Do you adjust your aim for different spins and speeds?

[td873]

speed itself isn't a force that acts directly on the OB's direction - it can only change the effectiveness of some other force that does act directly on the OB's direction

IMO, (changing the speed of a shot) which (changes the effectiveness of something else) which (ultimately affects the result), necessarily implies that speed affects the result. This appears to be a simple application of the transitive property. A affects B. B affects C. Thus, A affects C.

See grapsh 1-3 at each point (0,0). See also Dr. Dave "Speed has a large impact on both cut-induced-throw (CIT)..." and the OP "Speed alone has a considerable effect on the amount of throw"

The cut angle changes as speed changes because the friction between the two balls changes as speed changes

Can you please expound on how the friction (of a ball collision) changes? I am not seeing how hitting a ball harder/softer changes any physical properties or coefficient of friction between the balls. IMO, the friction is always the same.

Lastly, I am aware that there is an inherent ambiguity using just the word "throw" (i.e, without using EIT and CIT). Please use judgment and context as appropriate.

-td

 

[dr_dave]

friction ain't constant with speed

Can you please expound on how the friction (of a ball collision) changes? I am not seeing how hitting a ball harder/softer changes any physical properties or coefficient of friction between the balls. IMO, the friction is always the same.

Often friction coefficients are assumed to be constant (e.g., in basic physics books); but with pool balls, friction ain't even close to constant with speed (e.g., see the example data in TP A.14 and TP B.3).

Regards,
Dave

 

[whitewolf]

I have never read Dr. Dave and never will. No disrespect to you detailed guys because there are some who really appreciate your stuff.

I do everything by feel.

 

[dr_dave]

Do you dislike all books, or just mine?

I have never read Dr. Dave and never will.

That's a very strong statement. I can see why most people wouldn't want to read my TP stuff (that's just for the technical math/physics nerds out there), or even some of my more-technical articles, but do you even extend this statement to my book? I am proud that my book is well-illustrated with numerous full-color diagrams, photographs, and examples. That's why I gave it the title: "The Illustrated Principles of Pool and Billiards." Even people who don't like to read might still like (and maybe even benefit a little from) my book. But maybe you don't like any instructional pool books, in which case I am not offended.

Dave

 

[PKM]

I have never read Dr. Dave and never will. No disrespect to you detailed guys because there are some who really appreciate your stuff.

I do everything by feel.

You say no disrespect, but that came off as unnecessarily insulting. Unless there is something specific about Dr. Dave, just say you don't like to read any analysis of pool. There's nothing wrong with that. In which case why are you reading this thread? It seems someone always has to chime in with their contribution of: "just use feel."

I think almost anyone who enjoys learning about the game can learn something from Dr. Dave's book. It doesn't mean you have to start analyzing every shot any more than before (I should add, the book often has a more analytical approach than others but that is its value-added, it is still accessible and does not use math).

 

[Colin Colenso]

Here's what I think.............

You loved math class and I loved recess.

I live by "The Inner Game of Tennis" and you live by a physics book.

Seriously though, if you can visualize your shot then your subconscious mind can do all that (math) without your conscious mind (ego) getting in the way.

"trust in the force Luke"..................

td

There's no doubt that over thinking initially makes the game harder, but I look at it more like an air plane pilot. Years ago pilots flew mostly by instinct, today, in most circumstances the plane can fly more accurately using auto-pilot, which has over the years found ways to predict and adjust to the many variables used in flying a plane.

So if an adjustment method is developed for certain areas of pool aiming, then these factors can become like auto-pilot for the pilot that has learned that system well.

There is always plenty of scope for a player to use imagination, intuitive adjustments, touch and other variables that affect playing performance.

Colin

 

[Colin Colenso]

I do everything by feel.

No you don't and no player can. You hit the CB below center because you know it makes the CB come backwards. You use reflective systems when kicking off rails and even add english to expand or contract angles as required on these kick shots. You aim right of OB center when you want to cut the OB to the left and I'm sure you have developed other areas of systematic physical knowledge, albeit vague and imprecise that forms some backbone to your intuitive adjustments for shot execution.

Fact is everyone plays using physical knowledge systems, just some of us guess less than others and some of us use different systems to others.

It is probably more accurate to say that you don't like thinking about systems or physics. That's fine, the world needs dreamers too

 

[av84fun]

A more careful experiment shows the rather large effect of speed on throw. See http://www.sfbilliards.com/articles/1995-06.pdf and Phil Capelle's first book. A major point that many seem to overlook is that a stunned cue ball is like the first ball in a close combination for the purposes of throw. A follow-on is that a rolling cue ball is different from the first ball in a close combination.

Just for clarity, the portion of the post you quoted was my quotation of Jack Koehler and not my own views.

Regards,
Jim

 

[av84fun]

Of course youve gotta adjust for aim,speed,throw and squirt. I thought that was just a given.

But adjusting correctly is the issue...and the stuff of champions.

Regards,
Jim

 

[av84fun]

Don't forget swerve! Or by "squirt" do your mean "effective squirt" or "sqwerve," which accounts for both squirt and swerve?

Regards,
Dave

I always think in terms of "effective squirt" or the word you coined (I think) "sqwerve".

regards,
Jim

 

[td873]

Often friction coefficients are assumed to be constant (e.g., in basic physics books); but with pool balls, friction ain't even close to constant with speed (e.g., see the example data in TP A.14 and TP B.3).

Regards,
Dave

I have read and tried to digest these, but frankly, got lost in the TP a-14 at the description of limiting frictional effects (equation 15). I tried to bypass it, but the following Marlow table was not intuitive (to me anyway).

In any event, I am not confident that I was able to use the graphs provided to understand the relationship between friction and speed in any discernable way. Specifically referencing pg 6 of TP a-14 and pg 3 of TP B-3, the most I could gleen was that up to about 20 degrees in TP a-14 adn 30 degrees in B-3, the balls react similarly at all speeds. After that angle, the balls behave differently. That is, up to this angle, friction is the most limiting effect for all speeds. After 20/30 degrees, kinetics is the most limiting factor as speed increases. This may be backwards as well (making kinetics the limiting effect up to 20/30 degrees, and friction the limiting effect thereafter). In sum, I'm not sure if this is even close to accurate, but I am still assuming these are the data points you were referencing above.

Lastly, I'd be interested in a slightly higher level explanation to wrap my head around this concept in order to be able to discuss it further.

Regards,

-td

 

[Patrick Johnson]

IMO, (changing the speed of a shot) which (changes the effectiveness of something else) which (ultimately affects the result), necessarily implies that speed affects the result.

Yeah, that's probably why I said this:

Of course the cut angle changes as speed changes; it's just not because of "speed alone, independent of throw" as you said.

pj
chgo

 

[dr_dave]

Thank you.

I think almost anyone who enjoys learning about the game can learn something from Dr. Dave's book. It doesn't mean you have to start analyzing every shot any more than before (I should add, the book often has a more analytical approach than others but that is its value-added, it is still accessible and does not use math).

Thank you for the support and for the nice words about my book.

Regards,
Dave

 

[dr_dave]

understanding "friction vs. speed"

First of all, let me start with the statement at the top of the technical proofs (TP) section of my website:

NOTE: this information will be of interest only to people with
strong physics and mathematics backgrounds.
Others proceed at your own risk.
​

The reason why throw doesn't depend on speed at small cut angles (for CIT) and small amounts of English (for SIT) is:

If the speed of relative motion between the ball surfaces during impact is slow enough, the CB grabs the OB (i.e., friction is strong enough to prevent or stop sliding during impact). If the sliding stops during impact, then speed has no effect on the resulting throw. When there is sliding between surfaces, it turns out the friction force depends on the speed of the sliding (we're not in Kansas anymore). At slow sliding speeds, the balls grab a little more during sliding and create more throw. At faster sliding speeds (due to a larger cut angle and/or more English, especially "inside"), the surfaces tend to float on each other more and the little irregularities on the surface don't grab each other as readily. Marlow, Jewett, and I have done experiments to verify this effect (see my September '06 article).

I hope that helps,
Dave

I have read and tried to digest these, but frankly, got lost in the TP a-14 at the description of limiting frictional effects (equation 15). I tried to bypass it, but the following Marlow table was not intuitive (to me anyway).

In any event, I am not confident that I was able to use the graphs provided to understand the relationship between friction and speed in any discernable way. Specifically referencing pg 6 of TP a-14 and pg 3 of TP B-3, the most I could gleen was that up to about 20 degrees in TP a-14 adn 30 degrees in B-3, the balls react similarly at all speeds. After that angle, the balls behave differently. That is, up to this angle, friction is the most limiting effect for all speeds. After 20/30 degrees, kinetics is the most limiting factor as speed increases. This may be backwards as well (making kinetics the limiting effect up to 20/30 degrees, and friction the limiting effect thereafter). In sum, I'm not sure if this is even close to accurate, but I am still assuming these are the data points you were referencing above.

Lastly, I'd be interested in a slightly higher level explanation to wrap my head around this concept in order to be able to discuss it further.

Regards,

-td

 

[whitewolf]

It is probably more accurate to say that you don't like thinking about systems or physics. That's fine, the world needs dreamers too

I took 2 and 1/2 years of physics at UVa and did quite well thank you.

I personally like to spend my valuable time shooting versus thinking about pyhsics.

You guys just DON'T GET IT. Maybe you didn't take statistics in college.

It goes like this: you can study all of the physics you want to learn to have a decrease in the margin of error of 5% due to throw, etc. but if your stroke is off you could have a much larger increase in the margin of error. Things like stance, grip, pressure of the grip, the stroke - these are what are important! Not dilly dallying over stupid ass physics details.

To me, to reiterate, it is a matter of how best to spend my time when trying to get better at pool.

BTW Colin, you have an awesome break and I very much appreciated your clip. When you go back to the IPT, contrary to what I originally advised you to break softly, with a break like that, you should go for running out every time.

 

[Colin Colenso]

I took 2 and 1/2 years of physics at UVa and did quite well thank you.

I personally like to spend my valuable time shooting versus thinking about pyhsics.

You guys just DON'T GET IT. Maybe you didn't take statistics in college.

It goes like this: you can study all of the physics you want to learn to have a decrease in the margin of error of 5% due to throw, etc. but if your stroke is off you could have a much larger increase in the margin of error. Things like stance, grip, pressure of the grip, the stroke - these are what are important! Not dilly dallying over stupid ass physics details.

To me, to reiterate, it is a matter of how best to spend my time when trying to get better at pool.

BTW Colin, you have an awesome break and I very much appreciated your clip. When you go back to the IPT, contrary to what I originally advised you to break softly, with a break like that, you should go for running out every time.

Whitewolf,
I don't think I have any delusions of the potential of physics in the pool game,, though I'm surely more optimistic about its potential than the normal player.

You saw my break. That wasn't a result of pure intuitive force, but the result of studying biomechanics and breaking strategy. In the IPT this training took me from 35% balls made off break in the North American Open to around 70% balls made on break in the World Champs, and a resultant 31.25% Break & Run percentage which ranked me 56 of about 200 players, 100 of which were great players. Given more time,more tournaments and more skill, I believe I could have got the B&R percentage to 40%+ which would have put me into contention. I had had 7 years outside of serious pool before that tournament and limited experience with US tables and balls.

I don't presume that physics knowledge allows a player to become great by study alone. There are many factors in pool, including the trialling of systems that require hundreds, if not thousands of hours to develop control over.

I just think some aspects of play can be learned more quickly and efficiently if they are based on reliable systems, but these systems cannot be independent of skill.

My system is based on the assumption that a player can pocket most shots using natural medium speed roll with high regularity. To do this requires considerable diligence and talent.

In the coming months I'll explain more about this system and release a DVD that will hopefully make things clearer. I think every player can gain some improvements from a deeper knowledge of the physical interactions of balls and squirt and swerve..

Colin

 

[Patrick Johnson]

To me, to reiterate, it is a matter of how best to spend my time when trying to get better at pool.

So what are you doing on here?

pj
chgo

 

[unknownpro]

Squirt is the same on a block of ice as it is on a pool table. Swerve is what varies with friction between the ball and cloth. Squirt, swerve, and throw are separate effects that all come into play when using English. For more info, see:

http://billiards.colostate.edu/threads/aiming.html#compensation​

Regards,
Dave

Yes, but what is it? It's the same, ok. What is it for any specific reasonable cue. On a block of ice, or an imaginary pool table with no curve, how far is it possible to deflect a ball with any normal kind of cue without miscueing from the line of aim of the tip. Like in inches over a 6 foot shot or something. Or as an angular deflection. Are we talking an inch, two inches, two feet, or what?

 

[dr_dave]

squirt info and example value

Yes, but what is it? It's the same, ok. What is it for any specific reasonable cue. On a block of ice, or an imaginary pool table with no curve, how far is it possible to deflect a ball with any normal kind of cue without miscueing from the line of aim of the tip. Like in inches over a 6 foot shot or something. Or as an angular deflection. Are we talking an inch, two inches, two feet, or what?

I have links to some squirt data, from different sources, here:

http://billiards.colostate.edu/threads/squirt.html#data​

The amount of squirt depends on the "endmass" of the cue, the amount of tip offset, and the weight of the CB. If you just want a ballpark value for a typical cue for a maximum English shot, it is about 0.5 inch per foot; so over 9 feet, you could get about 4-5 inches of cue ball deflection!

If you want more info about squirt, I have lots of info and resources here:

http://billiards.colostate.edu/threads/squirt.html​

Regards,
Dave

 

[Patrick Johnson]

Yes, but what is it? It's the same, ok. What is it for any specific reasonable cue. On a block of ice, or an imaginary pool table with no curve, how far is it possible to deflect a ball with any normal kind of cue without miscueing from the line of aim of the tip. Like in inches over a 6 foot shot or something. Or as an angular deflection. Are we talking an inch, two inches, two feet, or what?

This is exactly what your shaft's "pivot length" tells you: the cue ball will be [tip offset] off line for each [pivot length] it travels.

So if you're using maximum sidespin (say your tip offset = 1/2"), and your pivot length = 12" (for example), then the cue ball will be 1/2" off line for each 12" that it travels.

If you think about it, this also explains why pivoting at the pivot point to apply sidespin compensates for squirt (if there's not much swerve).

pj
chgo

P.S. I've used 12" as the assumed pivot length in this example so it matches Dave's estimate (I think it's a fairly common pivot length), but if your pivot length is longer or shorter, then the amount of squirt will change proportionately. For instance, if your tip offset = the same 1/2" but your pivot length = 24" (a lower squirt shaft), then the cue ball will be 1/2" off line for each 24" of travel (half as much squirt). And if your pivot length = 6" (a higher squirt shaft), then the cue ball will be 1/2" off line for each 6" of travel (twice as much squirt).