Physics-Minded..How does the CB know?

CueAndMe

AzB Silver Member
Silver Member
I see it's been generally agreed upon that the mass in the first few inches of a shaft determines the amount of squirt. I can sort of grasp that, but I don't understand the effects of overall cue weight and weight distribution.

1)Say you're the cue ball. You're struck at the same speed and contact point by the same modern low-squirt shaft placed on two different butts. The first contact is from a 17 oz. total weight cue. The second contact is from a 25 oz. total weight cue. How do you know to react differently?

2)Same scenario, but the 17 oz. cue is being held with a death grip, and the 25 oz. cue is being held with a feather touch that allows the cue to be thrown into the cueball. Still both cues contacting the cueball at the same speed. How does this change things? Does the arm's mass with the 17 oz. shot come into play, in essence, fusing with the cue's mass?

3)How about 2 cues with the same shaft and overall weight but the first has most of its weight forward, the second has most of its weight rearward?

4)How about 2 cues with the same shaft and overall weight but the first has most of its weight around the perimeter, the second has most of its weight in its core?

What answers above would change depending on stick speed or CB contact point?

Thanks,
Jeff
 

worriedbeef

The Voice of Reason
Silver Member
well let's change the way you're thinking about it. imagine you're the CUE, not the cue ball. because it's the cue that reacts to hitting a solid object not the other way round. so when a cue with minimal end mass hits the edge of a cue ball it bends and deflects away, resulting in less squirt on the cue ball.

as for the weight distribution, it's not a key factor in squirt i don't think. it's stiffness. for example, if you had a cue with very low end mass towards the tip and it was hollow, but it was made out of steel, it would still squirt the cue ball off and not deflect.
 

Franky

woman I said NO!!!
Silver Member
Remember that the contact between the cuetip and the cueball is not instantaneous. Keeping this in mind, understand that during that contact, both the cueball and the front of the cue are acting as a unit...although one that is undergoing acceleration. The heavier the front of the cue, the more it will push the cueball to the side away from the side of the English applied during this contact because the front of the cue has a higher percentage of the mass of the "system" (cueball and front of the cuestick) than the same system would have had had a low-deflection shaft been used.

A lot of the energy that would go into deflecting the cueball with a traditional shaft instead goes into bending the front of the cue around the mass of the cueball in a lower deflection shaft. This is why most of these spliced shafts have vibration dampening material in them...because the shaft is going to flex more on contact, and that flex is going to straighten out after contact and wiggle a bit 'till it calms down.

Hope this makes some sense.
 

worriedbeef

The Voice of Reason
Silver Member
Patrick Johnson said:
I think it's the other way around.

pj
chgo

can you please explain? i think i have a pretty good understanding about squirt and deflection, and doesn't my example about the steel cue prove my point?
 

jongreve

AzB Silver Member
Silver Member
bluepepper said:
I see it's been generally agreed upon that the mass in the first few inches of a shaft determines the amount of squirt. I can sort of grasp that, but I don't understand the effects of overall cue weight and weight distribution.

1)Say you're the cue ball. You're struck at the same speed and contact point by the same modern low-squirt shaft placed on two different butts. The first contact is from a 17 oz. total weight cue. The second contact is from a 25 oz. total weight cue. How do you know to react differently?

2)Same scenario, but the 17 oz. cue is being held with a death grip, and the 25 oz. cue is being held with a feather touch that allows the cue to be thrown into the cueball. Still both cues contacting the cueball at the same speed. How does this change things? Does the arm's mass with the 17 oz. shot come into play, in essence, fusing with the cue's mass?

3)How about 2 cues with the same shaft and overall weight but the first has most of its weight forward, the second has most of its weight rearward?

4)How about 2 cues with the same shaft and overall weight but the first has most of its weight around the perimeter, the second has most of its weight in its core?

What answers above would change depending on stick speed or CB contact point?

Thanks,
Jeff


I would think that....

a higher momentum and/or force would more elongate the forward vector
(direction of travel)

momentum = mass x velocity
force = mass x acceleration
(it is near impossible NOT to have acceleration)

I also would think that....

a longer time of contact would more elongate the "squirt" vector


These statements assume identical deflection characteristics of the cues

Not exactly what you are looking for, but this is more complicated than it looks.
 

Cornerman

Cue Author...Sometimes
Gold Member
Silver Member
bluepepper said:
I see it's been generally agreed upon that the mass in the first few inches of a shaft determines the amount of squirt. I can sort of grasp that, but I don't understand the effects of overall cue weight and weight distribution.

1)Say you're the cue ball. You're struck at the same speed and contact point by the same modern low-squirt shaft placed on two different butts. The first contact is from a 17 oz. total weight cue. The second contact is from a 25 oz. total weight cue. How do you know to react differently?

2)Same scenario, but the 17 oz. cue is being held with a death grip, and the 25 oz. cue is being held with a feather touch that allows the cue to be thrown into the cueball. Still both cues contacting the cueball at the same speed. How does this change things? Does the arm's mass with the 17 oz. shot come into play, in essence, fusing with the cue's mass?

These are good questions that I believe have been answered before, but not as much as other squirt questions.

I believe the answer lies in the same question as "how much is 'the first few inches' and why?" The theory that makes the most sense is that the number of inches down the shaft is based on the lateral wave sent down and its speed. The normal axial shockwave is based on the speed of sound through the material, which is very fast. But the lateral wave is very slow. Predicted about 3 inches per millisecond. So, if the contact time is 2 milliseconds for the extreme english shots, then the cueball only "sees" about 6 inches worth of shaft. Therefore, theoretically, if this is correct then it won't matter what weight is behind those first several inches.

The unobtainable death grip (obtainable with a robot, but probably not with a human hand) would only affect things by increasing the contact time. Which it will. Lateral wave times the contact time equals more stick mass. The Jacksonville Project showed this. When they went to bubble wrap on the grip, it mimicked a human hand with its pliable flesh. Without the bubble wrap, the robot gave an unnatural amount of contact time, and really did "stroke through the cueball." Bob Jewett would have more information on that.

The other noteworthy area is if the bridge hand wasn't fleshy. Let's say, a solid V-block. If during tip contact, the lateral wave got to this solid block during tip/ball contact, then the cueball would again "see" more weight. I believe this is the problem with Bob Meucci's MythBuster set up, as far as testing Predator shafts is concerned.

None of these are set in stone, but I like the theories.

Fred
 

Bigjohn

Support Our Troops!
Silver Member
bluepepper said:
I see it's been generally agreed upon that the mass in the first few inches of a shaft determines the amount of squirt. I can sort of grasp that, but I don't understand the effects of overall cue weight and weight distribution.

1)Say you're the cue ball. You're struck at the same speed and contact point by the same modern low-squirt shaft placed on two different butts. The first contact is from a 17 oz. total weight cue. The second contact is from a 25 oz. total weight cue. How do you know to react differently?

2)Same scenario, but the 17 oz. cue is being held with a death grip, and the 25 oz. cue is being held with a feather touch that allows the cue to be thrown into the cueball. Still both cues contacting the cueball at the same speed. How does this change things? Does the arm's mass with the 17 oz. shot come into play, in essence, fusing with the cue's mass?

3)How about 2 cues with the same shaft and overall weight but the first has most of its weight forward, the second has most of its weight rearward?

4)How about 2 cues with the same shaft and overall weight but the first has most of its weight around the perimeter, the second has most of its weight in its core?

What answers above would change depending on stick speed or CB contact point?

Thanks,
Jeff

Who Cares?
 

CueAndMe

AzB Silver Member
Silver Member
Bigjohn said:
Who Cares?
It may seem like these questions are trivial, but after finding out that squirt is affected solely by a few inches at the end of the stick, I'm wondering if this area of the shaft is actually the ONLY thing important to how a cueball reacts, not just squirt-wise, but for all shots.

I understand the importance of choosing and customizing a cue for feel. But focusing solely on cueball response to a particular contact point at a particular speed with a particular shaft, does the rest of the cue matter?

Maybe it matters more on center ball hits than spin shots. Maybe it matters more with stiffer shafts than flexible ones. Maybe it matters more with high-squirt shafts than low-squirt shafts. I don't know. I'm curious.

Jeff
 

CueAndMe

AzB Silver Member
Silver Member
Still trying to take in everyone's posts here, and will later pick your brains some more with a reply. To clarify, it may have seemed that I was asking only about squirt, but I was actually interested in all shots.
Thanks for the replies.
Jeff
 

Patrick Johnson

Fish of the Day
Silver Member
worriedbeef:
...as for the weight distribution, it's not a key factor in squirt i don't think. it's stiffness.

Me:
I think it's the other way around.

worriedbeef:
can you please explain?

Many shafts, flexible and stiff, have been tested for squirt, and flexibility or stiffness has not been shown to be much of a factor compared with "end mass" (weight near the tip). When a stiff low-tip-mass cue is compared with a flexible high-tip-mass cue, the stiff one produces less squirt. Stiffness doesn't seem to matter much, if at all.

...doesn't my example about the steel cue prove my point?

It's not really an example unless you actually try it. It's not obvious from your "thought experiment" what would happen.

pj
chgo
 

JoeyInCali

AzB Silver Member
Silver Member
Patrick Johnson said:
Many shafts, flexible and stiff, have been tested for squirt, and flexibility or stiffness has not been shown to be much of a factor compared with "end mass" (weight near the tip). When a stiff low-tip-mass cue is compared with a flexible high-tip-mass cue, the stiff one produces less squirt. Stiffness doesn't seem to matter much, if at all.



It's not really an example unless you actually try it. It's not obvious from your "thought experiment" what would happen.

pj
chgo
So does that mean if a 13MM tip shaft is retapered down to 12 MM with a longer taper, it will have less cueball squirt?
 

worriedbeef

The Voice of Reason
Silver Member
Patrick Johnson said:
Many shafts, flexible and stiff, have been tested for squirt, and flexibility or stiffness has not been shown to be much of a factor compared with "end mass" (weight near the tip). When a stiff low-tip-mass cue is compared with a flexible high-tip-mass cue, the stiff one produces less squirt. Stiffness doesn't seem to matter much, if at all.



It's not really an example unless you actually try it. It's not obvious from your "thought experiment" what would happen.

pj
chgo

true i realise i havent really done a practical experiment but i cannot comprehend what i'm saying not being the case. oh well, i'll have to think about it some more. unfortunately i don't have a hollow stainless steel cue lol
 

Bob Jewett

AZB Osmium Member
Gold Member
Silver Member
bluepepper said:
I see it's been generally agreed upon that the mass in the first few inches of a shaft determines the amount of squirt. I can sort of grasp that, but I don't understand the effects of overall cue weight and weight distribution.

1)Say you're the cue ball. You're struck at the same speed and contact point by the same modern low-squirt shaft placed on two different butts. The first contact is from a 17 oz. total weight cue. The second contact is from a 25 oz. total weight cue. How do you know to react differently?

2)Same scenario, but the 17 oz. cue is being held with a death grip, and the 25 oz. cue is being held with a feather touch that allows the cue to be thrown into the cueball. Still both cues contacting the cueball at the same speed. How does this change things? Does the arm's mass with the 17 oz. shot come into play, in essence, fusing with the cue's mass?

3)How about 2 cues with the same shaft and overall weight but the first has most of its weight forward, the second has most of its weight rearward?

4)How about 2 cues with the same shaft and overall weight but the first has most of its weight around the perimeter, the second has most of its weight in its core?

What answers above would change depending on stick speed or CB contact point?

Thanks,
Jeff
The stick transfers energy to the cue ball by compressing like a spring along its whole length. The compression wave happens at the speed of sound in the stick, which is about 13000 feet per second. This speed is the fastest that the butt can learn of something colliding with the tip. Some people make the mistake of thinking of the cue stick as being perfectly rigid and incompressible, but it's not. So, the shot proceeds like this: the stick is coming forward and the tip meets the ball. The tip starts to compress, force and acceleration of the cue ball start to build up. The ball also starts to compress, since it too is not incompressible. The ball has started to move, but is not up to the speed of the stick yet, and the stick has started to slow down as its energy is transferred to the cue ball. This continues until the tip (and ferrule and joint and butt) reach maximum compression along the length. At this exact point some amazing things are happening. The stick and ball are moving at the same speed. The force between stick and ball are at their maximum. The compression along the length of the stick (including the tip) is at its maximum. The energy stored in the spring-like compression of the tip (and stick and ball) are at their maximum. For a typical ball and stick, the speeds of the ball and stick are 75% of the original stick speed.

After this point of maximum compression, the ball is pushed forward from the tip by the compression of system. The ball starts to move even faster from this force and the stick continues to slow down. This "unwinding" process continues until the ball finally leaves the tip. At that point, the ball is going at about 130% of the original stick speed, and the stick has slowed down to about 50% of its original speed. (The 130% would be 150%, but the tip is not perfect in springing back to its original shape, and energy is lost.)

Now the hand comes in. Human flesh makes a much "softer" spring than the leather of a tip or the wood that is compressed along the length of the stick. Think of the tip as about the stiffest car spring you can imagine and your hand like a rubber band. The cue ball is gone by the time your hand -- which is still moving forward at full speed -- can wind up even a little. As the hand winds up on the stick and relaxes, which takes about 20 milliseconds, the hand is slowed to about 80% of its initial speed and the stick goes from 50% back up to 80% of its initial speed. Of course this re-acceleration of the stick by your hand is useless in that the cue ball is long gone.

How does a heavier stick affect things? It changes that 130% number. The formula is in Byrne's Advanced book, and somewhere in my columns in Billiards Digest and certainly in Ron Shepard's paper and Dr. Dave's book. A heavier stick through the spring action, puts slightly more energy into the cue ball.

As for how the weight of the stick affects the squirt, I think the answer is that it doesn't, much. Squirt is caused by the spinning cue ball pushing the stick to the side during the contact time of an off-center hit. The amount of squirt is determined by the mass that is being pushed to the side. Since the stick is very floppy side-to-side (as compared to length-wise compression), only the front part of the stick can participate in the squirt during the 1 millisecond or so of contact time. A heavier stick will increase the contact time a little, and that will increase the squirt a little, but I think this effect is pretty small.

Phrased technically, the transverse wave has a very slow propagation velocity along the length of the stick, and so the joint and butt cannot participate in the sideways push that causes squirt.

You should find Mike Page's discussion of his experiment with vise grips on the shaft which determined how much of the shaft participates in squirt.

As Fred mentioned, a major problem with some of the Jacksonville Project was that Iron Willie had too stiff a grip -- like vise grips -- and too hard a bridge. I have heard that Predator's current cue testing robot has fixed those problems to hold the cue more like a human at both ends.

As for some of your other questions, in theory the squirt should depend on stiffness of the cue since that should change the speed of the transverse wave. In practice, "end mass" seems to be a much better indicator of squirt than stiffness. There are stiff cues with little squirt and stiff cues with lots of squirt. A major red herring along the path of squirt studies was the fact that carom cues tend to be stiff but have relatively low squirt. They usually have smaller tips than pool cues.
 
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JoeyInCali

AzB Silver Member
Silver Member
worriedbeef said:
true i realise i havent really done a practical experiment but i cannot comprehend what i'm saying not being the case. oh well, i'll have to think about it some more. unfortunately i don't have a hollow stainless steel cue lol
The low end mass works on wooden shafts b/c they are flexible enough that the front-end would deflect OFF the cueball before the cueball deflects off the tip.
A low end mass on steel shafts wouldn't be much of help because it will not bend away from the ball.
 

Bob Jewett

AZB Osmium Member
Gold Member
Silver Member
JoeyInCali said:
So does that mean if a 13MM tip shaft is retapered down to 12 MM with a longer taper, it will have less cueball squirt?
Yes, but also consider reducing the length of the ferrule. I think Z shafts have short ferrules for the same reason carom cues do.
 

JoeyInCali

AzB Silver Member
Silver Member
Bob Jewett said:
Yes, but also consider reducing the length of the ferrule. I think Z shafts have short ferrules for the same reason carom cues do.
So a carom shaft that is stiff will have less cueball squirt if it was taken down and with a longer barrel ( cylinder) ?
 

Bob Jewett

AZB Osmium Member
Gold Member
Silver Member
JoeyInCali said:
So a carom shaft that is stiff will have less cueball squirt if it was taken down and with a longer barrel ( cylinder) ?
I'm not sure what you are asking. Many carom shafts have nearly conical tapers which makes them feel "stiff." The also often have fairly small tips (12mm or less) and short (very light) ferrules. If a carom cue like that were modified by removing wood in the first six inches, it would probably have less squirt as a result.
 

JoeyInCali

AzB Silver Member
Silver Member
Bob Jewett said:
I'm not sure what you are asking. Many carom shafts have nearly conical tapers which makes them feel "stiff." The also often have fairly small tips (12mm or less) and short (very light) ferrules. If a carom cue like that were modified by removing wood in the first six inches, it would probably have less squirt as a result.
Thank you.
 

CueAndMe

AzB Silver Member
Silver Member
worriedbeef said:
unfortunately i don't have a hollow stainless steel cue lol
Sadly I do. It's one of those 3 footers that you grab when your room is too small to make a shot with a full length cue. It has one of those slip on cheapy tips though. I doubt much could be learned from an experiment with this little thing. But it sure is stiff.
Jeff
 
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