Talk:Energy

Tagged - summary article: rewrite required

I have added tags to the article. Currently it fails to meet what seems is its role: to be a summary article referencing detailed articles elsewhere. Instead it duplicates such information, in a way that is difficult to navigate, and attempts to resolve and reconcile the differing scientific definitions.

The introduction seeks to provide a singular definition while at the same time making it clear that such a definition does not exist. As there are different definitions for the term "energy" depending on the application/area/context, the introduction should simply state this basic fact and explain it, briefly. The first sentence of the Feynman quote provides a basis, though as the Wiki manual of style notes, quotes should not form part of an introduction.

Subsequent sections should then list the various fields concerned and, within each, briefly, elucidate the different interpretations, perspectives and uses for the term. Applying wiki style guidelines should then result in a contents box that allows and facilitates detailed navigation.

Currently the content of the article seems to me to be poorly structured. Reference to the different definitions/forms of energy appears only close to the end of the article though the fact of these are central to understanding the topic and should also inform the article's structure. Individual sections are too long, duplicating rather than summarising, succinctly, information in articles elsewhere. They also follow one another in a logic that I am unable to discern and which the content section is unable to reference hierarchically.

Overall I believe that the article could and should be substantially shortened, and that its style should be less colloquial and more concise. I can see no alternative but to completely rewriting it.

LookingGlass (talk) 15:06, 10 November 2012 (UTC)

For what it counts: I agree. --186.32.17.47 (talk) 19:45, 11 November 2012 (UTC)

"energy is a prerequisite for performing work" is the closest we've managed to get to something consise, it seems. Narssarssuaq (talk) 14:17, 12 November 2012 (UTC) High-grade energy and low-grade energy could be useful terms in order to distinguish further, but they don't even have an article. Narssarssuaq (talk) 14:19, 12 November 2012 (UTC)

I have come to this article after re-writes of several ionising radiation articles, which were in a similar state of confusion, with truncated comments, non-sequiters, lack of relevant information, plainly incorrect statements, poor readability, etc, in order to give a good link for energy of particles. The lead section would put off any "lay" reader, and needs a complete -rewrite and re-structure. I agree it must rely on linked articles to cover the specialist aspects of energy; the subject is too big for one article, and that is the problem. Where to start? I think the lead section could be sorted out as a short term measure, so that readers don't click away after 10 seconds.Dougsim (talk) 09:46, 27 December 2012 (UTC)

FWIW: Energy is not a physical unit. It is a philosophical concept and an accounting technique used to analyze mechanical exchanges. In nuclear physics it is defined as a color of light, in biology it is a synonym for metabolism, and in public utilities they say energy when they mean connectivity. Energy is not at all a synonym for power or work, even though a great many people think it is both those. The definition sometimes offered is "capacity to do work." Well, work is defined as disordering of energy, so then energy is "capacity to do disordering of energy", which is a circular definition. Sloppy use of this term is rampant. Jewels Vern (talk) 12:54, 10 October 2013 (UTC)

Maybe you could talk to my electric power company. They're under the mistaken impression that the "kilowatt-hours" I'm using are actually energy, and they are charging me for it. I tried to tell them that their electricity was really increasing the entropy and disorder in the neighborhood and therefore they needed to send around a crew to clean up, but they didn't listen. Typical ignorant socialist utility bureaucrats. --Chetvorno^TALK 13:42, 10 October 2013 (UTC)some thing on people is gay thar are a lot of paeple gay

Lead section

After having moved much material out of the lead section, and tidying up the body of the article, it was evident the lead section was still repeating detail which occurs later. I have reduced it to a minimum and have made the point that this is a summary article. The subject is far too big to explore in one article. Consequently the lead should be a summary of that summary, so it should be minimalist and help the reader to understand the purpose of the article.

History has been clarified a bit further but needs to remain prominent, as a fundamental concept is the complexity of energy and the time it took science to start understanding it.

Forms of energy are very important as this start the reader in exploring the subject. Each main article explored will explain energy in its particular context.Dougsim (talk) 09:47, 11 January 2013 (UTC)

Ok, it's definitely shorter; but now the article doesn't say what energy is, and doesn't even provide a Lie to children as a clue on where to start out. So there's nothing to grasp or work with, and I can't actually learn anything from it consequently :-/. At the moment the first revision - while perhaps slightly less accurate- is infinitely more useful as an encyclopedia article, because it gives one something to work with. <scratches head>

I guess we may have trimmed just a little too much ;-). What would be safe to re-add or rephrase and re-add? --Kim Bruning (talk) 19:20, 29 January 2013 (UTC)

The info you you are looking for is now in the third lede paragraph. I suggest moving it up front, getting rid of the Feynman quote, then adding a paragraph about energy's tricky relationship to mass. The present first paragraph makes a fine one to END a lede with , not start one. SBHarris 20:22, 29 January 2013 (UTC)

---

Thank you for pointing out the definition in the original revision; which actually does mean something. From a limited trawl though revisions/talk I think the "work" word got discredited, because energy does not always do work in the sense of classical mechanics, and it got lost in the swamp of academic equivocation. So I'm making a suggestion here, which gets rid of the hair splitting and qualifies the definition:

Energy is the ability of one object to affect another object, and the concept is of fundamental importance in natural science.

The natural basic units of measurement are those used for mechanical work; such as an equivalence to a unit of force multiplied by a unit of distance through which the force operates, or mass times velocity squared.

Energy comes in numerous forms, such as kinetic energy, potential energy, radiant energy, and many others; which are listed in this summary article. The question "what is energy?" is complex to answer in a simple, intuitive way, because so many forms exist. It is simpler to consider each form of energy separately. Consequently, this article gives an overview of its major aspects, and provides links to the many specific articles about energy in its different forms and contexts.

Dougsim (talk) 14:08, 21 February 2013 (UTC)

I share the concern that the introduction is incomplete. The current introduction is a perfect example of a common problem on WP; the definition in the lead gets expanded to be more technical and inclusive until it becomes too abstract to be understandable or even, as in this article, fails to define the term at all. This is a serious problem because the introduction is the part that non-technically-educated people will read. The majority of readers to this page will probably be unscientific people who want the simplest possible definition of what energy is (think primary school students writing a paper). The virtually content-free gobbledygook introduction will discourage them from reading further. --Chetvorno^TALK 04:31, 24 June 2013 (UTC)

This article should follow the example of other general-purpose encyclopedias and lead with a definition that is a compromise between the messy truth and lies-to-children. Although the intro should summarize the subject in all its complexity, it doesn't have to lead off with the most complicated definition, it can progressively expand on a simple definition. In most fields of science and engineering, most forms of energy are perfectly well-defined quantities. I understand the problems of ultimately defining energy in physics expressed on this talk page and in the Feynman quotes, and this should be mentioned in the introduction, but it doesn't have to be the only thing in the introduction.--Chetvorno^TALK 04:31, 24 June 2013 (UTC)

I suggest that the intro be structured on a principle of increasing abstraction. It should lead with a simple definition (e.g. Although it is difficult to give a general definition of energy because of its many different forms, it can be most simply defined as the ability to perform work.). It should go on to kinetic and potential energy, and that heat is a form of kinetic energy caused by the motion of molecules (I know, a simplification). One thing that should definitely be in the intro is that the reason energy is important is because of conservation of energy; energy cannot be created or destroyed but only changed in form; it is a function of a system or the universe which is constant with time. Then, moving to a higher level of abstraction, add that mass and energy can be converted into one another, so in atomic physics energy and mass are considered different aspects of the same quantity, mass-energy. The last paragraph can mention the cosmological difficulties of defining energy and include the Feynman quote, if desired. --Chetvorno^TALK 04:31, 24 June 2013 (UTC)

I think this has merit. It is important to make simple definite statements at the beginning. Abstraction can follow. Let's work on this. Dougsim (talk) 11:14, 27 June 2013 (UTC)

Since it was in such a bad state, decided to WP:BE BOLD and rewrite introduction. Just a first bite, go ahead and improve it. --Chetvorno^TALK 13:29, 19 July 2013 (UTC)

I've just spotted this re-write - a big step in the right direction. This article comes up first on UK Google when you put "energy" in; only to find a very weak lead which told you nothing. It was in a bad state, inspiration was lacking, and I think this will help a lot of readers. Dougsim (talk) 19:21, 30 July 2013 (UTC)

I added Chetvorno's suggestion in the lead section, first paragraph. It is crucial for non-technical readers to get a grasp of what the concept means before becoming too technical. Please discuss before reverting. --dionyziz (talk) 13:07, 28 February 2014 (UTC)

Feynman's unhelpful quote in the lead/lede

Feynman saying "we have no knowledge what energy is," is very philosophical but not very helpful. I'm as much an admirer of Feynman as anybody, but in this case, I think this kind of thing, without qualification, is "philos-awful-gul," to use Feynman's own term.

Here's the problem: one can technically say that we don't "have knowledge" even of what velocity or speed is. Sure, they're defined as ratios of space and time, but do we know what space is? What time is? At some point (as Feynman himself again said somewhere-- I think when talking about magnetic fields) explanations have to stop, as we've hit a place where the things we're talking about are so simple and primal that we don't understand them in terms of simpler, more primal, or more familiar things. So we understand velocity in terms of space and time, but don't understand space and time in terms of something simpler. If we add mass as a fundamental, now we understand force. Or perhaps we all have an understanding of force as a primal, as we all experience a push somewhat directly (or at least as directly as we experience space, and certainly more directly than we experience time!). And with mass, we can now define momentum, angular momentum, and energy. We "have knowledge" of what all these are, at that level. But no knowledge of what any of them are, if you insist on primal knowlege of "fundamental" units of mass, length, and time.

So let's put Feynman's quote someplace else, as it's mucking up the lede in a way we'd never tolerate in an article on force or momentum or mass! Poor energy deserves no worse treatment, or to be cloaked in more mystery than momentum, angular momentum-- or even force or velocity. Energy units are force*distance or mass*velocity^2, or mass*distance^2/time^2. All are equally correct and can all go in the lede (I did put one in, and I think I'll add the others per WP:BOLD). That is the extent to which we understand "energy." Perhaps we don't fundamentally understand the other things in its definition (mass, force, space, time), but that problem is not a problem we should tackle in a lede. I'll leave you all to comment on Feynman's quote staying up front. SBHarris 22:07, 22 January 2013 (UTC)

I have the same unease about the Feynman quote - it doesn't seem right to have it there, but I haven't touched it as I think it useful to have an indication of the elusive nature of energy, but I think it can be done better. Dougsim (talk) 16:47, 23 January 2013 (UTC)

Do you think energy is more elusive than, say, angular momentum? Or even linear momentum? SBHarris 19:02, 23 January 2013 (UTC)

Elusive in terms of being able to define it quite easily - I think yes. Both those quantities you mention have a fairly simple definition. There doesn't seem to be anyone coming forward with a definition of energy. When we get that, then perhaps Feynman can be put elsewhere. Perhaps the definition of energy is specific to its form, and that's what we should say? Dougsim (talk) 21:19, 28 January 2013 (UTC)

Momentum is gamma*mv and energy is gamma*mc^2. Each is simple to define but a bit opaque in meaning. Those definitions hold for massive particles. For massless ones you have p=E /c and E = pc. Are you going to claim advantage there?? SBHarris 21:42, 28 January 2013 (UTC)

Angular Momentum is what's left of the kinetic energy of a rotating body when the motion is restricted by either an internal or external point of rotation. And the kinetic energy of motion is the integral sum of the v^2/2 values of the constituents of the body. So energy is either matter and motion or else potential matter and motion.WFPM (talk) 23:12, 28 January 2013 (UTC)

Kinetic energy is not 1/2 mv^2 -- that's the low velocities approximation. It's actually (gamma-1)mc^2, which at low velocities reduces to 1/2vc^2. Total energy E is gamma mc^2, which at low velocies of course reduces to E = mc^2 + 1/2 mv^2. SBHarris 02:42, 29 January 2013 (UTC)

Well Maxwell didn't have E = mc^2 in the 9th EB about the atom. But he points out that although we don't know what energy is, we recognize it by what occurs as matter changes its relative position in space. If space gives it more energy, then it's a system of attraction and vice versa. But I don't think he would have gone along with this concept about energy without matter.WFPM (talk) 03:31, 29 January 2013 (UTC)

An EM wave carries energy without matter. Maxwell knew that. In fact the equation E = pc for light can be used to derive much of special relativity including E = mc^2 for matter. Einstein started with Maxwell, whose equations already have relativity built into them. The trick is showing how . SBHarris 09:37, 29 January 2013 (UTC)

Well okay? But I'm stuck with how our wavefront images of the Whirlpool galaxy can carry all the individual starlight emission details (plus obscuration factor and more distant details) to our point of view. I'm not arguing with the wavefront as a non material conceptual entity, but rather with how it is able to maintain the correct location of the details appropriate for any location of view. I can understand how this can be done with each star contributing directly to my point of view but not by the movement of a modulated wavefront.WFPM (talk) 18:21, 29 January 2013 (UTC) And I haven't looked up Parallax in Wikipedia, but I'm sure that there will be a discussion about each star's ability to alter its position to the point of view of each person's view of the astronomical image.WFPM (talk) 22:27, 29 January 2013 (UTC)So it would appear to me that when I look up into the hemisphere of night starlight from the stars that I am looking at light energy that is coming into the pupil of my eye from every direction of my hemisphere of view.WFPM (talk) 19:36, 31 January 2013 (UTC)

First Law of Thermodynamics

Equation: |$\Delta {}E=W$| Would contradict the First Law of Thermodynamics. Whenever energy is used to produce work a certain ammount of heat is generated. |$\Delta {}E=Q$| _may_ be true since energy can completely be transfered as work but if energy is used to do _work_ some heat is going to be generated _always_ The second law of thermodynamics goes on to establish relations regarding the ammount of heat that _must_ _at_least_ be released, defining the function of state "Entropy"... --Crio (talk) 00:38, 24 January 2013 (UTC)

I agree that delta E equals W, and delta E equals Q, are both inappropriate equations for an encyclopedia. They may be true in special circumstances, but they appear in Wikipedia as general truths and neither of them is a general truth. The First Law of Thermodynamics is a general truth and is usually presented as:

Q - W = delta U where U is internal energy.

If no-one gets to it before me, I will visit this article within the next few days and do some fine-tuning. Dolphin (t) 05:18, 26 February 2013 (UTC)

Okay, say a mass is falling through the vacuum of space due to the action of gravity. We have an energy conversion process. How does it follow that heat has to be generated?WFPM (talk) 20:32, 3 March 2013 (UTC)

British or American English

There is presently a discussion at Talk:Work (physics) about whether that article should be based on British English, or American English. One of the considerations is that this article, Energy, uses British English. I say this because it uses the spelling metre rather than meter. (The only application of the spelling meter is in longer words such as thermometer.) For this reason, I have added the "British English" banner at the top of this Talk page. Dolphin (t) 23:30, 27 March 2013 (UTC)

... although energy can be rigorously defined in theoretical physics

Suggest this be changed to "although energy is defined mathematically in ordinary physics, chemistry, and other sciences in an interrelated and coherent way as a rate of change of forces and is commonly defined as 'the ability to do work' ". Current text casts this vital rational concept which any ordinary person can understand as an esoteric and iffy epiphenomenon spun by some priesthood. 76.180.168.166 (talk) 20:32, 15 June 2013 (UTC)

Orders of magnitude

Why is "Orders of magnitude (energy)" not linked in "See Also"? — Preceding unsigned comment added by 97.115.149.126 (talk) 02:25, 19 July 2013 (UTC)

Done. Reatlas (talk) 02:49, 20 July 2013 (UTC)

trying to make the lead more consistent, accessible, & self-contained, per much of talk page in past year.

Although it has been improved a lot, the lead is still too long, inconsistent, inaccessible, and dependent on understanding terms that are only defined elsewhere.

You'll see I'm taking a bold shot at starting (2013-10-10) to improve its first couple of paragraphs of the lead, with the goal of eventually dealing with the rest of it and shortening the lead considerably.

I humbly request that you not revert it unless you feel that it is unsalvageably-worse than what we had before. I'm pretty sure we can make some compromises and reach consensus.

I didn't change the first sentence of the lede because I think it needs more discussion first, but I tried to at least make it more accessible by going on to state briefly what conserved and extensive mean!

Energy does have some universal meaning and is not simply an umbrella category for a collection of definitions of various disparate quantities or concepts in various fields (as some seem to have have alluded here). You can't just invent/discover a new form of "energy" unless it's consistent with this meaning/definition. Specifically, it has to be convertible, at least in principle, at least from some other form of energy such as mechanical energy (which can itself be defined independently), and must not break (in fact is often necessitated by) conservation of total energy.

I'm open to switching from a term like "definition" to a term like "partial definition" or "necessary conditions" or "universal aspects" of energy, etc.

As is already mentioned later, not all forms of energy can be completely converted to mechanical energy because of 2nd law of thermo, so I've said "to or from" instead of just "to". But I also mentioned "subject to other physical laws". Other editors may feel that it isn't necessary to do both (in the lede).

I tried to specify "mechanical work" because thermodynamic work is defined somewhat differently, but perhaps this is unnecessary here.

Work is not a form of energy (nor a property of a system) that other forms can be converted "to" or "from", but rather a [property of] a [type of] process in which a given amount of energy is transferred, or converted among forms such as mechanical energy (whether kinetic or potential).

BTW, another universal aspect of energy (completely independent of what form of energy it is), is that it contributes a proportionate amount of mass to a system, which is, in principle, measureable by the increase in its inertia. This is already mentioned later in the lede. Thus, a a given property of a system is in fact a form of energy if and only if it contributes a corresponding amount of inertia to the system. This could perhaps be used as a universal definition of energy, but it isn't (yet) customary to do so.

DavRosen (talk) 16:52, 10 October 2013 (UTC)

Split out detailed parts of lede to become a new first body section

As was pointed out by others above, the lede keeps getting expanded with too many details (I may be guilty of a bit of that myself :-). On the other hand, the body of the article currently launches into a "laundry list" Forms of energy section without first saying anything at all about energy in general (presumably because so much has been said in the lede).

So I'm thinking to create a new first non-lede body section (appearing after TOC & before Forms of energy) to state the current understanding of what energy is, which is a more fundamental topic than a list of known forms of energy (or even than the history of our understanding). This section could have any number of possible names such as (depending partly on what we end up putting in this section of course):

• The concept of energy
• Energy concepts and measurement
• The nature of energy
• {edit} Energy and related concepts
• Approaches to defining energy
• What is energy? {but is this an un-encyclopaedic tone?}
• What energy means and what it doesn't
• Energy measurement and criteria for discovering new forms
• Characteristics common to all forms of energy
• Current understanding of energy
• Characterising and measuring energy
• General characteristics of energy
• ...or others...

That way we can keep in the lede only a summary that the general reader can digest without further reading.

DavRosen (talk) 14:21, 15 October 2013 (UTC)

I've simplified some the lede (esp early parts) in preparation for possibly cutting it down and moving stuff into a new body section. Removed some details that could be re-added into a new section.

(-1,028)‎ . . (lede 1st para more self-containd. My "mech. E" back to emph. work (&heat) as processes. Remvd "Energy is nec. for ... change" & "reason for importance" in favor of final para. Use "transform" since "convert" can refer to units conversion. Remov redund)

DavRosen (talk) 21:49, 15 October 2013 (UTC)

You should do this, it has just got into a slab of text. I had a cleanup of information a while ago and marshaled a lot of disparate information to new headings and cut down the lead section.

There's also some odd stuff at the end about phonons with a 4 year old notice on it. Does this section belong in this article? No citations.

The section on measurement seems to be a great survivor, but it looks rather sad and I suggest should be removed. Measurement is covered in many other places and is implicit in much of the other text anyway.Dougsim (talk) 17:44, 2 March 2014 (UTC)

lede lacking a simple definition understandable by a high school student

User Dionyziz made some good points on my talk page after I undid his try at addressing the issue:

Hi Dav. I saw you reverted my changes on the energy article in which I modified the lead section to include a different definition. Thanks for helping improve wikipedia! I find the current lead section lacks a definition; when read, the beginning of the article doesn't really say anything to non-technical readers. I understand your objection for technical inaccuracy reasons, but these are adequately addressed in the rest of the article, as discussed in the article's talk page. In which way do you think we can have a lead section which allows readers such as high-school students to get an understanding of what energy is without requiring them to understand all the mathematical jargon of physics? Thank you for your time and attention. --dionyziz (talk) 00:58, 1 March 2014 (UTC).

I actually agree with Dionyziz that something simpler should be added that a nontechnical reader can easily grasp. In the previous talk section just above I also proposed moving moving much of the lede material down into the body and leaving a simpler lede -- but I haven't found time to work on this myself.

I don't think we should get too hung up on stating energy's 'definition' per se, as these are always problematic and ultimately misleading because they elevate one form of energy (or one type of energy conversion/transfer process like work) as being uniquely "defining" of energy and in terms of which the other forms must be defined. Rather, let's explain what its most important characteristics are and why it's useful, with familiar concrete examples of its forms or processes. There's a misconception that energy is just an umbrella term for a bunch of types that have been defined separately or by convention in various fields, as if energy could be simply redefined to include or exclude some types. So it's important not to just give a laundry list. Fundamental characteristics of energy include its conservation, interconvertibility, additivity, etc.

DavRosen (talk) 20:57, 1 March 2014 (UTC)

I think the current opening sentence you put in place is the best yet.

"In physics, energy is a property of objects, transferrable among them by fundamental interactions, and which can be converted in form but not created or destroyed."

There's a couple grammatical mistakes, but it seems clearer than the one I put up a few days ago. I'm all for keeping it. I concur with what you said about lede length. WP:Lead recommends 3-4 paragraphs for an article of this size. Energy currently has 6. Forbes72 (talk) 02:57, 8 April 2014 (UTC)

I understand why Forbes72/you removed the "and" in that first sentence of the lede, changing the above boxed sentence to:

In physics, energy is a property of objects, transferable among them via fundamental interactions, which can be converted in form but not created or destroyed.

But, without the "and", the "which" becomes ambiguous in that it could refer to the interactions (or possibly even the objects?) rather than the energy. The "and" made it clear that this is a second statement about energy. And perhaps worse, without the "and" the meaning depends critically on the reader paying attention to the comma before "which", since without that comma, the "which" would clearly refer to the interactions.

Wouldn't the "and" make sense in the following (technically the comma isn't needed but I thought it made the sentence easier to parse), and if so, then why not in the above?

In physics, energy is a property of objects, transferrable among them by fundamental interactions, and convertible to different forms but not creatable or destroyable.

(I'm not actually proposing this last example or the words creatable or destroyable -- it's just to explore the use of the "and".)

Or, in case I'm being a grammatical Neanderthal (or American anyway, although at least I did remember to use "metre"), this could be another way to avoid the incorrect interpretation of "which" (in this case by the singular "it" being incompatible with "interactions" or "objects"):

In physics, energy is a property of objects, transferrable among them by fundamental interactions; it can be converted in form but not created or destroyed.

(Or just turn the above into two sentences, the second beginning with "Energy")

Or this, where the "and" becomes necessary because it is the second "which" that refers to energy (again I find that the comma before "and" makes the sentence easier to read):

In physics, energy is a property of objects which is transferrable among them by fundamental interactions, and which can be converted in form but not created or destroyed.

One problem with this last version is that google will probably truncate it before the word "created", leaving it a bit incomplete for the googlers except for the fraction of them that click and read further. I know that's not an official WP editing principle but I thought I'd mention it :-)

DavRosen (talk) 05:57, 8 April 2014 (UTC)

Or should we begin by relating energy to work and heat?

To play the devil's advocate, before we wordsmith "and"...

Wouldn't it be more useful/usable to the avg reader to relate energy to work and heat before discussing the more-abstract underlying fundamental forces?

Just for a starting example (links omitted):

1. In physics, energy is a property of objects which is transferrable by work and heating and which can be converted in form but not created or destroyed. Energy arises in the fundamental interactions of nature.
2. In physics, energy is a property of a system; work and heating can transfer it or change its form but not create or destroy it. Energy arises in the fundamental interactions of nature.

Note that these are true statements but not definitional of energy, and especially not defining it exclusively in terms of work like some sources do. It does not say that only work and heating can transfer it.

DavRosen (talk) 14:45, 8 April 2014 (UTC)

To be honest, I didn't expect the "and" to be a deliberate decision. I thought it was just a grammar mistake, which is I marked the edit "minor".(I removed the second "r" in transferrable as well) If you think it's better with an "and" , I'm all in favor. My main concern is that we avoid the extremely broad definition we had before:

In physics, energy is one of the basic quantitative properties describing a physical system or object's state.

To quote a textbook author I came across:

A modern definition of energy, then must be based on both the first and second laws of thermodynamics. Anything less falsifies the picture.

www.loreto.unican.es/Carpeta2012/TPT%28Lehrman%29WorkEnergy.pdf

I don't want to tear apart every contraction and punctuation. I think the opening clause should mention conservation, and probably energy transfer. The details matter to me a lot less. #2 seems awkward, but the current definition with "and" or #1 are both fine. Forbes72 (talk) 20:33, 8 April 2014 (UTC)

Great article reference! Maybe we should start with its title: "Energy is not the ability to do work" :-) In any case, mentioning both heat and work in the first sentence (as in #1. above) at least tries to satisfy Lehrman's criteria of bringing in the 2nd law as well.
Now to play the "angel's advocate", I'm asking myself, how exactly does kinetic energy (or the energy-momentum four-vector for that matter) "arise in the fundamental interactions"?
DavRosen (talk) 21:30, 8 April 2014 (UTC)

On the other hand, in that article the author admits that all 12 HS textbooks he looked at start by defining energy as "the ability to do work". Maybe we ought to take that approach, considering that those books are written by experts for approximately the level of readers that this article's introduction should be aimed at. --Chetvorno^TALK 22:34, 8 April 2014 (UTC)

Is there anything wrong with mentioning heat as well? Regardless of what textbooks may have said in 1973, the modern concept of energy arose from the fusion of heat and work. All those textbooks presumably discussed heat as well, just maybe not in the same sentence. They don't actually use ability to do work as as the definition of energy, in that they don't claim that one can measure the energy of a system (in general) by how much work you can do with it. Also we already have an article on Exergy (Available Energy) which basically defines it as the ability to do work, so how can these both be correct? Those textbooks probably don't have a section on exergy so they don't have that problem. I doubt that most HS textbooks today (or college Physics-for-humanities-students textbooks) uncritically define (the amount of) energy as the (amount of) work that can be done. What some of the other-language WP's do is to mention the ability-to-do-work as an often-used simplification, but not to claim that it is an adequate definition of energy in itself. Anyway, most of the knowledge in WP doesn't appear in any HS textbook, so that can't be our standard in general.
DavRosen (talk) 22:57, 8 April 2014 (UTC)

I got caught up in this "definition" discussion, but perhaps more to the point, we aren't attempting to give a definition of energy in that first sentence, nor are we required to do so. We are stating some of the most notable (but hopefully understandable) characteristics of energy; the characteristics themselves aren't in dispute (I hope) so the only question is whether/where/how to state them:

1. Energy is a property of an object
2. Energy can be transferred by the act of work
3. Energy can be transferred by the act of heating
4. Energy can change in form
5. Energy can't be created or destroyed

If those aren't the most notable characteristics of energy, or if they aren't understandable enough to be mentioned so early, then let's discuss alternatives.
DavRosen (talk) 00:27, 9 April 2014 (UTC), edited 00:48, 9 April 2014 (UTC)

Oh, I see what I may be missing in your point: an important characteristic of energy is that it provides the ability to do something. How about something like (still omitting the links):

In physics, every object has an amount of energy, enabling it to do work or heat other objects, transforming or transferring (but never creating or destroying) some of that energy.

DavRosen (talk) 01:55, 9 April 2014 (UTC)