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Shaft
04-18-2007, 11:02 AM
Please indulge yet another squirt post, but I think the subject of squirt can be better discussed if we break squirt down into three sources. For all the talk about "what shaft is better," I contend that shaft deflection is probably the least significant of the three sources.

Here is how I view the sources of squirt:

1. Contact point squirt. By definition, we are hitting the cue ball off-center. Looking down on the cue, the intended ball path is 0 degrees (12 o'clock) and we put left english at 190 degrees (almost 7 o'clock). A FRICTIONLESS contact would send the cue ball off at 10 degrees with NO english. Tip FRICTION induces a clockwise spin on the cue ball and sends it in a direction somewhere between 0 and 10 degrees. The direction is less than 10 degrees because tip friction creates a "forward throw" on the ball. The more friction with the tip, the closer to 0 degrees. The problem is, the cue ball is is not moving at 0 degrees as we would like it, hence there is some amount of squirt.

"Well DUHH," you say. But realize that THIS EFFECT EXISTS EVEN IN A PERFECTLY RIGID SHAFT. The amount of Squirt #1 is determined by tip friction, and by the amount the cue ball is hit off-center.

2. Cue stick rotation squirt. When the cue ball is hit left-of-center, the inertial mass of the cue ball puts a sideways torque on the tip of the moving shaft, tending to rotate the entire cue stick counter-clockwise in the horizontal plane, aggravating (slightly) the side forces on the cue ball mentioned in Squirt #1 above.

AGAIN, THIS EFFECT IS PRESENT EVEN WITH A PERFECTLY RIGID SHAFT. The amount of stick rotation is primarily determined by the firmness of the bridge, the consistency of the shooting arm, and the mass of the stick. (In the real world, I admit that a flimsy shaft will absorb a very small amount of the applied torque by bending, REDUCING overall stick rotation.)

Due to the short duration of tip contact time (about 1/500th of a second at the outside), shaft rotation is probably not a huge factor, regardless of the firmness of the bridge or the mass of the stick. But it is a factor: imagine hitting english while holding the cue in a good bridge and then while resting it on a ruler's edge.

3. Shaft deflection squirt. (Oh, how many shafts have been bought and sold over this issue?) Assume the cue ball is 6 inches away from the bridge hand. Since no material is perfectly rigid, we know the shaft bends (ever-so-slightly) to the left as the tip moves forward in the shot. This theoretically aggravates the side forces on the cue ball mentioned in caused by Squirt #1 above.

The question is, "During the 1/500th of a second when the stick is in contact with the ball, what is the DIFFERENCE in bending deflection between the flimsiest and the stiffest cues, ACROSS THOSE SIX INCHES of shaft?"

Remember, too, that a flimsy shaft will reduce shaft rotation squirt. The two effects work in combination and offset each other.

Bob Jewett or Dr. Dave can do the calculations, or I can do them later, but I contend that the TOTAL deflection of even the flimsiest shaft is probably insignificant, but even more so will be the DIFFERENCE in deflection between the "flimsiest" and a "stiffest" shafts.

I have convinced myself to worry more about the tip and the chalk than the shaft, and to think about adjusting my contact point and aiming line. I have to figure out, for a 10 degree left-of-center contact, how much I need to shift my aiming line. Next drill.....

dr_dave
04-18-2007, 11:51 AM
Shaft,

I think even more goes on than what you describe. The best evidence we currently have for all of the physics is this high-speed video clip (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76_Austrian_HSV_tip_closeup.wmv). For more information, see the thread discussing the clip (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219578&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=&amp;vc=).

Regardless of how good the tip is or how well it is chalked, there will always be sideways motion that will result in squirt. The only way to reduce the amount of squirt (for a given tip) is to reduce the amount of shaft end-mass so there is less inertia to support (and create) sideways force. That's how low-squirt cues work: less end-mass = less sideways force = less squirt.

Regards,
Dave

<blockquote><font class="small">Quote Shaft:</font><hr> Please indulge yet another squirt post, but I think the subject of squirt can be better discussed if we break squirt down into three sources. For all the talk about "what shaft is better," I contend that shaft deflection is probably the least significant of the three sources.

Here is how I view the sources of squirt:

1. Contact point squirt. By definition, we are hitting the cue ball off-center. Looking down on the cue, the intended ball path is 0 degrees (12 o'clock) and we put left english at 190 degrees (almost 7 o'clock). A FRICTIONLESS contact would send the cue ball off at 10 degrees with NO english. Tip FRICTION induces a clockwise spin on the cue ball and sends it in a direction somewhere between 0 and 10 degrees. The direction is less than 10 degrees because tip friction creates a "forward throw" on the ball. The more friction with the tip, the closer to 0 degrees. The problem is, the cue ball is is not moving at 0 degrees as we would like it, hence there is some amount of squirt.

"Well DUHH," you say. But realize that THIS EFFECT EXISTS EVEN IN A PERFECTLY RIGID SHAFT. The amount of Squirt #1 is determined by tip friction, and by the amount the cue ball is hit off-center.

2. Cue stick rotation squirt. When the cue ball is hit left-of-center, the inertial mass of the cue ball puts a sideways torque on the tip of the moving shaft, tending to rotate the entire cue stick counter-clockwise in the horizontal plane, aggravating (slightly) the side forces on the cue ball mentioned in Squirt #1 above.

AGAIN, THIS EFFECT IS PRESENT EVEN WITH A PERFECTLY RIGID SHAFT. The amount of stick rotation is primarily determined by the firmness of the bridge, the consistency of the shooting arm, and the mass of the stick. (In the real world, I admit that a flimsy shaft will absorb a very small amount of the applied torque by bending, REDUCING overall stick rotation.)

Due to the short duration of tip contact time (about 1/500th of a second at the outside), shaft rotation is probably not a huge factor, regardless of the firmness of the bridge or the mass of the stick. But it is a factor: imagine hitting english while holding the cue in a good bridge and then while resting it on a ruler's edge.

3. Shaft deflection squirt. (Oh, how many shafts have been bought and sold over this issue?) Assume the cue ball is 6 inches away from the bridge hand. Since no material is perfectly rigid, we know the shaft bends (ever-so-slightly) to the left as the tip moves forward in the shot. This theoretically aggravates the side forces on the cue ball mentioned in caused by Squirt #1 above.

The question is, "During the 1/500th of a second when the stick is in contact with the ball, what is the DIFFERENCE in bending deflection between the flimsiest and the stiffest cues, ACROSS THOSE SIX INCHES of shaft?"

Remember, too, that a flimsy shaft will reduce shaft rotation squirt. The two effects work in combination and offset each other.

Bob Jewett or Dr. Dave can do the calculations, or I can do them later, but I contend that the TOTAL deflection of even the flimsiest shaft is probably insignificant, but even more so will be the DIFFERENCE in deflection between the "flimsiest" and a "stiffest" shafts.

I have convinced myself to worry more about the tip and the chalk than the shaft, and to think about adjusting my contact point and aiming line. I have to figure out, for a 10 degree left-of-center contact, how much I need to shift my aiming line. Next drill.....
<hr /></blockquote>

dr_dave
04-18-2007, 12:02 PM
For people new to the squirt discussion, many of the past highlights can be found under "squirt" here (http://www.engr.colostate.edu/~dga/pool/threads.html).

Regards,
Dave

SpiderMan
04-18-2007, 01:03 PM
Oh, man ..... I'll go out on a limb and say that I've never read a more confusing post on the relationship of shaft properties/dynamics and cueball squirt.

I say this, not to be unkind, but to prevent lurkers and other readers from becoming seriously misled.

Chalking has not been shown to significantly affect squirt. "Effective end mass" can be reduced to produce a measureable reduction in squirt, with shaft stiffness perhaps a distant second. Makers of reduced-squirt shafts and cues follow this formula because it is proven in both theory and practice.

Dr Dave's summaries are pretty easy to read, and would be a good place to start for an understanding of the basic principles. These are not new concepts - they were being discussed on RSB over ten years ago.

SpiderMan

<blockquote><font class="small">Quote Shaft:</font><hr> Please indulge yet another squirt post, but I think the subject of squirt can be better discussed if we break squirt down into three sources. For all the talk about "what shaft is better," I contend that shaft deflection is probably the least significant of the three sources.

Here is how I view the sources of squirt:

1. Contact point squirt. By definition, we are hitting the cue ball off-center. Looking down on the cue, the intended ball path is 0 degrees (12 o'clock) and we put left english at 190 degrees (almost 7 o'clock). A FRICTIONLESS contact would send the cue ball off at 10 degrees with NO english. Tip FRICTION induces a clockwise spin on the cue ball and sends it in a direction somewhere between 0 and 10 degrees. The direction is less than 10 degrees because tip friction creates a "forward throw" on the ball. The more friction with the tip, the closer to 0 degrees. The problem is, the cue ball is is not moving at 0 degrees as we would like it, hence there is some amount of squirt.

"Well DUHH," you say. But realize that THIS EFFECT EXISTS EVEN IN A PERFECTLY RIGID SHAFT. The amount of Squirt #1 is determined by tip friction, and by the amount the cue ball is hit off-center.

2. Cue stick rotation squirt. When the cue ball is hit left-of-center, the inertial mass of the cue ball puts a sideways torque on the tip of the moving shaft, tending to rotate the entire cue stick counter-clockwise in the horizontal plane, aggravating (slightly) the side forces on the cue ball mentioned in Squirt #1 above.

AGAIN, THIS EFFECT IS PRESENT EVEN WITH A PERFECTLY RIGID SHAFT. The amount of stick rotation is primarily determined by the firmness of the bridge, the consistency of the shooting arm, and the mass of the stick. (In the real world, I admit that a flimsy shaft will absorb a very small amount of the applied torque by bending, REDUCING overall stick rotation.)

Due to the short duration of tip contact time (about 1/500th of a second at the outside), shaft rotation is probably not a huge factor, regardless of the firmness of the bridge or the mass of the stick. But it is a factor: imagine hitting english while holding the cue in a good bridge and then while resting it on a ruler's edge.

3. Shaft deflection squirt. (Oh, how many shafts have been bought and sold over this issue?) Assume the cue ball is 6 inches away from the bridge hand. Since no material is perfectly rigid, we know the shaft bends (ever-so-slightly) to the left as the tip moves forward in the shot. This theoretically aggravates the side forces on the cue ball mentioned in caused by Squirt #1 above.

The question is, "During the 1/500th of a second when the stick is in contact with the ball, what is the DIFFERENCE in bending deflection between the flimsiest and the stiffest cues, ACROSS THOSE SIX INCHES of shaft?"

Remember, too, that a flimsy shaft will reduce shaft rotation squirt. The two effects work in combination and offset each other.

Bob Jewett or Dr. Dave can do the calculations, or I can do them later, but I contend that the TOTAL deflection of even the flimsiest shaft is probably insignificant, but even more so will be the DIFFERENCE in deflection between the "flimsiest" and a "stiffest" shafts.

I have convinced myself to worry more about the tip and the chalk than the shaft, and to think about adjusting my contact point and aiming line. I have to figure out, for a 10 degree left-of-center contact, how much I need to shift my aiming line. Next drill.....
<hr /></blockquote>

dr_dave
04-18-2007, 01:14 PM
FYI, there are also some good references for squirt and other pool physics stuff here (http://www.engr.colostate.edu/~dga/pool/physics/index.html). The most relevant and useful for this topic is Ron Shepard's paper on squirt (http://www.engr.colostate.edu/~dga/pool/physics/Shepard_squirt.pdf).

Happy reading,
Dave

Bob_Jewett
04-18-2007, 02:58 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> ... These are not new concepts - they were being discussed on RSB over ten years ago. ... SpiderMan
... <hr /></blockquote>
Yes, it more or less started in RSB in February 1997 with Thomas Wayne's "Rosabelle Believe" posting*. My understanding of squirt really developed as a result of the Jacksonville Project in December of 1998 (and to some extent the Meucci video before that) in which the rotation of the ball while the tip was on it was apparent. Thomas Wayne's earlier explanation was handwaving and opaque, and in hind sight I believe that he didn't really understand the mechanism.

* for those who are interested in that history, go to Google Groups, and search for the obvious words in the Usenet newsgroup "rec.sport.billiard"

cushioncrawler
04-18-2007, 03:38 PM
<blockquote><font class="small">Quote Shaft:</font><hr> ....The question is, "During the 1/500th of a second when the stick is in contact with the ball, what is the DIFFERENCE in bending deflection between the flimsiest and the stiffest cues, ACROSS THOSE SIX INCHES of shaft?"

.....I have convinced myself to worry more about the tip and the chalk than the shaft, and to think about adjusting my contact point and aiming line. I have to figure out, for a 10 degree left-of-center contact, how much I need to shift my aiming line...... <hr /></blockquote>Shaft -- I agree that the leather tip (to me) is more important than the cue, for sidespin (english billiards here). Chalk (and chalking) is not very important to me (for sidespin) -- but some chalks i wont uze koz they inkreece misscues and kicks (cling).

I allso agree that stiff cues are under-rated (for sidespin) -- i like their consistency -- u (i) get a more consistent line of travel. Sure, a stiff cue needs more allowance for the extra squirt -- but this allowance iz eezyly learnt. But a stiff cue with a damned soft leather qtip needs too much allowance.

All the same, i can see the benefit of uzing a non-stiff cue that suites one's preferred pivot-point etc. madMac.

cushioncrawler
04-18-2007, 03:58 PM
<blockquote><font class="small">Quote Shaft:</font><hr> .....Bob Jewett or Dr. Dave can do the calculations, or I can do them later, but I contend that the TOTAL deflection of even the flimsiest shaft is probably insignificant, but even more so will be the DIFFERENCE in deflection between the "flimsiest" and a "stiffest" shafts....<hr /></blockquote> Shaft -- I reckon that the deflection (bending etc) of a shaft can be significant -- and, a flimsy shaft much more than a stiff shaft koz....

....A stiff shaft bends much less koz the qball duz much of the bending (ie qball squirts more).
....A flimsy shaft bends more koz it makes more spin than a stiffy (ie qball revolves more).
....A flimsy shaft haz a longer contact time. madMac.

Shaft
04-18-2007, 06:23 PM
Dave and all:

The video suggests that there might in fact be two points of inflection. A bend in one direction due to the inertia of the cue ball (not visible on the extreme closeup video, but assumed to be there), and a smaller bend in the opposite direction due to the tip friction (visible on video). I'll concede that.

Other than that, the post you linked to actually supports my arguments.

If the cue tip were infinitely hard and there was no friction between tip and ball, the cue ball would go off on the angle of impact. (It is the same thing as two billiard balls colliding in space.)

The only reason the cue ball does not go off perfectly on that angle is because of friction between the tip and ball gives it some component of force in the same direction of the shaft axis, or the aiming line. I call this a "throw effect between the tip and cue ball," because it works the same as throw between the cue and object ball.

There are two orthogonal vectors here: the radial contact vector and the tangential friction vector. The resultant vector (squirt direction) is somewhere in between. Exactly where in between depends on the relative size of each force.

I did not say or imply that tip and chalk *eliminate* squirt. I did say that that tip friction (tip and chalk) moves the final ball direction *closer* to the axis of the stick, the aiming line. Because you can never get back exactly to the aiming line, I also said that some aiming adjustment will always be needed.

wolfdancer
04-18-2007, 06:52 PM
I can see where it is impossible to make a ball using english

wolfdancer
04-18-2007, 07:03 PM
This would be an extremely interesting subject, had I not skipped school they day they were discussing squirt.
It seems to me, that after all is said and done.....the important thing is the relationship between YOUR shaft and squirt. The two reigning experts on Squirt were Herb Bishop and Ed Mehren
Squirt can be a good thing though and here's everything you need to know about Squirt, that your father never told you:
web page (http://www.angelfire.com/tn/traderz/squirt.html)

Jal
04-18-2007, 07:04 PM
<blockquote><font class="small">Quote Shaft:</font><hr> ...
Here is how I view the sources of squirt:

1. Contact point squirt. By definition, we are hitting the cue ball off-center. Looking down on the cue, the intended ball path is 0 degrees (12 o'clock) and we put left english at 190 degrees (almost 7 o'clock). A FRICTIONLESS contact would send the cue ball off at 10 degrees with NO english. Tip FRICTION induces a clockwise spin on the cue ball and sends it in a direction somewhere between 0 and 10 degrees. The direction is less than 10 degrees because tip friction creates a "forward throw" on the ball. The more friction with the tip, the closer to 0 degrees. The problem is, the cue ball is is not moving at 0 degrees as we would like it, hence there is some amount of squirt.

"Well DUHH," you say. But realize that THIS EFFECT EXISTS EVEN IN A PERFECTLY RIGID SHAFT. The amount of Squirt #1 is determined by tip friction, and by the amount the cue ball is hit off-center.<hr /></blockquote>Colin Colenso, who sometimes posts here, believes that this very well could be a significant, though minor, contributor. This is against the grain of the standard model, but I can't say that I've seen proof that it doesn't play some roll. The idea suggests a touch of randomness, which does limit its possible influence.

<blockquote><font class="small">Quote Shaft:</font><hr>2. Cue stick rotation squirt. When the cue ball is hit left-of-center, the inertial mass of the cue ball puts a sideways torque on the tip of the moving shaft, tending to rotate the entire cue stick counter-clockwise in the horizontal plane, aggravating (slightly) the side forces on the cue ball mentioned in Squirt #1 above.

AGAIN, THIS EFFECT IS PRESENT EVEN WITH A PERFECTLY RIGID SHAFT. The amount of stick rotation is primarily determined by the firmness of the bridge, the consistency of the shooting arm, and the mass of the stick. (In the real world, I admit that a flimsy shaft will absorb a very small amount of the applied torque by bending, REDUCING overall stick rotation.)

Due to the short duration of tip contact time (about 1/500th of a second at the outside), shaft rotation is probably not a huge factor, regardless of the firmness of the bridge or the mass of the stick. But it is a factor: imagine hitting english while holding the cue in a good bridge and then while resting it on a ruler's edge.<hr /></blockquote>Tests have been done to check this by afixing weights at various points along the shaft. After a distance of 6" from the tip or so, they do not cause any more noticeable squirt according to the reports.

What can we conclude? Well DUHH!, that the rest of the cue doesn't matter. /ccboard/images/graemlins/smile.gif

<blockquote><font class="small">Quote Shaft:</font><hr>3. Shaft deflection squirt. (Oh, how many shafts have been bought and sold over this issue?) Assume the cue ball is 6 inches away from the bridge hand. Since no material is perfectly rigid, we know the shaft bends (ever-so-slightly) to the left as the tip moves forward in the shot. This theoretically aggravates the side forces on the cue ball mentioned in caused by Squirt #1 above.

The question is, "During the 1/500th of a second when the stick is in contact with the ball, what is the DIFFERENCE in bending deflection between the flimsiest and the stiffest cues, ACROSS THOSE SIX INCHES of shaft?"

Remember, too, that a flimsy shaft will reduce shaft rotation squirt. The two effects work in combination and offset each other.

Bob Jewett or Dr. Dave can do the calculations, or I can do them later, but I contend that the TOTAL deflection of even the flimsiest shaft is probably insignificant, but even more so will be the DIFFERENCE in deflection between the "flimsiest" and a "stiffest" shafts.<hr /></blockquote>Of course, stiffness is built into the notion of endmass - you can't have endmass without it (except for an infinitesimal slice). The endmass treatemnt is really a simplification of the true state of affairs, a dynamically loaded inhomogeneous, non-isotropic cantilever. But this is hard enough to say, much less analyze. To my understanding, which ain't much, the length of the cantilever, or at least the speed of transverse wave propagation is proportional to the radius of the cylindrical cross-section, and I think to the square-root of it's intrinsic stiffnes (Young's modulus).

So, if you knew the equation for the shape of the beam (cue) under sideways load, you could figure perhaps the amount of resistance the beam puts up as well as how much mass is displaced and put into motion (sideways). I've only seen equations for a static load and a freely vibrating beam (thank goodness), so I won't be putting pen to paper. (But if the two curves resemble each other, that suggests, in a cross your fingers sort of way, that maybe the loaded case is not too different.) You did mention doing some calculations....could you work it out and get back to us tomorrow?

My point is that while I surely don't know, stiffness may be more important than it is given credit for in the endmass treatment, as Mac (Cushioncrawler) may have been suggesting.

Jim

cushioncrawler
04-18-2007, 08:21 PM
<blockquote><font class="small">Quote Shaft:</font><hr> ....If the cue tip were infinitely hard and there was no friction between tip and ball, the cue ball would go off on the angle of impact. (It is the same thing as two billiard balls colliding in space.).... <hr /></blockquote>Shaft -- I reckon that it would be similar to a ball colliding with a hard imoovable wall (aligned on the tangent at that point), not another ball. madMac.

cushioncrawler
04-18-2007, 08:29 PM
<blockquote><font class="small">Quote Shaft:</font><hr> ....I did not say or imply that tip and chalk *eliminate* squirt. I did say that that tip friction (tip and chalk) moves the final ball direction *closer* to the axis of the stick, the aiming line. Because you can never get back exactly to the aiming line, I also said that some aiming adjustment will always be needed. <hr /></blockquote>Shaft -- U could allmost get back exactly to the aiming line, if u had super-chalk, with mu = say 100.

But i like to think about a qball where u have drilled a hole in the ball at the qtip contact point, the hole being aligned along the shaft (stroke) centerline, the hole stopping at the "center" of the ball. Now, when u hit the qball, ie hitting it at the end of the hole, there will be zero squirt. And, if u drill the hole a bit longer, past center, then u will get reverse squirt. Dont know if this helps anyone here. Sleep tight. madMac.

cushioncrawler
04-18-2007, 08:39 PM
<blockquote><font class="small">Quote Jal:</font><hr> ....Tests have been done to check this by afixing weights at various points along the shaft. After a distance of 6" from the tip or so, they do not cause any more noticeable squirt according to the reports....<hr /></blockquote>Jim -- Actually, they didnt ever check "after" -- they found a node and stopped the tests there -- which is the gist of my assertions in old postings that finding a 6" node (8" actually i think) karnt proov that the rest of the shaft etc duznt contribute to squirt -- they shood have gone further. madMac.

dr_dave
04-19-2007, 09:16 AM
<blockquote><font class="small">Quote Jal:</font><hr>My point is that while I surely don't know, stiffness may be more important than it is given credit for in the endmass treatment, as Mac (Cushioncrawler) may have been suggesting.<hr /></blockquote>I agree that stiffness is important, not because deflection of the shaft during contact (which would generate insignificantly small forces compared to the impact forces), but because a stiffer shaft will result in higher effective end-mass (because more mass comes into play at higher stiffnesses). Therefore, end-mass does still seem to tell the whole story.

Regards,
Dave

dr_dave
04-19-2007, 09:27 AM
<blockquote><font class="small">Quote Jal:</font><hr>Colin Colenso, who sometimes posts here, believes that this very well could be a significant, though minor, contributor. This is against the grain of the standard model, but I can't say that I've seen proof that it doesn't play some roll. The idea suggests a touch of randomness, which does limit its possible influence.<hr /></blockquote>I have also always believed that cue tip properties can affect the amount of squirt, but I have no experiments or analysis to prove it. But when I look at the Austrian high-speed video of the off-center hit (HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm)), I can't help but thinking the deformation and friction characteristics of the tip must play a role.

Regards,
Dave

dr_dave
04-19-2007, 09:54 AM
<blockquote><font class="small">Quote Shaft:</font><hr>The video suggests that there might in fact be two points of inflection. A bend in one direction due to the inertia of the cue ball (not visible on the extreme closeup video, but assumed to be there), and a smaller bend in the opposite direction due to the tip friction (visible on video). I'll concede that.<hr /></blockquote>The forces between the cue tip and ball depend on many factors, and I think it is difficult to visualize all of them in the video (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). We need a much fast camera and a much closer up view (and a further back view). Here are some of the factors that contribute to the force state during impact:
- compression characteristics of the tip.
- friction characteristics of the tip-ball interface (I suspect this is very complex on a small scale).
- inertial properties (translational and rotational) of the ball and the shaft assembly.
- constrained translation and rotation of the ball and motion of the tip while the tip is in contact with the ball.
- the types, speeds, and reflections of the various elastic waves that travel through the tip, ferrule, and shaft.
- etc.

I think it would take a much faster camera to help provide more physical insight, lots of sophisticated modeling to describe all of the physics, lots of experiments to quantify and verify all of the physical parameters and how they vary, sophisticated finite-element analysis (FEA) that incorporates all of the modeling and experimental knowledge, and a much faster camera that can provide video evidence that can help validate everything. We're probably talking several PhD dissertations in physics and/or engineering. The problem is that nobody would undertake such a significant project without significant funding, which would be extremely difficult to obtain.

<blockquote><font class="small">Quote Shaft:</font><hr>If the cue tip were infinitely hard and there was no friction between tip and ball, the cue ball would go off on the angle of impact.<hr /></blockquote>Agreed.

<blockquote><font class="small">Quote Shaft:</font><hr>The only reason the cue ball does not go off perfectly on that angle is because of friction between the tip and ball gives it some component of force in the same direction of the shaft axis, or the aiming line.<hr /></blockquote>Agreed.

<blockquote><font class="small">Quote Shaft:</font><hr>I did not say or imply that tip and chalk *eliminate* squirt. I did say that that tip friction (tip and chalk) moves the final ball direction *closer* to the axis of the stick, the aiming line. Because you can never get back exactly to the aiming line, I also said that some aiming adjustment will always be needed.<hr /></blockquote>Good summary!

Regards,
Dave

Eric.
04-19-2007, 10:54 AM
Oh brother. /ccboard/images/graemlins/confused.gif

Eric

Jal
04-19-2007, 12:13 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Shaft:</font><hr> ....I did not say or imply that tip and chalk *eliminate* squirt. I did say that that tip friction (tip and chalk) moves the final ball direction *closer* to the axis of the stick, the aiming line. Because you can never get back exactly to the aiming line, I also said that some aiming adjustment will always be needed. <hr /></blockquote>Shaft -- U could allmost get back exactly to the aiming line, if u had super-chalk, with mu = say 100.<hr /></blockquote>Mac, I see no reason to believe that you couldn't get back to the aiming line with normal friction if it weren't for other things, namely the sidways component of force between the tip and ball. This reduces the force in the tangential direction relative to the normal direction. If you eliminated the stick's resistance to sideways movement, mu would be sufficient to yield no squirt, as I see it. I don't think that 'friction' should be considered as a separate contributor to squirt, unless some slip is occurring.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>But i like to think about a qball where u have drilled a hole in the ball at the qtip contact point, the hole being aligned along the shaft (stroke) centerline, the hole stopping at the "center" of the ball. Now, when u hit the qball, ie hitting it at the end of the hole, there will be zero squirt. And, if u drill the hole a bit longer, past center, then u will get reverse squirt.<hr /></blockquote>Agreed. (You would have to stop just slightly short of center I think.)

Jim

Jal
04-19-2007, 12:22 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> ....Tests have been done to check this by afixing weights at various points along the shaft. After a distance of 6" from the tip or so, they do not cause any more noticeable squirt according to the reports....<hr /></blockquote>Jim -- Actually, they didnt ever check "after" -- they found a node and stopped the tests there -- which is the gist of my assertions in old postings that finding a 6" node (8" actually i think) karnt proov that the rest of the shaft etc duznt contribute to squirt -- they shood have gone further. madMac. <hr /></blockquote>This is over my head right now (and likely to stay that way), but if you care to expand on this...

Jim

dr_dave
04-19-2007, 12:25 PM
<blockquote><font class="small">Quote Jal:</font><hr>I don't think that 'friction' should be considered as a separate contributor to squirt, unless some slip is occurring.<hr /></blockquote>I think some slip occurs at some scale (due to tip deformation, shock waves, and motion), even for a good, well-chalked tip. It is certainly occurring (in my opinion) in HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). Do you agree? More clips can be found in HSV A.13 through HSV A.20 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html), but the frame rate and resolution are not quite sufficient to judge the amount of slip. I am currently getting my high-speed camera upgraded (better resolution, better lens), and I hope to get better images in the near future.

Regards,
Dave

wolfdancer
04-19-2007, 12:47 PM
"Oh, that way madness lies; let me shun that." (Bill S.)

Deeman3
04-19-2007, 01:01 PM
You guys have to get a life. /ccboard/images/graemlins/grin.gif

Jal
04-19-2007, 01:33 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>My point is that while I surely don't know, stiffness may be more important than it is given credit for in the endmass treatment, as Mac (Cushioncrawler) may have been suggesting.<hr /></blockquote>I agree that stiffness is important, not because deflection of the shaft during contact (which would generate insignificantly small forces compared to the impact forces), but because a stiffer shaft will result in higher effective end-mass (because more mass comes into play at higher stiffnesses). Therefore, end-mass does still seem to tell the whole story.<hr /></blockquote>Dr. Dave,

Yes, I agree that end-mass is the whole story in the sense of momentum conservation. But I believe I've seen statements to the effect that the shaft's stiffness plays little or no role. My point was the same as yours: that it is an integral part of end-mass.

I just brought it up because it can be a little confusing when you separate them out. Eg, what would happen if you had a shaft that was "stiff" but massless over some portion of its business end...would you get squirt? Well, the problem with this model, and the source of the apparent conundrum, is that it suggests that the shaft could produce sideways forces without mass, which just isn't so. Nor could it produce forces if it had mass but was perfectly flexible.

This is obvious to you, but it's a trap that I fell into at one time.

Jim

dr_dave
04-19-2007, 03:11 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>My point is that while I surely don't know, stiffness may be more important than it is given credit for in the endmass treatment, as Mac (Cushioncrawler) may have been suggesting.<hr /></blockquote>I agree that stiffness is important, not because deflection of the shaft during contact (which would generate insignificantly small forces compared to the impact forces), but because a stiffer shaft will result in higher effective end-mass (because more mass comes into play at higher stiffnesses). Therefore, end-mass does still seem to tell the whole story.<hr /></blockquote>Dr. Dave,

Yes, I agree that end-mass is the whole story in the sense of momentum conservation. But I believe I've seen statements to the effect that the shaft's stiffness plays little or no role. My point was the same as yours: that it is an integral part of end-mass.

I just brought it up because it can be a little confusing when you separate them out. Eg, what would happen if you had a shaft that was "stiff" but massless over some portion of its business end...would you get squirt? Well, the problem with this model, and the source of the apparent conundrum, is that it suggests that the shaft could produce sideways forces without mass, which just isn't so. Nor could it produce forces if it had mass but was perfectly flexible.

This is obvious to you, but it's a trap that I fell into at one time.<hr /></blockquote>Jim,

Good summary. The key is to talk about "effective end-mass" (i.e., the amount of mass that contributes to the squirt). The effective end-mass will be distributed differently based on shaft geometry and stiffness. For typical wooden cue sticks, only the 6-8 inches or so closest to the tip contributes to the "end mass." Obviously, this would not be the case with Mac's steel cue or the hypothetical cues you mention above.

Regards,
Dave

Bob_Jewett
04-19-2007, 03:42 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... Obviously, this would not be the case with Mac's steel cue or the hypothetical cues you mention above.... <hr /></blockquote>
I think that if the steel cue is the same length as the wooden one and it has the same fundamental frequency (transverse oscillation, one maximum, two nodes with "open" ends), then the length involved in determining the end mass is the same.

My experiment with a 5/8-inch aluminum rod showed huge squirt, but I did not measure the fundamental frequency or estimate total mass in the "end region."

(Ignore this if Mac's cue does not match the above, but I have great difficulty reading his posts, and I must have skipped that one.)

Bob_Jewett
04-19-2007, 03:45 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> ... Actually, they didnt ever check "after" -- they found a node and stopped the tests there -- which is the gist of my assertions in old postings that finding a 6" node (8" actually i think) karnt proov that the rest of the shaft etc duznt contribute to squirt -- they shood have gone further. madMac. <hr /></blockquote>
I think that the concept of a "node" is not valid in this situation. A node is not significant for a transient that is much shorter than the propagation time of the transverse wave down the stick.

Bob_Jewett
04-19-2007, 03:48 PM
<blockquote><font class="small">Quote Jal:</font><hr> ... This is over my head right now (and likely to stay that way), but if you care to expand on this... <hr /></blockquote>
I think it would have been a bad sign if you had understood it since I think Mac is mistaken in his approach.

Jal
04-19-2007, 04:01 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>I don't think that 'friction' should be considered as a separate contributor to squirt, unless some slip is occurring.<hr /></blockquote>I think some slip occurs at some scale (due to tip deformation, shock waves, and motion), even for a good, well-chalked tip. It is certainly occurring (in my opinion) in HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). Do you agree? More clips can be found in HSV A.13 through HSV A.20 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html), but the frame rate and resolution are not quite sufficient to judge the amount of slip. I am currently getting my high-speed camera upgraded (better resolution, better lens), and I hope to get better images in the near future.<hr /></blockquote>As I recall, that after you presented this (the Austrian film segment) in a sequenced still format, Mac noticed that the tip moved downward after contact without any apparent movement forward of the cueball. But someone, somewhere offered a counter-argument, perhaps that since the cueball didn't move, the initial slip had no real effect? (I forget the details.) I haven't got the time to look at the other videos right now, but will later (probably have seen most them).

I, for one, will really be looking forward to your next set of videos with the upgrades you have planned. (Not that the current ones aren't great too.)

Jim

dr_dave
04-19-2007, 04:04 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> ... Obviously, this would not be the case with Mac's steel cue or the hypothetical cues you mention above.... <hr /></blockquote>
I think that if the steel cue is the same length as the wooden one and it has the same fundamental frequency (transverse oscillation, one maximum, two nodes with "open" ends), then the length involved in determining the end mass is the same.<hr /></blockquote>Sounds reasonable to me, but wouldn't the fundamental frequency vary with stiffness?

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>My experiment with a 5/8-inch aluminum rod showed huge squirt, but I did not measure the fundamental frequency or estimate total mass in the "end region."<hr /></blockquote>That would make sense. A solid metal rod will have lots of mass close to the tip, and I would think the metal rod would be much stiffer than a wooden cue. I would expect this to increase the length contributing to the effective end-mass. Did you try your added-mass experiment with the metal rod to experimentally determine the end-mass effective-length? Those results would help shed some light on these discussions. It would also be interesting to try a steel rod or tube of the same weight (but stiffer).

Regards,
Dave

dr_dave
04-19-2007, 04:09 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr>I don't think that 'friction' should be considered as a separate contributor to squirt, unless some slip is occurring.<hr /></blockquote>I think some slip occurs at some scale (due to tip deformation, shock waves, and motion), even for a good, well-chalked tip. It is certainly occurring (in my opinion) in HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). Do you agree? More clips can be found in HSV A.13 through HSV A.20 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html), but the frame rate and resolution are not quite sufficient to judge the amount of slip. I am currently getting my high-speed camera upgraded (better resolution, better lens), and I hope to get better images in the near future.<hr /></blockquote>As I recall, that after you presented this (the Austrian film segment) in a sequenced still format, Mac noticed that the tip moved downward after contact without any apparent movement forward of the cueball. But someone, somewhere offered a counter-argument, perhaps that since the cueball didn't move, the initial slip had no real effect? (I forget the details.) I haven't got the time to look at the other videos right now, but will later (probably have seen most them).<hr /></blockquote>I think the closest I came to making conclusions is summarized here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219624&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). I think we need more data to be more confident.

<blockquote><font class="small">Quote Jal:</font><hr>I, for one, will really be looking forward to your next set of videos with the upgrades you have planned.<hr /></blockquote>Me too! Seeing is believing.

Regards,
Dave

Jal
04-19-2007, 04:48 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> "Oh, that way madness lies; let me shun that." (Bill S.) <hr /></blockquote>Actually, these things are an antidote to what might really drive me over the brink: Iraq, the state of American culture, the horrors inflicted upon the rest of the animal kingdom by this species "in action how like an angel! in apprehension how like a god! the beauty of the world! the paragon of animals!"

Playing several hours of actual pool a night would probably be better, but circumstances don't allow. Like pool, where you get to enjoy the illusion of mastery for a rack or two, physics provides another one: that of being in touch with the eternal verities. They may be elementary with pool, but eternal verities are eternal verities.

Jim

wolfdancer
04-19-2007, 05:44 PM
Jim, if i understood half of that you guys are writing about....I'd be right in the middle of the conversation.
I might kid a bit about the technical discussions...but they do sound interesting....
Pool for me is also cathartic...Hitting balls for a few minutes ..pretty relaxing....almost makes me forget about our beloved President....almost

cushioncrawler
04-19-2007, 06:08 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> ... Actually, they didnt ever check "after" -- they found a node and stopped the tests there -- which is the gist of my assertions in old postings that finding a 6" node (8" actually i think) karnt proov that the rest of the shaft etc duznt contribute to squirt -- they shood have gone further. madMac. <hr /></blockquote> I think that the concept of a "node" is not valid in this situation. A node is not significant for a transient that is much shorter than the propagation time of the transverse wave down the stick. <hr /></blockquote>Bob -- My BD email notifications havent been getting throo to me for a few days, so my apologies re the delay in getting back. "Node" mightnt be the correct term -- "Null" might be better.

Perhaps ordinary sideways "bending" (propogation) is (as u say) too slow to bring much of the cue into play during the short tip-to-ball impact time. But, there will be "non-ordinary" sideways bending due to "buckling" -- here the speedy compression wave will bring the full wt of the cue into play. Thusly, one might have 1 or 2 bending nodes, mixed with 1 or 2 buckling nodes.

Looking down on a cue during a shot (uzing english), i might see that 2 bits of the cue dont moov sideways during impact. One such bit (null) might be 8" from the tip, and the other say 30". Bits of the cue near these nulls wouldnt much affect (inkreece) squirt.

The 30" point might proov to be the best place for the joint, it might suggest that 3/4 jointed cues are better than 1/2 jointed cues. But "better" is different things to different people. One day i am going to make a cue with the max of rotational inertia, ie i will place wts well away from the 30" (or ??") null point, a bit like a modern bow. Such a cue might do good things. Wait -- another idea -- a small gyro(s) to keep the cue on-line. madMac.

cushioncrawler
04-19-2007, 06:44 PM
<blockquote><font class="small">Quote Jal:</font><hr> ...As I recall, that after you presented this (the Austrian film segment) in a sequenced still format, Mac noticed that the tip moved downward after contact without any apparent movement forward of the cueball. But someone, somewhere offered a counter-argument, perhaps that since the cueball didn't move, the initial slip had no real effect? (I forget the details.) I haven't got the time to look at the other videos right now, but will later (probably have seen most them)....<hr /></blockquote>Jim -- I reckon that a tip must allways firstly slip a bit, to "ruff-up" the qball to the max, and then slippage stops (hopefully).

A "good" tip will allow good slippage -- not too little -- not too much. A good tip will then make use of this ruffed-up area. If the leather is too hard and the shape too sharp, the ruffed-up area is "left behind" too much.

I dont think that a little bit of "tip-slip" is guilty of anything here. But, a big soft tip is murder. madMac.

Qtec
04-19-2007, 10:08 PM
Ever seen that nature doc from David Attenbourgh when he is in a cave in Borneo with a zillion bats? Anyway, at dusk, the bats start to leave the cave- millions of bats all heading for the exit. As we all know, bats emits high pitched sounds and can navigate in total darkness by hearing the echos . Its an amazing feat of nature/evolution buy there's a snag. These bats are tiny. So there brains are very small and according to the scientists it shouldn't be possible for the bats to do what they obviously do. Their brains are too small to do the neccessary computations to instantly react to the info they are recieving.
It should be impossible.

Q

Jal
04-20-2007, 12:36 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>I think the closest I came to making conclusions is summarized here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219624&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). I think we need more data to be more confident.<hr /></blockquote>Dr. Dave, there's no question about slip taking place in HSV A.16 and A.19, and a pretty large amount. What's interesting is that you didn't label them as miscues, although there is clearly a difference though between these two and the ones that you did call miscues. That you didn't perceive them as miscues has to make one wonder how many shots do involve significant slip? With HSV A.18 and A.20 it's obvious that not anywhere near this much is occurring, but hard to tell if there is absolutely none. Thank you for pointing these out.

Jim

dr_dave
04-20-2007, 09:09 AM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>I think the closest I came to making conclusions is summarized here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219624&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). I think we need more data to be more confident.<hr /></blockquote>Dr. Dave, there's no question about slip taking place in HSV A.16 and A.19, and a pretty large amount.<hr /></blockquote>I also believe there is slip during contact, but I don't think it is as obvious as you suggest. The limited frame rate and resolution make it difficult to pinpoint exactly when and where contact and "slip" start and stop. The chalk cloud doesn't help.

<blockquote><font class="small">Quote Jal:</font><hr>What's interesting is that you didn't label them as miscues, although there is clearly a difference though between these two and the ones that you did call miscues.<hr /></blockquote>In real life (i.e., not looking through the lens of a high-speed camera), it was obvious what was a miscue and what wasn't. I labeled them based on what the shooter sees.

<blockquote><font class="small">Quote Jal:</font><hr>That you didn't perceive them as miscues has to make one wonder how many shots do involve significant slip? With HSV A.18 and A.20 it's obvious that not anywhere near this much is occurring, but hard to tell if there is absolutely none. Thank you for pointing these out.<hr /></blockquote>Good points. I agree.

Regards,
Dave

dr_dave
04-20-2007, 09:22 AM
<blockquote><font class="small">Quote Qtec:</font><hr> Ever seen that nature doc from David Attenbourgh when he is in a cave in Borneo with a zillion bats? Anyway, at dusk, the bats start to leave the cave- millions of bats all heading for the exit. As we all know, bats emits high pitched sounds and can navigate in total darkness by hearing the echos . Its an amazing feat of nature/evolution buy there's a snag. These bats are tiny. So there brains are very small and according to the scientists it shouldn't be possible for the bats to do what they obviously do. Their brains are too small to do the neccessary computations to instantly react to the info they are recieving.
It should be impossible.<hr /></blockquote>Some scientists believe that, in some creatures, "intelligence" can be distributed throughout the entire nervous systems, and not just localized in the brain (although, the brain contains the largest concentration of neurons).

Those bats might be "smarter" than you think. /ccboard/images/graemlins/wink.gif

Dave

Deeman3
04-20-2007, 10:01 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> It should be impossible.

<hr /></blockquote>Some scientists believe that, in some creatures, "intelligence" can be distributed throughout the entire nervous systems, and not just localized in the brain (although, the brain contains the largest concentration of neurons).

Those bats might be "smarter" than you think. /ccboard/images/graemlins/wink.gif

Dave <hr /></blockquote>

<font color="blue"> I know I can't prove it with a high speed camera but some might feel God knows how this works. /ccboard/images/graemlins/smirk.gif I know it's not PC to say that, but what the heck? </font color>

dr_dave
04-20-2007, 11:23 AM
<blockquote><font class="small">Quote Deeman3:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr><blockquote><font class="small">Quote Qtec:</font><hr>It should be impossible.<hr /></blockquote>Some scientists believe that, in some creatures, "intelligence" can be distributed throughout the entire nervous systems, and not just localized in the brain (although, the brain contains the largest concentration of neurons).

Those bats might be "smarter" than you think. /ccboard/images/graemlins/wink.gif

Dave<hr /></blockquote><font color="blue"> I know I can't prove it with a high speed camera but some might feel God knows how this works. /ccboard/images/graemlins/smirk.gif I know it's not PC to say that, but what the heck? </font color><hr /></blockquote>Deeman,

I don't have a clue what you are trying to imply here; but whatever it is, I don't think I like it. /ccboard/images/graemlins/confused.gif

Regards,
Dave

PS:
I like bats. I think they are cute (and smart), even though their poop doesn't smell very nice. /ccboard/images/graemlins/wink.gif

When I lived in Austin, I used to love going down to Town Lake to watch them come out of the "cave" at dusk to eat all of those nasty mosquitoes.

Jal
04-20-2007, 11:53 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>I think the closest I came to making conclusions is summarized here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219624&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). I think we need more data to be more confident.<hr /></blockquote>Dr. Dave, there's no question about slip taking place in HSV A.16 and A.19, and a pretty large amount.<hr /></blockquote>I also believe there is slip during contact, but I don't think it is as obvious as you suggest. The limited frame rate and resolution make it difficult to pinpoint exactly when and where contact and "slip" start and stop. The chalk cloud doesn't help.<hr /></blockquote>I have to disagree a little here Dr. Dave. Looking at the sideways post-impact speed of the tip (downward in the videos), to me it is noticeably larger than the surface speed of the cueball from rotation. True, the ring on the cueball is not moving in a straight line in the transverse direction, but comparing these to A.18 and A.20, there is a clear difference. In A.18 and A.20, the tip remains nearly aligned with the contact region throughout, but in A.16 and A.19, I don't think it's even close.

That's why I'm surprised that it didn't feel like a miscue, though I'm not suggesting that anyone else would have perceived it as such.

Jim

Jal
04-20-2007, 12:06 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- I reckon that a tip must allways firstly slip a bit, to "ruff-up" the qball to the max, and then slippage stops (hopefully).

A "good" tip will allow good slippage -- not too little -- not too much. A good tip will then make use of this ruffed-up area. If the leather is too hard and the shape too sharp, the ruffed-up area is "left behind" too much.

I dont think that a little bit of "tip-slip" is guilty of anything here. But, a big soft tip is murder. madMac. <hr /></blockquote>Mac, I'm a little skeptical of this pre-roughing idea. I think that after a while, a new cueball will sort of reach an equilibrium state of roughness, and that any pre-roughing would only work against this by dredging out channels in the direction of slippage. This would, if anything, decrease the tip's grip on the ball, at least potentially. No?

Jim

wolfdancer
04-20-2007, 12:33 PM
trust me...you don't, but I need a drink after reading all this. If I am reading this right(with my tiny brain)..the discussion centers on the brief .002 seconds that the tip and ball are in contact???
the higher speed camera would add even more detail to that interval?
I'm comparing this to that theory that if you start out at point A, and move 1/2 the distance at a time towards point B...you'll never get there.....
I'm thinking you guys will never arrive at a consensus on this topic either
Worse thing is....you've drawn Mac into the debate...lol

Deeman3
04-20-2007, 12:50 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> quote]Deeman,

I don't have a clue what you are trying to imply here; but whatever it is, I don't think I like it. /ccboard/images/graemlins/confused.gif

Regards,
Dave

<font color="blue"> Dave,

Sorry (not really). It was probably over your head. /ccboard/images/graemlins/grin.gif</font color>

wolfdancer
04-20-2007, 03:04 PM
This is the kind of physics book I would read....
"The Dancing Wu Li Masters: An Overview of the New Physics"

"Amazon.com
At an Esalen Institute meeting in 1976, tai chi master Al Huang said that the Chinese word for physics is Wu Li, "patterns of organic energy." Journalist Gary Zukav and the others present developed the idea of physics as the dance of the Wu Li Masters--the teachers of physical essence. Zukav explains the concept further:

The Wu Li Master dances with his student. The Wu Li Master does not teach, but the student learns. The Wu Li Master always begins at the center, the heart of the matter.... This book deals not with knowledge, which is always past tense anyway, but with imagination, which is physics come alive, which is Wu Li.... Most people believe that physicists are explaining the world. Some physicists even believe that, but the Wu Li Masters know that they are only dancing with it.

The "new physics" of Zukav's 1979 book comprises quantum theory, particle physics, and relativity. Even as these theories age they haven't percolated all that far into the collective consciousness; they're too far removed from mundane human experience not to need introduction. The Dancing Wu Li Masters remains an engaging, accessible way to meet the most profound and mind-altering insights of 20th-century science. --Mary Ellen Curtin "

Deeman3
04-20-2007, 03:32 PM
I looked up Mary Ellen Curtin's dress during summer school... /ccboard/images/graemlins/smirk.gif

Jal
04-20-2007, 03:54 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> This is the kind of physics book I would read....
"The Dancing Wu Li Masters: An Overview of the New Physics"

"Amazon.com
At an Esalen Institute meeting in 1976, tai chi master Al Huang said that the Chinese word for physics is Wu Li, "patterns of organic energy." Journalist Gary Zukav and the others present developed the idea of physics as the dance of the Wu Li Masters--the teachers of physical essence. Zukav explains the concept further:

The Wu Li Master dances with his student. The Wu Li Master does not teach, but the student learns. The Wu Li Master always begins at the center, the heart of the matter.... This book deals not with knowledge, which is always past tense anyway, but with imagination, which is physics come alive, which is Wu Li.... Most people believe that physicists are explaining the world. Some physicists even believe that, but the Wu Li Masters know that they are only dancing with it.

The "new physics" of Zukav's 1979 book comprises quantum theory, particle physics, and relativity. Even as these theories age they haven't percolated all that far into the collective consciousness; they're too far removed from mundane human experience not to need introduction. The Dancing Wu Li Masters remains an engaging, accessible way to meet the most profound and mind-altering insights of 20th-century science. --Mary Ellen Curtin " <hr /></blockquote>I can't remember if I've read that (or any book on physics or anything for that matter), but to add to that, there's an excellent video series which may be available at your library as part of the SuperStar Teachers series, by Richard Wolfson. It's called "Einstein's Relativity and the Quantum Revolution: Modern Physics for Non-Scientists". Virtually no math, and what's there is brief and simple, but he gets to the heart of things. You may not be able to get a job at FermiLab afterwards, but you'll understand the central concepts and the crucial experiments that led to them.

AND!, it's guaranteed to add at least one ball to your game (but not by me).

Jim

cushioncrawler
04-20-2007, 04:58 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- I reckon that a tip must allways firstly slip a bit, to "ruff-up" the qball to the max, and then slippage stops (hopefully). A "good" tip will allow good slippage -- not too little -- not too much. A good tip will then make use of this ruffed-up area. If the leather is too hard and the shape too sharp, the ruffed-up area is "left behind" too much. I dont think that a little bit of "tip-slip" is guilty of anything here. But, a big soft tip is murder. madMac. <hr /></blockquote>Mac, I'm a little skeptical of this pre-roughing idea. I think that after a while, a new cueball will sort of reach an equilibrium state of roughness, and that any pre-roughing would only work against this by dredging out channels in the direction of slippage. This would, if anything, decrease the tip's grip on the ball, at least potentially. No? <hr /></blockquote>Jim -- Thoze slo-mo's of Dr Dave's are amazing -- i can hardly beleev that that much slippage occurs. It haz changed my thinking a bit. I would really love to see some very very slow, really clear videos or pics.

And, what we really need badly iz a microscopic view of all of the marks on a ball -- balltoball marks, tiptoball marks, misscue marks, cling marks. The ball surface (qball particularly) must be a mixture of fresh and old marks, with some areas highly polished and some (most??) not.

With balltoball impacts, it (friktion) must be like i say, a war between rough (abrazions) and rezidue (burnt and abraded bakelite). A microscope would tell.

God knows how much time i have spent doing test on all of this sort of stuff. Banging balls together to get impakt marks, doing friktion tests with virgin marks and with marks where i have gently remooved some or all of the rezidue, etc etc.

If an ordinary fresh qtip mark on the qball gets into a balltoball impakt, u get cling (kick) allmost az bad az with the much hated "pure" chalk-cling -- and here i am not talking about a chalky sort of qtip mark, i am talking about a "clean" qtip mark. We need a good microscope. madMac.

cushioncrawler
04-20-2007, 05:04 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> trust me...you don't, but I need a drink after reading all this. If I am reading this right(with my tiny brain)..the discussion centers on the brief .002 seconds that the tip and ball are in contact??? the higher speed camera would add even more detail to that interval?
I'm comparing this to that theory that if you start out at point A, and move 1/2 the distance at a time towards point B...you'll never get there.....
I'm thinking you guys will never arrive at a consensus on this topic either Worse thing is....you've drawn Mac into the debate...lol <hr /></blockquote>Woolfy -- If we only moov 1/2 way each interval, then we wont ever get there, thats a fact -- wont get any "real" arguements about that. madMac.

dr_dave
04-20-2007, 05:50 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Thoze slo-mo's of Dr Dave's are amazing -- i can hardly beleev that that much slippage occurs. It haz changed my thinking a bit. I would really love to see some very very slow, really clear videos or pics.<hr /></blockquote>I hope to have some better close-up shots within a month or so; although, it will be tough to match the visual quality of HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). That Austrian group has a nice camera; although, they use too much chalk!

I'll be sure to share the new videos as soon as they are available.

Regards,
Dave

dr_dave
04-20-2007, 06:35 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>I think the closest I came to making conclusions is summarized here (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219624&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1). I think we need more data to be more confident.<hr /></blockquote>Dr. Dave, there's no question about slip taking place in HSV A.16 and A.19, and a pretty large amount.<hr /></blockquote>I also believe there is slip during contact, but I don't think it is as obvious as you suggest. The limited frame rate and resolution make it difficult to pinpoint exactly when and where contact and "slip" start and stop. The chalk cloud doesn't help.<hr /></blockquote>I have to disagree a little here Dr. Dave. Looking at the sideways post-impact speed of the tip (downward in the videos), to me it is noticeably larger than the surface speed of the cueball from rotation. True, the ring on the cueball is not moving in a straight line in the transverse direction, but comparing these to A.18 and A.20, there is a clear difference. In A.18 and A.20, the tip remains nearly aligned with the contact region throughout, but in A.16 and A.19, I don't think it's even close.

That's why I'm surprised that it didn't feel like a miscue, though I'm not suggesting that anyone else would have perceived it as such.<hr /></blockquote>Jim,

I still don't think the videos are good enough to make too many claims about contact and/or slip. I think the best two to compare are HSV A.18 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-18.htm) and HSV A.19 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-19.htm). They have the most similar offsets and speeds. To help see the comparison, I captured stills from each video and posted them here (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSV_A18-19_stills.pdf). For me it is difficult to see the obvious differences between the amounts of tip slip. Now, in HSV A.18, the tip does seem to stay in contact with the ball a little longer, and deflect more, and the ball does seem to "take" more of the English, but I can't comfortably perceive what's going on with tip slip during contact. The shadows, and chalk clouds don't help with this perception. I will reserve judgment until I can shoot some video at higher frame rates and/or better resolutions and/or with better lighting.

Regards,
Dave

cushioncrawler
04-20-2007, 07:23 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Thoze slo-mo's of Dr Dave's are amazing -- i can hardly beleev that that much slippage occurs. It haz changed my thinking a bit. I would really love to see some very very slow, really clear videos or pics.<hr /></blockquote>I hope to have some better close-up shots within a month or so; although, it will be tough to match the visual quality of HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). That Austrian group has a nice camera; although, they use too much chalk! I'll be sure to share the new videos as soon as they are available....<hr /></blockquote>Dr Dave -- I think that a curved tip tends to target the same patch of new ruff (on the qball), as impact progresses. But, a flat tip can be used (for deep screw) perhaps 4 times without chalking, before misscueing raises its ugly head -- whats going on here ???

I think that "too much" chalk might be worth looking at. Zero chalk allso, ie a misscue. An oiled tip allso -- might show something interesting. A very hard (over-viced) tip.

On an earlyr posting i said that chalking (method) wasnt important, but in fact it iz important. Top snooker players tend to use a smidgen of chalk for every shot, instead of uzing a heap of chalk every now and again, for better consistency, and koz even dead center contacts need good chalk, ie good consistent friction. One only hazta hit a qball straight up the table, center ball, say 20 times, without chalking, to soon realize how important chalking is (can be) for every shot.

What about a slow-mo of a "target" stuck to some part(s) of the cue, showing the "bucking" etc that goes on at varyus parts of the cue. And, a target at/near the grip, in slo-mo and close-up, high-lighting the hand-finger-butt reaction at impact. madMac.

dr_dave
04-20-2007, 10:19 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>Thoze slo-mo's of Dr Dave's are amazing -- i can hardly beleev that that much slippage occurs. It haz changed my thinking a bit. I would really love to see some very very slow, really clear videos or pics.<hr /></blockquote>I hope to have some better close-up shots within a month or so; although, it will be tough to match the visual quality of HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm). That Austrian group has a nice camera; although, they use too much chalk! I'll be sure to share the new videos as soon as they are available....<hr /></blockquote>Dr Dave -- I think that a curved tip tends to target the same patch of new ruff (on the qball), as impact progresses. But, a flat tip can be used (for deep screw) perhaps 4 times without chalking, before misscueing raises its ugly head -- whats going on here ???

I think that "too much" chalk might be worth looking at. Zero chalk allso, ie a misscue. An oiled tip allso -- might show something interesting. A very hard (over-viced) tip.

On an earlyr posting i said that chalking (method) wasnt important, but in fact it iz important. Top snooker players tend to use a smidgen of chalk for every shot, instead of uzing a heap of chalk every now and again, for better consistency, and koz even dead center contacts need good chalk, ie good consistent friction. One only hazta hit a qball straight up the table, center ball, say 20 times, without chalking, to soon realize how important chalking is (can be) for every shot.

What about a slow-mo of a "target" stuck to some part(s) of the cue, showing the "bucking" etc that goes on at varyus parts of the cue. And, a target at/near the grip, in slo-mo and close-up, high-lighting the hand-finger-butt reaction at impact. madMac. <hr /></blockquote>Mac,

Thanks for the suggestions. I'll see what I can do. My list is things to film is already pretty long.

Regards,
Dave

Jal
04-21-2007, 01:35 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>I still don't think the videos are good enough to make too many claims about contact and/or slip. I think the best two to compare are HSV A.18 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-18.htm) and HSV A.19 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-19.htm). They have the most similar offsets and speeds. To help see the comparison, I captured stills from each video and posted them here (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSV_A18-19_stills.pdf). For me it is difficult to see the obvious differences between the amounts of tip slip. Now, in HSV A.18, the tip does seem to stay in contact with the ball a little longer, and deflect more, and the ball does seem to "take" more of the English, but I can't comfortably perceive what's going on with tip slip during contact. The shadows, and chalk clouds don't help with this perception. I will reserve judgment until I can shoot some video at higher frame rates and/or better resolutions and/or with better lighting.<hr /></blockquote>Dr. Dave,

Yes, I don't think we should draw any long range conclusions either. Thanks for the stills; it's a very nice arrangement for comparison purposes. Turning the brightness and contrast up on the videos helps too.

Looking at both these and the videos, it still looks pretty obvious (to me) that A.19 is showing considerable slip compared to A.18. I'm judging this mainly from where the edge of the ferrule is pointing relative to where the ring (chord in profile) intersects the edge of the cueball. Call this pont "P". In A.19, after only 4 or 5 frames after initial contact, the ferrule's edge is just about lined up with P, whereas in A.18, it never gets there (see the last two snapshot frames). I don't know if Mac is seeing the same thing, but he apparently agrees for this or other reasons.

Since point P gets pretty blurry and ill-defined in A.18, which I take to be the leading edge of the smear, some subjectivity and judgement does enters in. But even allowing for a little indeterminacy here, I still think there's a large enough difference between the two videos to be fairly certain that slip is taking place.

(Though I might be verging on mule-headedness here.)

Jim

wolfdancer
04-21-2007, 01:16 PM
Thanks, Jim....I'll see if that is available.
There is an out of print book "Quantum Golf"...I think the
concepts would adapt nicely, to pool

Jal
04-21-2007, 02:21 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Thanks, Jim....I'll see if that is available.
There is an out of print book "Quantum Golf"...I think the
concepts would adapt nicely, to pool <hr /></blockquote>And thanks Wolfdancer for your earlier book recommendation (I'll probably have a go at it), and for the reference to Zeno's paradoxes - I just read some interesting articles on them. I thought that calculus, ie, the concept of 'limit', had pretty much disposed of them....but maybe not so fast here!

Jim