Kiss Forward And The Question Of Overspin.
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That's what I thought, too, Neil, but Dr. Dave's video shows that you can, technically, get a very small amount of overspin just after the cue strikes the CB. This overspin is so rare, and so small, and dies so quickly that, for all practical purposes, we can all assume it does not exist.
I probably confused some folks. "Gearing" normally refers to the transfer of english from the CB to the OB. In this thread, when I spoke of "gearing," I meant that the CB was no longer sliding down the table; it was in full roll and in full contact with the cloth, like a pinion gear on a toothed rack (as in rack & pinion steering).
Since there is practically no such thing as overspin, a rolling/gearing CB will have a follow angle that completely depends on its speed, no matter how high you hit it to start with.
Now THAT is the useful nugget. :thumbup: Maybe some of you knew that, but I did not.
(Now, if you hit it hard with too little follow you might not be fully rolling at OB contact. That's a different issue.
)That's a pretty fair statement. There are some situations where you might be able to get more of it than indicated in the video.
I think Dr. Dave probably coined the term "gearing", and he generally uses it to mean the case where outside english on the CB essentially cancels the tangential component of CB velocity. This results in no throw and no spin imparted to the OB. In many other cases, the balls aren't "gearing" at the start of impact, but reach that state before the collision is over with. Here you do get throw and acquired english on the OB.
It's a good analogy and I think most knew what you meant.
Actually, it depends very little on speed, and not even that much on cut angle. Between a 3/4 and 1/4 ball hit, the follow angle, measured with respect to the CB's pre-impact direction, stays fairly close to 30 degrees.
Jim
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Marcus -
I like your shot.
I sense that you believe that I or others think overspin doesn't exist. I don't make that claim, and I don't know anyone else who makes that claim.
Please watch the last minute or so of my video: from 5:40 on
http://www.youtube.com/watch?v=1WzyxhCl0vs
Mike: The question on this thread was about overspin just after cue stick contact (not after OB contact).
Your video suggests there is no CB overspin after cue stick contact with the CB, and Dr. Dave's high speed closeup shows a very very small amount, but I think his video generally supports your results that, for practical purposes, it does not exist.
I have a different view on this point. I'll explain why.
Follow angle is determined by angular momentum, the energy stored in a spinning CB. That's why, even after OB contact has initially deflected the CB off at a 90 degree rebound angle, that stored spinning energy grabs the cloth and curves the CB path back towards the original pre-collision track.
A CB's angular momentum is a result of how fast it is spinning. A gearing/rolling CB's spin rate is mechanically tied to its forward speed. (One is a measure of the other. Your car's speedometer calculates you forward linear speed by measuring your wheel's spin rate.)
If you have two identical shots where the CB is rolling at 5mph, each CB has the same angular momentum, and the post-impact follow angle will be the same regardless of how many tips of Follow you applied initially at the CB. Counter-intuitive, but true.
OR......
If you have two identical cut shots, except the CB is rolling at 5mph in one and it is rolling at 10 mph in the other, the forward speed (which is a measurement of the spin rate and therefore angular momentum) will determine the post-collision path of the CB. The faster-moving (therefore faster spinning) ball will exhibit more follow than the slower-moving (therefore slower spinning) ball.
This does not contradict the "30 degree rule" (which is really a rule of thumb). Without experimentation,I am supposing that rule benefits from the fact that many shots are shot at a range of speeds around an average.
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The question was about overspin in Marcus's shot. Is there someone saying that kind of overspin-- prima facie overspin--is required for Marcus's shot?.
Yes, thanks. And I didn't mean to suggest that it can't be done or that someone hitting very close to miscue isn't getting any. Rather, a lot of people imagined that on a hard-hit, juiced-up, force follow shot, the cueball is loaded up with a bushel of prima facie overspin. And that just ain't true.
Actually, both experiment and physics show that the follow angle is the same on the two shots. For detailed, written explanations, see the articles and books written by Bob Byrne, Dr. Dave, Ron Shepard and http://www.sfbilliards.com/articles/BD_articles.html
Briefly, while the faster ball has more spin, it also has proportionally more speed which is increased in direct proportion because the cue ball is rolling smoothly on the cloth. During the curve the cue ball takes after it hits the object ball, the faster ball moves to the side more before it stops curving and continues along a straight line. The result is that for a particular cut angle, a rolling cue ball will end up going parallel to the same line at any speed, but the faster ball will slide "wider."
To do an experiment yourself, go to diagram 4 in http://www.sfbilliards.com/articles/2000-11.pdf and vary nothing except the speed of the rolling cue ball.
FYI to Shaft and others, Diagram 1 in my June '05 article shows this effect, and TP A.4 presents all of the math and physics.
Regards,
Dave
And while we're going on the record here, I don't like the term "gearing" in this context. I think its use propogates the incorrect visual model of interlocking gears for the ball-ball interaction, which as we know leads to wrong conclusions
I agree, but to be fair Dave only uses gearing to refer to ball contacts that don't involve a sliding contact. As when a ball contacts the cloth when rolling without slipping, gearing fits for that limited state. The problem is when it's generalized for slipping cases as well, like so many instructors have done in the past.
That's why I use the terms 'rolling' or 'natural' sidespin to indicate touching a ball or cushion with just the right amount of sidespin to roll against it without slipping. I think it's important to link it to the same principle as rolling on the cloth, and it's also important since it's the angle-dependent reference spin that divides running/reverse or under/overspin for any contact (rail, ball, cloth).
Robert
The shot belongs to bob byrne.
Your sense that I interpreted past threads as stating there is no overspin is correct.
I think the best way to put the question to bed is by filming the following shot: in one shot roll a stripe ball between the foot and head spot. Then set up the same ball on the foot spot and record shots using varying speeds and degrees of follow. Put the shots in slow motion, count the number of revolutions in each shot and compare. If there is a disparity between the number of revolutions then you have your answer. I can't do this with my camera because I can not capture enough frames per second to see the spin on the faster shots.
By the way, how is the room coming? When will we see pictures? I plan on visiting the room in the future.
This detail can be confusing because we tend to think of the CB's path as a straight line. Visualizing how it curves can help with accuracy, particularly estimating rebound angles off the rails.
pj
chgo