Usually gyroscopic action involves some kind of fixed axis on the gyroscope. A cue ball has no special axis. I think any torque applied to the ball is simply integrated into the current rotation to give a modified axis of rotation.
curving an object ball....
- Thread starter John Brumback
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With all due respect to the "scientists'...
I don't think 99+% of players here or in total give a rats ______ about the science.
But... they ALL would Love to be able to bank like John Brumback KNOWS how to do it.
Best 2 All,
Rick
I don't know but he must have been super good in math and science to be able to play like he does.
I hear Brumback knows how to fish well for different species too.
JoeyA
I think the precession is the wrong way, i.e. if you're shooting a bank from left to right (you're to the left of the side pocket, aiming to bank into the pocket), and you have right spin, you say it also picks up topspin. The precession would actual cause the angle to shorten even more. So if you're watching the cueball come off the rail at eye level, when it tips forward towards you (the top spin it's picking up), and it has right spin, there's a force that's trying to twist the cue ball in a counter-clockwise direction, shortening the angle.
I think it might be simply a matter of the cue ball's spin axis "tipping" when it comes off the rail with the additional top spin, and I think the gyroscopic forces are actually fighting you but maybe not significant.
Perhaps it explains John's shot, though, which has a lot more power behind it and perhaps has more significant forces.
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Never mind...right hand rule. The torque is actually in the direction to lengthen the shot! I always have to work it out again, and never remember it the right way.
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For those interested, Bob and I just had a long phone conversation about this. Gyroscopic effects do not apply to homogeneous spheres that have equal principle moments of inertia about all axes (i.e., the gyroscopic terms in Euler's Equations for Rotational Motion are all zero). Therefore, there are no gyroscopic effects in pool (unless the balls are not round or well-balanced).
Thanks to Bob for setting me straight on this. I should know better since I actually teach a graduate-level course in advanced dynamics (applied to mechanical engineering). If Bob were in my class, I'm sure he would get an A+ ... and probably be the subject of numerous "Little Johnny" jokes. :grin-square:
Good job Bob,
Dave
I agree with this entire post. Most people don't care how or why things works. Also, I (and others pool-playing "scientist") would love to be able to bank with the accuracy and consistency of a bank-pool champion like John.
Regardless, it would still be interesting to know why and how a banked ball's rebound path can curve. It would also be interesting to know how the amount of curve is affected both by things the player can control (e.g., speed, spin, angle, ball hop) and things the player can't control (e.g., rail, cushion, cloth, and ball conditions). This sort of "understanding" can actually be helpful to someone trying to learn or replicate these types of shots ... and this "understanding" could actually be useful to both "scientists" and "players."
Regards,
Dave
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Someone should tell the Gravity Probe guys that their experiment doesn't work. I'm sure there's some truth in this so that maybe it's not applicable, but I'm not sure I understand that gyroscopic effects don't exist, since they're basically just the results of angular momentum and torque.
Maybe to say it another way, if I take a sphere, and slice it up into disks, surely there are gyroscopic forces on the disks.
If I spin the disks all at the same rate, just as they would be in a ball, there are still gyroscopic forces.
If I put the disks arbitrarily close together, there are still gyroscopic forces.
How does all of this suddenly disappear when I glue the disks back together?
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The Gravity Probe guys are using perfect spheres as "gyroscopes" but there is no "gyroscopic effect" acting on those spheres. The spheres are merely rotating about fixed axes in space as the housing moves around them if there is any relative motion (which is being measured). A "gyroscope" (used to sense angular orientation) has little to do with "gyroscopic effects" (where torques act on non-spherical objects spinning about multiple axes). A "gyroscope" is gimbal-mounted (or floated in space) so no external torques can be applied.
Regards,
Dave
Haven't you ever spun a basketball on your finger?
Yes.
As with a "gyroscope," the rotation is very stable, and the axis wants to remain fixed in space.
Are you trying to make a point relevant to pool?
Regards,
Dave
A difference from anything we see on the pool table is that you are forcing an axis with your finger contact.
You can find the rotation of a radially uniform object (uniform sphere or shell, like a basketball) simply by integrating the torque around each axis. You can't do that with an asymmetric object, such as classical gyroscopes or bicycle wheels. The equations you have to deal with are Euler's equations (see wikipedia) and they look like:
![CropperCapture[16].png](https://forums.azbilliards.com/data/attachments/302/302445-91e40cdacf1578542ba554b94d230f97.jpg?hash=keQM2s8VeF "CropperCapture[16].png")
where the I's are the moments of inertia around the principal axes of the object. Since a uniform sphere has all I's equal, the "interesting" terms cancel out.
I believe you're looking at the Polhode motion of rotating body, i.e. how does the pole wobble in the absence of torque.
I don't know, Dave. I'm trying to be cordial and helpful. You can think about it for a bit, and maybe you'll change your mind. Maybe as a though experiment, figure out where the vector points for a rotating ball, apply a torque (figure out where THAT vector points), and see what happens.
But Dave, we really already know those things. Is that not physics?
What many need to know is the thinking of the likes of John Brumback & then what & how he does what he does & HIS reasons why he does them whether technically & scientifically properly said or not.
If we know what John is thinking & doing & 'why' so in his mind, then there is no need for a player to know the science to do what John does... because we KNOW what John does WORKS.
So why put any doubt into the minds of others whether John Brumback actually knows what he's talking about when he's talking about banking pool balls.
'Oh, John Brumback doesn't know what he's talking about because Dr. Dave & the science guys said xyz.'
Two options. Lessons on banking from John Brumback or lessons on banking from Dr. Dave.
Sorry Dave. You will not be seeing me for any banking lessons.
To be rather honest, as I always am, I think that the science guys do more harm in these types of forums than actual good when it come to actually helping others play better pool.
Perhaps the site should be divided into two sections.
Sec. 1. Knowledge & understanding the science behind pool by science guys.
Sec. 2. Learn how to play like a Pro... from those that are & do play like Pros, namely Pros Like John Brumback.
Well, I guess we really can't do that 2nd. sec. because 'all' of the Pros have been consistently driven off whenever they have come here to try to give back.
Like I have said, I am very glad that I started & learned much about playing the game more than 2+ years before my first physics class.
I NEVER think in what I would call physics terms or language when playing the game...
& don't think anyone else should either.
The game is PLAYED & that is what ball PLAYERS do. They PLAY their prospective games.
This technique works & it works better & more easily & with better results than that...
Why? Because it does.
If you want to find out why then learn to do it & perhaps then you can figure out the specifics of why... if you still care once you are getting the results & just know that is works.
Sorry, but that is how see matters as a Player that also has 3 years of physics education.
Regards,
& Best Wishes to ALL,
Rick
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A spinning pole wobbles for the same reason a top precesses ... gravity creates a torque that interacts with the spin axis (according to the Euler Equations Bob posted), causing rotation about another axis (i.e., "wobble" or "precession").
I'm trying to be cordial and helpful also. I honestly just don't know what point you are trying to make. Sorry.
Regards,
Dave
Dave, saying there is no precession is much different than saying there are no gyroscopic forces. For a guy who gets into the minutia of pool physics like no one else on the planet, I'm a little surprised you simply dismiss this.
I disagree. I don't think "we" (in this thread) have a real understanding of when a banked ball curves or not, and whether or not it is even possible under all playing conditions. I plan to do a lot more tests soon so I can better understand all of the factors. After that, I actually hope to be able to offer advice and explanations for people who would like to duplicate similar results. I was not able to generate a significant post-rebound curve on my equipment. Maybe it was due to my speed, spin, and/or angle not being right. Maybe it is not possible on my equipment (e.g., due to the cushion nose height, rail/cushion properties, and/or ball/cloth conditions). Again, I (and I think others) don't know. Although, I (and I think some others) would like to know. If I (and others) don't know what type of hit and conditions are required to curve the ball after rebound, how can we hope to use the shot in actual play (or even know when it can be used)?
Obviously, I (and I think many others) disagree with you on this point. On a personal note, my game has gotten much better as a result of things I have learned from pool-playing "scientists" like Bob Jewett, Ron Shepard, Mike Page, Bob Byrne, Patrick Johnson, Jim Valasina, and others. I would also put Tom Ross in that category. He was an excellent and experienced "player" (before his medical stroke), but he was as also a pool "scientist" by nature. He was always trying to better understand things and learn new effects to help expand his pool-playing arsenal of shots and techniques. I think I learned more about pool understanding while filming VEPS than I did over all of my years of personal experience playing the game up to that point.
Regards,
Dave
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changed my mind..maybe later when I have time.
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changed my mind..maybe later when I have time.
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So the experiment that might be done is to spin a ball in place and then shoot a soft 1/4-ball contact combo at it (where the striking ball is close to the spinning ball and so has no follow at contact). My prediction is that the two balls will go close to the same distance unaffected by whether there is spin or not. (This is the expected result for a 45-degree cut shot with stun -- both balls go the same distance.)
Dave,
The answer to your closing question of your first paragraph is you ask John Brumback & then you listen to his answer & then believe his answer & then you do what he says to do... because it WORKS.
Almost all pool players are doing what you say Tom Ross did & note that you said, 'pool-PLAYING arsenal of shots & TECHNIQUES'.
It seems that you were into science first or at least much more than you were into pool.
Others. most here I am rather sure, were/are into playing pool first... & as I said, I think most could not give a rats _____ about the science.
What was/is good for you is most probably NOT good for the vast majority of those here at AZB or those out there in the other real world either.
They want to know HOW & not why. Pros can tell HOW.
But they, The Pros, have 'all' been driven off because they could not explain the itty bitty why to support their know HOW.
It's fine if we disagree. It's not the first time.
Regards & All of the Best for You & Yours,
Rick