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Btw - 08-28-2019, 02:00 PM

Quote:
Originally Posted by jsp View Post
...Dr. Dave, Bob Jewett, Mike Page, and Ron Shepard...
Can we knight these people as The Four Horsemen of Pool Physics? You heard it from me first.
  
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08-28-2019, 02:06 PM

Im a bit confused.

Is the Imac007 post saying that at a certain distance right or left of center, with a cue (or stroking) line that is parallel to the ghost ball/vertical center cue (or stroking) line, the CB will travel in the direction of the stroke line because the squirt and the friction (with the cue tip) forces are offsetting? I’m thinking that this isn’t the proper translation, because if the OB is spinning, there will be some amount of swerve, even if inconsequential due to the speed and length of the shot.

Is the BC21 post saying something similar but slightly different: that at just the right (small) amount of tip offset, again using a “parallel” stroke line, the squirt and swerve will cancel each other out? I’m thinking that this is the proper translation, but that the conclusion doesn’t hold up UNLESS the CB is hit softly enough, and has enough travel time to swerve, prior to contact with the OB.
  
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08-28-2019, 02:17 PM

Quote:
Originally Posted by jsp View Post
I'm still unsure what point you're trying to make. If you want to to discuss pool physics, then you are not presenting anything that Dr. Dave, Bob Jewett, Mike Page, and Ron Shepard have not already talked about for years/decades.

If you're attempting to propose that a better understanding of the physics of side spin will help the average pool player, as it seems from the quote above, then I disagree. None of this stuff will help the average pool player.
You’re right. PJ and myself and the physics writers you mention are on the same page. The problem is that other popular discussion of side refers to tips of english and each are in relationship to the ghost ball line. My first point is that the distance the cue line is from center is the actual lever turning the ball. As long as we discuss old misconceptions and perspectives we learn nothing new.

Now to the new. I mentioned moving off the target line and then pointing the cue line back towards center. Imagine moving the cue line back towards center but not all the way. So imagine moving the width of two dimes away from center then pointing the cue line back half that distance, the width of one dime. Notice where the cue is pointing in relation to the original cue line, it now crosses onto the opposite side of the original cue line. NONE of the present parallel english, FHE or BHE methods of applying side converge back towards the shot line, they ALL diverge. So two new labels enter the conversation, divergent and convergent english. Here is the blasphemy, I’m using the ghost ball line as the reference line, because it is the aim line understood by a majority of players. Even Dr. Dave with his SAWS program uses the deflection adjusted ghost ball line as a reference then following that with a distance/pace adjusted combination of BHE and from the new back hand position a sweep with the front hand to a pre-calculated ratio final position. He recognizes the ingrained, although incorrect perception, of using the ghost ball line. He uses a known reference as a starting point. In that spirit, the terms divergent and convergent are cue line relationship terms relative to an adjusted ghost ball aim line.

This is the second insight, the cue line can be pointed back to and cross the original aim reference line, generating side on a convergent rather than divergent path.

Last edited by Imac007; 08-29-2019 at 12:19 AM.
  
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08-28-2019, 02:18 PM

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Originally Posted by Patrick Johnson View Post
And misses all shots except those where swerve (a variable depending on distance, speed, conditions, butt elevation, etc.) happens to exactly counteract squirt, right?
Um, aren't you forgetting about spin induced throw?

So I agree, parallel english misses "all shots"...except for some shots, and these shots, and maybe those shots, and don't forget these shots over here.

It's like complaining about the term "ghost ball" because the exact geometrically-determined ghost ball location is almost never the exact location it should be to pocket the shot because of friction.

Both parallel english and ghost ball are still very useful terms. Just know their limitations.
  
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08-28-2019, 02:27 PM

Quote:
Originally Posted by Imac007 View Post
Now to the new. I mentioned moving off the target line and then pointing the cue line back towards center. Imagine moving the cue line back towards center but not all the way. So imagine moving the width of two dimes away from center then pointing the cue line back half that distance, the width of one dime. Notice where the cue is pointing in relation to the original cue line, it now crosses onto the opposite side of the original cue line. NONE of the present parallel english, FHE or BHE methods of applying side converge back towards the shot line, they ALL diverge. So two new labels enter the conversation, divergent and convergent english. Here is the blasphemy, Iím using the ghost ball line as the reference line, because it is the aim line understood by a majority of players. Even Dr. Dave with his SAWS program uses the deflection adjusted ghost ball line as a reference then following that with a distance/pace adjusted combination of BHE and from the new back hand position a sweep with the front hand to a pre-calculated ratio final position. He recognizes the ingrained, although incorrect perception, of using the ghost ball line. He uses a known reference as a starting point. In that spirit, the terms divergent and convergent are cue line relationship terms relative to an adjusted ghost ball aim line.
I read this paragraph four times and I still don't understand what you're describing.
  
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08-28-2019, 02:52 PM

Quote:
Originally Posted by jsp View Post
Um, aren't you forgetting about spin induced throw?

So I agree, parallel english misses "all shots"...except for some shots, and these shots, and maybe those shots, and don't forget these shots over here.

It's like complaining about the term "ghost ball" because the exact geometrically-determined ghost ball location is almost never the exact location it should be to pocket the shot because of friction.

Both parallel english and ghost ball are still very useful terms. Just know their limitations.
Every spin shot has a combination of squirt and swerve to account for. The particular combination that results in cueing parallel to the shot line is no more likely to happen than any other cueing angle - a small fraction of all possible cueing angles, like any other single angle. Naming it as if it's a category or technique unto itself just misstates and confuses the actual dynamics IMO.

But it's only a misdemeanor, so no arrests.

pj <- this time
chgo
  
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08-28-2019, 04:57 PM

Quote:
Originally Posted by Seth C. View Post
Im a bit confused.

Is the Imac007 post saying that at a certain distance right or left of center, with a cue (or stroking) line that is parallel to the ghost ball/vertical center cue (or stroking) line, the CB will travel in the direction of the stroke line because the squirt and the friction (with the cue tip) forces are offsetting? I’m thinking that this isn’t the proper translation, because if the OB is spinning, there will be some amount of swerve, even if inconsequential due to the speed and length of the shot.

Is the BC21 post saying something similar but slightly different: that at just the right (small) amount of tip offset, again using a “parallel” stroke line, the squirt and swerve will cancel each other out? I’m thinking that this is the proper translation, but that the conclusion doesn’t hold up UNLESS the CB is hit softly enough, and has enough travel time to swerve, prior to contact with the OB.
This post shows a player jumping ahead trying to use conclusions based on experience with divergent side. It also reveals a mindset seeing the amount of side from the ball surface, not the center of mass. Despite the fact that I talked about an offset of the width of two dimes, the actual torque arm beside the ball center was set at a dimes width. Twice as wide at the surface than at the ball’s center guaranteed it was not parallel and not divergent. Simple geometry would tell you that the cue line would exit the cue ball crossing the original adjusted aim line at the exit point of that line.

Some things that Dr. Dave research has shown is
1. As the amount of side approaches zero so does throw.
2. As the amount of side approaches zero so does deflection.
3. Very small amounts of side have a very small amount of throw at all speeds.

The example given was a small amount on purpose just trying to bring attention to the fact that the cue line converges with and crosses the original aim line. Wrap your head around where the cue is now pointing. Depending on the distance between the balls, the cue could be pointing well away from the object ball or just a bit to the side. There needs to be a method of applying consistent amounts of side regardless of distance. That will be part of another post, a geometric solution.

Last edited by Imac007; 08-28-2019 at 10:41 PM.
  
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08-28-2019, 06:16 PM

Quote:
Originally Posted by Imac007 View Post
......
.....There needs to be a method of applying consistent amounts of side regardless of distance. That will be part of another post, a geometric solution.
Interesting. But I think the best method is called experience.

You could show someone exactly how you do it, as far as applying side spin based on a geometric solution, and if the person has the same stroke quality as you, and they use your cue to shoot each shot as instructed, then your method will work for them in the same manner it works for you. But if they have a better stroke than you, no steering flaws, etc... or if they have a worse stroke than you, unable to consistently strike the cb where they intend to strike it, then the method you show them will not be very consistent for them. And since their cue may cause more or less cb deflection than your cue, the method you show will have to be tweaked to work with a cue of different deflection than yours.

Compensating for english is a very subjective process that players learn through experience, through trial and error. Sure there are some basic methods that can be used to roughly adjust for this, like using bhe or fhe. But these aren't one-size-fits-all type methods because of the difference in individual strokes and individual cues. A player must experiment with his/her own playing cue in order to find the right bridge length that works for using bhe. And even that variable changes when the cb and ob are separated by a greater distance. So in the end it boils down to experience, to table time. But it would be interesting to see this geometric method you speak of, and to see how it can be adapted to different players and different cues.
  
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08-28-2019, 07:27 PM

Quote:
Originally Posted by jsp View Post
I read this paragraph four times and I still don't understand what you're describing.
Just so you won't feel too bad, I'll admit that I have the same problem.


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08-28-2019, 07:30 PM

Quote:
Originally Posted by jsp View Post
I read this paragraph four times and I still don't understand what you're describing.
I think he means something like this??
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08-28-2019, 07:37 PM

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Originally Posted by skins View Post
I think he means something like this??
I think it's better to wait for Imac007 to explain what he meant. In your diagram you are moving the cue stick parallel a dime and a half.

And when you pivot back half (except it's not half in your diagram), do you pivot about your bridge hand?


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08-28-2019, 08:03 PM

Quote:
Originally Posted by Bob Jewett View Post
I think it's better to wait for Imac007 to explain what he meant. In your diagram you are moving the cue stick parallel a dime and a half.

And when you pivot back half (except it's not half in your diagram), do you pivot about your bridge hand?
Hi Bob, I'm just giving the "jist" of what I think he's saying. The diagram is not meant to be exact in proportions....

As for pivoting, if I do, next time you're in the Chicago area we can hit some around and you can tell me what I'm doing..LOL

I agree. Lets wait for the OP to explain....


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Geometric adjustments
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Geometric adjustments - 08-28-2019, 10:16 PM

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Originally Posted by BC21 View Post
Interesting. But I think the best method is called experience.

You could show someone exactly how you do it, as far as applying side spin based on a geometric solution, and if the person has the same stroke quality as you, and they use your cue to shoot each shot as instructed, then your method will work for them in the same manner it works for you. But if they have a better stroke than you, no steering flaws, etc... or if they have a worse stroke than you, unable to consistently strike the cb where they intend to strike it, then the method you show them will not be very consistent for them. And since their cue may cause more or less cb deflection than your cue, the method you show will have to be tweaked to work with a cue of different deflection than yours.

Compensating for english is a very subjective process that players learn through experience, through trial and error. Sure there are some basic methods that can be used to roughly adjust for this, like using bhe or fhe. But these aren't one-size-fits-all type methods because of the difference in individual strokes and individual cues. A player must experiment with his/her own playing cue in order to find the right bridge length that works for using bhe. And even that variable changes when the cb and ob are separated by a greater distance. So in the end it boils down to experience, to table time. But it would be interesting to see this geometric method you speak of, and to see how it can be adapted to different players and different cues.
All of this is true, when it relates to divergent english. People already use perceived geometric ratios, like 1/2 ball and 1/4 ball, in their thinking. Meanwhile, when the effect of throw and deflection are all but eliminated, the primary adjustment that needs to be made concerns the new cue angle created by moving the cue into position, to apply the side. The adjustment that needs to be made differs based on whether the side converges from the inside side of the shot or whether the convergence comes from the outside side.

Outside converging side moves the cue line into a fat hit relative to the ghost ball line. Inside converging side moves the cue line into an overcut position relative to ghost ball. As a result, the aim line needs to be adjusted for each. In order to simplify and keep the adjustment simple, a geometric fact was used.

Since the cue line and the ghost ball line cross, the choice of where to cross, allows for a consistent ratio of 1:1 to be used. If the cue line originates from a point beside the center of mass and meets the reference aim line at its midpoint the amount of offset at the impact area is equal to the torque line created at the cue ball center. An elongated X crossing in the middle has equal distances between the ends of the lines. That is a 1:1 ratio. It’s a measurable amount of adjustment regardless of length of shot.

If a torque line the width of 2 dimes is used and crosses the ghost ball line at its midpoint and the converging side is inside side, the ball will be overcut into the far side of the pocket. To compensate for the overcut, the original aim line is adjusted to the undercut side of the pocket. Conversely if the converging side is outside side, the initial compensating aim is to the overcut side of the pocket.

The next post will focus on the reasons that convergent side might be chosen over center ball or divergent side.

Last edited by Imac007; 09-07-2019 at 08:43 AM.
  
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08-28-2019, 11:01 PM

Quote:
Originally Posted by Bob Jewett View Post
I think it's better to wait for Imac007 to explain what he meant. In your diagram you are moving the cue stick parallel a dime and a half.

And when you pivot back half (except it's not half in your diagram), do you pivot about your bridge hand?
If you are going to think in terms of the ghost ball line and pivots the following comes to mind. Divergent side and parallel side both occur in relationship to the ghost ball line. BHE and FHE pivot from that line. The ghost ball line does not end at the cue ball. It continues to the object ball. If you think about a pivot, the geometric solution I presented would be simply described as follows. Find the ghost ball line to the undercut side of the pocket. Now place your tip on the midpoint of that line between the two balls and pivot the butt of the cue so that the shaft line crosses to the inside side of the shot, the width of two dimes from the center of mass of the cue ball. Where that shaft line exits on the cue ball face is the cueing point on the surface. BTW the width of a dime is about 1.35mm. So 2 dimes width at 2.7 mm are less than a 1/4 tip using a 12mm tip. This qualifies as a small amount of side in Dr. Dave land. If outside side is preferred. Then start with an overcut ghost ball line. Now pivot from the midpoint to the double dime spot on the other side of the ball’s center. That is the cue line for the shot.

Last edited by Imac007; 08-28-2019 at 11:22 PM.
  
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08-29-2019, 12:29 AM

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Originally Posted by Bob Jewett View Post
Just so you won't feel too bad, I'll admit that I have the same problem.
Sorry guys hope subsequent explanations have made things clearer.
  
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