BHE and low deflection shafts

[Colin Colenso]

Yes, the Platinum Billiards numbers are correct.

There is no mystery - the "shoot into an object ball until the PP is found where the CB spins in place test" is greatly flawed due to the throw effect.

Try this test on a break shot (50") and you will find that the true PP is only lengthened by a couple inches over PB's numbers due to the throw effect. Try the same test with the OB just 10" away and the throw effect will falsely lengthen the apparent PP by more like 2 feet. This is why it is pretty much useless in actual play.

I have metioned before another method which is simple to set up and should convince anyone that tries it:

1) set up a couple of pins slightly more than a ball apart to create a "gate"

2) put a piece of masking tape on your shaft and mark in inches from the tip.

3) Align center ball to shoot thru the gate

4) hold the bridge hand still and pivot so that as example, the tip moves to apply right english and stroke.

5) if the CB hits the left pin, shorten the PP, if it hits the right pin, lengthen it.

This so simple to set up - use two bic lighters...whatever...anything to make a "gate".

Inthezone,

I suspect you are spot on regarding the 'Stop and Spin' shot variation from 50" v 10". This could very well be the major reason why some testers get results of 30+ inches for pivot points.

Thanks for making this seemingly obvious point clearer for me.

Colin

 

[Colin Colenso]

Colin, I certainly don't know if slip is taking place. But an increase in speed should have the tip and ball rotating a little longer together, thus slightly increasing the average tip offset. This should produce a little greater spin/speed ratio and a little more squirt...but not much. Perhaps testing with the same cueball under different surface conditions would reveal whether slip is a significant component?

Jal, that's a reasonable explanation.

I'm still a little confused why earlier theorists were so convinced that speed had no influence over squirt though.

On slip, I'm convinced it must happen to some degree, but it's relative contribution to squirt I am unsure about, especially with the possibility that Rotation Induced Squirt could also vary with speed as you suggest is a possibility.

As they both relate to tip properties, I suspect they may both be playing a significant role.

That's good to hear because that's what my calculations indicated too! Post-impact swerve can explain more of it, but I don't think all of it, unless people are elevating their cues much more than I would expect.

Quite possibly. And maybe in addition to this, some swerve is taking effect sooner than expected since the cueball is being driven downward into the cloth somewhat.

From an aficionado of BHE as yourself, this strongly suggests that the pivot point is as you indicated earlier, well within 20" of the tip. But, we shall see, since the 30-50" contingent are no slouches either.

Jim

Yeah, I'm in no rush to call them slouches. It's easy to fall into error when trying to wrap one's head around such puzzles One must be willing to take a bite of one's own foot every now and again, but there is never progress without sticking a foot out.

Colin

 

[Colin Colenso]

I've missed a lot of the disagreements that we;ve had in the past, because most of the time it is just a misunderstanding of terms because I come from a background of applied physics as opposed to official physics. I don't mean applied physics in the traditional term. I n fact I'm saying exactly that I don't use the official terms and that is the main difference.

What I meant when I said a parabolic curve of force is the way that force travels through a flexible object like a shaft if the force being applied is off center the flesing of the shaft occurs in a parabolic curve from the point of applied force to the place of force equality of ditribution opposite the side when compared to center line of the flexible object.
Take a piece of paper and apply pressure linearly to one side length ways and you'll see by the way it bends what I'm referring to.

In my diagram, I'm showing that the mass of the cue ball that is being pushed is off to the right of the shaft when left english is applied and the point of contact is off center line to the right. This would cause the line of force to be a parabolic line of force radiating to the opposite side of the shaft or curving to the left.

Hi Jaden,
Always appreciate hearing a different perspective.

I'm still struggling to perceive what you are describing as going on here though. I would have thought that the shaft actually bends in the other direction, away from the ball.

Perhaps during an initial compressive phase, as the tip and shaft compresses, the cue shaft bows slightly while still in contact. I imagine the nature of such a bow would be very small and would still essentially result in directing force along the line of the cue.

The other forces that I can percieve are:
1. The rotation of the cue ball pushes the cue, which puches back on the CB (causing squirt).
2. Slight slipping, making the collision partly elastic, producing a force at the normal angle to the tip CB contact point (causing squirt).

We accept that elastic Ball to Ball collision has around 2% grip. I don't think it is too hard to imagine that the Tip to CB collision is 98-99% grip. i.e. Not entirely static.

Colin

 

[Colin Colenso]

Jaden, this is how I think the forces should be viewed. The black arrows are the main (net) force and its components acting on the cueball. The red arrows are the reaction force and components acting on the stick. These are equal in magnitude but opposite in direction to the black ones.

Your model seems to leave out or minimize the tangential component. The sum of the tangential and normal components yield the net force which would point straight ahead in the ideal case. However, ball rotation (perhaps with a touch of slip), diminishes the tangential component a little. This reduced component, when added to the normal one, makes the net force point slightly toward the center of the cueball, causing squirt.

Since the red reaction force is pointing slightly to the left, that's the direction in which the stick will bend.

Jim

Jal,
I don't see it in the same terms as your diagram. See my diagram besides yours for contrast. Not well labelled but you should get the idea.

If in more detail, I would have included opposing forces along the normal, indicating a degree of elastic (slip) collision. This would add to the other two arrows vectorially.

Colin

 

[Jal]

Yes, the Platinum Billiards numbers are correct.

There is no mystery - the "shoot into an object ball until the PP is found where the CB spins in place test" is greatly flawed due to the throw effect.

Try this test on a break shot (50") and you will find that the true PP is only lengthened by a couple inches over PB's numbers due to the throw effect. Try the same test with the OB just 10" away and the throw effect will falsely lengthen the apparent PP by more like 2 feet. This is why it is pretty much useless in actual play.

What kind of throw numbers are you using to figure an increase of 2 feet? Any and all details as to your calcs would be welcomed because I don't see anything like this much difference.

Jim

 

[Jal]

...I'm still a little confused why earlier theorists were so convinced that speed had no influence over squirt though.

Colin, according to Steve Titus' results, for all practical purposes it doesn't. Ron Shepard says that it should have a minor effect, which is apparently right.

On slip, I'm convinced it must happen to some degree, but it's relative contribution to squirt I am unsure about, especially with the possibility that Rotation Induced Squirt could also vary with speed as you suggest is a possibility.

As I said, I surely don't know. But what persuades you that slip is a significant though minor factor?

Jim

 

[Jal]

...I don't see it in the same terms as your diagram. See my diagram besides yours for contrast. Not well labelled but you should get the idea.

Needless to say, how you dissect the net force is completely arbitrary, mathematically speaking, but some ways are more convenient than others in a given situation. For the current one, I fully agree that yours does the better job.

And the assumption in my diagram that the normal force remains the same, while only the tangential one is affected, can be taken with a grain of salt, at best. I just meant to indicate that the tangential component is affected more relative to the normal one, which is what we can infer from the direction on the cueball. At least that's my story.

But we have to keep our priorities straight: mine is prettier than yours.

Jim

 

[mikepage]

[...]
I'm still a little confused why earlier theorists were so convinced that speed had no influence over squirt though.

I don't think any theoretical result lead the early pioneers to this. Instead I think a summary of the best observations was the following.

Squirt

--varies considerable from stick to stick but is consistent for a given stick
--is roughly independent of speed
--is roughly proportional to offset
--is roughly independent of contact time (as in soft versus hard tip)
--is roughly independent of details of chalk layer (provided no miscue)
--is roughly independent of shaft flexibility (or at least not a simple function)

On slip, I'm convinced it must happen to some degree, but it's relative contribution to squirt I am unsure about, especially with the possibility that Rotation Induced Squirt could also vary with speed as you suggest is a possibility.

It's hard to measure the speed dependence--or lack of speed dependence-- of squirt. It's important to note, though, that the canonical view, i.e., that expressed in Ron Shepard's treatment, doesn't demand there is no speed dependence. That would be the result for a fixed "endmass," but there's no particular reason to believe endmass has no dependence on shot speed through a dependence on contact time.

In any case, Colin, my personal opinion on your slip ideas is that you would benefit from a visit from the ghost of Willie of Occam.

 

[inthezone]

What kind of throw numbers are you using to figure an increase of 2 feet? Any and all details as to your calcs would be welcomed because I don't see anything like this much difference.

Jim

A bit sloppy of me - sorry about that.

If the PP is lengthened due to throw by 2" over 50" (break shot), which is about right depending on conditions, then the PP should be lengthened by about 10" if the OB is 10" away (5X).

So the "shooting the cb into the ob PP test" with 10" between them should give the Predator 314 for example an apparent PP of about 23".

The ones that get 30" or even 40" may be testing in stickier conditions or using an even shorter distance between cb and ob.

 

[Colin Colenso]

Colin, according to Steve Titus' results, for all practical purposes it doesn't. Ron Shepard says that it should have a minor effect, which is apparently right.

As I said, I surely don't know. But what persuades you that slip is a significant though minor factor?

Jim

Jim,
It's mainly intuitive, via thinking about how the tip is colliding with the CB. But also it is supported in some way by my experience in playing with some bad tips and unchalked tips that have very large squirt despite giving any clear indication of a miscue.

I just find it hard to imagine that there is perfect gearing, especially with large offsets. I think that during the tip compression phase there must be some interations that produce forces tending in the normal direction.

Colin

 

[Colin Colenso]

I don't think any theoretical result lead the early pioneers to this. Instead I think a summary of the best observations was the following.

Squirt

--varies considerable from stick to stick but is consistent for a given stick
--is roughly independent of speed
--is roughly proportional to offset
--is roughly independent of contact time (as in soft versus hard tip)
--is roughly independent of details of chalk layer (provided no miscue)
--is roughly independent of shaft flexibility (or at least not a simple function)



It's hard to measure the speed dependence--or lack of speed dependence-- of squirt. It's important to note, though, that the canonical view, i.e., that expressed in Ron Shepard's treatment, doesn't demand there is no speed dependence. That would be the result for a fixed "endmass," but there's no particular reason to believe endmass has no dependence on shot speed through a dependence on contact time.

In any case, Colin, my personal opinion on your slip ideas is that you would benefit from a visit from the ghost of Willie of Occam.

Thanks Mike,
but I have an insatiable appetite for investigating the finest of intracacies of the minutist of variables. I'd have given Mr. Occam quite a headache

When I see "roughly independent" then I wonder if the tests are rough or if there is a variable or two or three at play. I'd just prefer to know what they are and how they affect what is going on. This may lead to advantageous knowledge for play or product design.

Colin

 

[Colin Colenso]

But we have to keep our priorities straight: mine is prettier than yours.

Jim

Mine has more colors ....

 

[whitey2]

some tips

[...]But also it is supported in some way by my experience in playing with some bad tips and unchalked tips that have very large squirt despite giving any clear indication of a miscue.

You are planning on performing these experiments with screw-on tips also, right? DOH!

 

[ShootingArts]

Colin's slip factor

Having read the entire thread but not the items linked to yet, I just feel a natural inclination to rattle the keys some!

When working in R&D we often had an "X" factor or often a combination of many known or unknown things that we could detect the effect of that we lumped together as the "X" factor. I suspect that Colin's slip factor would seem more reasonable to some if it was labeled as the "X" factor, including slip, compression of various components and the balls, flex, and contact time, no doubt other things I am leaving out. It isn't necessary to understand all that is taking place, just that other things not accounted for in the basic calculations are taking place and roughly the net effect of these things, Colin's "slip" that makes his cyphering work.

Once we give it the basics to work with the most powerful real time computer in the world, the one between our ears, will sort out the details of making a shot even if we can't put every tiny factor down on paper precisely.

Hu

 

[JimS]

Let me see if I have this right. You retested your cue and found that the object ball was going straightest when pivoting at about 12" ? If so, was the object ball wetted and how far was the cueball from the object ball? (If you minimized throw and swerve, then the answer is at hand, but it's not yet clear to me if you did.)

Jim #2

When I posted that my PP was 12" I had not tested w/a wetted ball at 1 diamond.

Tonight I did that test and the result is that w/a wetted ob,shooting fairly hard, w/the ob on the center spot, the cb on the "spot" between the center and head spots and my bridge on the head spot, the ob went to the bottom cushion, hit at middle diamond, rebounded back over the foot spoot and hit the cb 7/8flush on as it was spinning merrily just beyond the center spot.

When I say bridge hand at the foot spot I mean that with a closed bridge the portion of my hand where the cue went through my fingers (the pivot point) was at the foot spot.

It appears I found the pivot point of my Sailor cue.

 

[Jal]

A bit sloppy of me - sorry about that.

If the PP is lengthened due to throw by 2" over 50" (break shot), which is about right depending on conditions, then the PP should be lengthened by about 10" if the OB is 10" away (5X).

So the "shooting the cb into the ob PP test" with 10" between them should give the Predator 314 for example an apparent PP of about 23".

The ones that get 30" or even 40" may be testing in stickier conditions or using an even shorter distance between cb and ob.

My numbers are similar to yours if a throw angle of something in the range of 2-3 degrees is assumed. This is far more than I would have expected based on data reported in a physics book on pool. But it is plausible and more in line with what JimS found (posted earlier) after doing tests with nearly frozen balls. It's also plausible then that the rest (30-40") might be explained for the reasons you give and/or additional adjustments for post-impact swerve. (But JimS's latest post indicates that post-impact swerve is not much of a factor...not sure what to make of that.)

Jim

 

[Jal]

When I posted that my PP was 12" I had not tested w/a wetted ball at 1 diamond.

Tonight I did that test and the result is that w/a wetted ob,shooting fairly hard, w/the ob on the center spot, the cb on the "spot" between the center and head spots and my bridge on the head spot, the ob went to the bottom cushion, hit at middle diamond, rebounded back over the foot spoot and hit the cb 7/8flush on as it was spinning merrily just beyond the center spot.

When I say bridge hand at the foot spot I mean that with a closed bridge the portion of my hand where the cue went through my fingers (the pivot point) was at the foot spot.

It appears I found the pivot point of my Sailor cue.

It sure looks that way. I don't know why the cueball isn't moving off to the side more, but that's my problem. If you should do the exact same test with your Predator, it would be interesting to hear the results. (From your earlier posts, I take it that the Sailor doesn't have this shaft.)

Jim

 

[MOJOE]

Colin,

Thanks very much for sharing your knowledge and insight. The BHE video brought some serious light to some struggles that I have experienced for some time. I appreciate your sharing.

JBK

 

[jsp]

Thank you very much Jsp. Always good to hear from you.

Likewise Jal. Sorry for the delay in my response. I totally forgot about this thread.

I have a degree in this stuff from way back when, but your very question plagued me when I got back to it. It's like having a degree in math, but forgetting a digit between one and ten. (However, there is a story about some Nobel Laureates visiting the University of Chicago, and agreeing to take elementary level tests in their respective subjects. They did horribly, as the story goes. Some, I think, even failing. This was told by a professor at the university, Milton Rosenburg, on one of his nightly radio programs, so it's likely true. Maybe I shouldn't feel too bad.)

Lol, I totally understand. I'm an EE and if I took a beginner's exam in elementary circuit analysis right now without freshening up, I'd probably fail that too.

Anywhoo, the answer is that a purely tangential force (a component in our case) will not only cause spin, but will propel the object in the direction of the force, as if it were operating through the center of mass. F=ma applies just as much here as with a head on collision. But we have to be careful (and this is what bugged me and maybe you too), because it seems as if this might violate the conservation laws. After all, it looks as if just moving the point of application from center to edge gets you additional spin energy (along with the same translational energy you would get from a head on collision.)

This was exactly my concern. How can the same magnitude of force transfer different amounts of total energy just depending on the point of application from center to edge?

So the more the force is applied to the edge, the greater total energy? It's just so counterintuitive.

The answer to that is to consider the size of the force when a body collides with our object. It will be less if the contact is toward the edge than if it's directed through the center of mass. As a result, it won't acquire as much translational velocity as a necessary payment for the spin it gains. And the colliding body will of course be affected differently, so the conservation laws will be okay with the whole thing.

Yes, that makes sense. Basically what you're saying is that the more to the edge is the impact, the less force it exerts on the object.

Of course, the tangential force is only one component at the tip/ball. The net force, which is the sum of it and the normal component, gives the cueball its final direction. And, just to mention it, the force is not constant but builds up and then dies away during impact. The diagram really represents an average force, both in magnitude and direction. (I know you know.)

I think things are starting to make some sense. Again, for me it's just not very intuitive that a purely tangential force would also accelerate the ball's center of mass. I'm just having a hard time grasping that concept.

Thanks for your response though.

 

[Bob Jewett]

... Again, for me it's just not very intuitive that a purely tangential force would also accelerate the ball's center of mass. I'm just having a hard time grasping that concept....

The most common example of a purely tangential force accelerating the CM of the cue ball is when follow or draw causes the cue ball to change velocity. A "pull to the side" changes both rotation and center-of-mass velocity.