Talk:Energy

Magnetic energy?

there is no such thing as 'magnetic energy', as Magnetism is not energy but is actually a push or a pull, and this makes magnetism a force. Energy can be converted from one form to another, but that is not the case with magnetism, or 'magnetic energy'.--S9718483fb (talk) 13:59, 10 March 2009 (UTC) —Preceding unsigned comment added by S9718483fb (talk • contribs) 13:51, 10 March 2009 (UTC)

No. A magnetic field has energy, as you can see when you disconnect a powered solenoid and the magnetic field energy is converted to a spark (as in an old auto spark coil). The equations given in the article are correct. SBHarris 19:17, 17 April 2009 (UTC)

Definition

This article begins In physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force. On 21 April 2009 User:Wisnuops (talk) added the following comment:
(note: this is not the best definition. The word work is also defined by referring to energy. It creates a circular definition).

I have deleted the note from the article and transferred it here. It may stimulate debate. Dolphin51 (talk) 03:58, 22 April 2009 (UTC)

At the beginning definition it mentions forms of energy and lists Kinetic, Potential, Light, Elastic, Electromagnetic etc. Isn't Light already Electromagnetic Energy via the Visible Light part of the spectrum? If so this is redundant. Gheta (talk) 19:10, 22 July 2009 (UTC)

I agree that electromagnetic energy includes visible light. Dolphin51 (talk) 23:55, 22 July 2009 (UTC)

Circular Definitions

Either the work page or this should change definitions in the introductions. As it is, a curious individual, or perplexed student, comes to the energy page to see the definition of energy: Energy is a scalar physical quantity that describes the amount of work that can be performed by a force. Fair enough, so the inquisitive student will ask..."hmm, what's work?" being wikipedia one can conveniently click on the link, unfortunately one finds in the introduction: mechanical work is the amount of energy transferred by a force acting through a distance. It may make sense in the equations, but verbally it seems circular. 76.175.72.51 (talk) 04:22, 18 October 2009 (UTC)

Took out table "Magnitude comparison of different forms of energy"

I took out this table as potentially misleading. A form of energy doesn't have a magnitude. I guess it could be called "magnitudes of coefficients of equations for energy", but that doesn't seem like a meaningful or useful comparison. We already have the article Orders of magnitude (energy). --Suffusion of Yellow (talk) 08:24, 22 October 2009 (UTC)

Confusing list of forms

This sentence from the intro:

 "Different forms of energy include kinetic, potential, thermal, gravitational, sound, light, elastic, and electromagnetic energy."

is, in my opinion, poorly worded - even if it is technically true that each of those words can describe some form of energy. Kinetic and potential are a totally separate categorization of energy - in its current shape, the sentence can easily convince someone that thermal is something completely different from kinetic. Or, taken with the next sentence The forms of energy are often named after a related force., it could be taken to suggest that some sort of a "kinetic force" exists.

I suggest we remove the 'kinetic' and 'potential' words from that particular sentence - if we want to have a reference to them in the intro, we can add a sentence along the lines of 'Energy is often split into kinetic and potential' Ivancho.was.here (talk) 03:34, 11 December 2009 (UTC)

Kinetic and potential could be Mechanical. Grvitational could be removed, since gravity is a force and I'm pretty certain that it's called potential gravitational. Busha5a5a5 (talk) 18:18, 15 February 2010 (UTC)

Can "Energy" have a purely abstract, non-physical meaning?

I suggest that semantically, the word energy can have a purely abstract non-physical meaning, as "something that moves" (something else or itself), in any kind of reference system.

For example, one could say that there are "energies" in the psyche, in the sense that there are psychological motives or mechanisms that activate/move the psyche in a certain direction, or which inhibit and block certain other tendencies in the psyche.

There is no reason why the notion of energy should be the exclusive property of physical sciences. The purely abstract use of that word in any kind of reference system is perfectly legitimate. —Preceding unsigned comment added by 161.53.149.242 (talk) 15:36, 19 January 2010 (UTC)

Automate archiving?

Does anyone object to me setting up automatic archiving for this page using MiszaBot? Unless otherwise agreed, I would set it to archive threads that have been inactive for 30 days and keep ten threads.--Oneiros (talk) 13:45, 24 January 2010 (UTC)

 Done--Oneiros (talk) 00:27, 1 February 2010 (UTC)

Energy

What is energy? —Preceding unsigned comment added by 218.103.199.177 (talk) 14:32, 28 January 2010 (UTC)

Energy is not a scalar in special relativity

Energy is of course a scalar quantity in classical (non-relativistic physics); but it special relativity it is the time-component of the momentum four-vector and obviousley not a scalar. I think the opening lines of the article should be corrected this way: " in non-relativistic physics, energy is a scalar quanity". We then need to say, somewhere else that in relativity energy is only a component of a vector This is directly related to the celeberated E=mc^2. 95.82.51.176 (talk) 00:19, 1 February 2010 (UTC)

Well, TIME is a scalar quantity in classical physics, but can be regarded as a vector (or vector-space) in relativity. So what? It is of no help in understanding the nature of time, except to remind us that when the spacial quantities increase, the time-like thing decreases. If we want to use energy and momentum to calculate anything in relativity, such as the scalar invariant mass, we strip them of their vector properties and use the Minkowski norm, or 4-vector length. Here energy and net momentum subtract from each other as squares, followed by a root, just as would happen for the length of the vector connecting two perpendicular vectors. But the answer is not a vector. SBHarris 01:14, 9 February 2010 (UTC)

Example in second paragraph seems to be inaccurate

"When oil, which contains high-energy bonds, is burned, the useful potential energy in the oil is converted into thermal energy, which can no longer be used to perform work (e.g., power a machine) and is lost. Although the thermal energy may not be a useful form of energy, the total energy has remained the same."

Converting chemical energy to thermal energy is exactly what does produce the work. For instance in an internal combustion engine it is the thermal energy that causes the gases to expand and move the pistons. Also in a thermoelectric system it is the thermal energy that gets converted into electrical energy. Only where there is very low grade heat energy, not much higher in temperature relative to its surroundings, is thermal energy no longer able to perform work. --CharlesC (talk) 12:07, 13 February 2010 (UTC)

This article is about the scalar physical quantity. For other uses, see Energy (disambiguation).

Lightning is the electric breakdown of air by strong electric fields and is a flow of energy. The electric potential energy in the atmosphere changes into heat, light, and sound which are other forms of energy.In physics, energy (from the Greek ἐνέργεια - energeia, "activity, operation", from ἐνεργός - energos, "active, working"[1]) is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law. Different forms of energy include kinetic, potential, thermal, gravitational, sound, elastic, light, and electromagnetic energy. The forms of energy are often named after a related force.

Any form of energy can be transformed into another form, e.g., from potential to thermal, and dissipated into the atmosphere. When oil, which contains high-energy bonds, is burned, the useful potential energy in the oil is converted into thermal energy, which can no longer be used to perform work (e.g., power a machine) and is lost. Although the thermal energy may not be a useful form of energy, the total energy has remained the same. The total energy always remains the same whenever energy changes from one form to another, even if the energy loses its ability to be used for performing work. This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time.[2]

Although the total energy of a system does not change with time, its value may depend on the frame of reference. For example, a seated passenger in a moving airplane has zero kinetic energy relative to the airplane, but non-zero kinetic energy relative to the Earth