Talk:Energy (physics)/Archive 1

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Archive 1

Archive 2

(A definition of energy)

Energy definition is given at: http://www.kostic.niu.edu/energy Also see: http://www.kostic.niu.edu/Kostic-1st-Law-Proof.pdf and http://www.kostic.niu.edu/Kostic-2nd-Law-Proof.pdf

DEFINITION of ENERGY: "Energy is a fundamental property of a physical system and refers to its potential to maintain a system identity or structure and to influence changes (via forced interaction) with other system by imparting work (forced directional displacement) or heat (forced chaotic displacement/motion of a system molecular or related structures). Energy exists in many forms: electromagnetic (including light), electrical, magnetic, nuclear, chemical, thermal and mechanical (including kinetic, elastic, gravitational, and sound), where, for example, electro-mechanical energy may be kinetic or potential, while thermal energy represents overall potential and chaotic motion energy of molecules and/or related micro structure. "... Energy is the ‘‘building block’’ and fundamental property of matter and space and, thus, the fundamental property of existence. Energy exchanges or transfers are associated with all processes (or changes) and, thus, are indivisible from time." by M. Kostic: "Work, Power, and Energy" article in the Academic Press/Elsevier's Encyclopedia of Energy <http://www.kostic.niu.edu/energy>

add energy policy

from overall subject outline, don't know where "energy conservation" would be, Lovins' concept of a 'Negawatt' (watt not used due to performing function with higher efficiency device, such as a Compact Fluorescent Lamp (CFL)), nor where "energy efficiency" would be from an engineering/policy/public perspective, down to earth. Note that HP and Phillips Electronics are working on a Light Emitting Diode replacment for incandescent or fluorescent lamps! LEDs are close to immortal and 100% efficient.

I suggest that in all such discussions, some basic numericals ought to be given .For example, in the discussion of energy , it will be useful to give the energy content in a non-excited hydrogen atom withrespect to the space occupied by a hydrogen atom ( ie, the average distance between the nucleius and the orbiting electron ). pl respond to <theunnies@yahoo.com> Thank you.

Old discussions

Isn't it inaccurate to give a battery as an example of something having 'electrical energy'? The energy in it is, after all, conserved in chemical form and will only do work after certain chemical reactions occur.

I have a proposed new general definition for energy that can be derived from basic quantum theory. In any quantum system (thus, as far as we know, in the real world), energy can be shown to be the rate of computing that is going on in a system, expressed in terms of quantum computational operations per unit time; at least this is true if one defines operations in the right way. I work out the appropriate definitions in some of my research articles. However, this new computational interpretation of energy is not widely accepted (at least, not yet). Nevertheless I have found it helpful for my own understanding. -MikeFrank <mpf@cise.ufl.edu>

If Energy is defined as the ability to do work, I don't think work can be considered as a form of energy. Work is the result of the application of energy, but is not a form of energy.

In physics, work is a name to describe how much energy has gone in to a task. It is equal to force * distance and is measured in joules, so it definitely is a form of energy. -- sodium

The way we teach energy and work in our freshmen classes here is using the Work-Energy theorem, which says that the work done on a system is equal to the change in the energy of that system. So while work has units of energy, and is related to energy, it is in a sense only a mechanism for changing the energy of a system. I personally think that both Energy and Work are needed, both because of this distinction and because in higher levels of physics, energy is considered the more fundamental idea while work is abandoned. --Laura Scudder 17:22, 2 Apr 2005 (UTC)

More precisely, work is the mechanical process whereby energy is transfered from one form to another. For example when force from a potential field is applied over a given distance, such that work, W, is applied to the body, the kinetic energy of the body increases by the amount W, while the potential energy decreases by the same amount (W). In this sense, work is not itself energy, but refers to the amount of energy that is transferred from one form to another.--Matt Stoker

I've merged 'Work' into the 'Energy' article, and set a redirect. -- The Anome From the old Work/Talk page:

What about Angular Work done, ie Torque * angle swept out? -- Dweir

First, can someone define p in

KE = ∫ v·dp

Is that momemtum? And, just to clarify, that integral covers the relativistic and non-relativistic cases?

Second, and much more important: I feel this article is not yet terribly useful for the non-physicists in the audience. Does anyone have any ideas about how to answer questions like

What is energy?
Why does the energy concept enter into our theories? (Is it "real"? Is it useful? Why should anyone care?)

As far as I've been able to gather, the first question is a pretty philosophical one, along the lines of "What is a force?", and has no commonly accepted answer. Nonetheless, attributing energy to various situations enhances and simplifies our theories, so the concept is accepted on pragmatic grounds.

Thus we arrive at the second question. From my limited perspective, it seems like the concept of energy is chiefly useful because it allows us to predict things across problem domains. For example, applying the idea of energy, we can predict how fast a particular resting body would be made to move if a particular amount of heat were completely transformed into motion in that body. Similarly, it allows us to predict how much heat might result from breaking particular chemical bonds.

Without the unifying measure of energy, these comparisons and conversions would be much harder. I don't suppose it would be accurate to say it would be impossible, though, would it? If there were no equations involving energy, would there still be some way to say how much heat is equivalent to how much motion of a particular body?

Any comments on the accuracy of this explanation? Any references to articles that might explain this more coherently?

A more in-depth historical analysis than is available through the "What does energy really mean?" link might be interesting as well.

-- Ryguasu

I've revised the introduction again, mainly because I was uneasy about the connection between work and energy. After reading the Feynman reference, I feel that the previous summary

In physics, energy is defined as the ability to do work.

is either incorrect or unhelpful. (A little of each?) There is obviously a connection between work and energy, but I don't think it's quite that simple. I've tried to give an alternative explanation in the current revision.

I'm not sure that merging "energy" and "work" was ultimately productive.

Also, this definition was in the article:

One definition of work is applying a force through a distance. In the one-dimensional case, that is to say W = ∫ f(x) dx, where f(x) gives the amount of force being applied as a function of the distance moved.

I've modified it in the current revision to try to make the text flow better. As an aside, I think it is unhelpful to have an article that takes upon itself to explain what work is about explain only "one definition of work", instead of having a more general discussion.

I must admit, I'm not the most qualified to edit articles about physics. Nonetheless, the current state of the article is such that it really isn't very useful for the average Joe. I'm hoping that making a few changes might nudge it in the right direction. --Ryguasu 01:27 Nov 21, 2002 (UTC)

Energy is a very important concept, not easily understood. I see this article evolving while losing some important knowledge contained in earlier versions. Energy is definitely not only a state function of matter, and I think it needs to be defined around how much of it is contained in a system. For example, light is a form of energy which is not matter; it is an electromagnetic wave. Heat is another form of energy (this one is absorbed or released by matter, I convene). When one reads about annihilation or nuclear reactions, in particular nuclear fission and nuclear fusion it becomes clear that matter itself is also a form of energy. There is a common misconception about the fact that mass could be considered a form of energy, (because of the famous E₀=mC² equation) but it is not. Matter is. Mass is a physical property of matter, a quantification number, providing the force that is generated on matter in the presence of a gravitational field.

-- Louis May 20, 2004

Yes, the article lost some good information that is why I reverted it to the latest version of WWoods, I had no time yet to check which edits of Bensaccount were good and which were bad, but the end result was worse. I think I saw some good edit by Bensaccount but I need more time study them. Andries 16:47, 22 May 2004 (UTC)

The end results were not worse. I will give it another try though. Bensaccount 17:04, 22 May 2004 (UTC)

Bensaccount, please do not remove electric energy and chemical energy again unless you have good reason for that (but I can not think of any). Andries 17:22, 22 May 2004 (UTC)

Chemical energy is a form of potential energy and therefore should not be in a catagory next to potential energy otherwise it seems like there is kinetic energy, chemical energy, and potential energy and they are all completely different. Same goes for electrical energy.Bensaccount 17:29, 22 May 2004 (UTC)

Disambiguiation

The phrase "This page discusses the scientific quantity called energy" is bad wiki format and also conveys that the other page is not. The other page is also about the scientific quantity called energy but more spcifically it is about the source of energy for humanity.Bensaccount 17:29, 22 May 2004 (UTC)

Context

"From the perspective of physics and thermodynamics" is unnecessary, since this is the generally accepted meaning of energy. Also since thermodynamics is the study of energy it is kind of a circular explanation. Bensaccount 17:38, 22 May 2004 (UTC)

The definition

(Not even attempted) See Wikipedia talk: define and describe to understand what is going on here. Bensaccount 17:48, 22 May 2004 (UTC)

The current definition given at the top of the article is simply wrong and very misleading. No physics textbook, unless it was a very bad physics textbook, would ever define it in such a way, as most students paying any attention would immediately recognize the definition to be circular and therefore nonsense. This is the current definition given: Energy is defined as the amount of work required to change the state of a physical system.' You'll see that this is nonsense if you look at the definition of work: Work is the energy transfered by force to a moving object.

In most physics texts, the definition of energy is something along the lines of an abstract quantity important in the analysis of all physical systems, which is conserved in all closed systems. It doesn't sound like much of a definition, but it the best that can be done with energy, and with sufficient explanation it is the only definition that makes any sense in the long run. --Brentt 16:10, 18 September 2005 (UTC)

Useless text

I removed the following because it is useless, and slightly incorrect. Some of it is also biased.

The amount of energy is determined by taking the sum of a number of special-purpose equations, each designed to quantify energy stored in a particular way. -- That is one way to do it, but not the only way, and it doesn't determine it it merely predicts it. Bensaccount 17:57, 22 May 2004 (UTC)

In general, the presence of energy is detected by an observer any time there is a change in the properties of an object or system. -- Or when there is not a change (it is a state function). Bensaccount 18:03, 22 May 2004 (UTC)

There is no uniform way to visualize energy; it is best regarded as an abstract quantity useful in making predictions. In fact, many recognized forms of energy stored in such an object or system, are not easily detectible by the average observer. There is no "uniform" way to visualize anything. Who says that its best to regard it as abstract? As a quantity? Just because the aveage person can not see it doesn't mean it can not be defined. (This is biased.) Bensaccount 18:11, 22 May 2004 (UTC)

I was just about to comment about the definition, and seeing your post Bensaccount, makes me think that my comment that I thought would be uncontroversial among people who know physics well might be controversial on this page. The person who wrote "it is best regarded as an abstract quantity useful in making predictions." is entirely in line with the view of most modern physicists (see Richard Feynman's Six Easy Pieces, one of the lectures is dedicated to Energy, and the lecture is based on that one idea, that it ultimately is an abstract quantity, just a number really, which is impossible to define in terms of other concepts.) Anyay, so why is this a problem? See above under The Defintion disucssion.

Bensaccount's edits

This time I will provide a reason for every edit. I am not done; this article is still really bad. Bensaccount 18:42, 22 May 2004 (UTC)

thanks, providing reasons for deletions is enough for me. Useful additions don't have to be explained. Andries 19:17, 22 May 2004 (UTC)

Work & Heat

It seems to me that work and heat are not energy but rather transfer of energy. An analogy could be how trade is not merchandise but rather the exchange of mechandise. Bensaccount 21:27, 24 May 2004 (UTC)

Work done is the amount of energy added or subtracted from a body.

Heat is the random kinetic energy of moving molecules.

--wwoods 21:35, 24 May 2004 (UTC)

I disagree, according to the sources I have seen heat is the transfer of thermal energy between two sources. What you are speaking of is thermal energy. Bensaccount 21:47, 24 May 2004 (UTC)

Electromagnetic radiation

Bensaccount thinks that electromagnetic radiation is a form of kinetic energy but I don't believe it. The energy of a foton is E=hf=hc/w = planck constant*speed of light/wavelength The velocity is always the same=300,000km/s. So this can't be kinetic energy?? Andries 21:45, 24 May 2004 (UTC)

Consider electromagnetic radiation as a photon -- electromagnetic radiation has kinetic energy due to the velocity of the photon. Consider it as a wave -- The energy is the kinetic energy of the wave. I don't see the problem. Bensaccount 22:00, 24 May 2004 (UTC)

Bensaccount, your classification of electromagnetic radiation under kinetic energy is unusual. Could you please provide references for your opinion? Thanks in advance. Andries 19:16, 25 May 2004 (UTC)

Almost any reliable source will tell you that energy can only be in two forms: kinetic or potential. I think this website has what you are looking for.[1] Bensaccount 01:08, 26 May 2004 (UTC)

I agree - see also [2] for a very approachable discussion. You could also think of kinetic energy as being a kind of potential energy possessed by moving bodies. Ultimately, they are all just forms of energy, and the distinctions between different 'sorts' of energy are just ways of thinking about energy in different situations rather than hard boundaries. -- ALoan 10:39, 26 May 2004 (UTC)

Potential and kinetic are a very general classification of energy forms. As stated in the present version of the article, these are mostly useful in mechanics. Based on the fact that a photon has a zero rest mass, the equations that are given in the present definition of kinetic energy are not very useful to electromagnetic radiation. I must say I agree with Andries. Also, this article is part of an encyclopedia. Why should it be limited to the basic definitions of kinetic and potential energy forms and I see no reason why we are trying to associate energy forms as to being only potential or kinetic. I like the work done by Bensaccount, but I think it needs to be elaborated. Electrical energy, for example, has both forms of potential and kinetic energies. According to "Principles of science", 1966, the most common forms of energy are mechanical energy, chemical energy, heat energy, sound energy (compressional waves), light energy (electromagnetic radiation), electrical energy and nuclear energy. I think if someone would like to expand on these it would be benificial to everyone. -- Louis May 30, 2004

Commonly, energy is energy development, the field concerned with providing abundant and accessible energy to all humans.

I have no idea what group of people would find this statement "common" particularly in the general population. Seems like an attempt to create an association which does not yet exist in the general population. This statement may indeed becomme true in the near (or far) future but I do not see it as yet a part of everyday conversation or speech. Ten or more examples may convince me however. COMPATT 20:35, 19 Jul 2004 (UTC)

As far as I can see, this was added by Bensaccount on 18:24, 22 May 2004 (see [3]). Previously, it said "This page discusses the scientific quantity called energy. For discussion of energy development for humans, see Energy development." which makes a bit more sense (this was added by Hawstom on 00:16, 18 Mar 2004 - see [4]). On the whole, I think it could safely be deleted and Energy development added as a "see also". -- ALoan (Talk) 21:40, 19 Jul 2004 (UTC)

unitconversion.com

Do we really need both links or is it a link spam? abakharev 23:27, 10 October 2005 (UTC)

Proposed Merge

It seems to me that the entries on energy conversion, energy quality, energy form, and exergy all have a common theme and may benefit from greater clarification and a possible merge. Exergy aims at a quantification of an energy quality, and energy quality is merely a recognition of the different energy forms and their capacity to convert from one form or quality to another.

Sholto Maud 02:57, 13 December 2005 (UTC)

Antimatter and Energy

How does E = mc^2 relate to the energy created by the annhilation of matter and antimatter? 62.249.242.232 17:04, 21 December 2005 (UTC)

Well, if matter and antimatter annihilate, then their energy must go somewhere because it's conserved. So the annihilation must create some photons or other sort of product that can carry that energy off. The products of the annihilation will carry off exactly as much energy as the matter and antimatter carried in. That will include the mass energies mc^2. — Laura Scudder ☎ 19:20, 21 December 2005 (UTC)