Talk:Units conversion by factor-label

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[edit] Doesn't seem encylopedic

This doesn't seem encyclopedic. Perhaps this should be moved to Wikibooks? ―BenFrantzDale 06:44, 12 February 2006 (UTC)

I don't understand why you feel this isn't encylopedic. The factor-label method of using dimensional analysis for conversion of units has been in use by chemists and engineers for decades. Do a Google search on the keywords and phrases "units conversion", "factor-label", "dimensional analysis" and you will get a great many hits including very many high school and university course sources. The Wikipedia already includes an article on the more formal and rigorous use of dimensional analysis but it doesn't include the technique of conversion of units ... which I believe merits an article of its own.

mbeychok 18:14, 12 February 2006 (UTC)

I say it isn't encyclopedic because it seems very how-to. I think I am also biased against the article as is for style reasons (see my comments below). —BenFrantzDale 23:14, 13 February 2006 (UTC)

Also, one of the bolded AKAs is dimensional analysis, a page which already exists. ―BenFrantzDale 12:15, 14 February 2006 (UTC)

[edit] This page may need cleanup??

User:crissov has posted a tag saying this page may need cleanup but he did not explain why he had done so. If he will please tell me what he believes to need editing, I will do my best to cooperate. As the original author, I did my best to Wikify this page. The subject matter is not included anywhere else in the Wikipedia and I made a very diligent search before providing this contribution.

I have removed the tag until Crissov and I have had more discussion ... I hope that is okay.
mbeychok 02:33, 13 February 2006 (UTC)

I agree with the need for cleanup. It could do with a proper lead section before any named sections and with the first sentence answering the question "What is units conversion by factor-label?". Also, the math would be better as TeX markup than as HTML. —BenFrantzDale 23:14, 13 February 2006 (UTC)

BenFrantzDale:

Thank you for clarifying your perception of this article. There are a good many articles in the Wikipedia which do not have a lead-in section. However, I will add a lead-in section as you suggested as soon as I can. As for using TeX equations, I have been unable to find any way of striking through (i.e., lining through) parts of a TeX equation ... and that is essential to illustrating the cancelling of conversion factors that is the very heart of the Factor-label method. Also, one of the three equations in the article would be too long in TeX to display it in the width of the display space without horizontal scrolling.

If you can tell me how to strike through parts of a TeX equation and also how to create a TeX equation in a smaller font, I will change the equations.

Thanks again for your response.

mbeychok 01:28, 14 February 2006 (UTC)

Crissov:

First, let me say that I really like your editing of this article. In particular, I like how you revised the first two equations and placed them in a box. In fact, I think what you have done with the equations will satisfy BenFrantzDale's desire to change the equations.

There are some minor changes that I made as follows:

• Although physicists and chemists understand that a mol is really a gram-mole and use it as such, most engineers (in particular chemical engineers) and many others make a distinction between a gram-mol (gmol) and a kilogram-mol (kgmol). Therefore, I changed the  molecular weight of NOx = 46  to the  molar mass of NOx = 46 kg/kgmol. That makes it consistent with the 22.414 Nm³/kgmol used in the flue gas example ... since there are only 22.414 L/gmol (or 22.414 L/mol] and a liter is 1/1000th of a cubic meter.

• Also, most engineers and most people working for environmental regulatory agencies involved with air pollutants such as the nitrogen oxides refer to them as NOx rather than NO_x so I reverted those back to the NOx form. Also, that form is consistent with the NOx form used in the example conversion.

Sorry to be so long-winded, but I have one more comment that I hope will not offend you. Rather than just making the revisions without any prior discussion, it would have been nicer to be gentle and civil with a newcomer like myself by at least having some discussion and/or explanation.

Regards and thanks again. mbeychok 03:00, 14 February 2006 (UTC)

[edit] Addition of Physics Wiki Book to See also section

I see no harm to having had the FHSST Physics Wiki book included in the See also section. However, I would point out that it has a much less comprehensive coverage of the subject than does this article. - mbeychok 04:01, 26 February 2006 (UTC)

I think the issue is what should be in Wikipedia vs what should be in Wikibooks. There seems to be consensus that only general information should be in Wikipedia and more specific info should be in Wikibooks. I personally think everything should be in Wikipedia. I faced this same criticism myself and had to reluctantly moved material from trajectory into Wikibooks. Samw 05:06, 27 February 2006 (UTC)

[edit] Reason for reverting edit by User:217.84.189.114

Where did User:217.84.189.114 find a "rule" that brackets cannot be used around dimensional units? Even if such a rule exists somewhere, the case in point in this article is not a mathematical equation per se. Instead, it is an example of how cancelling dimensional units can be used to determine if a mathematical equation is dimensionally consistent. Replacing the brackets with parenthesis (as was done by User:217.84.189.114) resulted in double sets of parentheses which looks very confusing. It is much clearer when brackets are used. The edit by User:217.84.189.114 is a too rigid and too inflexible application of such a rule (if any exists). That is why I reverted his/her edit. - mbeychok 00:11, 24 July 2006 (UTC)

the rule is to find somewhere around or in ISO 31, but I don't insist on that because I don't know the source exactly - is there any reason not to use curly brackets instead? -- 217.84.175.39 09:38, 28 July 2006 (UTC)

Please, 217.84.175.39, stop messing around in the several "dimension" related articles. The square brackets mean "dimesion of" and in the articles where we have used italics, it is because they have been so used in the last 50 yrs. If there are "new" rules, show them . --Jclerman 10:58, 28 July 2006 (UTC)

Jclerman - did you even notice what I edited? The other ones were mistakes, which I accepted - no reason to pull out the lobe (is this the right expression in english?) -- 217.84.175.39 20:29, 28 July 2006 (UTC)

217.84.175.39, What you did in your edit (which I reverted) was to change:

(Pa) (m³) = (mol) [ (Pa·m³) / (mol · K) ] (K)

to this:

(Pa) (m³) = (mol) ( (Pa·m³) / (mol · K) ) (K)

and that, as I said before, resulted in double sets of parentheses which are very confusing. The primary purpose of Wikipedia is to provide information in a clear, easily understood manner. As I also said before, even if there is such a rule in ISO, so what? We shouldn't get excessively rigid and obsessive about such minutiae. Now, you changed the subject of your previous edit and asked Is there any reason not to use curly brackets instead? Yes, curly brackets would work but I like the look of square brackets better ... and as the original aurthor of this article, I chose what I liked better. Please honor that choice of mine. Surely, there are much more meaningful things in Wikipedia that need editing without concentrating on such trivial matters. - mbeychok 16:22, 28 July 2006 (UTC)

yes - it's your choice and I never said I wouldn't accept that ... I didn't make such a big thing out of that - I still think it is missunderstandable - but I don't really care, I just wanted to help and didn't make it worse - then I asked a question. So what? -- 217.84.175.39 20:28, 28 July 2006 (UTC)

[edit] Limitations section

Someone experienced, please just check if this new section I added is valid. It should be valid. --Ajo Mama 02:34, 12 December 2006 (UTC)

[edit] The factor-label method for converting units

Here are some comments about corresponding section in the article Units conversion by factor-label.

1. The following phrase,

For example, 10 miles per hour can be converted to meters per second by using the sequence of conversion factor fractions shown below:...:

should read something more like:

For example, 10 miles per hour can be converted to meters per second by using a sequence of conversion factors as shown below:...:

2. Consider the next sentence:

As can be seen, when the mile dimensions and the hour dimensions are cancelled out and the arithmetic is done, 10 miles per hour converts to 4.47 meters per second.

A mile is not a dimension. A mile is a unit (of distance). Likewise, an hour is not a dimension. An hour is a unit (of time). The word "dimension" is not a synonym of "unit" [1]. Therefore this sentence should change.

3. This point concerns one method of striking through a TeX equation. The math code under the "edit this page tab" creates a strike through mile as follows:

and strikes through mile and hour in a fraction as follows:

.

John David Wright 20:12, 12 March 2007 (UTC)

John, thank you for your comments. I will make the changes you suggested in your items 1 and 2. However, in all candor, I disagree with your reference that says dimensions and units are not synonymous. In many people's minds, they are used interchangeably ... but it is too trivial a point to quarrel about it.

As for item 3, if you would like to change the two equations in the article (the one about miles per hour and the one about the concentration of nitrogen oxides) to TeX using strike throughs, please do so. I would strongly recommend that you first do it in your personal sandbox because it looks as if it could get quite complicated. When finished in your sandbox, you could then easily copy and paste it into this article. Best regards, - mbeychok 22:56, 12 March 2007 (UTC)

Concerning item 1, the main point is that "conversion factor fraction" should change to "conversion factor". The term "conversion factor fraction" is redundant because the term "conversion factor" is defined as a ratio between two quantities of the same kind. [2]

As for item 2, dimensions and units differ in the following sense. Two different dimensions cannot have the same unit. For instance, the dimensions of length and mass clearly have different units. However, two different units can have the same dimension. For instance, the units of metre and mile have the same dimension, i.e., length. The point that different units can have the same dimension is crucial to the generation of a conversion factor. A conversion factor must be dimensionless in order to preserve the dimension of the original quantity to be converted. For instance, the conversion factor 1609 metre/mile has a dimension of length/length which is clearly a dimensionless quantity. Therefore, the conversion factor 1609 metre/mile converts the unit mile/hour to the quantity 1609 metre/hour but preserves its dimension of length/time.

As for item 3, I am not sure it worth the extra time to change the equations to TeX form. As you point out, the conversion could get complicated. Maybe the other user who suggested the conversion or someone else would like to make the change. I just wanted to point out a possible method. I think a cleaner method is possible which would make the conversion less time consuming. John David Wright 22:17, 13 March 2007 (UTC)

[edit] Nomenclature

1. This article is basically about "quantity calculus", the internationally-agreed nomenclature of which is set out in ISO 31. In ISO 31, a "physical quantity" is the product of a "number" and a "unit". There is no such beast as a "dimensional unit" (Units have dimensions, but dimensional equality does not guarantee unit equality) Thus some instances of "dimensional unit" in this article mean "unit", and the rest mean "dimension". The first line should simply state "A physical quantity is the product of a number and a unit".

2. The article presents the "factor-label method" as some important black-art, but by definition it is the only method for expressing quantities in different units.

3. There should be a link to Wikipedia ISO 31 article

4. The phrase "mathematical equation" should be "physical equation" Adamtester (talk) 00:51, 22 January 2008 (UTC)

As you suggested, I have just added a link to the ISO 31 article.

I have also just re-read this article and cannot fathom how you arrived at the conclusion that the article is presented as "some important black art". The conversion of units is a problem that engineers face very often and this article simply explains one method of performing such conversion. Calling such conversions "quantity calculus" would really convince readers that it is some sort of black art! As for using "physical equation" rather than "mathematical equation", that would also turn off most readers. - mbeychok (talk) 01:18, 22 January 2008 (UTC)