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dr_dave
12-04-2004, 01:35 PM
Q (from a BD reader):
With respect to spin-induced throw (SIT), I have been teaching this phenomenon & its use (a la Science of Pocket Billiards) for years. Recently, I've been told that the physics jockeys are now saying that no, while SIT may indeed be possible, it is too small an effect to use. Their "practical proof" is the following experiment: draw a line on the cloth (for example, a few feet on the long string), place a CB & OB on the line, shoot the CB at the OB with sidespin, aiming to hit the OB full on. What one finds, doing this, is you can't get the CB to stay on the line while having the OB throw off the line.

So, this is very interesting, and sure enough, I couldn't demonstrate throw in the experiment. But, the old SIT hypothesis does indeed explain & predict the types of results we get on the table, so while that model is at useful, I'd really like to know whether it is correct. They tell me what's really happening is simply that the CB is curving to the OB contact point that results in the line taken by the OB, giving the appearance that SIT is real.

A (from me):
SIT is definitely a real effect. Like cut-induced (collision-induced) throw, it is due to sideways friction force caused by relative sideways motion between the CB and OB during impact. NV 4.15, 4.16, 7.5, and 7.6 on my website (http://www.engr.colostate.edu/pool) show examples of various types of throw. The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).

Throw, resulting from CB English or cut angle, is most definitely real (and sometimes very useful)! It also must be accounted for at times; if not, you will sometimes miss what appear to be easy shots.

For more information, and a less scientific explanation, see pages 101-114 in "The Illustrated Principles of Pool and Billiards."

dr_dave
12-07-2004, 03:59 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
With respect to spin-induced throw (SIT), I have been teaching this phenomenon &amp; its use (a la Science of Pocket Billiards) for years. Recently, I've been told that the physics jockeys are now saying that no, while SIT may indeed be possible, it is too small an effect to use. Their "practical proof" is the following experiment: draw a line on the cloth (for example, a few feet on the long string), place a CB &amp; OB on the line, shoot the CB at the OB with sidespin, aiming to hit the OB full on. What one finds, doing this, is you can't get the CB to stay on the line while having the OB throw off the line.

So, this is very interesting, and sure enough, I couldn't demonstrate throw in the experiment. But, the old SIT hypothesis does indeed explain &amp; predict the types of results we get on the table, so while that model is at useful, I'd really like to know whether it is correct. They tell me what's really happening is simply that the CB is curving to the OB contact point that results in the line taken by the OB, giving the appearance that SIT is real.

A (from me):
SIT is definitely a real effect. Like cut-induced (collision-induced) throw, it is due to sideways friction force caused by relative sideways motion between the CB and OB during impact. NV 4.15, 4.16, 7.5, and 7.6 on my website (http://www.engr.colostate.edu/pool) show examples of various types of throw. The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).

Throw, resulting from CB English or cut angle, is most definitely real (and sometimes very useful)! It also must be accounted for at times; if not, you will sometimes miss what appear to be easy shots.

For more information, and a less scientific explanation, see pages 101-114 in "The Illustrated Principles of Pool and Billiards." <hr /></blockquote>
I'm surprised nobody responded to this item. Does that mean everybody agrees?

Tom_In_Cincy
12-07-2004, 06:48 PM
Dave,

I think a better response would be;

What is the minimum speed, distance and spin necessary to get a desired reaction?

I don't understand all the mathematical formulas or graphs in your PDF document. So, I can't apply them to a pool table and my stroke, cue ball hit and distance shots.

Do you have an idea what level of education a person should have to interprert your equations? Let alone, apply them to a pool shot?

Keith Talent
12-07-2004, 09:03 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Recently, I've been told that the physics jockeys are now saying that no, while SIT may indeed be possible, it is too small an effect to use.
They tell me what's really happening is simply that the CB is curving to the OB contact point that results in the line taken by the OB, giving the appearance that SIT is real.

The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).

I'm surprised nobody responded to this item. Does that mean everybody agrees? <hr /></blockquote>

Dave, Didn't the same sort of physicists also declare years ago that the curveball in baseball is an "illusion"?
Anyway, I took a look at those equations on your site describing the effect of throw and was amazed, absolutely. Not that I could make any sense of them (I just barely survived college algebra), but I was impressed that somebody would go to such lengths in the quest for intellectual entertainment.

For sure, if you play some, you get to know that spinning in balls is no illusion ... hell, it might be a necessity for us oldsters who can't focus so well on thin cuts anymore.

As far as the second point, I don't see how the ob is exerting force -- pushing back, as you say -- upon the cb here. Isn't the cb just spinning itself off line, just as happens when a juiced-up cb hits a rail? The amount it moves, obviously, is affected by how full the hit is ... which determines the effective mass it's reacting against, right? Then there's the forward speed of the cb and of the rotation, and the exact direction of that spin ...

Personally, I think this stuff has so many variables that you could never balance them all out precisely, and then go on to perform the shot that way even if you COULD make sense of it in your mind ... so that in many cases cueing becomes more of an art than a science. Make an educated guess, hit and hope. /ccboard/images/graemlins/crazy.gif

Ross
12-07-2004, 09:39 PM
Tom, you are asking Dave's Q&amp;A to do more than it was designed to do. (And I totally agree that what you are asking for would be useful). What Dave's Q&amp;A does (correctly, I think) is merely say that SIT really does exist, give mathematical equations to theoreticaly calculate its effects (which as you say is not useful for anyone in a game), and explain why the supposed "disproof" of CIT is incorrect.

So this Q&amp;A is useful in that it establishes that SIT is indeed real and may be need to be taken into account for some shots. What it doesn't do is give some practical rules of thumb (like the 30 degree rule) for practically estimating SIT effects for particular shots.

The next step would be to give info like: "Assume the cb is 1 diamond away from the ob and the ob is 4 diamonds away from the corner pocket. With relatively clean Aramith balls if the cb is shot at lag speed with maximum right english head on to the ob, it will throw the ob approximately X inches to the left. With relatively dirty, worn Aramith balls the ob throw is approximately Y inches."

And then determine empirically what Y is for this shot and for shots where the cb is closer or farther, hit softer or harder, and where you have a full, 3/4, 1/2, or 1/4 ball hit on the ob.

Of course I guess we don't need Dave to do this. We could go to a pool table and make our own measurements of these effects. Maybe this weekend...

Tom_In_Cincy
12-07-2004, 10:25 PM
Ross,
Your support for Dave's postualtions is admirable. I also have been following Dave's work in his BD articles.

I don't disagree with any of his math or his 'proofs'. SIT is not a new concept for a lot of us experienced players. But it is to a lot of the newer players. And, IMO, a math equation is not a practical explaination. Especially if you want someone to understand why SIT is happening.

IMO, the table diagrams with "distance, speed, cue ball hit points" would be much easier to explain and be understood by a lot of players.

GStrong
12-07-2004, 11:18 PM
Hi there... just an observation from a novice, but in NV 4.15 it appeared as though you cut the tape (maybe because of a miss) and then moved the object ball over a little bit, making the ball possible to make just by simply cutting it, without any throw necessary?

I really like your videos though and think your website is great, and agree that you can throw a ball, but that particular clip just doesn't look right.

Gary

Fred Agnir
12-08-2004, 07:28 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> I'm surprised nobody responded to this item. Does that mean everybody agrees? <hr /></blockquote>I think everyone agrees that SIT exists and that it's important. Since the original question from the reader was a slight misunderstanding of the importance or lack of importance or level of importance issue, then no response will make any sense.

In the end, what I have said is that most people confuse the effects of swerve as SIT.

Further, there are many standard shots that people have been "talking" about for years that supposedly show SIT, but in fact are impossible. The specific one in question is the idea of throwing the object ball, but while the cueball stays its normal path. This is shown in 99CS as well as others. It just doesn't happen that way, and you've described why: if the object ball throws one way, then the cueball must go the other way. So, in this particular shot, SIT doesn't do what many people have preached.

The importance of this is watching people attempt to throw balls in. Since many don't understand how much is due to throw and how much is due to swerve, I hear players forever saying things like "I threw it too much," or "I didn't throw it enough." I think it should be more like "I have no clue what throw or swerve does."

Fred

Fred Agnir
12-08-2004, 07:29 AM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> I'm surprised nobody responded to this item. Does that mean everybody agrees? <hr /></blockquote>I think everyone agrees that SIT exists and that it's important. Since the original question from the reader was a slight misunderstanding of the importance or lack of importance or level of importance issue, then no response will make any sense.

In the end, what I have said is that most people confuse the effects of swerve as SIT.

Further, there are many standard shots that people have been "talking" about for years that supposedly show SIT, but in fact are impossible. The specific one in question is the idea of throwing the object ball, but while the cueball stays its normal path. This is shown in 99CS as well as others. It just doesn't happen that way, and you've described why: if the object ball throws one way, then the cueball must go the other way. So, in this particular shot, SIT doesn't do what many people have preached.

The importance of this is watching people attempt to throw balls in. Since many don't understand how much is due to throw and how much is due to swerve, I hear players forever saying things like "I threw it too much," or "I didn't throw it enough." I think it should be more like "I have no clue what throw or swerve does."

Fred &lt;~~~ doesn't adjust for SIT much

SpiderMan
12-08-2004, 09:12 AM
I don't believe the quoted experiment is adequate to illustrate or disprove spin-induced throw.

A similar but more relevant experiment would involve an additional ball. I'd draw my "line" the length of the table and into a corner pocket for this illustration. Place the original object ball on the line, and the cueball about six inches to a foot away, also on the line, such that the two balls are aimed down the line and into the pocket.

Now place an additional ball off the line and midway between the CB and OB, such that it's edge just prevents you from making the straight-in shot. One way to achieve this placement is to freeze the "interference" ball to a "spacer" ball sitting on the line between the OB and CB, then remove the spacer ball. If you didn't freeze the two balls with their common centerline exactly perpendicular to the shot line, then the edge of the interference ball will ever-so-slightly occlude the straight-in shot.

Using nothing but sidespin, try to just miss the interference ball and throw the shot in. Can you do it? Use as level a cue as possible and medium speed. The balls are placed close together to help avoid unintentional CB curving, but you still have to resist the temptation of elevating the butt of your cue.

If SIT exists to a degree that measureably affects shot outcome, then you should be able to create a placement in this experiment where the shot cannot be made with centerball, but can be made with sidespin only.

This shot comes up quite often in games, but normally a slight masse or slight jump is chosen to avoid hitting the interference ball.

SpiderMan


<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
With respect to spin-induced throw (SIT), I have been teaching this phenomenon &amp; its use (a la Science of Pocket Billiards) for years. Recently, I've been told that the physics jockeys are now saying that no, while SIT may indeed be possible, it is too small an effect to use. Their "practical proof" is the following experiment: draw a line on the cloth (for example, a few feet on the long string), place a CB &amp; OB on the line, shoot the CB at the OB with sidespin, aiming to hit the OB full on. What one finds, doing this, is you can't get the CB to stay on the line while having the OB throw off the line.

So, this is very interesting, and sure enough, I couldn't demonstrate throw in the experiment. But, the old SIT hypothesis does indeed explain &amp; predict the types of results we get on the table, so while that model is at useful, I'd really like to know whether it is correct. They tell me what's really happening is simply that the CB is curving to the OB contact point that results in the line taken by the OB, giving the appearance that SIT is real.

A (from me):
SIT is definitely a real effect. Like cut-induced (collision-induced) throw, it is due to sideways friction force caused by relative sideways motion between the CB and OB during impact. NV 4.15, 4.16, 7.5, and 7.6 on my website (http://www.engr.colostate.edu/pool) show examples of various types of throw. The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).

Throw, resulting from CB English or cut angle, is most definitely real (and sometimes very useful)! It also must be accounted for at times; if not, you will sometimes miss what appear to be easy shots.

For more information, and a less scientific explanation, see pages 101-114 in "The Illustrated Principles of Pool and Billiards." <hr /></blockquote>
I'm surprised nobody responded to this item. Does that mean everybody agrees? <hr /></blockquote>

dr_dave
12-08-2004, 11:52 AM
<blockquote><font class="small">Quote Tom_In_Cincy:</font><hr>I don't understand all the mathematical formulas or graphs in your PDF document. So, I can't apply them to a pool table and my stroke, cue ball hit and distance shots.

Do you have an idea what level of education a person should have to interprert your equations? Let alone, apply them to a pool shot?<hr /></blockquote>

I'm not sure to which document you are referring. But you are correct, most of my TP analyses (OK ... maybe all /ccboard/images/graemlins/smirk.gif) are not well suited to a general audience. The disclamer on my TP web page (http://www.engr.colostate.edu/~dga/pool/technical_proofs/index.html) is quite accurate:

NOTE: this information will be of interest only to people with strong physics and mathematics backgrounds. Others proceed at your own risk.

My articles, videos, and book do not require an understanding of these TP analyses. I just use them help prove that certain claims are consistent with physics and geometry principles.

Fred Agnir
12-08-2004, 11:58 AM
<blockquote><font class="small">Quote Keith Talent:</font><hr> Dave, Didn't the same sort of physicists also declare years ago that the curveball in baseball is an "illusion"?<hr /></blockquote> Quite the opposite. It was the physicists who explained why a curve ball curves.

It was also the scientists who explained why a bumble bee flies and that the earth is indeed round. Contrary to the popular myths that always seem to say opposite.

Fred

dr_dave
12-08-2004, 11:59 AM
<blockquote><font class="small">Quote Keith Talent:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).<hr /></blockquote>

I don't see how the ob is exerting force -- pushing back, as you say -- upon the cb here. Isn't the cb just spinning itself off line, just as happens when a juiced-up cb hits a rail? The amount it moves, obviously, is affected by how full the hit is ... which determines the effective mass it's reacting against, right? Then there's the forward speed of the cb and of the rotation, and the exact direction of that spin ...
<hr /></blockquote>

This is a fine way to look at it, especially if it helps you make shots. That's what pool is all about.

However, there is a sideways friction force that throws the object ball. That's why it doesn't go straight (i.e., in the impact line direction). The cue ball provides this force. Whenever you push on something, it pushes back. That's why the cue ball is also thrown off line a little.

dr_dave
12-08-2004, 12:05 PM
<blockquote><font class="small">Quote GStrong:</font><hr>just an observation from a novice, but in NV 4.15 it appeared as though you cut the tape (maybe because of a miss) and then moved the object ball over a little bit, making the ball possible to make just by simply cutting it, without any throw necessary?
<hr /></blockquote>
You are absolutely correct ... there is an edit because I did miss the shot in NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV4-15.htm) the first time. The reason why I missed it is I hit it a little too hard. The amount of throw decreases dramatically at higher speeds. When I set up the shot the second time, I did not place the balls in the exact same locations as with the first shot (although this was not on purpose), but there is still significant throw on the shot.

I guess I should add this shot to my list of clips that I should redo.

Fred Agnir
12-08-2004, 12:12 PM
<blockquote><font class="small">Quote Dr. Dave:</font><hr>Throw, resulting from CB English or cut angle, is most definitely real (and sometimes very useful)! It also must be accounted for at times; if not, you will sometimes miss what appear to be easy shots.<hr /></blockquote>

<blockquote><font class="small">Quote Spiderman:</font><hr>Using nothing but sidespin, try to just miss the interference ball and throw the shot in. Can you do it? Use as level a cue as possible and medium speed. The balls are placed close together to help avoid unintentional CB curving, but you still have to resist the temptation of elevating the butt of your cue.
<hr /></blockquote>


Apparently Dave has already tried and failed that experiment because:

<blockquote><font class="small">Quote GStrong:</font><hr> Hi there... just an observation from a novice, but in NV 4.15 it appeared as though you cut the tape (maybe because of a miss) and then moved the object ball over a little bit, making the ball possible to make just by simply cutting it, without any throw necessary? <hr /></blockquote>

The attempt on NV 4.15 is clear to me that there was less SIT than the experimenter thought there would be . Even for uncleaned "for weeks" balls. I'm pretty sure this is good "proof" that people overestimate the amount of SIT.

Does someone else have a different conclusion? Maybe the experimenter didn't consider how much squirt there would be on such a slow shot?

Fred

dr_dave
12-08-2004, 12:15 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>
In the end, what I have said is that most people confuse the effects of swerve as SIT.

Further, there are many standard shots that people have been "talking" about for years that supposedly show SIT, but in fact are impossible. The specific one in question is the idea of throwing the object ball, but while the cueball stays its normal path. This is shown in 99CS as well as others. It just doesn't happen that way, and you've described why: if the object ball throws one way, then the cueball must go the other way. So, in this particular shot, SIT doesn't do what many people have preached.

The importance of this is watching people attempt to throw balls in. Since many don't understand how much is due to throw and how much is due to swerve, I hear players forever saying things like "I threw it too much," or "I didn't throw it enough." I think it should be more like "I have no clue what throw or swerve does."<hr /></blockquote>

Fred, believe or not, I think we actually agree on this one. /ccboard/images/graemlins/smile.gif /ccboard/images/graemlins/smile.gif /ccboard/images/graemlins/smile.gif

dr_dave
12-08-2004, 12:23 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote Keith Talent:</font><hr> Dave, Didn't the same sort of physicists also declare years ago that the curveball in baseball is an "illusion"?<hr /></blockquote> Quite the opposite. It was the physicists who explained why a curve ball curves.

It was also the scientists who explained why a bumble bee flies and that the earth is indeed round. Contrary to the popular myths that always seem to say opposite.

Fred<hr /></blockquote>

Fred,
Excellent reply!!! I was tempted to write something similar, but I'm glad I didn't. Now if somebody wants to disagree, they can come after you instead of me (for a change).

dr_dave
12-08-2004, 12:28 PM
<blockquote><font class="small">Quote Tom_In_Cincy:</font><hr> Ross,
IMO, a math equation is not a practical explaination. Especially if you want someone to understand why SIT is happening.<hr /></blockquote>

Please see my response to Keith Talent (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168742&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for a non-mathematical answer.

Rod
12-08-2004, 01:40 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>
The attempt on NV 4.15 is clear to me that there was less SIT than the experimenter thought there would be . Even for uncleaned "for weeks" balls. I'm pretty sure this is good "proof" that people overestimate the amount of SIT.

Does someone else have a different conclusion? Maybe the experimenter didn't consider how much squirt there would be on such a slow shot?

Fred <hr /></blockquote>

I think SIT is a bit overestimated by many. It's effect at higher speeds is almost non existant. I will offer up an example of SIT.

I shoot a trick shot sometimes, well it's not real tricky but it will clearly slow the effects of SIT at a slower speed. The most difficult part for most people is spinning the ball. I have a spin similar to Mike Massey but it's not necessary to spin as fast to see the effect.

OK, spin the one ball in place like a top, it's rotating clockwise. Shoot the one with the c/b dead straight ahead to point A. Shot speed is appx 1 3/4 table length speed. When the c/b contacts the one it immediately gets kicked or spun off to the right causing it to hit at point B. It then goes slowly into the side pocket. You can't aim at point B direct because it will go in the right corner pocket instead. The c/b will end up at appx point C.

OOPS better add the wei code- START(
%Al8F3%Pp3F3%QA3G8%RA1E4%Sm9H3%TZ4]2%WD1F4%Xm9F8%Y[1[7%ZC5F5
%]D3H7%^r2F2
)END

Most can't spin the ball that fast so the trick shot isn't important. I'm just using it as an example of SIT.

Rod

Bob_Jewett
12-08-2004, 04:26 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> I don't believe the quoted experiment is adequate to illustrate or disprove spin-induced throw. ... <hr /></blockquote>
An experiment that I think shows throw very clearly is shown at http://www.sfbilliards.com/throwtest.gif It was designed against those people who claim that throw does not exist -- some of them even write for magazines. It is not possible to get both balls to move to the same side without throw (assuming a level stick -- if you use masse, almost anything is possible).

You can try the shot shown with and without right english.

Keith Talent
12-08-2004, 04:50 PM
Dave, now that you and Fred are ganging up on me, let me say I perhaps should not have included physicists among the mistaken debunkers of the curveball (though I expect folks from all walks of life were part of that particular flat-earth society). But there was debate before modern cameras ended the argument.

This is a quote from a Web site on the physics of baseball:

For a long time, people have argued whether or not a curveball is really curving or if it is just an optical illusion. The argument was settled with the advent of fast photography. Using cameras, people were able to determine that, indeed, a curveball does curve. People (mostly physics professors) began wondering why a curveball curved and used Magnus' work to explain why.

Also, Dave, whether my non-technical understanding is a nice way to think of it or not, I was talking about the force you said the object ball exerted on the cue ball, not the other way around, which, obviously is what throw is about. I mean, the object ball is static, it ain't moving until the moment of contact ... perhaps you meant that the effect of the mass of the object ball when the cue ball hits it and then veers off away from the SIT direction would be considered "pushing back" by the object ball. I'm pretty sure I understand what you meant, but I tripped over the words.

Fred Agnir
12-08-2004, 06:00 PM
<blockquote><font class="small">Quote Keith Talent:</font><hr>
. People (mostly physics professors) began wondering why a curveball curved and used Magnus' work to explain why. <hr /></blockquote>Who else other than physics professors would be explaining why? I think the basics of fluid dynamics as it pertains to a stitched baseball is well within the grasp of any physics professor.

I think you're simply thinking about this idea from the wrong angle. If two hundred years ago, men argued the viability of flight, who would argue the possibilities? Physicists. Who would argue against? Other physicists.

In your baseball example, nobody would be arguing whether or not a baseball curves, but rather they would be arguing what is the science behind a curveball (when curveballs started appearing). And who would be doing the arguing? Physicists against each other. It sure wasn't policeman and housewives arguing about it.

Fred

Keith Talent
12-08-2004, 07:21 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>
I think you're simply thinking about this idea from the wrong angle. ...

In your baseball example, nobody would be arguing whether or not a baseball curves, but rather they would be arguing what is the science behind a curveball (when curveballs started appearing). And who would be doing the arguing? Physicists against each other. It sure wasn't policeman and housewives arguing about it.

Fred <hr /></blockquote>

Fred, you're a bulldog, no doubt. My example was a flawed memory, I admitted that. But there WAS some sort of public debate sometime last century about WHETHER curveballs curve, though it seems silly now.

Here's the source I quoted:
http://library.thinkquest.org/11902/physics/curve2.html?tqskip1=1

I am NOT thinking about spin-induced throw FROM this angle. It was merely an aside, something I found ironic. The baseball example was only meant to draw a parallel, a comment on the sort of mind that would need the assurance of an abstruse mathematical equation to explain an obvious fact, such as spin-induced throw. But what's not obvious, as you pointed out, is to what extent swerve might change the cut angle.

I actually admire the effort involved, though it seems a little wacky to me, something more suited to landing a space probe on Mars, maybe. But if pool physics equations are "useless," I ask myself, then how should I think of all the hours I spend at the table each week myself? /ccboard/images/graemlins/smile.gif

SpiderMan
12-29-2004, 10:08 PM
OK, I finally got around to (or, finally remembered while I was at the poolhall) trying the experiment, and was able to quantify the spin-induced throw achievable on that equipment. It was significant.

On a 9-ft gold crown with shimmed pockets (#13 at Rack Daddy's Abrams, possibly the tightest commercial table in Dallas), using balls that were neither clean nor filthy, I did the following:

I used the side of a wooden triangle to align the cueball and object ball, aimed diagonally for the corner pocket, at a near-maximum-achievable distance, with about 6" between the balls, and a path-occluding ball positioned as described in the quoted text.

Using only sidespin, I was actually surprised at the amount of spin-induced-throw I could achieve. With an occlusion such that a straight shot to bypass the interference would result in a miss by close to a half-diamond, I could still throw the ball in.

SpiderMan

<blockquote><font class="small">Quote SpiderMan:</font><hr> I don't believe the quoted experiment is adequate to illustrate or disprove spin-induced throw.

A similar but more relevant experiment would involve an additional ball. I'd draw my "line" the length of the table and into a corner pocket for this illustration. Place the original object ball on the line, and the cueball about six inches to a foot away, also on the line, such that the two balls are aimed down the line and into the pocket.

Now place an additional ball off the line and midway between the CB and OB, such that it's edge just prevents you from making the straight-in shot. One way to achieve this placement is to freeze the "interference" ball to a "spacer" ball sitting on the line between the OB and CB, then remove the spacer ball. If you didn't freeze the two balls with their common centerline exactly perpendicular to the shot line, then the edge of the interference ball will ever-so-slightly occlude the straight-in shot.

Using nothing but sidespin, try to just miss the interference ball and throw the shot in. Can you do it? Use as level a cue as possible and medium speed. The balls are placed close together to help avoid unintentional CB curving, but you still have to resist the temptation of elevating the butt of your cue.

If SIT exists to a degree that measureably affects shot outcome, then you should be able to create a placement in this experiment where the shot cannot be made with centerball, but can be made with sidespin only.

This shot comes up quite often in games, but normally a slight masse or slight jump is chosen to avoid hitting the interference ball.

SpiderMan


<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
With respect to spin-induced throw (SIT), I have been teaching this phenomenon &amp; its use (a la Science of Pocket Billiards) for years. Recently, I've been told that the physics jockeys are now saying that no, while SIT may indeed be possible, it is too small an effect to use. Their "practical proof" is the following experiment: draw a line on the cloth (for example, a few feet on the long string), place a CB &amp; OB on the line, shoot the CB at the OB with sidespin, aiming to hit the OB full on. What one finds, doing this, is you can't get the CB to stay on the line while having the OB throw off the line.

So, this is very interesting, and sure enough, I couldn't demonstrate throw in the experiment. But, the old SIT hypothesis does indeed explain &amp; predict the types of results we get on the table, so while that model is at useful, I'd really like to know whether it is correct. They tell me what's really happening is simply that the CB is curving to the OB contact point that results in the line taken by the OB, giving the appearance that SIT is real.

A (from me):
SIT is definitely a real effect. Like cut-induced (collision-induced) throw, it is due to sideways friction force caused by relative sideways motion between the CB and OB during impact. NV 4.15, 4.16, 7.5, and 7.6 on my website (http://www.engr.colostate.edu/pool) show examples of various types of throw. The reason the CB does not remain on the impact line for a direct hit on the OB is because when the CB throws the OB in one direction, the OB pushes back on the CB in the opposite direction, which throws the CB off the impact line. This is a result of Isaac Newton's Third Law of Motion (for every action there is an equal and opposite reaction).

Throw, resulting from CB English or cut angle, is most definitely real (and sometimes very useful)! It also must be accounted for at times; if not, you will sometimes miss what appear to be easy shots.

For more information, and a less scientific explanation, see pages 101-114 in "The Illustrated Principles of Pool and Billiards." <hr /></blockquote>
I'm surprised nobody responded to this item. Does that mean everybody agrees? <hr /></blockquote> <hr /></blockquote>

Bob_Jewett
12-30-2004, 11:38 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> OK, I finally got around to (or, finally remembered while I was at the poolhall) trying the experiment, and was able to quantify the spin-induced throw achievable on that equipment. It was significant.
... <hr /></blockquote>
As I understand your setup (shot partly occluded by middle ball) you do not control for swerve. "As level a cue as possible" is still not level. That's why I much prefer the setup I described earlier in which you have to move both cue ball and object ball to the same side of a line.

GeraldG
12-31-2004, 09:38 PM
Spin Induced Throw does exist in my world. I don't know the formulae to explain the physics behind it, and you know what? I don't CARE about the physics. I know how to use it, when to use it and that's all I care about. It works for me. If it doesn't exist in some Physicist's world, that's OK with me too.

The situation where I use it the most is when I have a near table-length shot that is nearly straight in, but has some angle and I have a need to hold the cue ball where it is. I can stop the cue ball by hitting the object ball dead center with left or right spin (depending upon which direction I need to throw), and spin the ball into the pocket. This actually comes up quite a bit in 9-ball.

mworkman
01-01-2005, 07:13 AM
START(
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)END
Wouldn't this shot prove SIT exists? While using a level stroke and with max left english it will throw to the right and in. You can't cut in because the 5 ball is in the way. You are not swerving the ball using a level stroke. Yes the cue ball will go a little to the left, but this is do to the gear effect when the balls collide. And you can't make it without the english. The contact point of object ball and cueball is what needs to be proven. If the contact point lines up with the rail to the left of the pocket and the ball still goes in, then SIT exists.. Right?

dr_dave
01-01-2005, 10:21 AM
<blockquote><font class="small">Quote mworkman:</font><hr> START(
%Aq3Q1%BL7P8%CJ5O4%DL7N1%Eo9S2%FK6P1%GK6N8%HM7N8%I L7O4%JK6M5
%KJ5P7%LJ5N2%MK6Q4%NJ5R0%OJ5M0%Pq3U1
)END
Wouldn't this shot prove SIT exists? While using a level stroke and with max left english it will throw to the right and in. You can't cut in because the 5 ball is in the way. You are not swerving the ball using a level stroke. Yes the cue ball will go a little to the left, but this is do to the gear effect when the balls collide. And you can't make it without the english. The contact point of object ball and cueball is what needs to be proven. If the contact point lines up with the rail to the left of the pocket and the ball still goes in, then SIT exists.. Right? <hr /></blockquote>

SIT most definitely does exists. Your example can be used to show it experimentally, and many of the ideas in this thread clearly explain why it exists. If anybody thinks it doesn't exist, they need to prove that the laws of physics somehow don't apply, and explain why.

doncartmill
01-01-2005, 12:21 PM
Everyone is gagging on a gnat. basically it should sufice to say that ,yes SIT exists ,it is however a realitively small reaction that in special circumstances we should be aware of the possibility it creates. It is pehapse more obvious that it exists ,when you consider a banked object ball.e,i, OB NOT on the rail and you are banking into the side pocket on your left. The angle is such that the cue ball must be shot with left english inorder to kill the OB,making it come back on a sharper angle (than no english) The CB must impart spin to the OB for this to happen. Now here is where ,if you aren't into the math ,just accept that when the CB hits the OB head on but with spin,there are 2 forces attacking the OB. 1) is the much larger force directly thru the center ,and 2) a small tangential force acting at the point of impact and 90 degs to the force thru the center (this is the force that imparts spin and in doing so causes SIP ) When you consider this in terms of a banked OB, it debunks the idea that SIT does not exist but is actually squirt causing the ball to move and maybe giving the appearence that said OB was "thrown". This is because ,if in the bank shot,left english is applied and the CB move right the shot would bank even longer. Bottom line is :the fact that spin is imparted to the OB,indicates a force acting at 90deg at point of impact,and therefore SIT must occur.

Fred Agnir
01-01-2005, 12:25 PM
<blockquote><font class="small">Quote GeraldG:</font><hr> Spin Induced Throw does exist in my world. <hr /></blockquote> Of course it does. I don't think anyone has said differently.

[ QUOTE ]
The situation where I use it the most is when I have a near table-length shot that is nearly straight in, but has some angle and I have a need to hold the cue ball where it is. I can stop the cue ball by hitting the object ball dead center with left or right spin (depending upon which direction I need to throw), and spin the ball into the pocket.<hr /></blockquote> Show me this imaginary shot. Actually, show yourself first, then show me. Video tape it. Provide a link. I'm prepared to be proven wrong. People talk about this shot like it actually is possible. It isn't. If the object ball throws to one side, the cueball must move to the opposite side. 99 Critical Shots is dead wrong on this shot.

[ QUOTE ]
This actually comes up quite a bit in 9-ball. <hr /></blockquote>I disagree.

Fred

Fred Agnir
01-01-2005, 12:35 PM
<blockquote><font class="small">Quote mworkman:</font><hr> START(
%Aq3Q1%BL7P8%CJ5O4%DL7N1%Eo9S2%FK6P1%GK6N8%HM7N8%I L7O4%JK6M5
%KJ5P7%LJ5N2%MK6Q4%NJ5R0%OJ5M0%Pq3U1
)END
Wouldn't this shot prove SIT exists? While using a level stroke and with max left english it will throw to the right and in. You can't cut in because the 5 ball is in the way. You are not swerving the ball using a level stroke. <hr /></blockquote> Again, nobody said it didn't exist. My contention is that most people grossly overestimate how much SIT influences a shot, and that furthermore people confuse reactions due to swerve with SIT.

Your statement "You are not swerving the ball using a level stroke" tells me that you grossly underestimate swerve. There are only a handful of shots that you can shoot with a level cue. And those shots are relatively uncomfortable stretch shots where the cue stick is completely over the table. All other times, you'll have elevation. And swerve becomes more significant than most people consider.

Dr. Dave has a video that is similar to your shot illustrated. Note that he had to move the cue ball. It is obvious to me that he overestimated how much (how little) SIT is really in a shot like that and had to move the cue ball into a position that he could make the shot. The final cue ball position was such that you didn't need any help to make the ball. A simple cut would suffice.

I find it strange that there is an obvious conclusion in video, but was ignored.


Fred

mworkman
01-01-2005, 04:43 PM
Could it be that everyone's stroke is different? It seems that with my stroke I end up adjusting more for deflection then I do for swerve. The only time I can get any swerve is when I intentionally try to do it (slight curve around a ball). Of course, speed is also a factor. I never shoot a shot and think that I need to aim more to the right because I'm using left english and the cue ball will then swerve into line. I suppose it's possible that I've been just compensating automatically without realizing what was really happening. /ccboard/images/graemlins/confused.gif

GeraldG
01-01-2005, 04:48 PM
I don't need to show it to myself. I know it can be done because I have done it. Repeatedly. Because you can't do it doesn't mean it can't be done. Disagree all you like. That's cool by me. I know what I know. I think maybe you are trying to split hairs here, if you're saying that you can't STOP the cueball with spin. OK...maybe the cueball moves a half inch in the opposite direction of the throw. Big deal. It's a lot less than it would move if you cut the ball instead of throwing it. The point is that I need to HOLD the cueball where it is...a half inch one way or the other is close enough. I'll call that stopping the cue ball...you call it what you like.

By the way, I can throw the object ball about 3 inches on a 3/4 table-length shot on a 9-foot table. That's a little more than an insignificant amount.

doncartmill
01-01-2005, 10:20 PM
I can see where on a length of table shot,if the object ball were hit dead center the relative distance that the cue ball moves off the point of impact could be so small that the "idea" of having stopped it dead could persist. e.g. if it were infact a dead center hit and the CB move 1/8" left,this would mean the OB is thrown an 1/8"right for some incremental distance down table (which probably varies with the speed of the shot...the softer shot taking the SIT better???) So say that were 1/8" per 6",then over the length of the table say 6 feet the SIT would be 12x 1/8" or 1 1/2". The cue ball for all intents and purposes has not moved (actually moved 1/8" )

GeraldG
01-02-2005, 07:11 AM
<blockquote><font class="small">Quote doncartmill:</font><hr> I can see where on a length of table shot,if the object ball were hit dead center the relative distance that the cue ball moves off the point of impact could be so small that the "idea" of having stopped it dead could persist. e.g. if it were infact a dead center hit and the CB move 1/8" left,this would mean the OB is thrown an 1/8"right for some incremental distance down table (which probably varies with the speed of the shot...the softer shot taking the SIT better???) So say that were 1/8" per 6",then over the length of the table say 6 feet the SIT would be 12x 1/8" or 1 1/2". The cue ball for all intents and purposes has not moved (actually moved 1/8" ) <hr /></blockquote>

Exactly.

dr_dave
01-02-2005, 12:15 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>Dr. Dave has a video that is similar to your shot illustrated. Note that he had to move the cue ball. It is obvious to me that he overestimated how much (how little) SIT is really in a shot like that and had to move the cue ball into a position that he could make the shot. The final cue ball position was such that you didn't need any help to make the ball. A simple cut would suffice.
<hr /></blockquote>

You are referring to the shot in NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/index.html). You are correct that I missed the shot the first time. This was because I hit the shot too hard, reducing the amount of throw. See my other response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168743&amp;Foru m=ccb&amp;Words=NV%204.15&amp;Match=Entire%20Phrase&amp;Search page=0&amp;Limit=25&amp;Old=3months&amp;Main=168241&amp;Search=tru e#Post168743) for more information. I do plan to reshoot this video in the near future (without edits or mistakes). I will post a message to this thread when it is available.

Ross
01-02-2005, 03:52 PM
Spiderman, I got similar results. In a CCB thread on 12/9/04 I described an experiment I did that measured spin-induced throw and ruled out the possibility of swerve contaminating the results.

I found: "For a straight-on hit with the ob about 4 or 5 inches away and a target about 4 diamonds away, a very slow hit with nearly maximum side english will throw the ball a little more than a balls width, or about 2 1/2 to 3 inches."

This would correspond to about 3 degrees of throw due to cb spin alone. If you add a little uncompensated cb swerve to this when using side under these conditions the ob may hit several inches away from where it would have for a center cb hit.

I then tested a couple of variations with the cb closer and farther from the ob. I found that the the amount of throw dropped off pretty quickly once the cb was more than 3 balls widths (about 7") away from the ob. Also, using a medium soft hit instead of a very soft shot reduced the amount of throw signficantly as well.

I didn't test the magnitude of SIT for cut shots though.

For details see thread:
http://www.billiardsdigest.com/ccboard/showflat.php?Cat=&amp;Board=ccb&amp;Number=168825&amp;page=4&amp;v iew=collapsed&amp;sb=5&amp;o=31&amp;fpart=1

Bottom line - SIT will throw the ob significantly off the "line-of-centers" if the following are true: a) you are using side english, b) the cb is less than a foot from the ob, c)you are hitting the ob head-on or close to head-on, and d) you are shooting fairly softly.

mworkman
01-03-2005, 09:14 AM
START(
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%KJ7P7%LJ7N2%MK7Q3%NJ7Q9%OJ7M0%P[3N3%Wa9U0%X\4I2%Y`1T5%Z\4H9
)END

Here is another example where SIT can be usefull. Your draw shot with english will come close to the green arrow. Straight draw will more resemble the red arrow. Shoot this shot by just barely making it in the right side of the pocket. Do this a number of times and you should be able to see the results. The english allows for a more straight on hit and will come back straighter also. At least it does for me.

Fred Agnir
01-03-2005, 10:42 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> You are referring to the shot in NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/index.html). You are correct that I missed the shot the first time. This was because I hit the shot too hard, reducing the amount of throw. See my other response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168743&amp;Foru m=ccb&amp;Words=NV%204.15&amp;Match=Entire%20Phrase&amp;Search page=0&amp;Limit=25&amp;Old=3months&amp;Main=168241&amp;Search=tru e#Post168743) for more information. I do plan to reshoot this video in the near future (without edits or mistakes). I will post a message to this thread when it is available. <hr /></blockquote>It is obvious to me that you overestimate how much SIT there is, and that having to say "I missed it because I shot it too hard," is proof of it. You missed it because there wasn't as much SIT as you anticipated. Which is the fact that I've pounding forever.

Why wouldn't you set it up exactly the same way and then shoot it soft enough?

Fred

Fred Agnir
01-03-2005, 10:45 AM
<blockquote><font class="small">Quote doncartmill:</font><hr> I can see where on a length of table shot,if the object ball were hit dead center the relative distance that the cue ball moves off the point of impact could be so small that the "idea" of having stopped it dead could persist. e.g. if it were infact a dead center hit and the CB move 1/8" left,this would mean the OB is thrown an 1/8"right for some incremental distance down table (which probably varies with the speed of the shot...the softer shot taking the SIT better???) So say that were 1/8" per 6",then over the length of the table say 6 feet the SIT would be 12x 1/8" or 1 1/2". The cue ball for all intents and purposes has not moved (actually moved 1/8" ) <hr /></blockquote>So... how does the end result differ than if you simply cut the ball and drift over 1/8"?

Fred

Fred Agnir
01-03-2005, 10:50 AM
<blockquote><font class="small">Quote GeraldG:</font><hr> I don't need to show it to myself. I know it can be done because I have done it. Repeatedly. Because you can't do it doesn't mean it can't be done. Disagree all you like. That's cool by me. I know what I know. I think maybe you are trying to split hairs here, if you're saying that you can't STOP the cueball with spin. OK...maybe the cueball moves a half inch in the opposite direction of the throw. <hr /></blockquote> Right. In other words, it can't be done. The cueball moves. Which is what I was saying. Are you changing your stance now?

[ QUOTE ]
It's a lot less than it would move if you cut the ball instead of throwing it. <hr /></blockquote>Obviously, you haven't tried this either. You'd surprise yourself. The end result are much closer than you think.

[ QUOTE ]
The point is that I need to HOLD the cueball where it is...a half inch one way or the other is close enough. I'll call that stopping the cue ball...you call it what you like.<hr /></blockquote> It's not up to me to change the definition of stopping the cue ball. Stop means stop. Do you normally move your cueball a full range of 1" when you want to stop the cueball and call that "close enough"? I wouldn't. Silly me.

Fred

Fred Agnir
01-03-2005, 10:54 AM
<blockquote><font class="small">Quote Ross:</font><hr> Bottom line - SIT will throw the ob significantly off the "line-of-centers" if the following are true: a) you are using side english, b) the cb is less than a foot from the ob, c)you are hitting the ob head-on or close to head-on, and d) you are shooting fairly softly. <hr /></blockquote>These are about as true a conclusion you can get. The additional conclusion should be that if you throw the object ball, the cueball must move in the opposite direction.

There is no long distant shot that stops the cueball and still throws the object ball to the left some significant amount. Yet, these and similar shots are what are always reported, and to which I always will object.

Fred

SpiderMan
01-03-2005, 11:39 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> OK, I finally got around to (or, finally remembered while I was at the poolhall) trying the experiment, and was able to quantify the spin-induced throw achievable on that equipment. It was significant.
... <hr /></blockquote>
As I understand your setup (shot partly occluded by middle ball) you do not control for swerve. "As level a cue as possible" is still not level. That's why I much prefer the setup I described earlier in which you have to move both cue ball and object ball to the same side of a line. <hr /></blockquote>

Bob,

Because getting a perfectly level cue is problematic, I placed the cue and object balls close to one another in order to discount swerve. This makes certain that the contact point is one that would "cut" the ball the wrong way, ie it would miss without the spin-induced throw.

The final path of the OB is definitely influenced by the cueball spin, and is far from what you would predict by the contact point achieved. Give it a try.

SpiderMan

dr_dave
01-03-2005, 12:54 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> You are referring to the shot in NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/index.html). You are correct that I missed the shot the first time. This was because I hit the shot too hard, reducing the amount of throw. See my other response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168743&amp;Foru m=ccb&amp;Words=NV%204.15&amp;Match=Entire%20Phrase&amp;Search page=0&amp;Limit=25&amp;Old=3months&amp;Main=168241&amp;Search=tru e#Post168743) for more information. I do plan to reshoot this video in the near future (without edits or mistakes). I will post a message to this thread when it is available. <hr /></blockquote>It is obvious to me that you overestimate how much SIT there is, and that having to say "I missed it because I shot it too hard," is proof of it. You missed it because there wasn't as much SIT as you anticipated. Which is the fact that I've pounding forever.

Why wouldn't you set it up exactly the same way and then shoot it soft enough?
<hr /></blockquote>

I explained what happened in my other response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168743&amp;Foru m=ccb&amp;Words=NV%204.15&amp;Match=Entire%20Phrase&amp;Search page=0&amp;Limit=25&amp;Old=3months&amp;Main=168241&amp;Search=tru e#Post168743). As I said, I will reshoot and post the video without edits or ball repositioning very soon (hopefully, this week). Then much of this discussion will be a mute point.

I agree with you and others that people sometimes overestimate the amount of throw they can achieve. But some people don't appreciate how important and useful it can be.

I regret that I made some mistakes with some of my original videos. People on the CCB have certainly found and pointed them out to me. I appreciate that very much and will correct them when I have time. Unfortunately, like everything else, it takes time to shoot, edit, and post the videos. My intial video taping, editing, and web work took over three weeks of solid work. I'm not making excuses, but it was very difficult being the camera man, lighting supervisor, author, technical consultant, narrator, shooter, editor, and webmaster all at once. I had no help whatsoever ... it was just me in my basement. Professionally produced videos involve many more people and lots more money. I think I shouted more profanities during the taping than I have the reft of my life. It was often frustrating and stressful when I would have to continually reshoot clips because I stuttered, missed a shot, hit the tripod by accident, casted an annoying shadow, etc. I was very glad when it was over and I am fairly happy that I don't have more mistakes than I do. But again, I will try to post improved clips, where appropriate. Thanks again for pushing me to do this.

doncartmill
01-03-2005, 02:59 PM
Now Fred be nice ! I was just playing devils advocat,mentioning that under the circumstances it would appear (if not observed too closely ) that the cue ball had not moved (while infact it had move 1/8") "Stranger" has now acknowledged that...OK CB does move when he throws a ball. As to why or how one would ever use SIT vs just cutting the OB. Imagine a line the length of the table off the left rail say 3". Now at the bottom of the table you have 3 balls whose edge cuts the line,starting 12" from end of table ,with the balls seperated about 3" center to center. The(cue ball)1st ball and 3rd ball are left of the line with their right edge just cutting the line ,the center ball is right of the line with its left edge just cutting the line. Now a cue ball stroked perfectly,with right hand english ,missing the 2nd ball by a hair and striking the 3rd ball dead center will throw the OB (3rd ball) into the pocket at upper end of table...the cue ball will move slightly to the right 1/8" to 1/2"maintaining desired position for next shot. A cut shot is immpossible unless a slight massie is used to cut the OB,which would have the CB moving incrementally more to the right after contact and possibly NOT maintaining the desired position. I think we have done as much damage as possible on this one. We are bound to have differences if we are talking apples and oranges.

GeraldG
01-03-2005, 09:12 PM
OK, I spent about 30 minutes playing with this shot tonight and proved to myself something I already knew.

I set the shot up along the long rail with the OB about 8 inches from the middle diamond and the cueball about 8 inches behind it, lined up so that if it were hit dead-on with a center-ball shot, it would contact the cushion between the 1st and 2nd diamonds by the corner pocket at the other end of that same long rail. That meant that I would need about 3" of throw to pocket the ball using a dead-on hit. I shot this shot 15 times with throw and 15 times cutting the ball. When I used sidespin to throw the ball and a dead-on hit, the cue ball would move less than 1" without fail. When cutting the ball the cue ball would move at least 4" every time, and most of the time would roll all the way to the cushion with a center ball hit.

I guess we're going to have to agree to disagree. You say that the amount of throw is insignificant, I say it is significant. You say you can't STOP the cue ball...OK, I'll give you that. You can't stop it precisely, exactly where it makes contact with the object ball. I don't think you can do that with a center ball stop shot either. It's going to move a tiny bit no matter what you do. But, within an inch is as close as I (or anyone I know) can ever play position on a ball anyway. The key is whether or not you are still in position for your next shot. Whether the cue ball stops precisely within a millimeter of where it made contact with the object ball is not important to me. I'll call it holding the cue ball, you call it whatever you want. I say the shot definitely exists for all practical purposes.

nhp
01-04-2005, 04:01 AM
Fred, I'm not sure if this is SIT, but haven't you heard of the famous Efren exhibition shot? He shoots a spot shot, with the cueball behind the line, and he pockets the object ball in the corner, and stops the cueball dead where the object ball was. He uses a ton of spin to do it. I've never seen him do it, but many, many people have seen him do it, and they all say the same thing, he stops the CB dead in it's tracks, but it's still spinning.

Also, is SIT also applied to when say, two object balls are frozen together, and you have the CB strike the first OB to a certain side to throw the other object ball off it's normal path? I shoot those shots sometimes just to experiment with how much I can get the balls to throw. Here is an example of a shot, and I think this is a pretty large amount of throw. Fred, is this the same SIT that you are discussing here?

START(
%AY2N9%IY2M7%P_6R2%WZ7D8%XY2M4%YZ0P2%Z^9R0%[Y2D7%\Y2O3%eC6a4

)END

And what about 'bending' the object ball? Has anyone heard of that? A friend of mine demonstrated this shot to me a few years ago. It's actually quite strange to see it done, because I bent down many times to see the path of the OB to the pocket, and it is completely blocked by the object ball, but the ball goes right in. I have no idea what spin he used, but I do know that he did not cheat the pocket, and it looked like there was absoloutely no way the ball would go in, even on loose pockets. He made it every time. Here is the shot:
(it's kind of hard for me to show exactly how it looked in the diagram, but this is as close as I can get. It's much more impressive if you see it in person)

START(
%Aj3Z2%Eg5Y3%Pn2T3%WE3Z8%Xi1Z2%Yk5Y8%Zm7T9

)END

DavidMorris
01-04-2005, 06:27 AM
<blockquote><font class="small">Quote nhp:</font><hr>Fred, I'm not sure if this is SIT, but haven't you heard of the famous Efren exhibition shot? He shoots a spot shot, with the cueball behind the line, and he pockets the object ball in the corner, and stops the cueball dead where the object ball was. He uses a ton of spin to do it. I've never seen him do it, but many, many people have seen him do it, and they all say the same thing, he stops the CB dead in it's tracks, but it's still spinning.<hr /></blockquote>
That would be pretty amazing to see!

<blockquote><font class="small">Quote nhp:</font><hr>Also, is SIT also applied to when say, two object balls are frozen together, and you have the CB strike the first OB to a certain side to throw the other object ball off it's normal path? I shoot those shots sometimes just to experiment with how much I can get the balls to throw. Here is an example of a shot, and I think this is a pretty large amount of throw. Fred, is this the same SIT that you are discussing here?<hr /></blockquote>
Yes, that is also throw, but commonly referred to as CIT or contact induced throw rather than spin induced throw. But in the shot you diagram, you're shooting from the wrong side. The throw would cause it to miss the pocket even wider than the straight line. Shoot it softly from the opposite side and it should go in. I usually demonstrate this with a corner pocket shot, with the OB's frozen in line to hit the cushion just behind the point. Before I showed him how, I challenged my son-in-law to take BIH and make this shot a couple nights ago. To a beginner it's counter-intuitive to shoot from the correct position, and he tried every way BUT the right way to make it. He finally said it wasn't possible. When I showed him in one shot he was amazed. /ccboard/images/graemlins/smile.gif

&lt;~~~ loves amazing rank beginners, they're the only ones I impress

PQQLK9
01-04-2005, 10:16 AM
I am thinking that the 1 ball actually is jumping over the edge of the 5 ball.

nhp
01-04-2005, 02:00 PM
David isn't the goal here to transfer right english to the ball you want to make in the side? If you hit the first ball from the other side, you will be putting right english on it, thus transferring left english to the ball, throwing it to the left. From the side I diagramed, you are putting left english on the first ball, thus transferring right english on the second ball, throwing it to the right. Am I correct? Here let me set up another diagram that would be better:

START(
%AY2N9%IY2M7%PY5T4%WZ7D8%XY2M4%YX8P1%ZY5T3%[Y2D7%\Y2O3%eC6a4

)END

DavidMorris
01-04-2005, 03:21 PM
<blockquote><font class="small">Quote nhp:</font><hr> David isn't the goal here to transfer right english to the ball you want to make in the side? If you hit the first ball from the other side, you will be putting right english on it, thus transferring left english to the ball, throwing it to the left. <hr /></blockquote>
No, the shot you describe has nothing to do with english transfer. The throwing action occurs because, due to friction (or elasticity?) at the contact point, the object balls cling to each other briefly. The first OB "pushes" the second OB offline before the second OB begins moving toward the pocket. That's why it is shot from the opposite side -- you are pushing the target ball towards the pocket.

Here's the way I demonstrate this shot:

START(
%Am6J4%BL7P8%CJ5O4%DL7N1%EM7P1%FK6P1%GK6N8%HM7N8%I n6I7%JK6M5
%KJ5P7%LJ5N2%MK6Q4%NJ5R0%OJ5M0%Pq1T2%Qm9O3%Rg8M8%S g6F7%Ws3D2
%Xo2I1%Ys2G1%Zo4I3%]s0E8%^o1I4
)END

If shot straight on, from position B, the 9B goes straight into the cushion right at the point of the pocket (the black line). If shot from C, CIT causes it to miss the pocket even further (the green line). Position C is where most beginners think you should hit this, as if you could cut the frozen ball in. Position A would be the correct position, to throw the 9B into the pocket along the red line. A soft stroke is required, a firm stroke reduces or eliminates the effects of throw. Oh, and hit the 1B head on, don't try to cut it, you'll just defeat the whole purpose and duplicate a straight on hit.

Try it, it is extremely easy to do once you understand the concept, and always amazes those who aren't "in the know." /ccboard/images/graemlins/smile.gif

Bob_Jewett
01-04-2005, 06:11 PM
<blockquote><font class="small">Quote mworkman:</font><hr>... While using a level stroke and with max left english it will throw to the right and in. You can't cut in because the 5 ball is in the way. You are not swerving the ball using a level stroke. .. <hr /></blockquote>
You are not using a level stroke. I'm willing to bet large sums on it. Your angle of stick elevation is not zero, unless you have ripped the rails off the table or are shooting through the webbing of a leather pocket. Until you shoot with a level stick, the naysayers can always point to your elevation and say that's what's moving the object ball over.

It is because of this niggling nitpicking by the naysayers -- including one former world champion -- that I came up with the SIT demo I've mentioned before.

And to clear up a point that was evidently confusing to someone, I'm absolutely sure that spin-induced throw exists, even though a former world champion has said it does not. You can't always believe the "experts."

Bob_Jewett
01-04-2005, 06:35 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> ...The final path of the OB is definitely influenced by the cueball spin, and is far from what you would predict by the contact point achieved. Give it a try. <hr /></blockquote>
I feel confident that I'll see what you predict, because I use such shots all the time in play. What I keep saying -- but evidently no one will listen, except maybe Fred -- is that if someone says you are getting the effect by masse, you have no good defense. In fact the cue ball WILL masse on its way to the object ball. You CANNOT STOP IT!!!! (Will you listen if I shout?) What I looked for, and I believe I found, was a demo of SIT that the nitpickers cannot object to. In my demo if there is swerve, it will act against the second requirement of the shot. In fact my demo does demonstrate that SIT exists, and will tell you how useful it is in holding the cue ball in place while englishing the object ball to the side.

I covered much of this in my April 2001 column, which was largely about Mosconi's "ring around the side" draw drill. Also in that column I pointed out that if you need to cut the object ball a little to the right, and also bring the cue ball to the right, you probably want right side spin, not left.

nhp
01-05-2005, 04:18 AM
David, in your diagram, are the balls frozen together?

This is all really new information to me, but I am skeptical because for the past 8 years it's been imprinted in my mind that you can throw frozen combinations off line by spin transfer. I probably learned this from a bunch of books on pool. When I first started playing I would spend hours at the bookstore reading all the instructional books on pool, learning about throw, etc, then I would go to the poolhall and spend twice as many hours practicing. I am going to set up another shot diagram, and then if you don't mind, please edit the diagram as to where you would place the cueball to throw the ball in the pocket, and what side of the first ball you would hit to make the shot:

The object here is to pocket the 2 in the corner by shooting the combination. In this situation, I would place the cueball as in the diagram, and strike the 1 on the right side, putting right english on the 1, which transfers left english on the 2, and throwing the 2 to the left and into the corner pocket. Here is the diagram:

START(
%Ao0N4%Bo5M4%Pp1T9%Ws1G0%Xn8N8%[o6O7%\p0T7%]r9D5%^o7L8

)END

Is this the wrong way to do it? Where would you strike the 1?

This is all entirely new to me, but it's interesting, although I am still not sure about what you are saying. The shot in the diagram I just made about 1 hour ago when I got off work (I work at a poolhall, and the balls were somewhat clean)

DavidMorris
01-05-2005, 06:38 AM
<blockquote><font class="small">Quote nhp:</font><hr> David, in your diagram, are the balls frozen together?<hr /></blockquote>
Yes, but IIRC the same concept applies even if there is a very slight gap, say 1/8", between the balls.

[ QUOTE ]
This is all really new information to me, but I am skeptical because for the past 8 years it's been imprinted in my mind that you can throw frozen combinations off line by spin transfer.<hr /></blockquote>
Perhaps Bob Jewett or Fred A. will disagree with me, but I don't believe that you can transfer enough spin to a 2nd frozen ball to affect the ball's path or throw it offline enough to make a shot like this. Transferred spin even to the first OB either by gear effect or cut is typically minimal as it is -- a small fraction of the spin applied to the CB by the cuetip. Unless you're using balls with a sandpaper finish. /ccboard/images/graemlins/wink.gif

[ QUOTE ]
I am going to set up another shot diagram, and then if you don't mind, please edit the diagram as to where you would place the cueball to throw the ball in the pocket, and what side of the first ball you would hit to make the shot:<hr /></blockquote>
No need for me to edit it, I would shoot it like you diagrammed it, except hitting the 1B a bit fuller. Your shot is basically identitical to the one I described, just at a shallower angle. It may just be your diagram, but as thin a hit as you're showing there on the 1B, the CB would likely hit the 2B before it could get away. If you're actually making this shot as you've diagrammed it, then I'll bet large sums that you're hitting the 1B a bit fuller, and the 2B is dropping due to CIT -- exactly as I described it. You're not "spinning" the 2B in, you're "pushing" it in thanks to CIT.

Try the shot using a stripe for the 2nd ball, and align the stripe perpendicular to the playing surface (up &amp; down) and aligned toward the pocket. Shoot the shot again and see how much spin you see on the striped ball. It's likely to wobble because there will be some friction between the cloth and ball as it is pushed offline, but I'll wager that you won't see much "spin" as if english were applied to it.

Keep in mind, as Bob has said, that there are distinct camps with regards to whether and how much SIT exists. Bob mentions a world champion (and I believe I know who he referring to) who swears it does NOT exist. I myself am convinced that it does. But I don't believe these shots you and I are discussing have as much to do with SIT than with CIT. I'm sure some will disagree.

doncartmill
01-05-2005, 09:24 AM
I thought I had saved the address that allows me to view these shot setups...can't find it Help !!!

SpiderMan
01-05-2005, 09:28 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> ...The final path of the OB is definitely influenced by the cueball spin, and is far from what you would predict by the contact point achieved. Give it a try. <hr /></blockquote>
I feel confident that I'll see what you predict, because I use such shots all the time in play. What I keep saying -- but evidently no one will listen, except maybe Fred -- is that if someone says you are getting the effect by masse, you have no good defense. In fact the cue ball WILL masse on its way to the object ball. You CANNOT STOP IT!!!!
<hr /></blockquote>

Bob, if you look at the portion of my statement that you edited out, note that I did not say I stopped or eliminated swerve, I only noted that by placing the cue ball and object balls close together I "discounted" the effect. In other words, I make it intuitive for any observer to conclude that there is not sufficient masse over that distance to cut the ball in, therefore the major effect used is the throw. As you noted, you have used this shot many times and the your own observations agree with mine. No one I have set this up for has concluded that the ball is made by masse, provided the cue-object distance is short.


<blockquote><font class="small">Quote Bob_Jewett:</font><hr>
(Will you listen if I shout?) What I looked for, and I believe I found, was a demo of SIT that the nitpickers cannot object to. In my demo if there is swerve, it will act against the second requirement of the shot. In fact my demo does demonstrate that SIT exists, and will tell you how useful it is in holding the cue ball in place while englishing the object ball to the side. I covered much of this in my April 2001 column, which was largely about Mosconi's "ring around the side" draw drill. Also in that column I pointed out that if you need to cut the object ball a little to the right, and also bring the cue ball to the right, you probably want right side spin, not left. <hr /></blockquote>

This should probably be addressed as a separate topic. If I understand correctly, your SIT demonstration would, for example, use left english on the cueball to cause an object ball to be thrown right and the cue ball (after impact) to also drift to the right of a line through their centers. Is that correct?

But your last sentence above (referencing the magazine article) then implies that right english should "probably" be used to achieve the same end. Would this utilize a different phenomenon than SIT to achieve that opposite effect? I don't have access to a table at the moment, but I am having a difficult time imagining right english moving both balls to the right of centerline without masse. Obviously it could be easily done by a right-breaking masse.

SpiderMan

dr_dave
01-05-2005, 10:38 AM
<blockquote><font class="small">Quote nhp:</font><hr>Also, is SIT also applied to when say, two object balls are frozen together, and you have the CB strike the first OB to a certain side to throw the other object ball off it's normal path? I shoot those shots sometimes just to experiment with how much I can get the balls to throw. Here is an example of a shot, and I think this is a pretty large amount of throw. Fred, is this the same SIT that you are discussing here?<hr /></blockquote>
There are two types of throw:
1) SIT (AKA spin-induced throw, English-induced throw, or just throw)
and
2) CIT (AKA collision-induced throw, cut-induced throw, cut throw, drag, or push)

All throw is a result of sideways friction force between two balls resulting from relative sideways motion (from spin or from cut angle). To me, all of the different effects are still "throw."

Your example actually involves at bit of SIT (because hitting the first object ball on the side induces some spin which interacts with the 2nd ball) and CIT (because there is an effective cut angle between the 1st and 2nd object balls). However, the throw is mostly due to CIT in your example.

I have online video demonstrations of SIT at NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV4-15.htm) and NV 7.6 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV7-6.htm) and of CIT at NV 4.16 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV4-16.htm) and NV 7.5 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV7-5.htm).

If you have a copy of "The Illustrated Principles of Pool and Billiards" you can find 22 pages of discussion, illustration, and examples of various types of throw shots, along with the principles involved (see pp. 101-114 and 209-216).

dr_dave
01-05-2005, 11:45 AM
<blockquote><font class="small">Quote doncartmill:</font><hr> I thought I had saved the address that allows me to view these shot setups...can't find it Help !!! <hr /></blockquote>
See my new thread (http://www.billiardsdigest.com/ccboard/showflat.php?Cat=&amp;Board=ccb&amp;Number=172787&amp;page=0&amp;v iew=collapsed&amp;sb=5&amp;o=&amp;fpart=1).

DavidMorris
01-05-2005, 11:56 AM
<blockquote><font class="small">Quote doncartmill:</font><hr> I thought I had saved the address that allows me to view these shot setups...can't find it Help !!! <hr /></blockquote>
The WEI table link is http://endeavor.med.nyu.edu/~wei/pool

I don't use the internet link though, because for some reason it hangs and will not finish loading now. I had saved the WEI files to my harddrive a long time ago, and created a shortcut to the files on my system.

There is also a Java applet version of WEI at http://rsbtable.leagueoperator.org (this requires a Java runtime plugin for your browser).

Bob_Jewett
01-05-2005, 12:35 PM
<blockquote><font class="small">Quote nhp:</font><hr> Fred, I'm not sure if this is SIT, but haven't you heard of the famous Efren exhibition shot? He shoots a spot shot, with the cueball behind the line, and he pockets the object ball in the corner, and stops the cueball dead where the object ball was ...

<hr /></blockquote>
It's a masse shot. It's easy to do in Virtual Pool. Use inside draw and elevate about 70 degrees.

Bob_Jewett
01-05-2005, 12:43 PM
<blockquote><font class="small">Quote nhp:</font><hr> ...
And what about 'bending' the object ball? Has anyone heard of that? <hr /></blockquote>
I've heard about it but no one seems to be able to make the object ball curve. I've had a standing offer out of $200 to anyone who can show me how to make the object ball curve significantly. I even asked a person who claims to show it on a video tape, and he realized immediately that he could not really make the object ball curve. (I have a standard setup that clearly separates curve from large pockets. The table has to be flat. The object ball cannot be jumped over the obstruction. You are not allowed to doctor the balls or use lopsided ones. Etc.)

If your friend really can curve the object ball, I've got $200 for him.

dr_dave
01-25-2005, 04:28 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Fred Agnir:</font><hr>Dr. Dave has a video that is similar to your shot illustrated. Note that he had to move the cue ball. It is obvious to me that he overestimated how much (how little) SIT is really in a shot like that and had to move the cue ball into a position that he could make the shot. The final cue ball position was such that you didn't need any help to make the ball. A simple cut would suffice.
<hr /></blockquote>

You are referring to the shot in NV 4.15 (http://www.engr.colostate.edu/~dga/pool/normal_videos/index.html). You are correct that I missed the shot the first time. This was because I hit the shot too hard, reducing the amount of throw. See my other response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168743&amp;Foru m=ccb&amp;Words=NV%204.15&amp;Match=Entire%20Phrase&amp;Search page=0&amp;Limit=25&amp;Old=3months&amp;Main=168241&amp;Search=tru e#Post168743) for more information. I do plan to reshoot this video in the near future (without edits or mistakes). I will post a message to this thread when it is available. <hr /></blockquote>
I finally found time to do a more careful job with this demonstration. It is now available online (see NV 4.15) (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV4-15.htm). Hopefully, most of the discussion surrounding this issue will now be a moot point.

Fred, thank you for indirectly encouraging me to re-shoot this video. I am much happier with the new version.

Rod
01-25-2005, 05:02 PM
Dave,

Your gonna get nit picked. /ccboard/images/graemlins/smile.gif Er, well, I'll hold my comments until it happens. I did notice another clip or two where a ball was moved but I think it's to be expected to some degree. The set up for some shots, even if a ball was moved slightly, wouldn't matter.

Rod

dr_dave
01-26-2005, 10:23 AM
<blockquote><font class="small">Quote Rod:</font><hr> Dave,
Your gonna get nit picked.<hr /></blockquote>
Did you see something in the video that was wrong of misleading? If so, please let me know. Or did you just assume that the anti-Dr.Dave crowd would just nit pick "gnat's a$$" kind of stuff just for the fun of it?
<blockquote><font class="small">Quote Rod:</font><hr>I did notice another clip or two where a ball was moved but I think it's to be expected to some degree. The set up for some shots, even if a ball was moved slightly, wouldn't matter.<hr /></blockquote>
Please let me know if any of the "video edits" misrepresent the intent of any of the clips. If so, I would be happy to add them to my re-shoot list. If you don't want to open me up to further attack, you could just send me a private message or e-mail.

Thanks for your input and concern.

Qtec
01-26-2005, 10:42 AM
It looks like you can make the ball without using SIT.
Swerve can still be a factor.
I think the comments you recieve will be the same as with the last video.
Qtec

dr_dave
01-26-2005, 10:57 AM
<blockquote><font class="small">Quote Qtec:</font><hr> It looks like you can make the ball without using SIT.<hr /></blockquote>
I agree that this is possible with a masse shot (with the cue stick elevated significantly).
<blockquote><font class="small">Quote Qtec:</font><hr>Swerve can still be a factor.<hr /></blockquote>
Agreed; although, I believe it was minimal in my shot, as compared to the throw effect.
<blockquote><font class="small">Quote Qtec:</font><hr>I think the comments you recieve will be the same as with the last video.<hr /></blockquote>
Well, if that's the case, so be it. If someone wants to create and post a more definitive video, they are welcome (I would even be happy to post it for them if they provide a tape); but I think I'm done with this topic. I have about 100 other things I want to study and understand better.

Fred Agnir
01-26-2005, 12:33 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> It is now available online (see NV 4.15) (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV4-15.htm). Hopefully, most of the discussion surrounding this issue will now be a moot point.

Fred, thank you for indirectly encouraging me to re-shoot this video. I am much happier with the new version. <hr /></blockquote>I was about to say how great a job it looked... but... and I really am not "nitpicking," but... I wish you had shot the shot as it lay in the begining of the video. The final placement looks like it is farther off from the one ball, and that it can be made by simply cutting the balls.

In fact, as you shoot the shot, it looks like you are indeed cutting the ball and not shooting straight ahead. The cut angle that the object ball takes looks like it's going exactly where you cut it. It looks once again that you proved what I was saying. That there isn't as much SIT than people think.

Do other people see it differently?

Fred

Qtec
01-26-2005, 01:20 PM
Didnt I tell you? /ccboard/images/graemlins/smirk.gif

[ QUOTE ]
Hopefully, most of the discussion surrounding this issue will now be a moot point. <hr /></blockquote>

Sorry Dave. Its not that easy here on the CCB. /ccboard/images/graemlins/grin.gif

After all, you did start this thread.
You cant quit now. /ccboard/images/graemlins/cool.gif


Qtec

dr_dave
01-26-2005, 01:36 PM
<blockquote><font class="small">Quote Qtec:</font><hr> Didnt I tell you? /ccboard/images/graemlins/smirk.gif

&lt;/font&gt;&lt;blockquote&gt;&lt;font class="small"&gt;Quote:&lt;/font&gt;&lt;hr /&gt;
Hopefully, most of the discussion surrounding this issue will now be a moot point. <hr /></blockquote>

Sorry Dave. Its not that easy here on the CCB. /ccboard/images/graemlins/grin.gif

After all, you did start this thread.
You cant quit now. /ccboard/images/graemlins/cool.gif
<hr /></blockquote>
On this topic, I give up (for now!). /ccboard/images/graemlins/confused.gif

Rod
01-26-2005, 02:26 PM
[ QUOTE ]
Did you see something in the video that was wrong of misleading? If so, please let me know. Or did you just assume that the anti-Dr.Dave crowd would just nit pick "gnat's a$$" kind of stuff just for the fun of it?
<hr /></blockquote>

Dave,

Your cue angle suggests you cut the ball in. I thought perhaps this angle was you compensating for squirt. However that would be a lot of compensation for such a short distance. If you'll notice, the one moves a fair amount. Although it would be expected to move slightly because the right hand spin off the o/b sends it that direction, however that should be very slight.

Notice the o/b hit the rail, it appears, over two diamonds before the pocket. That is a lot of throw. The shot would have looked much better if your cue was parallel to your aim line (cameras are deceiving) and the o/b went center pocket; with the one barely touched.

Either that or spacing the c/b out from the rail slightly more than the o/b. It wouldn't have to be much, the thickness of a match book perhaps .015 roughly. Then shoot the shot with no noticeable movement of the one. If the o/b barely goes in that illustrates SIT. To much angle then CIT will be credited for part the shot. Itís hard to win this deal. Swerve isnít even a factor. That would really be nit picking. It might even be said the extra .015 would cause CIT, really nit picky.

Having said that we know SIT and CIT exists. The video shows this even if it's not a perfect lab experiment. LOL If I was shooting a similar shot in a game, my execution would have to be near flawless. That is, make the o/b and not be called on a foul for a bad hit. BTW it is not necessary to use that much spin. A tip of English at slower speed has the same effect.

You want to redo it fine, if not fine, I can live with it, if you can. I realize this sort of thing takes time to set up and I appreciate your efforts. As I said before, most playerís strokes need far more improvement to be that critical or accurate. If I was to nit pick something it would be Virtual Pool, the physics arenít even close in many cases. People bought that game by the hundreds of thousands and I rarely hear anything mentioned. Swerve is a prime example.

Rod

SpiderMan
01-26-2005, 03:02 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> It looks once again that you proved what I was saying. That there isn't as much SIT than people think.

Do other people see it differently?
Fred <hr /></blockquote>

Fred,

I don't know how much SIT "most people" think there is, but when I tried my own experiment I actually observed "more" than I expected. I had thought I would only be able to throw an inch or two over the length of the table, but as it turns out that was conservative.

SpiderMan

dr_dave
01-26-2005, 03:04 PM
<blockquote><font class="small">Quote Rod:</font><hr>Your cue angle suggests you cut the ball in. I thought perhaps this angle was you compensating for squirt. However that would be a lot of compensation for such a short distance. If you'll notice, the one moves a fair amount. Although it would be expected to move slightly because the right hand spin off the o/b sends it that direction, however that should be very slight.<hr /></blockquote>
I agree with you that it is unexpected that the 1-ball would move so much with just throw effects. You are probably correct that there was a small cut angle. Maybe the 1-ball wasn't placed as exactly as I had hoped on the final "take" (I had to try the shot several times before I found the best combination of squirt correction and speed). Also, maybe there was a small amount of curve (swerve); although, I tried to minimize this by keeping the cue stick as level as possible.

<blockquote><font class="small">Quote Rod:</font><hr>The shot would have looked much better if your cue was parallel to your aim line (cameras are deceiving) and the o/b went center pocket; with the one barely touched.<hr /></blockquote>
The camera angle exaggerates the angle of the cue. It was much closer to parallel-to-the-rail than it looks in the video. I did adjust for squirt, but not as much as it would appear in the camera view. I tried to get a better view, but my cue was almost hitting the tripod as it was. Next time I re-shoot this (yes, I might redo it again!), I will work harder to get a better camera angle, and maybe "shoot" it from several different angles.

<blockquote><font class="small">Quote Rod:</font><hr>BTW it is not necessary to use that much spin. A tip of English at slower speed has the same effect.<hr /></blockquote>
Thanks for the tip. I look forward to trying this out.

dr_dave
01-26-2005, 03:08 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Fred Agnir:</font><hr> It looks once again that you proved what I was saying. That there isn't as much SIT than people think.

Do other people see it differently?<hr /></blockquote>
I don't know how much SIT "most people" think there is, but when I tried my own experiment I actually observed "more" than I expected. I had thought I would only be able to throw an inch or two over the length of the table, but as it turns out that was conservative.<hr /></blockquote>
If you want to see some bigger-than-expected throw, see the frozen throw shot in NV 7.6 (http://www.engr.colostate.edu/~dga/pool/normal_videos/NV7-6.htm). In fact, I had to do multiple "takes" (changing the impact line and amount of English) on this shot because I kept throwing it too much!

Rod
01-26-2005, 03:42 PM
Dave ,

I might add you must have hit that shot with a tad bit of top as well. At center ball - horizontal line - it should not have followed. If anything I'd favor a 1/4 tip or less of low. It will give you a better visual result.

Yes experiment with spin and speed. It takes more speed to increase spin so it starts becoming a trade off at some point, more speed, less throw. I only mentioned it because it should help with aiming and accuracy.

Rod

dr_dave
01-26-2005, 03:48 PM
<blockquote><font class="small">Quote Rod:</font><hr>I might add you must have hit that shot with a tad bit of top as well. At center ball - horizontal line - it should not have followed. If anything I'd favor a 1/4 tip or less of low. It will give you a better visual result.<hr /></blockquote>
Also, follow might actually reduce the throw a little since the friction force between the balls will point down a little, instead of completely to the left.
<blockquote><font class="small">Quote Rod:</font><hr>Yes experiment with spin and speed. It takes more speed to increase spin so it starts becoming a trade off at some point, more speed, less throw. I only mentioned it because it should help with aiming and accuracy.<hr /></blockquote>
Sounds reasonable. Thanks.

BlindPlayer
04-01-2005, 08:52 PM
Dear Dr. Dave,

I teach the sport and show young players whey they miss seemingly simple straight in shots. Their practice strokes are center ball (or close to it) but during the actual stroke they impart English on the CB and throw the OB off-line for a miss. Obviously, when controlled, shots that look impossible are possible when thrown off line on purpose. I've found that several things affect throw (in respect to changing the line of travel of the OB for the pocket)....(1) dirt: the dirtier the balls the greater the throw affect - friction is increased (2) the angle: greater the angle, less affect (3) Speed: slower speed more affect = faster speeds less affect (4) humidity may play a small role by reducing friction but I'm not sure. These, I'm sure, are the basics and that's why they don't appear on threads of this type.

TennesseeJoe
04-02-2005, 08:42 AM
Dr. Dave,
The big questions is"Why does throw decrease as the shot is hit harder?, Is it because there is less contact time?"
By the way--I appreciate your research and publications.

Fred Agnir
04-02-2005, 10:41 AM
<blockquote><font class="small">Quote TennesseeJoe:</font><hr> Dr. Dave,
The big questions is"Why does throw decrease as the shot is hit harder?, Is it because there is less contact time?"
By the way--I appreciate your research and publications.
<hr /></blockquote>The amount of throw decrease because the dynamic friction decreases as the relative surface speed increases.

I think "contact time" between balls is nearly constant across the range of normal shot speeds.

Fred

MrLucky
04-02-2005, 12:29 PM
The simple way of describing this is the harder the ball is hit the less time the spin has to affect the direction of the ball due to the friction decrease and speed increase ! /ccboard/images/graemlins/cool.gif

Bob_Jewett
04-02-2005, 06:34 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>...
I think "contact time" between balls is nearly constant across the range of normal shot speeds. <hr /></blockquote>
Theory says that contact time should decrease slightly on faster shots. You have to hit the ball 32 times faster to reduce the contact time by a factor of two, as I recall the formula.

Many people get hung up on contact time, thinking that a softer tip will give more english because it is on the ball longer and such. The present theoretical understanding of friction says that contact time is completely unimportant for the amount of throw or spin you get.

For a comparatively legible research paper about measuring ball-ball contact time, see http://ej.iop.org/links/q33/DhcwgEMv+GU3yGnTlRMnSA/jdv4i1p160.pdf
Those researchers used a technique a lot like Wayland Marlow used to measure contact time for pool balls.

nhp
04-02-2005, 07:18 PM
Bob, I heard somewhere that a well-chalked tip will help reduce deflection, is this true?

video
04-03-2005, 04:04 AM
Just wanted to jump in here and say I agree with whatever the heck Dave states.

After not shooting pool my whole life like since back in the Boy's Club days, I started giving it a shot again only to find out early on that I couldn't shoot worth a (beep)

Then one day goofing around on the web, I came upon Dave's Pool Instruction Videos. I watched and practiced what I saw on a daily basis and in a matter of about 2 weeks of practice I actually started to win some games up at the club where I was hanging out alot.

I now go back to Dave's videos on a steady basis to keep the stuff he's explained - fresh in my brain.

Hats off to you Dave! /ccboard/images/graemlins/cool.gif

I owe many of my wins to you.
My loss's I'm not worried about because I just generate 'new' excuses for everyone of them, no biggy. /ccboard/images/graemlins/laugh.gif

Take care, and keep up the great work on and off line!

Alias "Video"

dr_dave
04-03-2005, 12:15 PM
<blockquote><font class="small">Quote BlindPlayer:</font><hr>I've found that several things affect throw (in respect to changing the line of travel of the OB for the pocket)....(1) dirt: the dirtier the balls the greater the throw affect - friction is increased<hr /></blockquote>
Agreed, dirt and chalk on the balls definitely increases friction and throw.
<blockquote><font class="small">Quote BlindPlayer:</font><hr>(2) the angle: greater the angle, less affect (3) Speed: slower speed more affect = faster speeds less affect<hr /></blockquote>
For English-induced throw, the amount of throw is definitely larger for smaller cut angles and slower speeds.

For cut-induced throw (AKA cling), the throw is also larger for lower speeds, but it is actually greatest at about a 30 degree cut angle, which is a half-ball hit (see this message (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=175193&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for more info).

Dr. Dave

dr_dave
04-03-2005, 12:31 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote TennesseeJoe:</font><hr> Dr. Dave,
The big questions is"Why does throw decrease as the shot is hit harder?, Is it because there is less contact time?"
By the way--I appreciate your research and publications.
<hr /></blockquote>The amount of throw decrease because the dynamic friction decreases as the relative surface speed increases.<hr /></blockquote>
Agreed. Coriolis reported this effect back in the early 1800s. It is a common effect with most materials.

<blockquote><font class="small">Quote Fred Agnir:</font><hr> I think "contact time" between balls is nearly constant across the range of normal shot speeds.<hr /></blockquote>
Even if the contact time changed with shot speed, it is likely this effect alone would not change the amount of throw. If the friction were constant, the proportion of perpendicular (impact line) force to sideways (tangent line) force would still be the same (see TP 4.3 and 4.4 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/index.html) for the technical background).

Dr. Dave

dr_dave
04-03-2005, 12:42 PM
<blockquote><font class="small">Quote video:</font><hr>Just wanted to jump in here and say I agree with whatever the heck Dave states.<hr /></blockquote>
I would not advise listening to what anybody says on pure faith. Everybody makes mistakes and has trouble admitting they are wrong at times (me included). But thanks for your enthusiastic support. It feels good!

<blockquote><font class="small">Quote video:</font><hr>After not shooting pool my whole life like since back in the Boy's Club days, I started giving it a shot again only to find out early on that I couldn't shoot worth a (beep)

Then one day goofing around on the web, I came upon Dave's Pool Instruction Videos. I watched and practiced what I saw on a daily basis and in a matter of about 2 weeks of practice I actually started to win some games up at the club where I was hanging out alot.

I now go back to Dave's videos on a steady basis to keep the stuff he's explained - fresh in my brain.

Hats off to you Dave! /ccboard/images/graemlins/cool.gif

I owe many of my wins to you.
My loss's I'm not worried about because I just generate 'new' excuses for everyone of them, no biggy. /ccboard/images/graemlins/laugh.gif

Take care, and keep up the great work on and off line!

Alias "Video" <hr /></blockquote>
Wow! Thank you so much for that flattering message. I'm glad my stuff has helped you revitalize your pool game.

Dr. Dave

andy147
04-08-2005, 08:06 AM
Hi - I think you're both right!

I am actually a snooker player in England and find this message board interesting!

Here is my understanding having read a load of posts...

Hitting the cue ball on the left with outside english has 3 effects (even with a level cue)

1) The cue ball squirts to the right slightly
2) The cue then bends to the left (swerves if you like)
3) On contact the object ball is thrown to the right

Effects 1) and 2) are minimised on a soft short shot where effect 3) is dominant.

If you put enough bottom on the cue ball so that when it arrives at the object ball it has no top spin this is results in a stun shot.

With no english that means the path of cue ball and object ball are separated by 90 degrees (if we ignore collision induced throw).

By using left English the throw causes the paths of the cue ball and the object ball to be separated by more than 90 degrees.

This can be viewed 2 ways

a) If we hold constant the point at which the cue ball makes contact with object ball (e.g. 3/4 ball). With left english the spin will throw the object ball to the right. However the cue ball's direction is not affected by the english.

b) If we hold constant potting the object ball (a more practical thing to do) using left english means the object ball must be struck more full on i.e. a thicker contact is needed. This causes the cue ball to be thrown to left more than if the shot were played with no english.

But the crucial thing is that although the cue ball's direction is slightly to the left of what it would have been it has far less momentum. That is, the cue ball has far less speed relative to the speed of the object ball due to the thicker contact. Applying english can therefore be useful in holding the cueball.... /ccboard/images/graemlins/cool.gif