Simple Squirt Test

Patrick Johnson said:
Jim, after some thought I'm beginning to see your point (and thinking it's probably valid).
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PJ,

Do you not like the method described and demonstrated here?

It seems easier and less prone to errors, and the moving PostIt-note-dot shows you the actual pivot point on the shaft when you are done.

Regards,
Dave
 
dr_dave said:
Jim,

I'm not sure which video you are referring to, but cling may have been involved. In a few throw and spin-transfer videos, I sometimes added a chalk smudge at the CB-OB contact point to illustrate the effect of cling. If I did, it would be indicated in the video title or narration. Cling could certainly affect the results of PJ's experiment; but with enough trials, it should be clear if cling occurs....
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Hi Dr. Dave,

Well, I did feel a bit queasy about bringing it up since the discrepancy may be totally due to error on my part. I don't know exactly which video (it's on my other computer, which may be brought to life again shortly), but it wasn't, I'm pretty sure, one demonstrating cling. I realize that this doesn't jive with Marlow's data, from which you developed the dependence of mu (coefficient of friction) as a function of surface speed. It would be hard (for me) to explain. Even if the coefficient increased with pressure, why didn't it show up at the faster speeds Marlow used with his 45-degree cuts?

But, just in case, I thought maybe I should mention that throw might not drop off with high surface speed in the case of full or near full-ball hits. Hopefully that's wrong, and I apologize for tossing that out without further checking.

Jim
 
Jim:
...your arithmetic would produce a pivot distance roughly 1/3'rd less than the actual distance.
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Jim,

You're right. I've deleted my original post so as not to mislead anybody. Maybe I'll be able to come up with an accurate but Simple Squirt Test, but this apparently isn't it.

Thanks for the catch.

pj
chgo
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Patrick Johnson said:
Yes, I think I do like the traditional "aim and pivot" method better, Dave. I thought I liked the way my method directly showed the relationship between tip offset and pivot length, but I now see that was not the case (since Jim made me aware of the magnitude of the discrepancy caused by the offcenter hit on the tip itself).
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Thanks for acknowledging that, Patrick. I guess I'm biased by you know what, but it seems exceedingly rare around here where two parties can initially disagree on some aspect of geometry/physics, yet come to some definite conclusion which both accept. I don't know how you do it with your avowed "distaste" for some of the math (other than raw intelligence), but it took me quite awhile to understand what you were saying in your PMs...and eventually concur. :)

Jim
 
*BUMP*

I've re-posted my Simple Squirt Test after re-confirming its accuracy. The only change is that the center of the cue is used to aim rather than the tip's contact point. This makes the measurement accurate without any math or adjustment and also makes aiming (using the center of the cue) simpler and more familiar.

NOTE: The Simple Squirt Test is designed for Centennial balls because the edge of a Centennial's stripe is very nearly 1/2 the distance from center to edge of the ball. Other balls will not work with this test unless an aiming adjustment is made.

Also, since the edge of a Centennial's stripe is actually 1/32" less than 1/2 the distance from center to edge, in order for the test to be perfectly accurate it should be aimed 1/16" inside the OB's edge.

pj
chgo
 
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