Talk:Center of gravity

This page is ridiculous. The author throws in the words "or other object", and that should be most of the article. Aircraft should perhaps be mentioned at most in a footnote if at all. -- Mike Hardy

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OK, no problem with the addition of some stuff about aircraft, but the article should not make it look as if centers of gravity of aircraft are what the subject is primarily about. Someone experienced in physics pedagogy should add material. Michael Hardy 21:58 Jan 26, 2003 (UTC)

Centre of Gravity -- more about the spelling than the math?

Dear Editors,

While I very much appreciate the efforts of the editors and the authors to make Wikipedia one of the best sources and references for general knowledge on the web, I would recommend not to underestimate so much the intellectual faculties of the general public as to believe that we would actually neither need nor expect at least one formula in the article about Centre of Gravity. Having dedicated special attention to the spelling of the term (see the article) the author should have at the very least given some practical information on how to calculate the Centre of Gravity say of a collection of physical points. The formula is quite simple:

Xcg = (Σ Mi*Xi) / (Σ Mi), the sums are for i=1 to N

Ycg = (Σ Mi*Yi) / (Σ Mi), the sums are for i=1 to N

where Xcg and Ycg are x and y coordinates of the Centre of Gravity;

Xi and Yi are the x and y coordinates of a physical point;

Mi is the mass of a physical point;

N is the number of physical points.

Despite the simplicity of the above formula and its wide application for a quick and rough estimation of the Centre of Gravity (especially now that computers are commonly used) I had forgotten it and was looking for a place on the internet to check it. Wikipedia is usually my starting point in such searches. I was quite disappointed that in this particular case Wikipedia offered so little practical knowledge.

I found the required information elsewhere and used it in my MS Excel calculations to solve my problem.

I suggest the following:

1) include in the article the above formula for the Centre of Gravity of a collection of physical points as it is perhaps the most simple and the most widely applied formula on the subject (if one has an arbitrary 2-D or 3-D shape simply by dividing it into regular squares or cubes one could very quickly obtain a rough estimate of its Centre of Gravity using this formula and a PC).

2) include in the article a note that for an object with symmetry the Centre of Gravity necessarily lies on the axis of symmetry (implying homogeius density of the material). And since a large number of practical objects such as rectangles and rhombs have two axes of symmetry their Centre of Gravity lies on the intersection of the two and hence is easily found.

3) include in the article a note that there is no requirement for the Centre of Gravity to lie inside the physical object. E.g. for a horse shoe it lies outside.

4) finally include in the article a bit more practical information on how to find the centre of gravity of some simple shapes (e.g. a triangle).

Kind Regards,

Plamen Grozdanov

28/Aug/2004, Bristol

P.S. Just in case someone is interested: I am a software engineer.

P.P.S. One source to use to verify the above formula could be Centre of Gravity from the University of Winnipeg (http://theory.uwinnipeg.ca/physics/rot/node4.html)

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I plan to move most of this article to "Center of Mass". Then this article could focus on the few objects where the center of mass is *different* from the center of gravity. (Such objects that are in a non-constant gravity field, and are non-spherical). --DavidCary 03:41, 12 Feb 2005 (UTC)

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