut angle) hits at various speeds. Here is his data for contact times for three different speeds (from the corrected page 45 of his book):

0.559 ms @ 0.1 m/s
0.284 ms @ 1 m/s
0.144 ms @ 10 m/s

And again, this is for full-ball hits only. I would expect the contact times to decrease with cut angle, but I could be wrong.<hr /></blockquote>Thank you very much for the data. Very interesting. Hertz Law gives a contact time inversely proportional to the 1/5'th (0.2) power of speed. Marlow's numbers indicate a stronger relation, almost exactly 0.294. I didn't include the Hertz (1/5) adjustment because I had no idea at what impact velocity his 0.2 msec (which gets mentioned here and there) was obtained.

Your high speed filming agenda is probably full, but if you ever have the time and inkling, it would be of interest to some of us to set up a line of balls with a small gap between each one (say 1/32" or so), and then measure the time delay between the first and last balls being impacted, I think that pretty accurate and independent figures for the contact times could be obtained. Just a thought.

<blockquote><font class="small">Quote dr_dave:</font><hr>- Whatever you do, total momentum must be conserved after impact ... that's the only thing we know for sure. If you also assume e=1, then energy should also be conserved.

I have to admit that I'm still a little skeptical that the tiny ball deformations can have any significant affect on the tangent line offset or direction, but I'm still open to the possibility.<hr /></blockquote>Yes, as per above, I admit that my formula and calculations are not perfect. I suspect that a better treatment would not show major differences, but I could be wrong. Hope you get the time to apply your expertise.

Jim

cushioncrawler
04-09-2007, 07:45 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> .....I don't think you can assume the CB and/or CB velocities are constant during the impact...

.... I would expect the contact times to decrease with cut angle, but I could be wrong...

....I have to admit that I'm still a little skeptical that the tiny ball deformations can have any significant affect on the tangent line offset or direction, but I'm still open to the possibility...<hr /></blockquote>Dr Dave -- I think that the XX velocity can be considered to be constant if u assume zero friktion, or if u assume gearing english on the qball. Hencely, the balltoball line velocity (YY) can be ignored (depending on how one duz the calcs).

The contact times will decrease (slightly) with cut angle, but the "flatspot sqeez angle" increases anyhow, koz of the (not slightly) increased XX speed (qball).

My calcs show that one can get an "impact angle" of over 1.0dg for highish speeds (4m/s qball speed) and fine cuts (1/8th ball), which means that flatspot-sqeez (my term) can add as much as 0.5dg to the OB's cut angle (ie half of 1.0dg). The "impact angle" is the difference between the tangent line angle at initial contact and the tangent line angle at final contact (my own term and definition). madMac.

dr_dave
04-10-2007, 09:21 AM
<blockquote><font class="small">Quote Jal:</font><hr>Your high speed filming agenda is probably full, but if you ever have the time and inkling, it would be of interest to some of us to set up a line of balls with a small gap between each one (say 1/32" or so), and then measure the time delay between the first and last balls being impacted, I think that pretty accurate and independent figures for the contact times could be obtained. Just a thought.<hr /></blockquote>Jim,

I would be happy to add this or any other experiment to my list of things to shoot. I plan to do a filming session within the next month of so.

I wish I had an even better camera that could be used to directly and accurately measure ball contact times for various speeds and cut angles. Unfortunately, my high-speed camera is too slow to get accurate readings on ball contact times. I can film at up to 10,000 frames/sec (FPS); but the resolution is much too limiting at this fast a speed. I usually run at 1,000 FPS or 3,000 FPS.

Regards,
Dave

dr_dave
04-10-2007, 09:45 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> .....I don't think you can assume the CB and/or CB velocities are constant during the impact...

.... I would expect the contact times to decrease with cut angle, but I could be wrong...

....I have to admit that I'm still a little skeptical that the tiny ball deformations can have any significant affect on the tangent line offset or direction, but I'm still open to the possibility...<hr /></blockquote>Dr Dave -- I think that the XX velocity can be considered to be constant if u assume zero friktion, or if u assume gearing english on the qball. Hencely, the balltoball line velocity (YY) can be ignored (depending on how one duz the calcs).

The contact times will decrease (slightly) with cut angle, but the "flatspot sqeez angle" increases anyhow, koz of the (not slightly) increased XX speed (qball).

My calcs show that one can get an "impact angle" of over 1.0dg for highish speeds (4m/s qball speed) and fine cuts (1/8th ball), which means that flatspot-sqeez (my term) can add as much as 0.5dg to the OB's cut angle (ie half of 1.0dg). The "impact angle" is the difference between the tangent line angle at initial contact and the tangent line angle at final contact (my own term and definition). madMac.<hr /></blockquote>Mac,

It looks like you and Jal have thought about this a lot. Your reasoning sounds good. I'll try to look at this closer also, when I get some time.

Thank you (and Jal) for the further explanations,
Dave

Jal
04-10-2007, 10:35 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>..I would be happy to add this or any other experiment to my list of things to shoot. I plan to do a filming session within the next month of so.

I wish I had an even better camera that could be used to directly and accurately measure ball contact times for various speeds and cut angles. Unfortunately, my high-speed camera is too slow to get accurate readings on ball contact times. I can film at up to 10,000 frames/sec (FPS); but the resolution is much too limiting at this fast a speed. I usually run at 1,000 FPS or 3,000 FPS.

Regards,
Dave <hr /></blockquote>Dr. Dave, I was thinking that between the time delay from the first and last impacts, and the differential speeds of the first and last ball, you could extract a figure for both the impact duration(s) and coefficients of restitution(s). But I guess you would have to assume the functions, including the constants, which might not be too good an idea given Marlow's data for the impact times?

For curiousity sake, here are two plots of the compression angle using both Hertz' Law for the time durations (T ~ (1/V)^0.2), and Marlow's results (T ~ (1/V)^0.29). The numerators in the expressions for T below are an implicit 1 m/s and the 0.000284 sec is the corresponding impact time (from Marlow's data).

As you can see, there's not a heck of a lot of difference between them.

http://ww2.netnitco.net/users/gtech/CompressionAngleHertz.jpg

http://ww2.netnitco.net/users/gtech/CompressionAngleMarlow.jpg

As I see it, contact time increases with cut angle as vcos(phi) diminishes. It's only limited by the length of the chord in the direction of the cueball's pre-impact velocity. The plots then are shown up to 87 degrees, since this is where that limit is reached for the fastest speed (16 mph). The condition is:

2(Rsin(delta)) &lt;= (2R)cos(phi) or

sin(delta) &lt;= cos(phi)

which holds true in all of the above. But you and Mac might still disagree that contact time increases?

The plots get less accurate as you approach 87 degrees since I should have used vcos(alpha) [=vcos(phi+delta)] instead of vcos(phi) to get the contact times. But the plotting software isn't capable of solving for delta after substituting the expression for T in the expression for tan(delta).

Of course, your analysis may yield something completely different.

Jim

dr_dave
04-10-2007, 10:48 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>..I would be happy to add this or any other experiment to my list of things to shoot. I plan to do a filming session within the next month of so.

I wish I had an even better camera that could be used to directly and accurately measure ball contact times for various speeds and cut angles. Unfortunately, my high-speed camera is too slow to get accurate readings on ball contact times. I can film at up to 10,000 frames/sec (FPS); but the resolution is much too limiting at this fast a speed. I usually run at 1,000 FPS or 3,000 FPS.

Regards,
Dave<hr /></blockquote>Dr. Dave, I was thinking that between the time delay from the first and last impacts, and the differential speeds of the first and last ball, you could extract a figure for both the impact duration(s) and coefficients of restitution(s). But I guess you would have to assume the functions, including the constants, which might not be too good an idea given Marlow's data for the impact times?<hr /></blockquote>Agreed. Such an experiment would probably not be that useful.

<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>..I would be happy to add this or any other exFor curiousity sake, here are two plots of the compression angle using both Hertz' Law for the time durations (T ~ (1/V)^0.2), and Marlow's results (T ~ (1/V)^0.29). The numerators in the expressions for T below are an implicit 1 m/s and the 0.000284 sec is the corresponding impact time (from Marlow's data).

As you can see, there's not a heck of a lot of difference between them.

http://ww2.netnitco.net/users/gtech/CompressionAngleHertz.jpg

http://ww2.netnitco.net/users/gtech/CompressionAngleMarlow.jpg

As I see it, contact time increases with cut angle as vcos(phi) diminishes. It's only limited by the length of the chord in the direction of the cueball's pre-impact velocity. The plots then are shown up to 87 degrees, since this is where that limit is reached for the fastest speed (16 mph). The condition is:

2(Rsin(delta)) &lt;= (2R)cos(phi) or

sin(delta) &lt;= cos(phi)

which holds true in all of the above. But you and Mac might still disagree that contact time increases?

The plots get less accurate as you approach 87 degrees since I should have used vcos(alpha) [=vcos(phi+delta)] instead of vcos(phi) to get the contact times. But the plotting software isn't capable of solving for delta after substituting the expression for T in the expression for tan(delta).

Of course, your analysis may yield something completely different.

Jim<hr /></blockquote>It looks like you are getting better at doing fast analysis and making fast plots. I don't feel so special anymore.

Way to go,
Dave

Jal
04-10-2007, 01:14 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> It looks like you are getting better at doing fast analysis and making fast plots. I don't feel so special anymore.

Way to go,
Dave <hr /></blockquote>You're an inspiration, but I'll never break the five minute mark...or the one hour mark for that matter. /ccboard/images/graemlins/smile.gif

Jim

cushioncrawler
04-10-2007, 03:59 PM
<blockquote><font class="small">Quote Jal:</font><hr> ....which holds true in all of the above. But you and Mac might still disagree that contact time increases?

The plots get less accurate as you approach 87 degrees since I should have used vcos(alpha) [=vcos(phi+delta)] instead of vcos(phi) to get the contact times. But the plotting software isn't capable of solving for delta after substituting the expression for T in the expression for tan(delta)..... <hr /></blockquote>Jim -- I did say earlyr to Dr Dave that contact time "dekreeces" with finer contacts, but of course i shood have said "inkreeces". This makes the FlatSpot-Sqeez (angle) even larger, ie it rezults in a finer cut angle than simple contact-theory might suggest.

I karnt comment much about equations and accuracy. But, i do remember mentioning in similar threads about a year ago that my own "geometric" sort of analysis of impact had a major flaw when the contact got very very thin, at high speeds at least. I hadnt realized that the theoretical size (diameter, mm) of the FlatSpot iznt achieved here, koz the simple geometry of 2 "circles" "touching" places a limit on the size of the FlatSpot. Hmmmmm, perhaps i can explain a different way -- lets see. Early on, u would have calculated the balltoball contact (angle), probably Cos(), then u calculated the FlatSpot-Sqeez (angle) -- u call it Compression Angle i think -- now, u shood go back and modyfy your initial angle (cos) -- ie it shood be a sort of iteration process.

Did u remember to halve the "Impact-Angle" to get yor "Compression-Angle" ??? madMac.

Jal
04-10-2007, 06:06 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> ....which holds true in all of the above. But you and Mac might still disagree that contact time increases?

The plots get less accurate as you approach 87 degrees since I should have used vcos(alpha) [=vcos(phi+delta)] instead of vcos(phi) to get the contact times. But the plotting software isn't capable of solving for delta after substituting the expression for T in the expression for tan(delta)..... <hr /></blockquote>Jim -- I did say earlyr to Dr Dave that contact time "dekreeces" with finer contacts, but of course i shood have said "inkreeces". This makes the FlatSpot-Sqeez (angle) even larger, ie it rezults in a finer cut angle than simple contact-theory might suggest.<hr /></blockquote>Thank you very much Mac. I'm glad you agree (been wondering if I'm looking at it all wrong, although Dr. Dave may yet weigh in differently).

<blockquote><font class="small">Quote cushioncrawler:</font><hr> But, i do remember mentioning in similar threads about a year ago that my own "geometric" sort of analysis of impact had a major flaw when the contact got very very thin, at high speeds at least. I hadnt realized that the theoretical size (diameter, mm) of the FlatSpot iznt achieved here, koz the simple geometry of 2 "circles" "touching" places a limit on the size of the FlatSpot. Hmmmmm, perhaps i can explain a different way -- lets see.<hr /></blockquote>No need to, what you said is perfectly clear. Did you come up with a condition or criteria for determining when this point is reached? If so, I'm wondering if it is equivalent to the one I gave above?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Early on, u would have calculated the balltoball contact (angle), probably Cos(), then u calculated the FlatSpot-Sqeez (angle) -- u call it Compression Angle i think -- now, u shood go back and modyfy your initial angle (cos) -- ie it shood be a sort of iteration process.<hr /></blockquote>Yes, that would definitely work Mac, but I can't do that with the plotter software. I can do it another way (sans graphs), and I may try it because it should, I think, increase the angle even more. But it's a little pointless right now, perhaps, in that there is another correction that needs to be made, even for the non-friction/e=1 case, although hopefully it won't change things much. I though I might wait to see Dr. Dave's work, if he gets the time.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Did u remember to halve the "Impact-Angle" to get yor "Compression-Angle" ??? madMac. <hr /></blockquote>I'm not exactly sure what you mean by "impact angle" but the addition to the cut angle (shift of the tangent line) is delta as diagrammed above (ie, the angle subtended by half the chord). If you're getting different numbers, it might be that we're using different contact times. From what you've described in the past or from the materials you sent me, I suspect that our methods of calculating the overall effect are equivalent. I plan on looking through them again to see what you said, and if you have anything on the contact time (sorry, my damn memory). I do remember that Hertz is not your prefered means of travel. And apparently, judging from Marlow's results, as well as yours but whose details I've forgotten, you are right.

Jim

Qtec
04-10-2007, 09:11 PM
I thought a back cut was a shot that when focusing on the target/OB , the pocket was out of your line of sight. ie you can't see the pocket.

I'd just like to say tho that the graphs in this thread have totally turned my game around. Thanks guys./ccboard/images/graemlins/smirk.gif
Qtec

dr_dave
04-11-2007, 09:50 AM
<blockquote><font class="small">Quote Qtec:</font><hr> I thought a back cut was a shot that when focusing on the target/OB , the pocket was out of your line of sight. ie you can't see the pocket.<hr /></blockquote>I agree. The OB is being cut back to the pocket away from your field of view. That's why I'm sticking with the current rivision of the definition. Although, I can see how people might use Fred's definition also.

Dave

dr_dave
04-11-2007, 09:57 AM
<blockquote><font class="small">Quote Jal:</font><hr>Dr. Dave may yet weigh in differently.<hr /></blockquote>Jal,

I just wanted to let you know that I'm not trying to avoid the topic. I'm just very busy right now. Also, honestly, I don't feel super motivated to spend a lot of time on something that I think is a very small effect (and probably not that useful to know at the table). I think even the best shooters can rarely be accurate and repeatable to less than 1 degree. Also, as shown in TP 3.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-4.pdf), for cut shots typical OB errors will be more than 1 degree. Also, a 1-degree difference can be very difficult for a human to visualize.

I hope you don't take offense at these remarks. I just wanted to be honest about my lack of motivation.

Regards,
Dave

Jal
04-11-2007, 02:56 PM
<blockquote><font class="small">Quote Qtec:</font><hr> I thought a back cut was a shot that when focusing on the target/OB , the pocket was out of your line of sight. ie you can't see the pocket.<hr /></blockquote>What about if you have your eyes closed?

<blockquote><font class="small">Quote Qtec:</font><hr>I'd just like to say tho that the graphs in this thread have totally turned my game around. Thanks guys./ccboard/images/graemlins/smirk.gif
Qtec <hr /></blockquote>Qtec, I'm thrilled and delighted that they've helped someone so quickly. For your further edification and advancement:

http://ww2.netnitco.net/users/gtech/pie.jpg


Jim

Jal
04-12-2007, 01:28 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>I just wanted to let you know that I'm not trying to avoid the topic. I'm just very busy right now. Also, honestly, I don't feel super motivated to spend a lot of time on something that I think is a very small effect (and probably not that useful to know at the table). I think even the best shooters can rarely be accurate and repeatable to less than 1 degree. Also, as shown in TP 3.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/TP_3-4.pdf), for cut shots typical OB errors will be more than 1 degree. Also, a 1-degree difference can be very difficult for a human to visualize.

I hope you don't take offense at these remarks. I just wanted to be honest about my lack of motivation.<hr /></blockquote>Dr. Dave,

Not at all and thanks for the concern. It certainly is a small effect, but I think warrants some attention for its influence at large cut angles and high speeds.

For instance, one of Marlow's throw shots is at 10 m/s at a 45 deg cut angle, with a resulting measured "throw" of 0.57 deg (corresponding to mu=.01). However, the above theory (using Marlow's contact time data), yields an added compression angle of 1.14 deg, suggesting that the true throw was really 1.14+0.57=1.71 deg. This will have a significant effect on the mu vs speed curves, and I don't think one can be very satisfied that this is built into mu. (The compression angle for his 1 m/s shot is only 0.21 deg according to this.)

Jim

dr_dave
04-12-2007, 11:25 AM
<blockquote><font class="small">Quote Jal:</font><hr>It certainly is a small effect, but I think warrants some attention for its influence at large cut angles and high speeds.<hr /></blockquote>This is where the physics is a little suspicious to me. For large cut angles and high speeds, I think the assumption of a perfectly elastic collision (i.e., COR = e = 1) is a little dangerous. If the CB is sliding or rolling along the OB an appreciable amount during impact and compression, I think there is a chance the OB won't transfer the stored elastic energy back into the CB as efficiently. Maybe you can come up with some experiments to measure this effect, but it might be tough to get reliable data at large cut angles.

<blockquote><font class="small">Quote Jal:</font><hr>For instance, one of Marlow's throw shots is at 10 m/s at a 45 deg cut angle, with a resulting measured "throw" of 0.57 deg (corresponding to mu=.01). However, the above theory (using Marlow's contact time data), yields an added compression angle of 1.14 deg, suggesting that the true throw was really 1.14+0.57=1.71 deg. This will have a significant effect on the mu vs speed curves, and I don't think one can be very satisfied that this is built into mu. (The compression angle for his 1 m/s shot is only 0.21 deg according to this.)<hr /></blockquote>I agree that it is unsatisfying using Marlow's data for friction values because the values do not represent true friction. His numbers are "effective friction" values that take everything into consideration: friction, ball-compression and deflection-angle, variation in COR, etc. However, I don't know of any way to easily separate and measure all of the different effects. A more satisfying model for friction would include cut angle, speed,

I think using Marlow's "effective friction" model is Ok for making general conclusions about how throw varies with cut angle, speed, English, etc. I think it does a decent job at predicting trends useful to know at the table. The exact values for throw aren't so important because conditions can vary from one set of balls to the next. What is important is understanding the trends of how total "effective throw" varies for different types of shots. Experimental data has verified many of the trends predicted by the "effective throw" analysis (TP A.14 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-14.pdf)) using Marlow's data (see my September '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/sept06.pdf) and October '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/oct06.pdf) articles).

Bottom line: better models for friction, COR, and compression deflection-angle that take into account speed, cut angle, and English for each effect would be nice, but I think this is extremely difficult, and the payoff (in terms of better understanding of "effective throw" trends) might not be that great.

Thank you for your efforts. I had not really thought much about ball-compression deflection-angle effects before. I'm glad you and Mac brought it to my attention. I agree that your physics looks sound, based on your assumptions. Now, if you can give me separate models for COR, COF, and ball-compression deflection-angle (BCDA) as functions of cut-angle, speed, English, spin, and ball conditions, backed up by experimental data, I would be very happy (and forever in your debt). Then I could expand and improve my throw and spin transfer analyses. My suspicion is that the trends would not be very different (as compared to using the "effective friction" model), but this would certainly be interesting to see.

Thanks again,
Dave

PS: I just posted TP A.28 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-28.pdf). It includes graphs that show every effect related to cut-angle, speed, English, and vertical plane spin (follow/draw). It is based on my throw analysis that uses Marlow's "effective friction" values.

cushioncrawler
04-12-2007, 04:27 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> .....This is where the physics is a little suspicious to me. For large cut angles and high speeds, I think the assumption of a perfectly elastic collision (i.e., COR = e = 1) is a little dangerous. If the CB is sliding or rolling along the OB an appreciable amount during impact and compression, I think there is a chance the OB won't transfer the stored elastic energy back into the CB as efficiently. Maybe you can come up with some experiments to measure this effect, but it might be tough to get reliable data at large cut angles....<hr /></blockquote>Dr Dave -- I agree that there might be some minor side-effects of "e" affecting the accuracy of a simple impact model, but i think that "e" is allready mostly accounted for in the impakt time(s).

I agree that "e" for a cutshot will be lower than "e" for a fullball impakt. There is (woz) a bit of stuff (mostly rubbish) about this sort of thing if one googles "tangential COR". And, if the qball is rolling across the OB, then there must be rolling rezistance, hence e is lower, indirektly (no big deal).

And, if the 2 temporary flatspots are mooving across the balls, then some (parts) of the returning compression waves (forces) will find that they are orphans, koz the flatspot (mamma) has mooved (hence e is lower, direktly). This effect on e would be worse (for the qball, not the OB) for outside english, less bad for inside english.

All in all, i am thinking that the lesserer the (real) e, then the longer the impact time, then the more the "compression angle" (AKA madMac's flatspot-sqeez). madMac.

Jal
04-13-2007, 01:04 AM
Dr. Dave, let me begin by noting that I made a serious error in the geometry on the previous page. The distance the cueball will move for some half-chord length x is 2x, not x. This makes all the compression angles essentially 1/2 the values previously reported. The math and the graphs have been updated to reflect this. I now see why Mac suggested that the numbers might be twice as big as they should be. My apology for the misleading information.

So Marlow's 0.57 throw angle on his 10 m/s shot should have an associated compression angle of 0.58 deg, not 1.14. For the 1 m/s shot it's 0.11 deg. (if everything else is okay)

<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>It certainly is a small effect, but I think warrants some attention for its influence at large cut angles and high speeds.<hr /></blockquote>This is where the physics is a little suspicious to me. For large cut angles and high speeds, I think the assumption of a perfectly elastic collision (i.e., COR = e = 1) is a little dangerous. If the CB is sliding or rolling along the OB an appreciable amount during impact and compression, I think there is a chance the OB won't transfer the stored elastic energy back into the CB as efficiently. Maybe you can come up with some experiments to measure this effect, but it might be tough to get reliable data at large cut angles.<hr /></blockquote>As you get to cut angles very near 90 degrees, I do think the presented theory is somewhat questionable and needs a more thorough look at the contact times. But for more moderate angles, say 0-80 deg or so, I feel it may be okay. At least, regarding one reservation previously discussed: the slowing of the cueball along the altered tangent line direction (chord), there is a simple argument which shows, I think, that this is indeed a very, very small effect, regardless of e. Here is the math again for reference:

http://ww2.netnitco.net/users/gtech/CompressionAngle.jpg

Suppose we make the absurd but worst case assumption that the object ball acquires all of the momentum it can possibly have in the x-direction, and that the cueball, at the very beginning of impact, looses this momentum accordingly. The relevant OB momentum is vcos(phi)sin(delta), ignoring the mass. So the cueball would have a speed in the x-direction of:

vsin(phi+delta) - vcos(phi)sin(delta) = vsin(phi)cos(delta)

Comparing this to the cueball's initial velocity component in this direction by looking at the ratio of the two, we have:

vsin(phi)cos(delta)/vsin(phi+delta)

Since cos(delta) is very nearly equal to 1, the ratio is essentially:

sin(phi)/sin(phi+delta)

And this will be nearly 1 for all cut angles (delta gets very small as phi goes to zero), even with our crazy assumption. So I don't see e&lt;1 being a problem in the real situation where at least the majority of the cueball's momentum in this direction should be restored during the second half of impact.

<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>For instance, one of Marlow's throw shots is at 10 m/s at a 45 deg cut angle, with a resulting measured "throw" of 0.57 deg (corresponding to mu=.01). However, the above theory (using Marlow's contact time data), yields an added compression angle of 1.14 deg, suggesting that the true throw was really 1.14+0.57=1.71 deg. This will have a significant effect on the mu vs speed curves, and I don't think one can be very satisfied that this is built into mu. (The compression angle for his 1 m/s shot is only 0.21 deg according to this.)<hr /></blockquote>I agree that it is unsatisfying using Marlow's data for friction values because the values do not represent true friction. His numbers are "effective friction" values that take everything into consideration: friction, ball-compression and deflection-angle, variation in COR, etc. However, I don't know of any way to easily separate and measure all of the different effects. A more satisfying model for friction would include cut angle, speed,

I think using Marlow's "effective friction" model is Ok for making general conclusions about how throw varies with cut angle, speed, English, etc. I think it does a decent job at predicting trends useful to know at the table. The exact values for throw aren't so important because conditions can vary from one set of balls to the next. What is important is understanding the trends of how total "effective throw" varies for different types of shots. Experimental data has verified many of the trends predicted by the "effective throw" analysis (TP A.14 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-14.pdf)) using Marlow's data (see my September '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/sept06.pdf) and October '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/oct06.pdf) articles).

Bottom line: better models for friction, COR, and compression deflection-angle that take into account speed, cut angle, and English for each effect would be nice, but I think this is extremely difficult, and the payoff (in terms of better understanding of "effective throw" trends) might not be that great.<hr /></blockquote>I appreciate what you're saying and agree, for what it's worth. And since the geometry in your analysis is universal, and since there are, as you note, variations between ball sets, and since your graphs range over much more moderate speeds than Marlow's 10 m/s shot, I don't see them changing much if you accounted for this effect, or that there is a pressing need to do so. And it appears that the true throw was double, not triple the apparent throw for the 10 m/s shot, which also supports this. But I think the effect is large enough that it should be included in the analysis of some situations.

<blockquote><font class="small">Quote dr_dave:</font><hr> ... Now, if you can give me separate models for COR, COF, and ball-compression deflection-angle (BCDA) as functions of cut-angle, speed, English, spin, and ball conditions, backed up by experimental data, I would be very happy (and forever in your debt). Then I could expand and improve my throw and spin transfer analyses. My suspicion is that the trends would not be very different (as compared to using the "effective friction" model), but this would certainly be interesting to see.<hr /></blockquote>Mac has done testing and analysis of COR for a variety of balls. I plan on collecting data on throw for the balls at my room (if I ever get a stinking template made). But I honestly don't think that this compression angle (flatspot sqeeze, ok Mac?) is very sensitive to e (per above) or throw (except at small cut angles where it's exceedingly small anyway), but I am aware of who I'm talking to and will give it more thought.

<blockquote><font class="small">Quote dr_dave:</font><hr> PS: I just posted TP A.28 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-28.pdf). It includes graphs that show every effect related to cut-angle, speed, English, and vertical plane spin (follow/draw). It is based on my throw analysis that uses Marlow's "effective friction" values. <hr /></blockquote>Yes, I've already discovered it, a veritable encylopedia of throw. Once again, thank you for the great resource!

(I realize that you haven't been very interested in this topic, and so another thanks for your attention.)

Jim

Jal
04-13-2007, 01:30 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> ...I agree that "e" for a cutshot will be lower than "e" for a fullball impakt.<hr /></blockquote>Mac, why so? For a given cueball speed, why wouldn't e increase with the diminishing normal (impact line) speed as cut angle increases?

Jim

dr_dave
04-13-2007, 09:04 AM
Jim,

Thanks for the correction and the feedback.

Keep up the good work,
Dave

<blockquote><font class="small">Quote Jal:</font><hr> Dr. Dave, let me begin by noting that I made a serious error in the geometry on the previous page. The distance the cueball will move for some half-chord length x is 2x, not x. This makes all the compression angles essentially 1/2 the values previously reported. The math and the graphs have been updated to reflect this. I now see why Mac suggested that the numbers might be twice as big as they should be. My apology for the misleading information.

So Marlow's 0.57 throw angle on his 10 m/s shot should have an associated compression angle of 0.58 deg, not 1.14. For the 1 m/s shot it's 0.11 deg. (if everything else is okay)

<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>It certainly is a small effect, but I think warrants some attention for its influence at large cut angles and high speeds.<hr /></blockquote>This is where the physics is a little suspicious to me. For large cut angles and high speeds, I think the assumption of a perfectly elastic collision (i.e., COR = e = 1) is a little dangerous. If the CB is sliding or rolling along the OB an appreciable amount during impact and compression, I think there is a chance the OB won't transfer the stored elastic energy back into the CB as efficiently. Maybe you can come up with some experiments to measure this effect, but it might be tough to get reliable data at large cut angles.<hr /></blockquote>As you get to cut angles very near 90 degrees, I do think the presented theory is somewhat questionable and needs a more thorough look at the contact times. But for more moderate angles, say 0-80 deg or so, I feel it may be okay. At least, regarding one reservation previously discussed: the slowing of the cueball along the altered tangent line direction (chord), there is a simple argument which shows, I think, that this is indeed a very, very small effect, regardless of e. Here is the math again for reference:

http://ww2.netnitco.net/users/gtech/CompressionAngle.jpg

Suppose we make the absurd but worst case assumption that the object ball acquires all of the momentum it can possibly have in the x-direction, and that the cueball, at the very beginning of impact, looses this momentum accordingly. The relevant OB momentum is vcos(phi)sin(delta), ignoring the mass. So the cueball would have a speed in the x-direction of:

vsin(phi+delta) - vcos(phi)sin(delta) = vsin(phi)cos(delta)

Comparing this to the cueball's initial velocity component in this direction by looking at the ratio of the two, we have:

vsin(phi)cos(delta)/vsin(phi+delta)

Since cos(delta) is very nearly equal to 1, the ratio is essentially:

sin(phi)/sin(phi+delta)

And this will be nearly 1 for all cut angles (delta gets very small as phi goes to zero), even with our crazy assumption. So I don't see e&lt;1 being a problem in the real situation where at least the majority of the cueball's momentum in this direction should be restored during the second half of impact.

<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>For instance, one of Marlow's throw shots is at 10 m/s at a 45 deg cut angle, with a resulting measured "throw" of 0.57 deg (corresponding to mu=.01). However, the above theory (using Marlow's contact time data), yields an added compression angle of 1.14 deg, suggesting that the true throw was really 1.14+0.57=1.71 deg. This will have a significant effect on the mu vs speed curves, and I don't think one can be very satisfied that this is built into mu. (The compression angle for his 1 m/s shot is only 0.21 deg according to this.)<hr /></blockquote>I agree that it is unsatisfying using Marlow's data for friction values because the values do not represent true friction. His numbers are "effective friction" values that take everything into consideration: friction, ball-compression and deflection-angle, variation in COR, etc. However, I don't know of any way to easily separate and measure all of the different effects. A more satisfying model for friction would include cut angle, speed,

I think using Marlow's "effective friction" model is Ok for making general conclusions about how throw varies with cut angle, speed, English, etc. I think it does a decent job at predicting trends useful to know at the table. The exact values for throw aren't so important because conditions can vary from one set of balls to the next. What is important is understanding the trends of how total "effective throw" varies for different types of shots. Experimental data has verified many of the trends predicted by the "effective throw" analysis (TP A.14 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-14.pdf)) using Marlow's data (see my September '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/sept06.pdf) and October '06 (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/oct06.pdf) articles).

Bottom line: better models for friction, COR, and compression deflection-angle that take into account speed, cut angle, and English for each effect would be nice, but I think this is extremely difficult, and the payoff (in terms of better understanding of "effective throw" trends) might not be that great.<hr /></blockquote>I appreciate what you're saying and agree, for what it's worth. And since the geometry in your analysis is universal, and since there are, as you note, variations between ball sets, and since your graphs range over much more moderate speeds than Marlow's 10 m/s shot, I don't see them changing much if you accounted for this effect, or that there is a pressing need to do so. And it appears that the true throw was double, not triple the apparent throw for the 10 m/s shot, which also supports this. But I think the effect is large enough that it should be included in the analysis of some situations.

<blockquote><font class="small">Quote dr_dave:</font><hr> ... Now, if you can give me separate models for COR, COF, and ball-compression deflection-angle (BCDA) as functions of cut-angle, speed, English, spin, and ball conditions, backed up by experimental data, I would be very happy (and forever in your debt). Then I could expand and improve my throw and spin transfer analyses. My suspicion is that the trends would not be very different (as compared to using the "effective friction" model), but this would certainly be interesting to see.<hr /></blockquote>Mac has done testing and analysis of COR for a variety of balls. I plan on collecting data on throw for the balls at my room (if I ever get a stinking template made). But I honestly don't think that this compression angle (flatspot sqeeze, ok Mac?) is very sensitive to e (per above) or throw (except at small cut angles where it's exceedingly small anyway), but I am aware of who I'm talking to and will give it more thought.

<blockquote><font class="small">Quote dr_dave:</font><hr> PS: I just posted TP A.28 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-28.pdf). It includes graphs that show every effect related to cut-angle, speed, English, and vertical plane spin (follow/draw). It is based on my throw analysis that uses Marlow's "effective friction" values. <hr /></blockquote>Yes, I've already discovered it, a veritable encylopedia of throw. Once again, thank you for the great resource!

(I realize that you haven't been very interested in this topic, and so another thanks for your attention.)

Jim <hr /></blockquote>

dr_dave
04-13-2007, 09:15 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> ...I agree that "e" for a cutshot will be lower than "e" for a fullball impakt.<hr /></blockquote>Mac, why so? For a given cueball speed, why wouldn't e increase with the diminishing normal (impact line) speed as cut angle increases?<hr /></blockquote>With a full-ball hit, all of the stored elastic energy will tend to return along the normal. But if the balls are moving relative to one another during impact, some of the spring-back energy might be lost (because the normal is changing direction slightly during contact). This would result in a smaller COR (e). I think this effect would be even greater for faster speeds.

Dave

dr_dave
04-13-2007, 04:27 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I agree that there might be some minor side-effects of "e" affecting the accuracy of a simple impact model, but i think that "e" is allready mostly accounted for in the impakt time(s).<hr /></blockquote>I guess this would depends on how you are using the COR and impact time in your equations. Also, I don't think the COR and contact times should necessarily be correlated for all speeds, cut angles, and ball conditions, but I haven't done experiments to verify this or not. Have you?

Regards,
Dave

cushioncrawler
04-13-2007, 06:00 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- I agree that there might be some minor side-effects of "e" affecting the accuracy of a simple impact model, but i think that "e" is allready mostly accounted for in the impakt time(s).<hr /></blockquote>I guess this would depends on how you are using the COR and impact time in your equations. Also, I don't think the COR and contact times should necessarily be correlated for all speeds, cut angles, and ball conditions, but I haven't done experiments to verify this or not. Have you? Regards, Dave<hr /></blockquote>Dr Dave -- I think that it wouldnt be too difficult to repeat Marlow's direct (electricity flow) impakt time measurements and tests for varyus angles and speeds -- i might uze an OB on a pendulum to help measure speed and angle -- it would all show little difference in impakt time. I uze impakt time in my calcs, but i dont uze e -- perhaps i shood uze e, i will look into this.

There is a bit of stuff on google re oblique impact (balltoball i think) and tangential COR ( e can exceed 1.00 for sphere on plate) -- looked like rubbish to me. madMac.

cushioncrawler
04-13-2007, 06:14 PM
<blockquote><font class="small">Quote Jal:</font><hr> Dr. Dave, let me begin by noting that I made a serious error in the geometry on the previous page. The distance the cueball will move for some half-chord length x is 2x, not x. This makes all the compression angles essentially 1/2 the values previously reported. The math and the graphs have been updated to reflect this. I now see why Mac suggested that the numbers might be twice as big as they should be....<hr /></blockquote> Jim -- I made this same mistake when i first did theze calcs (years ago), took me a while to realize -- the distance travelled by the center of the qball during impakt needs to be equated to 2R (not 1R) to calculate the angle.

But that iz not the source of my warning re "2". My warning related to the need to (after firstly calculating the "impact angle" without tripping on "2R") halve the impact angle to arrive at the compression angle (AKA flatspot-sqeez angle). madMac.

cushioncrawler
04-13-2007, 06:30 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> ...I agree that "e" for a cutshot will be lower than "e" for a fullball impakt.<hr /></blockquote>Mac, why so? For a given cueball speed, why wouldn't e increase with the diminishing normal (impact line) speed as cut angle increases? Jim<hr /></blockquote>Jim -- Dr Dave's reply to this relates to orphaned phonons running around looking for mamma, which is correct. Nonetheless, az u say, "for a given qball speed", a finer cut will have a larger e, koz e inkreeces az impact dekreeces -- but, without checking, i would have been talking about "a given OB speed", not qball speed. madMac.

Jal
04-13-2007, 11:46 PM
Mac, my thanks to you and Dr. Dave for addressing the COR vs cut angle issue. Since the shift in tangent line looks to be about a half-degree on average, can we conclude that about one phonon in 720 will remain in its pitious state? (I'm not making fun, but admitting that I have no feel for what goes on internally, and how this exhibits itself in the behavior of the balls.)

<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I made this same mistake when i first did theze calcs (years ago), took me a while to realize -- the distance travelled by the center of the qball during impakt needs to be equated to 2R (not 1R) to calculate the angle.

But that iz not the source of my warning re "2". My warning related to the need to (after firstly calculating the "impact angle" without tripping on "2R") halve the impact angle to arrive at the compression angle (AKA flatspot-sqeez angle). madMac. <hr /></blockquote>By impact angle, I take it you mean cut angle, ie, the angle between the cueball's shot direction and the line between centers at impact? The above math doesn't halve this - I really don't see a reason to - but does use half the length of the chord to figure the compression angle. Please enlighten if you still think the numbers, as shown in the plots, are too big by perhaps 2X, or too small, or too whatever.

Jim

PS: I didn't mean to discard your "flatspot squeeze" terminology, but I doubt that many would know what it means. It's more colorful than "compression angle", but I think also more ambiguous. Since whatever term we use is unlikely to take its rightful place in Dr. Dave's glossary, this is probably moot, but I like "dwell angle" (short, sweet and descriptive).

dr_dave
04-14-2007, 08:30 AM
<blockquote><font class="small">Quote Jal:</font><hr> Mac, my thanks to you and Dr. Dave for addressing the COR vs cut angle issue. Since the shift in tangent line looks to be about a half-degree on average, can we conclude that about one phonon in 720 will remain in its pitious state? (I'm not making fun, but admitting that I have no feel for what goes on internally, and how this exhibits itself in the behavior of the balls.)<hr /></blockquote>Jim,

You are very welcome. But stop being hard on yourself. You have made many valuable contributions to this forum. You have certainly helped me find errors in some of my analyses and helped me look at a few things differently. Please continue to do so.

<blockquote><font class="small">Quote Jal:</font><hr>I didn't mean to discard your "flatspot squeeze" terminology, but I doubt that many would know what it means. It's more colorful than "compression angle", but I think also more ambiguous. Since whatever term we use is unlikely to take its rightful place in Dr. Dave's glossary, this is probably moot, but I like "dwell angle" (short, sweet and descriptive).<hr /></blockquote>Actually, I had already added:

ball-compression deflection angle: slight change in the object ball’s direction due to the slight amount of compression of the cue ball and object ball during impact.

I like "dwell angle"; although, being a mechanical engineer, it is hard to accept because it is a common term used to describe cams and camshafts. I also like "flat-spot squeeze", but I agree with Jim on that one. If you guys make your own glossaries, you can include your favorite term. I decided to just use the full descriptive phrase (ball-compression deflection-angle). Although, even this phrase probably doesn't belong in the glossary since it is not commonly discussed or written about.

Regards,
Dave

Jal
04-14-2007, 01:40 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>You are very welcome. But stop being hard on yourself. You have made many valuable contributions to this forum. You have certainly helped me find errors in some of my analyses and helped me look at a few things differently. Please continue to do so.<hr /></blockquote>Thank you very much Dr. Dave, although I'm not being hard on myself. I just can't picture the compression waves interacting with each other in any intelligible way. But I think I see what you and Mac are refering when translating it into the changing direction of the Vcos(alpha) component as alpha goes from phi to phi+delta.

<blockquote><font class="small">Quote dr_dave:</font><hr><blockquote><font class="small">Quote Jal:</font><hr>...Since whatever term we use is unlikely to take its rightful place in Dr. Dave's glossary, this is probably moot, but I like "dwell angle" (short, sweet and descriptive).<hr /></blockquote>Actually, I had already added:

ball-compression deflection angle: slight change in the object ball’s direction due to the slight amount of compression of the cue ball and object ball during impact.

I like "dwell angle"; although, being a mechanical engineer, it is hard to accept because it is a common term used to describe cams and camshafts. I also like "flat-spot squeeze", but I agree with Jim on that one. If you guys make your own glossaries, you can include your favorite term. I decided to just use the full descriptive phrase (ball-compression deflection-angle). Although, even this phrase probably doesn't belong in the glossary since it is not commonly discussed or written about.<hr /></blockquote>I was kidding about "rightful place" and agree that its inclusion is a bit iffy, though that's also moot as it's your glossary!

Mac has done much more thinking about this than I have, so I'll probably use "flatspot squeeze" on occasion in acknowledgement of that.

Jim

cushioncrawler
04-14-2007, 04:35 PM
Jim -- "Dwell Angle" i like -- ie to describe the gained cut-angle, ie gained due to ball(s) compression during impakt. Actually, there iz a slight problem with dwell-angle, koz, just thinking about it some more, dwell-angle could eezyly be very usefull for describing the total angle between the common tangent at first-touch and the common tangent at last-touch (which by the way iz what i mean by my "Impakt Angle"). I tryd to relate Impakt-Angle to Impakt-Time. Anyhow, i will uze Dwell-Angle in future -- Dr Dave's term is too long -- and "FlatSpot-Sqeez" suggests that it iz due to the flatspot, whereas it is actually due to the total "out of roundness" of the ball.

I woz never happy with my "impakt-angle" -- az u said, it seems to better relate to describing the fullness of the balltoball impakt, ie the aim, ie the initial balltoball contact, but i allways uze "Contact Angle" to describe fullness. Anyhow, all of theze terms (and others) are fraught -- it kumz down to which sounds sexyer.

Getting tecknikal again -- there will allways be a problem with defining dwell-angle. Do we inklood or disklood the throw-angle (if any).

Anyhow -- long live the "Dwell-Angle". madMac.

Jal
04-15-2007, 02:05 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- "Dwell Angle" i like -- ie to describe the gained cut-angle, ie gained due to ball(s) compression during impakt. Actually, there iz a slight problem with dwell-angle, koz, just thinking about it some more, dwell-angle could eezyly be very usefull for describing the total angle between the common tangent at first-touch and the common tangent at last-touch<hr /></blockquote>Mac, I suppose we could use semi-dwell angle, but now it begins to grow again as we speak.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>...(which by the way iz what i mean by my "Impakt Angle").<hr /></blockquote>Ah, in that case I did have the presence of mind to halve it.... small victories.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>...I tryd to relate Impakt-Angle to Impakt-Time<hr /></blockquote>I want to review the materials you sent since I think I can relate to them better now. But if you have something to say now about this here, I would be interested. As I see it, they are related as per the equation for tan(delta). But you might prefer another way of thinking about it.


<blockquote><font class="small">Quote cushioncrawler:</font><hr>Anyhow, i will uze Dwell-Angle in future -- Dr Dave's term is too long -- and "FlatSpot-Sqeez" suggests that it iz due to the flatspot, whereas it is actually due to the total "out of roundness" of the ball.<hr /></blockquote>Mac, thanks for your acceptance. Now we need to work on Dr. Dave, who would probably just as soon shove this portion of the thread up our noses. You first. /ccboard/images/graemlins/smile.gif (The nerve of that man preempting our decision as to what goes into his glossary!)

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Getting tecknikal again -- there will allways be a problem with defining dwell-angle. Do we inklood or disklood the throw-angle (if any).<hr /></blockquote>To me, they're separate effects, although throw does play into the dwell angle. In the case where the balls are sliding throughout, and where mu doesn't change (much) during impact, I think the second formula for tan(delta) does give this relation. That is, throw either reduces the average relative velocity of the balls in the dwell direction, or increases it. This is, as I see it, your "friction squeeze" at work, which reduces the dwell angle for "positive" throw (typical throw), thus increasing apparent throw, and increases it for "negative" throw (superspin), thus decreasing apparent throw. (Whew) But as you've calculated, it's a small modification except at small cut angles where delta is very, very small anyway.

Jim

dr_dave
04-15-2007, 08:03 AM
<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote cushioncrawler:</font><hr>Anyhow, i will uze Dwell-Angle in future -- Dr Dave's term is too long -- and "FlatSpot-Sqeez" suggests that it iz due to the flatspot, whereas it is actually due to the total "out of roundness" of the ball.<hr /></blockquote>Mac, thanks for your acceptance. Now we need to work on Dr. Dave, who would probably just as soon shove this portion of the thread up our noses. You first. /ccboard/images/graemlins/smile.gif (The nerve of that man preempting our decision as to what goes into his glossary!)<hr /></blockquote>Up your noses it goes. Make up your own glossary! /ccboard/images/graemlins/grin.gif

Sorry if I seemed snobby in this thread. "Flatspot squeez" is actually starting to grow one me.

Catch you later,
Dave

cushioncrawler
04-15-2007, 01:16 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> .... "Flatspot squeez" is actually starting to grow one me.... <hr /></blockquote>Dr Dave -- If u buy "FlatSpot-Sqeez", i will throw in "Friktion-Sqeez" for free. madMac.

dr_dave
04-16-2007, 11:18 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- If u buy "FlatSpot-Sqeez", i will throw in "Friktion-Sqeez" for free. madMac.<hr /></blockquote>Mac,

In your honor, I have added "flat-spot squeeze" to the glossary (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf).

What do you mean by "friction squeeze?" It sounds like "throw" or "cling" to me.

Regards,
Dave

dr_dave
04-16-2007, 11:23 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just posted an 18-page expanded glossary of pool and billiards terms and phrases. It can be found, with links to some other useful collections, under "references" in the instructor and student resources section of my website (http://www.engr.colostate.edu/~dga/pool/resources/index.html). Check it out. Please let me know if you think I left out any obvious or really important terms or phrases.<hr /></blockquote>Thanks to the many suggestions from people via postings, PM's, and e-mails, I've added a much more to the glossary (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf). It now contains 23 pages of terms and phrases. I've also added some more links and references to other supporting resources under "for reference" here (http://www.engr.colostate.edu/~dga/pool/resources/index.html).

I hope you find the resources useful,
Dave

cushioncrawler
04-16-2007, 04:51 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ....What do you mean by "friction squeeze?" It sounds like "throw" or "cling" to me.... <hr /></blockquote>Dr Dave -- Re "FlatSpot Squeeze", glad u like this term, it could possibly be called FlatSpot Squeeze Angle. Alltho Jim's "Dwell Angle" might be better.

Re "Friction Squeeze" -- This is the component of apparent-throw that iznt direktly due to balltoball friction. During a fullball impact, throw can be say up to 6dg. Much of this 6dg would be due to friction forces acting along the common tangent. But, as (while) the balltoball line moves from 00dg to ??dg, the direct balltoball non-friction forces will develop a significant XX component. Thusly, throw allways has a non-frictional component, and this can be i think (i calculate) up to 1% or even 2% of the total throw for a hi-speed impact, less for slow impacts. So, it aint much, but its the thort that counts. In the early days, i dreamt that Friction Squeeze could add up to 1.0dg to throw, but my calcs show that it might never exceed say 0.1dg.

FlatSpot Squeeze will affect all cut shots (gearing or not), and Friction Squeeze will affect all non-gearing shots (cut-shot or not). Actually, just thinking about it, Friction Squeeze karnt exist for all cut-shots, it can only exist for fullball shots or cut-shots with outside english (Jim will be tickled by this anomaly). madMac.

dr_dave
04-16-2007, 05:06 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ....What do you mean by "friction squeeze?" It sounds like "throw" or "cling" to me.... <hr /></blockquote>Dr Dave -- Re "FlatSpot Squeeze", glad u like this term, it could possibly be called FlatSpot Squeeze Angle. Alltho Jim's "Dwell Angle" might be better.

Re "Friction Squeeze" -- This is the component of apparent-throw that iznt direktly due to balltoball friction. During a fullball impact, throw can be say up to 6dg. Much of this 6dg would be due to friction forces acting along the common tangent. But, as (while) the balltoball line moves from 00dg to ??dg, the direct balltoball non-friction forces will develop a significant XX component. Thusly, throw allways has a non-frictional component, and this can be i think (i calculate) up to 1% or even 2% of the total throw for a hi-speed impact, less for slow impacts. So, it aint much, but its the thort that counts. In the early days, i dreamt that Friction Squeeze could add up to 1.0dg to throw, but my calcs show that it might never exceed say 0.1dg.<hr /></blockquote>Thanks for the explanation.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>FlatSpot Squeeze will affect all cut shots (gearing or not), and Friction Squeeze will affect all non-gearing shots (cut-shot or not). Actually, just thinking about it, Friction Squeeze karnt exist for all cut-shots, it can only exist for fullball shots or cut-shots with outside english (Jim will be tickled by this anomaly).<hr /></blockquote>Did you mean "cannot exist" instead of "can only exist?" With a gearing amount of outside English, there is no throw whatsoever (see TP A.26 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-26.pdf)).

Regards,
Dave

cushioncrawler
04-16-2007, 05:24 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> ....What do you mean by "friction squeeze?" It sounds like "throw" or "cling" to me.... <hr /></blockquote>Dr Dave -- Re "FlatSpot Squeeze", glad u like this term, it could possibly be called FlatSpot Squeeze Angle. Alltho Jim's "Dwell Angle" might be better.

Re "Friction Squeeze" -- This is the component of apparent-throw that iznt direktly due to balltoball friction. During a fullball impact, throw can be say up to 6dg. Much of this 6dg would be due to friction forces acting along the common tangent. But, as (while) the balltoball line moves from 00dg to ??dg, the direct balltoball non-friction forces will develop a significant XX component. Thusly, throw allways has a non-frictional component, and this can be i think (i calculate) up to 1% or even 2% of the total throw for a hi-speed impact, less for slow impacts. So, it aint much, but its the thort that counts. In the early days, i dreamt that Friction Squeeze could add up to 1.0dg to throw, but my calcs show that it might never exceed say 0.1dg.<hr /></blockquote>Thanks for the explanation.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>FlatSpot Squeeze will affect all cut shots (gearing or not), and Friction Squeeze will affect all non-gearing shots (cut-shot or not). Actually, just thinking about it, Friction Squeeze karnt exist for all cut-shots, it can only exist for fullball shots or cut-shots with outside english (Jim will be tickled by this anomaly).<hr /></blockquote>Did you mean "cannot exist" instead of "can only exist?" With a gearing amount of outside English, there is no throw whatsoever (see TP A.26 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-26.pdf)). Regards,Dave <hr /></blockquote> Dr Dave -- My wording is pretty much ok -- especially if one reads "can" as not meaning "does" (ie "allways does"). But, just to tighten things up, i could have added that "friction-squeeze can only exist if there is friction" -- or, i could have added that "friction-squeeze cannot exist if there is gearing". madMac.

Jal
04-16-2007, 11:39 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Dr Dave -- If u buy "FlatSpot-Sqeez", i will throw in "Friktion-Sqeez" for free. madMac.<hr /></blockquote>Mac,

In your honor, I have added "flat-spot squeeze" to the glossary (http://www.engr.colostate.edu/~dga/pool/resources/glossary.pdf).<hr /></blockquote>I'll drink to that!

<blockquote><font class="small">Quote dr_dave:</font><hr>What do you mean by "friction squeeze?" It sounds like "throw" or "cling" to me.<hr /></blockquote>It's been answered but I'd like to add that this effect is one of my favorites. There's something about it that's just nice. It's a shame though that it's so small, but maybe this is a part of its charm.

He has also ferreted out "Masse Veer" and "Spin Veer", the former of which I believe you're already familiar with (misalignment of imparted topspin/backspin with OB direction due to throw). The latter, well, I'll let him explain it if needed. I think he has more in the queue, but I don't have the foggiest.

Jim