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Bob_Jewett
03-19-2007, 10:04 AM
Over in that other on-line board, we have been discussing two impossible shots, a cross-side bank shot and a rather tough spot shot.

In the bank, the cue ball is frozen to the side cushion on the line, and the object ball is frozen to the same side cushion just the other side of the side pocket. The shot is to bank the object ball one-cushion cross-side.

In the cut shot, the object ball is on the spot. The cue ball is near one foot pocket. The shot is to cut the object ball into the other foot pocket. The cut angle is more than 90 degrees.

There are players who will bet on making these shots. Save your money. Here is a post from that other board.

Well, I got seven clips off the VHS tape, but they're pretty bad quality. Probably due to the built-into-the-TV VCR I was using at the pool hall. The one with Vernon Elliott's bank shot is http://www.youtube.com/watch?v=vEyCQSN8qU0 and the one with the impossible cut shot is http://www.youtube.com/watch?v=uHf3o6FtNnQ but it may take a while for them to be available.

BRussell
03-19-2007, 10:36 AM
Wow. I have enough trouble making a 75 degree cut.

But I have a question about that cut shot: I thought using outside english like that was supposed to make the cut "true," that it would simply cancel out cut-induced throw.

Apparently not.

dr_dave
03-19-2007, 11:49 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> Over in that other on-line board, we have been discussing two impossible shots, a cross-side bank shot and a rather tough spot shot.

In the bank, the cue ball is frozen to the side cushion on the line, and the object ball is frozen to the same side cushion just the other side of the side pocket. The shot is to bank the object ball one-cushion cross-side.

In the cut shot, the object ball is on the spot. The cue ball is near one foot pocket. The shot is to cut the object ball into the other foot pocket. The cut angle is more than 90 degrees.

There are players who will bet on making these shots. Save your money. Here is a post from that other board.

Well, I got seven clips off the VHS tape, but they're pretty bad quality. Probably due to the built-into-the-TV VCR I was using at the pool hall. The one with Vernon Elliott's bank shot is http://www.youtube.com/watch?v=vEyCQSN8qU0 and the one with the impossible cut shot is http://www.youtube.com/watch?v=uHf3o6FtNnQ but it may take a while for them to be available.<hr /></blockquote>Bob,

Thanks for the video links. I think the clips help reinforce the arguments that throw and spin transfer do in fact exist (for the hard-core nonbelievers out there).

Dave

Billy_Bob
03-19-2007, 12:08 PM
OK I'm totally perplexed!

With the first shot (Elliott's bank), how is he shooting this? What is going on? How is this possible?

SpiderMan
03-19-2007, 12:14 PM
I can't seem to view the video, but from Bob's description of the setup it would seem that the CB would have to have enough spin such that it's contact point with the frozen OB is actually moving back toward the shooter at the moment of contact. Some people refer to this as "retrograde spin", though that's not a common term.

Without masse, it would seem that retrograde spin would also be responsible for making the 90+ degree cut.

SpiderMan

SpiderMan
03-19-2007, 12:17 PM
<blockquote><font class="small">Quote BRussell:</font><hr> Wow. I have enough trouble making a 75 degree cut.

But I have a question about that cut shot: I thought using outside english like that was supposed to make the cut "true," that it would simply cancel out cut-induced throw.

Apparently not. <hr /></blockquote>

In this case, the shooter is using "much more than enough" outside spin, to throw the ball even a little more in the direction it is being cut.

SpiderMan

dr_dave
03-19-2007, 01:16 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> I can't seem to view the video, but from Bob's description of the setup it would seem that the CB would have to have enough spin such that it's contact point with the frozen OB is actually moving back toward the shooter at the moment of contact. Some people refer to this as "retrograde spin", though that's not a common term.

Without masse, it would seem that retrograde spin would also be responsible for making the 90+ degree cut.<hr /></blockquote>Agreed. Both shots are using extreme outside English. Squirt and swerve aim compensation must be near perfect (i.e., film numerous attempts, adjust your aim after every miss, and edit out all of the misses).

The beauty of these examples is that swerve cannot be used to "help" make the shots, because the swerve is in the wrong direction (i.e., it doesn't help reduce the cut angle). The throw (with the cut shot) and the spin transfer (with the bank shot) provide enough action to allow for a smaller cut angle (i.e., less than 90 degrees) on both shots.

Dave

dr_dave
03-19-2007, 01:31 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr>... the CB would have to have enough spin such that it's contact point with the frozen OB is actually moving back toward the shooter at the moment of contact. Some people refer to this as "retrograde spin", though that's not a common term.<hr /></blockquote>FYI to Billy_Bob and others, my January '07 article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2007/jan07.pdf) does a fairly good job at explaining and illustrating how "retrograde spin" and backwards throw is possible. For close to a 90-degree cut, a "gearing" (throw-less) amount of outside English is about 80%. So to achieve the retrograde (back-throw) spin, you need more than 80% outside English.

Regards,
Dave

Bob_Jewett
03-19-2007, 01:45 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> I can't seem to view the video, but from Bob's description of the setup it would seem that the CB would have to have enough spin such that it's contact point with the frozen OB is actually moving back toward the shooter at the moment of contact. Some people refer to this as "retrograde spin", though that's not a common term.

Without masse, it would seem that retrograde spin would also be responsible for making the 90+ degree cut.<hr /></blockquote>Agreed. Both shots are using extreme outside English. Squirt and swerve aim compensation must be near perfect (i.e., film numerous attempts, adjust your aim after every miss, and edit out all of the misses).... <hr /></blockquote>
Yes, I went for retrograde spin (my term). I'm convinced that it's essential for both shots. According to simple physics (without spin) both shots are impossible. I needed about 100 tries for each shot.

On that other BB, one poster suggested that there was a double kiss on the bank shot. I don't think so. If there were, the object ball would never get back across the table. The argument in favor of this is the apparent path of the cue ball on the shot that works.

As for being unable to view the videos, if you can see anything at youtube, you should be able to see these clips. Search on "vernon elliott" if you can't get to the clip with the posted link.

BRussell
03-19-2007, 01:47 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> For close to a 90-degree cut, a "gearing" (throw-less) amount of outside English is about 80%. So to achieve the retrograde (back-throw) spin, you need more than 80% outside English. <hr /></blockquote> What do these percentages mean? Does it mean 80% of maximum, or 80% away from the middle of the cueball, or what?

Bob_Jewett
03-19-2007, 01:49 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> OK I'm totally perplexed!

With the first shot (Elliott's bank), how is he shooting this? What is going on? How is this possible?
<hr /></blockquote>
As others have pointed out, it's just retrograde outside. The reason that people don't normally encounter this sort of thing is that very, very few people are willing to hit the ball far enough from center to get retrograde side spin. Carom billiards teaches you that skill. Of course all the spin causes aiming problems -- a thin hit on a ball two diamonds away -- but my Balabushka has less squirt than a typical Predator.

wolfdancer
03-19-2007, 02:40 PM
"Yes, I went for retrograde spin (my term). I'm convinced that it's essential for both shots. According to simple physics (without spin) both shots are impossible. I needed about 100 tries for each shot."
"The difficult is done at once; the impossible takes a little longer"
On one of your attempts there was a scratch in the opposite side....that proves (to me) that you really put max spin on the ball. doubt if many of us here have that kind of stroke...
Joe Tucker makes the bank 5 times in a row on video...?

dr_dave
03-19-2007, 02:49 PM
<blockquote><font class="small">Quote BRussell:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> For close to a 90-degree cut, a "gearing" (throw-less) amount of outside English is about 80%. So to achieve the retrograde (back-throw) spin, you need more than 80% outside English. <hr /></blockquote> What do these percentages mean? Does it mean 80% of maximum, or 80% away from the middle of the cueball, or what? <hr /></blockquote>My July '06 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/july06.pdf) explains and illustrates "tips" of English and shows why percentage English is a better measure. 80% is relative to the maximum tip offset allowed (at about half of the ball, beyond which miscues result). So to get retrograde back-throw, your tip needs to be offset more than 80% from the center, towards the miscue limit. Again, the article has good illustrations, examples, and explanations.

Regards,
Dave

Bob_Jewett
03-19-2007, 03:05 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> ...On one of your attempts there was a scratch in the opposite side....that proves (to me) that you really put max spin on the ball. doubt if many of us here have that kind of stroke... <hr /></blockquote>
Usually when I missed the ball entirely, the cue ball hit on the harder side of the opposite side pocket. On the shot you noted (the second shot on the clip?) I miscued. Note how slowly the ball was travelling.

As for Joe Tucker making the bank five times in a row, which video was it and are you sure it was the same shot?

wolfdancer
03-19-2007, 03:30 PM
Sorry, my numbers were off...it's 3 out of 4, with 1 hanger.
I've seen the video, and Scott Lee saw it in person (?)....just can't find the link.

ceebee
03-19-2007, 03:33 PM
Do you reckon the object ball is "pinched " into the side cushion, so that it is moved toward the opposite side pocket?

Qtec
03-19-2007, 07:08 PM
Outside E?
Mmmmm. I think this is one of those rare situations where just saying LHS would be more appropriate. I know what you mean tho.

This is reallly a Q for you Dave.
I was surprised that you dismissed swerve so quickly.
IMO, [ and I was surprised as anyone to see that ball go in- I didn't think it was possible- you learn every day! ]there must be a reason why the player HAS to shoot the QB into the rail to make the shot. Maybe the QB makes a curve? and with the added spin ?, the impossible becomes possible.

In JT's vid he makes the shot when the OB is 3rd ball past the mid pocket?!!
I'm not easily impressed but.........friggin hell. !!! Some of those shots!






Qtec ......

Bob_Jewett
03-19-2007, 07:47 PM
<blockquote><font class="small">Quote ceebee:</font><hr> Do you reckon the object ball is "pinched " into the side cushion, so that it is moved toward the opposite side pocket? <hr /></blockquote>
I think that the cue ball hits the object ball only once, and that the useful action is from the throw/transferred spin. The test for this would be to put the object ball 2mm off the cushion where there is no chance for any funny action with the two balls and the cushion all touching at once.

TennesseeJoe
03-19-2007, 09:11 PM
<blockquote><font class="small">Quote Qtec:</font><hr> Outside E?
there must be a reason why the player HAS to shoot the QB into the rail to make the shot. Maybe the QB makes a curve? and with the added spin ?, the impossible becomes possible.

!
What do you mean by this???





Qtec ...... <hr /></blockquote>

Bob_Jewett
03-19-2007, 09:20 PM
<blockquote><font class="small">Quote Qtec:</font><hr> ... there must be a reason why the player HAS to shoot the QB into the rail to make the shot. ... Qtec ...... <hr /></blockquote>
As TN Joe, said, hunh? For the bank shot, I was shooting the cue ball away from the cushion for the fairly thin hit on the object ball. The only time the cue ball went into the cushion was on miscues, which were quite frequent but never came close to making the shot.

Swerve makes the shots harder, or at least that's the way it feels to me. Try the shots a few times and let us know whether you prefer an elevated or a level cue.

TennesseeJoe
03-19-2007, 09:29 PM
Bob,
Thanks for your professional approach to this shot. I talked to Vern several times but could not get the information from him.

Did you use center left English? Was the shot hit very hard? It is hard to tell on the video.

Thanks again.

Tennessee Joe

Bob_Jewett
03-19-2007, 09:45 PM
<blockquote><font class="small">Quote TennesseeJoe:</font><hr> ... Did you use center left English? Was the shot hit very hard? It is hard to tell on the video.... <hr /></blockquote>
Slightly below center, hoping to have the equivalent of a stun shot at the object ball. I play both shots at about the same speed, and you can see in the cut shot how far the cue ball goes around the table -- five cushions but only barely. The table has cushions that are maybe a little below average in bounciness, but not by much.

dr_dave
03-19-2007, 10:12 PM
<blockquote><font class="small">Quote Qtec:</font><hr> Outside E?
Mmmmm. I think this is one of those rare situations where just saying LHS would be more appropriate. I know what you mean tho.<hr /></blockquote>Fair enough.

<blockquote><font class="small">Quote Qtec:</font><hr>This is reallly a Q for you Dave.
I was surprised that you dismissed swerve so quickly.
IMO, [ and I was surprised as anyone to see that ball go in- I didn't think it was possible- you learn every day! ]there must be a reason why the player HAS to shoot the QB into the rail to make the shot. Maybe the QB makes a curve? and with the added spin ?, the impossible becomes possible.<hr /></blockquote>Q,

As Bob has pointed out, you are off on this one. The CB is not hit into the rail, and swerve does not help. In fact, because of bottom-left English and cue stick elevation, the CB actually curves to the left a little, which makes the shot even tougher than it would be without the swerve.

Regards,
Dave

cushioncrawler
03-20-2007, 01:21 AM
Bob -- What is the best rezult(s) for that miracle double that u can get uzing....
..... Rolling,
..... Screw,
..... Stun,
..... Inside English plus stun.

And, as u said, what is the best rezult (uzing OE plus stun) with OB and qball both say 2mm off the cushion.

Can u do a slo-mo from overhead, uzing a marked OB to show sidespin.

I suspect that hitting the cushion at the same spot haz a lot to do with the rezult. 10 or 20 attempts in quick time must make some sort of temporary dimple in the rubber. And, 100 or 200 attempts over a few days likewize, ie one'z favorit trick-shot from one'z favorit pozzy. But, if one can sometimes get the shot allmost first shot on a "new" table, then that would rule out any "training" of the cushion. Karnt wait to try it on a 12' table. madMac.

Jal
03-20-2007, 07:37 AM
Post deleted by Jal

Jal
03-20-2007, 07:41 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr>In this case, the shooter is using "much more than enough" outside spin, to throw the ball even a little more in the direction it is being cut.

SpiderMan <hr /></blockquote>The "ideal" spin/speed ratio, at least for the cut shot, and for balls that conform to Dr. Dave's equations, is about 1.05. This is just slightly more than "gearing" spin with a ratio of 1, and considerably less than "maximum" spin with a ratio of 1.25. Even if the balls have double the amount of friction used in the theory, the ratio which would yield the most throw only goes up to about 1.10. For 1.25 to be ideal, the coefficient of friction would have to be about 0.4, which I think could only happen if skid/kick/cling takes place. The above are based on a cueball speed of 10 mph, which is pretty fast for the amount of english applied, and a geometric cut angle (w/o throw) of about 85 degrees.

But exactly where to contact the cueball to produce a particular ratio is problematic. First, squirt reduces the apparent ratio. If, for instance, the squirt angle is 2.5 degrees, then to get an actual ratio of 1.05 you would need to contact the ball at an offset corresponding to 1.15 (ie, about halfway between perfect gearing and the miscue limit).

Against this is the fact that the ball rotates during impact, increasing the initial offset and ratio. To know how much of an effect this is you would probably need to do a numeric integration. But this is complicated by the shape of the force vs time curve (non-sinusoidal) which is also severely nonsymmetric about the midpoint of the contact period.

But given the two opposing effects, it's possible that the initial tip offset which produces an actual ratio of 1.05 might not be much different than the apparent one (ie, just slightly more than 80% of max english at .42R). If ball rotation increases the effective offset more than squirt reduces it, then the initial tip offset would have to be even less than this. Why don't you or somebody work this out tonight and report back.

Jim

Billy_Bob
03-20-2007, 11:06 AM
Another question...

How *exactly* is the object ball set up?

Frozen to cushion?
Looks frozen but a "paper space" away from cushion?
Slightly off cushion? [How far?]

Seems to me this could be one of those trick shots where setting up the object ball just right might mean the difference between making it or not?

dr_dave
03-20-2007, 11:29 AM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Another question...

How *exactly* is the object ball set up?

Frozen to cushion?
Looks frozen but a "paper space" away from cushion?
Slightly off cushion? [How far?]

Seems to me this could be one of those trick shots where setting up the object ball just right might mean the difference between making it or not?<hr /></blockquote>I don't think setup is critical, and I think the shot could be made whether the object ball is frozen to the rail or not. The effects are the same as with the shot in NV A.21 (http://www.engr.colostate.edu/~dga/pool/normal_videos/new/NVA-21.htm); although, this extreme example (http://www.youtube.com/watch?v=vEyCQSN8qU0) is much tougher to execute (because the hit must be near perfect, with lots of English, for it to work).

Regards,
Dave

Bob_Jewett
03-20-2007, 11:39 AM
<blockquote><font class="small">Quote Billy_Bob:</font><hr> Another question...

How *exactly* is the object ball set up?

Frozen to cushion?
Looks frozen but a "paper space" away from cushion?
Slightly off cushion? [How far?]

Seems to me this could be one of those trick shots where setting up the object ball just right might mean the difference between making it or not?
<hr /></blockquote>
The object ball for the bank shot is frozen to the cushion (the cloth is old enough to have an effective rail groove) and completely on the flat part of the cushion -- not partly touching the corner of the side pocket.

Deeman3
03-20-2007, 12:08 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote Billy_Bob:</font><hr> Another question...

How *exactly* is the object ball set up?

Frozen to cushion?
Looks frozen but a "paper space" away from cushion?
Slightly off cushion? [How far?]

Seems to me this could be one of those trick shots where setting up the object ball just right might mean the difference between making it or not?<hr /></blockquote>I don't think setup is critical, and I think the shot could be made whether the object ball is frozen to the rail or not. The effects are the same as with the shot in NV A.21 (http://www.engr.colostate.edu/~dga/pool/normal_videos/new/NVA-21.htm); although, this extreme example (http://www.youtube.com/watch?v=vEyCQSN8qU0) is much tougher to execute (because the hit must be near perfect, with lots of English, for it to work).

Regards,
Dave <hr /></blockquote>

<font color="blue">I may be all wet here but I think, perhaps, that the ball frozen to the rail MAY have an advantage in making the bank. My reasoning is that there might be some "back pressure" (resulting in the unusual occurance of the gear effect "during" contact with both the spinning cue ball and object ball) against the passing/spinning cue ball that would "trap" the object ball for a nanosecond and, therefore, allow a little more transfer of the spin induced throw to adhere or "take' to the object ball.
Now all you P.H.D. nerds (name calling, I know) can asault me without mercy.... /ccboard/images/graemlins/smirk.gif </font color>

DeeMan

Bob_Jewett
03-20-2007, 12:36 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> ... For the bank shot, I was shooting the cue ball away from the cushion for the fairly thin hit on the object ball. The only time the cue ball went into the cushion was on miscues, which were quite frequent but never came close to making the shot. ... <hr /></blockquote>
For a much better video of the bank shot and with a more difficult setup, see Joe Tucker at http://www.youtube.com/watch?v=ql-vXWEA_TU

In fact, Joe is shooting the shot into the cushion, which I suspect helps get retrograde spin.

Jal
03-20-2007, 12:54 PM
<blockquote><font class="small">Quote Deeman3:</font><hr> <font color="blue">I may be all wet here but I think, perhaps, that the ball frozen to the rail MAY have an advantage in making the bank. My reasoning is that there might be some "back pressure" (resulting in the unusual occurance of the gear effect "during" contact with both the spinning cue ball and object ball) against the passing/spinning cue ball that would "trap" the object ball for a nanosecond and, therefore, allow a little more transfer of the spin induced throw to adhere or "take' to the object ball.
Now all you P.H.D. nerds (name calling, I know) can asault me without mercy.... /ccboard/images/graemlins/smirk.gif </font color>

DeeMan <hr /></blockquote>Unlikely. The object ball is in contact with the cushion for something like .006 seconds, while the cueball makes contact with object ball for about .0002 seconds. If you divide these two numbers (don't try it at home), you'll find that the ball/cushion time is 30X the ball/ball time. Unless a double kiss takes place, the cueball will be blithely unaware of the cushion since it takes a while for the cushion to build up any appreciable force as it compresses.

By the way, ball/ball compression may also help to make both shots in a significant way. If you don't get the english on the cueball just right, throw may be as little as two degrees. Compression adds around another degree, or about a third of the total, by causing the tangent line to shift.

Jim

Billy_Bob
03-20-2007, 01:11 PM
I suspect the secret to this shot is the "bridge gizmo" he is using. I can't shoot that far off center without miscueing.

It seems to me that his bridge gizmo is holding the tip of the cue in contact with the cue ball better than my hand can.

Also perhaps because the cue ball is frozen to the rail? Maybe when he hits the cue ball so far off center, it is jambing or sandwiching the cue ball between his tip and the cushion? Perhaps getting a little extra spin from rail friction?

i.e. Can this shot be made with the cue ball not frozen to the rail?

dr_dave
03-20-2007, 02:01 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote Deeman3:</font><hr> <font color="blue">I may be all wet here but I think, perhaps, that the ball frozen to the rail MAY have an advantage in making the bank. My reasoning is that there might be some "back pressure" (resulting in the unusual occurance of the gear effect "during" contact with both the spinning cue ball and object ball) against the passing/spinning cue ball that would "trap" the object ball for a nanosecond and, therefore, allow a little more transfer of the spin induced throw to adhere or "take' to the object ball.
Now all you P.H.D. nerds (name calling, I know) can asault me without mercy.... /ccboard/images/graemlins/smirk.gif </font color>

DeeMan <hr /></blockquote>Unlikely. The object ball is in contact with the cushion for something like .006 seconds, while the cueball makes contact with object ball for about .0002 seconds. If you divide these two numbers (don't try it at home), you'll find that the ball/cushion time is 30X the ball/ball time. Unless a double kiss takes place, the cueball will be blithely unaware of the cushion since it takes a while for the cushion to build up any appreciable force as it compresses.

By the way, ball/ball compression may also help to make both shots in a significant way. If you don't get the english on the cueball just right, throw may be as little as two degrees. Compression adds around another degree, or about a third of the total, by causing the tangent line to shift.<hr /></blockquote>Jim,

Excellent answer. I'll also add this to my high-speed-video things to film list, so people can better see what actually happens.

Regards,
Dave

Qtec
03-20-2007, 08:07 PM
Bob, on your video its impossible to see what is happening. My post was made on the basis of JT's video.

[ QUOTE ]
In fact, Joe is shooting the shot into the cushion, <hr /></blockquote>

So my observation was correct.

Qtec........

cushioncrawler
03-20-2007, 08:08 PM
Further to my earlyr posting. I would be interested to know what would be the effect of holding (pushing) the OB into the cushion, to make a dimple, before playing the shot. I reckon that the OB might get a mile too much angle. This wouldnt proov my idea that the cushion is "trained" in every case, but it wouldnt hurt my idea.

If "training" aint the answer, then here is idea No 2. Each 1.0 rev/sec of OB throw is ordinaryly accompanyd with 2.5 rev/sec of transmitted side. This TS would act on the cushion to give an allmost equivalent additional amount of throw to the OB, ie allmost a double-dose.

But there's more. The impulse on the cushion "pushes" the cushion along parallel to the cushion (in addition to the more obvious sqeez into the cushion). As the OB leevs the cushion the cushion will end up "pushing" and mooving back the opposite way (parallel), ie if there is no balltocushion slippage the OB will in fact have clockwize english. This little effect will add to the throw, ie there can be more than a double-dose of throw. madMac.

Qtec
03-20-2007, 08:11 PM
Take a look at JT's video Dave.
video (http://www.youtube.com/watch?v=ql-vXWEA_TU)
IMO,its as plain as day that the QB is being forced into the cushion.

Qtec

dr_dave
03-20-2007, 09:55 PM
<blockquote><font class="small">Quote Qtec:</font><hr> Take a look at JT's video Dave.
video (http://www.youtube.com/watch?v=ql-vXWEA_TU)
IMO,its as plain as day that the QB is being forced into the cushion.<hr /></blockquote>Agreed. It is too difficult to tell if this is true in the video posted originally (http://www.youtube.com/watch?v=vEyCQSN8qU0). Regardless, I think this point is unimportant. I think the shot can be made either way. Do you agree? If not, why not?

Regards,
Dave

Bob_Jewett
03-20-2007, 11:20 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> ... I think the shot can be made either way. Do you agree? If not, why not?... <hr /></blockquote>
It would be very remarkable for someone to disagree since the shot has in fact been made both ways.

I asked Joe Tucker why he shot into the cushion. He said that it was not his preference, but the laser fixture thingie his is using for a bridge would not let him both have the cue ball frozen and shoot away from the rail. It is too wide for that. So, he shot into the cushion. In fact that may be a better way to do it, but it certainly never occurred to me and probably didn't occur to Vernon Elliott either.

Jal
03-21-2007, 10:30 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Further to my earlyr posting. I would be interested to know what would be the effect of holding (pushing) the OB into the cushion, to make a dimple, before playing the shot. I reckon that the OB might get a mile too much angle. This wouldnt proov my idea that the cushion is "trained" in every case, but it wouldnt hurt my idea.<hr /></blockquote>Hi Mac. Can you actually dimple the cushion and if so, why would that help the shot?

<blockquote><font class="small">Quote cushioncrawler:</font><hr>If "training" aint the answer, then here is idea No 2. Each 1.0 rev/sec of OB throw is ordinaryly accompanyd with 2.5 rev/sec of transmitted side. This TS would act on the cushion to give an allmost equivalent additional amount of throw to the OB, ie allmost a double-dose.<hr /></blockquote>I believe you're right. The additional "throw" from the spin should be about 5/7'ths of the translational throw (ignoring bed friction).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>But there's more. The impulse on the cushion "pushes" the cushion along parallel to the cushion (in addition to the more obvious sqeez into the cushion). As the OB leevs the cushion the cushion will end up "pushing" and mooving back the opposite way (parallel), ie if there is no balltocushion slippage the OB will in fact have clockwize english. This little effect will add to the throw, ie there can be more than a double-dose of throw. madMac. <hr /></blockquote>I don't agree with this Mac. If I'm understanding, you're saying that the initial counter-clockwise spin on the OB will sort of distort (displace, twist) the cushion, and when it springs back it will drive the OB even more? If so, the action of distorting the cushion would rob the OB of some of the parallel speed it would have picked up from its spin. This is stored as potential energy by the cushion, and the best that can happen is for the OB to get all of it back. Of course it won't, there will be some energy loss associated with this, but even if it did, I don't see any additional gain.

Jim

Jal
03-21-2007, 02:07 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> ...
I asked Joe Tucker why he shot into the cushion. He said that it was not his preference, but the laser fixture thingie his is using for a bridge would not let him both have the cue ball frozen and shoot away from the rail. It is too wide for that. So, he shot into the cushion. In fact that may be a better way to do it, but it certainly never occurred to me and probably didn't occur to Vernon Elliott either. <hr /></blockquote>Whether he is aware of it or not, it's an amazing technique for generating consistent spin/speed ratios ever so slightly greater than 1, which happens to be just what this shot calls for. It shouldn't be too hard to get the ratio within +/- .006 of each other shot after shot.


Jim

BRussell
03-21-2007, 02:08 PM
I just wanted to point out, since I hadn't seen it mentioned in this thread, that this shot is much, much easier to make if the object ball is resting against another. It looks like this. (http://CueTable.com/P/?@4Aawm4BaxE1PbFk4Uawm2UdxA1kbFk4kXcg4kXcg@) It's pretty easy to make this shot at least 1/3 of the time, even if it's more than diamond beyond the side pocket.

ceebee
03-21-2007, 02:39 PM
I also wonder if the object ball's close proximity to the side pocket allows the rail to "give in" or diminish the angle back across to the opposite side pocket, when struck by the Cue Ball at a high to moderate speed.

The answer to this scenario can be probably be investigated by someone with a Pool Table nearby.

cushioncrawler
03-21-2007, 04:04 PM
<blockquote><font class="small">Quote Jal:</font><hr> .... Can you actually dimple the cushion and if so, why would that help the shot?...<hr /></blockquote>Jim -- I have never looked into possible temp dimpling. But, rubber iz very rubbery, and cushion rubbers are very fat. It would be eezy to push a ball into a cushion for a while and then see if hitting a qball squarely into the dimple gave erratic left and right rebounds. The main reezon i thort of dimpling iz koz of the emphasis on needing lots of attempts for the first bet, and then not so many attempts for later bets. And, the dimpling might be partly a cushion-cloth thing, ie the cloth would push along a bit at first and then be "tighter" in that direction for later attempts, less give. I thort that dimpling (training) woz worth mentioning, but its a long-shot.<blockquote><font class="small">Quote cushioncrawler:</font><hr> If "training" aint the answer, then here is idea No 2. Each 1.0 rev/sec of OB throw is ordinaryly accompanyd with 2.5 rev/sec of transmitted side. This TS would act on the cushion to give an allmost equivalent additional amount of throw to the OB, ie allmost a double-dose.<hr /></blockquote>I believe you're right. The additional "throw" from the spin should be about 5/7'ths of the translational throw (ignoring bed friction).<hr /></blockquote> Jim -- I am thinking that the 5/7ths only applyz when there iz balltocloth slippage. If zero slippage then it would be 7/7ths, except that there would be an "e" involved that might be about 5/7ths anyhow.<blockquote><font class="small">Quote cushioncrawler:</font><hr>But there's more. The impulse on the cushion "pushes" the cushion along parallel to the cushion (in addition to the more obvious sqeez into the cushion). As the OB leevs the cushion the cushion will end up "pushing" and mooving back the opposite way (parallel), ie if there is no balltocushion slippage the OB will in fact have clockwize english. This little effect will add to the throw, ie there can be more than a double-dose of throw. madMac. <hr /></blockquote>I don't agree with this Mac. If I'm understanding, you're saying that the initial counter-clockwise spin on the OB will sort of distort (displace, twist) the cushion, and when it springs back it will drive the OB even more? If so, the action of distorting the cushion would rob the OB of some of the parallel speed it would have picked up from its spin. This is stored as potential energy by the cushion, and the best that can happen is for the OB to get all of it back. Of course it won't, there will be some energy loss associated with this, but even if it did, I don't see any additional gain... <hr /></blockquote> Jim -- This stuff woz a big hurdle to me when i woz making a computer program for cushion rebound. I came to the realization that cushions have 3 "e"s, ie eXX, eYY, and eZZ, and i tryd to devize some apparatus and tests to meazure theze individually, but it woz too difficult. And i came to the realization that cushion rebound woz mainly a function of balltocloth slippage anyhow, which put a sudden end to my months of work.

But i am certain that there iz (or can be) a "3rd dose" of throw. It might not be much, and it might be difficult to see. I said that if the OB (in this trickshot) came off the cushion with some clockwize spin, then everyone would have to agree that a parallel component of cushion rebound duz (can) add to the throw (if zero slippage). But, even az i woz typing this stuff back then, i woz thinking that such clockwize spin wouldnt be seen (ie not in this sort of trick-shot test), and in fact CW spin wouldnt be necessary. Az long az the anticlockwize spin woz reduced then this "3rd dose" would have done its job here, ie inkreeced the OB's rebound angle off the cushion. But i wouldnt blame u if u found my reasoning difficult to follow, i might be able to explain better. madMac.

Bob_Jewett
03-21-2007, 04:15 PM
<blockquote><font class="small">Quote ceebee:</font><hr> I also wonder if the object ball's close proximity to the side pocket allows the rail to "give in" or diminish the angle back across to the opposite side pocket, when struck by the Cue Ball at a high to moderate speed.... <hr /></blockquote>
For Vernon Elliott's bank, the object ball is well away from the side pocket. In fact in Joe Tucker's video clip, you can see him put the object ball a full two balls below the side pocket and overcut the bank. It must be seen to be believed. Here's the link again in case you missed it the first time http://www.youtube.com/watch?v=ql-vXWEA_TU

The only "special" bank I know of using the special nature of the cushion by the side pocket is to put the object ball so it is on the flat of the rail but with the edge partly into the pocket area, put the cue ball straight out from this ball (near the center spot of the table) and bank the object ball one cushion to the side. This requires nice stiff facings in the side pocket.

Rod
03-22-2007, 12:56 AM
I haven't shot the shot but it appears it could be a double kiss back. May not be but where the c/b contacts the second rail would be a give away. Where does the c/b contact the second rail on a make or a near miss?

Rod

Bob_Jewett
03-22-2007, 02:02 AM
<blockquote><font class="small">Quote Rod:</font><hr> I haven't shot the shot but it appears it could be a double kiss back. May not be but where the c/b contacts the second rail would be a give away. Where does the c/b contact the second rail on a make or a near miss?

Rod <hr /></blockquote>
The angle is easier to see in the Joe Tucker clip on youtube. The hit is fuller than you might expect, but thin enough you don't get a kiss. If you did get a kiss, the object ball would never get across the table. Also,the impossible cut shot clearly has no kiss, and it uses the same stroke.

Rod
03-22-2007, 11:10 AM
I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.

Rod

TennesseeJoe
03-22-2007, 12:40 PM
Bob, This shot has facinated me for several years. I've tried it hundreds of time without success. I have been able to get within 8 inches of the target pocket by shooting into the rail as shown in Joe's vidoe. Any suggestions???( Predator 314, Kamouri soft, dime radius.)

Deeman3
03-22-2007, 01:10 PM
<blockquote><font class="small">Quote Rod:</font><hr> I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.

Rod <hr /></blockquote>

<font color="blue">Rod,

Be careful, I was admonished earlier for this same suggestion. /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/smirk.gif </font color>

Jal
03-22-2007, 01:54 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- I have never looked into possible temp dimpling. But, rubber iz very rubbery, and cushion rubbers are very fat. It would be eezy to push a ball into a cushion for a while and then see if hitting a qball squarely into the dimple gave erratic left and right rebounds. The main reezon i thort of dimpling iz koz of the emphasis on needing lots of attempts for the first bet, and then not so many attempts for later bets. And, the dimpling might be partly a cushion-cloth thing, ie the cloth would push along a bit at first and then be "tighter" in that direction for later attempts, less give. I thort that dimpling (training) woz worth mentioning, but its a long-shot.<hr /></blockquote>Of course another explanation is that they tend to hone in on the shot over time (bet you didn't think of that one /ccboard/images/graemlins/smile.gif).

<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I am thinking that the 5/7ths only applyz when there iz balltocloth slippage. If zero slippage then it would be 7/7ths, except that there would be an "e" involved that might be about 5/7ths anyhow.<hr /></blockquote>But there should be ball/cloth slippage since the induced spin (surface speed RW) is 5/2's the throw velocity. And it's likely there is very little initial velocity parallel to the rail in the desired direction since the throw has a big job just to cancel the geometry, which by itself wants to send the OB in the wrong direction down the rail. If there weren't slippage, then the spin could not contribute to its parallel speed (well a little bit in opposing bed friction.)

<blockquote><font class="small">Quote cushioncrawler:</font><hr>...But, even az i woz typing this stuff back then, i woz thinking that such clockwize spin wouldnt be seen (ie not in this sort of trick-shot test), and in fact CW spin wouldnt be necessary. Az long az the anticlockwize spin woz reduced then this "3rd dose" would have done its job here, ie inkreeced the OB's rebound angle off the cushion. But i wouldnt blame u if u found my reasoning difficult to follow, i might be able to explain better. madMac. <hr /></blockquote>I've been trying to think this one through as best I can, and still feel there is no 3rd effect. Even if the cushion is pushed sideways, the relatively small spin induced on the object ball should bring gearing into effect early on in the collision with the cushion. The cushion should have plenty of time to stop moving, spring back, and then reach a state of zero sideways motion while the ball is still in contact with it, I think. Assuming static friction holds throughout these latter phases (after gearing is reached), and say little or no energy is lost internally, it seems to me that the ball should end up with the same speed as spin as if none of this took place. But I don't feel completely comfortable with this and I'd be interested in any further explanation Mac.

Jim

Jal
03-22-2007, 02:01 PM
<blockquote><font class="small">Quote Deeman3:</font><hr> <blockquote><font class="small">Quote Rod:</font><hr> I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.

Rod <hr /></blockquote>

<font color="blue">Rod,

Be careful, I was admonished earlier for this same suggestion. /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/smirk.gif </font color> <hr /></blockquote>Deeman,

I hope my response to your earlier post on this didn't come off as strident. If so, tough teats. /ccboard/images/graemlins/mad.gif /ccboard/images/graemlins/smile.gif /ccboard/images/graemlins/smile.gif

Jim

dr_dave
03-22-2007, 03:08 PM
<blockquote><font class="small">Quote Rod:</font><hr> I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.<hr /></blockquote>
I've added this to my high-speed-video shoot list. I hope to do a bunch of filming at the end of May or early June. I camera will reveal all of the effects and non-effects.

Regards,
Dave

Rod
03-22-2007, 03:21 PM
<blockquote><font class="small">Quote Deeman3:</font><hr> <blockquote><font class="small">Quote Rod:</font><hr> I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.

Rod <hr /></blockquote>

<font color="blue">Rod,

Be careful, I was admonished earlier for this same suggestion. /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/smirk.gif </font color> <hr /></blockquote>

Dee, the tech boys have an answer to disprove everything it appears. It seems to me they should supply proof it doesn't happen rather than just spouting off numbers.

One possible way is make this shot with the o/b and c/b equal distance off the rail, say 1 mm. I say that to keep the angle consistent. If they can make it that way it would be a pretty convincing argument. Oh, and the ones that say pinching/gearing isn't possible gets to shoot the shot! LOL Until then I rest my case. /ccboard/images/graemlins/grin.gif

Rod

cushioncrawler
03-22-2007, 03:26 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I am thinking that the 5/7ths only applyz when there iz balltocloth slippage. If zero slippage then it would be 7/7ths, except that there would be an "e" involved that might be about 5/7ths anyhow.<hr /></blockquote>But there should be ball/cloth slippage since the induced spin (surface speed RW) is 5/2's the throw velocity. And it's likely there is very little initial velocity parallel to the rail in the desired direction since the throw has a big job just to cancel the geometry, which by itself wants to send the OB in the wrong direction down the rail. If there weren't slippage, then the spin could not contribute to its parallel speed (well a little bit in opposing bed friction.)<hr /></blockquote>Jim -- Slippage would depend on the OB speed into the cushion. Here this speed is say 10 times (or even 20 times) the throw (or TS), so slippage is i think unlikely.<blockquote><font class="small">Quote cushioncrawler:</font><hr>...But, even az i woz typing this stuff back then, i woz thinking that such clockwize spin wouldnt be seen (ie not in this sort of trick-shot test), and in fact CW spin wouldnt be necessary. Az long az the anticlockwize spin woz reduced then this "3rd dose" would have done its job here, ie inkreeced the OB's rebound angle off the cushion. But i wouldnt blame u if u found my reasoning difficult to follow, i might be able to explain better. madMac. <hr /></blockquote>I've been trying to think this one through as best I can, and still feel there is no 3rd effect. Even if the cushion is pushed sideways, the relatively small spin induced on the object ball should bring gearing into effect early on in the collision with the cushion. The cushion should have plenty of time to stop moving, spring back, and then reach a state of zero sideways motion while the ball is still in contact with it, I think. Assuming static friction holds throughout these latter phases (after gearing is reached), and say little or no energy is lost internally, it seems to me that the ball should end up with the same speed as spin as if none of this took place. But I don't feel completely comfortable with this and I'd be interested in any further explanation Mac. Jim <hr /></blockquote> I agree that the parallel "sqeez" probably ends very early, in which case the balltocushion contact would be "vibrating" backwards and forwards while the OB woz rebounding, and either the BW or the FW (or null) will be extant "in the end", in which case the "3rd dose" could be positiv or negativ or null. But its the thort that counts. Forum members will be required to do a test on this sort of stuff later in the year, and i wouldnt like it if the AZers scored better than us. madMac.

cushioncrawler
03-22-2007, 03:35 PM
<blockquote><font class="small">Quote Rod:</font><hr> ....Dee, the tech boys have an answer to disprove everything it appears. It seems to me they should supply proof it doesn't happen rather than just spouting off numbers. <hr /></blockquote> I have a book in front of me that tells me that a double kiss is possible if the qball is further than 6 balls clear of the OB. Thusly, it iz possible to get a DK for this trick shot. But, the book goze on to say that a DK iznt possible unless the contact is thicker than 1/4 ball, ie much thicker than what we are talking about in this trickshot. madMac.

Bob_Jewett
03-22-2007, 03:39 PM
<blockquote><font class="small">Quote Rod:</font><hr> I'm sure your right Bob. However there must some gearing effect with the c/b pinching the o/b against the rail just the right amount. As you said its not as thin as one would think.

Rod <hr /></blockquote>
An example bank in a similar situation is at one pocket when a ball is frozen on the long rail just above your opponent's pocket and the cue ball is on the foot spot. You can bank this cross-corner and get out of the kiss-out by the cue ball rattling in your opponent's pocket. (I'm sure Rod is familiar with the shot, but I'm describing it for those who have not played it a hundred times.)

I don't think that cross-corner bank is a kiss, and it seems to me that Vernon's bank is no more likely to be a kiss. I think the rail is soft enough and the balls are hard enough that ball-ball contact happens very quickly and the ball-rail contact happens much more slowly. I have calculated that ball-cushion takes 30 times a long as ball-ball.

Of course, on a shot that seems to defy the laws of physics, more careful study may be needed. Careless physicists might have told us a month ago that both of the shots now captured on video were obviously impossible. To finance the study, I am arranging a syndicate of backers and we will descend on the annual conference of the American Physical Society. We will set our nets out in the local pubs. The plan is to wait for the fish to come in after the meetings and then to try the shot repeatedly, missing it by a diamond each time. The tipsy physicists will start quoting Einstein, Newton and Hertz at us, and shortly we will have all their per diem money. If you would like to join the syndicate, contact me privately.

Deeman3
03-22-2007, 03:40 PM
/ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif

Deeman3
03-22-2007, 03:44 PM
<blockquote><font class="small">Quote Jal:</font><hr> <hr /></blockquote>Deeman,

I hope my response to your earlier post on this didn't come off as strident. If so, tough teats. /ccboard/images/graemlins/mad.gif /ccboard/images/graemlins/smile.gif /ccboard/images/graemlins/smile.gif

Jim <hr /></blockquote>

<font color="blue"> Jim,

I am not one known as thin skined, light skinned, perhaps, but I didn't take your terse, bold and insensitive response personally. By the way, how tough are those teats anyway? I don't have a pair myself!/ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/grin.gif /ccboard/images/graemlins/smirk.gif </font color>

Jal
03-22-2007, 05:29 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- Slippage would depend on the OB speed into the cushion. Here this speed is say 10 times (or even 20 times) the throw (or TS), so slippage is i think unlikely.<hr /></blockquote>Mac, I'm not sure why you come to this conclusion, rather than it just ending early, but I'll concede the possibility of zero slippage from the start. It should still be true though that 2/7'ths of the "spin" (surface speed RW) will end up as translational velocity, regardless of whether it's sliding or static friction. Since RW is 5/2 of the initial throw velocity, you don't quite get a doubling of throw (7/7), but 5/7 (=2/7*5/2). This follows from the effects of any force applied tangentially to the surface of a sphere and its moment of inertia. (I know you know.)

<blockquote><font class="small">Quote cushioncrawler:</font><hr> I agree that the parallel "sqeez" probably ends very early, in which case the balltocushion contact would be "vibrating" backwards and forwards while the OB woz rebounding, and either the BW or the FW (or null) will be extant "in the end", in which case the "3rd dose" could be positiv or negativ or null. But its the thort that counts. Forum members will be required to do a test on this sort of stuff later in the year, and i wouldnt like it if the AZers scored better than us. madMac. <hr /></blockquote>I agree Mac. If the cushion is still moving, it could go either way. I have serious doubts about it oscillating up to the end, but can't say I've looked at this and do concede that your 3rd dose is therefore a possibility. Perhaps the high speed videos will show something.

Jim

cushioncrawler
03-24-2007, 09:50 PM
<blockquote><font class="small">Quote Jal:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr>In this case, the shooter is using "much more than enough" outside spin, to throw the ball even a little more in the direction it is being cut.
SpiderMan <hr /></blockquote>The "ideal" spin/speed ratio, at least for the cut shot, and for balls that conform to Dr. Dave's equations, is about 1.05. This is just slightly more than "gearing" spin with a ratio of 1, and considerably less than "maximum" spin with a ratio of 1.25. Even if the balls have double the amount of friction used in the theory, the ratio which would yield the most throw only goes up to about 1.10. For 1.25 to be ideal, the coefficient of friction would have to be about 0.4, which I think could only happen if skid/kick/cling takes place. The above are based on a cueball speed of 10 mph, which is pretty fast for the amount of english applied, and a geometric cut angle (w/o throw) of about 85 degrees.

But exactly where to contact the cueball to produce a particular ratio is problematic. First, squirt reduces the apparent ratio. If, for instance, the squirt angle is 2.5 degrees, then to get an actual ratio of 1.05 you would need to contact the ball at an offset corresponding to 1.15 (ie, about halfway between perfect gearing and the miscue limit).

Against this is the fact that the ball rotates during impact, increasing the initial offset and ratio. To know how much of an effect this is you would probably need to do a numeric integration. But this is complicated by the shape of the force vs time curve (non-sinusoidal) which is also severely nonsymmetric about the midpoint of the contact period.

But given the two opposing effects, it's possible that the initial tip offset which produces an actual ratio of 1.05 might not be much different than the apparent one (ie, just slightly more than 80% of max english at .42R). If ball rotation increases the effective offset more than squirt reduces it, then the initial tip offset would have to be even less than this. Why don't you or somebody work this out tonight and report back. Jim <hr /></blockquote>Jim -- I dusted off my old cushion-rebound program and crunched a few numbers. U are correct. This trick-shot duznt need anywhere near 1.25 of spin, 1.05 looks about enuff to me. Here are my figures, inklooding a few guesses and estimates and shortcuts.

Qball iz 15 balls away from OB.
Contact on OB is 1/128th.
Ht of cushion = 0.65D.
Cushion e = 0.75.
At (initial) contact, qballtoOB contact-angle is 7.1666dg.
Qball speed is 4.0m/s, stun.
OB speed is 0.5m/s.
I adopted balltoball friction of 0.12.
Initial throw-angle woz 6.8428dg.
OB rebound angle off cushion woz -7.0dg.
After skidding finished, angle woz -5.2dg.
Needed angle to get a cutback equiv to 2 balls (ie 2.0D) at opposite cushion iz -4.9dg.
Actual cutback achieved = 2.8D.
Spin Ratio adopted woz max of 1.25.
But, slightly over 1.0 (eg 1.05) woz good enuff.

It would take me a few weeks to audit this program and the calcls to check exactly what/how my program worked all of this out. Anyhow, it supports the beleef that this shot can be gotten without resorting to trickery. One other thing, the lower the cushion the eezyr the shot. madMac.

Jal
03-25-2007, 01:21 PM
Hi Mac. Interesting results. You mention an OB contact of 1/128. That's about 1/64" = .45mm. Looking at a ruler graduated in 1/64", it's amazing that such a slight cut can be made, and that the OB can be driven enough to make it across the table.

I wrote a program for the cushion some time ago but never fired it up to even debug it. I think I will now and perhaps we can compare results (and theory). To test it I'll probably take measurements off of Dr. Daves vidoes, which you might be interested in. (One video that I did measure shows a rebound angle in good agreement with a crude version of the theory, but it's one of the simplest cases.)

My calculations agree with yours up to a point. You used a ball/ball friction coefficient of .12. With a spin ratio of 1.25 and speed of 4 m/s, Dr. Dave's theory (my implementation) shows a throw of only about 2.55 deg, corresponding to a coefficient of about .045. We discussed a potential problem with the dependence of mu on surface speed (tests done with frozen balls?), so I can't say I'm confident in any particular value. Your value of .12 may be realistic, especially with dull/diry balls. Maybe you have some data to support that?

But using your number, I get a rebound angle of about -2.3 deg rather than -7 deg. One thing we might differ on is the incident cushion angle, which I get as 10.96 minus the throw angle of 6.84. The 10.96 includes the approach angle of the cueball measured with respect to the line of centers of the two balls, which is 3.79 deg for a cut angle of 82.83 deg (1/128 ball). In other words, the cueball is moving away from the cushion at that angle (3.79).

10.96 = 180 - (90-3.79) - 82.83

And, as we discussed earlier, I used not quite a throw doubling, but 5/7'ths of it for the spin contribution to the OB's parallel speed (multiplied by the cosine of the cushion height angle...which doesn't change things much).

In order to make it across the table (9'), I think the cueball has to be going considerable faster than 4 m/s. Another program figures the OB's normal speed into the cushion needs to be around 2 mph (=.9 m/s). The cueball's speed therefore has to be something like 7 m/s (=16 mph) at this cut angle. With this much tip offset, these speeds are not easy to obtain! Have you obtained other figures for this?

Using Dr. Dave's version of throw (mu values), a spin ratio of somewhere between 1.05 and 1.08 is not only sufficient, but quite necessary I think, because this yields maximum throw of about 5 degrees at these cut angles and speeds (2.55 deg won't cut it unless you increase cut angle and speed!). If Bob Jewett made the shot with a ratio around 1.25, then this indicates that mu is probably quite different than what Dr. Dave's theory predicts. (Using Marlow's data as well, my version of throw produces results close to Dr. Dave's.)

Of course, you should get around another degree of assistance from the flatspot too.

Jim

cushioncrawler
03-25-2007, 04:56 PM
Jim -- Yes the OB's attack angle is az u say 10.9593dg -- I forgot to add the qball's travel angle which is 3.7926dg from parallel. In fact this ignores the qball's swerve angle which would be a couple of degrees allso.

So, i recrunched the numbers, and i found that i got my desired cut-back of 2 balls if the balltoball friction woz 0.15 instead of the 0.12 that i had adopted previously. What do u think about the acheevability of 0.15???? Az u say, the trickshot actually needs just enuff superspin, else balltoball the friction will be too low.

Re the needed qball speed, and the needed OB speed, and the needed contact thickness, these inputs into my cushion rebound program were all guestimates. But i dont see much wrong here. The main problem is that the OB hazta get to the pocket. Iz an initial OB speed of 0.5m/s (into the cushion) enuff????

A 1/128th contact would give the qball a stun deflexion angle of allmost 7.17dg. By memory this angle iz about what is acheeved by Bob and ??? in the videos. And, i can see the difficulty of hitting the qball at 4m/s plus getting superspin, but i think that 4m/s is fairly consistent with what we see in the videos. What do u think.

I karnt eezyly find where my program calculates the balltocushion slippage energy loss (up to 2/7ths). But the program tells me that the OB's energy pre-impact is 0.0184J, at rebound is 0.0081J, at end of skidding is 0.0042J. Total loss is 0.0142J, made up of jumping 0.0032J, in cushion 0.0071J, skidding after rebound 0.0039J. madMac.

cushioncrawler
03-25-2007, 09:05 PM
Jim -- Another thing is that my program thinks that the cushion is pretty efficient in putting topspin etc on a ball. In my program the low cushion (0.65D) duznt put much topspin on the OB, the cushion spits the OB out with some skidding. The OB then slows some as it skids and gets some extra topspin and eventually begins rolling. The acquired topspin is acting square to the cushion, whereaz the OB is skiding/rolling at an angle. Hence the OB swervz some, the lost angle being 1.2196dg. Nowadayz i am not so impressed with the efficiency of cushions, and i think that all of this topspin duznt exist. If i ignore all of the "lost angle", then the balltoball friction needs to be only 0.137 instead of 0.150. But i havnt yet taken into account the qball's swerve on the way to the OB.

Regarding ever doing tests for max friction -- i suppoze that balltoball friction karnt exceed what u get with cling (chalk-kick), ie a throw angle of about 1 in 4 (0.25). And, for a 2ball frozen set, the best i can uzually get is about 1 in 6.88, which is 0.1453, and i karnt see ordinary 2 ball impacts acheeving that much friction and throw unless an old impact mark gets involved in the act.

So, perhaps we shood be looking for something else in this trickshot, even if it iz only minor. A 3rd dose of throw??? Cushion "training"????. madMac.

Jal
03-26-2007, 12:19 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- Yes the OB's attack angle is az u say 10.9593dg -- I forgot to add the qball's travel angle which is 3.7926dg from parallel. In fact this ignores the qball's swerve angle which would be a couple of degrees allso.<hr /></blockquote>Mac, at the seeming superspeed required, swerve would probably not be much of a factor. But at your prompting I looked at the videos again, and you're right about the speeds they used. With a frame rate of 30/sec, Bob Jewett's worked out to be roughly 6 mph (2.7 m/s), and Joe Tucker's about 8 mph (3.6 m/sec)...I emphasize 'rough'.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>So, i recrunched the numbers, and i found that i got my desired cut-back of 2 balls if the balltoball friction woz 0.15 instead of the 0.12 that i had adopted previously. What do u think about the acheevability of 0.15???? Az u say, the trickshot actually needs just enuff superspin, else balltoball the friction will be too low.<hr /></blockquote>0.15 is only slightly outside the range on which Dr. Dave's treatment is based. If you get the spin just right (max throw), it might be reachable, especially with old balls. But I think you know much more about this than me.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Re the needed qball speed, and the needed OB speed, and the needed contact thickness, these inputs into my cushion rebound program were all guestimates. But i dont see much wrong here. The main problem is that the OB hazta get to the pocket. Iz an initial OB speed of 0.5m/s (into the cushion) enuff????<hr /></blockquote>For 100 speed cloth and a cushion e of 0.75 and ball/cloth mu of 0.2, mathland says that you need an immediate rebound speed of about 1.5 mph (0.67 m/sec), and therefore about 2 mph (0.9 m/s) going in (this without going through the exact path/swerve calculations which should make only very small differences, I think). Rough measurements off the videos are in agreement with this.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>...And, i can see the difficulty of hitting the qball at 4m/s plus getting superspin, but i think that 4m/s is fairly consistent with what we see in the videos. What do u think.<hr /></blockquote>After taking the measurements as indicated above, I agree.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>I karnt eezyly find where my program calculates the balltocushion slippage energy loss (up to 2/7ths). But the program tells me that the OB's energy pre-impact is 0.0184J, at rebound is 0.0081J, at end of skidding is 0.0042J. Total loss is 0.0142J, made up of jumping 0.0032J, in cushion 0.0071J, skidding after rebound 0.0039J. madMac. <hr /></blockquote>I haven't calculated energy losses yet (and don't plan to except at gunpoint /ccboard/images/graemlins/smile.gif ).

Jim

Jal
03-26-2007, 01:15 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- Another thing is that my program thinks that the cushion is pretty efficient in putting topspin etc on a ball. In my program the low cushion (0.65D) duznt put much topspin on the OB, the cushion spits the OB out with some skidding. The OB then slows some as it skids and gets some extra topspin and eventually begins rolling. The acquired topspin is acting square to the cushion, whereaz the OB is skiding/rolling at an angle. Hence the OB swervz some, the lost angle being 1.2196dg. Nowadayz i am not so impressed with the efficiency of cushions, and i think that all of this topspin duznt exist. If i ignore all of the "lost angle", then the balltoball friction needs to be only 0.137 instead of 0.150. But i havnt yet taken into account the qball's swerve on the way to the OB.<hr /></blockquote>Hi again Mac! The high speed videos I've looked at don't show any imparted topspin, if I remember correctly. As I recall, the cushion tries, but the spin immediately gets damped out by the cushion itself or the bed. I will keep an eye out for it though.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Regarding ever doing tests for max friction -- i suppoze that balltoball friction karnt exceed what u get with cling (chalk-kick), ie a throw angle of about 1 in 4 (0.25). And, for a 2ball frozen set, the best i can uzually get is about 1 in 6.88, which is 0.1453, and i karnt see ordinary 2 ball impacts acheeving that much friction and throw unless an old impact mark gets involved in the act.<hr /></blockquote>I agree although I think you know much more about it than me.

<blockquote><font class="small">Quote cushioncrawler:</font><hr>So, perhaps we shood be looking for something else in this trickshot, even if it iz only minor. A 3rd dose of throw??? Cushion "training"????. madMac. <hr /></blockquote>Given the slowish cueball speeds coupled with the relatively robust object ball speeds, something funny is going on. Clearly they're not cutting the OB at the angles we've been discussing.

You mentioned the cueball's post-impact direction earlier. A rough measurement of Joe Tucker's shots yields about 15- 20 degrees with respect to the starting cushion. Although harder to see, it looks something like this on Bob Jewett's shot.

Jim

cushioncrawler
03-26-2007, 02:42 AM
<blockquote><font class="small">Quote Jal:</font><hr> .....Given the slowish cueball speeds coupled with the relatively robust object ball speeds, something funny is going on. Clearly they're not cutting the OB at the angles we've been discussing.

You mentioned the cueball's post-impact direction earlier. A rough measurement of Joe Tucker's shots yields about 15- 20 degrees with respect to the starting cushion. Although harder to see, it looks something like this on Bob Jewett's shot. Jim <hr /></blockquote>Jim -- An attack angle of 10.96dg, plus an impact angle of 7.17dg, givz 18.13dg, which iz nearnuff what Bob n Joe are doing. So, i think 1/128th contact iz about right.

Thoze energy losses i mentioned earlyr, theze are based on my small ballz, ie 2-1/16" and 140gm. madMac.

Jal
03-26-2007, 12:51 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> .....Given the slowish cueball speeds coupled with the relatively robust object ball speeds, something funny is going on. Clearly they're not cutting the OB at the angles we've been discussing.

You mentioned the cueball's post-impact direction earlier. A rough measurement of Joe Tucker's shots yields about 15- 20 degrees with respect to the starting cushion. Although harder to see, it looks something like this on Bob Jewett's shot. Jim <hr /></blockquote>Jim -- An attack angle of 10.96dg, plus an impact angle of 7.17dg, givz 18.13dg, which iz nearnuff what Bob n Joe are doing. So, i think 1/128th contact iz about right. <hr /></blockquote>Mac, 10.96 is the object ball incident angle into the cushion measured from the perpendicular, and before the throw angle is subtracted from it (for a 1/128 hit). The 3.79 angle is the relevant one here, which when added to the post-impact angle of 7.17 gives you about 11 degrees. That is, without anything else happening, the cueball should exit the shot at approximately 11 degrees from the long cushion. Do you agree?

The fact that it comes off closer to 20 degrees tells us that either some trickery was being used, such as a blocker behind the OB along with a fuller hit, or as Rod suggested earlier, a double-kiss is taking place. From the discussion in this thread, I don't think any deception was employed, so that leaves a double-kiss (which also adds a 'third dose' of throw).

On the face of it, it would appear as if a second collision would more or less quelch the object ball's cross table velocity. But this isn't true because the cueball is now moving away from the long cushion. It's easy to see how this movement affects things by switching to a frame of reference moving along with the cueball after the first collision. To do so you subtract the cueball's velocity from the object ball to get the OB's velocity in this new frame, and then add it again after the second collision to get the OB's velocity in the original (table) frame. In a manner of speaking, the cueball's velocity is "hidden" from the second collision in the moving frame, then restored to the object ball in the stationary (table) frame.

In my opinion, there is no other explanation for the cueball's final trajectory coupled with the fact that the OB actually makes it to the pocket (and assuming near normal "unjuiced" balls and no other deception). It allows for a little bit fuller hit on the OB too (I think). Any thoughts?

Jim

cushioncrawler
03-26-2007, 04:09 PM
<blockquote><font class="small">Quote Jal:</font><hr> ....10.96 is the object ball incident angle into the cushion measured from the perpendicular, and before the throw angle is subtracted from it (for a 1/128 hit). The 3.79 angle is the relevant one here, which when added to the post-impact angle of 7.17 gives you about 11 degrees. That is, without anything else happening, the cueball should exit the shot at approximately 11 degrees from the long cushion. Do you agree?<hr /></blockquote>Jim -- I agree. The qball is pre-impact going at 3.79dg away from the cushion, and the impact-angle is 7.17dg, and the qball's deflexion-angle is more or less at 90dg to the balltoball line, ie 10.96dg. This 10.96dg will actually be a little less koz e iz less than 1.00. But, the OB's throw haz little effect on this 10.96dg, ie there is little need to "worry about" the balltoball friktion and/or the spin on the qball. However draw or topspin would have a big effect on the deflexion-angle.<blockquote><font class="small">Quote Jal:</font><hr>The fact that it comes off closer to 20 degrees tells us that either some trickery was being used, such as a blocker behind the OB along with a fuller hit, or as Rod suggested earlier, a double-kiss is taking place. From the discussion in this thread, I don't think any deception was employed, so that leaves a double-kiss (which also adds a 'third dose' of throw). On the face of it, it would appear as if a second collision would more or less quelch the object ball's cross table velocity. But this isn't true because the cueball is now moving away from the long cushion. It's easy to see how this movement affects things by switching to a frame of reference moving along with the cueball after the first collision. To do so you subtract the cueball's velocity from the object ball to get the OB's velocity in this new frame, and then add it again after the second collision to get the OB's velocity in the original (table) frame. In a manner of speaking, the cueball's velocity is "hidden" from the second collision in the moving frame, then restored to the object ball in the stationary (table) frame. In my opinion, there is no other explanation for the cueball's final trajectory coupled with the fact that the OB actually makes it to the pocket (and assuming near normal "unjuiced" balls and no other deception). It allows for a little bit fuller hit on the OB too (I think). Any thoughts? Jim <hr /></blockquote> Jim -- I read that a double-kiss is impossible when the qball is frozen to the cushion less than 6 balls clear of the OB. Hencely, a double-kiss is possible in our trick-shot. But, i allso red that in this instance a DK would need a contact no thinner than 1/4 ball, in which case a DK iznt a factor here. So, a qball trajektory of about 20dg smells a bit -- something else could be going on -- drugz?????.

But, perhaps balltoball friktion iz a bit more than what we thort possible, or there is something else going on. But, as a starter, i reckon that someone shood do some attempts at this trickshot uzing ...zero spin, ...top, ...draw, ...inside-english, and compare the rezults to outside-english. madMac.

Jal
03-26-2007, 04:57 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> <blockquote><font class="small">Quote Jal:</font><hr> ....10.96 is the object ball incident angle into the cushion measured from the perpendicular, and before the throw angle is subtracted from it (for a 1/128 hit). The 3.79 angle is the relevant one here, which when added to the post-impact angle of 7.17 gives you about 11 degrees. That is, without anything else happening, the cueball should exit the shot at approximately 11 degrees from the long cushion. Do you agree?<hr /></blockquote>Jim -- The qball is pre-impact going at 10.95dg away from the cushion, and the impact-angle is 7.17dg, and the qball's deflexion-angle is more or less at 90dg to the balltoball line, ie 18.12dg. This 18.12dg will actually be a little less koz e iz less than 1.00. But, the OB's throw haz little effect on this 18.12dg, ie there is little need to "worry about" the balltoball friktion and/or the spin on the qball. However draw or topspin would have a big effect on the deflexion-angle.<hr /></blockquote> Mac, I still think that for the 15-ball separation distance, the cueball has to be off the parallel cushion direction by 3.79 degrees for a 1/128 ball hit (discounting swerve). Later tonight I'll try to make up a diagram which shows the geometry clearly (as I see it).

<blockquote><font class="small">Quote cushioncrawler:</font><hr>Jim -- I read that a double-kiss is impossible when the qball is frozen to the cushion less than 6 balls clear of the OB. Hencely, a double-kiss is possible in our trick-shot. But, i allso red that in this instance a DK would need a contact no thinner than 1/4 ball, in which case a DK iznt a factor here.<hr /></blockquote>I'll also try to prove one way or another whether a double-kiss is possible for the thinner than 1/4 hit, but this might be difficult (or easy...don't know). It's not obvious when viewing the films, even frame by frame.

Jim

cushioncrawler
03-26-2007, 05:08 PM
Jim -- My editing of my earlyr reply, and your reply, crossed in cyberspace. Yes, i now agree that the qball'z trajektory shood be about 11dg, not the 20dg that (u say) is evident. Alltho, my stuff is based on the qball being about 15 balls from the OB, ie 14 balls clear -- not sure what Bob n Joe actually had in the videos. I karnt get to my table for a while, and anyhow it haz flat-faced-cushions (12'), so i karnt really help much re additional testing. madMac.

Jal
03-26-2007, 05:14 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- My editing of my earlyr reply, and your reply, crossed in cyberspace. Yes, i now agree that the qball'z trajektory shood be about 11dg, not the 20dg that (u say) is evident. Alltho, my stuff is based on the qball being about 15 balls from the OB, ie 14 balls clear -- not sure what Bob n Joe actually had in the videos. I karnt get to my table for a while, and anyhow it haz flat-faced-cushions (12'), so i karnt really help much re additional testing. madMac. <hr /></blockquote>Thanks Mac, that saves a diagram. I'll look at the actual ball separations more carefully.

Jim

Jal
03-28-2007, 12:13 AM
<blockquote><font class="small">Quote cushioncrawler:</font><hr> Jim -- I read that a double-kiss is impossible when the qball is frozen to the cushion less than 6 balls clear of the OB. Hencely, a double-kiss is possible in our trick-shot. But, i allso red that in this instance a DK would need a contact no thinner than 1/4 ball, in which case a DK iznt a factor here. So, a qball trajektory of about 20dg smells a bit -- something else could be going on -- drugz?????.<hr /></blockquote>Mac, a model of the shot indicates that what you read is essentially correct. It shows a second collision occurring up to about 65-70 degrees of cut angle. But it's quite possible that a real cushion might provide a longer contact time than the model uses (.006 sec), especially since the OB penetration is relatively slight for this shot. This would reduce the maximum cut angle of course.

A couple of Joe Tucker's shots had the cueball flying off at only about 14 degrees away from the cushion (again roughly measured), but one definitely did take off at about 20 deg or slightly more (shot was successful). It doesn't appear that this can be explained by a double-kiss then. Reducing the cushion contact time to 0.004 does push the 65-70 up to 75-80 degrees, but this is probably stretching it. The model doesn't do anything more than test for the double-kiss at this point. And it's not what you would call the standard-bearer of applied physics. /ccboard/images/graemlins/smile.gif

Jim

cushioncrawler
03-28-2007, 01:09 AM
Jim-- Can u do me a favor. Uze a cue to double a qball (ie faux OB) at about the place and angle az in the trickshot, hitting just hard enuff to drop. Now, place the qball frozen to the cushion at that point, and, then, place an object (ruler) on top of the cushion at that point, the ruler reeching out to touch the frozen qball. Note how far out (or in) the ruler reeches relativ to the face of the cushion. Then, moov the ruler back say 5mm from that point, fix the ruler at that spot uzing a wt. Then play that qball double that we mentioned earlyr, at the same dead pocket pace. Repeat this test, mooving the ruler further out 1mm at a time, untill the qball iz seen to contact the ruler. Now u know how far the cushion yields for this shot. I need this info to calibrate my cushion rebound program, so that i can look into a few ideas that i have. madMac.

Jal
03-28-2007, 02:01 PM
Mac, I'll be happy to but I don't have a table and am getting precious little time at my room lately. It may take a day or two (or three), and if you have any follow up test in mind, let me know now.

Jim

cushioncrawler
03-28-2007, 05:02 PM
Jim -- I sent a PM re this stuff. U could check cushion ht allso, i am uzing 0.65D at prezent. madMac.

cushioncrawler
03-29-2007, 08:50 PM
<blockquote><font class="small">Quote Jal:</font><hr> .....Of course, you should get around another degree of assistance from the flatspot too....<hr /></blockquote> Jim -- I think i have found the missing "3rd dose" holy grail. My rough calcs suggest that the flatspot-sqeez angle is 0.8dg. But, the added rebound angle iznt 0.8dg, it iz actually 2.7dg.

Its like this. I input a balltoball friction of 0.12 (6.8428dg), which is i think about the max that Dr Dave etc would permit. But, this 6.8428 inkloodz FSS -- thusly this 6.8428 iz actually made up of 7.6428dg of true friktion minus 0.8dg of FSS.

Nextly, koz we have superspin, the FSS needs to be added, not subtracted. Thusly, the true-friktion (true-throw) of 7.6428dg is helped by the FSS, ie it becomes 8.4428dg. Thusly, FSS immediately adds 1.6dg to the OB angle, before it "hits" the cushion. Inputing theze new values into my cushion rebound program, i can now get the miracle trick shot on paper -- ie i can exceed the needed 85.1187dg.

But it would be good to get thoze test rezults we mentioned earlyr. And, i havta do a proper audit of my program. madMac.

Jal
03-29-2007, 11:50 PM
Mac, unfortunately, I think there might be a problem with the asumption that -0.8 deg is included in the throw angle corresponding to mu=0.12. From Dr Dave's document on throw, Marlow got a coefficient of 0.11 with a very slow shot speed of 0.1 m/s at a 45 deg cut angle. This works out to an included flatspot effect of only about 0.01 deg (assuming a contact of 0.2 msec). Doubling the contact time and therefore doubling the 0.01 deg doesn't of course do much either. Sorry Mac, or am I not seeing this right?

Jim

cushioncrawler
03-30-2007, 02:46 AM
<blockquote><font class="small">Quote Jal:</font><hr> Mac, unfortunately, I think there might be a problem with the asumption that -0.8 deg is included in the throw angle corresponding to mu=0.12. From Dr Dave's document on throw, Marlow got a coefficient of 0.11 with a very slow shot speed of 0.1 m/s at a 45 deg cut angle. This works out to an included flatspot effect of only about 0.01 deg (assuming a contact of 0.2 msec). Doubling the contact time and therefore doubling the 0.01 deg doesn't of course do much either. Sorry Mac, or am I not seeing this right?... <hr /></blockquote>Jim -- U are correct. So, recrunching the numbers (using 0.1dg, and 0.8dg, and true-friktion =0.1218), the corrected 3rd-dose brings the cutback angle to only 85.88dg at best, a bit short of the needed 85.12dg.

But, if Marlow's maximum friction (0.11) woz gotten at 0.1m/s, then this opens up a huge new avenue of investigation, ie to find whether friction can exceed 0.11 in some circumstances. Certainly, a creampuff 0.1m/s is just arseking for a kick up the behind. I'll be back. madMac.

dr_dave
03-30-2007, 12:58 PM
<blockquote><font class="small">Quote cushioncrawler:</font><hr>... if Marlow's maximum friction (0.11) woz gotten at 0.1m/s, then this opens up a huge new avenue of investigation, ie to find whether friction can exceed 0.11 in some circumstances. ...<hr /></blockquote>Higher friction values most certainly occur when the balls are clingy due to roughness, dirt, and/or chalk smudges. FYI, on pages 6 and 7 of TP A.27 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-27.pdf), I show the effects of various ball conditions on both throw and spin transfer.

Regards,
Dave

Paul_Mon
03-30-2007, 04:09 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> Higher friction values most certainly occur when the balls are clingy due to roughness, dirt, and/or chalk smudges. <hr /></blockquote>

Dave,

I'm convinced that the polish used at the pool hall I frequent is "sticky" on ball to ball collisions causing excessive throw. And yet the cue ball slides like a normal polish. This is not necessarly a bad thing, just something different that you need to adjust for. Many of the "cue ball induced throw" shots are much easier because of this. I'll try and get the name of the stuff this weekend.

regards.......Paul Mon

cushioncrawler
03-30-2007, 06:13 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote cushioncrawler:</font><hr>... if Marlow's maximum friction (0.11) woz gotten at 0.1m/s, then this opens up a huge new avenue of investigation, ie to find whether friction can exceed 0.11 in some circumstances. ...<hr /></blockquote>Higher friction values most certainly occur when the balls are clingy due to roughness, dirt, and/or chalk smudges. FYI, on pages 6 and 7 of TP A.27 (http://www.engr.colostate.edu/~dga/pool/technical_proofs/new/TP_A-27.pdf), I show the effects of various ball conditions on both throw and spin transfer. Regards, Dave<hr /></blockquote>Dr Dave -- It will be August before i can get around to looking into balltoball friction. I have Koehler under my desk as i speak (type), but he duznt say much about effect of speed etc. I would like to have Marlow under my desk allso, perhaps later in the year, so that i can check his work. I hate friction tests. Polishing the balls on your shirt each time. Looking closely to find a pristene area (of ball) without impact marks. Stuffing up the pace. I think it all needs a very accurate and very large ball-ramp. Plus, this time, i will havta check True-Friction (uzing a pendulum for the OB), and Pure-Friction (wait a minute, i dont think there is any such term, i just made it up???). madMac.