Talk:List of second moments of area

message: There's something wrong with the displaying of some of the formulas in the table.  At least two of them are displaying the code and not the proper formula.  Couldn't figure out what the problem was.  —Preceding unsigned comment added by 76.65.22.70 (talk) 00:45, 23 November 2008 (UTC)
replies: text: I couldn't figure out what caused it either, but simplifying the code slightly seems to have worked. Thanks for leaving a note here. Hemmingsen 14:52, 23 November 2008 (UTC)
thread_title: first comments

message: Shouldnt the formula for the polar moment of inertia of a filled circle be Ip=pi * R^4/2 instead of r^4/4 ? It's right there in the cited reference.  — Preceding unsigned comment added by 77.54.89.249 (talk) 21:18, 30 May 2012 (UTC)
replies: text: The moment of inertia along the z-axis (perpendicular to the plane) is \frac{\pi}{2}R^4, but this article is about the moment of inertia along the x-axis. Ulflund (talk) 06:26, 31 May 2012 (UTC)

text: Oh okay, but that isn't very useful, at least from an engineering viewpoint. Most of the time we use moments along the z-axis, in shafts and things like that. I'm a student, and that /4 part made me lose half an hour trying to figure it out. I think the axis part should be more explicit, or there should be another article with the moments along the z-axis.  — Preceding unsigned comment added by 77.54.89.249 (talk) 01:58, 1 June 2012 (UTC)

text: Maybe the moments could be listed like here http://www.efunda.com/math/areas/Circle.cfm, with three columns for the different axis.  — Preceding unsigned comment added by 77.54.89.249 (talk) 02:01, 1 June 2012 (UTC)
thread_title: Filled cirlce

message: The formula for the filled circular sector seem to be wrong. It gives negative result with some angles value.
The correct formula should be the one at http://www.efunda.com/math/areas/CircularSection.cfm
If nobody as objection I can modify the formula with the correct one.  — Preceding unsigned comment added by 79.2.53.113 (talk) 20:55, 5 May 2013 (UTC)
thread_title:  filled circular sector 

message: I am trying to look up some of the references from this page, but the efunda website is just redirecting me to a paywall (it allows approx 5 page views before cutting you off). Does anyone know of a better website to link to? MathWorld has several pages on this topic, e.g. http://mathworld.wolfram.com/MomentofInertia.html  — Preceding unsigned comment added by 129.169.141.108 (talk) 12:44, 24 February 2014 (UTC)
thread_title:  Robust references 

message: Is it possible to have more information on the simplification?  It's ambiguous why the terms with t^x , x>1 disappear.
:This is a common enough practice to ignore higher order terms of small numbers. It's assumes that r>>t So think something like r=100,t=0.01. Now compare the size of the terms r^3t=10000,r^2t^2=1,rt^3=0.0001,\ldots. Clearly 10001.0001\approx10000 and we can save a lot of trouble by not calculating the smaller numbers. Now this is an exaggeration in terms of the size difference needed to make the higher order terms negligible. Usually r>10t suffices to make it a good enough approximation for most engineering applications. So basically we have r^3t=1000t^4, r^2t^2=100t^4, rt^3=10t^4,\ldots and clearly the first is an order of magnitude larger than the second which gives about a 10% error. Different authors give different acceptable relationships between r and t. But 10 is a common one. Personally, this is a common enough practice that these deep details could be spared in the table listing the equations. The details present should be enough to make the point clear without exaggerated example or a relationship limit. BeaumontTaz (talk) 09:21, 7 October 2014 (UTC)
thread_title: Annulus

message: e.g. for the annulus, the r's look like lowercase y's.  — Preceding unsigned comment added by 24.43.3.130 (talk) 00:34, 10 December 2014 (UTC)
replies: text: Fixed --IngenieroLoco (talk) 20:17, 16 April 2016 (UTC)
thread_title:  characters in figures are illegible 

message: None of the formula's display for me. At first I thought it was vandalism, but the math tags and text are still there, they just aren't rendering. This is the last revision I was able to view them in. Zephalis (talk) 07:27, 2 April 2015 (UTC)
replies: text: I don't see any problem with the formulas. --IngenieroLoco (talk) 20:18, 16 April 2016 (UTC)
thread_title:  Formula's not showing