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I am looking for the generic term comprising all of the following:

$23.42\,\text{m}$
$200\,\text{K}$
$123\,\text{MeV}$
$ħ$

with other words, everything that can be reasonably represented with a number and a physical unit. I have no preference as to whether this term includes dimensionless scalars such as $π$ or $1.2345$. In particular this term should distinct the above entities from more abstract ones such as length, temperature or resistance. For example, I could use the desired term in the following way:

$23.42\,\text{m}$ is a [term], $200\,\text{K}$ is a [term], but length is not a [term] but [other term].

The reason I am asking this question is to get a third “opinion” on this. To avoid bias, this is also why I avoided to use any term so far. Some candidates are:

  • physical quantity
  • physical constant
  • physical magnitude
  • physical value
  • values of physical quantities or values of physical magnitudes

I am not interested in mere personal opinions – I have already heard plenty of those and they were not consistent. I am rather interested in answers backed up by examples¹ from the scientific literature, preferrably in a context which ensures that the author has clearly made up his mind as to what term to use. Well-reasoned opinions are also welcome.

While I would prefer a general answer (if one exists at all), I am also happy to know terms that are only consistently used in the desired way by a specific community.

¹ Be aware of references in which it is not clear whether what is being referred to is, e.g., 2 m, length or the length of this table.

Wrzlprmft
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  • The place where this comes up is actually in programming libraries. In those cases, the two I've seen used are "physical quantity" and "value". – DanielSank Oct 15 '14 at 19:07

3 Answers3

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If you want to restrict the question to numerical quantities that have physical units, sometimes they are called "dimensionful quantities" in contrast to "dimensionless quantities" that have no units, see p. 6 of Introduction to Classical Mechanics by David Morin for an example of such usage.

Hypnosifl
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  • This hardly answers my question, which rather was whether quantities (or anything else) is an appropriate term for certain entities at all. (In the cited book, it rather seems as if quantities is used to refer to such things as length, resistance and so on – in contrast to 2 m, 42 Ω etc.) – Wrzlprmft Oct 15 '14 at 14:50
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    You just asked for a "generic term" for "everything that can be reasonably represented with a number and a physical unit", you didn't specify that you wanted to know about the appropriate usage of the specific term "quantities"--if that's what you're interested in, I would suggest modifying the question to make this more clear. – Hypnosifl Oct 15 '14 at 15:11
  • Let me try to explain my criticism with other words: You answer which adjective I can use to distinguish between dimensionless and dimensionful [entities]. My question however was what the appropriate word (i.e., the generic term) for [entities] is or whether quantity, magnitude, constant or any other word is appropriate for [entities] (I only mentioned quantities in my first comment, because that’s what you used, also note the word rather). The text you cite clearly uses quantities for something that is not clearly [entities]. – Wrzlprmft Oct 15 '14 at 15:25
  • By [entities] do you just mean something like "any numerical value that is assigned some physical meaning"? If so think there are a number of interchangeable terms for this idea--I would probably favor "value" myself--although some of the terms you mention have a more narrow meaning (for example, if I measure something to have a speed of 5 meters/second, I wouldn't call that a 'constant' since it could change at a later time due to forces acting on the object). – Hypnosifl Oct 15 '14 at 15:38
  • [entities] is “everything that can be reasonably represented with a number and a physical unit” from my question, i.e., what I want to have named. “any numerical value that is assigned some physical meaning” may be this, if you define numerical value in a way that is not restricted to numbers. – Wrzlprmft Oct 15 '14 at 16:01
  • @Wrzlprmft - The difference between my phrase and yours is not in "number" vs. "numerical value" (which don't mean anything different), but rather in "assigned some physical meaning" vs. "a physical unit". Dimensionless physical constants would be covered by my phrase, but not by your phrase, since these constants don't have physical units. Do you want them to be included in your question, or are you asking specifically about physical values that are not dimensionless? – Hypnosifl Oct 15 '14 at 16:10
  • Let us continue this discussion in chat. – Wrzlprmft Oct 15 '14 at 16:14
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Now that I have a better understanding of what you're asking, I think a good candidate would be "quantity value", also known as the "value of a quantity", from p. 28 of the International Vocabulary of Metrology, Basic and General Concepts and Associated Terms (VIM) by the Joint Committee for Guides in Metrology, online in pdf form here. I found this linked in the "physical quantity" wiki article, and although that term is also close to what you're asking, it appears to include vectors. "Quantity" is defined on p. 18 of the pdf file as:

property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference

Note 2 explains that by "reference" they mean a reference to a physical unit, measurement procedure, or "reference material" (not sure if that refers to a type of physical material or to 'reference material' in the literary sense of texts that people can refer to for more information):

NOTE 2 A reference can be a measurement unit, a measurement procedure, a reference material, or a combination of such.

And on p. 19 they add the following (somewhat confusing) note to this definition, which seems to say that vectors can be included in this term:

NOTE 5 A quantity as defined here is a scalar. However, a vector or a tensor, the components of which are quantities, is also considered to be a quantity.

The term "quantity value" on p. 28 (with two synonyms listed below it, "value of a quantity" and "value") is defined more narrowly to be a magnitude rather than a vector, though (it can be the magnitude of a vector, but not the vector itself):

quantity value

value of a quantity

value

number and reference together expressing magnitude of a quantity

So combined with the earlier definition of quantity as something that "can be expressed as a number and a reference", this seems to fit the the bill. I think the synonyms "value of a quantity" and just "value" sound a bit more natural, I believe I've read physicists using them in the past, but I can't remember reading anyone talk about a "quantity value" before.

Hypnosifl
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I don't see any reason not to suggest "scalar".

Yes, the word is usually used to make a distinction vis a vis vectors and higher rank tensors, but it seems to be exactly applicable.

dmckee --- ex-moderator kitten
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