Talk:Mechanical energy

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Problems

Energy is a state function and work is not. That is covered under those terms. Mechanical energy and mechanical work should be separate articles and not merged. I don't have time to improve this article right now, and it's properly labeled as a stub. I'm removing the merge tag and adding the expansion tag here. Flying Jazz 02:56, 30 December 2005 (UTC)

Agree. As regards the stub tag, though, I'm not sure what more there is to say. --Smack (talk) 17:10, 30 December 2005 (UTC)

Expansion request removal

I would like to remove the expansion request. This article should give people a general idea of what's going on, and point them to one of the articles in the see-also list. --Smack (talk) 06:46, 29 January 2006 (UTC)

Expansion request filled

Good grief; entire textbooks could be written on this subject. This is definitely a fundamental topic that schoolchildren will look up and will need help understanding. This article should give a clear explanation of the concept, with examples, without depending on other articles for necessary background. I've an article from scratch to try and do this. The next thing to add would probably be illustrations. -- Beland 23:18, 5 March 2006 (UTC)

Looks pretty decent. Now if someone could reconcile it with mechanical work, so that they refer to each other in the right places and don't duplicate anything that they shouldn't, it would be really nice. --Smack (talk) 04:41, 8 March 2006 (UTC)

Energy stored in compressed gas is kinetic, not potential.

For example, compressed gas exerts pressure because electromagnetic forces between particles tend to push them apart. Compressing a gas (moving the particles "uphill" against repulsive electromagnetic forces) stores potential energy in a similar way that pushing a boulder up a hill does (moving the object uphill against the attractive gravitational force of the Earth).

The above statement is just wrong. It would be correct for a solid, but not for a gas. The particles in a gas are always moving. The pressure of a gas gives the force it can apply, not the energy it contains. The temperature of a gas together with the number of particles gives the energy. After all, nRT is energy. Pressure is force per unit area, as in pounds per square inch, which happens to be equal to energy per unit volume, because work (change in energy) is force times distance.

See Joule-Thomson effect. For non-ideal gasses, compression adds or removes potential energy depending on circumstances.

http://www.chem.arizona.edu/~salzmanr/480a/480ants/jadjte/jadjte.html "This is an important and useful result. It says that the internal energy of an ideal gas is not a function of T and V, but of T only."

An actual definition

I was reading through this and I don't think I can find an actual clear definition of the term. Not anything special, just have it set in stone. "Mechanical energy is..."

That's all for now...

DUbblecoMB 18:55, 9 May 2007 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:00, 10 November 2007 (UTC)

Wow

I don't really have time to write this article, but "the principle of general conservation of energy is so far an unbroken rule of physics - as far as we know, energy cannot be created or destroyed, only changed in form"?!! E=mc^2??? That's embarassing, but i'll leaveit so others can see it was, in fact, actually on this page. But I should stop talking, since I don't have time to do anything about it. . . —Preceding unsigned comment added by Drock2289 (talk • contribs) 05:12, 8 April 2008 (UTC)

Ideas

As some might have noticed, I'm working on this page and trying to get it up to the level it deserves.

If anybody has any ideas for improvement, I will be very interested in hearing them. At the moment I am focusing on conversion of mechanical energy and will briefly describe inventions like the electric motor, generator, internal combustion engine, and turbine. I feel like mentioning the relatively new ocean buoys that use the mechanical energy of the oceans' tides and waves to create electricity but on the other hand it just seems like a further development of the generator. Does anybody have an opinion on that matter? Otherwise I might just put it in the see also section.

Last thing: is the section that describes the difference between the energy forms necessary in this article? I will have to either expand and verify it or delete it.

Thanks in advance to everybody :-) Mottenen (talk) 21:04, 7 September 2011 (UTC)

I think there is a risk that this article might stray so close to Energy that there will be grounds for the two articles to be merged. We shouldn't encourage any merger.

Under the heading Conversion there is a paragraph about the principle of the electric motor - most of it is out of place in an article on mechanical energy. I am comfortable with the sentence An electric motor converts electrical energy into mechanical energy but I think everything after that should be removed. If necessary, it can be moved to an article on electric motors.

Mottenen, you have included the electric motor in your list of potential topics. I think that should be left out. It is true that electric motors convert electrical energy into mechanical energy but no further coverage of the electric motor is warranted in this article. Dolphin (t) 02:46, 8 September 2011 (UTC)

At first, I was skeptical, but now I agree with what you say. I've made the "Conversion" section into a list of categories of devices that convert mechanical energy. I hope this was what you proposed. Any other suggestions, please tell me :-) ----Regards, Mottenen (talk) 16:11, 9 October 2011 (UTC)

Tamil

Can I translate into Tamil? Mahesh967787 (talk) 12:15, 22 February 2019 (UTC)

Hi Mahesh967787 (talk) 12:15, 22 February 2019 (UTC)

Inelastic collisions

On 30 September 2020 User:Julian Benali made a minor amendment to this article. His edit summary says “Elastic/Inelastic refers only to kinetic energy. Total mechanical energy may or may not be conserved during inelastic collisions.” See his diff. I challenged the notion that mechanical energy may be conserved in an inelastic collision.

I reverted this good-faith edit but Julian and I ended up discussing it in depth on his Talk page. See User talk:Julian Benali#Mechanical energy. His explanation of his statement “Total mechanical energy may or may not be conserved during inelastic collisions” makes use of Classical Mechanics by John Taylor. (This source is not currently cited in the article, and I don't have access to a copy.) Julian has written “For an example of an inelastic collision where mechanical energy is conserved, see problem 4.53 in John Taylor”

4.53** (a) Consider an electron (charge $-e$ and mass $m$) in a circular orbit of radius $r$ around a fixed proton (charge $+e$). Remembering that the inward Coulomb force $ke^{2}/r^{2}$ is what gives the electron its centripetal acceleration, prove that the electron's KE is equal to $-{\tfrac {1}{2}}$ times its PE; that is, $T=-{\tfrac {1}{2}}U$ and hence $E={\tfrac {1}{2}}U$. Now consider the following inelastic collision of an electron with a hydrogen atom: Electron number 1 is in a circular orbit of radius $r$ around a fixed proton. (This is the hydrogen atom.) Electron 2 approaches from afar with kinetic energy $T_{2}$. When the second electron hits the atom, the first electron is knocked free, and the second is captured in a circular orbit of radius $r'$. (b) Write down an expression for the total energy of the three-particle system in general. (Your answer should contain five terms, three PEs but only two KEs, since the proton is considered fixed.) (c) Identify the values of all five terms and the total energy $E$ long before the collision occurs, and again long after it is all over. What is the KE of the outgoing electron 1 once it is far away? Give your answers in terms of the variables $T_{2},r,$ and $r'$.

Indeed, mechanical energy is conserved in this scenario even though kinetic energy is not and the method for solving part (c) is to invoke conservation of mechanical energy. Thus, the total mechanical energy may or may not be conserved in an inelastic collision.

My understanding of mechanical energy is confined to situations where an object’s potential energy is due solely to the gravitational field. In example 4.53 quoted above, the potential energy of protons and electrons is also due partly to an electric field. This appears to be the clue to understanding Julian’s edit summary.

I am persuaded by the logic expressed by Julian Benali and John Taylor so I will erase my most recent edit and restore the article to the version established by Julian. I am grateful to Julian for introducing this improvement into the article. Dolphin (t) 12:23, 5 October 2020 (UTC)

I have now erased my most recent edit. See my diff. Dolphin (t) 12:28, 5 October 2020 (UTC)

Conservation of mechanical energy

An important issue related to the conservation of mechanical energy is presently under discussion at Wikipedia talk:WikiProject Physics#Inconsistencies related to mechanical energy. Dolphin (t) 13:56, 1 December 2022 (UTC)

The discussion is now archived at Wikipedia talk:WikiProject Physics/Archive December 2022#Inconsistencies related to mechanical energy. Dolphin (t) 21:28, 27 January 2023 (UTC)