Does the measle cue ball cause more skids

[nataddrho]

I had totally overlooked the (possible) moment of inertia issue with cue balls so thanks for raising it!

ChatGPT thinks suspending each ball with a thin wire to create a pendulum, and measuring the period of oscillation, is the best experimental way to evaluate the comparable moments of two equal size and mass balls.

Or for best results apparently MRI data can be used to numerically estimate moment of inertia.

By the way, moment of inertia (or a ball with heterogenous MOI) actually has no affect on the trajectory of the ball, because it produces no net torque. What it does do is modulates the rotational velocity of the ball per rotation, but extremely extremely small amounts.

A rolling ball is a precessional object like like a rolling coin or a top. Only a perfectly balanced ball has a logarithmic spiral radius of infinity, and rolls in a straight line. If you move the center of mass of the ball from center by even a fraction of a percentage (sub 0.1%) then you will start to see roll-off.

This analysis is well known in sports such as bowling (which specifically has an off-center ball for curves), lawn-bowls, golf, etc.

Here is some work I have done...

 

[kling&allen]

By the way, moment of inertia (or a ball with heterogenous MOI) actually has no affect on the trajectory of the ball, because it produces no net torque. What it does do is modulates the rotational velocity of the ball per rotation, but extremely extremely small amounts.

A rolling ball is a precessional object like like a rolling coin or a top. Only a perfectly balanced ball has a logarithmic spiral radius of infinity, and rolls in a straight line. If you move the center of mass of the ball from center by even a fraction of a percentage (sub 0.1%) then you will start to see roll-off.

This analysis is well known in sports such as bowling (which specifically has an off-center ball for curves), lawn-bowls, golf, etc.

Here is some work I have done...

View attachment 705342View attachment 705343View attachment 705344

Thanks. I assume you've done these calculations for your cue ball, which has the same total mass and center of mass as a regular cue ball, but not the same moment of inertia because you have a plug of electronics and not 100% phenolic? Meaning that proper center of mass is way more important than moment of inertia when evaluating how a cue ball rolls?

 

[Chip Roberson]

Kamui chalk and Toam sticky chalk cause more than any cueball

About the time I bought my first cylinder of Toam Chalk, I had bought 2 cue balls. One the black Aramith Tourney Ball and one Blue Circle to match
my centennial set. With Masters chalk the Blue Circle would need lots of attention to remove chalk marks while the Black Aramith would need
the ball to be cleaned a lot less. I would notice more skids with the Blue Circle also. This was with about 2 hours of play a day for about a month. There were many times I had skids happen and it happened more with the Blue Circle. When I started play with the Toam chalk, I haven't had a problem one with cue ball skid,,not one--none. Once in a great while do I even have a faint spot one the cue ball from the Toam chalk.
I tried the Kamui chalk for giggles and threw it away as soon as I saw the mess it made on my table and how it clung to the cue ball. By what I have observered The Masters chalk caused more skids on my table than the Toam chalk. Cleaner table cleaner game . The Measle ball is made by Aramith as well as the black tourney and the Blue Circle, but the finish on the Black Tourney Ball, I think is different than the other two. Because of the
difference, the other two balls for some reason gather more contaminates to adhere to the cue balls and then causing a more skids. I gave away the Masters chalk I had at home to a rec-center near by . They were happy to get it , and I was happy to be rid of it. For my home use , Toam chalk only.
My 2 cents

 

[pvc lou]

By the way, moment of inertia (or a ball with heterogenous MOI) actually has no affect on the trajectory of the ball, because it produces no net torque. What it does do is modulates the rotational velocity of the ball per rotation, but extremely extremely small amounts.

A rolling ball is a precessional object like like a rolling coin or a top. Only a perfectly balanced ball has a logarithmic spiral radius of infinity, and rolls in a straight line. If you move the center of mass of the ball from center by even a fraction of a percentage (sub 0.1%) then you will start to see roll-off.

This analysis is well known in sports such as bowling (which specifically has an off-center ball for curves), lawn-bowls, golf, etc.

Here is some work I have done...

View attachment 705342View attachment 705343View attachment 705344

I'll come back an read this more closely later, but what is a "heterogeneous" moment of inertia? (MOI is an integrated quantity...not a distribution.)

 

[pvc lou]

Not that anyone cares in the world but the two of us, but I wasted some time the last few days thinking about moment of inertia.

I think you're right about this, lol.

I think in general a fully solid ball with roll 1.67 times as far as a hollow ball, where each ball has the same mass, center of mass, and dimensions. The ratio of the distances rolled by a solid sphere to a hollow sphere is equivalent to the ratio of their accelerations under the same applied force. The acceleration of the solid sphere is (5/2)μg, while that of the hollow sphere is (3/2)μg, leading to a ratio of 5/3.

Here's the backup math:

Moment Of Inertia Of Sphere Derivation

Moment of inertia is an essential segment in the umbrella of rotational dynamics of Physics. The moment of inertia of a solid sphere is vital from a 3-D perspective.

unacademy.com

Of course, two cue balls with dots or not will be much closer to the solid cue ball than the hollow sphere, but perhaps there could be some difference in play if the measles are a lot more dense than the white phenolic.

(edit: you can work out the equations in more detail using Dr. Dave's constants from his website).

I suspect the MOI effect is very small, if it is there at all. It was just a thought. I may have a closer look on pen and paper (or python) later. Let me get some chores done first.

 

[Bob Jewett]

... a fully solid ball with roll 1.67 times as far as a hollow ball, where each ball has the same mass, center of mass, and dimensions. ...

It depends on the initial conditions. If the two balls are rolling smoothly on the cloth at 1 MPH, the hollow ball has more stored energy and as a result will roll farther. The rotational energy at a given speed of rolling is proportional to the moment of inertia which is 2/5 for the uniform sphere and 2/3 for the hollow sphere.

If the two cue balls hit object balls full, I think the hollow sphere will then follow farther by the ratio of stored energies, which is 67% farther than the normal ball.

In any case, I think all the normal cue balls have uniform density or very close to uniform.

 

[kling&allen]

It depends on the initial conditions. If the two balls are rolling smoothly on the cloth at 1 MPH, the hollow ball has more stored energy and as a result will roll farther. The rotational energy at a give speed of rolling is proportional to the moment of inertia which is 2/5 for the uniform sphere and 2/3 for the hollow sphere.

If the two cue balls hit object balls full, I think the hollow sphere will then follow farther by the ratio of stored energies, which is 67% farther than the normal ball.

In any case, I think all the normal cue balls have uniform density or very close to uniform.

Yes, good points. I was assuming starting from rest with the same force (and force duration) applied to each ball.

 

[pvc lou]

By the way, moment of inertia (or a ball with heterogenous MOI) actually has no affect on the trajectory of the ball, because it produces no net torque. What it does do is modulates the rotational velocity of the ball per rotation, but extremely extremely small amounts.

A rolling ball is a precessional object like like a rolling coin or a top. Only a perfectly balanced ball has a logarithmic spiral radius of infinity, and rolls in a straight line. If you move the center of mass of the ball from center by even a fraction of a percentage (sub 0.1%) then you will start to see roll-off.

This analysis is well known in sports such as bowling (which specifically has an off-center ball for curves), lawn-bowls, golf, etc.

Here is some work I have done...

View attachment 705342View attachment 705343View attachment 705344

The moment of inertia of the ball absolutely has an impact on the trajectory of the ball. In the simplest case, it has an effect on how long the ball will roll. The rolling friction from the cloth is what slows the ball. A ball with larger moment of inertia will have more rolling kinetic energy, as explained by Jewett above, and will therefore roll farther before being stopped by the rolling friction.

Rolling off is another question, altogether. Since, we have only posited a spherically symmetric mass distribution in the sphere, roll-off is not relevant here.

 

[trob]

OMG, dude. The blue circle is not heavier, its exactly the same weight of the Centennial balls.

Blue circle, Red circle, measle, Arcos2 measle, they all weigh 167/168 grams when new. The weight difference comes from age and use.

I meant heavier than the red circle cue ball. I don’t know.. I never weighed them nor do I care because
a) I don’t play with anything but the red circle anyplace I go
and
b)no matter how great a game straight pool is it bores me to death. Second only to 1 pocket lol

 

[trob]

The blue circle made by Hyatt for Brunswick was indeed slightly heavier and favored by straight pool players as a pack breaker.
The red circle, slightly lighter, was favored by 9-ballers.
All that is old news….there is no difference weight-wise any more by color coding for a long time.

….when I was a kid, there was also the green dot, also known as the Macon ‘fast draw’…had to be 1/4 ounce lighter.

Thank you .. I think he thought I meant heavier than the rest of the balls. I meant heavier than a red circle.

 

[jtompilot]

Thank you .. I think he thought I meant heavier than the rest of the balls. I meant heavier than a red circle.

The blue circle in my 25 year old Centennial set weighs the same as a new red circle. 167 grams.

 

[pt109]

The blue circle in my 25 year old Centennial set weighs the same as a new red circle. 167 grams.

I made a mistake in my earlier post….the Hyatt Centennial cue ball was a blue DOT…they went out of business in the 70s sometime.
Saluc-Aramith made the blue CIRCLE for Brunswick.

 

[nataddrho]

Thanks. I assume you've done these calculations for your cue ball, which has the same total mass and center of mass as a regular cue ball, but not the same moment of inertia because you have a plug of electronics and not 100% phenolic? Meaning that proper center of mass is way more important than moment of inertia when evaluating how a cue ball rolls?

Exactly.

 

[nataddrho]

The moment of inertia of the ball absolutely has an impact on the trajectory of the ball. In the simplest case, it has an effect on how long the ball will roll. The rolling friction from the cloth is what slows the ball. A ball with larger moment of inertia will have more rolling kinetic energy, as explained by Jewett above, and will therefore roll farther before being stopped by the rolling friction.

Rolling off is another question, altogether. Since, we have only posited a spherically symmetric mass distribution in the sphere, roll-off is not relevant here.

To answer your question, I was thinking in terms of axes. MOI around one axis being different than the perpendicular ones I used the term heterogeneous.

Small variations in spherical MOI per axis has less affect than offset CoM

 

[pvc lou]

To answer your question, I was thinking in terms of axes. MOI around one axis being different than the perpendicular ones I used the term heterogeneous.

Small variations in spherical MOI per axis has less affect than offset CoM

Right. You meant that the center of mass is not at the center of the sphere. Not the point of the question of moment of inertia. The point is that it is possible to have two spheres with the same mass and diameter, where one rolls "heavier" than the other...(implicitly i guess) ignoring any displacement between the center of mass and geometric center of the cue ball.

 

[nataddrho]

Right. You meant that the center of mass is not at the center of the sphere. Not the point of the question of moment of inertia. The point is that it is possible to have two spheres with the same mass and diameter, where one rolls "heavier" than the other...(implicitly i guess) ignoring any displacement between the center of mass and geometric center of the cue ball.

Ah, yes this is possible. A ball with mass distribution further from the center will have more inertia.

Manufacturing such a thing by mistake is very difficult. The resin doesn’t set in a way that makes this a concern. I don’t think there exists pool balls with the same weight but vastly different MOI.

 

[justnum]

Ah, yes this is possible. A ball with mass distribution further from the center will have more inertia.

Manufacturing such a thing by mistake is very difficult. The resin doesn’t set in a way that makes this a concern. I don’t think there exists pool balls with the same weight but vastly different MOI.

Theoretically they exist as one could cure resin in layers. Hollow out a spherical center, then add shavings to the resins to adjust for weight loss. The benefits of the cavity allow for variations on MOI.

 

[nataddrho]

Theoretically they exist as one could cure resin in layers. Hollow out a spherical center, then add shavings to the resins to adjust for weight loss. The benefits of the cavity allow for variations on MOI.

The derivative of the integral of the space-time flux capacitance says the relativity of this proposition is green.

 

[Bob Jewett]

I bought a blue circle cue ball a long time ago. I think it was made by Hyatt, but I'm not sure. It was significantly off-center judging by funny rolls on simple lags.

Later I saw a blue circle that had broken open. It had a center of some other material, maybe the size of a golf ball or a little larger. It was not centered in the ball.

 

[trob]

The blue circle in my 25 year old Centennial set weighs the same as a new red circle. 167 grams.

Then I guess it was the old straight pool players feeling something that wasn’t there lol