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View Full Version : The effect of speed on English deflection (squirt)



dr_dave
12-04-2004, 01:42 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
Does English deflection (squirt) change with ball speed?

A (from me):
I've done some experiments and have posted a video to show the results. See NV A.17 on my website (http://www.engr.colostate.edu/pool/). Deflection (squirt) at high speed was about 3 times larger than deflection at low speeds. The deflection at low speed is small, but it is not zero. Practically speaking though, slow speed side-English shots would typically only be used for fairly short shots where deflection would not be of much concern (especially compared to English throw, which could be a major concern).

The next time I get access to the high-speed camera, I will try to shoot some video to help shed more light on the underlying physics of deflection (squirt).
<hr /></blockquote>
<blockquote><font class="small">Quote Ross:</font><hr> Dave, I don't think you can tell the speed/squirt relationship from your video for a couple of reasons. One is you are not subtracting out the effects of cb curve, which is greater at slower speeds and which works in the opposite direction to squirt. So what appears to be less squirt at slow speeds may be just the effect of the cb curving back on line more. An overhead shot on a precisely marked table would help determine if that is the case.
<hr /></blockquote>

I doubt there is any significant curve (swerve) in the shots in my video. My cue stick was nearly horizontal and I hit through the cue ball horizontal plane on every shot. My actual cue stick elevation was only about 1.4 degrees per my measurements and analysis TP A.3 on my website (http://www.engr.colostate.edu/pool). Also, any curve (if there was any) was too small to observe, at any speed. This is difficult to prove from the low resolution video posted, but it was clear in person. Try the experiment yourself and let me know if you observe any curve.

<blockquote><font class="small">Quote Ross:</font><hr> The second problem with your experiment is that it does not ensure that you are hitting the cb each time at the exact same sideways offset (or vertical axis either). If unconsciously you tend to hit the cb with a mm more side english when stroking hard than when stroking softly, this could explain most of the effects you see.
<hr /></blockquote>

You are correct. I am not a machine and I am not able to guarantee a perfectly consistent stroke. However, by observing my follow-through (on the video) and the chalk mark on the cue ball after every shot, I assure you that my stroke was fairly consistent for every shot I included on the video. I actually executed many more shots than I included in the final version. I threw out all shots that were not consistent, due to direction of follow-through or chalk mark placement. Bottom line: I stand by my consistency, although I admit it might not have been perfect.

<blockquote><font class="small">Quote Ross:</font><hr> So I remain unconvinced that there is more squirt at higher speeds. You definitely have to compensate more at faster speeds but that may be due to reduced swerve effects and not increased squirt.
<hr /></blockquote>

Regardless of what we think and how we explain it, the effective "squirt" is larger at higher speed and it must be accounted for.

dr_dave
12-04-2004, 02:03 PM
<blockquote><font class="small">Quote Rod:</font><hr> I agree there Dr. Dave. The effect of swerve wonít really be a factor. Swerve needs an elevated cue at slower speeds, or a downward type stroke with side english. Itís very, very, tiny, minute effect, if any is immeasurable. Far more important is the quality of your stroke.<hr /></blockquote>
Good explanation. I agree totally.

<blockquote><font class="small">Quote Rod:</font><hr>As an example I set up two balls to shoot between. They are 3/8Ē to each side of the c/b on the end rail. Some will need to set these balls farther apart, at least in the beginning. I set them slightly less, about 5/16Ē. Use the c/b on the end rail as a guide. This gives a person a clue how much there shaft squirts, quality of stroke, and how it affects aim. Really you should be able to drive a truck through there but for most it will be a toy truck. LOL<hr /></blockquote>
Great idea!

<blockquote><font class="small">Quote Rod:</font><hr>With no english at any speed it should be simple. Add English and speed, the target becomes much smaller for most.
An example of what should happen if you clear both balls at a very firm speed loaded with right English.
Wei Table (http://endeavor.med.nyu.edu/~wei/pool/) START(
%AC7Q0%BC7M9%Pg6O5%WW5E4%XC7O4%]D8O7%^g1O7%eC7a4

)END

If the c/b doesn't hit in this area and goes a lot longer then little or less right was used. If it hits well short, the speed was to slow. I think it's worth a note, the less English the more accurate.<hr /></blockquote>
Agreed.

<blockquote><font class="small">Quote Rod:</font><hr>Which brings me to -- How much does varying amounts of side English only, and at different speeds, effect squirt? I could be wrong but Iím saying amount of english has near or as much effect as speed. <hr /></blockquote>
I would agree with this but I have not shot video or done analysis to prove it yet. I'll add it to my list.

<blockquote><font class="small">Quote Rod:</font><hr>Not that we really need to know all of this stuff because every player needs to know their stroke and equipment, thatís how we develop consistency. Knowing is fine but I doubt it would make a pimple on flyís butt. Itís curiosity more than anything because overanalyzing causes many players to fault an area when itís not even a factor.<hr /></blockquote>
I think it helps to know, but your point is well taken.

Fred Agnir
12-04-2004, 03:14 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
Does English deflection (squirt) change with ball speed?

A (from me):
I've done some experiments and have posted a video to show the results. See NV A.17 on my website (http://www.engr.colostate.edu/pool/). Deflection (squirt) at high speed was about 3 times larger than deflection at low speeds.
<hr /></blockquote> How does your results on video compare to the physics model?

Fred

dr_dave
12-04-2004, 03:50 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> Q (from a BD reader):
Does English deflection (squirt) change with ball speed?

A (from me):
I've done some experiments and have posted a video to show the results. See NV A.17 on my website (http://www.engr.colostate.edu/pool/). Deflection (squirt) at high speed was about 3 times larger than deflection at low speeds.
<hr /></blockquote> How does your results on video compare to the physics model?
<hr /></blockquote>
I don't know of any physics model that can accurately predict the relationship between squirt and speed. However, I do plan to do some high-speed-video studies to try to better understand the underlying physics. I'll post an update if and when I find time to do the study.

Fred Agnir
12-04-2004, 03:55 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>
I don't know of any physics model that can accurately predict the relationship between squirt and speed. However, I do plan to do some high-speed-video studies to try to better understand the underlying physics. I'll post an update if and when I find time to do the study. <hr /></blockquote>Well, for starters, we've discussed conservation of energy and the speed of the transverse wave down the shaft.

Search groups.google.com.

Fred

Billy_Bob
12-05-2004, 10:57 AM
I have read that tip radius (dime, nickel, quarter) will have an effect on cue ball deflection, yet I have never seen any testing done in this area.

And many players I know don't pay much attention to the shape of their tip, then they get a new tip - shape it, then their playing goes out the window until the "get used to the new tip".

I always keep my tip a dime shape. When I get a new tip and give it a dime shape, it plays just like my old tip.

Many players will spend a lot on money on a fancy cue butt, but will balk at spending $15 for a good tip.

It seems to me that the tip is the *most* important part of the cue since it is the "business" end. I would think that an accurate and consistant tip radius and a consistant tip surface would be an essential component to consistant play with certain shots. (Along with chalking before each shot of course.)

So far as tip surface, I have noticed that pig skin tips as compaired with leather tips is sort of like compairing a low pile carpet (pig skin) to a shag carpet (leather). It seems that the pig skin would have more contact points on the cue ball [more friction] and the leather would have gaps between the contact points on the cue ball [less friction].

dr_dave
12-05-2004, 11:12 AM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> I have read that tip radius (dime, nickel, quarter) will have an effect on cue ball deflection, yet I have never seen any testing done in this area.<hr /></blockquote>
I would also agree with this intuitively, but I have not studied it. I will add it to my "things to film with high-speed camera" list.

<blockquote><font class="small">Quote Billy_Bob:</font><hr>I always keep my tip a dime shape. When I get a new tip and give it a dime shape, it plays just like my old tip.<hr /></blockquote>
I prefer a nickel shape; but if you need to execute a shot with lots of English (which I try to avoid at all costs in normal play), the dime shape is probably better.

<blockquote><font class="small">Quote Billy_Bob:</font><hr>Many players will spend a lot on money on a fancy cue butt, but will balk at spending $15 for a good tip.

It seems to me that the tip is the *most* important part of the cue since it is the "business" end. I would think that an accurate and consistant tip radius and a consistant tip surface would be an essential component to consistant play with certain shots. (Along with chalking before each shot of course.)<hr /></blockquote>

I totally agree, as long of the cue stick is in decent shape.

<blockquote><font class="small">Quote Billy_Bob:</font><hr>So far as tip surface, I have noticed that pig skin tips as compaired with leather tips is sort of like compairing a low pile carpet (pig skin) to a shag carpet (leather). It seems that the pig skin would have more contact points on the cue ball [more friction] and the leather would have gaps between the contact points on the cue ball [less friction].<hr /></blockquote>
I don't have experience with this. Maybe others can respond.

tateuts
12-05-2004, 11:42 PM
From a players standpoint, I know I have to adjust my aim more for a harder hit shot when using english than a softer shot. I'm not sure why, but I suspect the cue ball squirts more, in some cases a lot more.

Chris

Fred Agnir
12-06-2004, 07:16 AM
<blockquote><font class="small">Quote tateuts:</font><hr> From a players standpoint, I know I have to adjust my aim more for a harder hit shot when using english than a softer shot. I'm not sure why, but I suspect the cue ball squirts more, in some cases a lot more.

Chris <hr /></blockquote>Swerve.

DickLeonard
12-06-2004, 07:24 AM
MY only thought on this subject has to do with Earl Anthony the bowler. Someone radar gunned him and his ball speed was always 16 miles per hour, if my memory serves me.

To Controll your swerve, your stroke has to be radar controlled. Generate your speed by a longer follow thru as opposed to hitting the ball harder.####

dr_dave
12-06-2004, 10:27 AM
<blockquote><font class="small">Quote tateuts:</font><hr> From a players standpoint, I know I have to adjust my aim more for a harder hit shot when using english than a softer shot. I'm not sure why, but I suspect the cue ball squirts more, in some cases a lot more.<hr /></blockquote>

You make a good point. Whatever you call it (squirt, deflection, or "effective squirt"), you still need to adjust more at higher speed.

tateuts
12-06-2004, 11:52 AM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote tateuts:</font><hr> From a players standpoint, I know I have to adjust my aim more for a harder hit shot when using english than a softer shot. I'm not sure why, but I suspect the cue ball squirts more, in some cases a lot more.

Chris <hr /></blockquote>Swerve. <hr /></blockquote>

Fred,

You've mentioned this before and I thought it was right, at least I suspected it was right because you usually are, but I came to the conclusion it wasn't, and here's why:

This is the shot I use to see if I can play well with a particular cue. I'll hit this shot with high inside english hard enough to send the cue ball three or four rails.

START(
%HP5E6%P\9L3%Uj8D8%VP7Z7%WF6D9%XO1E5%_P6Z3%`C4J3%a M9C5%bO9D3
%cR4F0%d\2K6
)END

With my own cue, which has a low deflection (Predator) shaft most of the time I can make the shot aiming pretty much straight at the object ball (hard with high left and a level cue). If I shoot soft, I can almost aim along the usual aim line.

If I use a regular cue with high amounts of deflection, I will miss the pocket by a couple of inches to the left - overcutting the shot. I have to aim well left of the usual line to pocket the ball. Again, if I shoot this at slow speed, I am pretty much aiming at the center of the ball and squirting the cue ball over to the correct line.

If the only difference is the amount of deflection built into the cues, why would swerve have anything to do with this?


Chris

Fred Agnir
12-06-2004, 12:14 PM
<blockquote><font class="small">Quote tateuts:</font><hr>
With my own cue, which has a low deflection (Predator) shaft most of the time I can make the shot aiming pretty much straight at the object ball (hard with high left and a level cue). If I shoot soft, I can almost aim along the usual aim line.

If I use a regular cue with high amounts of deflection, I will miss the pocket by a couple of inches to the left - overcutting the shot. I have to aim well left of the usual line to pocket the ball. Again, if I shoot this at slow speed, I am pretty much aiming at the center of the ball and squirting the cue ball over to the correct line.

If the only difference is the amount of deflection built into the cues, why would swerve have anything to do with this?


Chris <hr /></blockquote>I see what you're asking, but without watching you, I couldn't give a real answer. Suffice it to say, there are enough people who see a difference hitting slow vs. fast with a Predator that (opposite to what you're saying), so both you and they can't be correct at the same time.

I'd be interested in your results in shots that have a shot down the throat rather than down the cushion. Something more like:

START(
%HU0O6%Pg0O6%Uj8D8%VP7Z7%WE0Z4%XS4O9%eA7a3%_P6Z3%` C4J3%aM9C5
%bN8D7%cP8G7%dU3N5
)END

... and what do you mean in what is boldfaced above? Are you hitting the cushion on the way in?

Fred

Rod
12-06-2004, 01:12 PM
Fred,

Is this shot, shot from where the c/b is sitting? If so, do you think swerve is a factor?

If your just discussing squirt then it's relatively small IMO. However distance magnifies even a small amount of squirt. Something that can not be left out is execution, there is the big difference. One player will experience more squirt where another will experience less. That's not hard to understand it's just differences in there stroke/style of play.

When all the dust settles though it is my opinion that speed increases squirt. I make slight adjustments depending on english, distance and speed. You have to, even a with the (God like) Predator shaft. LOL

For those that don't think so their probably compensating their aim and don't even realize its happening.

Rod

tateuts
12-06-2004, 01:33 PM
Fred,

I'll try it tonight.

Chris

Fred Agnir
12-06-2004, 01:49 PM
<blockquote><font class="small">Quote Rod:</font><hr> Fred,

Is this shot, shot from where the c/b is sitting? <hr /></blockquote>Sitting and spinning? No, that's not the shot I diagrammed.

The shot I diagrammed is an inside three railer (pool's version of an umbrella shot) like Chris' shot, except the the object ball's in the middle of the table rather than near the cushion.

Fred

Rod
12-06-2004, 01:54 PM
LOL Fred, read again. I didn't say sitting and spinning. Just sitting, and yes the longer three rail shot as mentioned.

Rod

dr_dave
12-06-2004, 02:14 PM
<blockquote><font class="small">Quote Rod:</font><hr>If your just discussing squirt then it's relatively small IMO. However distance magnifies even a small amount of squirt. Something that can not be left out is execution, there is the big difference. One player will experience more squirt where another will experience less. That's not hard to understand it's just differences in there stroke/style of play.

When all the dust settles though it is my opinion that speed increases squirt. I make slight adjustments depending on english, distance and speed. You have to, even a with the (God like) Predator shaft. LOL

For those that don't think so their probably compensating their aim and don't even realize its happening.
<hr /></blockquote>

Well stated. I agree 100%!

Fred Agnir
12-06-2004, 02:17 PM
<blockquote><font class="small">Quote Rod:</font><hr> LOL Fred, read again. I didn't say sitting and spinning. Just sitting, and yes the longer three rail shot as mentioned.

Rod <hr /></blockquote>Sorry, Rod. I couldn't understand what you were asking. Yes, the shot as diagrammed from where the cueball is sitting.

Fred

Ross
12-06-2004, 03:14 PM
Ok here is what I'm pretty sure is true:

1. Squirt is the angle between the direction the cue is moving and the direction that the cb leaves the stick.

2. Considerable research has shown that the size of this squirt angle is mainly determined by the mass of the last few inches of the tip end of the stick.

3. Everytime you shoot with your cue passing across a rail your cue has some downward angle. Because of this there is some, maybe very small, masse effect (swerve) on every shot.

4. All else being equal, the slower the shot the more the swerve.

5. The aim adjustment you have to make when shooting with side is a function of both deflection and swerve, which work in opposite directions.

6. You have to adjust your aim more when you shoot firmly with side than when you shoot softly.

So here is the debate:

Is number 6 due to increased deflection at higher speeds or due to decreased swerve at higher speeds?

Available evidence:
Dave's video, which I would say is inconclusive because it was not set up to see subtle curving of the ball.

Evidence we need:
Find a table that is about to have its cloth replaced. Then put a grid of parallel lines going down the center of the table. This time shoot the same videos that Dave shot, but this time shoot with an overhead camera. This should make it possible to accurately see any curving of the cb.

Alternative test:
Shoot Dave's test on a bed of ice! Then there will be no swerve and all of the observed differences will be due to deflection.

So who has cloth ready to be replaced and a setup where they could have an overhead camera? Alternatively, who has a local ice rink AND the nerve to go out and shoot pool balls on it?! /ccboard/images/graemlins/tongue.gif

TennesseeJoe
12-06-2004, 03:34 PM
dr dave
In reply to your quote, "Something that can not be left out is execution, there is the big difference. One player will experience more squirt where another will experience less. That's not hard to understand it's just differences in there stroke/style of play."

Most players experience an increase in deflection with a faster speed. IMO this increase is deflection is due to less friction between the tip and the ball in relation to the force/speed. Most think that friction is caused by the size of the contact area and the amount of abrasion between the surfaces. I believe the length of time the tip and ball remain in contact is an additional factor that can be controlled and can increase or decrease the amount of deflection. If a player accelerates his cue in the follow through stage of his stroke, this will increase the amount of time the cue is in contact with the cue ball and therefore increase the total amount of friction. Thus more friction and less deflection. (Most players seem to have reached optimal speed at time of contact, therefore more deflection).

With respect, I would enjoy your thoughts.

Tennessee Joe

dr_dave
12-06-2004, 03:44 PM
<blockquote><font class="small">Quote TennesseeJoe:</font><hr>
Most players experience an increase in deflection with a faster speed. IMO this increase is deflection is due to less friction between the tip and the ball in relation to the force/speed. Most think that friction is caused by the size of the contact area and the amount of abrasion between the surfaces. I believe the length of time the tip and ball remain in contact is an additional factor that can be controlled and can increase or decrease the amount of deflection. If a player accelerates his cue in the follow through stage of his stroke, this will increase the amount of time the cue is in contact with the cue ball and therefore increase the total amount of friction. Thus more friction and less deflection.<hr /></blockquote>

I have similar thoughts (i.e., I agree with everything you say); however, I have not verified this with experiments. I hope to do some close-up high-speed video with various tips and strokes when I get some time. I agree with your qualitative physical arguments, but the only way to be sure is actual testing.

Thank you for your insightful posting.

dr_dave
12-06-2004, 03:52 PM
<blockquote><font class="small">Quote Ross:</font><hr>Evidence we need:
Find a table that is about to have its cloth replaced. Then put a grid of parallel lines going down the center of the table. This time shoot the same videos that Dave shot, but this time shoot with an overhead camera. This should make it possible to accurately see any curving of the cb.

Alternative test:
Shoot Dave's test on a bed of ice! Then there will be no swerve and all of the observed differences will be due to deflection.
<hr /></blockquote>

Excellent suggestions. I will add the first idea to my list of things to do, but my list is very long already.

Concerning the ice idea, laying a sheet of glass over a table might be a more practical option. The glass could even be lubricated to further reduce friction.

Ross
12-06-2004, 03:55 PM
TennesseJoe, while what you say seems like a reasonable theory, fairly extensive tests carried out with an extremely high speed camera have found that over a variety of types of strokes and stroke speeds the cuetip is in contact with the ball approximately .001 seconds (one ten-thousandth of a second). This experiment was called the Jacksonville Project and run by a bunch of physicists and players, including Bob Jewett. You can find out all about it if you search RSB with the term "Jacksonville." You can even buy a VHS tape showing the highspeed photography.

RSB had many very long protracted discussions about whether certain players could keep the tip on longer to special effect. But the final consensus of most (but not all) was that the tip contact time was so short that there was nothing a "special" stroke could do in that time. Of course this doesn't prove that this conclusion is correct, but the arguments made then ended up being pretty persuasive, at least to me.

Ross
12-06-2004, 03:58 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>
Concerning the ice idea, laying a sheet of glass over a table might be a more practical option. The glass could even be lubricated to further reduce friction. <hr /></blockquote>

Good point! Any smooth flat surface would work. Maybe I will try a test on my dining room table this evening. /ccboard/images/graemlins/smirk.gif

Fred Agnir
12-06-2004, 04:07 PM
<blockquote><font class="small">Quote Ross:</font><hr>
Available evidence:
Dave's video, which I would say is inconclusive because it was not set up to see subtle curving of the ball. <hr /></blockquote>But... I can see it. I didn't really look before, but when I did, it looked obvious.

The slow shots broke at about the first hash mark. The very first shot, by far the slowest started breaking before the first hash mark.

The medium shots broke at about the second.

Fred

Rod
12-06-2004, 04:08 PM
[ QUOTE ]
So here is the debate:

Is number 6 due to increased deflection at higher speeds or due to decreased swerve at higher speeds?
<hr /></blockquote>

Ross, is that really the debate? I could answer Yes and Yes. There could be more up for grabs. If swerve is a factor at a slight cue angle, it's always decreased at higher speeds. I should say it doesn't exist.

If a ball with a cue angle of 2 degrees (at centerline) actually did swerve at slow speed it would be very minute if any. It would have to be hit with low and side english to have any measurable effect. That changes the cue angle, possibly call it three + degrees to give it a number.

This is where the cue operator/player comes in. LOL So now that is in question as well. Even more so than one would think for even more reasons. I ain't writing a book. Really it has to be a controlled test, which wouldn't be human powered.

The c/b needs tortional sp? rotation to create swerve and at two degrees it would be such a tiny amount you would not actually see any effect.

Ok got to go for a bit but that's my two bits at the moment.

Rod

Fred Agnir
12-06-2004, 04:10 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> I have similar thoughts (i.e., I agree with everything you say); however, I have not verified this with experiments. <hr /></blockquote>Jacksonville Experiment.

Fred

dr_dave
12-06-2004, 04:14 PM
<blockquote><font class="small">Quote Ross:</font><hr> TennesseJoe, while what you say seems like a reasonable theory, fairly extensive tests carried out with an extremely high speed camera have found that over a variety of types of strokes and stroke speeds the cuetip is in contact with the ball approximately .001 seconds (one ten-thousandth of a second). This experiment was called the Jacksonville Project and run by a bunch of physicists and players, including Bob Jewett. You can find out all about it if you search RSB with the term "Jacksonville." You can even buy a VHS tape showing the highspeed photography.

RSB had many very long protracted discussions about whether certain players could keep the tip on longer to special effect. But the final consensus of most (but not all) was that the tip contact time was so short that there was nothing a "special" stroke could do in that time. Of course this doesn't prove that this conclusion is correct, but the arguments made then ended up being pretty persuasive, at least to me.<hr /></blockquote>

Per videos HSV A.13 through A.20 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html), I have also observed cue tip contact times of approximately one thousanths of a second (1/1000 = 0.001), but I have not tried a wide variety of tips, speeds, and stroking styles.

I have seen the Jacksonville Tape (Bob Jewett was kind enough to send me a copy). I look forward to looking through some of the past RSB discussion concerning the project.

dr_dave
12-06-2004, 04:16 PM
Please see my response (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=168494&amp;page =0&amp;view=&amp;sb=&amp;o=&amp;fpart=&amp;vc=&amp;PHPSESSID=).

Fred Agnir
12-06-2004, 04:21 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> I agree with your qualitative physical arguments, Thank you for your insightful posting.
<hr /></blockquote>Which qualitative physical arguments are you talking about?

What is the formula that has friction and contact time in it? And how is it applied?

If speed is a factor in the squirt angle, what is the physics that changes the ratio of the vector scalars? I haven't seen anything.

What is the physics that suggests "accelerating the cue" through contact? There's too much information out there that shows that a human physically cannot accelerate the cue during contact.

What range of contact times do you believe is possible? The Jacksonville Tape showed a contact time in the order of .001-.002 sec. depending on tip durometer and hit offset. That contact time is so short that by the time a human starts to re-accelerate his cue, the object ball is long gone.

These are real physics questions, IMO, have been answered (or at least gives a much better understanding) by various controlled testing and video-taping. Wouldn't those tests be appropriate research material for you?

Fred &lt;~~~ hello, wall

dr_dave
12-06-2004, 04:24 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>
The slow shots broke at about the first hash mark. The very first shot, by far the slowest started breaking before the first hash mark.<hr /></blockquote>
Fred,
When I was shooting the shots, I was looking straight down the cue stick and could not see any curve (swerve) effects. It is difficult to see (or not see) swerve in the small, compressed, low resolution video posted.

Again, my cue stick was very close to horizontal (about 1.5 degrees), and I struck the cue ball through a horizontal plane through its center, so there should not be any significant masse effect.

I don't think more talk will answer these questions. People should try it for themselves.

dr_dave
12-06-2004, 04:32 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr>

What is the formula that has friction and contact time in it? And how is it applied?

If speed is a factor in the squirt angle, what is the physics that changes the ratio of the vector scalars? I haven't seen anything.

What is the physics that suggests "accelerating the cue" through contact? There's too much information out there that shows that a human physically cannot accelerate the cue during contact.

What range of contact times do you believe is possible? The Jacksonville Tape showed a contact time in the order of .001-.002 sec. depending on tip durometer and hit offset. That contact time is so short that by the time a human starts to re-accelerate his cue, the object ball is long gone.

These are real physics questions, IMO, have been answered (or at least gives a much better understanding) by various controlled testing and video-taping. Wouldn't those tests be appropriate research material for you?<hr /></blockquote>

I don't have answers to all of your questions, but I think they are all good questions that I hope to study more. I also intend to do more homework by studying the Jacksonville tape more and looking a past RSB discussion. Also, one day, I hope to shoot some high-speed video at a higher frame rate, zoomed up more on the tip-ball interface to better understand what is happening during the 0.001-0.002 seconds, for different stroke and tip conditions.

Fred Agnir
12-06-2004, 04:44 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Fred,
When I was shooting the shots, I was looking straight down the cue stick and could not see any curve (swerve) effects. It is difficult to see (or not see) swerve in the small, compressed, low resolution video posted.<hr /></blockquote> How can you say this after I just said I can clearly see the swerve? You have hash marks as markers, and the cue ball swerves. Your very first shot was quite clearly swerving.

[ QUOTE ]
I don't think more talk will answer these questions. People should try it for themselves. <hr /></blockquote>Well, now, isn't that a peculiar response. Why now wouldn't you want to talk about it? Are your videos or aren't they up for discussion?

Fred

Fred Agnir
12-06-2004, 04:55 PM
<blockquote><font class="small">Quote Rod:</font><hr> If a ball with a cue angle of 2 degrees (at centerline) actually did swerve at slow speed it would be very minute if any. <hr /></blockquote>My friend, I have watched the video in question over and over, and it clearly shows that the cueball starts to swerve at the first hash mark on the slowest shots, and about the second hash mark on the medium shots.

The difference between the firm shots and the slow shots over the distance of the table length is about 4".

Edit: note on this: the 4" was for left english due to the very first slow/high swerve shot. For right english, swerve was more obvious on the slow shots, yet overall there was less range of difference with the shots with right english. The medium shots looked to have identical effective squirt as the fast shots.

If everything else is controlled as Dr. Dave has indicated, and I can clearly see the breaking point that begins swerve (I don't know why others can't see it; it seems quite evident on my monitor), then swerve is responsible for all of the difference. That's not my definition of "minute."

Fred

Ross
12-06-2004, 06:28 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote Rod:</font><hr> If a ball with a cue angle of 2 degrees (at centerline) actually did swerve at slow speed it would be very minute if any. <hr /></blockquote>My friend, I have watched the video in question over and over, and it clearly shows that the cueball starts to swerve at the first hash mark on the slowest shots, and about the second hash mark on the medium shots.

The difference between the firm shots and the slow shots over the distance of the table length is about 4".

Edit: note on this: the 4" was for left english due to the very first slow/high swerve shot. For right english, swerve was more obvious on the slow shots, yet overall there was less range of difference with the shots with right english. The medium shots looked to have identical effective squirt as the fast shots.

If everything else is controlled as Dr. Dave has indicated, and I can clearly see the breaking point that begins swerve (I don't know why others can't see it; it seems quite evident on my monitor), then swerve is responsible for all of the difference. That's not my definition of "minute."

Fred <hr /></blockquote>

Fred, I just re-watched the videos and I see the same "breaking" points. But to me it looks like for slow shots the cb path curves UNTIL the 1st hash mark then goes straight on that line. And it looks like it does the same thing at the 2nd hash mark for the medium shots. For even the firm shots I think I see a very slight curve (much less pronounced than for the medium and slow shots) over the whole path. That would make sense as well, since the curve continues until friction with the cloth converts the spin to natural roll (which happens early for soft shots and late for harder shots).

Of course it is very hard to tell for sure without finer markings on the table. Now if we had a STRO-MO camera we could tell easily. I've watched soccer games with these cameras and it is cool to see the path of the ball curving around the defenders and into the net.

So that is the next suggestion - use time lapse photography with a strobe light.

Rod
12-06-2004, 07:02 PM
Fred, I didn't see the swerve. I noticed the first soft shot with left appeared to swerve and may have but the cue was aligned slighty to the left. That existed to some extent in other shots. There is no answer here because of descrepancys.

Except for the first shot which appeared to cross the center line, why didn't the c/b get to or cross the center line of other slow shots? It always appeared to hit the end rail on the opposite side of english used.

I don't trust those hash marks as being spaced consistant either. They appear to be different sizes as well so that at best is confusing. In the end there is just to many variables to come to any conclusion.

Well that is you see swerve and I don't so that is one conclusion. We see different.

Oh, I wanted to mention the slow and medium shots did appear to be very close to the same squirt effect. Of course tip offset with any shot is a variable as well. I believe more offset = more squirt.
We can't see his back hand motion so all we have to rely on is the shaft motion which isn't always the same. Like I said, to many variables.

It looks like Dave is more comfortable shooting with right english though.

Rod

TennesseeJoe
12-06-2004, 07:24 PM
Ross,
Thanks for your reply. Two questions:

1. You can find out all about it if you search RSB with the term "Jacksonville." What is RSB and how do I find it?

2. Even if contact time is only .001 but you are able to increase it to .002---could this give you twice as much friction?

Bob_Jewett
12-06-2004, 07:54 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> I have read that tip radius (dime, nickel, quarter) will have an effect on cue ball deflection, yet I have never seen any testing done in this area.
... <hr /></blockquote>
Predator did tests on this and a smaller tip radius got slightly less squirt, as I recall. I think the results were on their web site.

Bob_Jewett
12-06-2004, 08:04 PM
<blockquote><font class="small">Quote TennesseeJoe:</font><hr> Ross,
Thanks for your reply. Two questions:

1. You can find out all about it if you search RSB with the term "Jacksonville." What is RSB and how do I find it?

2. Even if contact time is only .001 but you are able to increase it to .002---could this give you twice as much friction? <hr /></blockquote>
RSB is rec.sport.billiard a Usenet newsgroup. There are many ways to read Usenet newsgroups. One way is to go to http://groups.google.com and put in jacksonville video as the words to search for. The "advanced" search interface lets you restrict the search to one newsgroup.

As for contact time increasing friction, the basic answer is no, increasing contact time doesn't help. In fact, the longer the contact time, the more chance of a miscue, at least in one simple model.

tateuts
12-06-2004, 10:59 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> I see what you're asking, but without watching you, I couldn't give a real answer. Suffice it to say, there are enough people who see a difference hitting slow vs. fast with a Predator that (opposite to what you're saying), so both you and they can't be correct at the same time.

I'd be interested in your results in shots that have a shot down the throat rather than down the cushion. Something more like:

START(
%HU0O6%Pg0O6%Uj8D8%VP7Z7%WE0Z4%XS4O9%eA7a3%_P6Z3%` C4J3%aM9C5
%bN8D7%cP8G7%dU3N5
)END

... and what do you mean in what is boldfaced above? Are you hitting the cushion on the way in?

Fred <hr /></blockquote>

Fred,

You are right. On this shot, using a center ball left english punch stroke, the point of aim stays pretty much the same no matter how hard you hit the cue ball.

I believe that at this particular angle, the throw has something to do with it - compensating for the squirt.

On my other shot, I don't think there is as much throw
involved, so the shot squirts more.

If nothing else it's confusing that's for sure.

Chris

Qtec
12-07-2004, 11:14 AM
Ok, here,s my take on this.

There is a basic flaw in Dave,s experiment.If you want to measure the squirt on the Qball you should measure the path it takes immediately after contact with the cue, not where the ball ends up. I agree with Fred that the only reason the Qball hits the rail at different points, at different speeds is because of swerve. Sidespin can only have an effect on the Qball,s path when it gets a grip on the cloth. If the forward motion of the Qball is great enough it will continue on its path, despite whatever sidespin it has on it.Its only when the ball slows down that the swerve takes effect. [ Anybody understand that? /ccboard/images/graemlins/laugh.gif]

What I am saying is this, Dave,s hard shot squirted , lets say a full ball to the left[ with right side],on a 8ft table. If he played the same shot on a 16ft table, he would observe the squirt as at least 2 full balls.

Also I observed that the axis of spin was more thru 11 o,clock to 5 o,clock, instead of thru 12 and 6.

Qtec

Wally_in_Cincy
12-07-2004, 12:05 PM
<blockquote><font class="small">Quote tateuts:</font><hr>
If nothing else it's confusing that's for sure.
<hr /></blockquote>

yep /ccboard/images/graemlins/smile.gif

I can't wait until we talk about banks /ccboard/images/graemlins/cool.gif

Ross
12-07-2004, 12:10 PM
<blockquote><font class="small">Quote Qtec:</font><hr>
Sidespin can only have an effect on the Qball,s path when it gets a grip on the cloth. If the forward motion of the Qball is great enough it will continue on its path, despite whatever sidespin it has on it.Its only when the ball slows down that the swerve takes effect. [ Anybody understand that? /ccboard/images/graemlins/laugh.gif]
...
Also I observed that the axis of spin was more thru 11 o,clock to 5 o,clock, instead of thru 12 and 6.

Qtec <hr /></blockquote>

You are leaving out an important issue in your analysis Qtec: for slow to moderate speed shots with side, the side spin "wears off" (axis of rotation becomes more horizontal) significantly as the cb travels. In fact for the slow shots in Dave's videos you can see that the cb has nothing but topspin at the end of its path. So, in general, when shooting with side at slow to moderate speeds the cb starts off curving a little then curves more (breaks) and then straightens out.

This is exactly what a masse shot does, and swerve is just mild masse.

dr_dave
12-07-2004, 12:18 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>
I don't know of any physics model that can accurately predict the relationship between squirt and speed. However, I do plan to do some high-speed-video studies to try to better understand the underlying physics. I'll post an update if and when I find time to do the study. <hr /></blockquote>Well, for starters, we've discussed conservation of energy and the speed of the transverse wave down the shaft.
<hr /></blockquote>

IMO, a physics model (or thorough experimental study) would need to include many factors to have a chance at describing and predicting the relationship between squirt and speed, under various conditions. IMO, the most important factors might include:
<ul type="square"> tip properties (e.g., shape, hardness, stiffness, friction)
cue stick shaft properties (e.g., longitudinal and transverse stiffness)
the hand grip (e.g., Iron Willie vs. firm or soft human grip)
speed and acceleration at impact
obviously, the amount of eccentricity (how far the cue ball is hit off center)
cue stick weight
[/list]
Other factors might include:
<ul type="square"> type of chalk and how it is applied
humidity and temperature (e.g., the high-intensity lights required for the high-speed camera get really hot!!!)
the stroke style (e.g., driving follow-through vs. punch stroke)
other factors that might be discovered during such an exhaustive study.
[/list]

The Jacksonville Project, and the collection of clips (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html) I have posted, do not come close to addressing even a small number of these factors. In fact, now that I think about it more, I don't think I could ever have enough time or ambition to begin to take on such a daunting task (developing an accurate model, backed up by experimental evidence). I would like to better understand all of the physics; but for me, at this point, it is good enough to just know that for a high-speed shot with English (which I personally try to avoid like the plague), you need to account for more squirt (and less swerve?).

Fred Agnir
12-07-2004, 12:31 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>
IMO, a physics model (or thorough experimental study) <hr /></blockquote>I realize you are a college professor, but I find it odd that your definition of "physics model" is so drastically different than ... any I've heard.

A thorough phyical experiment is an experiment. A model is a model. And in squirt's case, I think the model is a straightforward collision with conservation of energy. The normal discussion is one of "effective mass" in the conservation equation.

The idea of transverse (sideways) wave down the shaft is an interesting one because if a tip collision is only .001 - .002 secs., then the effective mass from the shaft seems to be how much mass is in motion due in that sideways wave in that .001-.002 seconds. Some initial measurement has that at about 6" of the shaft. Not so coincidentally, that's about how far Predators are bored.

That's the model that I've been working under. I think that tip style, hardness, chalk, and phases of the moon, though possibly having an effect, that those effects are negligible (neglagerbil?) in the model.

Bob?

Fred

Deeman2
12-07-2004, 12:37 PM
You guys are giving me a headache. I'll give the 8 and the break to anyone who understands all this. /ccboard/images/graemlins/smirk.gif

I think it was Fred who once (on this forum) told me he thought it hurt, not helped, to be an engineer in understanding pool!

Deeman
put's his BSME on hold during a match....

Fred Agnir
12-07-2004, 01:24 PM
<blockquote><font class="small">Quote Deeman2:</font><hr>
I think it was Fred who once (on this forum) told me he thought it hurt, not helped, to be an engineer in understanding pool!<hr /></blockquote> Probably.

[ QUOTE ]
Deeman
put's his BSME on hold during a match.... <hr /></blockquote>Me too.

Bob_Jewett
12-07-2004, 04:51 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> ...
Bob? <hr /></blockquote>
I think the end-mass model of squirt explains nearly all of the things I've seen related to squirt. There are a few minor anomalies, such as the report that tip curvature has an influence, but those might be related.

As far as the relation between speed and english, I think it is important to either have the stick level or to measure the amount of swerve versus speed. I think it is not easy to measure the swerve, and I agree with Fred that most people underestimate both how elevated the stick is on all shots and how much swerve there is.

There is a fairly simple formula that gives the amount of swerve based on Coriolis's law for masse shots. In fact, it is identical to masse. A lot of people don't understand the connection.

dr_dave
12-07-2004, 05:26 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>There is a fairly simple formula that gives the amount of swerve based on Coriolis's law for masse shots.<hr /></blockquote>
Bob,
Could you provide a website or detailed book citation (with page numbers) that describes this law in detail? I would like to look at it. Thanks, Dave

Bob_Jewett
12-07-2004, 05:47 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>Could you provide a website or detailed book citation (with page numbers) that describes this law in detail? I would like to look at it. Thanks, Dave <hr /></blockquote>
It's in Coriolis's book (Theorie mathematique ...) but its statement is very simple.

On a side-spin shot when the stick is elevated, the projection of the tip-ball contact point along the axis of the stick points to a spot on the cloth. The cue ball will initial start parallel to the axis of stick (projected onto the plane of the table) and turn in a parabola and then follow a straight line parallel to the a line joining two spots. Those spots are the initial resting spot of the cue ball and the projected spot on the cloth found above. This idea is illustrated on the cover of Byrne's "Advanced Technique" book and is discussed in there.

Fred Agnir
12-08-2004, 07:19 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> The cue ball will initial start parallel to the axis of stick (projected onto the plane of the table) and turn in a parabola and then follow a straight line parallel to the a line joining two spots. Those spots are the initial resting spot of the cue ball and the projected spot on the cloth found above. This idea is illustrated on the cover of Byrne's "Advanced Technique" book and is discussed in there. <hr /></blockquote>This seems to hold true (almost true?) for massť shots, but do you see the same final path (parallel to the line that connects the two points) on normal draw with slight elevation? It seems that it comes up short of parallel. Maybe due to the cloth slowing down the cueball?

Fred

dr_dave
12-08-2004, 11:44 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>Could you provide a website or detailed book citation (with page numbers) that describes this law in detail? I would like to look at it. Thanks, Dave <hr /></blockquote>
It's in Coriolis's book (Theorie mathematique ...) but its statement is very simple.

On a side-spin shot when the stick is elevated, the projection of the tip-ball contact point along the axis of the stick points to a spot on the cloth. The cue ball will initial start parallel to the axis of stick (projected onto the plane of the table) and turn in a parabola and then follow a straight line parallel to the a line joining two spots. Those spots are the initial resting spot of the cue ball and the projected spot on the cloth found above. This idea is illustrated on the cover of Byrne's "Advanced Technique" book and is discussed in there. <hr /></blockquote>

I wish I could read French so I could see Coriolis' work. Do you know if an English translation is available? I haven't seen one.

I have seen this in Byrne's book, and I think it is a good rule of thumb, but it is easy to hit masse shots where the path doesn't come anywhere close to the described direction. Stroke speed and follow-through can sometimes have a big effect on the outcome (i.e., the curved direction).

dr_dave
12-08-2004, 02:00 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>As far as the relation between speed and english, I think it is important to either have the stick level or to measure the amount of swerve versus speed. I think it is not easy to measure the swerve, and I agree with Fred that most people underestimate both how elevated the stick is on all shots and how much swerve there is.

There is a fairly simple formula that gives the amount of swerve based on Coriolis's law for masse shots. In fact, it is identical to masse. A lot of people don't understand the connection.<hr /></blockquote>

Bob,
As I understand masse action, it creates curve (swerve) only while the cue ball is sliding (i.e., not rolling). Once the cue ball starts rolling, it cannot curve due to masse action. Do you agree?

With the soft shots in NV A.17 (http://www.engr.colostate.edu/~dga/pool/normal_videos/new/NVA-17.htm), the cue ball begins to roll almost immediately, well before the first tape mark. Therefore, any swerve would need to take place within the first few inches of motion.

I look forward to hearing your thoughts (and from others) concerning these comments.

dr_dave
12-08-2004, 02:09 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>It's in Coriolis's book (Theorie mathematique ...)<hr /></blockquote>
Is that the same Coriolis as the famous physicists/mathematician that came up with "Coriolis force" that predicts/explains why hurricanes and draining liquids turn counterclockwise in the northern hemisphere?

Bob_Jewett
12-08-2004, 04:30 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>... but it is easy to hit masse shots where the path doesn't come anywhere close to the described direction. Stroke speed and follow-through can sometimes have a big effect on the outcome (i.e., the curved direction). <hr /></blockquote>
Well, yes, sometimes the cue ball sticks to the cloth, and then the shot is totally ruined. Also, it is not so easy to either set the projected spot on the cloth or to hit where you intend on masse shots. In any case, you "aim" the masse shot by two points that are very close to each other for full masse shots, and that's guaranteed to be inaccurate.

Fred Agnir
12-08-2004, 05:55 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr>It's in Coriolis's book (Theorie mathematique ...)<hr /></blockquote>
Is that the same Coriolis as the famous physicists/mathematician that came up with "Coriolis force" that predicts/explains why hurricanes and draining liquids turn counterclockwise in the northern hemisphere? <hr /></blockquote>Same guy. Gustav Coriolis. If you're going to do any serious physics study on forces and reactive forces related to spinning bodies, Coriolis should be the primary reference.

Fred

DickLeonard
12-09-2004, 06:56 AM
My other thought on this subject is when the cue is propelled at higher speeds to produce speed, does the cue turn into a Tuning Fork?####

dr_dave
12-09-2004, 07:57 AM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr>It's in Coriolis's book (Theorie mathematique ...)<hr /></blockquote>
Is that the same Coriolis as the famous physicists/mathematician that came up with "Coriolis force" that predicts/explains why hurricanes and draining liquids turn counterclockwise in the northern hemisphere? <hr /></blockquote>Same guy. Gustav Coriolis. If you're going to do any serious physics study on forces and reactive forces related to spinning bodies, Coriolis should be the primary reference.<hr /></blockquote>

Well, now I must get a copy of his book and find somebody that can read French, because that guy was brilliant.

Does anybody know if (and where) English translations are available?

joliek
12-10-2004, 11:14 AM
Just wanted to say I checked out your website and I appreciate your simplistic approach to explain how to correctly execute a shot. The 30 and 90 degree rules were extremely helpful as well as the effects you achieve depending on how hard or soft you hit the cueball. I have looked at other instructional websites, and I must say, yours is by far the best and easiest to understand. Thank you.

dr_dave
12-10-2004, 11:19 AM
Thank you very much. I appreciate the positive feedback. It gives me encouragement to continue to work hard on my site.

joliek
12-10-2004, 12:51 PM
No problem. I feel I can take the things I have learned from your website and go a very long way. My goal is to someday participate in tournaments and take home some money!

JimS
12-11-2004, 06:57 AM
<blockquote><font class="small">Quote joliek:</font><hr> My goal is to someday participate in tournaments and take home some money! <hr /></blockquote>

Two words: GET LESSONS!

dr_dave
12-15-2004, 03:05 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr>It's in Coriolis's book (Theorie mathematique ...)<hr /></blockquote>
Is that the same Coriolis as the famous physicists/mathematician that came up with "Coriolis force" that predicts/explains why hurricanes and draining liquids turn counterclockwise in the northern hemisphere? <hr /></blockquote>Same guy. Gustav Coriolis. If you're going to do any serious physics study on forces and reactive forces related to spinning bodies, Coriolis should be the primary reference.<hr /></blockquote>

If anyone is interested, I found a good bibliography of Mr. Coriolis (http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Coriolis.html) online. I'm still trying to track down an English translation of his book. Anyone ever see or hear of one?

Bob_Jewett
12-15-2004, 03:20 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>... I'm still trying to track down an English translation of his book. Anyone ever see or hear of one? <hr /></blockquote>
There is no published translation that I know of. George Onoda, who used to write a technical column for Billiards Digest, got a partial hand-written translation done, but I think that the people who did the translating knew very little physics, mathematics or billiards.

There is another translation currently in progress, and I will send you a contact.

dr_dave
12-15-2004, 03:47 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>... I'm still trying to track down an English translation of his book. Anyone ever see or hear of one? <hr /></blockquote>
There is no published translation that I know of. George Onoda, who used to write a technical column for Billiards Digest, got a partial hand-written translation done, but I think that the people who did the translating knew very little physics, mathematics or billiards.

There is another translation currently in progress, and I will send you a contact. <hr /></blockquote>
Thanks Bob. I knew I could count on you to know this type of thing.