$100 Spin Challenge

[SJDinPHX]

Excellent post.

I would like to add that sometimes improved understanding and knowledge does lead to useful information that can be applied at the table. It can also help somebody learn, teach, and improve more effectively. Also, sometimes physical understanding might help the cue industry create better products.

Bad information and myths can and have slowed progress of the industry and individuals wished to learn and improve at the game. I don't think we need to defend ourselves for trying to help create understanding, even if this understanding can't "create a champion." I think it is ridiculous to even suggest information, knowledge, and understanding can "create a champion." Champion-level pool requires too much feel, hand-eye coordination, visual perception, etc. That kind of stuff can come only with natural talent and many years of successful practice and experience.

Regards,
Dave

John B., P.J., and Dave,

In my diatribes against "science based aiming systems" you guys are under the mistaken impression I am holding myself up as an example.
I am (was) only a shortstop compared to guy's like Earl, Johnny, Buddy, Efren etc.
My skill level maxed out learning one pocket moves, I have always been envious of their potting skills. You are right John, I have spent a lot of time in the trenches against some great player's, but not at games like 9/10 ball.
I think Dave's last paragraph pretty well sums up what I've been saying all along.
Having been duly chastised, I shall take my balls (whats left of them) and go back to 1P.org. :smile:

Carry on men,

Dick

P.S.(Parting Shot) I still think old "war stories" are more enjoyable than debating the laws of physics.

PS> PJ, very nice of you (and IUTBR, indirectly) to contribute to OTR. You've shown us all you are stand-up guys. Have a great New Year !!!

 

[SJDinPHX]

John B., P.J., and Dave,

In my diatribes against "science based aiming systems" you guys are under the mistaken impression I am holding myself up as an example.
I am (was) only a shortstop compared to guy's like Earl, Johnny, Buddy, Efren etc.
My skill level maxed out learning one pocket moves, I have always been envious of their potting skills. You are right John, I have spent a lot of time in the trenches against some great player's, but not at games like 9/10 ball.
I think Dave's last paragraph pretty well sums up what I've been saying all along.
Having been duly chastised, I shall take my balls (whats left of them) and go back to 1P.org. :smile:

Carry on men,

Dick

P.S.(Parting Shot) I still think old "war stories" are more enjoyable than debating the laws of physics.

PS> PJ, very nice of you (and IUTBR, indirectly) to contribute to OTR. You've shown us all you are stand-up guys. Have a great New Year !!!

Can you hear me now ?

 

[SpiderWebComm]

Can you hear me now ?

I hope you don't leave azb because you're frustrated with a handful of science guys. Yeah, they're like having an itchy asshole when you have stumps for arms, but they're good people. They just like to prove that the angle of the dangle is inversely proportionate to the heat of the meat and how it applies to the SIN and COS of the angle of your dogs urine stream. None of it applies to actually playing - they just like to figure out why the sky's blue. Can't hate on them for that.

I really like to read you input on a lot of things - you're one of the very top players on here. Tell people to f off more often than to get upset, take your balls and go to 1p.org. Just my opinion.

Dave

 

[Thunderball]

No rep for you Dave,although you achieved belly laugh...that spread em around thing.

Yeah, they're like having an itchy asshole when you have stumps for arms, but they're good people. They just like to prove that the angle of the dangle is inversely proportionate to the heat of the meat and how it applies to the SIN and COS of the angle of your dogs urine stream.

 

[dr_dave]

Dr. Dave,

Glad to see you're apparently feeling better. What I meant was that the effective offset b' is given by:

b' = Rsin[arcsin(b/R) - A + k(Wav)T]

where b is the initial contact point offset, A the squirt angle, and the last term is the amount of ball rotation during impact that contributes to the final effective offset. For an approximately symmetric force function over time, Wav (the time-averaged angular velocity) is about half the final angular velocity. The factor k, as best I can figure, is something like 1/5 or 1/4, which comes from considerations of the time-averaged torque divided by the time averaged force. It's somewhat dependent on the shape of the force-time curve, but doesn't vary much with different curves.

So if you compare two shots struck at (2/5)R at two different speeds, with total ball rotations of 2 and 4 degrees (WavT), respectively, using k=.25, and assuming squirt angles of 2.5 degrees with a high squirt stick, and 1.8 degrees with a low squirt stick, the ratios of effective tip offset are:

lower speed (2 degrees of rotation):

(b'/R)lowSq/(b'/R)highSq = sin[23.578 - 1.8 + .25(2)]/sin[23.578 - 2.5 + .25(2)] = 1.031

higher speed (4 degrees of rotation):

(b'/R)lowSq/(b'/R)highSq = sin[23.578 - 1.8 + .25(4)]/sin[23.578 - 2.5 + .25(4)] = 1.030

The calculation is a "first order" type since everything affects everything else. But the "perturbations" are very small. Nevertheless, it seems I grossly overstated the effect of ball rotation at higher speeds smoothing out the differences between cues! Intuition suggested it would be more than this. Do you agree, more or less, with the logic and conclusion?

My intuition agrees with your basic analysis results. A couple of degrees of rotation doesn't change the mechanics very much. I'm glad, because I think the effects would be difficult to model accurately without lots of super-high-speed video (and/or accelerometer) experiments.

One thing that it indicates is that the difference in resultant spin/speed ratios between the hypothetical high and low-squirt cues is about 3%. This is pretty small, but larger than a fraction of a percent. Does this sound reasonable?

I need to look back to see where I got the fractional percent. I'll let you know when I do.

Jim (and Colin),

I finally got around to checking all of my numbers, and my result now agrees with yours. A low-squirt cue should only be able to create about 2-3% more spin than a typical regular-squirt cue at maximum tip offset. The analysis and results can be found in TP B.7. Sorry for the tardiness in my reply. I've been quite busy trying to catch up with things lately.

Regards,
Dave