Talk:Dimensionless quantity

message: I think that "atomic mass" is not dimensionless and should be removed from the list. Atomic mass is measured in amu, atomic mass units. I am not knowledgable to know for sure. Can someone correct me on this if I am wrong, or correct the article if it is wrong? Thanks. --Atraxani
:You're right - it's entirely dimensional, so i removed it.  --Whosyourjudas (talk) 00:08, 14 Nov 2004 (UTC)
replies: text: If it not express in units of mass (g, kg), but just in a relative way (amu or dalton (unit)), then it is surely dimensionless.--188.26.22.131 (talk) 11:21, 24 February 2014 (UTC)
thread_title:  Atomic Mass 

message: Amount of substance is also dimensionless or pseudo-dimensional, although it appears dimensional. It can be compared to angle whose unit radian is a dimensionless unit. Mole has a similar dimensional status with radian. Amount is the ratio of two masses: a given value of mass of a substance divided by the molar mass which is a material/substance constant. Molar mass itself is the expression in units of mass of relative molecular mass which contains Avogadro number of particles.--188.26.22.131 (talk) 11:09, 24 February 2014 (UTC)
thread_title: Amount of substance

message: Our definition says: "a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units". This is only superficially true. Beside the example given by The Anome there is an easier case, as Pdn pointed out on Category_talk:Dimensionless numbers:
:The example given by Anome is not a counterexample, for reasons stated above. 216.167.142.251
:'fraid "pH" is not dimensionless at all - as I remember (from Chem 2 at Harvard, 1953) it is the negative logarithm of the hydrogen ion concentration in moles per liter.  I think it's based on the common logarithm, not the natural one.  So it involves moles and liters, which are based on dimensional standards.  OK, a logarithm is "dimensionless" perhaps to a mathematician, but not really.  It a logarithm were always dimensionless we could take the distance to the Sun, about 1.5 *10^11 meters, take its logarithm (a little over 11), and claim  the distance to the Sun is dimensionless. [...]
One might object that pH should be measured in bel, but we can't set standards for chemistry here. Fact is that our intruduction contains a wrong statement. If you're a quantity, having dimension 1 (or 0?) is not equivalent to being "pure" – you may still have physical units in your definition. — Sebastian (talk) 18:18, 2005 May 21 (UTC)
:No, you're wrong. 100 cm/1 m has NO units, there is no such thing as a "unit" of "cm/m". This "unit" is equal to the dimensionless constant 1/100.
:: Dimensionless numbers can have units. A simple example: an angle is measured in radians or degrees. The angle is always a number with dimension 1, but radians and degrees are different units. Units tell you in which system of measurement one works. You may throw in that both are only "supplementary units" but this concept does not exist anymore since 1995. -- 86.32.108.65 (talk) 16:16, 31 January 2010 (UTC)
thread_title: dimensionless &#8800; pure 

message: Isn't any cardinal number dimensionless? For example, four, or twenty six? If "dimensionless numbers" refers to ratios which have been found to be useful in some discipline, wouldn't pi count? Perhaps someone can write an introductory paragraph to this article, which would explain this category of numbers a little better? Thanks! --24.190.141.119 14:37, 19 Apr 2005 (UTC)
thread_title:  Dumb questions from a newbie 

message: Encouraged by the comment of one contributor above, who suggests that "quantity" should be referred to in place of "number" in the introduction to this article, I propose that in fact the entire article (including its title) should be revised to refer to dimensionless quantities. All numbers are dimensionless. It is the physical quantity, expressed by a number and its unit, that may be dimensionless. Contradictions invited.
I concur
:The article as it exists now is a conflation of the two somewhat separate ideas, that of a dimensionless numbers which are used to measure some property, and that of particular dimensionless numbers which are dimensionless physical constants rather than quantity (which I'd take to be something like "mass" for something measured in units of "pounds").  "Dimensionless quantity" is a less interesting concept, maybe applying to things like the abolishment of the class of "supplemental" units in SI and instead describing them as "derived units" of the quantity "one".  
:Just look at all the dimensionless numbers in the lists on this article's page which have the word number in their own article titles.  That is a pretty good indication that the current title is a reasonable one. I say keep it here Gene Nygaard 07:27, 20 October 2005 (UTC)
thread_title:  Rename to "Dimensionless quantity" 

message: I would argue that Rockwell Hardness is not a true dimensonless quantity because without knowing the scale used it is useless. For that reason the scale itself becomes a dimension.  For example the hardness number is referred to by the scale used, e.g. 60 HRB, which becomes a unit itself.  Reading the way these are derived, the actual number is a constant minus a depth in mm, so the actual unit seems to be mm.  If others concur we should remove this from the list.
:You seem to be conflating unit with dimension. For example: length is a dimension which can be represented in different units such as meters. A scale in this context is just a method to assign meaning to otherwise arbitrary quantities. This is thus distinct from the concept of dimension.--217.84.29.188 (talk) 13:15, 20 July 2011 (UTC)
thread_title:  Rockwell Hardness Scale 

message: 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, at least,  in the last 50 yrs. If there are "new" rules, show them . --Jclerman 11:03, 28 July 2006 (UTC)
replies: text: 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 20:19, 28 July 2006 (UTC)
thread_title:  Notation: italics and brackets 

message: In my understanding, this section is completely wrong. In the Planck system, constants like c are used as units, but this does not make them dimensionless. If you look up the Planck units article, the dimensions of all constants are even indicated. In case of c, the dimension is L/T. Therefore, those constants are by no means dimensionless and the section should be deleted.
What happens is the following: instead of the "normal" system of base quantities (which you find in the article about physical quantity) the Planck system uses another system of base quantities which is based on natural constants. That's all. It is also not true that the quantities have no units, as many people think.  They have units but they unfortunately are not used. For example, when indicating a velocity v in Planck System the unit of v is c ([v] = c).  Most people, however, do not say "v = 0.8 c", they only say "v = 0.8" which is convenient but lazy and inaccurate.
The notion that in the Planck system the constants are "eliminated" is also inaccurate. What in short is called a physical constant is more precisely a constant physical quantity. A physical quantity Q, however, consists of two things, a numerical factor {Q} and a unit [Q]. In the case where the numerical factor {Q} = 1 the quantity Q is by no means eliminated, it still has the unit [Q]. (Otherwise one could say that the original meter in Paris would be "eliminated" because its numerical factor is also 1, but in fact we need it because of its unit, the meter.)
--Kehrli 12:56, 31 July 2006 (UTC)
thread_title:  section Dimensionless Phyical Constants is a misunderstanding 

message: I had never heard the term "pure number" until about a month ago (I had heard of dimensionless though), the mark scheme for a CCEA A level physics question "explain why the quantity x (or whatever it was actually called) does not have units" said that the correct answer was the obvious "it's in a log" and the weirder terminolgy "it is a pure number", so I assumed pure = dimensionless. So now pure number redirects here. Stuart Morrow 00:11, 30 December 2006 (UTC)
thread_title:  Pure number redirects here. 

message: Would it be correct to add normalized moments (see moment) to the list of dimensionless quantities? EverGreg 13:08, 20 September 2007 (UTC)
thread_title:  Normalised [[Moment]] 

message: The example, given at the article's beginning, of radians as a dimensionless quantity is very confusing. While technically expressing a ratio, radians function a lot like units and are often seen combined with units (e.g. rad/s rather than Hz). It seems like the example is more complex and confusing than the concepts it's trying to clarify.
jdg (talk) 19:40, 29 February 2008 (UTC)
replies: text: radians are a unit of angle, and angle is a dimensionless quantity. This is what the article should say. I cannot think of a good way to write this 64.91.186.214 (talk) 16:29, 7 March 2008 (UTC)

text: I tried anyways, but it just seems to have made it more complicated... 64.91.186.214 (talk) 16:40, 7 March 2008 (UTC)
replies: text: Using the illustration in the radians article might help EverGreg (talk) 22:32, 7 March 2008 (UTC)
thread_title:  Need a better example than radians 

message: Cannot radians be expressed with a small "r".  I know it's optional, but couldn't one be put in parens or something.  Asmeurer (talk  ♬ contribs) 15:15, 16 October 2008 (UTC)
thread_title:  Radians 

message: Should not Chandrasekhar number be a part of list? ~Divij (talk) 11:17, 25 March 2009 (UTC)
replies: text: Yes. You can just add it. -- Crowsnest (talk); 12:01, 25 March 2009 (UTC)
replies: text:  Finally did it after nearly 3 years ~Divij (talk) 11:24, 19 January 2012 (UTC)
thread_title:  Addition in List 

message: I removed Berchak number from the list, since both an article on the subject and reliable sources are missing. It can be re-instated once this entry is verifiable. -- Crowsnest (talk) 19:03, 15 April 2009 (UTC)
thread_title:  Berchak number 

message: Regarding the table, entry "Decibel", "ratio of two intensities, usually sound". 1) There is a non-linear transformation involved (log, base 10), not just the ratio 2) dB is also commonly used for ratios in electronic systems, e.g. -3 dB frequency cutoff (ratio between input and output signal, possibly normalised) and signal-to-noise ratio.  --Mortense (talk) 18:27, 15 November 2010 (UTC)
thread_title:  Decibel 

message: :for instance, the number of people N in a room is a dimensionless quantity.
Wouldn't the dimension of the number people in a room be "people" or "persons"?
If I were calculating the ratio of apples to people in a room, and I had, say, 10 apples and 5 people, I would have 2 apples/person.
Ktwombley (talk) 17:49, 4 February 2011 (UTC)
replies: text: The key word here is "number" of people. Numbers themselves have no dimension. Your ratio is dimensionless. Sometimes they are considered as having a dimension for the purpose of dimensional analysis, for example to make sure conversion factors are applied correctly for dimensionless quantities. As an example of this: say I have a variable measured in degrees and another measured in radians; comparing them directly would be possibly meaningless even though they are dimensionless. To catch this mistake, I treat the units much like dimensions so I can make sure that the units are converted where appropriate.--217.84.29.188 (talk) 13:31, 20 July 2011 (UTC)
replies: text: I would argue that the dimension here is numerosity (cardinality), and the unit of measure is 'person' if we measure only persons, but depending of the scope of measurement it could be something more or less specific that characterises the population whose numerosity is being measured: e.g. 'item', or 'being' if we want to broaden the count, and allow computations with this quantity in a broader sense. Alternatively we could assign e.g. 'students' as the 'unit of measurement' (the benchmark with which we establish the count) and make the counting even more specific. Gyomaigy (talk) 18:21, 11 April 2023 (UTC)
thread_title:  First paragraph example - is it correct? 

message: People seem to be confused by the difference between these two related concepts. Any suggestions for how to make the article address this better?--217.84.29.188 (talk) 13:17, 20 July 2011 (UTC)
thread_title:  unit versus dimension 

message: Reference 26 (to Strouhal Number) is broken.  Please fix. Tkemp (talk) 16:17, 21 February 2013 (UTC)
thread_title:  broken link 

message: The list of dimensionless quantities has become large enough that I think it would be best to have the list moved to a page of its own.  I feel it is necessary and useful for wikipedia to include the information together as a list, but the list is significantly larger that the article itself, and I think that for a list size detracts from the article.  We might keep a short (10-15 item) summary list to show the variety of dimensionless quantities throughout science (see the way the list looked c.2006), but otherwise the bulk of the information would only be in the new List of page. Thoughts? Rememberlands (talk) 05:16, 26 November 2013 (UTC)
replies: text: Currently the link to the "Main article: List of dimensionless numbers" links to itself on this page. I don't think that is intended. Any Thoughts? --Ramses303 (talk) 09:19, 9 February 2015 (UTC)
replies: text: Ramses303, the list has been moved to it's own page.  I've made your change so the the list of dimensionless numbers is simply redirected to list of dimensionless quantities.  In regards to my previous comment, I don't think that this article will need any table in it from here on.  Examples of special importance can be elaborated on in the examples section to help convey specifically what dimensionless quantities are—without need for any large list.  I will continue reducing the use of bullet lists, because a paragraph structure is much better for an encyclopedia article.  The section on Origins and derivations should make the numbers more accessible to the reader and frame their importance in practice.  Still plenty to be done, but with the list separated, I think this article will soon clean up nicely. Rememberlands (talk) 23:13, 7 October 2015 (UTC)
thread_title:  New Page: List of dimensionless quantities? 

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thread_title:  External links modified 

message: According to the Buckingham  theorem the space spanned by a set of fundamental dimensions, scaled in some units can be spanned by any appropriate set of dimensions with units, suitably selected. So dimensions, as well as units, are are not inherently affixed to physical quantities, but assigned in a reasonable act of caprice, making up a useful set of dimensions with units (see atomic units, natural units, Planck units, ...). As a consequence, physical quantities do not have innate dimensions, but these are assigned notions, to the taste of the current theory. Purgy (talk) 10:21, 14 July 2018 (UTC)
thread_title:  "Dimensions" of physical quantities 

message: why the modal "may"? Either it is or isn't. --Backinstadiums (talk) 22:45, 9 August 2019 (UTC)
thread_title:  ...may also... 

message: Hello,
I wonder if albedo and reflectance should be added to the dimensionless quantities list.
2A02:2788:22A:100D:4169:D178:FCCC:5DDD (talk) 12:22, 9 October 2020 (UTC)
thread_title:  [[Albedo]] and [[reflectance]] 

message: A note for future reference: it seems that the term "quantity of dimension one" will be replaced by the term "quantity with unit one" in VIM4 (draft) §1.8.  An explicit symbol for the dimension of such a quantity (previously taken to be 1) becomes unmentioned, so it becomes unclear what symbol will be used.  —Quondum 18:22, 13 May 2021 (UTC)
thread_title:  "quantity with unit one" 

message: In most of the examples the actual quantities do not become unitless: what happens is that the denominator becomes the new benchmark for measurement, which is often context dependent.
Strain as described in the above example is still a quantity which has a dimension of type 'length' and its unit of measure is 'the original length'.
What happens here is similar to when we divide the distance of 'jupiter and sun' with the distance of 'earth and sun' both expressed in kilometers, and the resulting ratio of 5.2 is not considered a unitless number but it is the 'jupiter - sun' distance in astronomical units (i.e. multiples of 'earth -sun' distances). 
I think it is worth mentioning this alternative interpretation somewhere in the article. Gyomaigy (talk) 18:15, 11 April 2023 (UTC)
thread_title:  dimensionless quantity - new interpretation: change of units of measures