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I have mostly seen "fluxes" but I could not find a definitive answer in some dictionary. As it come from the French, I am enclined to think it is "flux" in the plural though.

Edit : I am talking about the flow of a quantity, as an air flux.

Example : "The sum of all air fluxes was zero".

alex_reader
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4 Answers4

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I worked for a company which supplied metallurgical chemicals internationally to steel making and foundry businesses. One category of products were known as 'fluxes', each with its own product name and specification.

WS2
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You could avoid this problem by using similar forms as one uses for "force" or "intensity". In physics on would speak of a "net force" for the sum of all forces, and the "total intensity" from various light sources, speaking of 'force' and 'intensity' as abstract qualities which are due to causes, but not belonging to those causes per se.

Thus one could say:

The net air flux was zero

or

The total air flux was zero.

Niel de Beaudrap
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    This is the correct usage (especially net flux). Flux is a summation of flow, you wouldn't pluralize it. – David M Feb 21 '14 at 16:44
  • Mathematically, a flux is simply the integral of a vector over a surface, so I do not see why there cannot be any plural. – alex_reader Feb 21 '14 at 16:50
  • Whether or not a plural exists, what I've written is what is idiomatic in the North-American-Physicist dialect of English. – Niel de Beaudrap Feb 21 '14 at 21:29
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The entry for flux in the Oxford dictionaries does not show any use of flux in plural. It actually annotates some of the uses as mass nouns.

However, the plural form fluxes is often found in technical texts. Here's a quote from a very well-known text-book on Physics:

"If we now add Eqs. (3.14) and (3.15), we see that the sum of the fluxes through S1 and S2 is just the sum of two integrals which, taken together, give the flux through the original surface S=Sa+Sb." (The Feynman Lectures on Physics, Volume II)

If you still prefer to avoid the use of the plural form fluxes, you could do so by replacing the sum of fluxes with the total flux.

EDIT

With @alex_reader's help, I've found that the oldest occurrence of fluxes linked by Google's n-gram viewer is:

"There are some which become tarnished by fluxes, that contain the oxydes of lead." (The circle of the mechanical arts -- Thomas Martin, 1813)

Nico
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  • So the plural only stems from a technical use and did not exist before, say 1900 ? – alex_reader Feb 21 '14 at 16:14
  • @alex_reader: see my last edit. 1899 is the oldest occurrance I've found. The question I'm asking myself now is whether phrases such as in all states of flux actually derive from the technical term. – Nico Feb 21 '14 at 16:39
  • Thanks for the research. After looking at the n-gram viewer with a larger span, I think the notion may not have been much used before 1900. Even so, I think physics use mostly the notion of "flow", while mathematics may write it as a sum of several terms. – alex_reader Feb 21 '14 at 16:42
  • @alex_reader: thanks for the tip with the n-gram viewer. I've update the answer accordingly. – Nico Feb 21 '14 at 17:02
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    I'd like to point out that - while Richard Feynman is one of my personal heroes - he probably shouldn't be taken as an authority on the English language; he was notoriously unconcerned about rules and correctness in anything but science. – MT_Head Feb 21 '14 at 17:41
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    @MT_Head: Good point. I have also to say that in my experience physicists often use the expression sum of the fluxes. In fact, paraphrasing Lord Rutherford, I would say: "I have dealt with many different transformations with various periods of time, but the quickest that I have met was the transformation in one moment from a mass noun to a countable noun". – Nico Feb 21 '14 at 17:59
  • @Nico - I didn't mean to imply that he was wrong; your experience with other physicists tends to support him. I'm just saying that - in terms of English-language usage - while I wouldn't assume that Feynman was wrong, I wouldn't take his sole word on it either. On most questions of physics, safecracking, frigideira playing, or O-ring plasticity I would give him MUCH more credence. – MT_Head Feb 21 '14 at 19:20
  • Also, I like your paraphrase. – MT_Head Feb 21 '14 at 19:21
  • Fluxes is pretty commonly used in Physics in Electric and Magnetic field theory. The field flux from different sources is combined using integration and each source has its own contribution to the whole. Thus "sum of the Fluxes" is typical shorthand for "Sum of the Flux from each of the Sources" – Oldcat Feb 21 '14 at 20:06
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The American Heritage Dictionary doesn't list any plural for the noun. (They have a verb flux, one of whose forms they give as fluxes.) Wiktionary gives the plural as fluxes. Your example sounds right to me:

The sum of all air fluxes was zero.

I searched the text of this book on electricity and magnetism, and found 138 uses of flux but no fluxes, but that may just mean that the need to refer to the plural doesn't come up very much.

Google ngrams shows fluxes with about 1/6 the frequency of flux, but that doesn't prove that it's correct or that it's the plural noun rather than the verbal form.

  • I think fluxes is a misappropriation of the verb form which is being incorrectly applied as a plural. – David M Feb 21 '14 at 16:40