×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

(OP)
I recently noticed how similar the equations for the radius of gyration and the standard deviation (for a population) appear.

Can anybody explain their similarities (and maybe differences)?

#### Quote (Wikipedia)

"It (the Radius of Gyration) also can be referred to as the radial distance from a given axis at which the mass of a body could be concentrated without altering the rotational inertia of the body about that axis.

Does it follow that the standard deviation can be referred to as the distance from a given mean at which the population could be concentrated without altering the precision around that mean?

A clear lack of similarity I see is, in mechanics, a higher radius of gyration is desirable, whereas in statistics a lower standard deviation is desirable.

Oh the things we do on a weekend when our significant other is out of town...

"Does it follow that the standard deviation can be referred to as the distance from a given mean at which the population could be concentrated without altering the precision around that mean?"

No. The standard deviation results in the capturing 68.27% of a Gaussian probability distribution. I have no idea why they would be confluent at all.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

(OP)
Just found this:

#### Quote (Engineering Mechanics: Statics By I. C. Jong, B. G. Rogers)

A centroidal radius of gyration represents the standard deviation of the distances of the area elements from the centroidal axis

This text says that they are. If N (the population or sample) is analogous to 'area' then it makes sense.

"in mechanics, a higher radius of gyration is desirable"

Sometimes, not always. For example many column inches have been wasted on the preference for low polar moment of inertias for racing cars.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

(OP)
Good catch. I am from a building structures perspective, and you don't see that too often. I should have been more specific. :)

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!