physics-based draw shot advice

[scottjen26]

All makes sense, thanks for posting!!!

I recently inadvertently discovered/confirmed #'s 2 and 3. I hurt my left thumb (torn ligament), swollen and sore etc. Made bridging and stretching my hand difficult for a few weeks. I actually started aiming my draw shots a little higher on the cue ball - I was flinching before contact because of the anticipated pain and miscuing a lot. Once the thumb healed more, I noticed I was actually getting a little more draw, and more consistently, at my new position, and my risk of miscuing went to nearly 0!

Scott

 

[shinigami]

I think Koehler's book is excellent. I used it as a resource when I was working on my book. However, I don't agree with his statements about acceleration. Cue speed, not acceleration, is what gives the CB speed and spin. Most people accelerate very little at ball impact. And acceleration during impact will have negligible effect with a normal pool stroke anyway. Actually, if you accelerate too late, you have lost the opportunity to create more cue speed (by accelerating earlier). For more info, see the video, article, and analysis links here:

http://billiards.colostate.edu/threads/stroke.html#acceleration​

Having said all of this, the advice to "accelerate into the ball" might actually help some people create a smoother stroke with more cue speed and a good resulting follow through. But again, the final cue speed (just before impact), and the tip offset, are what are important.

Regards,
Dave

A very polite, but nonetheless, absolute ownage...great post Dr.Dave

 

[Patrick Johnson]

Good draw requires an accelerating cue (stick). The speed at contact is irrelevant. The speed of the cue at loss of contact is the key issue.

All three of these statements are backwards. Good draw requires a cue that's moving fast. Acceleration (positive or negative) is irrelevant. The speed of the cue at loss of contact is irrelevant (in fact, it's about half what it was at impact).

If you misunderstood my experiment, it was a "limiting case."

To be a limiting case it would have to be an event similar in character to the case in question. Pushing the cue ball isn't similar to hitting it.

Move the cue tip a millimeter away from the cue ball and do the same experiment.

It wouldn't be the same experiment, but OK.

At contact the cue is moving mighty slowly. At loss of contact, a fraction of a second later because the cue is accelerating, the cue is humming right along.

No matter how far away the cue starts, it will lose speed upon impact, not gain it (and, by the way, acceleration can mean lose speed too, so you have to be careful with your terms).

Draw!

Again, I doubt it, but it's irrelevant to this.

[snip another irrelevant thought experiment]

pj
chgo

 

[mikepage]

[...] Unless I am missing something, I think everything is hunky-dory. Please let me know if you still think otherwise.[...]"

No, I believe you. Thanks.

There is some ambiguity to the phrases "more draw" and "maximum draw."

Your analysis is looking at maximizing cueball spin at object ball impact, right? That would make the cueball draw back the farthest on a full shot.

That particular sense of maximum draw doesn't care how fast the cueball was going when it struck the object ball.

In some situations, a player wants maximum draw for a given object ball speed (like for instance lagging a ball toward your pocket in one pocket and getting maximum draw distance).

Another situation is an angeled shot where you want to pull the cueball back to miss another ball or miss the side pocket or strike as far back on a rail as possible. Here again you want a high spin-to-speed ratio at a relatively low speed.

Another is the draw drill where you put the object ball a diamond from the headrail and see if you can get the cueball back to the headrail before the object ball hits the footrail.

So a common sense of "maximum draw" is maximizing the spin-to-speed ratio at object ball impact.

How would your analysis differ with this stuff in mind?

 

[nickgeo]

QUOTE=Patrick Johnson]All three of these statements are backwards. Good draw requires a cue that's moving fast. Acceleration (positive or negative) is irrelevant. The speed of the cue at loss of contact is irrelevant (in fact, it's about half what it was at impact).

The speed of the cue at loss of contact is the speed of the surface of the ball moving away from it.



To be a limiting case it would have to be an event similar in character to the case in question. Pushing the cue ball isn't similar to hitting it.

A hit is simply a push of short duration.


It wouldn't be the same experiment, but OK.

No matter how far away the cue starts, it will lose speed upon impact, not gain it (and, by the way, acceleration can mean lose speed too, so you have to be careful with your terms).

The cue tip may slow at initial contact (cue and ball both deform) but by continuing the stroke and increasing the cue speed (acceleration) more draw will result.



Again, I doubt it, but it's irrelevant to this.

[snip another irrelevant thought experiment]

pj
chgo[/QUOTE]


Nick

 

[CreeDo]

Dave, nice links in your reply, they cleared up everything for the most part.

One last question, or maybe it's a restatement of my question before.

Given that throwing a ball in with sidespin reduces drift, will I always be better off using side if my goal is to try to draw as straight back as possible? Or are there rare situations where it's preferable to go with pure draw, no side?

I ask this because... years ago, I had of those pool epiphanies. I think this is correct anyway, you can tell me if the physics backs this up.
I wanted to make a rail cut with inside english and get maximum effect, sending the CB as far 'forward' as possible. I figured out that high+inside was not getting as much action as pure side (or even low+inside, a sort of draw-drag version of the pure side).

Normally I'd think that if follow makes the ball go more forward, and inside does as well, then the combination of them would get the absolute maximum effect. But it doesn't. The best way I could wrap my mind around that is to think of the topspin 'diluting' the inside spin on the ball, and the added help from topspin was not as useful as the added effect of extra sidespin grabbing that rail. All of this is based on natural topspin, not force follow btw.

Aaaanyway, long story short, now I'm wondering if the draw effect isn't slightly diluted by using low+outside rather than pure draw, in situations where I really want to draw as straight back as possible.

?

 

[dr_dave]

All makes sense, thanks for posting!!!

I recently inadvertently discovered/confirmed #'s 2 and 3. I hurt my left thumb (torn ligament), swollen and sore etc. Made bridging and stretching my hand difficult for a few weeks. I actually started aiming my draw shots a little higher on the cue ball - I was flinching before contact because of the anticipated pain and miscuing a lot. Once the thumb healed more, I noticed I was actually getting a little more draw, and more consistently, at my new position, and my risk of miscuing went to nearly 0!

Scott

I can't believe so many people are agreeing with these conclusions. I certainly was a little uncertain at first.

Thank you for the feedback.

Regards,
Dave

 

[dr_dave]

No, I believe you. Thanks.

There is some ambiguity to the phrases "more draw" and "maximum draw."

Your analysis is looking at maximizing cueball spin at object ball impact, right?

You are correct. The "maximum draw" results are based on maximizing CB spin at OB impact.

That would make the cueball draw back the farthest on a full shot.

Yes.

That particular sense of maximum draw doesn't care how fast the cueball was going when it struck the object ball.

Yes.

In some situations, a player wants maximum draw for a given object ball speed (like for instance lagging a ball toward your pocket in one pocket and getting maximum draw distance).

Another situation is an angeled shot where you want to pull the cueball back to miss another ball or miss the side pocket or strike as far back on a rail as possible. Here again you want a high spin-to-speed ratio at a relatively low speed.

Another is the draw drill where you put the object ball a diamond from the headrail and see if you can get the cueball back to the headrail before the object ball hits the footrail.

So a common sense of "maximum draw" is maximizing the spin-to-speed ratio at object ball impact.

Excellent points and examples. Thank you for sharing those. Agreed ... in these cases, the "spin-to-speed ratio at OB impact" is what is important.

How would your analysis differ with this stuff in mind?

When I get some time, I'll add some "spin-to-speed ratio at OB impact" plots and conclusions to the analysis. My intuition tells me you want to hit as close to the miscue limit as you can (reliably, without miscue) with these types of shots, but I'm not sure.

Regards,
Dave

 

[dr_dave]

Dave, nice links in your reply, they cleared up everything for the most part.

One last question, or maybe it's a restatement of my question before.

Given that throwing a ball in with sidespin reduces drift ...

... but remember, these types of shots are practical only when the CB and OB are fairly close. See the paragraph after Diagram 3 in my July '07 article.

... will I always be better off using side if my goal is to try to draw as straight back as possible? Or are there rare situations where it's preferable to go with pure draw, no side?

I'm not sure about the answers to these questions, but I do plan to do more analysis over the next couple of weeks to help provide some solid answers.

Thank you (and Mike Page) for the excellent questions that are helping to inspire me to do more analysis.

I ask this because... years ago, I had of those pool epiphanies. I think this is correct anyway, you can tell me if the physics backs this up.
I wanted to make a rail cut with inside english and get maximum effect, sending the CB as far 'forward' as possible. I figured out that high+inside was not getting as much action as pure side (or even low+inside, a sort of draw-drag version of the pure side).

Normally I'd think that if follow makes the ball go more forward, and inside does as well, then the combination of them would get the absolute maximum effect. But it doesn't. The best way I could wrap my mind around that is to think of the topspin 'diluting' the inside spin on the ball, and the added help from topspin was not as useful as the added effect of extra sidespin grabbing that rail. All of this is based on natural topspin, not force follow btw.

Sounds reasonable to me. FYI, I have lots of high-speed clips (and a feature on my HSV DVD) covering these types of shots. For more info, see:

http://billiards.colostate.edu/threads/English.html#rail​

Aaaanyway, long story short, now I'm wondering if the draw effect isn't slightly diluted by using low+outside rather than pure draw, in situations where I really want to draw as straight back as possible.

Sounds reasonable to me. I'll post something after I find time to analyze it.

Regards,
Dave

 

[OILED]

What about.....cloth, balls, humidity, the tip on the cue, player ability and most of all "STROKE". good players can adjust to these conditions with a minimum of work and get maximum draw while weaker players will have much more difficulty with all of the above conditions.

have you ever seen a weaker player try to draw the ball? they use a jabbing like stroke and try to get the tip of the stick out of the way of the QB. they just were never taught how to draw correctly.

when I was taught by my grandfather years ago how to shoot pool he would always say you have to "stroke the ball" and as a beginner I had no idea what he was talking about but then one day I "STROKED" the ball and felt what it was all about.

it was like a lightswitch, in an instant I went from not knowing to knowing what stroke was and once I had the feel of it I knew it, from then on I was drawing the ball like crazy (which may have been a bad thing to this day I prefer to draw the ball rather than follow) I dont know if stroke can be taught for me it was a "feel it" thing more than someone trying to explain it

later on as I got older and started to understand the physics involved I realize in its simplest form the best draw stroke gets the QB spinning with maximum amount of reverse spin before contact with the OB at which time the sudden stop results in all that spin grabbing the cloth and reversing the path of the ball.

of course the QB is actually "sliding" forward but spinning backwards. sometimes when I am in dead stroke I can hit the ball so soft and get a full table draw and at other times when not in dead stroke I can still draw the ball but it seems to take much more effort.

as I mentioned above the cloth is a major factor, simonis and centennial draw like crazy while standard felt still goes but with a lot more stroke and effort. If it is humid the balls don't go as fast. if the balls are dirty or are not of good quality they are hard to move. the choice of tip will effect the way the ball draws. and player ability wow this one can go on and on I know players that have been in our league and at some tournaments that play exactly the same today as they played years ago, no advancement in thier game or thier abilities.

anyway thats my two cents sorry if it went on long but I guess I had a lot to say

 

[Patrick Johnson]

The speed of the cue at loss of contact is the speed of the surface of the ball moving away from it.

The ball leaves the cue at a speed greater than the maximum speed of the cue. It's counterintuitive, but true.

A hit is simply a push of short duration.

A "push shot of short duration" is not a push shot. The cue interacts with the ball in different ways for a push shot vs. a normal shot - that's why a push shot is illegal.

The cue tip may slow at initial contact (cue and ball both deform) but by continuing the stroke and increasing the cue speed (acceleration) more draw will result.

The ball is gone before your cue can speed up again at all - in fact, the cue never reaches its impact speed again, much less exceeds it. This has been shown with high speed video.

pj
chgo

 

[CreeDo]

doc, it's cool you're gonna research those things, I can't wait to check the result. I actually had seen your page before and downloaded every clip on it about a year ago. I seem to remember some awesome slo-motion slaps too lol. So it's nice to meet the guy who makes it happen. I never thought I could get real scientific testing and calculations for these things.

Is there math that could calculate the deflection of any given stick, if there were some reliable way to measure its whippiness or whatever we want to call it? Or are there too many variables for such a thing?

Another subject (anyone can answer this). I've heard that a push is legal if the CB and OB are truly frozen, because there's no double hit involved... the 2 balls flee from the tip at the same time as one piece, and double hitting is impossible here. But if there's a tiny bit of air between them the CB hits the OB, freezes for a split second, and then the tip smacks it a second time to create the foul we call a push.

So do people go by the book and call 'em like this? Our local leagues barely know about push, and I'm not sure a lot of them understand it, so nobody even tries to make a distinction between frozen or not.

 

[Solartje]

Dave ive been reading and watching this thread, and ive got a question/observation. IF i understand it all well, this shouldnt be a stupid question.

ITs about cue-elevation (i know you still have to analyse this in more depth) but it might be something to put on the list of goals.


If you bridgehand with closed bridge is at the hight (compared to the slate) of 1ball diameter - (1/2 of shaft diameter). AKA the exact hight to hit centerball.

If now you aim with the same bridge to the 80% limit, you get the best powerdraw according to the plots.


Now is it safe to say:
That the speed the cb will travel to the ob, depends on the angle between the centerline of the shaft and the horizontal line true the CB absolute center(as the movement is horizontal)
The bigger the angle , the slower the CB will travel, the more lag, the less draw you get.

Now if you use a openbridge, flatten your hand, so that the hight of the bridgehand is only 0.5". If you hit the cb at the exact same place as with the closed bridge, the angle i described before is smaller.
Smaller angle, means faster cb, means less drag, means more spin.

So for powerdraw shots, i think that using a flat open bridge helps on powerdraw

Now i know that elevating the cue gives more spin. Apart from the jumping, i think the main reason why you get more spin, is because your increase the tip offset, even though you are hitting the same offset. sounds weird, but itsnt. The bigger tipofset, gives more spin.

elevating the cue's impact on CB jumping.
Jump distance = influenced by speed and angle its stroked.
elevated cue + closed bridge = Big angle + low speed (cfr post before, where bigger angle reduces speed)
Elevated cue + open bridge = smaller angle + higher speed.

Now wich of the two is the best?
Its the open bridge, as the max height the cb gets is lower, the energy lost on impact is lower (gravitation is dependend on height...)

So for each shot= the perfect combination of ofset and speed changes as the plots show, but on general rule, a open bridge gives you more draw if you are able to controle the cb as well as with a closed bridge.


brbr gonna make some quick drawings to clear the things up :embarrassed2: i dont think anyone got what i wanted to explain... grmbl

edit 1 : in short: you havent put the hight of the griphand in all the math, where it is an important given. I supose on all the callculations you used the center of the cue at griphand exactly as high as the mass centre of the cb right?

 

[Solartje]

ok basic drawings:

So
A= elevated cue due to closed bridge = more spin, less speed
B= "flatter" cue due to open bridge = less spin, more speed.

As dave stated=

Long cb-ob distance, the better is less spin, more speed. wich corresponds with a open bridge or non elevated cue.
short cb-ob distance, the better is more spin, less speed. Wich corresponds with an closed bridge or elevated cue.


the jumpdistance is close to equal i think . On one the angle is higher but the speed is slower, so the cb jumps as far as a lower angle with a high speed. Same distance jumped, aka same amount of drag after the jump, but with a low angle, high speed aka open bridge the force lost on impact is smaller as the cb falls from less high.

So i asume that when you use a slight jump to increase the draw (mostly on long distance shots. i dont see any point in jumping on distances lower then 1 feet, as amount of energy won by not draging aquals the amount ot energy loss by contact on slate after jump (more or less , ofcourse) , the best is to use a open bridge (aka explanation i gave before) + small elevated cue (to jump and reduced drag) but not lose to much energy on impact with the slate...

Are these asumptions right?
they do say the same as what i have experienced with power drawshots.

 

[Clark_the_Shark]

Before answering my question, I'm really interested in the answer to Solartje's question right above mine. His question brings to mind a few players I know that look like they aim at center ball, but on last stroke hit down on the ball and get massive draw. This larger angle here he is referring to must be what I'm seeing....

So, to my question (probably a stupid one given the intellectual pool superiority of most of the respondents) but here goes...

Sometimes, I hit the ball I would say "very hard" and low on the cue ball. How low? I don't know, probably not at miscue limit, but low enough) but the ball doesn't "snap" back hardly at all. It will draw, but not very far, and this would be from a distance of say 3-5 feet between OB & CB. Is it possible that the draw "doesn't have time to fully accumulate on the CB" because of the high speed in which it was hit? And that if the OB was further away it would have drawn further? I know that my CB has a tendancy to draw further the slower I hit it, but when the distance gets larger between OB & CB, I just can't seem to get it into my mind to hit it softer over that far of a distance.

I hope this makes sense and doesn't sound too stupid, but thanks for your help.

 

[mikepage]

[...]
Sometimes, I hit the ball I would say "very hard" and low on the cue ball. How low? I don't know, probably not at miscue limit, but low enough) but the ball doesn't "snap" back hardly at all. It will draw, but not very far, and this would be from a distance of say 3-5 feet between OB & CB. Is it possible that the draw "doesn't have time to fully accumulate on the CB" because of the high speed in which it was hit? And that if the OB was further away it would have drawn further?

Definitely NO to both questions.

I know that my CB has a tendancy to draw further the slower I hit it, but when the distance gets larger between OB & CB, I just can't seem to get it into my mind to hit it softer over that far of a distance.

I highly suspect that when you hit harder, you're not hitting as low on the cueball as when you hit softer. This is very common. If you use a striped ball as a cueball, you can check after the shot to see where the chalk mark appears. I recommend trying this.

 

[dr_dave]

high-speed video stroke analysis

The ball leaves the cue at a speed greater than the maximum speed of the cue. It's counterintuitive, but true.

A "push shot of short duration" is not a push shot. The cue interacts with the ball in different ways for a push shot vs. a normal shot - that's why a push shot is illegal.

The ball is gone before your cue can speed up again at all - in fact, the cue never reaches its impact speed again, much less exceeds it. This has been shown with high speed video.

Here is one such video that demonstrates and explains the speed and acceleration changes during the stroke:

HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett​

Regards,
Dave

 

[dr_dave]

the chalk mark doesn't lie

I highly suspect that when you hit harder, you're not hitting as low on the cueball as when you hit softer. This is very common. If you use a striped ball as a cueball, you can check after the shot to see where the chalk mark appears. I recommend trying this.

I concur. I have seen this with many people (including myself), and some people (including myself) refused to believe it until you use a striped ball (or Elephant Practice ball or Jim Rempe CB). The chalk mark doesn't lie.

Regards,
Dave

 

[dr_dave]

Is there math that could calculate the deflection of any given stick, if there were some reliable way to measure its whippiness or whatever we want to call it? Or are there too many variables for such a thing?

This would be tough to calculate accurately with just math; although, you can find the math and physics basics here:

http://billiards.colostate.edu/technical_proofs/new/TP_A-31.pdf​

However, squirt is relatively easy to measure:

http://billiards.colostate.edu/threads/cue.html#pivot​

Another subject (anyone can answer this). I've heard that a push is legal if the CB and OB are truly frozen, because there's no double hit involved... the 2 balls flee from the tip at the same time as one piece, and double hitting is impossible here. But if there's a tiny bit of air between them the CB hits the OB, freezes for a split second, and then the tip smacks it a second time to create the foul we call a push.

See:

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

Regards,
Dave

 

[dr_dave]

The "tip offset" is always measured between the line of action of the cue and the center of the CB, regardless of the cue elevation (e.g., see the diagram here:

http://billiards.colostate.edu/technical_proofs/new/TP_A-22.pdf​

If you account for squirt (CB deflection), then the effective tip offset is defined a little differently (see the diagrams in TP B.7), but cue elevation is still handled the same way.

When you elevate the cue, but maintain the same tip offset, you lose some forward speed as the CB is driven down into the table. You also lose some spin, depending on how much ball is off the tip while it is rebounding off the table. While the CB is airborne, between bounces, it loses no speed or spin. There is a lot going on here. That's why I need to do more filming and more analysis.

Regards,
Dave

Dave ive been reading and watching this thread, and ive got a question/observation. IF i understand it all well, this shouldnt be a stupid question.

ITs about cue-elevation (i know you still have to analyse this in more depth) but it might be something to put on the list of goals.


If you bridgehand with closed bridge is at the hight (compared to the slate) of 1ball diameter - (1/2 of shaft diameter). AKA the exact hight to hit centerball.

If now you aim with the same bridge to the 80% limit, you get the best powerdraw according to the plots.


Now is it safe to say:
That the speed the cb will travel to the ob, depends on the angle between the centerline of the shaft and the horizontal line true the CB absolute center(as the movement is horizontal)
The bigger the angle , the slower the CB will travel, the more lag, the less draw you get.

Now if you use a openbridge, flatten your hand, so that the hight of the bridgehand is only 0.5". If you hit the cb at the exact same place as with the closed bridge, the angle i described before is smaller.
Smaller angle, means faster cb, means less drag, means more spin.

So for powerdraw shots, i think that using a flat open bridge helps on powerdraw

Now i know that elevating the cue gives more spin. Apart from the jumping, i think the main reason why you get more spin, is because your increase the tip offset, even though you are hitting the same offset. sounds weird, but itsnt. The bigger tipofset, gives more spin.

elevating the cue's impact on CB jumping.
Jump distance = influenced by speed and angle its stroked.
elevated cue + closed bridge = Big angle + low speed (cfr post before, where bigger angle reduces speed)
Elevated cue + open bridge = smaller angle + higher speed.

Now wich of the two is the best?
Its the open bridge, as the max height the cb gets is lower, the energy lost on impact is lower (gravitation is dependend on height...)

So for each shot= the perfect combination of ofset and speed changes as the plots show, but on general rule, a open bridge gives you more draw if you are able to controle the cb as well as with a closed bridge.


brbr gonna make some quick drawings to clear the things up :embarrassed2: i dont think anyone got what i wanted to explain... grmbl

edit 1 : in short: you havent put the hight of the griphand in all the math, where it is an important given. I supose on all the callculations you used the center of the cue at griphand exactly as high as the mass centre of the cb right?