Talk:Energy (science)

Name?

If the distinction is between energy as discussed in physics and as discussed in psychology, then the former should not be titled energy (science), but energy (physics), since many people consider psychology, too, to be a science. I don't know that psychologists discuss energy under that title... Another obvious sense is energy in the sense of oil, solar, nuclear, etc. ...

And weren't we preferring to redirect energy to energy (disambiguation)? Just curious, maybe not. --Larry Sanger 07:49, 22 May 2008 (CDT)

Larry, there are more sciences than physics that use the concept energy. Personally, I don't see psychology as a science (my late father, who was a psychologist, agreed with me on this). In any case, in psychology (science or not), energy has a completely different meaning than in physics, chemistry, engineering, biology, and so on. For one, energy (psychology) is not measurable, i.e., cannot be expressed in joule (or do you say to mrs. Sanger in the morning: "I have 10 kJ today and will write a nice blog and do some other work, whereas yesterday I had only 0.1 kJ and didn't get much done")?--Paul Wormer 08:40, 22 May 2008 (CDT)

I think there are good arguments both ways. Physics is certain the field in which energy is defined, although others (e.g. chemistry) make use of it.

I don't really have any strong feelings one way or the other about the best name - I would only ask people that we discuss potential new names before we start moving articles around; since cluster moves are not (yet) automated (although I've just found some stuff that may enable us to make it easier), moving from name to name is a pain.

As to the correct target for the redirect at energy (whether to go here, or the dab page) - it's not that important, frankly. As long as there's a redir there, and all articles which reference this concept eventually get linked directly here, that's all that matters. I think most links to the name energy do mean this one, so it's probably reasonable to go here. J. Noel Chiappa 09:54, 22 May 2008 (CDT)

I do not claim that psychology is or is not a science: it depends on how one defines the key terms, of course, and the position one takes on the question probably reflects personal philosophical biases more than anything more interesting. But CZ is neutral, and there are many people who insist that psychology (or the experimental parts of it) is a science. Hence, to use energy (science) and distinguish that from energy (psychology) is to take a stance with which many well-informed people will disagree, and a stance we are not forced to take. So I'd like to ask someone to change this. How to change it, I leave up to you. I'm sure there are many suitable alternatives, if you are creative.

This is a style of thinking and dispute-resolution that I hope we can get more into the habit of using...it's not particularly difficult or subtle, but it will help us in the long run to keep a smoothly-running community, as well as a resource that scholars of all sorts can respect. --Larry Sanger 10:19, 22 May 2008 (CDT)

I chose the name "Energy (science)" because the then article "Energy" did not only deal with the physical but also the chemical aspects of the topic. This was not meant as an offense to the field of psychology (which can be viewed either way, I agree) but also as a reminder that further restructuring might be necessary, since most people would find the term "Energy (science)" odd and prefer something like "Kinetic energy", "Chemical energy" and "Nuclear energy" instead. The question for me is now whether we keep these notions all in one article or split it up. I would prefer the latter, though the current preamble at "Energy" might well be extended a bit. -- Daniel Mietchen 05:20, 28 May 2008 (CDT)

Update: A related discussion on article naming is here. -- Daniel Mietchen 05:02, 29 May 2008 (CDT)

Comment deleted?

I seem to recall that I wrote a comment on this talk page when I started the article "energy". It was something like: Large subject, with many angles, science, economy, politics, etc., important that there is at least something, that is why I start. Also I seem to remember that I got some comments, as usual, that my writing was too difficult. Do I just imagine this, or did the talk page get lost?--Paul Wormer 10:12, 22 May 2008 (CDT)

Are you sure it was not on a different page? I see no sign of a comment similar to that here or on Talk:Energy. Chris Day 10:21, 22 May 2008 (CDT)

Umm, this is the old Talk:Energy - check the history. It got moved here. Talk:Energy is just a redir that got created when the article was moved here.

But yeah, could have been somewhere else - the history of this one goes back a ways. J. Noel Chiappa 10:32, 22 May 2008 (CDT)

To Chris and Noel: No I'm not sure. In the meantime I found the comment about its degree of difficulty (by Anthony.Sebastian) on my own talk page. This other comment may be something I thought of writing, but never did. Anyway, in the article I only touched the surface of the iceberg that is "energy", there is much more to say about it, also from the point of biology, world politics (oil is now $132/barrel), and so on. --Paul Wormer 10:39, 22 May 2008 (CDT)

To Larry: I did not make the move from "energy" to "energy (science)", but I don't mind it either. A little bit flippant I wanted to explain to you that the concept energy, as in "energetic person", does not have anything to do with the concept in science. And I agree that much more must be written about all aspects of energy.--Paul Wormer 10:39, 22 May 2008 (CDT)

Your point about the lack of relationship between "energy" as used in physics, e.g., and as used colloquially about talking about human motivation, was perfectly obvious. My objection is not really to energy (science) but to the juxtaposition of that title with energy (psychology). That implies that psychology is not a science, which is a position we need not take.

We can solve this problem handily by simply not planning to have an article about "energy" as used in psychology (though we might, less confusingly, have an article titled energy psychology, which--I'm scanning Google--looks like some sort of therapeutic technique).

This also does not solve the other and more interesting problem, described below--what articles will we have, related to energy? I think that's the question we really need to be tackling. --Larry Sanger 08:45, 6 June 2008 (CDT)

As the "psychology as science or not" discussion is just eating away energy here, I put it off the disambiguation list for the time being. It had just come there as one example that energy is not only used in one sense. Now, this placeholder function is taken over by Energy (politics). -- Daniel Mietchen 09:43, 6 June 2008 (CDT)

What articles on energy should exist?

I doubt anyone deliberately deleted the comment (that's not the sort of thing we do!); but I don't know where it is.

But you raised a good point anyway that needs to be thought about here. Perhaps there should be a general article about energy that covers the various things that people say about it--at least as to engineering and power generation, economics, politics and geography, and policy. I suspect that those topics are closely enough related that it would be useful to have an article about that, e.g.: energy (social aspects). Then the distinction could be made between that and energy (physical aspects) (if you don't like "physics"), which concerns the physical, chemical, etc., aspects of the topic. As to psychological aspects, probably energy (psychology) would be best redirected to motivation or motivation (psychology). --Larry Sanger 10:36, 22 May 2008 (CDT)

Definition and introduction

Both the definition of energy and the introductory paragraph of the article leave much to be desired. There are many measurable properties of a system, and the definition doesn't explain which property is "energy". The introductory paragraph describes some manifestations of energy, but doesn't say what it is that those manifestations have in common.

If I knew how to state the definition well, I'd do so, but my introductory physics textbooks are at home and I'm at work; and my pride prevents me from looking it up on Wikipedia. Anthony Argyriou 12:53, 24 June 2008 (CDT)

Anthony, I'm curious to see what you will write, but don't underestimate the difficulty of defining energy. For instance, the definition of Chambers: "The capacity of a body for doing work" is much too limited. An iceberg floating in the ocean has lots of energy of all kinds (potential, thermal, even nuclear), yet it is hard to see how this particular body may do work. When one hears "Saudi Arabia must increase its energy production" (as I did on the news after I finished the first part of this message), I don't believe that "Saudi Arabia must produce more bodies capable of doing work" is a striking alternative. So, please give the intro a fresh try and make an attempt to write a conclusive definition of energy. But, don't be surprised when it turns out that I will have problems with your definition.

I'm not too proud to have peek at our large neighbor, their first two sentences are in essence:

In physics and other sciences, energy is a scalar physical quantity that is a property of objects and systems which is conserved by nature. Energy is often defined as the ability to do work.

Comments:

1. "scalar physical quantity that is a property of objects and systems" is not far from "measurable property of a physical or chemical system" (my writing); the more so if one knows that only scalar quantities are directly measurable.
2. "Energy is often defined as the ability to do work" can be compared with "Roughly speaking, the energy of a system is a measure of the amount of work that the system is able to perform on its environment" (my writing).

--Paul Wormer 13:34, 24 June 2008 (CDT) and --Paul Wormer 02:39, 25 June 2008 (CDT)

Well, I hope we can do better than our large neighbor. Poking around a little, I find that the definition seems to be somewhat circular - energy is the ability to do work, work is the transfer of energy. Apparently, Richard Feynman said that there was no consistent non-circular definition of energy, though I can't find a good source for that quote. If nothing else, I'd like to put the "scalar property of a system" after "ability to do work" - there are many scalar properties of systems which aren't energy, and "a scalar property of a system" doesn't actually give any clue as to what sort of property one is talking about. Anthony Argyriou 13:42, 25 June 2008 (CDT)

The circularity is one thing (in classical mechanics work is force times path; no circularity there), but my reference to the iceberg points to another problem. From the second law of thermodynamics follows that not all energy is convertible to work. If it were we wouldn't have an "energy crisis".--Paul Wormer 03:03, 26 June 2008 (CDT)

I spent some time looking at the problem, and people who ought to know say that it's hard or impossible to define "energy" in one particular way; the best is to offer a catalogue of types of energy. It appears to me that most energy is either potential energy or kinetic energy, but that excludes relativistic mass-energy and EM radiation (and gravitational radiation, too?), and perhaps other forms, also. Hmm - here's a proposed intro paragraph:

Energy is a scalar property of physical systems, measured in units with dimensions M⋅L²⋅T^-2. Energy occurs in several forms; these are potential energy, kinetic energy, electromagnetic radiation, and, according to Einstein's special relativity, mass-energy. Some forms of kinetic energy (such as thermal energy) are often treated separately, because of the historic circumstances of their discovery, and for convenience. One fundamental law of physics is that energy is conserved - it can change in form, but the total energy of a closed system cannot change, and the energy coming into an open system must equal the energy leaving the system.

The dimensions of energy correspond to the application of a force over a distance. Potential energy represents the potential for this to occur, as in the potential of an object to fall in a gravitational field, where the potential is for the force of gravity to be applied to the object over the distance which in can fall. Kinetic energy is the energy of motion, and is equal to ½mv², where m is the mass of the object, and v is the velocity. Special relativity shows that mass can be converted to energy, and that the energy of mass at rest is equal to mc², where c is the speed of light. Special relativity also shows that kinetic energy increases with velocity faster than predicted by Newtonian physics; that additional energy increment is considered to increase the mass of the moving object, as described by the Lorentz equations.

Electromagnetic radiation is also a form of energy ... (There needs to be more here, but I'm running out of steam to write this section.)

The SI unit of energy is the joule (unit).

This introduction would set up sections on potential energy, force, kinetic energy, thermal energy, relativistic mass-energy, EM radiation, etc. Anthony Argyriou 18:41, 14 July 2008 (CDT)

Answer to Anthony's comments

Anthony writes as if he takes issue with the text in its present form, but much of what he proposes is already there. Because of the importance of the topic I will go through his comments in detail. But first let me say that I tried to write an introduction for non-scientists. I don't have much experience in non-science writing, so I'm open for comments that will make the intro more accessible. Having said this, I must say that I don't believe that Anthony's comments shed much new light. I quote Anthony in italics and write my comment in roman directly below it.

People who ought to know say that it's hard or impossible to define "energy" in one particular way

I agree as I side with the people "who ought to know".

the best is to offer a catalogue of types of energy. It appears to me that most energy is either potential energy or kinetic energy, but that excludes relativistic mass-energy and EM radiation (and gravitational radiation, too?), and perhaps other forms, also.

The present intro mentions "a catalogue of types of energy" in the following order

1. Amount of work
2. Chemical energy
3. Kinetic energy
4. Heat
5. Potential energy
6. Nuclear energy
7. Electric energy stored in battery

Then a paragraph is devoted to conservation of energy and the different manifestations of energy. The same types of energy are mentioned again and electromagnetic radiation is added to the list. The different sections in the article treat in more detail potential and kinetic energy, and relativistic mass-energy. The energy of an EM field is indeed lacking, a section on this should indeed be added. Gravitational radiation is way beyond my horizon, but if somebody can write a nice piece about, it I will applaud it.

Energy is a scalar property of physical systems, measured in units with dimensions M⋅L²⋅T^-2.

The present text says measurable instead of scalar and mentions chemical systems as well. The text gives joule as unit of energy. The dimension of joule in base SI units is kg⋅m²/s². If M⋅L²⋅T^-2 is more didactic than joule, then in the very least one should define M, L and T.

Energy occurs in several forms; these are potential energy, kinetic energy, electromagnetic radiation, and, according to Einstein's special relativity, mass-energy.

The first three forms are being mentioned in the intro and, indeed, Einstein's famous relation may be added to the list, but please don't overlook section 6, completely devoted to it!

Some forms of kinetic energy (such as thermal energy) are often treated separately, because of the historic circumstances of their discovery, and for convenience.

That is beside the point, thermal energy is always treated separately because it can only be converted partially into mechanical work, see section 2 where the notorious 2nd law of thermodynamics is introduced.

One fundamental law of physics is that energy is conserved - it can change in form, but the total energy of a closed system cannot change, and the energy coming into an open system must equal the energy leaving the system.

Do you feel that this principle is not stressed enough in the present intro?

The dimensions of energy correspond to the application of a force over a distance. Potential energy represents the potential for this to occur, as in the potential of an object to fall in a gravitational field, where the potential is for the force of gravity to be applied to the object over the distance which in can fall. Kinetic energy is the energy of motion, and is equal to ½mv², where m is the mass of the object, and v is the velocity.

The very same thing is explained in section 1 in much more detail. I have my doubts that giving this info in condensed form in the intro will improve the readability of the intro.

Special relativity shows that mass can be converted to energy, and that the energy of mass at rest is equal to mc², where c is the speed of light. Special relativity also shows that kinetic energy increases with velocity faster than predicted by Newtonian physics; that additional energy increment is considered to increase the mass of the moving object, as described by the Lorentz equations.

The very same thing is explained in section 6 in much more detail. I doubt it that giving this info in condensed form in the intro will improve the readibility of the intro.

Electromagnetic radiation is also a form of energy

As I already said, there should be a section on this, I could write it, I know enough about it.

The SI unit of energy is the joule (unit).

This is stated in the 2nd sentence of the present intro.

This introduction would set up sections on potential energy, force, kinetic energy, thermal energy, relativistic mass-energy, EM radiation, etc.

I don't understand what you mean by set up, do you mean to say that the intro should give in words a table of contents?

Finally, I like to add that it would be advantageous if more knowledgeable people would give their opinion and put some effort into this article. I appreciate it that Anthony spent time on it, more people should follow.--Paul Wormer 04:27, 15 July 2008 (CDT)

I was a bit remiss in not looking over the entire article when I proposed a rewrite of the introduction, but I was more concerned with how the introduction reads, and how it introduces the in-depth discussions of various forms of energy. I don't see any real factual errors in the existing introduction, but I do see a lack of coherence, and a few omissions. Some comments on my proposed rewrite and the existing intro:

• I think it's important to mention, early on, that energy is scalar. Velocity is measurable, but cannot be properly expressed by a single real number (because it's a vector). I've included the dimensions of energy, and maybe the SI unit sentence should go immediately after that. If the dimensions are unclear, they could be spelled out.

• The (existing) second paragraph presents a definition, then undermines it. The discussion of the complexity of "work" versus "energy", and thermodynamics should perhaps be saved for later in the introduction, if not the Energy in thermodynamics section.

• The second paragraph then presents a catalog of different types of energy, on several different levels of abstraction, as an introduction to a not-terribly-clear statement of the Law of Conservation of Energy. I think that expressing it more clearly is better than adding a superfluous sentence saying that it's really, really, important.

• The third paragraph is an example, which isn't bad, though I think it could be clarified. I'd be happy to keep it at the end of the introduction.

• My introduction doesn't mention that thermal energy can't all be converted to work, but I've avoided use of the term "work" entirely, as an unnecessary complication. Work probably should be mentioned in the sections on different forms of energy as appropriate, but thermodynamics shows the two are not equivalent.

• I could have added a little more about thermal energy as a form of kinetic energy - that would be appropriate, as would discussing chemical energy as a form of potential energy. I also would not mind trimming off the equations in the introduction; I think they're useful, but not essential.

• I do think that the introduction should reflect the table of contents, though not exactly parrot it. That said, there should probably be a section specifically addressing the Law of Conservation of Energy, and better distinction of potential energy in the sections on chemical and electric energy.

Anthony Argyriou 13:38, 15 July 2008 (CDT)

Paul Wormer informs me that Milton Beychok has proposed an alternate introduction, to be found at User:Milton Beychok/Sandbox2. I find that it is an improvement over the existing version, in a copyediting sense. The proposed revision does not address what I see as structural issues with the introduction. The existing introduction is not well organized, changes level of abstraction erratically thus conflating chalk and cheese, and gives two lists of examples, without much in the way of any organizing principle for the examples. My proposal attempts to address these problems. It, too, could certainly be improved upon.

The difference between the existing version and Milton's version can be seen here; the difference between Milton's version and mine can be seen here. (If you must, the difference between the existing version and mine is here.) Anthony Argyriou 21:37, 25 July 2008 (CDT)

Comment on site by Glenn Elert

Anthony Sebastian put into the article a link to a site by Glenn Elert. I looked at the site and my first impression was of nice surprise. When I started reading, however, I became less enthusiastic. For instance, Glenn Elert writes:

All forms of energy are either kinetic or potential. The energy associated with motion is called kinetic energy. The energy associated with position is called potential energy.

The energy stored in a barrel of crude oil is definitely not kinetic energy, so presumably it is potential energy. But, how is it "associated with position"? Does its energy content change when it is transported from Saudi Arabia to New Jersey?

I made this comment to underscore how difficult it is to write logically and coherently about energy.

--Paul Wormer 04:07, 1 August 2008 (CDT)

Paul, What Elert meant by "position" is probably the "height" or "elevation" position. Milton Beychok 10:01, 1 August 2008 (CDT)

In classical mechanics you're right: a cannon ball on top of a tower has more potential energy than at the foot of the tower. But a barrel of oil does not contain more chemical energy on top of tower than at its foot. The point is that the division of energy in just two kinds (kinetic and potential) is artificial and gives problems. This division doesn't cover chemical and nuclear energy, because neither chemical nor nuclear energy depend on position or velocity. These energies cannot be called potential energy (at least, not in the classical mechanics sense of the word). --Paul Wormer 11:07, 1 August 2008 (CDT)

I agree, and regret the link to Elert may have misled. However, it remains true that "The energy associated with position is called potential energy.", as Elert writes. Elert should not have started with "all forms of energy are either kinetic or potential" without defining "potential", inasmuch as a barrel of oil does have potential energy, if we define potential appropriately. Potential energy comes in several forms: gravitational potential energy; elastic potential energy; chemical potential energy. --Anthony.Sebastian 00:42, 22 February 2009 (UTC)

Quotation

It's easy to say foolish things about thermodynamics, and some very wise people have said foolish things.

John Ross, Stanford University, in Science News, Vol. 158, No. 15, Oct. 7, 2000, p. 234

--Paul Wormer 08:29, 4 August 2008 (CDT)

My confusion

As a non-scientist, I have trouble understanding the first two paragraphs of this article:

In science, energy is a measurable physical quantity of a system which can be expressed in joules (the metric unit for a quantity of energy) or other measurement units such as ergs, calories, watt-hours or Btu.

Energy is commonly defined as the amount of work that a system is capable of performing. However, the second law of thermodynamics states that some kinds of energy cannot be converted completely into work. Hence, this definition is not fully general and should be used with care.

The first sentence lacks a definition. It just says that energy is a measurable physical quantity, and that it can be expressed in all sorts of units that many people might not be familiar with, if they actually need to read an article titled "energy (science)". The second sentence says that the definition is commonly defined as "the amount of work that a system is capable of performing," but then says that some kinds of energy cannot be converted completely into work. First, what kinds of energy can't be converted into work? Second, I have a philosophical question for you: in virtue of what do you call "energy" whatever it is that can't be converted into work? If it can't be converted into work, there must be something else that makes you call this thing/process/state "energy." What is it? (And why aren't we just using whatever your answer is to that question as the definition of "energy"?)

I think that, since this article is for a lay audience and not an audience of scientists, it really needs to begin with an intuitive explanation of the whole idea of "doing work"--what scientists mean when they say, for example, that an electrical current can do work, etc. You can't really expect people to understand what you're talking about if you use yet more jargon to explain some jargon. The most obvious example is to move objects. But work also includes raising temperature (or lowering it, right?), and, I don't know, changing colors or making other perceptible changes, right?

Finally, what exactly would it mean to use the common definition "with care," anyway? Can you state this thought more explicitly, please?

I am not writing as Editor-in-Chief here but only as a reflective non-specialist who wants CZ to be pristinely clear to non-specialists. --Larry Sanger 16:48, 23 February 2009 (UTC)

Larry, Milton and I are the main authors of the intro. I will consult with Milton and see how we can answer your problems. From the top of my head: it is difficult to give a one-sentence definition because energy takes so many different forms. That is why we have this elaborate story about pumping up water. This has the purpose to give the reader a "feel" for the concept. --Paul Wormer 17:16, 23 February 2009 (UTC)