modern cueball finishes and weight distribution

Franky

Franky

woman I said NO!!!
Silver Member
Does anyone know if moment of inertia of the measles cueball is greater than that of the matching object balls? I was trying a drill just now and it appears to me that it may be. I don't like light or heavy cueballs, but one with a higher moment of inertia may just be OK.

I would intuitively guess that it does due to the different (harder/thicker?) finish on the ball. Anyone have more specifics on this?
 
I don't think you understand what inertia is. Inertia is an unquantifiable scientific principle, and therefore one can't say that one cueball has a higher moment of inertia than another. Maybe you mean to say momentum?

As for the change you are noticing with your new cueball, there could be many reasons for that. You may have been using a cueball that had significant wear and was smaller and lighter than the new one, or you may have been using a cheaper cueball made from polyester or acrylic resin rather than the phenolic resin the measles ball is made of.

Cueballs made from different materials have different friction coefficients and resiliency, and therefore react differently on the table. The friction coefficient can also be affected by how dirty the balls are, or how well they have been polished, but cueballs don't (or shouldn't) have any finish applied to them.
 
Did your dotted cb come as part of the set of your other balls? If not, then they may not be compatible even if they are of the same brand.

Balls wear down eventually therefore a set must be played as a set. If you introduce a new ball even if it's of the same product line, it'll play differently than the rest of the set. The Aramith dotted cb is designed for Aramith's top of the line SUPER ARAMITH PRO wherein the balls' weights, surface, etc are almost the same. Since the Super Pro's have hardest surfaces, they wear out the longest, therefore you can introduce a new ball and it will still play like a set.

We have tried placing the dotted cb & the rest of the PRO CUP'S together with other less than a year old Aramith Premium line and it was very obvious that the Pro Cups were larger.

Out of curiosity, I've just tried weighing my Super Aramith Pro-Cup TV balls using a digital weighing scale. I'm quite surprised to find out that even in a set, the balls can have weight variation of up to 3grams (167g #4,5,13 & dotted cb, others were 168-169g, #15 is 170g!) :eek:

If you want to have a consistent play, use the balls that come as a set.
 
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desert1pocket said:
I don't think you understand what inertia is. Inertia is an unquantifiable scientific principle, and therefore one can't say that one cueball has a higher moment of inertia than another. Maybe you mean to say momentum?...
Click to expand...
I'll go along with everything else you said, but I'm having a problem with this.

There is a way, by measuring throw, to get a ball's moment of inertia, but the catch is that you have to know the other ball's moment of inertia. You could assume (2/5)mR^2 for the other ball, and then go on to measure its mass and radius. But since the original poster is looking for what is probably a fine difference, any such assumption is not really in the spirit of the thing.

Jim
 
desert1pocket said:
I don't think you understand what inertia is. Inertia is an unquantifiable scientific principle, and therefore one can't say that one cueball has a higher moment of inertia than another. Maybe you mean to say momentum?

As for the change you are noticing with your new cueball, there could be many reasons for that. You may have been using a cueball that had significant wear and was smaller and lighter than the new one, or you may have been using a cheaper cueball made from polyester or acrylic resin rather than the phenolic resin the measles ball is made of.

Cueballs made from different materials have different friction coefficients and resiliency, and therefore react differently on the table. The friction coefficient can also be affected by how dirty the balls are, or how well they have been polished, but cueballs don't (or shouldn't) have any finish applied to them.
Click to expand...

I do speak some "physics". The moment of inertia can be thought of as the analog to mass for rotational situations. It is quantifiable. Two cueballs can certainly have different physical characteristics:

http://en.wikipedia.org/wiki/Moment_of_inertia
http://en.wikipedia.org/wiki/Angular_momentum

I have brand new super aramith pro TV cup balls. They're clean. I asked this question because it appears to me that the spotted cueball will roll slightly farther than an object ball if they start out at the same translational velocity (if they both have non-slipping forward roll). This could be explained if the cueball's finish layer was somewhat denser than the rest of the ball, increasing its moment of inertia.

"For an object with a fixed mass that is rotating about a fixed symmetry axis, the angular momentum is expressed as the product of the moment of inertia of the object and its angular velocity vector..."

This essentially means that a naturally rolling ball with a higher moment of inertia will travel farther even though the starting angular velocity is the same, hence my question. Sorry I didn't spell out the details in the first post! :o
 
Franky said:
I do speak some "physics". The moment of inertia can be thought of as the analog to mass for rotational situations. It is quantifiable. Two cueballs can certainly have different physical characteristics:

http://en.wikipedia.org/wiki/Moment_of_inertia
http://en.wikipedia.org/wiki/Angular_momentum

I have brand new super aramith pro TV cup balls. They're clean. I asked this question because it appears to me that the spotted cueball will roll slightly farther than an object ball if they start out at the same translational velocity (if they both have non-slipping forward roll). This could be explained if the cueball's finish layer was somewhat denser than the rest of the ball, increasing its moment of inertia.

"For an object with a fixed mass that is rotating about a fixed symmetry axis, the angular momentum is expressed as the product of the moment of inertia of the object and its angular velocity vector..."

This essentially means that a naturally rolling ball with a higher moment of inertia will travel farther even though the starting angular velocity is the same, hence my question. Sorry I didn't spell out the details in the first post! :o
Click to expand...

Sorry I misread your original post. From what I understand, the measles ball, which is the same as the red-circle cueball, is made of a slightly different phenolic resin than the object balls. It is actually made from the same type of resin used for carom pool, and is slightly more resilient. The reason they do this is to help mediate the much faster wear of the cueball than the object balls. The blue circle is supposed to be the same material as the centennial object balls though. I have trouble switching back and forth between the red circle and blue circle cue balls, and can definately tell a difference in how far they roll. It seems to me like the red circle maintains english much longer than the blue also. All of this information is second or third hand, so I am not sure how accurate it is, but I hope it helps.
 
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I would be amazed if this data were available. Sounds like someone should test the various cue balls.

Dave, busy for a while
 
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