Deflection, Endmass and Shaft Design

[HittMan]

Not sure if this has been asked, but does the pressure exerted on the cue by the bridge (especially a closed bridge) have an effect on squirt? Intuitively, it seems to me that bridge pressure would at least have an effect on the transverse wave, if the bridge length is short enough. Would this also have an effect on either shaft deflection or squirt? On this, intuition becomes pure conjecture for me. I'm guessing that bridge grip pressure does have an effect on shaft deflection. I'm also guessing that the wave doesn't start until after the CB has left the tip, so therefore, the bridge grip pressure should not affect squirt. However, if I understand the transverse wave properly, it sort of defines the effective end mass. If bridge pressure affects the transverse wave, then the effective end mass is being changed, which in turn should alter squirt. The intuitive conclusion I've reached is that bridge pressure does affect squirt. Is this a valid conclusion? I've made a lot of assumptions, guesses, etc., and I don't have an empirical leg to stand on, but I'm curious, since I play with a fairly short bridge length (usually no more than 6").

-djb

This is where I started...go back to post number 1 and begin again...do not pass go, do not collect $200.
Sorry...I just needed a little humor...this is probably as little as you are likely to see today.

 

[Fred Agnir]

OK...I use the speed of sound as an approximation from which to begin...I think you will find that it is not far off.

I think the speed of sound down the shaft is many times faster than the transverse wave. In the .001", I believe the sound wave has traveled the entire length of the cue. The transverse wave has only traveled ~ 6".

Further, I agree that there is a limited length directly involved. But do you agree that resistance to sideways motion may include resistance to deformation (bending). Clear your mind...why wouldn't it?

Do I agree that resistance to sideways motion may include resistance to bending? Sure.

But does that truly relate to your questions on squirt and what affects it? I dont' think so. I don't know of a theory that states that if the material was the same weight but had less resistance to bending or less deflection per known force that the squirt angle would be different. I don't know of how to test it, and I don't know of a theory or physical model to test it. What physical model of collisions include material deflection parameters? If we started with a model, we could all work toward a test.

Fred

 

[HittMan]

I think the speed of sound down the shaft is many times faster than the transverse wave. In the .001", I believe the sound wave has traveled the entire length of the cue. The transverse wave has only traveled ~ 6".

Fred...I compared the two in jest...the transverse wave in the discussion is precisely the mechanical speed of sound in transverse axis (if you will) through a dense medium...they are the one and the same...absolutely no difference...period. There are only two broad categories of waves...electromagnetic (light and magnetic) and mechanical (sound). If we cannot agree to this then this is hopeless.

Do I agree that resistance to sideways motion may include resistance to bending? Sure.

But does that truly relate to your questions on squirt and what affects it? I dont' think so.

I'm not sure what you think my question is, but for clarity, here it is again:
1)The parameter Mtip is defined in the paper as "...not the total stick mass. Rather it is the intertial resistance to sideways motion that the tip possesses. This effective mass Mtip..." (this is a direct quote). It appears that the article is drawing an effective parallel between mass and inertial resistance to force...and further ...that the value of "endmass" (as previously defined) equals the weight of the tip or last 6" or so of the shaft AND that this is the most significant factor in the actual resistance to sideways motion. If you agree, as you did above, that resistance to bending may be included then we can EASILY test for it.

I don't know of a theory that states that if the material was the same weight but had less resistance to bending or less deflection per known force that the squirt angle would be different. I don't know of how to test it, and I don't know of a theory or physical model to test it. What physical model of collisions include material deflection parameters? If we started with a model, we could all work toward a test.
Fred

You don't know of a theory because you have been argueing against it...while agreeing with its component presumptions. I have already proposed a test to Bob Jewett (see post #72 of this thread) that could be useful by introducing a variable and a value into this rigid body analysis. I think we already have a model...Mr. Shepard's work is (as I have said repeatedly) a reasonable start to a very complex problem. I am trying to build upon or augment this work. The only difference between a rigid body analysis (one that does not include a variable for the resistance that sets up the transverse wave we all keep talking about) and a semi-plastic analysis would traditionally be adding in factors (variables) for deformation, friction (skid...the essential essence of deflection and throw), and rotation (to name a few). You act as though I don't understand, but quite the contrary. I am simply suggesting that we (that includes us) translate all the OBVIOUS values (the ones that you can easily see...ie...degrees of freedom of movement) before we attempt to complete or leave this work for others OR more importantly, endorse it. This is NOT a difficult step if you look at the complexity of the whole (the whole being a finite element analysis of the dymanics).

I am really almost through with this thread...there is an undercurrent of resistance here that, regardless of motivation, is very difficult to overcome. I, unlike many others, have no investment in this popular notion. It, in fact, makes no difference to me that the conclusions of this "paper" are, in my opinion, dubious at best. When I looked at the conclusions of the paper, I tried to gently question the single, most obvious shortcoming that would have the greatest effect on the conclusions...without flaming anyone. It is no accident that few remain to discuss this flaw in logic.
Additionally, the effect of squirt is but one of a robust series of phenomenon that might be explained by observation and dynamic examination, but to what end? The knowledge alone will not make a better player if he cannot predict the magnitude. Thus the camel/gnat analogy. The conclusions though, are quite another matter. Many people have taken these conclusions as gospel and directed their money toward the promise of an easier/better way. I have no investment here also...but my assumption was that those who did would like a shot at redemption...my error...not to be repeated.
I appreciate your continued involvement and I apologize for my lack of patience. You may contact me through my private message box at any time.