Talk:Kinetic energy

Make technical articles understandable

Our article on kinetic energy is clearly a technical article. A large amount of useful information on these articles is provided at WP:Make technical articles understandable.

The lead section of the article on kinetic energy does not fare well when reviewed using the principles at “Make technical articles understandable”. Here are two of the violations I see in the lead section:

1. The first paragraph contains “Formally, a kinetic energy is any term in a system’s Lagrangian which includes a derivative with respect to time and the second term in a Taylor expansion of a particle’s relativistic energy.” I don’t doubt this is true, but not everything true can, or should, be placed in the first paragraph of the lead section of an article. WP:EXPLAINLEAD is highly relevant and shows why the lead of this article, and particularly the first paragraph, is failing.
2. The first paragraph contains “It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.” If this were true it means the concept of kinetic energy is subordinate to the concepts of work and acceleration; readers will not be able to comprehend the concept of kinetic energy if they don’t already have an understanding of both work and acceleration. This is clearly an invalid implication because kinetic energy can be readily understood by readers who don’t have an understanding of work or acceleration. The first paragraph of the lead can introduce the quantitative meaning of kinetic energy simply by saying it is ${\tfrac {1}{2}}mv^{2}$. More complex properties of kinetic energy deserve a place in the article, but not in the first paragraph of the lead, and maybe not even in the lead itself.

WP:Make technical articles understandable gives the following advice: “If an article is written in a highly technical manner, but the material permits a more understandable explanation, then editors are strongly encouraged to rewrite it.”

We should rewrite it. I’m interested in what other Users think, and what changes they might propose on this Talk page. I’m willing to start work on rewriting in a few days Dolphin (t) 09:31, 8 March 2023 (UTC)

I agree that both of the sentences you identified are problematic. Because the connection to special relativity from sentence (1) is described in the relativistic kinetic energy section, I think that removing that comment is justified. Some connections between kinetic energy and Lagrangian mechanics are contained in the Lagrangian mechanics article, so, for now, it might be helpful to link to that article somewhere in this one. Eventually, I think a discussion of connections to Lagrangian mechanics contained directly in the kinetic energy article could be helpful. IncompleteBits (talk) 19:02, 8 March 2023 (UTC)

I have taken the existing lead section, amended, added and subtracted various bits and come up with a new lead. What do others think?

In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion.(Ref 1)

In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is ${\textstyle {\frac {1}{2}}mv^{2}}$.(Ref 2)

It can be shown that the kinetic energy of an object is equal to the work needed to accelerate an object of mass m from rest to its stated velocity. Having gained this energy during its acceleration, the object maintains this kinetic energy unless its speed changes. The same amount of work is done by the object when decelerating from its current speed to a state of rest.(Ref 2)

The standard unit of kinetic energy is the joule, while the English unit of kinetic energy is the foot-pound.

In relativistic mechanics, ${\textstyle {\frac {1}{2}}mv^{2}}$ is a good approximation of kinetic energy only when v is much less than the speed of light.

Ref 1: Mahesh C. Jain, Textbook of Engineering Physics (Part I)

Ref 2: Resnick & Halliday (1960), Physics, Section 7-5 — Preceding unsigned comment added by Dolphin51 (talk • contribs) 10:37, 1 September 2023 (UTC)

No objection has been raised to my proposed new lead section after a week so I will paste it into the article as the new lead. Dolphin (t) 12:22, 8 September 2023 (UTC)

Sorry I was away for the US holiday so my comment comes late.

Overall your changes are a great improvement, thanks.

However, one aspect concerns me: possession of kinetic energy. As I heard it put one time: energy is not a magical fluid added and removed from objects. Rather it is a relative property, useful only by comparison. Objects have different amounts of kinetic energy depending on the reference frame. We humans assign kinetic energy to objects based on our analysis of the object's velocity relative to our chosen reference frame.

Now I understand that introductory discussions choose to ignore these basics. Introductory works imply an Earth bound frame of reference as absolute and universal. Having been taught to think of energy as possessed by objects, I found relativity to be simply unbelievable. Had I been introduced to idea that kinetic energy only has meaning between two objects or between an object and a collections of objects, I would not have had to unlearn the "fluid" model of energy.

There are some hints at this point of view in the article. Unfortunately the relativity section fails to discuss physics and jumps right to math.

It seems to me that this fundamental, critical aspect of kinetic energy deserves attention in the lead. If you think the article needs more referenced content along these lines first, please let me know. Johnjbarton (talk) 15:25, 8 September 2023 (UTC)

Thanks for your thoughtful reply. I think your comments are entirely valid, but I doubt that the lead section is the place to resolve these concerns. Your principles have universal truth and can be applied to every Wikipedia article - if a reader is to acquire a mature understanding of a subject, the lead section of the Wikipedia article will never be sufficient; a mature understanding will always require the reader to go beyond the lead section and begin to absorb some or all of the information in the body of the article. WP:EXPLAINLEAD says it all.

I suggest you proceed with one or both of the following steps:

• Start a new discussion thread on this Talk page to raise your concerns. (It could contain a cut/copy and paste of your comments immediately above.) It could also include a draft of your proposed changes (or a link to your sandbox in which you have written your proposed new version of one or more sections for this article.)
• Use your sandbox to draft a new version of one or more sections for this article. When completed, or well advanced, you could use this Talk page to direct interested Users to your sandbox and invite them to provide their comments.

Dolphin (t) 22:50, 8 September 2023 (UTC)

Further information: Self-powered dynamic systems

@JoeNMLC I have reverted a change to add template Further information: Self-powered dynamic systems to the section "Kinetic energy of systems". The section is about internal kinetic energy of eg the Solar System. The referenced article is about systems that use energy harvesting internally. While there might be some overlap, the referenced article is not "further information" about the concept of kinetic energy.

If the kinetic energy article had an Applications section, the reference article might be linked there. (this would have to be a general purpose section with more than just the single application). Johnjbarton (talk) 02:26, 8 July 2023 (UTC)

@Johnjbarton - Thankyou for explaining the revert. I'm totally okay with that. While I did have two semesters Physics, it was so many years ago, I am out of my element on this topic. Regards, JoeNMLC (talk) 03:12, 8 July 2023 (UTC)

Newtonian kinetic energy?

how Newton is related to history of kinetic energy?

It is classical kinetic energy and not whole classic Physics is produced by Newton. 79.202.40.58 (talk) 07:17, 27 August 2023 (UTC)

I agree. Fixed.

Resolved

Johnjbarton (talk) 14:53, 27 August 2023 (UTC)

Kinetic energy as a relative concept.

(Follow up from a previous topic)

One aspect of the current article concerns me: possession of kinetic energy. As I heard it put one time: energy is not a magical fluid added and removed from objects. Rather it is a relative property, useful only by comparison. Objects have different amounts of kinetic energy depending on the reference frame. We humans assign kinetic energy to objects based on our analysis of the object's velocity relative to our chosen reference frame.

In one sense this is obvious: velocity is relative. Object's don't possess velocity, thus they cannot possess kinetic energy. The difficult part is presenting this naturally and clearly for an introductory audience and with sufficient reliable references.

I think such changes are important for this kind of article as noted in WP:OVERSIMPLIFY.

My proposal is to first develop a short section explaining 1) why kinetic energy is not an object property and 2) why assigning kinetic energy to objects is so darn useful.

And second to make small changes to the article to reduce the dependence on the possession model. For example, rather than

• the kinetic energy of an object is the form of energy that it possesses due to its motion

we might say

• the kinetic energy of an object is the form of energy associated with its motion.

I will look for appropriate references first. Johnjbarton (talk) 01:04, 9 September 2023 (UTC)

Unfortunately I don't have the right books needed to add references to this article. Johnjbarton (talk) 22:39, 9 September 2023 (UTC)

Semi-protected edit request on 16 November 2024

In the section on Relativistic kinetic energy, I would like to add this note citing Einstein himself for the Taylor expansion of the relativistic energy:

Although Einstein does not explicitly refer to a Taylor expansion, in equation 45 of The Meaning of Relativity, Einstein "develop[s] ${\displaystyle E}$ in powers of ${\displaystyle q^{2}}$". In equation 45, ${\displaystyle q}$ is the magnitude of the velocity (${\displaystyle q}$ is defined on page 38), and the velocity of light is the unit (page 46).

The note would be placed after the first mention of "Taylor expansion" in the article:

"This is done by binomial approximation or by taking the first two terms of the Taylor expansion<<insert note here>> for the reciprocal square root: ..."

-- 50.47.156.69 (talk) 22:24, 16 November 2024 (UTC)