Quote from: Aloarjr810 on June 08, 2016, 12:28:41 PM

And if you think RG matters then you don't know anything about modern ball motion and that you and 99% of the ball Mfg. Ball reps. PBA players, PSO's don't either and are still using outdated information.

So how often do you compete on tour, or on conditions beyond THS (that are designed to make most bowling balls seem similar)?

 If you competed at some of the highest levels, you would know that ball motion as it pertains to the core, becomes a factor, when bowling on more demanding conditions, and just "adjusting the cover stock" isn't always the answer.

House conditions are designed to give the widest variation of players, releases, and equipment a fair shot at hitting the pocket and striking. Ball science becomes marginalized. When on tour, it becomes MUCH more important.

Just so you know, I didn't say that stuff . That's just what I was told when bringing up talk about a balls RG and was just sharing.

AloarJR-  I believe you completely missed my point . I stated that when looking a CORE
designs, I place most of my emphasis on RG values. I fully understand that surface composition and (surface) preparation play a huge role in determining ball motion .
I am also aware that the Rg values listed are for undrilled balls. However, an undrilled ball with say, an Rg value of 2.28 will react quite differently than a ball with an undrilled Rg value of 2.58, all other things being the same. The undrilled numbers are quite important. Not considering undrilled Rg values is like saying that there is
no difference between a higher performance car and a "regular" car. It depends on whose foot is on the pedal.

I didn't miss your point, I understood  you, I agree with what you just said here.

I was just warning you that is a hot button topic, on certain forums. And those were examples of what those that will disagree with your view will throw at someone that brings it up.

 

However, an undrilled ball with say, an Rg value of 2.28 will react quite differently than a ball with an undrilled Rg value of 2.58, all other things being the same.

First off, an undrilled ball with say, an Rg value of 2.28 would be considered illegal, so I guess it would perform similar to one of those illegal Motiv balls.  i.e. Sit nice and pretty on the shelf.

ICDeadmoney-  You are correct when you state that if you increase a core's density its moment of inertia (I) increases--  I=mr^2 where m= mass of the imbalance & r= its distance from the center of rotation. 

In addition, Rg= the square root of I/M . (M= total mass of the object) , so this shows that increasing a core's density ( mass is the more correct value to use but since mass is directly proportional to density, but it's acceptable to use "density" (D) as long as the object's volume doesn't change -- (D=m/v.)  will also increase the Rg value since  increasing the core's mass will also result in an increase in the overall mass of the object in question (in our case a bowling ball). 

Increasing the density of the core doesn't increase the Rg value.

Lets use a simple bicycle wheel analogy to make the math very simple.

We design a hub shape that has an RG of 1".
We define a rim shape that has an RG of 10".

When we manufacture the hub, and rim out of aluminum, both pieces have a mass of 1 unit. (not sure how big that unit is in reality, but it will be constant so we don't need to know exactly).

We also manufacture the hub and rim out of gold..  In this case both pieces have a mass of 7 units.

Gold is approximately 7 times as dense as aluminum.

Lets assume we make the spokes out of carbon nano tubes so they represent negligible mass... again to make the math easier to follow.

When we use an aluminum hub, and an aluminum rim the math works as follows.

I = 1u * 1" + 1u * 10"^2 = 101
M = 1u + 1u = 2u
Rg = sqrt(101/2) = 7.11"

When we swap the aluminum hub for the gold hub (i.e. increase the density of the core)

I = 7u * 1" + 1u * 10"^2 = 107
M = 7u + 1u = 8u
Rg = sqrt(107/8) = 3.66"

As you see, the moment of inertia increased, while the Rg decreased.

Because moment of inertia and Rg are not directly proportional, it's bad science to say what Nick wrote in the pdf file.

"Thus, in simple terms, the radius of gyration determines how easy it is for the bowling ball of particular weight to rotate about a given axis"

The part that is missing, is as you increase the density of the core, you need to decrease the density elsewhere to maintain the same overall mass.

If we start with an aluminum hub, and a gold rim.

I = 1u * 1" + 7u * 10"^2 = 701
M = 1u + 7u = 8u
Rg = sqrt(701 / = 9.36"

Increase the hub to gold, while decreasing the rim to aluminum we get:

I = 7u * 1" + 1u * 10"^2 = 107
M = 7u + 1u = 8u
Rg = sqrt(107/8) = 3.66"


In this case we get the expected decrease in moment of inertia as well as decrease in Rg.

One quick thing to note about Rg.

It's about the design of the pieces, not what they are made out of.

It's not until you combine pieces of different density that RG changes to values other than the original design.

Let compare aluminum hub, aluminum rim to gold hub, gold rim.

aluminum

I = 1u * 1" + 1u * 10"^2 = 101
M = 1u + 1u = 2u
Rg = sqrt(101/2) = 7.11"

Gold

I = 7u * 1" + 7u * 10"^2 = 707
M = 7u + 7u = 14u
Rg = sqrt(707/14) = 7.11"

Same Rg, but significantly different moment of inertia.

The overall mass of an object has a lot to do with how easy it will "rev up"

Where torque come in is the friction between the ball and the lane.

In bowling terms, if you want to increase the rate the ball will rev up, you can sand the surface to increase the torque, or select a ball of the same weight with a lower Rg.

If you select a ball with a higher weight but lower Rg, you may end up with a ball that revs up slower.

You can weigh a ball to find it's mass, but not many have an Rg swing to know what the RG is of the PAP.

So you have to get out there and throw the ball for yourself and determine if the results match what you expect when selecting based off the published numbers.

Nick shouldn't say things like increasing the core density makes the ball rev up quicker, decreasing the core density makes the ball rev up slower, and the Rg determines how easily the ball will rev up.

Next thing you know, someone is going to start quoting that bad science as gospel.

Lot's of discussion. Glad this article has created some conversation.
I'm not a scientist or a physics major, but I'm fairly certain that a lower RG core will rev up quicker than a high RG core.

Ok you're not a scientist, or a physics major, then why are you fairly certain?  Because someone told you?

Think a figure skater spinning. Arms out, spins or revolves slower = high RG. Conversely, arms tucked in spins quicker = low RG. RGs are measure from the center of the core out to the edge.

No, RGs are measured by taking timings in a device that works like a horizontal pendulum.  Based on the how long it takes for the ball to swing one way, then back, the moment of inertia can be calculated.   By measuring the weight of the ball, the Rg can also be calculated.

I believe USBC has a video of this on YouTube demonstrating how RGs are measured. From what I understand, this process takes several hours per ball and it is done a few times to get precise measurements. USBC Bowling Academy has another one explaining RGs as well. So the long and the short is yes the RG will determine how easily a ball will rev up.

You've gone from fairly certain to absolutely sure, by watching a USBC video, which you clearly didn't understand, because at most it takes 20 minutes to complete all of the repetitions.

Maybe you can answer this maybe not. Just curious, if we take the Truths core for a 15lb ball with a rg 2.48 and a diff 0.055 and then a different brands core with the same specs and a different shape and put them in the same global coverstock with the same drilling and surface finish and have a throwbot throw both will we see a noticeable difference?

Assuming both have different  shapes and likely different densities.

A quick note.  The core doesn't have an Rg of 2.48, and a diff of 0.055.

It's not until you wrap the filler and coverstock around the core do you end up with those specs.

If you take the core from different companies ball that has the specs 2.48 and 0.55, and use G-900 filler and coverstock, you're likely to end up with a ball that has different specs, because the density of the filler and coverstock is different.

But if you were able to find a different companies core than when wrapped with G-900 filler and coverstock, that resulted in the same specs as the Truth, there is no reason to expect different results.

Quote from: ICDeadMoney on June 11, 2016, 03:50:05 AM

Quote from: kidlost2000 on June 10, 2016, 10:25:06 PM

Maybe you can answer this maybe not. Just curious, if we take the Truths core for a 15lb ball with a rg 2.48 and a diff 0.055 and then a different brands core with the same specs and a different shape and put them in the same global coverstock with the same drilling and surface finish and have a throwbot throw both will we see a noticeable difference?

Assuming both have different  shapes and likely different densities.

A quick note.  The core doesn't have an Rg of 2.48, and a diff of 0.055.

It's not until you wrap the filler and coverstock around the core do you end up with those specs.

If you take the core from different companies ball that has the specs 2.48 and 0.55, and use G-900 filler and coverstock, you're likely to end up with a ball that has different specs, because the density of the filler and coverstock is different.

But if you were able to find a different companies core than when wrapped with G-900 filler and coverstock, that resulted in the same specs as the Truth, there is no reason to expect different results.

I understand what you are saying ICD, but why wouldn't shape matter? If you could make a sphere shaped core have an rg and diff of say 2.50 and .50, and a diamond (not comparing to Lane 1) with the same numbers by way of densities. Would the diamond not create a different roll than a sphere shaped core?

I need to add a minor point to be more complete.

I'm assuming when the other core is wrapped by a G-900 filler and coverstock the ball will have the same specs.

However once the ball is drilled with the same layout, the density of the material removed may be different, causing a final ball with different specs.

In the drilling stage, the shape of the core can make a difference because if you drill into the core of one ball, the same depth and location may not drill into the core of another shape core.

If the drilling instead only penetrates the coverstock, and filler in both the pure G-900, and the G-900/other ball hybrid, the final specs should be identical.