The Stroke Thread

[Patrick Johnson]

Me:Yes. Hitting with sidespin also extends contact time. But not enough to make a controlled difference in the outcome in either case.

Because the stick is effectively stopped by ("bounces off") the cue ball when it makes contact and doesn't regain speed until after the cue ball is gone, there's no such thing as "acceleration through the cueball".

ThePoliteSniper:
So then what JimmyWhite said in his first paragraph is actually wrong.

Originally Posted by JimmyWhite
If your stroke is moving straight forward smoothly accelerating, the compression of the tip is bigger as it contacts the CB for a longer period of time. Take a ball, put your index finger and push the ball lightly with it while maintaining the same velocity with the finger. You will see that the ball will very soon stop making contact with your finger and roll forward freely. If you make the same thing, but with an accelerating motion, your finger will always remain in contact with the ball. Now imagine doing this with your cue (accelerating and pushing forward aka follow through). If you have a nice accelerating motion, the time where the tip is contacting the CB and is compressed against it is greatly increased. Therefore, more "spinning energy" is passed to the CB. The softer the tip, the more it compresses, so the more it can spin the ball. (note that by spin, I mean english and draw and follow)

Yes, I believe it's wrong in two ways:

1. You can't greatly increase contact time.

2. Even if you could greatly increase contact time, it wouldn't increase spin any more than you could by hitting normally but a little more offcenter. And it wouldn't increase maximum spin.

pj
chgo

 

[hunger strike]

Switching to voice of Festus Hagin from Gunsmoke...

Yes, I believe it's wrong in two ways:

1. You can't greatly increase contact time.

2. Even if you could greatly increase contact time, it wouldn't increase spin any more than you could by hitting normally but a little more offcenter. And it wouldn't increase maximum spin.

pj
chgo

Now Maaaa-theewww, do you mean to tell me you cain't greatly increase contact time in finite milliseconds, in percentage of contact time, or in amount of energy transfer? A Frenchman in, I believe, the 1600's came up with equations proving that increasing contact time increases energy transfer between colliding objects. What if the change in energy transfer is logarithmic? Just sayin' Maaa-thewww, you shouldn't just go-a-traipsin' into the Long-Brainch unarmed.....

 

[Bob Jewett]

... increase contact time in finite milliseconds, in percentage of contact time, or in amount of energy transfer?

The most useful way to phrase it is as a percentage. If you are accelerating the stick at the time of impact, you can get something like a 1% increase in contact time.

A Frenchman in, I believe, the 1600's came up with equations proving that increasing contact time increases energy transfer between colliding objects.

Equations to not compel, they only incline. In any case, just the opposite is true for cue tips on cue balls: the harder the tip and the shorter the contact time, the more energy is transferred. That's the reason that people use phenolic tips on break cues. Evidently hard synthetic tips are more efficient than leather, which is not real surprising.

What if the change in energy transfer is logarithmic? ...

No need to go nonlinear.

 

[Patrick Johnson]

Me:
Even if you could greatly increase contact time, it wouldn't increase spin any more than you could by hitting normally but a little more offcenter. And it wouldn't increase maximum spin.

hunger strike:
...do you mean to tell me you cain't greatly increase contact time in finite milliseconds, in percentage of contact time, or in amount of energy transfer?

Yes.

What if the change in energy transfer is logarithmic?

How would more energy transfer translate to "greater spin"? Why wouldn't simply hitting harder do the same thing?

pj
chgo

 

[hunger strike]

Switching to the voice of Michael Caine....

Yes.


How would more energy transfer translate to "greater spin"? Why wouldn't simply hitting harder do the same thing?

Well, spin is energy, specifically rotational energy (as opposed to the translational energy of relative movement through space.) Yes, hitting harder would increase spin, and that's why we call people "bangers."

 

[hunger strike]

Switching to voice of Schroedinger's Cat......

Equations to not compel, they only incline. In any case, just the opposite is true for cue tips on cue balls: the harder the tip and the shorter the contact time, the more energy is transferred. That's the reason that people use phenolic tips on break cues. Evidently hard synthetic tips are more efficient than leather, which is not real surprising.

In terms of pure energy transfer, I agree. However, what about the efficiency of a particular material in transferring a percentage of the overall momentum into rotational as opposed to translational energy? If a phenolic tip is more efficient at transferring spin, then I am going to stop chalking my cue on draw shots, and you should too.... hey, did someone just hit that vial of poison gas with a ball peen hammer? I can't tell, it's dark in this box.......

 

[Neil]

............

 

[dr_dave]

Could a softer cue tip result in a longer contact time?

Yes, but this effect is not as important as some people might think, per the explanations here:

tip contact time
tip hardness effects​

Now, a softer tip will usually be less efficient (less CB speed for the same cue speed) and result in a different "feel." For more info, see:

cue tip efficiency
cue "hit," "feel," and "playability"​

What about different cues?

For a given tip, I wouldn't expect the tip contact time to vary much among cues because the tip is so flexible compared to the axial stiffness of the cue. Now, with a very hard tip (e.g., phenolic), I wouldn't be surprised if there were slight contact-time differences for different shafts (e.g., with carbon fiber vs. wood); however, as mentioned above, this isn't as important as some people might think.

Now, different cues (with the same tip and weight) will have differences in efficiency and "feel." Also, weight can affect a player's stroke, the CB's speed, and "feel."

Is the acceleration through the cueball always an insignificant factor?

How one accelerates before and after tip contact is not "insignificant," because these are important elements of one's stroke. The manner in which you stroke into the ball determines how much speed the cue has when the tip hits the ball, which is important to most shots. Also, if you are not following through after contact, this usually indicates something about the motion and speed into the ball. Acceleration during tip contact is insignificant because the tip contact time is so, so small. For more info, see:

stroke acceleration
effects of light vs. tight grip
follow through​

Regards,
Dave

 

[pooltchr]

The cue ball doesn't know what you were doing before the tip hit it, any more than it knows what you do after it separates from the tip. All the cue ball can react to is the direction the tip is traveling, and the speed it is traveling at contact. Anything else is just setting up for that contact, and bringing the cue to a stop after separation. There is about 1 to 2 1000ths of a second that actually determines where the cue ball will go.

Steve

 

[justnum]

The gist is some people don't believe that a stroke can demonstrate the property of pre-determining the path of the CB after collision with an OB.

Or is the gist some people don't believe that are multiple ways to shoot a draw shot?

Either way the idea I am going to demonstrate is that as the cue stick strikes the cue ball it can happen in such a way that the cue ball path is determined by the stroke.

i.e. for follow the stroke can be created from a range BCEC positions,
the draw stroke can be created from a range BCEC position,
and lastly a person can stroke the CB so after it collides with an OB it follows a pre-determined path.

If there are any disagreements with these ideas or concepts, I most likely will not address it. If there are disagreements then those are the issues I aim to resolve.

 

[Patrick Johnson]

Yes.


How would more energy transfer translate to "greater spin"? Why wouldn't simply hitting harder do the same thing?

Well, spin is energy, specifically rotational energy (as opposed to the translational energy of relative movement through space.) Yes, hitting harder would increase spin, and that's why we call people "bangers."

The relevant measure in pool is "spin-to-speed ratio" (RPMs per unit of translational travel). Greater RPMs with proportionally greater speed doesn't change the effect of sidespin.

pj
chgo

 

[justnum]

The relevant measure in pool is "spin-to-speed ratio" (RPMs per unit of translational travel). Greater RPMs with proportionally greater speed doesn't change the effect of sidespin.

pj
chgo

What are you final conclusions so far?

if you need more time go ahead. I will post the vid and text later.

 

[Patrick Johnson]

...what about the efficiency of a particular material in transferring a percentage of the overall momentum into rotational as opposed to translational energy?

Do you know of a material that changes the percentage of energy translated to rotational vs. translational? If so, the physicists of the world are eagerly awaiting the publication your discovery.

pj
chgo

 

[Patrick Johnson]

The gist is some people don't believe that a stroke can demonstrate the property of pre-determining the path of the CB after collision with an OB.

Or is the gist some people don't believe that are multiple ways to shoot a draw shot?

I don't think anybody has said either of these things.

Either way the idea I am going to demonstrate is that as the cue stick strikes the cue ball it can happen in such a way that the cue ball path is determined by the stroke.

I don't think anybody has disagreed with this either.

The disagreement is about whether anything can happen during contact that changes the outcome.

i.e. for follow the stroke can be created from a range BCEC positions,
the draw stroke can be created from a range BCEC position

What's a "BCEC position"?

and lastly a person can stroke the CB so after it collides with an OB it follows a pre-determined path.

Sure, but it's all determined by the part of the stroke that comes before contact with the CB. You need to say these things more carefully if you want to have meaningful discussion of them.

pj
chgo

 

[Bohemian]

A Picture Is Worth A Thousand Words...

Dr. Dave on the Draw Stroke...
http://www.youtube.com/watch?v=Uoz7f8-wRRc

TP A.20
The effect of spin, speed, and cut angle on draw shots
http://billiards.colostate.edu/technical_proofs/new/TP_A-20.pdf

HSV 4.1 - Draw shot
http://billiards.colostate.edu/high_speed_videos/HSV4-1.htm

HSV A.4 - 9-ball power break with draw (close-up, side view)
http://billiards.colostate.edu/high_speed_videos/new/HSVA-4.htm

HSV A.24 - "The Hustler" draw-massé shot
http://billiards.colostate.edu/high_speed_videos/new/HSVA-24.htm

HSV A.32 - Kick shot with medium approach angle and draw
http://billiards.colostate.edu/high_speed_videos/new/HSVA-32.htm

HSV A.35 - Draw shot with small offset, light grip, good follow-through, slow speed, and about 1.75 feet of draw
http://billiards.colostate.edu/high_speed_videos/new/HSVA-35.htm

HSV A.38 - Draw shot with large offset, light grip, good follow-through, fast speed, and about 7 feet of draw
http://billiards.colostate.edu/high_speed_videos/new/HSVA-38.htm

TP B.4 Stroke speed and acceleration vs. distance
http://billiards.colostate.edu/technical_proofs/new/TP_B-4.pdf

Plenty more where this came from...

The Illustrated Principles of Pool and Billiards
http://billiards.colostate.edu/

peace.

 

[Patrick Johnson]

No need to go nonlinear.

Now you tell us...

pj
chgo

 

[Jaden]

hitting harder with greater velocity...

Yes.


How would more energy transfer translate to "greater spin"? Why wouldn't simply hitting harder do the same thing?

pj
chgo

Hitting harder would increase the longitudinal transfer of energy, not necessarily the tangential transfer of energy which is what creates spin....

Jaden

 

[Jaden]

wait a minute?????

Equations to not compel, they only incline. In any case, just the opposite is true for cue tips on cue balls: the harder the tip and the shorter the contact time, the more energy is transferred. That's the reason that people use phenolic tips on break cues. Evidently hard synthetic tips are more efficient than leather, which is not real surprising.

In terms of pure energy transfer, I agree. However, what about the efficiency of a particular material in transferring a percentage of the overall momentum into rotational as opposed to translational energy? If a phenolic tip is more efficient at transferring spin, then I am going to stop chalking my cue on draw shots, and you should too.... hey, did someone just hit that vial of poison gas with a ball peen hammer? I can't tell, it's dark in this box.......

What the hell kind of a voice would a cat that's both dead and alive have, and what cats have you been talking to in English????

Jaden

 

[JimmyWhite]

Yes, I believe it's wrong in two ways:

1. You can't greatly increase contact time.

2. Even if you could greatly increase contact time, it wouldn't increase spin any more than you could by hitting normally but a little more offcenter. And it wouldn't increase maximum spin.

pj
chgo

So if you make a normal follow through, the contact time is not increased?
So theoretically, you can make an accelerating hit and manage to grab the cue and prevent it from going forward right after the contact with the CB. And this would have no effect on your hit?

 

[pooltchr]

Why make this more difficult than it needs to be. We know that energy in = energy out.
The energy we put into the shot is all delivered through the tip of the cue stick when it strikes the cue ball. Now, there are two ways that energy can show up in the cue ball...directional speed or rotational speed. If you hit perfectly center ball, all of the energy becomes directional energy. If you hit off center, some of that energy is translated to rotational energy. The farther from center you move the contact point, the less energy goes into directional speed, and the more goes into rotational speed.

If you increase the amount of energy going into the shot by increasing cue speed at impact, you can get more rotational speed and more directional speed, but it is still going to be divided the same way. The only ways to get more rotational speed are to either move the contact point out to the edge of the usable area (half way between center and edge of the ball), or increase the speed of the cue at contact.

The only questions to ask are Where is the tip coming from and heading toward when it makes contact, where is it making contact reletive to center, and how fast is it moving when it makes contact.
This is all you have any control over, and it is all that really matters.

Steve