Question about intentional swerve

Quote:
Originally Posted by dr_dave View Post
NV F.2 - Swoop Stroke Experiment - Can swooping create extra spin on the cue ball?

dr_dave said:
Thanks to 12squared (Dave Gross) for helping me with the tests. Dave's experience and skill level are always appreciated.

Thanks Dave,
Dave
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Hi Dave,

I only watched it once but here is what I noticed. When the 'swoop' strokes were performed the cue stayed in or on the bridge, hence limiting the extent.

It's not so much about the swoop that occurs prior to impact or contact & then move 'straight' but instead it is about the swooping that occurs DURING contact.

IMHO the swoops were not well timed & were to me early & then limited by the cue staying on the bridge. (perhaps your outlier of 11+ was better timed)

In a good swoop stroke, IMO, the tip is actually moving in an arc with more of a lateral movement or component than what I would think occurred with the strokes that I saw in you 'experiment'.

When I want to max the spin to speed (I know we disagree) I align with a parallel cue stick & then swoop with the cue leaving my open bridge.

Also, take a look at your example of Mr. Gross's stroke. It 'swoops' but then finishes in the opposite direction. So what really happened when & what actually happened during contact.

I don't mean to argue but this proved nothing, to me.

To me, it was a fairly good attempt on your part but, to me, the conclusion is ill based, based on poor parameters.

What it did, to me, is compare BHE with a pivot before making the stroke to BHE while making the stroke.

Given that, I can certainly agree with the results & the conclusion.

Now...

Imagine the tip on the ball & while in contact with the ball it is changing directions by adding a more lateral component than normal.

To me that is what happens for what I term as a swoop stroke. I guess my 'definition' is different than what many if not most would deem as a swoop stroke.

It's sort of like the fact that there is more than one type of top spin shot in tennis. There is one where the racket drives through & turns down & then there is one where the racket starts much low & comes more up fast on the ball than it drives through the ball. With those two one get different amounts of spin with different amounts of forward velocity.

Naturally all of this is just how I see it & I'm not looking to argue or prove anything.

Each individual can & will make their own determination & that is how it should be.

Your video & conclusion may keep some or many from ever trying what I call a swoop stroke & that may be best for them. Who knows?

No one taught me the stroke that I use. I just stumbled upon it by hitting so many balls when I was much younger.

Best 2 You & All,
Rick
 
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Mikjary said:
the player's (Mr. Dave Gross) interpretation of swooping the cue and what I do are different. He seems to be applying BHE rather than applying spin as he strokes through the cue ball.
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Actually, he uses a combination of BHE and swoop, but there is clearly a strong swooping motion during and after contact.

Regardless, for the last set of tests, I did all of the shooting, and I was careful to use a strong swoop motion, with no pre-stroke BHE-like pivot.

The first time we ran through the experiments, both Dave Gross and I did complete sets of shots with both cues and both types of strokes; but, unfortunately, when I looked at the results, they were all over the place because we didn't control all of the variables carefully enough. I threw out all of that work and redid the tests myself (I couldn't impose on Dave Gross again). I made sure the cue was at the same elevation for each shot, that the tip contact point was on the horizontal centerline of the CB, and that the CB hit the 1st cushion in the same spot. It wasn't easy to do all of this stuff (it would be much easier with we had a robot that could stroke accurately and consistently with either straight or with a swoop), but the Elephant Practice Ball check was helpful (with careful alignment of the ball on each shot), as was the use of the two obstacle balls on the 1st rail (which we did not include with the original set of tests that I threw out).


Mikjary said:
I did a short experiment similar to your setup with about ten shots each. I used a hard tip on a maple shaft and got different results. Possibly because I'm more familiar with the swiping stroke than in your example.
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When we switched cues and tips, it took us a while to dial in the aim and speed necessary to get the exact same CB direction and speed. Were you careful with this in your experiment?

Mikjary said:
One last thought, in the first part of the video, a larger result of 11.4 occurred on your swooping demonstrations.
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Actually, the 11.4 result was with the straight stroke (no the swoop stroke).

Mikjary said:
Possibly, the answer is in the technique. I won't dwell on this because it is a hotly debated point here, but it is what I'd call digging into the cue ball, or pinning the cue ball.
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I mention this in the video. There are two effects that can change the effect of the english ... hitting below center, creating a spin-intensifying drag effect; and elevating the cue slightly, creating a swerve (and drag) effect. Both of these effects are demonstrated and described earlier in the video.

Mikjary said:
As soon as I saw the stroke, before I saw the results, I said to myself from experience the player just pinned the cue ball. The audio portion of this stroke is slightly different if you compare it to the previous strokes.
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The sound is different because the cue hit the rail during the stroke (due to very slight elbow drop), but I think the CB was already gone before the drop occured. I was keeping the cue as level as possible with almost no clearance above the rail, so the cue did hit the rail on many of my attempts (partly due to the thicker part of the cue approaching the rail during the stroke, and sometimes due to slight unintentional elbow drop after the hit).

Thank you for your input,
Dave
 
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ENGLISH! said:
I only watched it once but here is what I noticed. When the 'swoop' strokes were performed the cue stayed in or on the bridge, hence limiting the extent.
It's not so much about the swoop that occurs prior to impact or contact & then move 'straight' but instead it is about the swooping that occurs DURING contact.
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Did you look at the swoop strokes used in the actual experiment, starting here: https://www.youtube.com/watch?v=JOHee4z3abA#t=627

I can assure you that there is significant sideway swooping/swiping during these hits. This is totally clear when I played the original video back in slow motion.

See also my replies to Mikjary that address most (if not all) of your comments.


ENGLISH! said:
I don't mean to argue but this proved nothing, to me.
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I certainly encourage you and others who might doubt the results to do your own set of careful tests (and posts videos if possible). If you get different results, I'm sure there will be logical explanations for the discrepancies (assuming there are videos documenting the work).

Regards,
Dave
 
dr_dave said:
Did you look at the swoop strokes used in the actual experiment, starting here: https://www.youtube.com/watch?v=JOHee4z3abA#t=627

I can assure you that there is significant sideway swooping/swiping during these hits.
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FYI, this is clear in the video not just by seeing the swooping motion, but by also looking at the center-ball aim (before the swoop). The cue is actually being aimed to the right of target, as if the left-spin shot is creating "negative CB deflection." This isn't what is actually happening, but I was a honestly a little surprised by how much my aim was different with the swoop stroke as compared with the straight stroke, with everything else being the same. The significant swooping motion does change the direction of the CB (in addition to creating extra spin for the given tip contact point) as illustrated in the diagram in the video.

Regards,
Dave
 
dr_dave said:
The significant swooping motion does change the direction of the CB (in addition to creating extra spin for the given tip contact point) as illustrated in the diagram in the video.
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For those interested, here's the diagram mentioned:

swoop_experiment.jpg

Regards,
Dave
 
Patrick Johnson said:
dr_dave said:
A swoop stroke can create more spin for a given aim and tip contact point, but it cannot create more spin in general.
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I don't get the distinction. Can you expand a little?
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The part of the video with the diagram explains this briefly. Here's the diagram again:

swoop_experiment.jpg

Both of these shots produce the same CB direction and same CB spin. The swoop stroke has the same "effective tip offset," but the actual tip offset (the perpendicular distance between the blue dotted line and the black dot at the center of the CB) is less than with the straight stroke. If a straight stroke were executed in the swoop stroke direction with the same tip contact point, less spin would be imparted to the CB (and the CB would head in a different direction). Please watch the video again, especially the discussion at the end, and let me know if it is clear or not. And if you can think of a way to make it more clear (with a better diagram and/or explanation), please let me know.

Thanks,
Dave
 
Thanks, Dr. Dave for your comments. I was limited on time in my first set of trial strokes, hence the "short" experiment phrase. Despite the controls being limited in my trial strokes, the applications were my main concern.

I appreciate your exhaustive research on the subject and your commitment to detail. It's easy for me to just armchair your results and find small irregularities and inconsistencies, but that isn't my purpose with my responses.

I actually DID :) get on the table and try out what you found in your experimentation. I'll try to spend more time on the controls and most likely validate your findings. The only change for me will be in the application of the cue ball swiping. It will be more from experience than I feel either you, or Mr. Gross have at this time.

The ultimate answer is, like I said, get Larry Nevel on video with his swipe stroke. That'll be truly, what is possible for a human to do. :cool: That begs another caveat for your parameters...you showed us what mere mortals are capable of doing. :grin-square:

Best,
Mike
 
Dave

First, thanks for the videos. The time and effort you put into resolving these questions about pool physics is amazing. It's greatly appreciated!

I do have a question though.

At the speed of these shots, what would you approximate the ball to tip contact time to be?

For a swoop shot to work, there must be a fairly significant difference between the contact point where the tip first contacts the ball, to the tip position when the ball leaves the tip.

I understand what proponents of this shot believe is happening, but I'm not sure there's enough time for the lateral tip movement necessary for the shot to be effective, to occur before the tip leaves the ball.


Thanks again

Royce
 
dr_dave said:
The part of the video with the diagram explains this briefly. Here's the diagram again:

swoop_experiment.jpg

Both of these shots produce the same CB direction and same CB spin. The swoop stroke has the same "effective tip offset," but the actual tip offset (the perpendicular distance between the blue dotted line and the black dot at the center of the CB) is less than with the straight stroke. If a straight stroke were executed in the swoop stroke direction with the same tip contact point, less spin would be imparted to the CB (and the CB would head in a different direction). Please watch the video again, especially the discussion at the end, and let me know if it is clear or not. And if you can think of a way to make it more clear (with a better diagram and/or explanation), please let me know.

Thanks,
Dave
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I think the part in blue above is what confused me. I'd say the "actual tip offset" (i.e., the angle of the shaft at contact) is purely incidental, and the "effective tip offset" (i.e., the angle of tip movement at contact) is the relevant measure for comparing spin effectiveness.

A straight stroke with the shaft at the same angle as a swooped shaft at contact isn't a real alternative to the swooped stroke because they send the CB in different directions.

Thanks,

pj
chgo
 
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I want to believe you, however.......

Bob Jewett said:
A small nit.... The path of the cue ball is a parabola from the time it leaves the tip until it starts rolling straight. That means it's curving right from the start.
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So there's no deflection at all? Hmmmm

I want to believe you, however, this is not my experience, maybe it's how I'm aligning.

Also it may depend on the level of acceleration I'm getting, slower and it does curve right away, however, not when I get close to maximum cue speed.

I aim the masse' shots as if the ball that's obstructing the shot isn't even there. This does take some understanding, I'll experiment with it later and see for sure.
 
Bob:
The path of the cue ball is a parabola from the time it leaves the tip until it starts rolling straight. That means it's curving right from the start.
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CJ:
So there's no deflection at all?
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A shot with deflection is the same as a shot aimed in a slightly different direction without deflection. The curve will begin happening immediately either way.

pj
chgo

P.S. This is why you don't need deflection for those "masse around the edge of a blocking ball" shots. You can just aim the CB where deflection would have taken it.
 
RBC said:
Dave

First, thanks for the videos. The time and effort you put into resolving these questions about pool physics is amazing. It's greatly appreciated!
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You're welcome ... and thank you.

RBC said:
I do have a question though.

At the speed of these shots, what would you approximate the ball to tip contact time to be?
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Whether there is swooping or not, the tip contact time is roughly 0.001 seconds (about a thousandth of a second). This varies a little with shot speed and tip hardness, but it is always extremely small. For those who want proof or more info, see cue tip contact time.

RBC said:
For a swoop shot to work, there must be a fairly significant difference between the contact point where the tip first contacts the ball, to the tip position when the ball leaves the tip.

I understand what proponents of this shot believe is happening, but I'm not sure there's enough time for the lateral tip movement necessary for the shot to be effective, to occur before the tip leaves the ball.
Click to expand...
The lateral motion does need to occur during the hit. Even though the tip isn't in contact for very long, the lateral motion does have an effect. The lateral motion changes the effective direction of the force and the effective tip offset, as demonstrated in the video and illustrated in the diagram:

swoop_experiment.jpg

The lateral motion during contact is a result of what the stroke does on the way to the ball. Extra swooping action can't be added during the incredibly brief contact time. Maybe that is what you (or others) are thinking. The spin is affected only by the forward and lateral speed of the tip coming into the ball. What happens during contact is really out of our control. All of our control is in what we do during the forward stroke into the ball (before contact).

Thanks for the comments and questions, Royce.

Regards,
Dave
 
Patrick Johnson said:
dr_dave said:
swoop_experiment.jpg

Both of these shots produce the same CB direction and same CB spin. The swoop stroke has the same "effective tip offset," but the actual tip offset (the perpendicular distance between the blue dotted line and the black dot at the center of the CB) is less than with the straight stroke. If a straight stroke were executed in the swoop stroke direction with the same tip contact point, less spin would be imparted to the CB (and the CB would head in a different direction).
Click to expand...
I think the part in blue above is what confused me. I'd say the "actual tip offset" (i.e., the angle of the shaft at contact) is purely incidental, and the "effective tip offset" (i.e., the angle of tip movement at contact) is the relevant measure for comparing spin effectiveness.
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Agreed, but not everybody thinks of it this way ... and maybe that's part of the confusion and misunderstanding with this topic. That's why I'm careful to distinguish between the two interpretations.

Patrick Johnson said:
A straight stroke with the shaft at the same angle as a swooped shaft at contact isn't a real alternative to the swooped stroke because they send the CB in different directions.
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Agreed.

It's good to have you back on the forum again to continue to keep us honest.

Catch you later,
Dave
 
CJ Wiley said:
Bob Jewett said:
A small nit.... The path of the cue ball is a parabola from the time it leaves the tip until it starts rolling straight. That means it's curving right from the start.
Click to expand...
So there's no deflection at all?
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For soft speed shots, especially with added cue elevation, some of the swerve (parabolic curve) can actually happen as the CB is driven down into the table (before it travels hardly at all). I call this effect "immediate swerve." The rest of the swerve might then occur over a very short distance (that might not even be noticeable). In cases like these, it can seem like there is no squirt (CB deflection), but there is ... it is just being counteracted by the swerve.

For more info, see:

squirt (CB deflection) speed effects
squirt/swerve cue elevation effects
squirt/swerve tip contact height (draw/follow) effects

Enjoy,
Dave
 
dr_dave said:
It's good to have you back on the forum again to continue to keep us honest.

Catch you later,
Dave
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Thanks. I hope you don't think I was trying to correct you (a man's gotta know his limitations :)) - just trying to understand and clarify.

pj
chgo
 
Patrick Johnson said:
Thanks. I hope you don't think I was trying to correct you (a man's gotta know his limitations :)) - just trying to understand and clarify.
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Not at all. I agree with you that clarification was important in this case. Clarification is always good. You have certainly helped create lots of clarification on this forum over the years ... when you're weren't getting into trouble. I hope you stay unbanned for a while.

Catch you later,
Dave
 
dr_dave said:
You're welcome ... and thank you.

Whether there is swooping or not, the tip contact time is roughly 0.001 seconds (about a thousandth of a second). This varies a little with shot speed and tip hardness, but it is always extremely small. For those who want proof or more info, see cue tip contact time.

The lateral motion does need to occur during the hit. Even though the tip isn't in contact for very long, the lateral motion does have an effect. The lateral motion changes the effective direction of the force and the effective tip offset, as demonstrated in the video and illustrated in the diagram:

swoop_experiment.jpg

The lateral motion during contact is a result of what the stroke does on the way to the ball. Extra swooping action can't be added during the incredibly brief contact time. Maybe that is what you (or others) are thinking. The spin is affected only by the forward and lateral speed of the tip coming into the ball. What happens during contact is really out of our control. All of our control is in what we do during the forward stroke into the ball (before contact).

Thanks for the comments and questions, Royce.

Regards,
Dave
Click to expand...


Dave

Thanks for that answer.

Actually, it's exactly what I expected.

In order for the swoop shot to do what it's proponents say it can do, that time would have to be longer. The fact that it's not able to lengthen the contact time, further supports your findings that swoop shots can't do anything that a normal shot couldn't.

I've known many who use the swoop. I've always felt that all it really did was change the spot on the ball they actually hit.


Thanks again

Royce
 
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