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Author Topic: Radius of Gyration - RG  (Read 5404 times)

J_w73

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Radius of Gyration - RG
« on: December 05, 2008, 05:56:08 AM »
Does anyone have a good definition or explanation of the RG.

here is what I found.. is this accurate.

The radius of gyration is a numerical value equal to the radius of a thin hoop of the same mass, having the same moment of inertia as the bowling ball.

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skbowl800

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Re: Radius of Gyration - RG
« Reply #1 on: December 05, 2008, 03:02:59 PM »
Basically how I understand it is the lower the RG the faster the ball spins off your hand.
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VIXIV

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Re: Radius of Gyration - RG
« Reply #2 on: December 05, 2008, 03:18:21 PM »
quote:
Basically how I understand it is the lower the RG the faster the ball spins off your hand.
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This is my basic understanding, also. A ball with a lower RG core (like Ebonite's VII) will roll earlier since the mass is closer to the center of the ball. A ball with a higher RG core (like a Power Groove) will start to roll later because the mass is closer to the coverstock.

There are lots of very knowledgeable people here who can explain it in much, much better detail.
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J_w73

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Re: Radius of Gyration - RG
« Reply #3 on: December 05, 2008, 03:19:09 PM »
yes.. I understand that..

low rg spins faster with a given force

higher rg spins slower with the same given force.

What I am asking is different.. I want to know the definition or explanation of the RG as it applies to bowling balls.
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Dan Belcher

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Re: Radius of Gyration - RG
« Reply #4 on: December 05, 2008, 04:06:26 PM »
http://www.bowl.com/articleView.aspx?i=12811&f=21 says this:

quote:
Technically speaking, the radius of gyration is defined as the square root of the moment of inertia divided by mass of the object. Therefore, the radius of gyration is the distance that, if the entire object's mass were together at only that specific radius, would yield the same moment of inertia. The moment of inertia for an object is the ratio of applied torque and the resultant angular acceleration of the object. Translating the physics definition, the moment of inertia measures how easy an object will rotate when a force is applied. 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 and is a measurement of where the weight is located inside the ball relative to the center.

To help explain this concept further, imagine a figure skater twirling on the ice. If the skater spins with arms extended out, the rate of rotation is slower than if the arms are pulled inward toward the body. The same physics principle applies for a designed core inside of a bowling ball. For a given core shape, the more dense (heavier) the inner core becomes, the more the bowling ball will simulate rotation like a figure skater with arms tucked close the body.  In other words, the core will have a low RG and will help the ball rev up quickly.  The less dense (lighter) the inner core, the more the ball will behave as a spinning figure skater with arms extended out and it will take longer for the ball to rev up as it travels down the lane, thus, having a higher RG. The low RG ball allows friction with the lane to add to rotation for a sooner and more arcing break point. The high RG ball will resist rotation longer than the low RG and it becomes harder for friction to add to the ball's rotation, resulting in a ball that slides further down lane before hooking. The radius of gyration is measured in inches. The USBC has a lower limit of 2.43 inches and an upper limit of 2.80 inches.  More aggressive bowling balls on the market have an RG close to the lower limit, while plastic balls will have an RG value near the upper limit.
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J_w73

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Re: Radius of Gyration - RG
« Reply #5 on: December 05, 2008, 04:18:33 PM »
quote:
http://www.bowl.com/articleView.aspx?i=12811&f=21 says this:

quote:
Technically speaking, the radius of gyration is defined as the square root of the moment of inertia divided by mass of the object. Therefore, the radius of gyration is the distance that, if the entire object's mass were together at only that specific radius, would yield the same moment of inertia. The moment of inertia for an object is the ratio of applied torque and the resultant angular acceleration of the object. Translating the physics definition, the moment of inertia measures how easy an object will rotate when a force is applied. 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 and is a measurement of where the weight is located inside the ball relative to the center.

To help explain this concept further, imagine a figure skater twirling on the ice. If the skater spins with arms extended out, the rate of rotation is slower than if the arms are pulled inward toward the body. The same physics principle applies for a designed core inside of a bowling ball. For a given core shape, the more dense (heavier) the inner core becomes, the more the bowling ball will simulate rotation like a figure skater with arms tucked close the body.  In other words, the core will have a low RG and will help the ball rev up quickly.  The less dense (lighter) the inner core, the more the ball will behave as a spinning figure skater with arms extended out and it will take longer for the ball to rev up as it travels down the lane, thus, having a higher RG. The low RG ball allows friction with the lane to add to rotation for a sooner and more arcing break point. The high RG ball will resist rotation longer than the low RG and it becomes harder for friction to add to the ball's rotation, resulting in a ball that slides further down lane before hooking. The radius of gyration is measured in inches. The USBC has a lower limit of 2.43 inches and an upper limit of 2.80 inches.  More aggressive bowling balls on the market have an RG close to the lower limit, while plastic balls will have an RG value near the upper limit.


I think that is what I was looking for.. I couldn't remember where I had seen it .. thanks..

So . the core's physical size isn't necesarrily between 2.43 and 2.80 inches in radius... right??

just it can't have a radius of gyration (like explained above) of more or less than these numbers??
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1MechEng

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Re: Radius of Gyration - RG
« Reply #6 on: December 05, 2008, 06:03:31 PM »
J-w73 -
You're correct in your assumption.

On edit - the Rg refers to the whole ball (not just the core).

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Dan
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Engineering * Bowling = a fun and practical application of rotational kinematics.

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Edited on 12/5/2008 7:04 PM
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Dan

J_w73

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Re: Radius of Gyration - RG
« Reply #7 on: December 06, 2008, 12:19:54 PM »
quote:
J-w73 -
You're correct in your assumption.

On edit - the Rg refers to the whole ball (not just the core).

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======================
Dan
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Engineering * Bowling = a fun and practical application of rotational kinematics.

Bowling Nerd Herd (TM) Member

Edited on 12/5/2008 7:04 PM


thanks man..
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