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There are already several terms I know to denote surfaces on which a certain quantity is constant:

  • equipotential surface: a surface of equal potential energy
  • isobaric surface: a surface of equal pressure

How would I denote a surface of equal energy without falling back on equi-energy surface?

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If you know isobaric, what's wrong with isothermic? Voting to close as general reference. – FumbleFingers Jan 1 '12 at 17:19
I need a more general term, isothermic to me denotes surfaces with equal temperature, energy can come in other forms than temperature (I'm working on quantum mechanic energy densities). Why exactly are you voting to close? I haven't really read the term for this stack site, but since the single-word-requests tag exist I thought I could request a single word no? – romeovs Jan 1 '12 at 17:23
Yeah, I think this is a perfectly good question. Isothermic means something completely different from what the OP is looking for, and the answer doesn't seem that easily searchable. – alcas Jan 1 '12 at 17:46
I'm no physicist, but I thought "heat" and "energy" were effectively equivalent at the technical level. Anyway, if OP wants an even more specialised term then I'd still have voted to close on the grounds that it's "too localised". We can "invent" terminology here, but if this concept is consistently meaningfu to specialists they probably already have their own word - which I don't think ELU should be concerned with identifying. – FumbleFingers Jan 1 '12 at 18:07
Heat is just another form of energy. Magneteic energy, for example, has nothing to do with temperature, and although all forms of energy can be changed into one another, I would feel awkward if talking about isothermic surfaces when the subject is on magnetic energy – romeovs Jan 1 '12 at 21:56
up vote 6 down vote accepted

Wiktionary lists isoenergetic as "Having the same, or constant, energy". You might peripherally introduce a definition, e.g. "... the diagram illustrates quantum-mechanical energy isosurfaces, or isoenergy surfaces ...".

The terms isoline and isosurface are used generically for 2D and 3D equal-quantity cases, respectively. After a phrase like "... the diagram illustrates quantum-mechanical energy isosurfaces ..." has introduced your terminology, references thereafter to isosurfaces would be understood as isoenergetic surfaces.

If only certain units of energy are used in the particular problem, tack iso on the front and see if it works. That seems to be what was done for isobel.

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Look up the etymology of energy. It's Greek: ἐνέργεια. The rule is to use a Greek prefix with a Greek root, so you want Gk iso- rather than Latin equi- to mean "equal".

Putting iso- and energeia together and adding a little ordinary derivational morphology gives isoenergetic, which should work in context.

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Thanks very helpful post. – romeovs Jan 1 '12 at 21:53
+1 for the rationale. – Kris Jan 2 '12 at 11:24

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