Talk:Energy/Archive 5

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ENERGY, "ENERGY", energy, and "energy"

The problem with this page seems to be that it discusses an entity which is very abstract. ENERGY is the collection of phenomena under study, each form forever beyond the reach of our direct knowledge, while energy is but one of these phenomena. "ENERGY" is the sum of our models concerning um, maybeeee.....energy? While "energy" is the particular model under discussion in any singular way.
So, ENERGY cannot be defined, nor can energy, and "ENERGY" is too big to handle except in one of its specific instances, e.g., E=mc^2, I ran out of _energy_ for more examples...etc. So, therefore, Q.E.D., only "energy" can be defined fairly well. Link this page to these other uses, and stop trying to stretch the Sierpinski Carpet.

Or in other words, "HEY YOU KIDS! GET OFF MY LAWN!"

Now go wash your hands and have a cup of tea and a sit-down.

Thanks. --TheLastWordSword (talk) 22:09, 15 November 2010 (UTC)

If you use a single dimensional (S versus T) diagram to depict the physics of motion, But supplement it with a force vector, which sticks perpendicularly out of the paper to depict the magnitude of any force that causes a motion in the S-T diagram, Then you have a way of relating the force to the indicated motion in the indicated manner. An integration of the force vector during the applied time interval (Delta T)will give you the value of the impact that was applied to the impelled particle, and therefor, if you know its mass, you can calculate its change in momentum (M x delta V). Also if you integrate the force vector over the distance traveled (Delta S) by the particle during a time interval, you can calculate its change in kinetic energy of motion, which is M/2 times the integral of F squared. And since you soon note that to give additional energy to a moving particle you first have to catch up to it with your impelling force, it makes apparent the difficulty in causing a particle to achieve a velocity limit by sending out an impelling force.WFPM (talk) 13:20, 16 November 2010 (UTC)

Energy is described not defined.

Energy is described via its manifestations upoin matter. So what is enery? Bcuratolo (talk) 16:58, 24 January 2011 (UTC)

I agree, this is one of the worst opening paragraphs on wikipedia. [comment by 92.17.89.69]

Okay, a bold edit needed

Okay, agreeing with these many complaints and seeing not much done, I've been WP:BOLD and rewritten the LEDE to define energy as the ability to do work, which work exerts pushes and pulls through distances. It's also equivalent to mass, and never appears without mass. Potential energy appears as trapped energy, when pushes and pulls through forces are made, and the new configuration is locked so it cannot relax (like a spring). Heat is resolved to EM or kinetic energy, and thermal energy to kinetic and potential. The last part of the lede in which entropy, which conservation, conversion, and so on are discussed, is not changed as much. I've pointed out that if you transfer energy to another sytem by any means than just adding some matter to it, you're going to change it, because you've done work on it. SBHarris 01:04, 10 February 2011 (UTC)

Lots of weirdness

Energy, momentum, potential energy, speed, relative mass etc are all definitions created in their relation. When you use them you 'lend from time', that is define a coming 'moment in time' as a possible interaction, and then define whatever property you use from looking at that possible interaction. You have invariant mass defined as invariant in all frames and motions, not relativistic as that is a definition of a relative mass (relation), and that goes for momentum too as far as I know. If you don't get the basics right you will stare yourself blind at equations made from flawed premises. It's strange, you guys should really know this? Do you have any General relativity in your courses, or is it all 'quanta'?

What goes for momenta "as far as you know"? There is no "invariant momenta". The invariant quantity is the E,p,p,p 4-vector that includes energy. And the length of which is invariant mass. But this is not an article about mass, or rest energy. It's an article about energy so we are stuck dealing with the fact that it is conserved but relative to the observer. SBHarris 18:53, 9 March 2011 (UTC)

==

Momentum in a photon is a relation to a invariant speed 'c', from any frame measured, expressed differently from any of those frames as 'energy', when measured from whatever frame, depending on its speed relative that 'photon/wave'. And so it is 'relative'. Seen as a 'lightquanta' we express it differently. But a photon have no 'rest frame' as I know? Am I wrong there?

No. you're correct. The momentum a single photon is anything you like (down to something approaching zero, or large wihtout bound), since your observer of the photon can be in any frame you like. All of them see the photon moving at c, but each sees a different photon E and p. Kinetic energy for massive objects (the photon has no mass = rest mass) is the same, in a way. For any single particle kinetic energy can be anything you like, down to zero (rest frame of the moving object). Rest energy = rest mass is the minumum energy for massive objects. For systems of particles where we cannot find a frame where the KE of every particle is zero, the minimum total energy is in the center of momentum (COM) frame where system p is zero. Im that frame, the residual kinetic energy of the system contributes to its invariant mass (as do the various rest energies and potentials). See systems section in kinetic energy. That is sort of the "rest frame" of the system, even though parts of it are moving. Systems of photons also have an invariant mass, which is their mass in their COM frame (which doesn't change in a particle annihillation that makes photons, for example, so invariant mass is conserved).

If The mass and (equivalent energy value) of a system is considered to be an invariable property of a system, how can Feymnan's assertion (In QED), that light can be sent through a distance of space in two beams and then canceled out by proper separation spacing of the exit beams at the end? In other words can light energy cancel itself out?WFPM (talk) 22:23, 26 October 2011 (UTC)

=

"For systems of particles where we cannot find a frame where the KE of every particle is zero, the minimum total energy is in the center of momentum (COM) frame where system p is zero. Im that frame, the residual kinetic energy of the system contributes to its invariant mass (as do the various rest energies and potentials). See systems section in kinetic energy."

Thanks for your answer SB :) and, I have no problems with your statement, that energy is measurable after all. That is, you are referring to the system 'jiggling', as I read it? And that's also my point :) 'Energy' needs to be able to be measured if you want to refer it as belonging to a single object. And there we have 'jiggling' and compression as the telltales I know off. Compression as the spring still have a added 'invariant mass' even after the dissipating kinetic energy, produced in the compression, is gone.

==

"Potential energy appears as trapped energy, when pushes and pulls through forces are made." is terribly wrong. Where the he* do you get the idea that 'potential energy' pushes and pulls?

That's not what the sentence says. It says "potential energy appears as trapped energy, when pushes and pulls through forces are made." Which it does. There may be other ways to store potential energy besides letting a force act through a distance where the energy doesn't go into some other form of energy like kinetic E, but this method is the most common one. How do you make potential energy except by doing work? SBHarris 18:53, 9 March 2011 (UTC)

==

'Trapped energy' Can you prove that experimentally? Except in a compression? Are you thinking of 'relative mass' too? I'm sorry, maybe I'm not getting your idea right? Energy is interactions to me, or as expressed in a compression. Can you show me any proof for a speeding spaceship for example, storing 'energy' in its relative motion? If you mean the 'stress energy tensor', the warping of SpaceTime by 'relative speed' I might agree, although I have trouble defining its speed even so, maybe SpaceTime hasn't though? But as far as I know there is no 'energy' stored in that Spaceship I mentioned here? It makes me head hurt assuming that we have all kinds of 'secret, invisible, and unmeasurable, energy stored in that Spaceship :) Or? Can you prove my assumption wrong? If so I'm very interested. You just need to link me to the experiment proving it.

You can see energy stored when mass changes. In fusion, you bring two charged nuclei together and they are compressed against their EM fields like springs, until they reach a point that the nuclear force draws them in where they bind. That is a process that stores energy, if you are a supernova making (say) atoms of uranium. Each uranium nucleus now sits like a coiled spring, with more mass than the nuclei it was made from, and the extra is the mass that you trapped when you did the work on it (the temperature and kinetic energy did the work, and was trapped). When the uranium is split later, the opposite process happens. All these energies are stored as nuclear and EM potential energies, which trade off (move of one is made than the other is destroyed). Experimentally, this stuff is called nuclear fission and fusion. Potentials in both (fields which have mass) are converted to kinetic energies and EM radiation. There is nothing special about your coiled spring-- it's just another system that has stored potential. It's like a book that you picked up and put on a table. You store energy in that system. When the book falls, it's converted to kinetic energy, then heat (which is purely kinetic energy in monatomic gases, but half EM potential energy and half kinetic energy in solids). SBHarris 21:28, 10 March 2011 (UTC)

The Book is a interesting example. I can see some of your thoughts on the subject there but as far as I know there is no measurable new energy stored in that book, although there is different views on it :) simply expressed I would formulate it as 'gravity' is no force, therefore you won't get any extra energy stored in the book, that it will interact differently when falling is not a result of its 'intrinsic energy' being changed, to me it's a result of a different position in SpaceTime relative the object it may interact with, and that I see as a result of 'distortion/potential gravity/stress energy tensor'. As for why I call the spring the only example I know of? Well, it's not true, as it to me is the exact same principle as the one making a Black Hole, compression but there's my reason for accepting it. "You can see energy stored when mass changes. In fusion, you bring two charged nuclei together and they are compressed against their EM fields like springs, until they reach a point that the nuclear force draws them in where they bind. That is a process that stores energy." That one I will need to think off, I'm not sure. But I enjoy your views and I will get back to you when I sorted my thoughts out. What I can say though is that as long as we're discussing 'energy' as a concept I have no problem with adding different 'energies' interacting into a greater amount of 'stored energy', as long as we are discussing the same principle that, in time :), fill up a Black hole with more 'energy', coming from the infalling 'debris' well, sort off :)

A pleasure reading you. Yoron.

==

To make my point clearer, consider that spaceship crashing at three possible locations simultaneously, ala Feynman 'paths' :), delivering you three different 'energies' in those interactions. So, which one had it 'stored'? That one isn't that clear though as you can define it as a relation relative those objects, although when in a uniform motion you are free to define all motion to only one of those objects and if we have three (same exact invariant mass) uniformly moving at different speeds relative you, giving you three different energies? Still, better to consider how you define that 'stored energy' right :) You do it through using your inertial frame, don't you? Like Earth. So when you speak of that stored energy you mean 'relative Earth as a 'inertial frame' '. Or do you know any other way? And as all uniform speeds are the same in a black box, so your definition becomes not only relative, but also indefinite as I see it.

Here you are talking about kinetic energies, which are not stored in single objects (for reasons discussed above) but are stored in a dispersed and non-locatable way, in SYSTEMS of objects (and such minimal kinetic energies, easily seen in the system COM frame, are invariant). Potential energies don't involve motion, and because of that, they store energy in a way that is invariant from the beginning, but that's natural because they always involve doing work against some field/force, so a system of two objects (at minimum) is always involved anyway. Compress a spring and its increased mass is the same in all frames, since the mass increase shows up in the COM frame, and is invariant mass. However, like the book on the table, there's no motion storing the energy. The field and configuration of objects does it. Pull two objects appart gravitationally and that system stores the energy without storing it kinetically. This storage is also invariant and is seen by all observers, even though you cannot locate it precisely in space. Gravitational waves are one more interesting system where the energy is stored as a potential, but not in any location smaller than the wavelength of the wave. You have to "stand back" and look at the thing from a distance to "see" the effect of the energy (which is that the wave carries off energy and mass from systems, just must contain energy in itself somewhere, albeit diffusely). SBHarris 21:28, 10 March 2011 (UTC)

Yes I agree, by defining a arbitrarily chosen 'system' you can define a 'potential energy', or just 'energy', as a relation existing between the objects in that 'system'. What I don't like is when it sounds as if this 'energy' actually 'exists'. It doesn't, not until the interaction. I differ between measurable 'energy' (compressed spring) and conceptual 'energy' as in a 'system' where you want to light up the possible interactions and relations existing. Gravitational waves is to me 'vibrations' in the 'Jello field of gravity/SpaceTime', not 'energy' per se and the reason is that there is no 'force' involved. To me SpaceTime is somewhat like a Jello :) You can send 'chock waves' through it that 'distorts' it, propagating, but there is no 'energy' involved, that is when you're inside the distortion I don't expect you to weight/invariant mass more (as long as we're not talking a compression). Still, I see why it's seen as a very useful concept when manipulating mathematics, and I better add that I didn't react on your article as such, just on some comments I found unclear in the talk session. But, to me a added 'energy' should also be measurable, as 'jiggling' or as an added invariant mass (greater gravitational potential). I'm afraid this talk page may grow :)

==

Entropy is very simple to understand if you look at it as 'energy'. Not that we can lift up a ounce of 'energy' but it is a very useful concept. Then entropy will be that 'energy' interacting and so doing lose some of its 'energy' falling into a lower state. That why you will find our universe to equalize out in the end, all energy states being at that level where none can be used anymore, also called 'work done'. Why we don't do that spontaneously is because you need to add some 'energy' to any system you want to start interacting losing 'energy'. And that saves us all from instantly decaying. If you want to understand your equations you need to look behind them, to the concepts they manipulate. In chemistry entropy is expressed as heat, but the real state that change is 'energy', even though not defined by itself. Maybe you could use the word radiation instead of heat, I don't know, but 'energy' is the proper one for it I think as even radiation has a end state, as in a photon interacting annihilating itself.

"Energy is described via its manifestations upoin matter" If you by that mean relations interacting, losing energy by it and falling into lower energy states, as seen for the whole system? But there are no manifestations, only transformations. Some of them may end in a higher energy for part of those relations but always losing energy as a whole 'system'. The only thing 'defining' energy that I know of is the compression of a spring. After the kinetic energy has 'clung out' there will still be an added 'invariant mass' to that compressed spring as compared to it before getting compressed. And that's the only proof I know for the idea of 'energy'. But it's perfectly sufficient too :)

If you look at the stress energy tensor you will see that it uses property's only defined in a relation, like momentum. The energy that transforms into 'oblivion/SpaceTime' is expected to add to that tensor as I see it. And why it has to do so is because all interactions not only transforms, but also loses some of that 'energy'. As we have a definition of 'conservation of energy' we still need it to stay trapped. So it has to add to 'SpaceTime', and then the stress energy tensor is what you have left, as I know that is. The universe is weird :)

Yoron. User:178.30.6.228 12:52, 9 March 2011 (UTC)

Break

Look, nobody has time to go into this with you. Read the article carefully first. The stress-energy tensor only talks about energy-momentum flow through a point, and if you want energy in a volume you need to integrate around the volume of the thing. That's why some energies can't be expressed as dE/dV quantities-- you have to define your volume, integrate around it, and then step away and look at it from flat space. The energy that volume contains is then its invariant mass and the thing that generates that volume's gravitational field. There's your energy.

Gravitational waves are like shock waves (especially shear waves in a solid) but they carry away energy just as shock wave does. They do work (force x distance) on the emitter, and on the receiver. They exert forces on the emitter and the receiver. Example: read the article on the Hulse-Taylor binary system, which is a system of two neutron stars, one of which is a pulsar. This system orbits with a period of only 7.75 hours, coming as close to each other as twice the distance from Earth to moon. The power of the gravitation radiation from this is calculatable in general relativity and is 7.35 trillion trillion watts (10^24 watts). That's almost 2% of the energy that our Sun puts out as light, only this is coming out as gravitational waves. It exerts a force on the system and causes the stars to in-spiral as they lose energy and angular momentum-- they might as well be swimming in some viscous fluid. That's real work, a real force, and a real effect, which has been measured because the rotating pulsar is so great as a clock. Because it's polarized gravitational wave radiation, it carries away the angular momentum from the system, like a polarized light beam would do, but not like any nonpolarized EM radiation from any star (like ours) would do. It only has one possible explanation, and it fits Einstein's prediction over 30 years to within 0.2%. It won a Nobel Prize in 1993 for the guys who discovered and analyzed it (that's from your country, Sweden).

So-- the book raised to the table only increases the potential of the system, but its mass wouldn't change if the force and distance to put it there didn't come from somewhere else in the system (like my muscles, or you could do it with a coiled spring). The mass and gravity field of the whole Earth wouldn't change if you just moved energy from here to there like that, but if you believe energy left the coiled spring, you must believe it went into the system of book+Earth. Just WHERE, you can't say, but from far away, it's still there, even though not in the spring. So where else would it be? In the gravitational potential.

Finally, remember where those atoms heavier than iron and nickel come from. It takes energy to make them and fusion to larger atoms is losing propositon that saps and stores energy, not creates it. So where does this energy come from. It turns out that it's mostly gravitational energy from the collapse of a supernova, so that's stored gravtiational potential also-- except this time in heavy atoms. On a larger scale you can see that a planet like Jupiter still radiates more energy than it gets from the Sun. It's obviously still slowly colapsing, and that potential energy is converted to infrared.

and would you please sign your posts with four tildes: ~~~~. Or pick a username like Yoron? SBHarris 07:56, 12 March 2011 (UTC)

Hm.

Okay, maybe you feel that I'm attacking your article? if so, nope, as for signing every comment, you filled in my original writing with yours, I answered them, staying inside the caption I made originally? Anyway, you raise a question I'm not sure I can answer, with your statement that gravity is energy, as that seems to be the way you look at it? In a way I agree, maybe I don't see it clear enough? Or possibly gravity and its gravitational quadrupole moment are different. Einstein himself seemed to have changed views on gravity waves a couple of times :) so I think I'm excused if so. Gravity is definitely related to 'energy', but it's not a 'force'. If you state that energy contain gravity though, I have no problem agreeing. When it comes to the book I still say you will find no new energy in it. But we seem to agree there? When you define the energy as existing as a gravitational potential, I call it a 'stress energy tensor'. As for defining a arbitrarily chosen system, trusting this to 'define' the energy's boundaries? Then I don't agree, you can always widen this 'system' book-ground, to the whole universe if you like, and still find the same 'energy' released in the final interaction with the book hitting ground, with that 'energy' having been 'somewhere' inside your 'new system' too, as I see it?

This one seems to mirror my confusion, well, slightly :) http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Relativity/GR/energy_gr.html

But you've given me a lot to think of, and it still was a pleasure reading you. Yoron. 178.30.69.236 (talk) 23:07, 12 March 2011 (UTC)

Nuclear binding energy is converted

The table in this section looks like it has been vandalized.User:Bleeisme

I don't see where the problem is. Anyway, the place to make this comment is on the TALK page of nuclear binding energy. Please sign your comments with four tildes: (~~~~) SBHarris 21:47, 10 March 2011 (UTC)

Nuclear binding energy is converted

The table in this section looks like it has been vandalized.User:Bleeisme

I don't see where the problem is. Anyway, the place to make this comment is on the TALK page of nuclear binding energy. Please sign your comments with four tildes: (~~~~) SBHarris 21:47, 10 March 2011 (UTC)

Hamiltonian

The article says that the total energy of a system "is sometimes called the Hamiltonian".

It should read:

The Hamiltonian is a function (or in general a functional) of the configuration of a physical system and its values are the total Energy of that system. 91.137.20.132 (talk) 13:43, 8 August 2011 (UTC)

Energy and Work different in what ways?

As a Dutch its funny to see the Brits wrestle with Energy versus work. In its original 1850's high society use, Energy was felt as a property of the blue blooded folks: the ability to make the peasant or worker do work. That shaped the application of these words in physics. So the original definition of energy was only that what we today consider the definition of potential energy: the ability to do work. But today, after thermodynamics have been worked over by Einstein, the work itself and even the RESULT of work is also expressed as energy, even if the resulting object can't do work, because they are a mass of dumm atoms, moving randomly because of their temperature, surrounded by warmer atoms.

So work refers to the deed itself, and it is the act of moving something against a force. Energy is what you use to do this work, or what you need to do work in the future (potential energy), or what you used while doing work in the past. (This is for instance the amount of KWH you have to pay for on your energy bill.)

Anyone still hangs for the old blue blooded definition? In that case the 'Froms of energy' section has to be cleaned from all non potential energies.Pieter Felix Smit (talk) 08:50, 22 April 2012 (UTC)

The King has no clothes?

The article starts wtih "ἐνέργεια energeia "activity, operation"[1]) is a quantity that is often understood as the ability a physical system has to do work on other physical systems."

Shoudn't the article start wth a definition of what the heck it is talking about? The article says "is often understood as." IMHO, if you are going to launch forth on a topic, at least you should unambiguously define the concept you are talking about. (EnochBethany (talk) 23:59, 4 April 2011 (UTC))

Good point. Our article should begin with a simple explanation of what is meant by energy. Over the years there has been a lot of discussion on this Discussion page about what should be said to define energy. Check threads above, and also the archive. It looks like no consensus was ever reached about how to define it. Dolphin (t) 00:10, 5 April 2011 (UTC)

The article says that "...and energy (like mass), cannot be created or destroyed..."; but mass does can be created or destroyed, that is one of the main results of Relativity. and is evidently proved by nuclear bombs and many other phenomena. — Preceding unsigned comment added by 67.0.51.207 (talk) 06:51, 20 April 2012 (UTC)

The article DOES start like that:

In physics, energy (Ancient Greek: ἐνέργεια energeia "activity, operation"[1]) is a quantity that is often understood as the ability a physical system has to do work on other physical systems.[2][3] Since work is defined as a force acting through a distance (a length of space), energy is always equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length.

What's wrong with the above? What isn't clear? We've even defined the sub-terms for you. A Push/pull exerted over a distance. What is it you don't understand about push/pull or distance? SBHarris 02:18, 5 April 2011 (UTC) == Initial Definition is weak -- why?

"In physics, energy is a quantity that is often understood as the ability a physical system has to do work on other physical systems"

This is just simply awkward bad grammar, in addition to being a very weak statement.

Why does it not read:

"Energy is the measured quantity of a physical system to do work on other physical systems"

Because it's not really what it is. You can have energy which can't do work due to second law thermodynamics. But I agree grammar is awkward and have rewritten. Gerardw (talk) 18:33, 19 May 2011 (UTC)

I don't know what the word "measured" is doing in that sentence, but the rest is correct in the limit of a heat engine with a thermal reservoir at absolute zero. You can get as close to converting heat to work as you like, that way. So in theory, and in limit, energy is the capacity to do work, given the correct circumstances. We have to talk about entropy limits (and do) but can only mention it in passing in the lede. SBHarris 00:21, 11 June 2011 (UTC)

Energy Definition Difficulties

The discussion on the best definition of energy is quite fascinating. The conundrum is considerable. Energy is actually quite an abstract idea in its technical sense. Most of the posts show an awareness of this. The problem is to find a way of presenting a somewhat colloquial description that is easy to understand without being technically misleading or erroneous.

The difficulties sensed with defining energy as "the ability to do work" are well placed. Despite the well meaning efforts to find a simple definition, such a a definition is so erroneous as to be completely misleading, despite the fact that probably over half the world's introductory engineering texts define energy exactly that way. Nevertheless it is wrong. Energy, of itself has no intrinisc ability to do work of any kind whatsoever. Ultimately it is "lack of entropy" which has the ability to do work. Unfortunately, this definition cannot provide the kind of convenient handle for the idea that we need here because it introduces another equally, or even more abstract idea that has not been defined.

I would like to help with the definition of energy here, but have decided not to edit the text because I think it needs approval from everyone concerned before it is changed again, especially considering the mention of the debatge spanning several years.

Instead, I would like to offer some suggestions, phrases and simple sentences that might be suitable for working into an appropriate definition of energy. If these suggestions are rejected, I shall understand why. Energy is diffiult to define simply.

Suggestions: 1. Start with reference to the colloquial use (E.g. A very widespread and colloquial definition of energy is that it is something that has the ability to do work. This is not quite technically correct but it has helped many students start out with an immediate notion that can be very helpful with getting on to the equations and relationships in energy considerations. However, we will eventally have to learn, if we want to get to the bottom of things, that energy itself, in its essence does not have that ability. This distinction is important if we want to try to understand the essence of this thing called energy. It turns out that it is various distributions of energy that provide that ability, not something that is intrinsic to energy itself.

2. Describe Energy in its widest sense, and describe its multitude of forms, briefly. (E.g. When we drive a car, the car's fuel has energy that we convert into a mechanical form that moves the car. The sun's energy is something we see and feel everyday. That energy is a different form altogether, starting with atoms, that, during a process of fusion, produces light and heat, both other forms of energy. So we can see that energy comes to us in a multitude of forms. It is everywhere, in our lives and throughout the universe.

3. Approach the subject of the "usability of energy". (E.g. The first step in coming to understand what energy is, and what it is not, is to think about where and how energy appears "usable" to us. We use energy to heat our homes. We burn fuel to do that. After the fuel is burned and our homes have been heated, is the energy in that fuel available for anything else? It is now in the form of heat. Could we use that heat to propel a car? The answer is, we might, if we found some way of getting it to "flow". So then we have to think about how energy flows, why it flows and under what conditions it flows from one place to another. )

4. Bring it around to the idea that energy in any form, can have a useful part and when we "use" it, there is always a part that cannot be used (Link to entropy). (E.g. All of us are familiar with the idea of friction. It is something that reduces the usability of the energy we are using to get something done. As it turns out, when friction occurs, it is dissipating as heat some of the useful part of the energy we are using, so there is less remaining for doing the useful work. OR We must turn to the notion that energy, to be useful must involve a gradient of some kind. If there is no gradient, that is an unequal distribution of some kind, it will not be useful for doing work. )

5. Then to a more general definition - (E.g. Energy itself can be seen as the medium through which all forces in the universe are transmitted. According to conventional and traditional theory, it is seen as something that can neither be created nor destroyed, nor wasted. For the energy conservationists, energy cannot be NOT conserved. It is always conserved. (Energy conservationists are really concerned with the usable part. Perhaps also add something like - When we have used the "usable" part of energy supplied to us in soem stored form, that usability is gone forever. The energy is still there, but in a less usable form. The universe changes irrevocably every time we use energy.

6. A TECHNICAL DEFINITION OF ENERGY. A technical definition of energy might be most easily done by reference to its dimensions. Energy can be defined as a product of more basic dimensional units representing the basic measurable quantities in the universe such as mass, length, time, charge, etc. For example: we can refer to the E=Mc^2 formula and note the dimensions implicit in this as: MASS multiplied by the dimension of VELOCITY squared. VELOCITY, however, can be further reduced, as a composite dimension to the basic dimensionality of LENGTH/TIME. Thus ENERGY has the dimensions of MASS times DISTANCE squared divided by TIME squared. ( M DISTANCE(or LENGTH) ^2/TIME^2) It can also be pointed out that WORK, having the same dimensions as ENERGY, also can also be defined in those basic dimensions. By way of explaining the various forms in which energy can be represented, WORK appears to have different dimensions from those above for ENERGY, (e.g WORK = FORCE times DISTANCE), but in fact can be seen to transform consistently to the same basic dimensions of ENERGY. (E.g WORK = FORCE times DISTANCE and F = MA implies dimensions: Force = mass multiplied by acceleration, which reduces to MASS multiplied by DISTANCE divided by TIME squared. Since WORK => FORCE X DISTANCE, we can reduce the dimensions of FORCE to its basic dimensions resulting in (MASS X DISTANCE / TIME squared) X DISTANCE which can be reduced to: MASS X DISTANCE squared /TIME squared => MASS X VELOCITY squared, which the same dimensions as the above definition of energy.

In summary: energy is defined dimensionally as MASS * DISTANCE ^2 / TIME ^2.

All forms of energy, whatever they will reduce to this basic dimensionality.

Hope some of these suggestions help.

UpToTheMinute (talk) 22:56, 5 July 2011 (UTC)

It could also be mentioned that since ENERGY and WORK have the same dimensions, saying ENERGY has the ability to DO WORK, would be like saying ENERGY has the ability to DO ENERGY, rather meaningless.

COMMENT. It's not meaningless to say that one thing is not the other, the argument being that they have the same dimensions. Work is measured in units of energy, but that doesn't mean it IS energy. It is not energy, but rather the effect of energy, and the act of transfer of energy. Many kinds of energy are clearly NOT work and won't be for the foreseeable future. All potential energies, for example. And the energy that is trapped as rest mass in particles and as invariant mass in systems. And (for that matter) also kinetic energy. Energies carried by rest-massless particles like photons and gravitons, also are not work. Work is force x distance. It isn't a "thing," but rather an action. Energy can perform work (or not) and work always produces energy of some kind, but they are not the same. One is a noun and the other a verb! SBHarris 18:28, 8 August 2011 (UTC)

The reference 3 doesn't state that energy quantifies "the ability a physical system has to do work on other physical systems" but that "energy is the capacity to produce change" (page 23) and that "work and heat are two of many forms of energy" (same page). The definition of energy is dificult to state, but it isn't really that from the article, even if some books and webs use it. The energy quantifies the capacity of a body to produce changes on other bodies (when the energy is transferred and lost, in the form of work and heat) or on the same body (when the energy is transformed, such as the case of deformation, in the form of work on itself). Using changes instead of work includes those cases when no work is done at all (i.e. full transfer of energy in heat form, such as the collision of a flying metallic ball (at a moderate speed, i.e. not a bullet) against a metallic wall: no deformation at all, no work). LaosLos (talk) 17:22, 10 August 2011 (UTC)

"Change" is far too wishy-washy and general a word to even be useful. I can produce a "change" in a ball of clay by molding it to a different shape, or painting it. None of this has to do with energy. There are infinite ways to change composition of things and keep net energy change at zero. This is just a word to stay away from, SBHarris 17:38, 10 August 2011 (UTC)

This is only because energy implies changes, but not always changes implies energy. We are not talking about changes in general, but about energy, and energy is measured through its effects (the changes).

By the way, your examples are not true: you cannot change the form of anything without force and displacement (no displacement, no change of form), and you cannot do any chemical reaction (composition change) with zero energy (this would be the perpetuum mobile of chemistry, if in equilibrium, or nothing at all, if irreversible).

LaosLos (talk) 18:07, 10 August 2011 (UTC)

I agree... Actually I would think that molding clay involves a complex series of energy transactions in muscles and in the clay and in the surroundings. Similarly for painting the clay. I'm not convinced that any change can occur that does not involve energy transactions. Granted that "change" is not a defined term in a technical sense. However, anything that is colloquially understood as change would seem to involve energy processes. Even a color change (autumn leaves or bleaching) involves chemical processes that in turn involve changes in molecules that necessarily involve energy transactions (reactants to transition states to products, transitions in energy levels of electrons.

If change does not always imply energy then change cannot be used as a definition of energy. When heat spreads out in an object, the energy does not change-- only the distribution changes. But it is a change. A pendullum in a box changes every moment, but that's one sort of energy chaging into another, not a change in energy. Very similarly, vibration of atoms in an ordinary "unchanging" object are just like the pendullum-- as they vibrate back and forth, they trade kinetic for potential energy. Does an object just sitting there, at any real temperature, "change" from moment to moment? The answer depends on what scale you choose to look at. In short, this is a bad definition. SBHarris 19:20, 10 August 2011 (UTC)

"If change does not always imply energy then change cannot be used as a definition of energy", this is really non-sense, energy is not change, energy is measured by the changes it produces, that's all. By the way, the references in the article explains why not to use the word "work". For example, reference 11 does not include any kind of careful definitions of energy (it defines the energy à la Feynmann, with the mathematical expressions of all its forms), but in 1.5 it explains some misunderstandings associated with the use of the concept of "work" in the definition of energy. And in What is the Definition of Energy? the author explains very well the problems related with the definition of energy and he has found some definitions from a variety of books. LaosLos (talk) 19:54, 10 August 2011 (UTC)

Please don't yell. (i.e. cool it with the all caps).

Energy is an abstract quantity that can be measured, but only indirectly. It is useful because it is conserved. I'm gonna argue work is energy is heat. (Joules is joules.) However, most texts follow the historical approach -- it took awhile for science to understand heat is energy, so we treat them as separate things. While "ability to do work" is imperfect, it's probably as good a starting point as any. Regardless of what definition we end up with, it needs to be reliably sourced, not the product of original research. Gerardw (talk) 19:59, 10 August 2011 (UTC)

I aggree with you Gerard, it needs to be reliably sourced, and this is the reason why I'm searching in the references that the article already has. Moreover, I think that the definition of energy should make clear that heat is a form of transfer of energy, in the same way the work is. So, to me, the "ability to do work" sounds like the "ability to produce heat". Then, yes, the energy, when transferred, does work and/or produces heat. If produces changes (a standard definition, reliably sourced) is not a good definition for you, then we can choose the "ability to do work and/or produce heat" option (a very thermodynamical definition) but, as far as I know, this is not a standard one, and I don't know references for this definition. Loosely, we can consider this definition as the outcome of the first principle of thermodynamics (even if the first principle is not actually a definition of energy). LaosLos (talk) 20:32, 10 August 2011 (UTC)

"Produces changes" is NOT a standard definition! Bodies like NIST and ISO produce "standard definitions" in physics. Definitions in physics are not produced by consulting random undergrad college texts, of which there are hundreds, and most don't agree with each other (you should see the argument we had about this on the TALK page of weight; it's gruesome). College texts tell us nothing more than what one random author of one college text thinks, and that is all. White's Geochemistry is just a ridiculous source to draw a definition of "energy" from. Sorry.

Yes, energy is measured by the changes it produces, when it produces a change, and when it's a particular kind of change (one that involves energy units and a form of energy to be defined). That's not very profound, and you might as well back up a step and define the various forms of energy and say that "energy" generic involves any one of them. To address your specific point, many changes really do take no energy, and shape changes consume no energy unless PV work is done, which isn't always the case (the volume change of the system may be zero, and often is, in which case the system shape may change as a result of random thermal motion, but energy does not change). Energy doesn't produce some generic change like color or shape or even entropy content. It produces changes in a system's content of thermal energy or work or mass or something with an equivalent energy value. "Change" isn't measured in joules. SBHarris 21:33, 10 August 2011 (UTC)

Whatever definition is used it needs to be worked out in conjunction with the article on Work (physics). At present this article and the one on work are together faulty, in that this one defines energy in terms of work and the other article defines work in terms of energy. Circular definitions are obviously unsatisfactory. Either this article or the other one need to be changed. Would anyone like to suggest which? One solution, though in my view an unsatisfactory one, would be to merge the articles. 18:00, 24 September 2011 (UTC) — Preceding unsigned comment added by Treesmill (talk • contribs)

Work can be defined as "the work of a force", without reference to energy (by the well-known path integral and its translation into words), which I actually decided to do in the work article. This allows for the the reference to work in the energy article, and I believe it should be kept there, although some refinements would be helpful, following the suggestions by UpToTheMinute.

However, his suggestion to define a physical quantity by its dimension does not reflect standard practice at this elementary/basic level. Also, I agree that the "ability to cause change" is in no way specific to energy.

Finally, I support the suggestions by UpToTheMinute that the lead should illustrate the various forms of energy, and how "useful" it is. But I believe it should end with the classical physics "quantity that is conserved due to the homogenous flow of time" and then with the transition to the mass-energy equivalence.Ilevanat (talk) 00:18, 1 October 2011 (UTC)

It is easy to define Energy, it is only difficult to get the definition accepted. Energy is mass, typically expressed in other units. 68.144.100.86 (talk) 09:38, 10 May 2012 (UTC)

Energy is motivation.

Energy cannot be either created or destroyed therefore energy is a static eternal, unlimited medium. When energy is limited by the Nothingness of the limit of the observer’s I it becomes a unit ‘now’ of consciousness of the observer. The observer can then interact with other such limited units of energy. Two different ‘now’ create a difference which motivates for change. The change can be registered by the observer only as the static difference when he compares two static pictures which exist in two moments ‘now’ of time. Transformation from the static state in the first ‘now’ to the static state in the second ‘now’ is not observed unless the interval of the time of transformation can accommodate the unit ‘now’. The three static elements namely the two pictures and the difference between them is one observation located in the current ‘now’. To transform from the first picture to the second picture requires that the first picture is motivated by an independent cause because static state has no initiative. The cause of the transformation is the energy observed as, and contained within the difference. When the interval of transformation is large and when it can accommodate a limited plurality ‘c’ of the units ‘now’ of the observer’s consciousness, the interval of transformation becomes the sum of the small transformations 1/c. This can be symbolized by (0<u<1) where ‘0’ is the first picture, ‘u’ is the current ‘now’ of the observer, and ‘1’ is the end of the transformation and it is the second picture. The static states of ‘0’, ‘u’ and ‘1’ are one static self-sufficient system if ‘1’ is the cause of change for the picture in ‘0’. The energy contained within the self-sufficient, perfect system is then neither lost nor gained. When the system is imperfect energy is gained from the outside of the system and lost from the inside of the system. If energy is eternal it has no beginning and no end and it neither exists or non-exists. It simply IS as the duality of existence non-existence created by the observer of the energy. It is the duality of existence non-existence that has the beginning ‘0’ and the end ‘1’ together with the dynamism between them created by the observer. KK (78.146.64.106 (talk) 16:09, 23 October 2011 (UTC))

Archimedes Plutonium, is that you? SBHarris 16:36, 23 October 2011 (UTC) No! It is not. Is that you Pythagoras?

Edit request from , 23 November 2011

change "physically impacting it, but that case the energy of motion in an object, called kinetic energy"

to

"physically impacting it, but in that case the energy of motion in an object, called kinetic energy"

173.71.207.63 (talk) 02:30, 23 November 2011 (UTC)

First sentence

It should read:

"...indirectly observed quantity often understood as the ability of physical system to do work on other physical systems."

combine the sentences, and get rid of "has" — Preceding unsigned comment added by 38.98.88.24 (talk) 06:51, 20 January 2012 (UTC)

I don't understand precisely what is being suggested. Nobody Ent 12:33, 26 January 2012 (UTC)

"otheruses"

"otheruses" should be "other uses" in the second line of wiki text. — Preceding unsigned comment added by 76.94.171.77 (talk) 06:38, 26 January 2012 (UTC)  DoneNobody Ent 12:33, 26 January 2012 (UTC)

The international green energy Edit request on 7 March 2012

http://www.sfdsolar.com Domestic solar water heater used for family washing, bath,it is absoulte high quality hot water system, "green finance" allow the ordinary person to install a solar geyser Two primary types:closed loop system solar water heatr, Open loop System solar water heater — Preceding unsigned comment added by Sunfieldsolar (talk • contribs) 05:35, 7 March 2012 (UTC)

A link to an advertisement for your company's products is probably going to be regarded as spam and shouldn't be added. --Old Moonraker (talk) 07:56, 7 March 2012 (UTC)

Clarification on Power vs Energy entry

In an unsigned comment on my talk page, somebody (apparently S), wrote:

"Can I ask for clarification on the edit you made here:

http://en.wikipedia.org/w/index.php?title=Energy&diff=422793403&oldid=421132955

"My reading of this is that you're making the specific point that when used conversationally / by laymen / in a domestic context, the terms power and energy are often conflated and are hence regarded as synonymous.

"But in fact, this is an example of a fairly widespread vernacular use that should not be employed when discussing these concepts in a technical quantitative manner, i.e. they are not actually synonymous

"Is my interpretation of your addition correct? I ask because I'm seeing the fact you draw attention to this common misconception as somehow endorsing it as correct."

So, here's my answer: Yes, the passage is making the point that, in colloquial English, the terms power and energy are often used interchangeably. That does not mean that it'd be acceptable to interchange them in technical contexts! So that comment should not be interpreted as either endorsing or condemning the usage in non-technical contexts; it merely reports the popular usage to help non-specialists step from their familiar (the words are synonyms) to their novel (they have distinct meanings).

And here's another reason the article takes such a permissive stance on that usage: physicists and engineers do not hold legal title to words—indeed the colloquial usage was current for ages before scientists borrowed the words for specific technical meanings. So any such blanket objection to the colloquial usage would be roughly as arrogant and uninformed as a particle physicist's protesting the exclamation, "Oh, what a lovely charm bracelet!" on grounds that charm names a quantum number.

Hope that helps.—PaulTanenbaum (talk) 13:05, 14 May 2012 (UTC)

Do you have a reliable source for the claim power and energy are colloquial synonyms? Nobody Ent 02:03, 15 May 2012 (UTC)

I do not have a source handy that asserts the synonymy in so many words. But look at the names that utility companies choose for themselves: Constellation Energy, but Florida Power & Light. Duke Energy, which used to be Duke Power. And then there's Kansas City Power & Light, which bills itself as "a full-service energy provider." So that one (http://www.kcpl.com/about/about_corpintro.html) is a source that comes pretty close to sealing it.—PaulTanenbaum (talk) 02:32, 15 May 2012 (UTC)

Proposal for renaming and redirect (see above)

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Yo Yo Honey Singh - 4 times

Our basic problem is that energy as a search-term directs to this science page, which is actually energy (physics), and should be titled that. Plain energy should really direct to the energy (disambiguation) page, exactly as happens with the terms work and power which have exact physics/science meanings, but also older colloquial meanings, which aren't as technical. And which both now direct to the dab pages, NOT to the science pages work (physics) and power (physics).

So I hereby propose that the redirect be done, and (as a separate issue) that this page be retitled energy (physics). SBHarris 01:36, 18 May 2012 (UTC)

Concur with concept. I think this page has to be moved to energy(physics) to allow the redirect to the disambig page to exist. Nobody Ent 02:07, 18 May 2012 (UTC)

I agree that that would be helpful. But I don't know that it would eliminate the need for the para (in the physics article) that clarifies the difference between this technical term and the other technical term.—PaulTanenbaum (talk) 02:10, 18 May 2012 (UTC)

Well, perhaps it would not. But at least it could say that when power and energy are used as synonyms, one of them is being used untechnically! For example, your electric "power company" doesn't actually sell you power, rather it sells you kilowatt-hours, or in other words, units of energy. That's what comes out on your bill. SBHarris 02:30, 18 May 2012 (UTC)

Mine's in dollars. It's a hair split -- it could also be argued the company provides potential (volts) from which we take energy by varying the load. Nobody Ent 02:33, 18 May 2012 (UTC)

Your bill has more than dollars on it, I promise (look closely). The company doesn't just provide volts (access to the potential) but also access to the coulombs of charge that wiggle back and forth, and the more coulombs that are wiggled for you by the power company (voltage being the same), the larger your electric bill will be: volts*coulombs = joules. Another way of saying this, is that you get not only volts but also amps for a period of time, and volts*amps*time = joules is (more or less) what they bill you for (neglecting power factor and complexities of AC). In the end it all comes out in joules, convertable to kw-hr at the rate of 3.6 million J per kw*hr. SBHarris 02:43, 18 May 2012 (UTC)

The question whether Energy should go directly here or to energy (disambiguation) depends on the question whether the technical / scientific meaning is the dominant one or not. This is hard to decide, likely with no clear yes or no. Likely we had that discussion before.--Ulrich67 (talk) 17:39, 7 August 2012 (UTC)

Should we not add end less energy or use of potential energy in a transducer?

depending on what type of exam it is. if it is a simple class test you can usually write yours notes on the page where your answers will also be. you do this by writing your notes on the previous page with alot of force causeing the writing to press trough the next page. another way is to paut your notes between da pages within your refill pad and then you just have to be careful not to get caught flicking through your refill pad. another great trick is to leave a ruler in the page of the book where your notes are this way you can just open the book with the ruler and this way you can see your answers.

when it comes to state exams it is alot harder and when examiners cheak you for cheates they also see through the water and then they can see you notes.

you can buy cheat rulers which have either hidden paper of compartments this is easier and noone ever finds out unless you get caught.

so these techniques need to be practised as much as one would practise for cheating at a blackjack game as other wise you will get cought. i hope this helps......

but the best way not to get cought is to study obviously. 5 years ago Report Abuse

ironman virtually u cheat yourself. by cheating, your actual merit is far less than that scored in the examination and u will not survive withot cheating rest of your life. so it is better to prepare well and appear in full confidence. but i suggest, the important matters that u need to copy in exam- just write on small sheets. write the slips again and again. ultimately, it will give u such preparation, that u will not need to use in exam. once i had prepared some small slips to take to examination hall. but the very process helped me learn and i needed no unfair. o 5 years ago Report Abuse 2 people rated this as good

Cem Doğan lots of best way to cheat in an exam .. for instance l m gonna write some of them and l wish they'd be helpful for you.. 1. writing them on your legs if you are a girl ( cuz they not look ur legs ) 2. write them in small peaces and put them under your desk 3. write copies papers and glue them under your friend's shoes and he must sit front of you and when you need it then just say him to pick up his shoes and when teacher he will already put them down.. remember copy paper will be stick and glued to your friends shoes.. 4-one of your friend must wait under the window and you should give him the question by rope then after he search then he will convert the copy papers with original papers my friend.. 5- write original question and during the exam suddenly hold your stomach and say it hurts then go to WC and give them to your friend then turn back and wait after little time passed again hold your tummy and say l need to go WC then go there and convert resolved question and back to class .. 6-write anything to your paper and give its empty ways and after you sit then suddenly say that you forgot to write your name go there take someones paper and remove his or her name and write your own name..

l did ( number 5-3) and it worked l got A point my friend.. :D 5 years ago Report Abuse 1 person rated this as good

a n n a I have a few methods. However these methods only work if they allow these items inside.

1. Put cheats in your pencil case. The teacher's will think you're looking for a pencil or pencil sharpener.

2. Get a bottle of water with a label around it. Tear off the label and write cheats on the inside of the paper. Stick the paper back on and fill it up with a drink. The teachers will think it's only a drink.

3. Get something that records your voice. Record some cheats. When you're in class, listen to it. The teachers will think you're listening to music.

4. Cough or sneeze in class. When you move your head, look at the other person's answer.

5. Try to get a hold of previous exam papers. Or ask a friend if they had an exam previously. Usually teachers repeat or ask a similar question. Familiarize yourself with them.

Goodluck on your exam! 5 years ago Report Abuse 2 people rated this as good

Msbearr You might not want to hear this but here goes. I used to cheat on my test/exams. Were did it get me in my adult life? No were. Due to the fact of my cheating for so many years and lack of learning what I needed to know I am now having to go back and relearn it. I wished I had taken the extra time to study and go the extra mile, back then, because I sure would not have made the mistakes I have over the years and most of all I wouldn't have to go back and relearn it now.

The best way is to learn it the first time. (STUDY). 5 years ago Report Abuse 9 people rated this as good

Helen Clark (3rd account) Um... one of my best techniques is to wear a loose button up shirt that has a front pocket. Since it's loose, I just put my little piece of paper in the bottom pocket facing up to me. I can easily read this, and just lean over when the teacher comes past. Always do it on the computer, you can do it much neater and clearer this way. Some schools allow mp3 players to help the students relax. This is the perfect way to cheat. My school dosen't, so I can't do this, but if yours does then this is the way to go. Just record yourself and put it on the mp3. This really is a great way of cheating. Personally, I don't copy on my neighbor unless I really need to. This depends a lot on how neatly they write. If they get something wrong or spell it wrong and you go and copy it, you're stuffed. They aren't stupid and will quite likely notice if you both have exactly the same mistakes. If you are allowed to have a pencil case, then this is ideal. Just stick a note in there. If not, and you have one of those calculators that have case case that clips on, you can just write it on the back of this (my favorite technique). The main thing with cheating is to play it cool. Inexperienced people will get scared, their heart will start beating really fast etc... Just calm down. Do it sensibly, but you (depending on your level of experience) can almost forget about the teacher. Don't look at him / her or they'll suspect something. Keep this in mind and you'll do just fine. Source(s): Been at school for ten years now (I'm 15), and have been my class's best cheater for 13 of them. 5 years ago Report Abuse 2 people rated this as good

WindWhis... Simple: Don't!!! I know that my University takes it so seriously that if you are caught cheating in any fashion they can actually kick you out of uni :S Not worth it at all - Just study!

Plus it's the people that cheat and therefore get all the answers right that push the grade boundaries up , making it harder for us decent people who actually work to get results that reflect our hard work- shame on you, boo hiss boo! 5 years ago Report Abuse 3 people rated this as good

Divesh R i have never tried the water bottle thing dunno if its effective

1. the calculator thing is the best - u can put paper with notes written on it between the calculator and its case - or write with pencil on the back of the calculator and dnt worry, during exams with plenty of light on, the graphite writing will shine. (write in small caracters in order to be able to get maximum notes written on it!)

2. put text books or notes inside toilets before exams and during, go to toilets

3. write with pen on ur arms (formulae and definitions) then wear long sleeves

4. keep notes inside ur pocket and go to toilets.

5. write notes in your mobile, put on silent and put in between ur legs (on the chair) before exams start. during exams, look at ur pants (!) 5 years ago Report Abuse 1 person rated this as good

☼ kayla ☼ Take the paper thing off a water bottle, and on the back of it write down any info that you need to know. put it back on the water bottle, and keep it on your desk.

but it's best it you just study... if you get caught for cheating, you can have your exam taken away. Source(s): i've never cheated before... i've just heard of this a lot of times. =] 5 years ago Report Abuse 2 people rated this as good

Irony Man Look at the past years exam papers.

Usually the teachers repeat some of the questions for current year.

So by focusing your studies on these exam questions, you can reduce the number of pages you need to read to pass your exam. Source(s): Personal experiences. 5 years ago Report Abuse 4 people rated this as good

X.sunset... keep notes in your blazer pocket, read over exam, memorise questions you do not know, Ask to go toilet, look through your notes. heh it took me some time to think of that now, although i'd never ever cheat, and dont you do it either =] x 5 years ago Report Abuse 1 person rated this as good

Male-pro... unless your home schooled, your S.O.L. The ole' looking on the smart guy's paper usually works. know your smart guy though. Or, just study next time and put the women or weed down for a moment. lol good luck and dont get caught, teachers hate that. 5 years ago Report Abuse 2 people rated this as good

Bùi Văn Hoà Ha ha The best way is to study hard until you have an exam. As long as you have a firm knowledge you'll get confident and cheating is no problem. 5 years ago Report Abuse 2 people rated this as good

Jules The easiest is to pay someone who will definitley pass. Uni students are always looking for a quick buck, so they are perfect - cheap and intelligent! I've never been asked for ID when taking an exam... 5 years ago Report Abuse 1 person rated this as good

sonu d i do't know your question, it mean, to behave in a dishonest way in order to get what you want, please find another question, 5 years ago Report Abuse 2 people rated this as good

Lil Miss dont cheat at all... when you get the results u wont feel nefink frm it like... that you have achevived anything but cheating theres no point coz like it aint your hard work 5 years ago Report Abuse 2 people rated this as good

xtine_li... put ur book in ur table drawer,, during the exam, pretend tat u r touch up ur hair style or anything or drink water than see it!! wkwk... 5 years ago Report Abuse

gudy_16 you should study, remember, god watches you 5 years ago Report Abuse 2 people rated this as good

Tinkerbe... its not,cos if you got caught then you wouldnt get any marks! just do your best! 5 years ago Report Abuse 2 people rated this as good

misskitt... no way is best just hit the books and good luck

regards x kitti x 5 years ago Report Abuse 3 people rated this as good

custard! write as much on the inside of your clothes lol, ur hands and your rubber and ruler! 5 years ago Report Abuse

maca if you try then you are ultimately cheating yourself 5 years ago Report Abuse 4 people rated this as good

johny the pencil case one write the answers on your case 5 years ago Report Abuse 2 people rated this as good

. No best way, cheating won`t help you in the long run....... 5 years ago Report Abuse 3 people rated this as good

Duke75 Get the questions and answers beforehand. 5 years ago Report Abuse 1 person rated this as good

ktsteer8... sneak a lil bit of paper in with u, dont make it obvious that u r looking @ it. It worked for me :) 5 years ago Report Abuse 2 people rated this as good

chintz There is no "best" way, goodness, society these days. 5 years ago Report Abuse 3 people rated this as good

Natasha Don't cheat! revise! 5 years ago Report Abuse 2 people rated this as good

Sara Sit next to someone smart...lol...or put notes in a calculator case!! 5 years ago Report Abuse 1 person rated this as good

Mr. Q study. 5 years agoIn a transducer if we try to make use of an object with its potential energy like a super advanced pendulum, we could reach up to another new heights of energy 'conversion' after research cause on using potential energy to create kinetic energy in a pendulum with a magnet as the pendulum's bob striking a coil with its magnetic field we have converted energy in the desired form. But still according to your statements right mechanical energy keeps converting from potential to kinetic and vice versa there is no creation or emmition, when you go for electric energy its like nuclear energy keeps attracting positive and negative charges to each other while creating electricity we just bring out that nuclear energy to separate nucleons and electrons. Thus energy is the same always in matter whether mechanical or nuclear. Khpatil (talk) 05:04, 10 August 2012 (UTC)

Wrong thermodynamics perspective

"With thermal energy, however, there are often limits to the efficiency of the conversion to other forms of energy, as described by the second law of thermodynamics.". Wrong. The laws of thermdynamics apply. The entropy of the universe tends to a maximum, does not matter if you're talking about "thermal energy" or not. — Preceding unsigned comment added by 186.32.17.47 (talk) 06:59, 30 October 2012 (UTC)

i.e. in an electrical motor, in the conduction of electricity through wires, in chemical reactions: The laws of thermodynamics always apply. — Preceding unsigned comment added by 186.32.17.47 (talk) 07:02, 30 October 2012 (UTC)

"If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations—then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." — Sir Arthur Stanley Eddington — Preceding unsigned comment added by 186.32.17.47 (talk) 07:25, 30 October 2012 (UTC)

Well, the energy in the spinning of a flywheel is not associated with any entropy, so the thermodynamic limiting efficiency on converting it into another form of energy is exactly 100%. Ditto chemical energy, gravitational potential energy, etc. Thermal energy is associated with nonzero entropy, so it can only be converted at less than 100% efficiency. If thermal energy is the only kind of energy associated with entropy, then I don't think the text of the article is misleading. Is it? Or are there others? Can you give an example? --Steve (talk) 13:19, 30 October 2012 (UTC)

Friction. Narssarssuaq (talk) 13:16, 5 November 2012 (UTC)

"The Second Law

The number of quantum states plays an important role in the settlement of physical equilibrium, for instance the cooling down of a cup of tea, the fading out of a flywheel’s rotation etc. These numbers of quantum states being very large in physical systems, brings about that any difference between two macrostates of the same system is generally coupled with a correspondingly large disparity of those numbers. An example is a system with two parts at different temperatures moving spontaneously towards equal temperatures. Think of an isolated system with two copper blocks of one mole each, beginning at the temperatures 299 K and 301 K respectively, moving to the state with both blocks at 300 K. The molar heat capacity of copper is 24.44 J/(molK). A relatively simple calculation shows that in the process the entropy increased with 0.00027 J/K, seeming a small increase, nevertheless being important, since it corresponds with a large disparity of the number of quantum states: the effect of the process comes out to be an increase with the factor:

Energy being constant, all those quantum states have the same probability and the system will wander blindly over the enormous quantity of quantum states of both types ending up (almost) certainly in one of the quantum states of the macrostate with equal temperatures, merely driven by the large disparity of numbers. (Compare with the ‘pixel hopper’ in figure 2.)"

http://en.wikibooks.org/wiki/Entropy_for_Beginners

In all physical procecess that involve the transformation of energy there is some entropy involved.

"Considerations

In this discussion we will take a closer look at the definition of entropy and the Second Law of Thermodynamics. In classical thermodynamics the entropy is introduced as follows: For any physical system a function of state, S, exists, called “entropy”. For homogeneous closed systems it increases, after a small heat supply δQ at a system temperature T, according to ...............................(1) noting that δQ is an inexact differential. The entropy is a state function and dS is an exact differential. For non-homogenous systems the entropy is the sum of the entropies of the various subsystems. Here we will follow an approach along the lines of the statistical thermodynamics. It involves wave mechanics and is known as Boltzmann’s statistical approach. In the next paragraphs we will introduce entropy, almost without mathematics. It will be shown that this definition is in accordance with the classical one, given above, and a link to the following chapters of thermodynamics is made. This introduction begins with the discussion of ‘quantum states’." — Preceding unsigned comment added by 186.32.17.47 (talk) 16:11, 30 October 2012 (UTC)

Also see "http://books.google.co.cr/books?id=ZKPGzjS0IhcC&printsec=frontcover&dq=entropy&hl=es&sa=X&ei=0P6PULf1Forq8wTPz4CoDg&ved=0CCoQ6AEwAA#v=onepage&q=entropy&f=false"

Entropy is a function of _state_ not asociated with a path between equilibrium states. It can be computed in different ways but, when a process is irreversible, a reversible process that changes the system between the same two states would yield an ammount of heat where dQrev/T=deltaS... and so on. Free energy is the ammount of energy free to do work of a system. It is a function of state. Even when entropy is "small" it is still there. One can do engineering calculations regarding, i.e. Exergy, so that some simplifications can be made, but that does not mean that there is no entropy. There are no "perpetuum mobile" although you can get close, depending on the system. — Preceding unsigned comment added by 186.32.17.47 (talk) 16:36, 30 October 2012 (UTC)

If you take your time and read you will find that entropy is associated with _any_ physical process, not with "thermal energy". Entropy is a function of the _state_ of the system, not of it's path. _Any_ mechanism that changes the state of the system from state A to state B involves the _same_ change in entropy. — Preceding unsigned comment added by 186.32.17.47 (talk) 16:49, 30 October 2012 (UTC)

There seems to be also a confussion of "heat" with "thermal energy". Heat is the quantity that is transfered in "heat transfer phenomena". Thermal energy is all energy that is a function of general "temperature" of the system. Heat is transfered from higher temperature to lower temperature via radiation, convection or conduction. All of the internal energy of a system is a function of it's temperature, disregarding the kind. The basic equations of thermodynamics apply for _all_ procecess, not only the exchange of heat. E=Q+W. dS=dQrev/T where the dS is a function of _state_ and dQrev of path.

The laws of thermodynamics hold true even in general relativity (http://authors.library.caltech.edu/2576/) and quantum mechanics (http://farside.ph.utexas.edu/teaching/sm1/lectures/node46.html)

The general concept of entropy tends to be equated with the heat death of the universe as a whole and the arrow of time: when an object freefalls and generates heat (kinetic energy) when it hits .i.e. a table (even if it is in a vacuum) the process is not reversible: heat of the table does not send the object upward by itself (E=Q+W). dS=dQ/T. The universe has a latent radiation temperature of around 3K. It is a "heat sink". As energy is being used up as heat all procecess tend to cease. Of course in big bang or "eternity" or quantum situations it might be that all is not as it seems from the (abstract) thermodynamics of Josiah Willard Gibbs but up to now it seems that what always holds, as sir Edington said, are the laws of thermodynamics. (i.e. Newton was wrong, Einstein was wrong, etc. But the laws of thermodynamics, even though changed, still hold true). — Preceding unsigned comment added by 186.32.17.47 (talk) 17:11, 30 October 2012 (UTC)

A brief description of the laws of thermodynamics would be: If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other. The energy of the universe is constant. (mass-energy in modern therms). In any spontaneous process, there is always an increase in entropy of the universe. The entropy of a perfect crystal at 0 kelvins is zero. These laws are _universal_. They apply to _any_ physical process.

Let's say we are trying to transform gravitational potential energy into chemical energy, e.g. charge a AA battery by lowering water down a hill. The article as written right now seems to imply that exactly-100% efficient transfer is possible in this situation ("When energy is in a form other than thermal energy, it may be transformed with good or even perfect efficiency, to any other type of energy"). You are saying, "Maybe 99.99999% efficiency is possible, but because of friction, electrical resistance, and other such losses in the real world, 100% perfect efficiency can never be possible. Therefore the article is misleading." Is that a correct characterization of your complaint? --Steve (talk) 23:33, 30 October 2012 (UTC)

No it is not. My complaint is that the article is trying to reduce the role of thermodynamics and it's laws to some aspects of physics, when they are of wide application in physics (and chemistry). Entropy is a function of state. In the particular escenario proposed, as in others, the ammount of entropy of the universe (sum of entropy of the system and the sorroundings) is a function of the state of the system (Temperature, Pressure, composition, molar volumes, etc.) and sourroundings in the initial and ending states. The ammount of entropy is given also by dS=dQrev/T. That means that, if you find a reversible process that links both states the ammount of heat released (an inexact differential) divided by T is equal in magnitud to a differential increase in entropy (exact differential). The most efficient process you could get is given by Gibbs free energy exactly and by the exergy of the system in a simplified form. The example pointed out in the above paragraph is actually more complex than what might be thougth of at first glance since the battery involves also chemical equilibria, but that is besides the point; the main point is that the article and a bunch of other articles related to thermodynamics seem to have a limited understanding of the concepts and generality of the laws of thermodynamics. — Preceding unsigned comment added by 190.211.94.19 (talk) 02:25, 31 October 2012 (UTC)

I'm happy that you understand many properties of entropy, but I'm still struggling to understand exactly what aspect of the article text is wrong or misleading. I want to start by asking you a simple question, like you might see on an undergraduate thermodynamics homework. Let's say we are trying to transform gravitational potential energy into kinetic energy -- we want to get a flywheel to spin fast by lowering water down a hill. We want to do it at 99.999% efficiency, e.g. we want to reduce the water's gravitational potential energy by 100 joules, while increasing the flywheel's rotational kinetic energy by 99.999 joules. According to the laws of thermodynamics, is it possible to design a system which accomplishes that goal, or is it fundamentally impossible? --Steve (talk) 13:19, 31 October 2012 (UTC)

As per example on the efficiency of flywheels: http://www.jimloy.com/physics/2ndlaw.htm http://poisson.me.dal.ca/~dp_08_04/Theory.html http://www.mdpi.com/1996-1073/5/8/2794 http://www.distributedenergy.com/DE/Articles/1745.aspx http://www.wisegeek.com/why-is-perpetual-motion-considered-to-be-impossible.htm

On the example proposed: a lot is involved in the design and what efficiency you are measuring. You have a certain mass of water at a certain height. This mass of water "goes down hill" transforming part of the positional potencial energy on a gravitational field into kinetic energy. Part of that energy moves the flywheel around. Part of that energy goes into friction. The regime of the water could be turbulent flow or it could be laminar flow, etc. In order to have a better example is easier to consider only the flywheel: the energy stored in the flywheel's rotation and it's transfer to other mechanical devices in a vaccum. Still, some of the energy stored in this rotation is lost, through time, as heat, specially when you device a way in order to transorm that energy into work (the path escalar integral of a force through position). The maximum possible efficiency of a physical process depends on the state of the system and sorroundigs before and after the phenomena. An interesting solution is found in: http://books.google.co.cr/books?id=hBl2IIcbLy0C&pg=PA262&lpg=PA262&dq=water+flywheel+entropy&source=bl&ots=xjWJrkNDOz&sig=hp7CEq24py2x--bdXHqVk5a1lMc&hl=es&sa=X&ei=AXKRUOTiKIWQ8wStn4C4Dg&ved=0CBwQ6AEwAA#v=onepage&q=flywheel&f=false

Regarding flywheels I've been doing some research and the highest eficciency claimed I have seen is 98%. — Preceding unsigned comment added by 186.32.17.47 (talk) 18:59, 31 October 2012 (UTC)

http://en.wikipedia.org/wiki/Flywheel_energy_storage#cite_note-Beacon2-26 "Conversely, flywheels with Magnetic bearings and high vacuum can maintain 97% mechanical efficiency, and 85% round trip efficiency.[27]". — Preceding unsigned comment added by 186.32.17.47 (talk) 19:08, 31 October 2012 (UTC)

I don't care what measured efficiencies are here. They are not limited by thermo, and ideally could be 100%. Conversion of potential to kinetic energy is often perfect, as when electrons move in an atom. I encourage the user above posting from 2 IPs to learn the basics of WP. Pick a username. Sign comments. Be concise. As it is, you waste our time with comments unintelligible, irrelevant, or just plain wrong. SBHarris 19:34, 31 October 2012 (UTC)

Person 1 says to you: "I have invested billions in R&D to create a machine that can lower water down a hill and convert 120% of its gravitational energy into the rotational energy of a spinning flywheel. I will not show you the machine, it's a secret." I would respond, "No you don't, that's impossible, it violates the laws of thermodynamics."

Person 2 says to you: "I have invested billions in R&D to create a machine that can take heat from a 350K object, use 70% of it to recharge a battery, and deliver the other 30% as heat going to a 300K river. I will not show you the machine, it's a secret." I would respond, "No you don't, that's impossible, it violates the laws of thermodynamics. (The Carnot efficiency is only 15% in this case.)

Person 3 says to you: "I have invested billions in R&D to create a machine that can lower water down a hill and convert 99.999% of its gravitational energy into the rotational energy of a spinning flywheel. I will not show you the machine, it's a secret." I would respond, "Well, that would require new technological advances in ultra-low-friction bearings, etc. etc. I'm extremely skeptical that this machine really exists. But I don't know for sure. Maybe you are telling the truth"

Do you see how there is a very significant and sharp difference between the claims of person 1 and 2 on the one hand, and person 3 on the other hand? This is related to what physicists normally mean when they say that a certain feat does or does not violate the laws of thermodynamics, or that a certain efficiency is the thermodynamic limit efficiency for a certain process... --Steve (talk) 21:04, 31 October 2012 (UTC)

What SBharris says is _untrue_. The laws of thermodynamics apply to _all_ physical phenomena not just to those he wishes. Electrons do not "move" in an atom: they have a probability function. I do not know why he finds my comments uninteligible: probably he is not an engineer, nor a physicist. I _can_ comment on a wiki's talk page _without_ having a username. It isn't the wiki's policy that, in order to comment, one _has_ to have a username. Now, if you guys want to keep articles that are _clearly_ wrong from a thermodynamics perspective Go right ahead! It is wikipedia's loss not mine. Ideally efficiency in any process is limited by the ammount of heat that is lost, and the ammount of heat that is lost is, at most, the heat lost in a reversible process. dS=δQrev/T. The ammount of heat that _must_ be lost is the integral of the function of state "entropy (S) over absolute temperature. Themodynamics deals with _all_ physical processes, not only "thermal" ones. SBharris seems to confuse heat transfer with thermodynamics.--201.204.200.18 (talk) 23:37, 31 October 2012 (UTC)

I am not a physicist: I am a Chemical Engineer. Still our training in physics, physical chemistry, thermodynamics, transport phenomena and such was deep enough. I am not an expert on flywheels but I do think http://en.wikipedia.org/wiki/Flywheel_energy_storage gives a good enough explanation with a reference [27] that claims an mechanic efficiency of 97% and a round trip efficiency of 85%.

In any case I think what it says on http://people.eng.unimelb.edu.au/montyjp/Thermofluids1/lecture%208.pdf is a good persective: "a freely rotating flywheel is connected to an electrical generator which in turn is connected by wires to a resistor in the reservoir" "the flywheel will eventually come to rest, with the (finite) electrical energy generated becoming heat in the resistor that then diffuses into the reservoir. The heat generated is equal to the original kinetic energy of the flywheel". And when you try to do work yo will loose some energy in the form of heat, wheather it is the work performed in order to start the rotation of the flywheel or the work intended to be done with the energy stored in the fliwheel. I do not know why Sbyrnes321 is making this discussion of the "Wrong Thermodynamics Perspective" of, i.e. Sbharris, about the possible maximun efficency of a flywheel, nor do I have the whole picture as to how to calculate the entropy on this flywheel example; in part because in the example it is not clear what _work_ is going to be done with the energy, but also because I am not an expert on flywheels. Al I know is that they are quite efficient, but regardless of the efficiency of a flywheel, thermodynamics is about _all_ physical phenomena not solely about "thermal" phenomena. We use thermodynamics in mechanics, in optics, in chemical reactions, in solutions, y vapor liquid equilibria, in nuclear reactions: we even measure thermodynamic variables in quantum mechanics and in general relativity.

I really can't get past the fact that people that think that "electrons move in the atom" are the people writing wiki's articles on physics.--201.204.200.18 (talk) 00:01, 1 November 2012 (UTC)

Electron motion (or lack of it) in an atom is an odd quantum thing that cannot really be visualized. Doesn't matter. Electrons certainly move from one atom to another, and then that happens, kinetic and potential energy are still perfectly transduced. This also happens in elastic collisions between atoms, in chemical reactions between atoms, and so on. The second law of thermodynamics is statistical and it doesn't apply to simple systems where you cannot calculate an entropy. One atom does not have a temperature, and does not have an entropy.

The laws of thermodynamics apply to all systems, except for systems where they are irrelevant. SBHarris 00:47, 1 November 2012 (UTC)

No, electrons do not move about an atom. In quantum mechanics the duality of particle/wave implies a _probabilistic_ wave function for the electron that, in an atom, constructs chemical orbitals; it also happens in chemical compounds: this does not mean that they "move" because their not particles nor waves but exhibit particle wave duality. Electrons (in the conduction band)do move in metals when subjected to a diference of potential, and when they do, they release heat and there is an entropy associated as there is an entropy associated with chemical reactions. Actually entropy _is_ the quantity that defines wether a chemical reaction is spontaneous or not. As per thermodynamics in the quantum level see http://en.wikipedia.org/wiki/Quantum_thermodynamics and http://www.quantumthermodynamics.org/. The atom described has an entropy related to it's kinetic energy and possible microstates of ln(omega). Only if the atom is at absolute zero on a crystal _then_ it has zero entropy (the third law of thermodynamics). If the atom is above absolute zero it _has_ entropy. See: http://books.google.co.cr/books?id=cw0QV7l559kC&pg=PA80&dq=%22entropy+of+an+atom%22&hl=es&sa=X&ei=r8yRUNOCBoa88wTEv4Eg&ved=0CCoQ6AEwAA#v=onepage&q=%22entropy%20of%20an%20atom%22&f=false The laws of thermodynamics apply to all physical phenomena discovered up to now; exact conservation laws are those that have yet to be disproven, the second and third laws of thermodynamics also have not been disproven. See http://en.wikipedia.org/wiki/Conservation_law and http://en.wikipedia.org/wiki/Second_law_of_thermodynamics As per the above quote: "If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations—then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." — Sir Arthur Stanley Eddington" Also: The second law of thermodynamics is, without a doubt, one of the most perfect laws in physics. Any reproducible violation of it, however small, would bring the discoverer great riches as well as a trip to Stockholm. The world’s energy problems would be solved at one stroke. It is not possible to find any other law (except, perhaps, for super selection rules such as charge conservation) for which a proposed violation would bring more skepticism than this one. Not even Maxwell’s laws of electricity or Newton’s law of gravitation are so sacrosanct, for each has measurable corrections coming from quantum effects or general relativity. The law has caught the attention of poets and philosophers and has been called the greatest scientific achievement of the nineteenth century. Engels disliked it, for it supported opposition to Dialectical Materialism, while Pope Pius XII regarded it as proving the existence of a higher being. Ivan P. Bazarov, "Thermodynamics" (1964) A theory is the more impressive the greater the simplicity of its premises, the more different kinds of things it relates, and the more extended its area of applicability. Therefore the deep impression that classical thermodynamics made upon me. It is the only physical theory of universal content which I am convinced will never be overthrown, within the framework of applicability of its basic concepts. Albert Einstein (author) --201.204.200.18 (talk) 01:38, 1 November 2012 (UTC)

You do not need to convince anyone that the second law of thermodynamics is applicable in all circumstances. I promise that you, me, and SBHarris already agree with this. When you are discussing football with your friends, do you bring up the second law of thermodynamics? No. Do you believe that the second law of thermodynamics is true during football games. Yes. But it's just not really relevant to the discussion of which team will win. By the same token, an argument that the second law of thermodynamics should not be mentioned in the description of a certain fact is not the same as an argument that the second law of thermodynamics is not true!

My argument is that, when applied to the conversion of electrical energy to mechanical energy, or mechanical energy to gravitational potential energy, etc. etc., the second law of thermodynamics does not tell us anything we didn't already know.

Is it possible (or even guaranteed) that friction etc. will turn some of the energy to heat? Yes, we already know that friction exists. (Friction is not quite inevitable, e.g. superfluids can flow without friction, but it is almost always impossible to avoid.) We don't need to invoke the second law to explain to readers why friction and other losses exist; the readers already know that friction exists.

Is it true that when friction generates heat, the conversion efficiency must be below 100%? Yes: By conservation of energy, the energy that goes into friction-related heat is energy that does not go to other destinations. The second law is not relevant to this, just conservation of energy.

So far, all we need is conservation of energy and common sense. The second law does not add anything to our understanding of the conversion of electrical energy to mechanical energy. Therefore it is not worth mentioning in that particular context, even though it is still true.

By contrast, in the case of thermal energy, the second law says something very important and unexpected: The efficiency with which thermal energy can be converted into another form is not just limited to be below 100%, but it is in fact limited to the Carnot efficiency, usually much less than 100%.

(Why does thermal energy have this property while gravitational potential energy (for example) does not? Because an object gains entropy in the process of receiving thermal energy, but does not gain entropy in the process of receiving gravitational potential energy, i.e. being lifted up.) --Steve (talk) 20:08, 1 November 2012 (UTC)

Actually, when you lift a body against a gravitational field you are transforming energy into work, which implies you are releasing heat somehow and increasing the entropy of the universe, somehow. The body that is "lifted" does not increase it's entropy but the entropy of the universe increases. ΔE=Q+W. ΔSTot>0, that is why you need to exert work on the body in order to raise it and, if not supported by a normal force it will fall, realising heat, either as friction or on impact. This is why the process is irreversible (the body is not going to spontaneously gather heat from the sorroundigs and lift itself). Of course when you take quantum dynamics into account it becomes a probabilistic phenomena, of course when you take the general theory of relativity into account you have to deal with the energy equivalent of the mass as E=mc2 and things get complicated (objects increase their mass in the presence of a gravitational field as GMmo/rc^2, etc.). So in dealing with why some transformations of energy into work are reversible and which ones are reversible entropy _does_ play an important role. Actually talking about transformations of energy without refering to ΔE=Q+W and dS=δQrev/T where ΔSTot>=0 seems (to me) preposterous. Now if your only concern is the ammount of gravitational potential energy of the body it's only the change in position in the gravitational field taht is of interest, but how did you achieve that? by doing work against the gravitational field and, thus, increasing the entropy of the universe (unless lifting a body in a gravitational field is spontaneous).

You claim that SBHarris agrees that entropy is "applicable in all circumstances" but he does not seem to understand this, as per his indications above, where he seems to claim that thermodynamics does not apply to a whole bunch of systems, even where they are of extreme importance (He seems to claim that thermodynamics do not apply on chemical reactions! he should at least browse a physical chemistry book). I do not doubt SBHarris or Sbyrnes321 have the best of intentions but I do believe that there is a wrong thermodynamics persective on a bunch of assertions in a bunch of articles on energy and thermodynamics. I do think it important to point this out so a physicist or a chemical physicist or a physical chemist with expertise on thermodynamics would take the time to review the articles. I am a chemical engineer and a bit out of practise on thermodynamics issues so I won't attempt to rewrite what I think is wrong with the articles themselves.

I _do_ believe that you are wrong in trying to diminish the role of thermodynamics in _all_ transformations of energy, wether the energy is later on accumulated in another system or not. Energy is (more or less) the potential to do work. Work is a scalar entity that quantifies the exertion of a force through position. (W=INTEGRAL(Fdotdx)). Heat is what energy is lost during the conversion of energy into work. Work and heat are the two ways in which energy is transfered (either by the exertion of work or by the tranfer of heat via i.e. convenction conduction or radiation). The minimal ammount of energy lost as heat is given by the second law of thermodynamics, when entropy is quantified as a change of state of the system and the sorroundings and then δQrev=dS*T. One can develop quantities such as exergy in orther to simplify or use the free energy of the system (the ammount of energy that is not requiered as a minimum of heat released to the environment, more or less). In respect with the general theory of relativity and quantum dynamics new redifinitions of what entropy and energy mean have been formulated or are being studied. But on _any_ article on energy and it's transformation the role of entropy as, i.e. "the arrow of time" (which a mere mechanical analysis of systems does not provide for) is fundamental. Of course there are problems in mechanics that one can solve based only on mechanics (changes of momentum, angular momentum, potential energy in gravitational fields, etc.) or one can solve energy related issues, but the study of thermodynamics _is_ the study of energy (as a physical quantity), and it's transformations through work and heat... Sorry if I do not have the time to summarize better, as we say in spanish "I wrote you this long letter because I do not have the time to write a shorter one". My best regards to all wikipedians. — Preceding unsigned comment added by 201.204.200.18 (talk) 21:19, 1 November 2012 (UTC)

Actually: another aspect regarding the body on a gravitational field: here it is clear that the energy (in this case the potential energy) of the system is a function of state (in this case the position in the gravitational field) but the ammount of work used is a function of the path taken, as is the heat released, and the total energy "used up" for the increase of potential energy will be a function of state of the system plus a function of state of the universe... hence the importance of the laws of thermodynamics (and really all conservation laws and the law of the increase of entropy). Actually, when solving problems what we used to have to do, in "mathematical modelling of processes" was to clearly define the system in study, clearly define the conservations laws at play and entropy increase conditions as needed, substitute consitutive relations (i.e. physical laws or theories that apply), substitute properties of the system or their models, and solve either differential or integral or finite differences, etc. equations. — Preceding unsigned comment added by 201.204.200.18 (talk) 21:33, 1 November 2012 (UTC)

No, the entropy of a single atom isn't "kinetic energy" times ln(omega). It has nothing to do with kinetic energy, which is frame-dependent. Entropy, by contrast, is Lorentz invariant. The entropy of a bottle of gas is the same no matter what frame you view it in, although its total energy and temperature depend on the observer. The kinetic energy of a given atom can always be made zero by simply observing it in its rest frame, which is why you need many atoms to have an invariant quantity (as you move to one atom's rest frame, another one speeds up, and so on, and this makes S invariant). The entropy of a perfect crystal at 0 K is zero, and if that crystal goes by you at high velocity and high kinetic energy, guess what? Its entropy is still zero. If it had a temperature, that temperature would differ in different frames by a factor of gamma, but since it has a temperature of zero, its temperature stays zero even when it moves rapidly. When you understand this, you'll be wiser.

You are all mixed up about friction, which doesn't need to happen, or can be reduced as much as you like. The Earth in its ellipitical orbit (Mars is actually a better example) trades kinetic energy for potential energy every moment, and the efficiency departs from perfection only due to some dust in the way and radiation of gravitatitonal waves. But these are so close to 100% that you'd be hard-put to calculation how many 9's there are in the 99.99,,,,% conversion. It's been going on for billions of years, trading off maximally four times a year as the Earth is farthest from the Sun every 6 months, then nearest every 6 months. But as noted, it happens every instant since the orbit isn't perfectly circular. The amount of heat generated is neglectable, and certainly isn't involved with the (very large) conversion of kinetic to potential energy! The second law of thermodynamics tells you nothing about this process. And as has been pointed out, there are many processes like superfluid flow, where there is no friction. Even in your own example of electrons moving in a metal, if the metal is a superconductor there is no friction and thus no resistance and no heat generated by the current. The second law of thermodynamics has no use here. And so on. There's no point in talking about the second law where it doesn't do anything.SBHarris 01:24, 2 November 2012 (UTC)

I did not say "kinetic energy" times ln(omega) I said S=ln(omega), as stated in the reference, avaiable online, "At absolute zero, the kinetic energy of each classical atom is 0; the atoms are motionless in their cavities. At absolute zero, the entire crystal is one state. Each atom can be located exactly. The absolute entropy of an atom in the crystal at 0K is S=kbln(omega)=kbln(1)=0." but you can go ahead and read that page of the book directly in Google books (Energy and Entropy: Equilibrium to Stationary Sates, Michael E. Starzak. Entropy is not about friction. Entropy is a function of the state of a system. I stand by this summary, albeit simplified: Energy is the capacity of a system has to do work. Energy is transfered as work or heat. Work is a force exerted trough a distance. Heat is the ammount of energy rejected to the sorroundings of the system, usually via radiation, conduction or convection. Total energy is conserved. Conservation laws basically imply that input minus output is accumulation. When energy is used to generate work there is _always_ an ammount of energy rejected as heat. There is a quantity called entropy of the system such as that it's change is the ammount of heat released by an equivalent reversible process over temperature. The entropy of the universe increases for irreversible processes and remains constant for reversible process. Entropy might be related to the arrow of time.

I have not studied superfluids but in http://books.google.co.cr/books?id=-0OWF1Z6vRIC&pg=PA241&dq=entropy+superfluid&hl=es&sa=X&ei=rEGTUJGQC5O60QHR5oDACA&ved=0CDgQ6AEwBQ#v=onepage&q=entropy%20superfluid&f=false seems to refer to two phases in the superfluid phenomena, one which carries entropy and one that does not, and also it seems to point out that this two phase model is only a "conceptual framework". In http://books.google.co.cr/books?id=HWnDpQPpM3kC&pg=PA92&dq=superconductor+entropy&hl=es&sa=X&ei=f0OTUIvfMMLD0QHSwoDwBA&ved=0CC0Q6AEwAQ#v=onepage&q=superconductor%20entropy&f=false the entropy of the superconductor is actually _measured. — Preceding unsigned comment added by 201.204.200.18 (talk) 03:59, 2 November 2012 (UTC) In http://www2.mate.polimi.it/ocs/viewpaper.php?id=37&cf=6 you can verify about entropy and the general theory of relativity, which is concerned mainly with gravity. One problem here is that events on a cosmological scale Regarding the temperature and entropy of a single particle you should read: http://en.wikipedia.org/wiki/Boltzmann_constant — Preceding unsigned comment added by 201.204.200.18 (talk) 04:40, 2 November 2012 (UTC) I remit you _again_ to this quote: "The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. Sir Arthur Stanley Eddington, The Nature of the Physical World (1915), chapter 4". I'm sorry if I believe one of the great physicist of all time and not SBHarris. Any attempt to transform energy into work without increasing entropy seems to be condemned to failure (until now). — Preceding unsigned comment added by 201.204.200.18 (talk) 04:45, 2 November 2012 (UTC) Of course there is also that stuff about gravity _being_ an entropic force at http://www.nytimes.com/2010/07/13/science/13gravity.html?pagewanted=all&_r=0 and http://en.wikipedia.org/wiki/Entropic_gravity — Preceding unsigned comment added by 201.204.200.18 (talk) 05:06, 2 November 2012 (UTC)

SBHarris, the earth orbiting around the sun inevitably generates entropy by gravitational wave emission :-P

SBHarris, it is incorrect in my opinion to say that any energy-converting process can be exactly 100% efficient in the real world. At least I don't know any process that does not have any losses ... however small ... not even parts-per-hillion-jillion ... not even gravitational wave emission. As I suggested way above, I don't mind changing the wording to say that losses are inevitable ... "When--186.32.17.47 (talk) 16:46, 2 November 2012 (UTC) energy is in a form other than thermal energy, it is theoretically possible to transform it with very high efficiency to any other type of energy, including electricity or production of new particles of matter. (Exactly 100% efficiency is impossible because of friction and similar losses.)" --Steve (talk) 12:22, 2 November 2012 (UTC)

Okay, I point to the zero point vibration of a ground state hydrogen molecule, which emits no waves. Kinetic and potential energy here trade off, yet they sum to a constant, per the Schroedinger Hamiltonian (you have to write both energy terms or you cannot even solve the system quantum mechanically, so don't tell me it doesn't happen). There is perfect interconversion of these types of energy, as in a two balls on a spring, except no friction. This ground state system has only one state, so log omega (which is one) is zero, and thus entropy considerations do not apply. QED. Of course it's the same in a 0 K crystal, too. Our IP user is wrong that the atoms don't move. They do move. They move back and forth with differing velocities over time. SBHarris 17:10, 2 November 2012 (UTC)

I don´t know: I mean, here http://www.trilexinc.ca/media/other/692215-FBN_01.pdf the company Crest claims efficiencies of up to 99%. That is quite high for a boiler... I think it is quite daring to claim that efficiency depends on the "type" of energy. --186.32.17.47 (talk) 16:39, 2 November 2012 (UTC)

I would like also to thank Sbyrnes321 and SBHarris for their commitment to work on the wikipedia: I don't want to make this personal; actually I think it is great that people are willing to contribute to such a project. But there are some things that are complicated (a clear understanding of thermodynamics is not an easy matter: that is why I refer to a lot of books: It is not about what I think but what the state of science is on the matter at hand). It is better written in this quote "Every mathematician knows it is impossible to understand an elementary course in thermodynamics. V.I. Arnold, "Contact geometry: The geometrical method of Gibbs' thermodynamics," in Proceedings of the Gibbs Symposium, D. Caldi and G. Mostow, eds. (American Mathematical Society, 1990), p. 163" or "Isn’t thermodynamics considered a fine intellectual structure, bequeathed by past decades, whose every subtlety only experts in the art of handling Hamiltonians would be able to appreciate? Pierre Perrot, "A to Z Dictionary of Thermodynamics"" or "Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, it doesn't bother you any more. Arnold Sommerfeld".

SBHarris, I don't think that the zero point "vibration" of a ground state hydrogen atom counts as 100%-efficient energy conversion, because it's a stationary state. The expectation value of kinetic energy is the same at every moment, the expectation value of potential energy is the same at every moment. Describing it as having zero-point "motion" or "vibration" is sort of poetic, not really accurate. So this is not a process where energy is converting from one type to another... At least not in the sense that most people would imagine. :-) --Steve (talk) 23:01, 2 November 2012 (UTC)

Well, what sense DO you imagine it? Expectation values are averages. I understand stationary states in the sense of standing waves (as here), but on the other hand, you're trying to convince me of a system in which kinetic energy is manifestly non-zero and (so you say) also unchanging. But also (so you say) there's no motion in this system (no vibration). Huh? What, then, do you MEAN by "kinetic energy." In what sense is it present here, if nothing is moving? By definition of kinetic energy, I think you contradict yourself. SBHarris 01:23, 3 November 2012 (UTC)

See http://en.wikipedia.org/wiki/Ground_state — Preceding unsigned comment added by 186.32.17.47 (talk) 05:34, 3 November 2012 (UTC)

I know what a ground state is. I don't know what kinetic energy without motion is. SBHarris 06:37, 3 November 2012 (UTC)

If people read a phrase like "energy is converted from kinetic to potential energy" in the context of the article section in question, I think they would imagine that the system starts out at time 0 with a lot of kinetic energy and very little potential energy, and then a little while later it has a lot of potential energy and very little kinetic energy. For example, water has been lowered and a flywheel has started spinning. Whereas a 1s hydrogen atom at time 0 is exactly the same system, with exactly the same mix of energies, as a 1s hydrogen atom at any other time. So that's not a pertinent example, when taken in context here. :-) --Steve (talk) 12:06, 3 November 2012 (UTC)

I read and reread and can't find anywhere where it is stated that there is "kinetic energy without anything moving".According to http://en.wikipedia.org/wiki/Absolute_zero "At temperatures near 0 K, nearly all molecular motion ceases and, when entropy = S, ΔS = 0 for any adiabatic process, pure substances can (ideally) form perfect crystals as T → 0. Max Planck's strong form of the third law of thermodynamics states the entropy of a perfect crystal vanishes at absolute zero. The original Nernst heat theorem makes the weaker and less controversial claim that the entropy change for any isothermal process approaches zero as T → 0:

The implication is that the entropy of a perfect crystal simply approaches a constant value. The Nernst postulate identifies the isotherm T = 0 as coincident with the adiabat S = 0, although other isotherms and adiabats are distinct. As no two adiabats intersect, no other adiabat can intersect the T = 0 isotherm. Consequently no adiabatic process initiated at nonzero temperature can lead to zero temperature. (≈ Callen, pp. 189–190) An even stronger assertion is that It is impossible by any procedure to reduce the temperature of a system to zero in a finite number of operations. (≈ Guggenheim, p. 157)" There is also the concept of negative temperature to take into account "http://en.wikipedia.org/wiki/Negative_temperature"

But I stand by what started this wide, and interesting, discussion on the subject. "With thermal energy, however, there are often limits to the efficiency of the conversion to other forms of energy, as described by the second law of thermodynamics." and other assertions like this are wrong. The second law of thermodynamics and, actually, all of the four laws of thermodynamics, are of _general_ applicability on any physical process that involves the transformation of energy, up to today. There has not been a single subject matter in physics where they have been proven not to work and they are basic to the transformation of energy, up to what we know about the physical world. Energy is the capacity to do work. Energy is transfered from one system to another through work and heat. The total Energy (actually mass-energy) of the universe is constant. Work is the exertion of a force through distance. When the energy of a system is used to do work there is a minimal ammount of energy not converted into work (δQrev). There is a quantity called entropy, that _is_ a function of state, that can only increase or remain zero for the universe in _any_ transformation of energy; it remains zero for reversible processes and increases for irreversible processes. The entropy of a system is defined as dS=δQrev/T. On a microscopical level entropy has been defined as S=-kbln(Σ(piln(pi)))where pi is the probability of the "microstates" of the system, where a "microstate" is an specific microscopic configuration that the system might occupy during it's thermal fluctutations. The entropy of an atom in a perfect crystal as it aproaches zero tends to zero. Of course in small enough systems related to quantum dynamics and systems where the general theory of relativy apply all conceptualizations of physics are being challenged and the laws of thermodynamics have been reexpresed (as in black hole thermodynamics, gravitational waves, quantum entropy in quantum information theory... even some theorist making bold attempts to postulate that gravity is an entropic force). Even after all the proposed escenarios ranging from gravitational phenomena to quantum states the laws of thermodynamics hold true. — Preceding unsigned comment added by 186.32.17.47 (talk) 21:38, 3 November 2012 (UTC)

Deterministic fallacy

It would appear that living organisms are remarkably inefficient (in the physical sense) in their use of the energy they receive (chemical energy or radiation), and it is true that most real machines manage higher efficiencies.

Extended content

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crystalgibson This is amazing. Thank goodness I'm not from North Dakota and thank goodness I have no relationship status.This makes the shaky assumption that we know all of the biological purposes of each organism. Many complex chemical reactions occur within the organism that can make up for a large quantity of this supposedly *wasted* energy.

68.84.158.248 (talk) 20:38, 23 October 2012 (UTC)

Biochemists fondly believe that ATP is the energy currency of the cell, and that anything the cell does that requires an free energy input (even things we don't know about) will require ATP to do. Since we know the [input energy ==> ATP] conversion efficiency, that implies that we know the overall efficiency. It won't be markedly different unless we find some pathway in which cells use a lot of energy in a way that doesn't need ATP (other than make heat in homeotherms, which we know about). It's a valid point to say that we don't know what we don't know, but on the other hand, these other processes are like Bigfoot and the Yeti-- they have less and less room to hide every year. Major processes should be like an elephant in the bedroom; there's just not room for it in your closet or under your bed. SBHarris 22:24, 23 October 2012 (UTC)

There's a lot of things we don't know the why of, like why we should need Iodine to control our metabolism. And unfortunately, our best explainers have a tendency to die off at about the time they get to explaining well, like Asimov.WFPM (talk) 20:15, 3 March 2013 (UTC)

Definition

The definition in the introduction now says:

In physics, energy (Ancient Greek: ἐνέργεια energeia "activity, operation"[1]) is an indirectly observed quantity that is often understood as the ability of a physical system to do work on other physical systems.

But isn't this rather the definition of free energy, i.e. thermodynamic free energy? The definition now used simply appears to be wrong. Narssarssuaq (talk) 11:56, 5 November 2012 (UTC)

I can see that this is also the general topic of the thread directly above. The conflict may arise from the use of different system boundaries within physics and thermodynamics, respectively. However, physics makes a claim to being more general, or fundamental, than thermodynamics. Is, however, thermodynamics more fundamental than physics in some respects? If this is a fundamental debate, we should try to find some well-cited info which can be added. Narssarssuaq (talk) 13:29, 5 November 2012 (UTC)

I agree that the current definition of "energy" in the first sentence has a problem, but I can't think of anything better. Can you?

I remember in the past year or two, I read a book review in a magazine. Someone apparently wrote a whole book (for general audiences), called something like "What is energy?" The book discussed mechanics, Noether's theorem, thermodynamics, quantum mechanics, and on and on. But the reviewer said, even with this whole book, there was never really a satisfying answer to the question "What is energy?" :-P --Steve (talk) 03:12, 6 November 2012 (UTC)

"It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. Richard Feynman, in The Feynman Lectures on Physics (1964) Volume I, 4-1" http://en.wikiquote.org/wiki/Energy --98.197.30.38 (talk) 04:09, 6 November 2012 (UTC)

Energy is, at least, closely related to the ability to perform work and to produce heat. In mechanics and particle physics, the definition is pretty straightforward, because we are then dealing with a kind of ideal or idealised systems. In more complex systems, i.e. where many objects or particles are involved, energy also involves friction, random movement, heat production and the likes, where energy does not disappear, but becomes unable or less able to perform work. Not everyone knows that the First law of thermodynamics is complemented by the Second law of thermodynamics. There is a relation to the concept of exergy. In sum, the definition we've got is valid "for idealised systems" (objects), whereas in "real life" (systems) this definition rather refers to free energy. How to phrase this in words I do not know. As this is one of the most vital articles on Wikipedia, we should resolve this issue. Narssarssuaq (talk) 06:09, 6 November 2012 (UTC) More info here: [1] Narssarssuaq (talk) 06:42, 6 November 2012 (UTC)

I added some ideas to the introduction per the above. Now for the sentence "Since work is defined as a force acting through a distance (a length of space), energy is always equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length." In saying "against the basic forces of nature", it touches the thermodynamic objection to the general validity of this idea, but it is still poorly formulated, I think. Narssarssuaq (talk) 13:01, 6 November 2012 (UTC)

Here's how I would open the article:

In physics, energy (Ancient Greek: ἐνέργεια energeia "activity, operation") is an indirectly observed quantity. Energy comes in many forms, such as kinetic energy, potential energy, light energy, and many others. Energy can neither be created nor destroyed ("Conservation of energy"), but it is often possible to convert energy from one form to another. The question "what is energy?" is difficult to answer in a simple, intuitive way,^[ref] although energy can be rigorously defined in theoretical physics.^[ref]

While I think that free energy belongs in the introduction, being an important related concept, I think it's better to focus on energy itself first and foremost. Free energy and "the ability to do work" would be discussed maybe in the second paragraph. :-) --Steve (talk) 21:57, 6 November 2012 (UTC)

What about

In physics, energy (Ancient Greek: ἐνέργεια energeia "activity, operation") is an indirectly observed quantity. Energy comes in many forms, such as kinetic energy,potential energy,radiant energy, and many others. Energy can neither be created nor destroyed ("Conservation of energy"), but it is often possible to convert energy from one form to another, through heat and work (physics), The question "what is energy?" is difficult to answer in a simple, intuitive way,^[ref] although energy can be rigorously defined in theoretical physics. Only a certain ammount of energy can be used to peform work (physics) as some energy is always dispersed as heat according to the second law of thermodynamics. The energy that can actually perform work is dubed free energy ^[ref]

--98.197.30.38 (talk) 22:38, 6 November 2012 (UTC)

Nice! For energy conversion, "through heat and work" is a bit confusing I think. Are you saying heat and work are the only possible ways for energy to convert from one form to another? What about when an LED turns a battery's chemical energy into light energy? It seems that neither heat nor work created the light. There are many other examples. I would rather just spell out one example using a few more words, e.g. "it is often possible to convert energy from one form to another, for example when friction turns kinetic energy into heat". Other than that (and fixing the spelling errors) it's great in my opinion. :-) --Steve (talk) 03:33, 8 November 2012 (UTC)

We should perhaps keep what is already indicated about system boundaries, because energy = ability to produce work in some "myopic" or highly idealised contexts such as within the discipline of mechanics, and energy != ability to produce work within more "holistic" or system-based contexts such as thermodynamics, and this ambiguity is of vital importance to the definition. In order to illuminate this ambiguity, energy might also be contrasted with energeia. Narssarssuaq (talk) 12:19, 8 November 2012 (UTC)

Actually, radiation _is_ a form of heat transfer: the most predominant in the universe... (radiation, conduction and convection...) from what I can gather from my courses in thermodynamics energy is transformed from one form into another _through_ heat and work (thus the first law of thermodynamics delta(E)=Q+W. — Preceding unsigned comment added by 98.197.30.38 (talk) 05:22, 9 November 2012 (UTC)

So you are arguing that heat and work are the only possible ways for energy to convert from one form to another?

I use a battery to charge a capacitor. Energy has been transferred from chemical energy to electrical potential energy -- do you agree? If so, is the mechanism heat, or is it work? It seems to me that the answer is "neither"... --

Steve (talk) 20:08, 9 November 2012 (UTC)

Actually it is both: the work generated related to the electrical field in the capacitor and the heat released (as the capacitor heat's up and rejects heat to the environment, as they usually do...). See http://en.wikipedia.org/wiki/Capacitor, specially "Energy of electric field Work must be done by an external influence to "move" charge between the conductors in a capacitor. When the external influence is removed the charge separation persists in the electric field and energy is stored to be released when the charge is allowed to return to its equilibrium position. The work done in establishing the electric field, and hence the amount of energy stored, is given by:..." "Ripple current causes heat to be generated within the capacitor due to the current flow across the slightly resistive plates in the capacitor. The equivalent series resistance (ESR) is the amount of external series resistance one would add to a perfect capacitor to model this. ESR does not exactly equal the actual resistance of the plates."

Having done some rationalisation of the main article - see elsewhere for descritpion, why not use this as the opening? It summarises the kind of things the reader wants to know immediately. The Greek ref I have moved to sit with the history of understanding to prevent yet more barriers for the reader to clamber over. (The "history of energy" goes back to the big bang, so that heading has been changed). What about the rest of the lead section? Dougsim (talk) 13:47, 27 December 2012 (UTC)

Energy is not a physical unit. It is a philosophical concept, or an accounting technique for analyzing mechanical interactions. In nuclear physics energy is defined to be a color of light, in biology it is a synonym for metabolism, and in public utilities people often say energy when they mean connectivity. This does not cause confusion in electrical matters, since electrical people are so accustomed to it, but if you hear the word in any other context, the speaker either doesn't know what he is talking about or is trying to sell something you don't need.

Some physics texts try to define energy as "capacity to do work." But work is defined as "disordering of energy", so then energy is capacity to do disordering of energy, which is a circular definition. The page entitled "JOULE" defines the joule to be the unit if energy, but in fact the joule is the unit of work. I did not edit that page, preferring to wait for more discussion on the subject.

Jewels Vern (talk) 12:32, 1 April 2013 (UTC)

Work is not a disordering of energy--who says that? Work is force applied through distance. Since energy is ability to do work, it is measured in the same units (joules, etc). Any use of the word that can't be measured in joules is not talking about the physics definition, but some other one. And strictly speaking the color of light is not an energy but an energy/photon. Not the same. SBHarris 16:05, 1 April 2013 (UTC)

Forms of energy

Why does the article not mention kinetic energy under "Forms of Energy?" RonCram (talk) 05:52, 15 December 2012 (UTC)

Gravitational energy is missing under "Forms of Energy". It is the stored energy an object has when it is above the earth's surface. — Preceding unsigned comment added by Mirage KNyte (talk • contribs) 01:04, 25 May 2013 (UTC)

Seeking Energy Experts

Seeking Energy Experts comments and recomendations,

For years we have see many articles written on energy and the conversion of energy, yet were always looking to find new ways to convert energy from one form to a different form. The Wikipedia site provides a great tool to do research on, since it provides multi links to every aspect of physics.

Where can one go to collectively tap into the resources of so many experts on the topic of energy and to have these experts review a new exciting concept of energy conversion?

The concept that I would like to start a dialog on is related to QED, magnetics, superconductors, photonics and the Casimir Force. Naturally thermodynamics will be included in these technical discussions as well as the physics.

The reason for placing this discussion on Wikipedia, is to place this discussion out in the open, for all to read and benifit. What better way to get peer review at the highest level in real time.

Energy Quest — Preceding unsigned comment added by Energy Quest (talk • contribs) 17:59, 23 December 2012 (UTC)

The universe consists in matter and associated energy within a volume of space. And some of the energy cannot be directly associated with the matter because our minds are not capable of conceiving a material way of transporting it. But we will!!WFPM (talk) 01:10, 26 February 2013 (UTC)

Improving readability and flow of narrative

Having looked at how to shorten the lead section, which was very confusing and took the reader immediately down into detail, it was obvious this could not be achieved without first sorting out the headings and text flow of the main article. This I have done to a certain extent, so that repetitions have been removed, and orphaned text has now been grouped under new headings to help with accessibility for the new reader. The lead section still needs sorting, but it's easier to do when there are definite areas to which to move detailed text. Dougsim (talk) 12:59, 27 December 2012 (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)

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)

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)

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)

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)

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)

... 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)— Preceding unsigned comment added by 50.198.36.137 (talk) 16:05, 10 April 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)

Though the concept of fundamental interactions is important, it isn't central to the minimum that the average reader needs to know about energy to understand its pragmatic implications for phenomena, technology, and societal policy developments that they will encounter. The 1st or 2nd sentence should at least mention the most important aspects to summarize these, which will then be expanded on slightly in the lede and then covered in more depth in the body sections.

Energy in itself doesn't "enable" the amount of work that can be done, but provides the "potential" (or enough "capacity to") do work which can then be "enabled" only within the limits imposed by entropy and the 2nd law. But without mentioning entropy or the 2nd law (at the top of the lead), we can use the word "available" and give some meaning to this term by stating (in a 2nd sentence) that this availability is reduced by when energy is used for heating (objects). Also you can't create new energy but can use energy that was previously stored'. What's just as important but less obvious to some readers is that, although you can't destroy energy, something very important is indeed "lost" when you use it for processes that involve any heating. These are very rough but you get the idea:

In physics, energy is a storable capacity both to do work further limited by its availability, and to heat objects, while being converted among its forms or transferred. Energy can never be destroyed, but its availability to perform any further work is reduced when any heating occurs.

Put another way, energy is the maximum work that can could possibly be done; within that upper limit the portion available to actually do work depends on the situation (e.g. forms of energy, temperatures, etc.):

In physics, an object's energy is its ability to heat, or the most work it could possibly do subject to its availability. Energy can be converted among its forms or transferred, but not created or destroyed, though when its transfer involves any heating this permanently degrades its availability to do work in the future.

Of course some editing of the rest of the lede would also be necessary to avoid redundancy (at least within some proximity).

DavRosen (talk) 18:28, 13 April 2014 (UTC)

mistake on the figure 'Energy and human life'

The image 'Energy and human life' shows that ATP comes before Metabolism. This is incorrect. Instead Metabolism is the process that breaks up food and produces carbon dioxide, water, heat, and ATP. Wytse (talk) 07:41, 17 May 2014 (UTC)

Energy is not a reality, it is a definition

It's funny to give a definition of Energy, when actually Energy is a definition. The experiment A : You take a 1 kg mass and you push it to accelerate it with a acceleration of 1 m/s2 over a distance of 1 meter (This is the experiment we call a Joule). You look at that and you give it a name: Energy. You establish that experiment and you call it Energy, it is that simple. Energy do not exist, it is an experiment that you define as a Joule. You then use this experiment to compare machine who can reproduce the experiment. Machine A produce 1 Joule of energy if it can reproduce the experiment you did while pushing it yourself. If anything double: acceleration, mass or distance traveled you tell that the machine produce 2 joules of energy. Energy is not a value, Energy is not a properties. Energy is a definition. A name you give to the experiement A. You then compare it to what a machine can do compare to the experiment A. Heat is one type of process that can eventually produce a push against a mass to accelerate it over a distance. A mass will be accelerated when another mass will push it. In a machine many internal push between mass happen, we call this Energy moving but it is not, only Mass push other Mass, energy is when you compare the result to experiment A. Energy is when you compare Machine efficiency to a basic experiment A we called 1 Joule. A Machine of 10 Joule is ten times better then Experiment A. You could have made Experiment A to be something else and give it a name. YOU defined it. Energy is a definition. Not a real thing. — Preceding unsigned comment added by EMvague (talk • contribs) 00:15, 23 June 2014 (UTC)

Indeed energy is a definition: a quantity that can be calculated (no experiment needed!) with the practical property that it is conserved. If this property is taken as a given, it can be used to calculate various physical phenomena. In that respect, it is similar to impulse, another physical quantity that is conserved. But unlike impulse, the conservation of enery also has an economic meaning: one can trade something that is conserved. This conservation also gives energy an intuitive identity to humans, although one can not see it (directly).

The definition of enery is force multiplied by distance multiplied by the cosine of the enclosed angle.

Talking about the enery of objects unduly complicates the topic. Sitting in a car or on a bicycle, kinetic energy seems a meaningful concept, but it violaes even a classical (Newtonian) relativity principle: an object apparently in rest (=without kinetic energy) has kinetic energy reltive to an other uniformly moving reference frame. Similary, an object lying on the ground apparently has no potential energy, but if you dig a hole in the ground, the object can fall into the hole, thus displaying potential energy. Rbakels (talk) 09:58, 16 September 2014 (UTC)

I don't like "object" as it seems to limit us to some kind of ponderable matter. I don't think of a radio wave as an object, and a static electric or magnetic field even less so, but they all have energy (the fields represent energy per volume).

The discussion of whether energy is a linguistic construct or a "real thing" is unnecessarily Platonic and philosophical-- here is not the place to recap the debate between realism and idealism. We have words for useful concepts. Is gravity a real thing? And not only in physics are we stuck with this. Example: is money a real thing? I can see bills and coins but what is "money"? Most of it seems to be 1's and 0's with connections to social security numbers in banking computers. They are conserved but what else can we say of them? If imaginary, would you mind to transfer some of "yours" to me? And what about government? I went to Washington DC and saw buildings and met people but could not see the "government" they talk of. Is it real or just a definition? Is the United States real? Are Labrador retrievers real? It's all a big rabbit hole we'd like to avoid.SBHarris 17:37, 16 September 2014 (UTC)

I agree with Sbharris's last paragraph. I don't think the philosophizing above contributes anything to the discussion of the article. All scientific properties are defined via definitions (duh). None of the examples above contradict anything in the article or add anything that will be useful. Lord knows there is enough verbal diarrhea in the article's introduction already, we don't want to add to it. --Chetvorno^TALK 19:25, 16 September 2014 (UTC)

Semi-protected edit request on 29 September 2014

Please, please please include something like the phrase 'Simply put, energy can be considered as the ability to do work', or a simplified one-sentence explanation, as part of the introduction. I had to read the Polish version of this article to understand the concept. The English article is *extremely* complicated with nothing for a non-physicist to latch onto. 14.35.105.1 (talk) 07:20, 29 September 2014 (UTC)

"Work and heat are two categories of processes or mechanisms that can transfer a given amount of energy"

does this sentence, which is the first sentence of the 2nd paragraph give that information? Cannolis (talk) 08:40, 29 September 2014 (UTC)

I absolutely agree. The definition of energy as the ability to do work was once in the introduction, but as often happens in WP articles, the definition has been abstracted and generalized until it is now pretty much incomprehensible. I'd like to point out that the "ability to do work" is included in almost every reliable source's definition of energy, but the gobbledygook now in the intro is not sourced. Thanks for pointing out that the emperor has no clothes, Cannolis. --Chetvorno^TALK 09:44, 29 September 2014 (UTC)

"energy is a universal and fundamental quantity that describes fundamental physical interactions" -- not helpful in 1st sentence

Several days ago, Chjoaygame changed 1st sentence of lead from this:

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.

to this:

In physics, energy is a universal and fundamental quantity that describes fundamental physical interactions. It is conserved, being neither created nor destroyed.

While the original left something to be desired, I think this edit is a step in the wrong direction. Energy merely "describes" a fundamental interaction? That doesn't say much at all. It no longer tells us that energy is a property of something (yes, something more general than "object" but this keeps the first sentence accessible and can obviously be generalized), that it can be transferred among such things, that it has different forms, or that it can be converted from one form to another, all of which are important. (It also isn't clear what "universal" means, or why we need to use the word "fundamental" twice in the first sentence.)

I undid it for now; let's discuss. There were a lot of other scattered and unrelated changes to different parts of the lead in the same edit -- let's split them up so we can discuss one paragraph at a time, perhaps starting with the beginning.

DavRosen (talk) 23:11, 5 November 2014 (UTC)

Better to leave it to you.Chjoaygame (talk) 10:43, 6 November 2014 (UTC)