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Patrick Johnson
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01-23-2016, 09:29 AM

Quote:
Originally Posted by Bob Jewett View Post
I have held in the past that stiffness can affect squirt. It clearly will determine how much of the front of the stick will be included in the effective end mass.
Do we have a sense for what fraction of total squirt effect is caused by end mass (including stiffness determining that) vs. stiffness directly resisting the CB's rotation?

I'm guessing direct resistance from stiffness is a very small part of the equation...

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01-23-2016, 09:31 AM

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Originally Posted by Bob Jewett View Post
It was rough analysis based on transverse wave propagation. Stiffness affects the effective "impedance" of the interaction.

But I think a good scientist (or anyone who tries to understand how things work) relies on intuition to find promising directions. The important part comes after the direction is decided -- the analysis and objective testing of the idea begins.
I concur.

"In the past" your intuition was correct. Today there is more empirical evidence of that.

"Stiffness affects effective impedance" ergo, stiffness is a component of "effective end mass" and not just the static weight (mass) of the front of the shaft alone.

Back 50 years ago, I used to sand my shaft diameter down and because being thinner it was easier to see the axial line. For me and without any instrumented empirical evidence, thought it played better as well and noticed it would bend away. Today I use a Z2 for the same reasons and no more sandpaper.

That's all and not a dig on your "past" if that was what you took away. I have learned a lot from you.

The article is what it is and it's conclusion can be challenged.

Thanks and be well.


dumluk

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Jal
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01-23-2016, 09:35 AM

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Originally Posted by LAMas View Post
[I]For all these years, It has been held here that only end mass determines squirt and when I proffered that I thought that the flexing or bending of the shaft is also an important component, I and others were dismissed.
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
  
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Patrick Johnson
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01-23-2016, 09:38 AM

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Originally Posted by Corwyn_8 View Post
I haven't gotten all the way through it, but I did notice:



Which would appear to violate Euler's rotation theorem which states that "any displacement of a rigid body such that a point on the rigid body remains fixed, is equivalent to a single rotation about some axis that runs through the fixed point.".

One could argue that the point is semantic, but I wouldn't expect such a fundamental mistake in a peer reviewed article.

Thank you kindly.
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.

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01-23-2016, 09:38 AM

Quote:
Originally Posted by Patrick Johnson View Post
Do we have a sense for what fraction of total squirt effect is caused by end mass (including stiffness determining that) vs. stiffness directly resisting the CB's rotation?

I'm guessing direct resistance from stiffness is a very small part of the equation...
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
  
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Patrick Johnson
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01-23-2016, 09:43 AM

Quote:
Originally Posted by dr_dave View Post
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.

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01-23-2016, 09:43 AM

Quote:
Originally Posted by Patrick Johnson View Post
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
  
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01-23-2016, 09:58 AM

I agreed with everything in your previous excellent post except this:

Quote:
Originally Posted by Jal View Post
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
  
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01-23-2016, 10:05 AM

Quote:
Originally Posted by Jal View Post
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.
  
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01-23-2016, 10:11 AM

Quote:
Originally Posted by ENGLISH! View Post
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
  
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01-23-2016, 10:21 AM

Quote:
Originally Posted by dr_dave View Post
... 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.

Last edited by ENGLISH!; 01-23-2016 at 10:31 AM.
  
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01-23-2016, 10:33 AM

Quote:
Originally Posted by ENGLISH! View Post
Quote:
Originally Posted by dr_dave View Post
... 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
  
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01-23-2016, 10:51 AM

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Originally Posted by dr_dave View Post
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?

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01-23-2016, 11:03 AM

Quote:
Originally Posted by Patrick Johnson View Post
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.
  
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01-23-2016, 11:05 AM

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Originally Posted by LAMas View Post
Hmmm...spheres being rotated...bad?

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