Squirt. End Mass and Cue Flexibility.

Patrick Johnson

Fish of the Day
Silver Member
I haven't calculated and/or measured this before, but I'll add it to my list.

I would suspect that the direct stiffness effect would be a tiny fraction (maybe less than 1%) of the effective endmass effect.

I'll reply to this post if and when I'm able to do the calculations.

Regards,
Dave
Thanks, Dave. You da science Man.

pj
chgo
 

dr_dave

Instructional Author
Gold Member
Silver Member
You can express the same rotation as either rotation about a single axis or as the combined "components" of rotation about multiple axes.

For instance, a rolling ball with side spin rotates about a single tilted axis, which is also the combined components of rotation about the vertical axis and a horizontal axis. We choose to separate the single axis of rotation into vertical and horizontal rotational components because pool is played on a horizontal surface with vertical surface boundaries (rails), so those are the effects that matter most.
For those interested, a good explanation and demonstration of this can be found in the following video:

NV B.10 - Drag spin loss and sidespin persistence

Enjoy,
Dave
 

dr_dave

Instructional Author
Gold Member
Silver Member
I agreed with everything in your previous excellent post except this:

2) Stiffness ... is necessary for there to be any endmass at all

As the CB turns and pushes the tip sideways during an off-center hit, mass alone is enough to provide a reaction force. According to Newton's "for every action, there is an equal and opposite reaction," because force is required to push the endmass sideways, there is an equal and opposite sideways force on the CB that causes squirt (AKA, CB deflection). For those who want to learn more about this, the following resource page explains, illustrates, and demonstrates it fairly well:

what causes squirt (CB deflection)

In the experiments Mike Page, I, and others have done, where we change the stiffness of the end of the shaft (by removing material beyond the "endmass" distance), the change in stiffness has no measurable affect on the resulting squirt. For those interested, articles and videos dealing with this topic can be found on the endmass and stiffness resource page.

Enjoy,
Dave
 

ENGLISH!

Banned
Silver Member
It is only endmass in the following sense:

1) The cueball is deflected in the transverse direction according to the mass of the cue that's put into motion in the opposite direction (momentum). If the end of a cue was perfectly rigid, but somehow lacked any effective endmass, no squirt would take place.

2) Stiffness, but in a sort of trivial way, is necessary for there to be any endmass at all (see Dr. Dave's reference to a wet noodle earlier). However, once you get to a stiffness level represented by a wooden rod, the differences in stiffness you're going to encounter amongst cues isn't likely going to make any significant difference in squirt. That's because:

2.1) Given the shape the end of the cue takes on as it bends, it's the mass nearest the tip that contributes the most to the momentum of the endmass.

2.2) Different stiffnesses primarily affect the shape of the bend further down the cue away from the tip. Because of that location, the additional mass doesn't contribute much to the cue's sideways momentum.

I once thought that stiffness was an integral part of endmass (it is in the trivial sense noted above), but repeated assertions by Patrick Johnson and Dr. Dave eventually drove home the "proper" view of it.

Now you can go. :) :)

Jim

Hi Jim.

Steel golf shafts were rated for their flex. Then came rating them for their bend point, low, mid, & high.

The main component to the angle that a golf ball is launched is the loft of the club head.

The flex of the shaft along with the timing & power & even style of one's golf swing affect how the angled loft of the club head is delivered & makes contact with the golf ball.

The bend point of the shaft ALSO affects the angled loft that the club head is delivered & makes contact with the golf ball.

Relative to the loft of the club head the affect of the bend point is small...

but it does have an effect.

If one is hitting the golf ball too low they might re-shaft the head with a low bend point shaft of the same flex designation of regular or stiff that would result in the ball being launched higher & if they are hitting the ball too high they might re-shaft with a high bend point shaft that hits lower.

I know this is NOT a direct analogy & it is not intended as such.

It is just intended as food for thought in regards of what research & develop of an extensive nature can reveal.

Best 2 You & All.
 

dr_dave

Instructional Author
Gold Member
Silver Member
Steel golf shafts were rated for their flex. Then came rating them for their bend point, low, mid, & high.

The main component to the angle that a golf ball is launched is the loft of the club head.

The flex of the shaft along with the timing & power & even style of one's golf swing affect how the angled loft of the club head is delivered & makes contact with the golf ball.

The bend point of the shaft ALSO affects the angled loft that the club head is delivered & makes contact with the golf ball.

Relative to the loft of the club head the affect of the bend point is small...

but it does have an effect.
... only during the swing, not during contact with the ball.

In pool, the cue does not flex (in a practical sense) during the swing, nor does the tip have much mass (as with a golf club).

Regards,
Dave
 

ENGLISH!

Banned
Silver Member
... only during the swing, not during contact with the ball.

In pool, the cue does not flex (in a practical sense) during the swing, nor does the tip have much mass (as with a golf club).

Regards,
Dave

I certainly understand that & I said that it was not intended as a direct analogy but merely as food for thought in regards to what extensive research & development can reveal.

BUT... that was in the part that you conveniently cut out when you quoted me.
 
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dr_dave

Instructional Author
Gold Member
Silver Member
... only during the swing, not during contact with the ball.

In pool, the cue does not flex (in a practical sense) during the swing, nor does the tip have much mass (as with a golf club).
I understand that & I said that it was not intended as a direct analogy but merely as food for thought in regards to what extensive research & development can reveal.
The problem with inappropriate and misleading analogies is that they can mislead people and cause misunderstanding and inappropriate extrapolation (as with the ping pong paddle and large rubber ball in the swoop thread).

I agree with you 100% that "extensive research & development" and the scientific process can reveal a tremendous wealth of knowledge, better products, and smarter techniques.

Regards,
Dave
 

LAMas

AzB Silver Member
Silver Member
The problem with inappropriate and misleading analogies is that they can mislead people and cause misunderstanding and inappropriate extrapolation (as with the ping pong paddle and large rubber ball in the swoop thread).

I agree with you 100% that "extensive research & development" and the scientific process can reveal a tremendous wealth of knowledge, better products, and smarter techniques.

Regards,
Dave

Hmmm...spheres being rotated...bad?

analogy.jpg
 

Corwyn_8

Energy Curmudgeon
Silver Member
You can express the same rotation as either rotation about a single axis or as the combined "components" of rotation about multiple axes.

For instance, a rolling ball with side spin rotates about a single tilted axis, which is also the combined components of rotation about the vertical axis and a horizontal axis. We choose to separate the single axis of rotation into vertical and horizontal rotational components because pool is played on a horizontal surface with vertical surface boundaries (rails), so those are the effects that matter most.

Which is why I made the caveat about semantics. But I don't expect (nor should I) that the simplification, badly phrased should appear in a peer-reviewed article.

Thank you kindly.
 

ENGLISH!

Banned
Silver Member
I am ALL FOR scientific research & development...

but like it has been done for golf it NEEDS to be ONGOING.

They are NOT manufacturing golf club heads in the same manner based on the same "scientific thinking" & principles that they were just 10 or less years ago.

They found a way to get so much more distance that restrictions had to be placed on club heads.

The same thing had to be done for non wooden bats used in college, etc.

Science should be an ongoing study & should not stagnate at a point & then have definitive statements made SO definitively as to suggest that ALL is known.

Certain statements should have qualifiers attached to them so has to not give false impressions or 'allow' false assumptions to be made.

If shaft flex is merely a 3% contributor then it should NOT be said that the ONLY component that contributes to the reduction of CB squirt is a reduction of front end mass.

And what defines how much is "front end"? Where does the reduction of mass stop effecting squirt? Is THAT dependent on the flex of a shaft?

I have a McDermott i2 shaft that has a hollow carbon fiber tube running the 'full' length of the shaft. The G-Core shaft has one for just the first 9" or so.

The I2 squirts less then the G-Core in every human comparison that I've seen. Granted that has only been a few. But it brings up food for thought. Should the G-Core maybe go all the way to what would have been the normal pivot point of the shaft before it was cored? Where in the i2 does the coring & tube insertion stop being of benefit? Does it matter in any negative way that it goes the 'full' length?

That probably is not how the manufacturing process is done but perhaps 12" or 15" would yield better results than just the 9" of the G-Core.

And that is just for solid cored maple shafts & not pie, etc. pieced together shafts that certainly affect flex in some manner.

Then we get to the tip end & the composition of a ferrule. What about a long light weight flexible ferrule?

What about the load on a shaft or an entire cue say at the joint & perhaps beyond for 1 tip of offset vs 3 tips of offset?

Should an individual that likes staying closer to center be playing with a different cue than one that prefers going farther out for what ever reason?

Pool research & development is light years behind that of other sports & is only relatively recently starting in that direction.

When Predator started out they made a visit to Bob Meucci.

ALL of the above is intended just as food for thought.

PS If anyone wants to jump the 'light years' reference as not technically correct, have at it.
 
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Corwyn_8

Energy Curmudgeon
Silver Member
Im not qualified to talk about such but what about off center hits, high or low? Do they not spin sideways while rotating end over end to some degree?

Not really (or at least, that is a confusing way to think of it). Imagine, if you will, a cue ball with only side spin, the axis of rotation is vertical (up for right spin); it is perpendicular to the line between the contact point and the line parallel to the cue direction, passing through the center of the ball; it is also perpendicular to the direction of the hit. On the other hand imagine hitting with just draw, the axis is pointing directly to the right (relative to cue direction). Hitting with low right, therefore gives you an axis in between those two, namely an axis canted to the right, in the plane perpendicular to the direction of the cue.

Now as the draw wears off, it is easy to visualize the axis swinging from that slanted axis to one straight up, followed by one slanted to the left, as forward roll is acquired. If you practice this with a striped ball you can sometimes get it to show in an obvious way. Try it with the stripe angled at your intended start axis.

This in a excellent demonstration of precession, should you want further thought on the matter.


Thank You kindly.
 
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Patrick Johnson

Fish of the Day
Silver Member
...what about off center hits, high or low? Do they not spin sideways while rotating end over end to some degree?

Not really (or at least, that is a confusing way to think of it).
For understanding the effects of rotating balls in pool, I think that's the clearest way to think of it. For instance, a rolling ball with sidespin curves a little - that's easiest to understand when we realize that a component of its total spin is some rotation about the horizontal axis parallel with its direction of travel ("masse spin").

And when the same rolling ball with side spin hits a rail, it's easiest to understand the angle change that occurs when we realize that another component of its total spin is some rotation about the vertical axis.

pj
chgo
 

dr_dave

Instructional Author
Gold Member
Silver Member
I haven't calculated and/or measured this before, but I'll add it to my list.

I would suspect that the direct stiffness effect would be a tiny fraction (maybe less than 1%) of the effective endmass effect.

I'll reply to this post if and when I'm able to do the calculations.
FYI, to those interested, I did some measurement and calculations. The analysis is here:

TP B.19 - Comparison of cue ball deflection (squirt) "endmass" and stiffness effects

For the example numbers I used, the direct stiffness effect is only about 1.5% of the total cue ball deflection (squirt) effect. That is indeed very small.

Regards,
Dave
 

Patrick Johnson

Fish of the Day
Silver Member
FYI, to those interested, I did some measurement and calculations. The analysis is here:

TP B.19 - Comparison of cue ball deflection (squirt) "endmass" and stiffness effects

For the example numbers I used, the direct stiffness effect is only about 1.5% of the total cue ball deflection (squirt) effect. That is indeed very small.

Regards,
Dave
Wow - quick turnaround, Dave!

The effect of stiffness on squirt appears to be even smaller than I thought - inconsequential at the level you suggest.

Thanks for keeping us as real as possible under the circumstances.

pj
chgo

P.S. Does 1.5% include the increase of involved end mass attributable to stiffness?
 
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Corwyn_8

Energy Curmudgeon
Silver Member
For understanding the effects of rotating balls in pool, I think that's the clearest way to think of it.

Opinions clearly differ, but whatever works for you.

For me, I never understood ball spin until I got that there is only one axis (and the torque acted at right angles to applied force). What really did it for me was trying figure out what a natural rolling left english ball would do after hitting cushion. Now 'top' isn't top any longer. What is it? Can you quickly intuit what the new direction of travel will do to the current spin? It is pretty easy if you consider the existing spin axis and the new force applying torque perpendicular to the new (friction) force. For me anyway.

Thank you kindly.
 

336Robin

Multiverse Operative
Silver Member
I understand

Not really (or at least, that is a confusing way to think of it). Imagine, if you will, a cue ball with only side spin, the axis of rotation is vertical (up for right spin); it is perpendicular to the line between the contact point and the line parallel to the cue direction, passing through the center of the ball; it is also perpendicular to the direction of the hit. On the other hand imagine hitting with just draw, the axis is pointing directly to the right (relative to cue direction). Hitting with low right, therefore gives you an axis in between those two, namely an axis canted to the right, in the plane perpendicular to the direction of the cue.

Now as the draw wears off, it is easy to visualize the axis swinging from that slanted axis to one straight up, followed by one slanted to the left, as forward roll is acquired. If you practice this with a striped ball you can sometimes get it to show in an obvious way. Try it with the stripe angled at your intended start axis.

This in a excellent demonstration of precession, should you want further thought on the matter.


Thank You kindly.

For understanding the effects of rotating balls in pool, I think that's the clearest way to think of it. For instance, a rolling ball with sidespin curves a little - that's easiest to understand when we realize that a component of its total spin is some rotation about the horizontal axis parallel with its direction of travel ("masse spin").

And when the same rolling ball with side spin hits a rail, it's easiest to understand the angle change that occurs when we realize that another component of its total spin is some rotation about the vertical axis.

pj
chgo

I understand the both of you. I get it very much and thank you both.
 

LAMas

AzB Silver Member
Silver Member
FYI, to those interested, I did some measurement and calculations. The analysis is here:

TP B.19 - Comparison of cue ball deflection (squirt) "endmass" and stiffness effects

For the example numbers I used, the direct stiffness effect is only about 1.5% of the total cue ball deflection (squirt) effect. That is indeed very small.

Regards,
Dave

Thanks Dave,
I hope that I get a 1.5% raise next month...it will mean a lot to my wife...rather than getting cut.

Rod Cross, Physics Department, University of Sydney invested a lot of time resources and science to conclude that a thinner shaft reduces squirt. I hope that he is informed that his study was not for naught and contributes 1.5% according to your calculation. Even scientist can be punked.
 
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LAMas

AzB Silver Member
Silver Member
Im not qualified to talk about such but what about off center hits, high or low? Do they not spin sideways while rotating end over end to some degree?

Hi,
From the OP by Rod Cross:

III. EXPERIMENTAL METHODS
When a ball is struck with side spin on a billiard table, the amount of sidespin is difficult to measure experimentally because the ball initially slides and then rolls forward. The ball therefore rotates about two different axes simultaneously.

Be well
 

SilverCue

Sir Raksalot
Silver Member
FYI, to those interested, I did some measurement and calculations. The analysis is here:

TP B.19 - Comparison of cue ball deflection (squirt) "endmass" and stiffness effects

For the example numbers I used, the direct stiffness effect is only about 1.5% of the total cue ball deflection (squirt) effect. That is indeed very small.

Regards,
Dave

Dr Dave
Wouldn't it depend on the end mass vs flexibility?
What if you had a 14 mm tip with brass ferrule and the last
10 inches shaped like an hour glass with the mid point 9 mm?
Verses same 14 mm shaft with pro taper?






Sent from my SAMSUNG-SM-N910A using Tapatalk
 
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