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View Full Version : cue tip, squirt, & friction insight and questions



dr_dave
02-23-2006, 04:38 PM
Here's an image from some high-speed video filmed by a group from Austria a couple of years ago:

http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/Austrian_HSV_image.gif

The full video clip can be viewed at HSV A.76 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76.htm) (it is the third clip in the sequence). The video was shot at 2000 frames per sec with a high-resolution color camera.

FYI, the Austrian group's work was discussed some in a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&Board=ccb&Number=182561&page =0&view=collapsed&sb=5&o=&vc=1). Also, Bob Jewett wrote a nice article about the group's work in his May '05 BD article (http://www.sfbilliards.com/articles/2005-05.pdf).

I've collected a sequence of images from the video clip and have made them available in MS Word (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/Austrian_HSV_stills.doc) and PDF (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/Austrian_HSV_stills.pdf) formats. The MS Word file is large (1.7 MB), but it is very useful. If you page down through the file to load all of the images, you can then use the scroll bar to simulate a flip-book animation. The faster you scroll, the faster the simulated "video" plays. The images are 1/2000 second (0.0005 or 5 ten-thousandths of a second) apart.

Here are some observations, insights, and questions from the collection of stills:

- The tip is probably relatively soft based on the contact time and amount of deformation. Contact lasts about 4 frames (over frames 3-6), which corresponds to about two thousandths (0.002) of a second. See a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&Board=ccb&Number=201666&page =0&view=collapsed&sb=5&o=&vc=1) for more info.

- The cue tip seems to stay in contact with the ball as the ball starts to rotate, which might contribute to the amount of cue stick deflection. So should a harder tip (with less contact time) exhibit less cue ball squirt? I don't think this is the case (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&Board=ccb&Number=201674&page =0&view=collapsed&sb=5&o=&vc=1) for more info).

- With better friction between the cue tip and the ball, I would expect there to be less squirt (because there would be less slip and a straighter resulting impulse). I would think that alternative materials for the tip and chalk might help reduce squirt, but I'm not aware of any studies that have been done in this regard. Maybe, in addition to reducing shaft end-mass (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&Board=ccb&Number=176714&page =0&view=collapsed&sb=5&o=&vc=1) for more info), cue stick manufacturers can try to develop better tips that might also help reduce squirt.

- The cue tip had an excessive amount of chalk on it (as evidenced by the pre-impact chalk trail through the air and by the huge chalk cloud after impact).

I look forward to reading the thoughts, ideas, and information from others concerning the images and some of the observations above.

Regards,
Dave

Bob_Jewett
02-23-2006, 06:16 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Here's an image from some high-speed video filmed by a group from Austria a couple of years ago:

http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/Austrian_HSV_image.gif

... <hr /></blockquote>
When I first saw this deformation of the tip, I thought it must be some special, extra thick tip just to emphasize the effect, but Andreas Efler (the shooter in the clips) assured me that it was just his regular Moori tip.

I think the ball always begins rotating while the tip is on it, and that there is negligible slip of the tip on the ball for any normal shot. At the instant the tip leaves the ball (during spin shots) the spin reaches its peak value.

Cornerman
02-24-2006, 07:48 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>
- With better friction between the cue tip and the ball, I would expect there to be less squirt (because there would be less slip and a straighter resulting impulse). <hr /></blockquote>Good post. Did you actually observe slip? I didn't see it.

Fred

SpiderMan
02-24-2006, 08:43 AM
Fascinating - thanks for hosting these videos so we can all have a look.

SpiderMan

dr_dave
02-24-2006, 09:04 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>When I first saw this deformation of the tip, I thought it must be some special, extra thick tip just to emphasize the effect, but Andreas Efler (the shooter in the clips) assured me that it was just his regular Moori tip.<hr /></blockquote>
Bob, thanks for the info. I was also a little shocked by the amount of deformation. It amazes me that tips can withstand this amount of abuse and retain their shape and resilience so well.

I've also sent an e-mail to Robert Leitner (the Austrian guy with the camera), asking him to contribute to our discussion here if he has any additional info or insight.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>I think the ball always begins rotating while the tip is on it<hr /></blockquote>
Agreed.

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>and that there is negligible slip of the tip on the ball for any normal shot.<hr /></blockquote>
This, I'm not so sure about. If there were no slip at all (at a micro or macro scale), I would expect very little or no squirt (or maybe even negative squirt).

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>At the instant the tip leaves the ball (during spin shots) the spin reaches its peak value.<hr /></blockquote>
Sounds reasonable to me and I think I agree with you; although, Coriolis believed otherwise (see my October '05 article (http://www.engr.colostate.edu/~dga/pool/bd_articles/oct05.pdf) for more info).

Regards,
Dave

Billy_Bob
02-24-2006, 09:12 AM
FYI...

"Predator research has clearly shown that a dime radius (or shape of a dime) will produce 5 percent to 10 percent less cue ball deflection than the more commonly used nickel shape. The cue ball deflection is reduced because the dime radius centralizes the hit to the center, or strong part, of the shaft."

[And I think Predator recommends a medium hardness tip, but I am not sure on that???]

See "Shape Your Tip" 3/4 way down page...
http://www.predatorcues.com/predator_cues_tech_tips.html

Billy_Bob
02-24-2006, 09:25 AM
Also I would like to add that I thought a very soft Elk Master tip played quite a bit different from other tips.

And when using a very soft Elk Master tip and shooting a very fast hit like a hard bank shot, the tip would have a concave dent in it after shooting (like above).

And it seems to me a Moori Q Hard tip has similar "gripping or friction qualities" as a soft Elk Master.

So maybe some tips "squish in more" conforming to the shape of the ball more than other tips. And maybe this would make them play differently.

Of course I am not a robot, so my testing of tips is not very scientific in the least.

Also if anyone is interested in experimenting with various tips, following is all sorts of tip replacement tools. Learn to replace tips on a cheap cue first...

http://www.poolndarts.com/index.cfm/fuseaction/Catalog.Category/categoryID/46.cfm?CFID=1550405&amp;CFTOKEN=1de306337e6f2c10-4D7739B0-D61C-4F06-BC47C3401E62078D

dr_dave
02-24-2006, 09:25 AM
<blockquote><font class="small">Quote Cornerman:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>
- With better friction between the cue tip and the ball, I would expect there to be less squirt (because there would be less slip and a straighter resulting impulse). <hr /></blockquote>Good post.<hr /></blockquote>
Thank you Fred. That means a lot to me coming from you.
<blockquote><font class="small">Quote Cornerman:</font><hr>Did you actually observe slip? I didn't see it.<hr /></blockquote>
I think the evidence from the images and video is inconclusive on this. I can sometimes convince myself there is slip. I can also see why one might think, after viewing the images, that there is no slip. What we need is an even better camera (e.g., 50,000 frames per sec with high resolution and fast aperture time), a closer up view of the contact area, and a cue ball with more markings. I wish I had such a dream camera.

I have some close-up shots filmed at 3000 frames per second (a little faster than the images posted here), but the resolution is not as good, and there is image blurring (I think, due to poor effective aperture times). The clips can be found at HSV A.13 - A.20 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html). That's pretty much the best I can do with my equipment. Some slip is evident (I think) for the non-miscue shots in HSV A.16 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-16.htm) and HSV A.19 (http://http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-19.htm). Also, as I implied in my message to Bob, even if slip were not evident at large scale, there still might be slip on a smaller scale as the tip deforms on the ball during the large-force portion of the impulse.

Regards,
Dave

dr_dave
02-24-2006, 09:27 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> Fascinating - thanks for hosting these videos so we can all have a look.<hr /></blockquote>
You're welcome. I only wish we had even better equipment so all questions could be more easily answered.

Regards,
Dave

dr_dave
02-24-2006, 09:35 AM
<blockquote><font class="small">Quote Billy_Bob:</font><hr>"Predator research has clearly shown that a dime radius (or shape of a dime) will produce 5 percent to 10 percent less cue ball deflection than the more commonly used nickel shape. The cue ball deflection is reduced because the dime radius centralizes the hit to the center, or strong part, of the shaft."<hr /></blockquote>
Billy_Bob, thanks for the quote. I would agree that a smaller radius would help centralize the force and might help minimize sideways and rotational effects (and maybe reduce squirt a little).

<blockquote><font class="small">Quote Billy_Bob:</font><hr>[And I think Predator recommends a medium hardness tip, but I am not sure on that???]<hr /></blockquote>Sounds reasonable to me (based on my comments about contact time), but I'm not sure either (per my previous thread summarizing some video results (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=201674&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1)).

Regards,
Dave

SpiderMan
02-24-2006, 09:45 AM
Dave,

Would the macroscopic effects on ball behavior be similar for slip vs tip deformation?

In other words, if the tip deforms substantially, such that the relative motion of shaft and CB mimics slight slippage of the tip-ball interface, do you think we would observe a similar impact on squirt?

In both cases, the shaft becomes mechanically uncoupled from the ball.

SpiderMan

dr_dave
02-24-2006, 09:54 AM
I think slip would have a much bigger effect than deformation alone. Slip indicates that not enough friction is being generated to support the tangential portion of the impact force. That would cause the resultant impulse direction to be slightly off line from the cue stick.

The deformation changes the geometry a little, but if the friction is there, the forces will still hold better (and result in a straighter impulse?).

Just food for thought,
Dave

<blockquote><font class="small">Quote SpiderMan:</font><hr> Dave,

Would the macroscopic effects on ball behavior be similar for slip vs tip deformation?

In other words, if the tip deforms substantially, such that the relative motion of shaft and CB mimics slight slippage of the tip-ball interface, do you think we would observe a similar impact on squirt?

In both cases, the shaft becomes mechanically uncoupled from the ball.

SpiderMan <hr /></blockquote>

SpiderMan
02-24-2006, 10:05 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> If there were no slip at all (at a micro or macro scale), I would expect very little or no squirt (or maybe even negative squirt).<hr /></blockquote>

Dave,

I can't seem to come up with a scenario that would predict negative squirt, unless you're thinking the CB "clings" to the tip long after normal contact and gets pulled back in that unlikely direction as the shaft oscillates /ccboard/images/graemlins/grin.gif

If I think about conservation of momentum in only one plane, actually only one dimension (left/right as viewed from above the shot), "classical" negative squirt would require the shaft to deflect toward the ball rather than away from it.

For example, in order for right english to result in CB squirt to the right, then the shaft would have to be forced to the left. But the only contact point on the tip is on the left. The normal force is perpendicular to contact - it has no component trying to push the shaft left. Similarly, the friction force (slip or no slip) is parallel to the contact surface, and also has no component to move the shaft to the left.

If I also consider the CB spin, a no-slip situation means the tip is carried to the right, so it can't wind up left of it's origin until after contact expires. If the shaft doesn't wind up on the left, then how would the CB wind up on the right?

SpiderMan

dr_dave
02-24-2006, 10:19 AM
Ok, I agree with you that the possiblility for "negative squirt" might have been an exaggeration. I was just thinking that if the cue tip stayed in solid contact with the cue ball as the ball began to rotate, and if the tip continued to exert significant force during this rotation, then the direction change of the force might be significant. Assuming the end-mass inertial effects were small (compared to the impact forces), the change in direction of the impact force might have an effect. But I agree that this is quite a stretch and probably not likely.

Dave

<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> If there were no slip at all (at a micro or macro scale), I would expect very little or no squirt (or maybe even negative squirt).<hr /></blockquote>

Dave,

I can't seem to come up with a scenario that would predict negative squirt, unless you're thinking the CB "clings" to the tip long after normal contact and gets pulled back in that unlikely direction as the shaft oscillates /ccboard/images/graemlins/grin.gif

If I think about conservation of momentum in only one plane, actually only one dimension (left/right as viewed from above the shot), "classical" negative squirt would require the shaft to deflect toward the ball rather than away from it.

For example, in order for right english to result in CB squirt to the right, then the shaft would have to be forced to the left. But the only contact point on the tip is on the left. The normal force is perpendicular to contact - it has no component trying to push the shaft left. Similarly, the friction force (slip or no slip) is parallel to the contact surface, and also has no component to move the shaft to the left.

If I also consider the CB spin, a no-slip situation means the tip is carried to the right, so it can't wind up left of it's origin until after contact expires. If the shaft doesn't wind up on the left, then how would the CB wind up on the right?

SpiderMan <hr /></blockquote>

Bob_Jewett
02-24-2006, 10:23 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>...
This, I'm not so sure about. If there were no slip at all (at a micro or macro scale), I would expect very little or no squirt (or maybe even negative squirt).
... <hr /></blockquote>
If the front of the shaft moves to the side of the english, as it must if there is no slip, then something must move in the opposite direction to conserve left-right momentum which is initially zero. That something is the cue ball. If there is slip, as during a miscue, there will be more movement of the stick to the side and less slowing of the forward movement of the cue stick (and less forward movement of the cue ball) so there will be more "squirt" but the mechanical process is different.

I think that if slip did occur on most spin shots, they would be nearly uncontrollable. I have never seen any evidence that there is slip on normal spin shots nor does the theory, as I understand it, require any slip. That theory is detailed in http://www.sfbilliards.com/Shepard_squirt.pdf (or http://www.sfbilliards.com/sqrt.htm for a summary).

dr_dave
02-24-2006, 01:42 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>If the front of the shaft moves to the side of the english, as it must if there is no slip, then something must move in the opposite direction to conserve left-right momentum which is initially zero. That something is the cue ball.<hr /></blockquote>
Agreed.
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>If there is slip, as during a miscue, there will be more movement of the stick to the side and less slowing of the forward movement of the cue stick (and less forward movement of the cue ball) so there will be more "squirt" but the mechanical process is different.<hr /></blockquote>
Agreed. However, I wonder if it is possible that the direction of the main impact force might change some during contact with the cue ball (per my reply to Spiderman (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=219631&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1)).

<blockquote><font class="small">Quote Bob_Jewett:</font><hr>I think that if slip did occur on most spin shots, they would be nearly uncontrollable. I have never seen any evidence that there is slip on normal spin shots nor does the theory, as I understand it, require any slip. That theory is detailed in http://www.sfbilliards.com/Shepard_squirt.pdf (or http://www.sfbilliards.com/sqrt.htm for a summary).<hr /></blockquote>I still haven't seen enough conclusive evidence that there is no slip on normal spin shots (per my reply to Fred (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 agree that slip is not required to get squirt. However, I still think squirt could be less if there were less slip (at macro or micro scales). I think that some slip might be observable if we had a much faster camera and were able to zoom up on the contact zone.

I fully agree with Shepard's end-mass theory and arguments, I just still think cue tip and friction properties, which are not included in his theory, still might be pertinent (but I'm not sure).

Regards,
Dave

Jal
02-24-2006, 01:43 PM
Hi Dr. Dave,

On the subject of viewing videos frame by frame, here is some free software that converts .wmv files to .avi (first link) which can then be viewed/edited with VirtualDub (second link). Maybe there is better but I've found it useful in trying to extract data from your videos.

http://www.stoik.com/products/svc/

http://virtualdub.sourceforge.net/

<blockquote><font class="small">Quote dr_dave:</font><hr>...So should a harder tip (with less contact time) exhibit less cue ball squirt? I don't think this is the case (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=201674&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for more info).<hr /></blockquote>It seems to me that this could be the case (less squirt) for the following, but not very justified I'll admit, reasons.

Let's assume that treating the cue as a statically bent cantilever beam might at least give us a very crude approximation of the dynamic situation.

For a static load applied to the end of the beam, the average lateral displacement of the beam's mass (a sort of "center of mass" position) is proportional to the cube of the beam's length. With the reduced contact time of a harder tip, the effective length of the cue is also reduced because of the slow shear propagation, so the lateral mass displacement (endmass) should be less.

However, I think it's the lateral displacement of the tip during contact that is, so to speak, the driving force. For a given displacement of the end of a cantilever, its average lateral mass displacement is independent of its length and is simply proportional to the displacement of its end. So for a given amount of spin applied, and given that a harder tip with its reduced contact time should displace less in the sideways direction during impact, less "endmass" should then be displaced. That is, this should be true if the static treatment is at all indicative of what's going on in the dynamic case.

I don't know much about this and will happly bow to your expertise. My entire knowledge of beams comes from this:

http://www.efunda.com/formulae/solid_mechanics/beams/theory.cfm

which is a particularly good presentation I think.

<blockquote><font class="small">Quote dr_dave:</font><hr>...- With better friction between the cue tip and the ball, I would expect there to be less squirt (because there would be less slip and a straighter resulting impulse). I would think that alternative materials for the tip and chalk might help reduce squirt, but I'm not aware of any studies that have been done in this regard. Maybe, in addition to reducing shaft end-mass (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=176714&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for more info), cue stick manufacturers can try to develop better tips that might also help reduce squirt.<hr /></blockquote>As Bob indicated, I would think that slippage would introduce an element of randomness. While it might be there, I doubt that it's a significant factor. Colin Colenso, who has posted here on occasion but usually on AZB, thinks that this might very well be significant (unless he's changed his mind). But the reduction in squirt that Predator achieves by removing wood seems to argue against this.

However, there seems to be two schools of thought on this. One believes that Predator's pivot point is around 30" or more, the other (Platinum Billiards) believes that it's much shorter than this. Platinum Billiards and apparently many posters arrive at pivot points, in general, much shorter than those in the first camp. Platinum argues that the aim-and-pivot test does not account for throw (the cueball should not stop dead for a straight on hit). But a calculation that I did indicates that this introduces only a very small error, roughly 1/2" in the location for a "typical" position. Can you offer some clarification on all of this?

Jim

dr_dave
02-24-2006, 03:24 PM
<blockquote><font class="small">Quote Jal:</font><hr>On the subject of viewing videos frame by frame, here is some free software that converts .wmv files to .avi (first link) which can then be viewed/edited with VirtualDub (second link). Maybe there is better but I've found it useful in trying to extract data from your videos.

http://www.stoik.com/products/svc/

http://virtualdub.sourceforge.net/
<hr /></blockquote>
Jim,

Thanks for the info. I was planning to look for a utility to convert between video formats for another project I am working on. You just saved me some time. Thanks!

<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>...So should a harder tip (with less contact time) exhibit less cue ball squirt? I don't think this is the case (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=201674&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for more info).<hr /></blockquote>It seems to me that this could be the case (less squirt) for the following, but not very justified I'll admit, reasons.

Let's assume that treating the cue as a statically bent cantilever beam might at least give us a very crude approximation of the dynamic situation.

For a static load applied to the end of the beam, the average lateral displacement of the beam's mass (a sort of "center of mass" position) is proportional to the cube of the beam's length. With the reduced contact time of a harder tip, the effective length of the cue is also reduced because of the slow shear propagation, so the lateral mass displacement (endmass) should be less.

However, I think it's the lateral displacement of the tip during contact that is, so to speak, the driving force. For a given displacement of the end of a cantilever, its average lateral mass displacement is independent of its length and is simply proportional to the displacement of its end. So for a given amount of spin applied, and given that a harder tip with its reduced contact time should displace less in the sideways direction during impact, less "endmass" should then be displaced. That is, this should be true if the static treatment is at all indicative of what's going on in the dynamic case.<hr /></blockquote>
Your arguments sound reasonable; although, I'm not as comfortable applying static equations to complicated impact phenomena. I wish I had a better feel for how the force varies during the contact time and as the cue ball starts to turn. I also wish I had a clearer picture of what the deformation looks like and how much slip occurs (even if only at a small scale in the deformation region). More information and data would help make me more comfortable to make more conclusions. I still think cue tip and friction properties might be important factors, but I don't have any hard data or equations to back up this claim.

<blockquote><font class="small">Quote Jal:</font><hr><blockquote><font class="small">Quote dr_dave:</font><hr>...- With better friction between the cue tip and the ball, I would expect there to be less squirt (because there would be less slip and a straighter resulting impulse). I would think that alternative materials for the tip and chalk might help reduce squirt, but I'm not aware of any studies that have been done in this regard. Maybe, in addition to reducing shaft end-mass (see a previous thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=176714&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1) for more info), cue stick manufacturers can try to develop better tips that might also help reduce squirt.<hr /></blockquote>As Bob indicated, I would think that slippage would introduce an element of randomness. While it might be there, I doubt that it's a significant factor. Colin Colenso, who has posted here on occasion but usually on AZB, thinks that this might very well be significant (unless he's changed his mind). But the reduction in squirt that Predator achieves by removing wood seems to argue against this.<hr /></blockquote>
I don't doubt that end-mass is important. However, I think squirt might be decreased even further with alternative tip materials. I'm not suggesting that there is large macro slipping during typical impacts. I'm suggesting that there might be a small amount of slip (not easily seen with the currently available video images); and if this slip were reduced, the squirt might also be reduced.

<blockquote><font class="small">Quote Jal:</font><hr>However, there seems to be two schools of thought on this. One believes that Predator's pivot point is around 30" or more, the other (Platinum Billiards) believes that it's much shorter than this. Platinum Billiards and apparently many posters arrive at pivot points, in general, much shorter than those in the first camp. Platinum argues that the aim-and-pivot test does not account for throw (the cueball should not stop dead for a straight on hit). But a calculation that I did indicates that this introduces only a very small error, roughly 1/2" in the location for a "typical" position. Can you offer some clarification on all of this?<hr /></blockquote>I don't have anything to add at this time.

Regards,
Dave

cushioncrawler
02-24-2006, 04:04 PM
Dr Dave -- thanks for the pics -- some of my thorts.
1. If one measures from the sides and tops of pictures, uzing a rule, on the face of the monitor, there is clearly lots of slip evident in frames 3 and 4 (i can send my measurements if u wish). This tends to confirm my old theoryz -- that the tip initially slips and abrades the ball -- hence the high friction between tip and ball.

2. I like hard tips -- they squirt less. I used to uze leather tips, hardened in a vice, or by hitting a brick. But i couldnt get these for some years, so i learnt to use elkmaster (and blue diamond), hardened in a vice. Every snooker and billiards player that i know (in Victoria) use elk or blue diamond (are these made any more) -- one player that i know (in New South Wales) allso (like me) likes hard leather tips (french tips he sez).

3. I have to talk about the time that i won a screwing contest. The red sat on The Spot on a 12' by 6' table (ie near the end cushion) and the Qball on the baulk-line -- u screw back off the red, back towards the baulk-line. The second placegetter screwed back about 12" -- i screwed back to exactly halfway between the center spot and the baulk-line. This was on an oldish and slowish cloth -- ie it was not one of those fast new slippery cloths on which some players say that they can screw back into baulk (alltho i have yet to see any of them do it -- my best is 2" short of baulk). The reason i mention this is this -- i was the only one to use a real leather tip -- it was so old and compressed and worn that the dime shape included much of the (fibre) ferrule. The cue was one-piece, and more flexible that average. But i wouldnt recommend uzing such a (small) tip -- when too small, u get a lot of missed-cues, the shear strength of the leather iz exceeded and it fails -- but a small hard tip is lovely for feel (for English billiards).

4. History -- miscue was earlyr called miss-cue, and was earlyr called missed-cue.

5. I think that Squirt is difficult to define and difficult to measure (for side-spin here). The bed reaction and swerve affect squirt in the realworld. But the only time that i ever measured squirt, i meazured "pure" squirt, with the object ball hanging on a cotton pendulum, to remove any bed reaction.

6. Yes, there is a lot of chalk flying off the tip. This reminds me that i am allways amuzed by the sight of pool players drilling for oil in their cube of chalk -- there must be way too much chalk on the tip -- they should klunk the excess off on a leg of the table. I have never in my life seen a snooker player or billiards player drill for oil -- the favoured technique is to very gently wipe the cube across the tip for every shot. This doez 2 things -- it minimizes the amount of excess chalk -- and it ensures a consistent squirt. I think that if u drill for oil and play a shot uzing sidespin -- and then repeat the same shot without chalking up -- u will get a different result (squirt). Hence, if u like to drill for oil -- at least do it for every shot.

7. Regarding the spin (side or screw) being at a maximum at the moment the tip leaves the ball -- this is mostly correct most of the time. But it reminds me of the time i did some tests uzing a very thick stiff cue -- when i hit the cueball well above center, in my normal fashion, i couldnt get much roll (ie topspin) -- the cueball stunned off the objectball unless the objectball was a long way away. Here, i reckon, by the end of contact, the stiff cue was sick of bending, and it was allready thinking about going back the other way. Hmmmmmmmm.

dr_dave
02-27-2006, 09:54 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Dr Dave -- thanks for the pics -- some of my thorts.
1. If one measures from the sides and tops of pictures, uzing a rule, on the face of the monitor, there is clearly lots of slip evident in frames 3 and 4 (i can send my measurements if u wish). This tends to confirm my old theoryz -- that the tip initially slips and abrades the ball -- hence the high friction between tip and ball.<hr /></blockquote>
I'm not so sure the video evidence is conclusive concerning slip. Have you accounted for rotation of the ball in your measurements? I don't see how, because there are no easy markers to visualize.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>2. I like hard tips -- they squirt less. I used to uze leather tips, hardened in a vice, or by hitting a brick. But i couldnt get these for some years, so i learnt to use elkmaster (and blue diamond), hardened in a vice. Every snooker and billiards player that i know (in Victoria) use elk or blue diamond (are these made any more) -- one player that i know (in New South Wales) allso (like me) likes hard leather tips (french tips he sez).<hr /></blockquote>
Do you have some data that show that harder tips cause less squirt? If so, please share it with us.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>5. I think that Squirt is difficult to define and difficult to measure (for side-spin here). The bed reaction and swerve affect squirt in the realworld. But the only time that i ever measured squirt, i meazured "pure" squirt, with the object ball hanging on a cotton pendulum, to remove any bed reaction.<hr /></blockquote>
I like your pendulum idea. Good one. Again, if you have some interesting results, please share them with us.

Regards,
Dave

SpiderMan
02-27-2006, 04:51 PM
Jal,

Windows Moviemaker, which is bundled as part of windows, will also output .avi files and has frame-by-frame viewing/editing options. I learned to use it because I can count on it being available at 'most any workstation.

SpiderMan

cushioncrawler
02-27-2006, 06:19 PM
Measuring pdf frames 1 to 8, at 150%, on the face of my monitor, i measure that the qtip moovz down 2.5mm (not real mm) between frames 2 and 3 (tip contact looks to start in frame 2 and end in frame 7). In the same time, the ball moovz forward 0.0mm (there must have been some ball forward moovment, but it didnt show). Hence, the tip woz slipping. My measurements were from the left of picture window, and from the top of window. Between frame 3 and 4, the tip mooved down an additional 2.6mm, while the ball mooved forward 1.9mm -- this suggests some slippage allso. Between frame 4 and 5, the figurez are 4.0mm and 4.2mm -- which perhaps showz zero slippage.

There iz no doubt in my mind that squirt iz less with a hard tip, especially a small-hard tip. But i dont think that i have ever meazured this. The acid test for English billiardz iz the long-jenny from in-hand -- this loozer iz played with max check-side (inside english). I know that, over many yearz, uzing the one cue, whenever i tried to uze a soft tip (elkmaster), or whenever i used a new leather tip without firstly vicing it, i felt that i had to aim towards the door of the lady'z toilet to get the shot (long-jenny).

Likewize (starting a new-old arguement), i know that when i uze a light old-fashioned 2-finger grip, i get less squirt (contrary to Shepard and otherz). And, in addition, the looseness of the way the cue sits in your bridge (i allwayz uze a Vee) affects the squirt. But i know that none of this accords with what iz written by otherz. So, i have allwayz wondered what sort of grip and bridge iz uzed by Iron-Willie and other robots????

The only (pure) squirt tests that i did, uzing the objectball hanging on a cotton pendulum, was to simply satisfy myself that a stiff cue squirts more (120mm) than a medium cue (100mm), which squirts more than a soft cue (80mm). And that a slow shot squirts about 25mm wider than a fast shot. This was all very rough -- it would have been eezyr and more accurate if i had had an assistant. The next time i do the tests (pendulum), i will try to check the affect of the grip and bridge.

Jal
02-28-2006, 12:29 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>... Measuring pdf frames 1 to 8, at 150%, on the face of my monitor, i measure that the qtip moovz down 2.5mm (not real mm) between frames 2 and 3 (tip contact looks to start in frame 2 and end in frame 7). In the same time, the ball moovz forward 0.0mm (there must have been some ball forward moovment, but it didnt show). Hence, the tip woz slipping. My measurements were from the left of picture window, and from the top of window. Between frame 3 and 4, the tip mooved down an additional 2.6mm, while the ball mooved forward 1.9mm -- this suggests some slippage allso...<hr /></blockquote>I'll second your observation here in case no one else has bothered to measure it. The tip does appear to be moving in a straight line (or nearly so) between frames 1 &amp; 2, so that more or less eliminates rotation of the cue as a whole.

Jim

cushioncrawler
02-28-2006, 02:24 PM
Hi Jim -- Yes, the figures for the downwards moovment (mm -- not real mm) of the qtip, allready have the initial downward moovment (ie between frames 1 &amp; 2) deducted. So, the figurez allready exclude the downward moovment due to the (obvious) angle of the cue, and allso any due to initial rotation of some sort (if any - az u mention -- alltho i hadnt thort of this).

If there iz (woz) some initial cue (ie tip) clockwize rotation, then my figurez for slippage should in fact be increased ( ie my slippage understates the true slippage) -- just a subtle minor matter, due only to my way of doing the correction (and hence invizible to all but me).

I neglected to say that there appearz to be a small chalky smudge on the ball, above the tip, in frame 2, and this smudge iz longer in frame 3 (or woz it 3 &amp; 4?) -- if so, a smudge would proov slip -- but the smudge might be difficult to differentiate from the beginningz of the giant chalky explozion vizible later. madMac.

dr_dave
03-03-2006, 10:34 AM
Spiderman,

Thanks for the info. I just used Movie Maker to edit HSV A.76 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76.htm). I easily isolated the portion of the clip of interest (HSVA-76_Austrian_HSV_tip_closeup.wmv (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76_Austrian_HSV_tip_closeup.wmv)). I also was easily able to convert this to an AVI file (using "DV-AVI (NTSC)" under the movie save options). I plan to try to analyze the clip in detail using a new package I just got called VideoPoint, which allows for easy motion analysis of AVI files (unfortunately, the package can't read WMV files directly). I hope to use this package to get useful data from many of my past and future clips. I think somebody on the CCB also recommended this software to me. Whoever it was, thank you!

For those who are interested, Movie Maker is accessible under the "Start" menu, under "All Programs," under "Accessories" as "Windows Movie Maker."

Regards,
Dave

<blockquote><font class="small">Quote SpiderMan:</font><hr> Jal,

Windows Moviemaker, which is bundled as part of windows, will also output .avi files and has frame-by-frame viewing/editing options. I learned to use it because I can count on it being available at 'most any workstation.

SpiderMan <hr /></blockquote>

dr_dave
04-19-2007, 11:51 AM
FYI, the isolated clip of the close-up of the tip contact can now be found at HSV A.76a (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76a.htm).

Sorry for the confusion,
Dave
<blockquote><font class="small">Quote dr_dave:</font><hr> Spiderman,

Thanks for the info. I just used Movie Maker to edit HSV A.76 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76.htm). I easily isolated the portion of the clip of interest (HSVA-76_Austrian_HSV_tip_closeup.wmv (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-76_Austrian_HSV_tip_closeup.wmv)). I also was easily able to convert this to an AVI file (using "DV-AVI (NTSC)" under the movie save options). I plan to try to analyze the clip in detail using a new package I just got called VideoPoint, which allows for easy motion analysis of AVI files (unfortunately, the package can't read WMV files directly). I hope to use this package to get useful data from many of my past and future clips. I think somebody on the CCB also recommended this software to me. Whoever it was, thank you!

For those who are interested, Movie Maker is accessible under the "Start" menu, under "All Programs," under "Accessories" as "Windows Movie Maker."

Regards,
Dave

<blockquote><font class="small">Quote SpiderMan:</font><hr> Jal,

Windows Moviemaker, which is bundled as part of windows, will also output .avi files and has frame-by-frame viewing/editing options. I learned to use it because I can count on it being available at 'most any workstation.

SpiderMan <hr /></blockquote> <hr /></blockquote>