AzBilliards.com Cueball Physics - The Force of the Cueball
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 (#16) MitchAlsup AzB Silver Member   Status: Offline Posts: 1,717 vCash: 500 iTrader: 0 / 0% Join Date: Mar 2009 Location: Austin Texas 08-13-2019, 01:21 PM As one versed in Physics: you are using the word force improperly. In physics we have F = M × a A perfectly well defined definition of what the word "force" means. The word you want to use is mostly "Spin" but occasionally you want to use the word "energy". Energy contains both the forward rolling velocity plus the spin component carried by the rolling ball. For example: a ball rolling at 1 foot/second will travel a certain distance A ball traveling at 1 foot/second with side spin will travel a much greater distance. The ball with sidespin has greater energy (in this case through rotational inertia).

(#17)
mikepage
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08-13-2019, 02:05 PM

Quote:
 Originally Posted by MitchAlsup As one versed in Physics: you are using the word force improperly. In physics we have F = M × a A perfectly well defined definition of what the word "force" means. The word you want to use is mostly "Spin" but occasionally you want to use the word "energy". Energy contains both the forward rolling velocity plus the spin component carried by the rolling ball. For example: a ball rolling at 1 foot/second will travel a certain distance A ball traveling at 1 foot/second with side spin will travel a much greater distance. The ball with sidespin has greater energy (in this case through rotational inertia).
Once the ball leaves the tip, the force acting on the ball is the force the cloth exerts on it from friction. And that is only there when the ball is sliding (not rolling) on the cloth. He is showing that just by noting the direction of that force (cloth on ball), a number of apparently complex motions of the cueball suddenly make sense.

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(#18)
Bob Jewett
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08-13-2019, 02:22 PM

Quote:
 Originally Posted by MitchAlsup ... For example: a ball rolling at 1 foot/second will travel a certain distance. A ball traveling at 1 foot/second with side spin will travel a much greater distance. The ball with sidespin has greater energy (in this case through rotational inertia).
I believe that a ball with lots of sidespin will not go farther for a given initial speed than a ball without sidespin. The exception is if it hits a cushion and thereby translates the sidespin into linear motion. This is not too hard to test.

Bob Jewett

(#19)
MitchAlsup
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08-13-2019, 02:51 PM

Quote:
 Originally Posted by Bob Jewett I believe that a ball with lots of sidespin will not go farther for a given initial speed than a ball without sidespin. The exception is if it hits a cushion and thereby translates the sidespin into linear motion. This is not too hard to test.
Bob,

Consider that a ball hit with sidespin has energy in 2 directions, 1) the typical forward direction, and 2) the spinning direction.

After a short distance over the cloth, the side spin and the forward roll on the ball converge at the place the CB touches he cloth. The ball has forward roll, and also has side spin, If both the forward roll and the amount of sidespin were equal, at CB contact,
The roll axis on the CB is now at 45º with respect to vertical. The point of contact of the CB with the cloth now circulates from the bottom of the CB to the <say> leftmost side of the CB.

The rotational inertia of a ball rolling at such an angle is greater than the rotational inertia of a ball rolling naturally forward at the same speed but without sidespin.

Thus there is more "energy" in the CB and it will roll farther.

(#20)
MitchAlsup
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08-13-2019, 02:55 PM

Quote:
 Originally Posted by mikepage Once the ball leaves the tip, the force acting on the ball is the force the cloth exerts on it from friction.
Ignoring air resistance;

Quote:
 And that is only there when the ball is sliding (not rolling) on the cloth.
The forward rolling CB still has friction while rolling on the cloth--just a lot less than before it accumulated natural forward roll.

Quote:
 He is showing that just by noting the direction of that force (cloth on ball), a number of apparently complex motions of the cueball suddenly make sense.
My only complaint was the misuse of the word "force" in conjunction with the physical explanation. Physics has a strict definition of what a "force" is.

And while the video was both entertaining and well executed, nicely demonstrating the effects. The word "force" is inappropriate in a physics context.

(#21)
mikepage
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08-13-2019, 03:43 PM

Quote:
 Originally Posted by MitchAlsup Ignoring air resistance;
Yes.

Quote:
 The forward rolling CB still has friction while rolling on the cloth--just a lot less than before it accumulated natural forward roll.
Before it achieves natural roll there is a real friction force on the cueball. Once it achieves natural roll, there is no more friction force. There is a "rolling resistance," where the cueball slows down because it is constantly trying to climb out of its own divet. If we squint, we can think of this as like a friction force. But it is actually different and kind of irrelevant here.

Quote:
 My only complaint was the misuse of the word "force" in conjunction with the physical explanation. Physics has a strict definition of what a "force" is.
And I think he is using it appropriately. If there is anything nonstandard, it is that he refers to it as the "force OF the cueball," rather than the "force ON the cueball."

Quote:
 And while the video was both entertaining and well executed, nicely demonstrating the effects. The word "force" is inappropriate in a physics context.
.

Once again all the acceleration of the cueball he refers to--speeding up, slowing down, and turning--is a direct result of the force he discusses. The physics is fine.

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(#22)
Ralph Kramden
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08-13-2019, 04:00 PM

.
Quote:
 Originally Posted by MitchAlsup . Ignoring air resistance; The forward rolling CB still has friction while rolling on the cloth--just a lot less than before it accumulated natural forward roll. My only complaint was the misuse of the word "force" in conjunction with the physical explanation. Physics has a strict definition of what a "force" is. And while the video was both entertaining and well executed, nicely demonstrating the effects. The word "force" is inappropriate in a physics context.
Sorry.. but I do like the word FORCE.
As for anyone ignoring air resistance.

Jack Nicklaus was once asked why he always tees the ball so high?
He replied that air resistance was so much less than dirt resistance.

May the FORCE be with you...

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Recognize a 1/2 ball 30 degree cut, and the 1/8 ball angles.
Paralysis by aiming analysis happens by thinking too much.

To play at top speed.. You must own the stop shot line.

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pwd72s
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08-13-2019, 04:40 PM

Quote:
 Originally Posted by Sharivari Thank you guys. Great to hear that all the work I put in is appreciated
very much appreciated...thank you!

(#24)
MitchAlsup
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08-13-2019, 05:17 PM

Quote:
 Originally Posted by mikepage Before it achieves natural roll there is a real friction force on the cueball. Once it achieves natural roll, there is no more friction force. There is a "rolling resistance," where the cueball slows down because it is constantly trying to climb out of its own divet.
That "rolling resistance" is friction of the CB compressing the cloth as it rolls over.
{Plus that completely negligible air resistance.}

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Bob Jewett
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08-13-2019, 07:43 PM

Quote:
 Originally Posted by MitchAlsup That "rolling resistance" is friction of the CB compressing the cloth as it rolls over. {Plus that completely negligible air resistance.}
Well, Wikipedia has this to say about rolling stuff:
"Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc. is recovered when the pressure is removed. Two forms of this are hysteresis losses (see below), and permanent (plastic) deformation of the object or the surface (e.g. soil). Another cause of rolling resistance lies in the slippage between the wheel and the surface, which dissipates energy. Note that only the last of these effects involves friction, therefore the name "rolling friction" is to an extent a misnomer."
I think this looks reasonable and correct.

Bob Jewett

(#26)
dr_dave
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08-13-2019, 08:06 PM

Quote:
 Originally Posted by Sharivari Hi AZB, I just released a video that took me over 40 hours to produce. And because thats a lot of time for a just 12 minute long video I want to share it with as many players as possible. And of course I want to know what you think of it, how I can improve my videos in general and what I am most interested in. Did you learn something new? I am asking because I don't only want to produce videos that are helpful for beginners, but also for experienced players. So if you're interested in the cueball behaviour you should give this one a try https://youtu.be/KL0W45AkNMo Sharivari
Excellent work as always.

Keep up the good work,
Dave

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