Talk:Flux

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[edit] headings

I added the headings to this article in hopes that people will be more willing to contribute to the idea of flux, and how it is used in their specific field without making the whole article too genre specific. If anyone can think of more headings to add please do. Also, I just made headings for each of the specific definitions already there. For instance I think fluid systems would fall under Physics, but I don't know enough about fluid systems to tell whether or not it warrants it's own heading.

Also there was some information in there that was commented out that sounded like it was a def. of flux in some specific field. I deleted it(editing around the comments was irksome), but maybe someone can go back and take a look at it to see if they know what it would fall under. Thanks! Starfoxy 03:03, 5 Feb 2005 (UTC)

Looks good. I'm going to edit the top paragraph/definition for clarity. I feel that the mathematics definition is in most basic terms; we can then use it to expound on other types of flux in other disciplines. If you don't like this, let me know, we can debate it and do some reverting ;) Tygar 06:12, Feb 7, 2005 (UTC)
I've created and added a diagram for the concept of flux. How is it? Would you change anything at all? -RadRafe 05:22, 16 Mar 2005 (UTC)

[edit] Split the article?

I think that this article actually covers two distinct concepts. One concept is that of the quantity defined by the integral of a vector field across a surface. This is what we see in electromagnetism. The other concept is that of material flow across a surface. This is what we see in diffusion.

If matters were this clear, I would not hesitate to create Flux (of a vector field) and Flux (of substance), and set about trying to get the disambiguation page moved to this location. However, there are other kinds of flux that do not fall neatly into one category or the other. For instance, the fluid-mechanics definition of flux clearly deals with a material flow, but I imagine that one could (though it would be nontrivial) define a vector field which, upon integration over a surface, yield the amount of fluid passing through the surface.

So what do people think? Is this really a single article, or two articles lashed together? --Smack (talk) 04:57, 28 Mar 2005 (UTC)

I would not be as quick for splitting the article. It looks to me that all these concepts share the same idea, that of a flow through a surface, be that flow of energy or electrons (well, here I am not sure), or of liquid, or the abstract math definition with vector field. This article would indeed need more work, and some sections could (but don't have to) be made shorter and with the more in-depth stuff moved to new articles. But I would say that an article trying to show the big picture behind all those fluxes is necessary. Oleg Alexandrov 18:51, 28 Mar 2005 (UTC)

The two definitions are more related than may be apparent. The difference is not vector field vs. material flow. The distinction is between a vector field and the integral of that vector field over a surface. (Note that using the first definition the flux of material flow is in general a vector field) Some areas of science call the integral the "flux". The vector field can then be called "flux density". Other areas call the vector field the "flux". The integral could then be called the surface integral of the flux.

Worse, the usage doesn't break cleanly by subject area. In the study of electromagnetic radiation, it's common to use the first definition of flux (which makes sense, since one is really dealing with energy transport).--Srleffler 05:41, 11 November 2005 (UTC)

[edit] Entry from Pages Needing Attention

  • Flux - a haphazard jumble of vague special-case definitions
I split the special case definitions into a series of headings, and added a blanket explaination to the beginning. Flux is used so specifically in each branch that splitting it up seemed like the only way to go. I think some equations with explanations would be in order if someone has the tex skills to put them in. Starfoxy 03:07, 5 Feb 2005 (UTC)
I think the page is sufficiently improved now. The general definition of flux is better treated, with examples, analogies, and a diagram. Specialized definitions are clearly separated into their respective subjects. —RadRafe 07:40, 19 Mar 2005 (UTC)

I removed this from the physics pages needing attention. I think the article is no longer in desperate need of fixing and is really rather nice right now. Starfoxy 16:10, 30 Apr 2005 (UTC)

[edit] Definition of flux / lead para

I think this definition is starting to get muddied again by introducing a diametrically opposite statement to the first, right in the second sentence. Also I feel the term 'vector density' whilst being no doubt correct, is going to start to overload some peoples brains (like mine). Can we put vector density in braces after the words flux density? Anyway good to see youre still around Patrick.--Light current 22:28, 25 September 2005 (UTC)

Thanks. I rephrased the intro (and made various other additions and changes).--Patrick 10:15, 26 September 2005 (UTC)


I have changed the first paragraph to include very clear language stating that in Transport Phenomenon flux is implied to be per area per time, while in Electromagnetics flux is the integral of the vector field over a finite area. Neither of these definitions is "correct", and as the article now stands, the E+M definition is given the most prominent position. I would suggest reading Maxwell(1892 p.13 Treatise on Electricty and Magentism) for a very early statement that confirms the Transport definition. "In the case of fluxes, we have to take the integral, over a surface, of the flux through every element of the surface. The result of this operation is called the Surface-integral of the flux. It represents the quantity which passes through the surface." This definition is clearly not what is being presented as the primary defintion in this article. I am reorganizing this entry and adding references where I can. Thanks to all who helped add links and formatting to my text !! Luckymonkey 14:50, 14 December 2005 (UTC)

"How much stuff goes through your thing"? That doesn't seem like a very clear sentence..." --Scottbert who has yet to get a user account

It isn't very clear, but I came to wikipedia trying to understand this damn concept and that sentence was the best one I've heard - it all fell into place when I read that. I give it 2 thumbs up! 09:43, 3 November 2007 (UTC)

[edit] an archaic use in biology

Flux is also an archaic term for dysentery, but also seems to cover any extensive flow of fluid from the body, so there's bloody flux, etc.

[edit] Flux is Flux - there is only one type

There seems to be some confusion as to whether there are two types of "flux" or one. There is only one from a mathematical standpoint, the integral of a vector quantity over a surface. Of course, there are different "types of fluxes" in that the physical quanity integrated across the surface can vary but they are still the same in their core definition. The first definition in this article is the same as the second, it just uses synonyms. Someone added "Flux in this definition is a vector" -- but flux always has a direction, across the surface, and that direction is the surface normal -- which is only defined after integration as either the average surface normal or, in the case of a flat surface, the constant surface normal. (BTW I write fluid simulators for a living -- see my homepage for videos) --Ben Houston 03:02, 21 August 2006 (UTC)

Reading the discussion on this talk page has me doubting myself. I just checked Encarta's dictionary (see Encarta: Flux definition) and found only these two physics-related definitions, both of which reinforce my original belief that there is only one definition:
"3. physics rate of flow across area: the rate of flow of something such as energy, particles, or fluid volume across or onto a given area
4. physics strength of field in particular area: the strength of a field such as a magnetic or electric field acting on a particular area, equal to the area size multiplied by the component of the field acting at right angles to the area"
--Ben Houston 03:07, 21 August 2006 (UTC)

In my understanding, the first definition breaksdown into measuring the rate of transport of something across a surface and is measured in "units of something" per metre per second. Whereas, in electromagnetism the things which are called 'flux' are rarely measured in this way. For example, current density (charge flux) and magnetic flux density (?) are flux by the [unit]/m^2.s definition, but are not refered to as flux rather as density. This leads me to consider that flux in EM means something different to it's meaning in transport phenomena.

While we're at it... for me, the first two biology definitions of flux fall under the transport phenomena defintion, i.e. the rate of transport of a quantity (molecules across a cell membrane, carbon through an ecosystem) across a surface or boundary. Journeyman 04:01, 21 August 2006 (UTC)

I was wrong, I see your point. The difference seems to be related to "flux" and "net flux" (the integral of flux on a surface).
Thus I think the current definitions are exactly backwards - in physics flux is a scalar, not a vector as it is currently stated. And in electromagnetism, flux is a vector quantity since it is the physics type of flux integrated across a surface to produce a "net flux" that has direction. --Ben Houston 05:25, 21 August 2006 (UTC)
Still not sure about the vector issue. In membrane technology we don't tend to talk in terms of vectors. Yet the flux does have both quantity and direction. The direction is related to the net driving force: temperature, pressure, concentration, etc. Although this could just be considered 'sign'. I'm sure this has been resolved before, we just need the references. Journeyman 02:31, 28 August 2006 (UTC)

The flux over the surface of a sphere enclosing a charged particle is non-zero, and ‘flux’ comes from the latin for ‘flow’, so how come there is nothing flowing across the surface (there isn't - the Coulomb field of a charged particle does not flow away from it)? The point is that vector fields often represent movement, so the relevant integral does indeed give a flow (of e.g. energy, particles). But with E and B (the electric and magnetic fields) the direction at a point in the field does not represent an actual movement. It is like the steepness of a hill as opposed to, say, the blowing of the wind. So what we have are two different types of thing that vector fields represent, and so we do have a corresponding two different types of thing that the flux can represent (one with flow, one without). I do think flux is always a scalar though, since it is the surface integral of a vector field. The direction is implicit, since flux is flux over a specified surface.

[edit] why is this not in simple words

the internet is meant to be simple not confusing —Preceding unsigned comment added by VMMK (talk • contribs)

Says who? And if you want simple, I suggest not reading articles about difficult concepts. 09:45, 3 November 2007 (UTC)

[edit] References

References are indicated with superscripts in the text but do not exist at the bottom of the page. Unusual Cheese 14:38, 31 August 2007 (UTC)

[edit] This lede is terrible.

This lede is terrible. It puts me right off reading the rest (and Im an engineer) trouble is, how to rewrite --TreeSmiler (talk) 00:38, 6 January 2008 (UTC)