Talk:Friction

Article merged: See old talk-page here

Semi-protected edit request on 20 February 2021

The reference to the NASA document: Barrett, Richard T. (1 March 1990). "(NASA-RP-1228) Fastener Design Manual" This is used as a source for the static and dynamic friction of wood and other materials. This document has absolutely nothing to do with friction and includes no such reference data. 149.167.140.87 (talk) 03:31, 20 February 2021 (UTC)

 Not done: Have a look at Table IV on page 20. It seems the data the document is used as a source for is present. Volteer1 (talk) 03:48, 20 February 2021 (UTC)

Semi-protected edit request on 17 June 2021

The description of normal reaction N is completely wrong. N is NOT the the force that compresses the two surfaces together. N is a pair of electrostatic repulsion when the surfaces are brought in contact. The statement that N=mg is also partially incorrect since it is only true on a horizontal flat surface. On an incline plane N=mg cos(theta) where theta is the angle of incline. One should also explain that the statement N=mg does NOT mean that these the normal reaction is the same as gravity. The ambiguity must be explained; the magnitude of normal reaction is equal to the magnitude of gravity (on flat horizontal plane) but N and mg are two forces acting on two different points of action (mg acts at center of mass and N acts at a point of surface of contact), the direction of gravity is opposite of direction of N AND the nature of gravity and N are different (gravity & electrostatic force). These big mistakes must be corrected. They mis-inform physics students Pari-sterzinger (talk) 02:13, 17 June 2021 (UTC)

 Not done: It's not clear what exactly you want to be changed (please state it in the suggested "x to y" format), and what would actually be helpful would be finding some sources to cite for this information (which you have provided exactly zero examples of) RandomCanadian (talk / contribs) 03:36, 17 June 2021 (UTC)

Proposed merge of Friction Acoustics into Friction

I don't see any particular reason for "Friction Acoustics" to be an independent article at this time. I recommend merging into the section under "Energy of friction" Polyamorph (talk) 13:17, 3 February 2022 (UTC)

Weak oppose: while I agree that the current article is weak, the topic has sufficient scope to be developed. Hence, I think that ímprove rather than merge, would be the better action. Klbrain (talk) 19:59, 23 August 2022 (UTC)

Closing, given the uncontested objection and no support. Klbrain (talk) 10:08, 27 December 2022 (UTC)

Edit request

Plinius the elder and Vitruvius are Romans not Greeks and not even remotely contemporary. 151.35.217.119 (talk) 14:29, 6 July 2023 (UTC)

Done by removing the "Greek" as is was superfluous. Ldm1954 (talk) 20:20, 31 August 2023 (UTC)

Wiki Education assignment: 4A Wikipedia Assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 21 August 2023 and 16 December 2023. Further details are available on the course page. Student editor(s): FranciscoCa27, Esteban282 (article contribs). Peer reviewers: ThomasDLV, GoldenGecko.

— Assignment last updated by Kmijares (talk) 22:40, 15 November 2023 (UTC)

"Kinetic energy is converted to thermal energy whenever motion with friction occurs"

The lead states

Kinetic energy is converted to thermal energy whenever motion with friction occurs

Is that always true? If you drop (or perhaps gently lower) a brick onto the roof of a train moving at a constant speed, so that friction accelerates the brick till it moves at the same speed as the train, the kinetic energy of the train is constant, and that of the brick is increasing. - My mechanics classes were long ago; I may have gotten this wrong. The train engines may have to work a little harder, so it is not a closed system. Also, seeing things from the inertial frame of the moving train, the statement is true. Still, is the statement too absolute? Nø (talk) 11:00, 24 August 2024 (UTC)

The statement is true. In your case the train engine is doing some work on nanoscale protrusion at the brick/train interface which will elastically bend then be restored. (Think of the contact as a comb, not quite right but a decent analogue.) Since it is not 100% elastic then some energy is lost to heat.

Note that not 100% of the energy has to be heat, some could be light or potential energy but that does not make the statement wrong. Ldm1954 (talk) 11:19, 24 August 2024 (UTC)

Editor Nø raises a good question. I am thinking from the point of view of clear language, not seeking to debate the particular case that he raises.

The language of the quoted sentence might be criticized in various ways.

The phrase thermal energy is one to be avoided wherever possible. It is often used as a cover for loose thinking. The present Wikipedia article on thermal energy starts:

The term "thermal energy" is used loosely in various contexts in physics and engineering, generally related to the kinetic energy of vibrating and colliding atoms in a substance. It can refer to several different physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, defined as a type of energy transfer (as is thermodynamic work); and the characteristic energy of a degree of freedom, $k_{\mathrm {B} }T$, in a system that is described in terms of its microscopic particulate constituents (where $T$ denotes temperature and $k_{\mathrm {B} }$ denotes the Boltzmann constant).

The clause whenever motion with friction occurs is vague, perhaps deliberately so, but still vague. It seems to me that it would refer, amongst other things, to a case in which an imposed force, not described simply by the term kinetic energy, causes a dragging or rubbing of surfaces against each other, through a distance. The operative factor will be the mechanical work done other than that ascribable to the kinetic energies of the rubbing bodies.

The meaning of motion with friction is not clear as to whether moving friction or static friction is intended. In the present case, the brick may simply stick to the surface of the top of the train. In that case, there would be some possibility of elastic or inelastic interaction between the top of the train and the bottom of the brick. Or perhaps, in addition, the brick may slip along the top of the train.

Editor Nø's talk of "a train moving at constant speed" is a little loose. The forces between the brick and the train top will not be transmitted instantaneously to the engine, so that the train's speed will hardly be perfectly "constant". Editor Nø's use of the phrase "not a closed system" is confusing. If the engine is a diesel engine that is working all the time, the system is not closed.Chjoaygame (talk) 22:16, 24 August 2024 (UTC)

Sorry, but no, here the term thermal energy is exactly correct. Furthermore the lede is certainly not where fine details should be discussed. Ldm1954 (talk) 22:51, 24 August 2024 (UTC)

Let me expand slightly; tribology is one of my research areas. When two bodies contact it is not flat-on-flat, it is asperity contacts as mentioned with relevant sources at the end of Friction#History, as I mentioned before. Friction is due mainly to elastic/plastic deformation of these asperities, perhaps with some Triboelectric contribution. The anelastic component is mainly converted into thermal energy (phonons), although some can go into other inelastic channels.

N.B., of course you don't have motion with stiction, and kinetic energies are not relevant unless the bodies are moving at a sizeable fraction of the local speed of sound.

Sorry @Chjoaygame and @Nø, as written the article lede is rigorous. Ldm1954 (talk) 01:27, 25 August 2024 (UTC)