Talk:Force

Erased paragraph from "First law"

I have deleted the third (final) paragraph from Force#First law. See my diff. The paragraph is mostly off topic or misleading. Most of it is unsourced. I’m happy to discuss with others interested in the topic.

My objections to the contents of the paragraph are as follows:

• The concept of inertia explains the tendency of objects to continue in many different forms of constant motion, even those that are not strictly constant velocity.

".. even those that are not strictly constant velocity." Really? No example or clarification given so the sentence is enigmatic and not appropriate in an encyclopedia.

• The rotational inertia of planet Earth on its axis is what fixes the constancy of the length of a day.

This section introduces Newton’s First law of motion which can be comprehensively described without digressing to angular velocity and rotational inertia. The Earth rotates at constant speed but the length of a day is not constant – see Equation of time.

• Albert Einstein extended the principle of inertia further when he explained that reference frames subject to constant acceleration, such as those free-falling toward a gravitating object, were physically equivalent to inertial reference frames.

In a section introducing Newton’s First law of motion, Albert Einstein is off topic.

• This is why, for example, astronauts experience weightlessness when in free-fall orbit around the Earth, and why Newton's Laws of Motion are more easily discernible in such environments.

Astronauts experience weightlessness in free-fall orbit because of Einstein’s ideas on accelerating reference frames? In an introductory article on mechanics and Newton’s laws I think it would be much more appropriate to reinforce the notion that astronauts in orbit have weight almost equal to their weight when stationary on the Earth’s surface.

• If an astronaut places an object with mass in mid-air next to himself, it will remain stationary with respect to the astronaut due to its inertia.

And is this because of Newton or Einstein? Unsourced. Looks like a student essay. When introducing Newton's First law of motion there is no need to focus on astronauts!

• This is the same thing that would occur if the astronaut and the object were in intergalactic space with no net force of gravity acting on their shared reference frame.

Readers are people with no experience in intergalactic space! If an example is required, there is an abundance of examples related to day-to-day experiences on the Earth’s surface. Wikipedia is an encyclopedia, not a textbook.

• This principle of equivalence was one of the foundational underpinnings for the development of the general theory of relativity.

This section is an introduction to Newton’s First law of motion. General theory of relativity is off topic. Dolphin (t) 13:01, 28 April 2017 (UTC)

I support the removal. Muddy, wandering paragraph. Rracecarr (talk) 14:28, 28 April 2017 (UTC)

Fundamental forces

6.1 Gravitational

The last paragraph states: "For example, a basketball thrown from the ground moves in a parabola, as it is in a uniform gravitational field. Its space-time trajectory (when the extra ct dimension is added) is almost a straight line,..."

What is "ct"?

--Harry Audus (talk) 12:43, 18 July 2017 (UTC)

Well spotted! It is probably intended to be "curvature of space-time" but there is no explanatory text before or after, so it is a complete orphan. Orphans like this have no place in an encyclopedia. Hopefully, someone will add some clarifying text in the next day or so. If not, I will erase it. Dolphin (t) 13:10, 18 July 2017 (UTC)

No offer to clarify yet, so I have suspended the offending comment from view - see the diff. If nothing turns up in the next day I will delete it. Dolphin (t) 21:40, 19 July 2017 (UTC)

A week has passed and no-one has offered to clarify the statement about "when the extra ct dimension is added." I have now erased it. See the diff. Dolphin (t) 04:27, 27 July 2017 (UTC)

Semi-protected edit request on 26 August 2017

there is written that force when not opposed please change it to when unbalanced. 139.167.15.148 (talk) 03:32, 26 August 2017 (UTC)

 Not done Every Physics textbook uses the term unopposed not unbalanced. SparklingPessimist ^{Scream at me!} 10:59, 26 August 2017 (UTC)

why do they use unopposed instead of unbalanced 197.214.99.145 (talk) 12:21, 25 April 2022 (UTC)

Newton Spring Balance

Plese create an article regarding Newton Spring Balance as there is no an article on that Seniru pahasara kamkanamge (talk) 07:20, 22 November 2018 (UTC)

Is spring balance what you have in mind? If not, what is a Newton spring balance? Dolphin (t) 07:54, 22 November 2018 (UTC)

Force

Force does not have the physical power or strength to be exerted upon an object(s) to push, pull, shape, work, or do anything for that matter. Force, by any definition, does not exist physically in the same way that an object with mass does. Force, as we know it, turns out to be nothing more than an expression to express an idea like one would use the word “Love” to express one’s feelings. ~Guadalupe Guerra — Preceding unsigned comment added by Pro3144 (talk • contribs) 15:10, 11 September 2020 (UTC)

Original second law

The article says "The original form of Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time." Actually, he didn't. He said force is proportional to velocity. That's because what Newton called force, we now call impulse. Admittedly, they are equivalent formulations, but we shouldn't be saying Nerwton said something he didn't. SpinningSpark 13:29, 15 August 2021 (UTC)

Are you implying that impulse “is proportional to velocity”? Such an implication is questionable because impulse is equal to the change in momentum (or is proportional to the change in velocity.) I don’t object to the current wording in the article. The matter is complicated because, as well as the changes in terminology, Newton wrote his Principia in Latin. Dolphin (t) 14:22, 15 August 2021 (UTC)

Sorry, my mistake, it was force is proportional to motion (changed). For which we have to read force=impulse and motion=momentum. Here is an English translation of the relevant page in the Principia. SpinningSpark 14:38, 15 August 2021 (UTC)

The Four Fundamental Forces chart

Right in the middle of this article we have the chart showing the four fundamental forces and their varying properties. Except this chart has FIVE COLUMNS! To the average reader this is beyond confusing. I have a (admittedly very basic) grasp of physics and I don't understand why some of the columns are split into sub-columns. The other confusing thing is that the headers of the columns don't have the traditional names (gravitational, weak nuclear, strong nuclear, electromagnetism). Perhaps someone with experience in the field could make this chart a (bit) more approachable for the casual reader? Or is that just a silly request because I'm not understanding the concepts properly? MrAureliusR_Talk! 11:32, 6 December 2021 (UTC)

Definition of a force

In the lead paragraphe, the force is only defined through its effect on a motion, that is a dynamical effect. However Force can also be defined, studied and measured in statics, by the study of objects deformations and equilibrium. As a matter of fact forces are measured in practice with dynamometers. I would therefore suggest to add in the lead paragraph this other way to define a force. — Preceding unsigned comment added by Jmcourty (talk • contribs) 17:36, 19 March 2022 (UTC)

Please sign all your talk page messages with four tildes (~~~~) — See Help:Using talk pages. Thanks.

Yes, but i.m.o. we don't have to mention all the other manifestations, occurrences and definitions in the lead. - DVdm (talk) 19:59, 19 March 2022 (UTC)

Maximum force

I recently learned from https://www.motionmountain.net/maximumforce.html that there is such a thing as maximum force, apparently the most recent law of nature to be discovered (1973), and was surprised to find that this article on Force makes no mention of it (first I searched Wikipedia for 'maximum force' which got me a video game, then page-searched this article for both the word 'max' and relevant parameters such as the speed of light and the gravitational constant).

Searching the web a bit further, I found a physicsforum thread from last month that links some papers and suggests there is no real consensus on it yet. Is that why it hasn't been included, has this been talked about already? I didn't spot the topic on the current talk page or first and second archive pages.

Should this be included? Even if it's currently being debated, to me it seems like something to mention (with the qualification included).

LucGommans (talk) 18:11, 20 March 2022 (UTC)

The source is a personal website around Schiller's self-published book. No matter the quality of the book, unless this is extensively treated in the relevant literature, Wikipedia can't have it. This is just not a wp:reliable source in the Wikipedia sense. - DVdm (talk) 18:40, 20 March 2022 (UTC)

I'm not sure which book you are referring to, he seems to have self-published a few. But his paper was published in Physical Review D. Gibbons' paper mentioned in the link is also reliably published [1] and seems to support the idea of maximum force as far as I can see from the abstract. It might or might not support Schiller's assertion that General Relativity can be derived from the principle, and we should be cautious of making that claim based only on Schiller, being as he has a reputation as a crackpot. SpinningSpark 21:39, 20 March 2022 (UTC)

what is force

What is force 2409:4063:6E92:CD29:A964:66B4:66B4:1656 (talk) 04:43, 26 March 2022 (UTC)

The third sentence in the lead says: “A force can also be described intuitively as a push or a pull.” That is en excellent introductory comment about force. Dolphin (t) 07:53, 26 March 2022 (UTC)

Another answer is do your own homework. SpinningSpark 16:56, 26 March 2022 (UTC)

who wrote this source?

are they a specialist in the field?

why did you write this article? 103.12.191.189 (talk) 13:10, 23 April 2023 (UTC)

GA Reassessment

Force

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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Article (edit | visual edit | history) · Article talk (edit | history) · Watch • Watch article reassessment page • Most recent review

Result: Kept, with thanks, once again, to XOR'easter. ~~ AirshipJungleman29 (talk) 13:05, 11 August 2023 (UTC)

GA from 2008. Quite a lot of uncited material in the article. Onegreatjoke (talk) 16:10, 22 July 2023 (UTC)

This page needs work. I completely disagree with the definition, which is only for moving objects. I can think of many examples where this is not a useful definition.
I would use the standard definition of force as the change in energy with position, since energy is fundamental. The derivative part should be added after the lead as KISS. Ldm1954 (talk) 17:10, 22 July 2023 (UTC)

I don't think that defining force in terms of an even less familiar concept, energy, is the right way to begin an article of this sort. XOR'easter (talk) 01:44, 23 July 2023 (UTC)

Force is a derivative term, it is not fundamental. Some examples are static friction, rolling friction, Hellman-Feynman, the derivatives of a Landau expansion of electromechanical terms, capillary. All of these are derivatives, most have nothing to do with motion in the way described by this article.

As one common example of a mistake, dynamic friction is the derivative with respect to motion of dissipative energies such as phonon/electron/plastic/elastic. Static friction is a derivative with respect to movement of the integrated. elastic strain energy.

Just my opinion that force needs rigor in definition. Not everyone may agree. Ldm1954 (talk) 02:06, 23 July 2023 (UTC)

Trying to squeeze every concept of "force" up to and including those derived from quantum field theory into the first two sentences of a Wikipedia article that will be read by high-school students is an exercise in futility. We could try to cover Hellman–Feynman, gauge bosons, and the Einstein field equations, but we'd just be talking to ourselves. XOR'easter (talk) 02:24, 23 July 2023 (UTC)

(I'm reading your reply as to my comment).

Sorry my list wasn't clear: the items were no for the lead but the article. The lead needs small work. But the overall concept of "force" has history that illuminates its curious role in physics, eg action at a distance / general relativity. So just some missing content that makes Force less "good". Johnjbarton (talk) 12:46, 23 July 2023 (UTC)

My reply wasn't to your comment, but to the comment just above it. My own feeling is that getting the lead exactly right should be the last part of the revision; it's hard to write a good summary without having the material that needs summarizing already in hand. XOR'easter (talk) 16:11, 23 July 2023 (UTC)

There is a lot of good material here.

Lead definition is wrong, as shown in the section "Third law" in this very article.

No mention of action-at-distance issues, one of the core aspects of "force" as a concept.

No mention of general relativity converting Newtonian gravitational "force" into geometry.

Section "Descriptions > Quantum mechanics" is unreferenced and a muddle. Johnjbarton (talk) 21:20, 22 July 2023 (UTC)

There actually was a little bit about general relativity in the "Gravitational" subsection. Rather than repeating that, I added a pointer to it from the end of the special relativity part. XOR'easter (talk) 16:27, 23 July 2023 (UTC)

I've added some words about "action at a distance" to the segue from Newtonian to Einsteinian gravity.

What we probably ought to do now is run a fine-toothed comb through the text and scrape out weird niche stuff (like one person's pet peeve with how everyone else in physics talks about force, which they wrote into the Wikipedia article in 2004, where it has sat ever since — that kind of thing). Some of the references may be substandard. There's no real reason to cite, e.g., press releases for a topic like this one. XOR'easter (talk) 00:11, 24 July 2023 (UTC)

The GA criteria now explicitly call for at least one citation per paragraph. (I think this is carrying a reasonable rule-of-thumb too far, for the sake of having a box to check off, but them's the breaks.) This probably isn't too hard to meet in this case, since we can raid the shelf of introductory physics textbooks [2][3]. XOR'easter (talk) 21:03, 27 July 2023 (UTC)

Well, I'm happier with this article now than I was when we started, so that's something. XOR'easter (talk) 16:54, 29 July 2023 (UTC)

The OED provides the etymology and historical quotations for strong force and related terms as meaning 7.g of "strong". Unfortunately, our {{cite OED}} template doesn't seem to provide a ready way to cite individual senses of a word. XOR'easter (talk) 18:21, 4 August 2023 (UTC)

Ok but I wonder if the physics sources used by OED would be more useful. (The ref as it reads in the article sounds like "here dummy this is the definition of "strong"; we can't tell that it says anything about "force"). Johnjbarton (talk) 18:24, 4 August 2023 (UTC)

They pick primary sources that illustrate the sense in which a term is being used, as is their typical M.O. Skipping past the secondary/tertiary source to cite primary sources directly goes against our typical way of doing things. I tweaked that reference (in what might be an off-label use of the citation template, but whatever) to indicate that we're citing it for the specialized physics meaning. XOR'easter (talk) 18:32, 4 August 2023 (UTC)

There are seven citations to University Physics, Sears, Young & Zemansky, pp. 18–38. Given the profusion of textbook editions, that's not really specific enough to be verifiable. The editions with only those three authors all seem fairly old, too; for example, the 12th edition (2008) also includes Freedman and Ford. (And the page range 18–38 is definitely not correct for that edition.) XOR'easter (talk) 18:47, 4 August 2023 (UTC)

This page range matches a chapter which introduces forces in the 6th edition (1982). Here's a link to archive.org: [4] Jähmefyysikko (talk) 19:25, 4 August 2023 (UTC)

Thanks. I was thinking that we'd have to go back to the '80s to find an edition that matched. If everything attributed to that book is in that stretch of the 6th edition (I can't check at the moment), then we can go ahead and fill in the metadata appropriately, and the article will be in decent shape overall. XOR'easter (talk) 20:27, 4 August 2023 (UTC)

Metadata now filled in. XOR'easter (talk) 23:17, 5 August 2023 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

A fundamental problem with fundamental forces.

As I am reading more about the QM section issues in this article it slowly dawns on me that a large chunk of this article may make no sense at all.

The section "Fundamental interactions" exists to summarize an article of the same name, Fundamental interactions. These fundamental interactions acquired the synonym "fundamental forces" through lazy discussions in the far past. "Force" is an entirely classical idea, by history and by its nature as an average over macroscopic scale. So the meaning and nature of the "fundamental forces" bears no direct relationship to the classical Newtonian force. To say the same thing differently, the long ago meaning of force was probably "interaction" but this was refined by Newton to very specific meaning in classical mechanics which has no QM equivalent. Rather, the physicist describing strong/weak/electromagnetic interactions fell back on the casual use of the term "force". Clearly these fundamental interactions bear almost no relation to Newtonian force.

I can change the Description > Quantum mechanics section to discuss force as an average via Ehrenfest theorem. But the section on QFT and on "fundamental interactions" are a more delicate problem. Legitimate reliable references will call fundamental interactions "forces". Finding a reliable reference that explains, "no these are not Newtonian forces" will be much more difficult.

Just to be clear, my goal would be to preface the fundamental discussion with something about the distinct difference in the meaning of "Force" in these cases rather than removal. Johnjbarton (talk) 01:19, 23 July 2023 (UTC)

Look like @XOR'easter beat me to the Ehrenfest theorem thing ;-) Johnjbarton (talk) 02:18, 23 July 2023 (UTC)

I'm surprised I was able to make any edits on this page at all.... XOR'easter (talk) 02:35, 23 July 2023 (UTC)

I agree that one needs to make the distinction between the microscopic forces and the classical force clear. But I do not see there would be a sharp distinction between the two, or at least one can find a strong connection between the two. For example, if one considers the quantized electromagnetic field and calculates the interaction energy E between two classical point charges, one gets exactly what would expected from the Coulomb law, although the interaction is now described as being mediated by virtual photons.(Zee, QFT in nutshell, p.32) Force would be obtained as F=dE/dx, where x is the distance between the two charges. Thus, the quantization of the EM field alone does not matter. Then if we add a quantized electron field to the mix, but still consider two classical charges as source terms, we get the same result with some QED corrections.

But I agree that if we consider a fully quantum mechanical case (e.g. the interaction energy between electrons bound to the same nucleus) the concept of force cannot be formulated anymore. The classical force is probably only recovered when the distance between the electrons becomes large. In the end, it will be about finding a reference which makes the connection clear and provides enough discussion. Jähmefyysikko (talk) 08:11, 23 July 2023 (UTC)

Yes, I guess the other way to look at this is that "Force" is the name of the intuitive physics notion which Netwon associated with (now) classical mechanics. All we need to do is clarify that the modern "forces" are not directly participants in F=ma. Johnjbarton (talk) 16:24, 23 July 2023 (UTC)

I feel the structural changes to the page address this issue sufficiently.

Resolved

Johnjbarton (talk) 23:18, 23 July 2023 (UTC)

"Non-fundamental types"

The section "Non-fundamental types" are topics related to classical mechanics. Microscopically they derive from electromagnetic forces but that seems unimportant to the topics. So the category name seems wrong.

Maybe we could rename this section "Other classical force concepts" and move it above the "Revisions of the force concept"? Johnjbarton (talk) 16:50, 23 July 2023 (UTC)

Yes, it does seem more like an "Examples of forces in classical mechanics" section. XOR'easter (talk) 17:59, 23 July 2023 (UTC)

Done. Also moved Torque and rotation. Seems like Torque and rotation could be sub-ed under Combining forces? Johnjbarton (talk) 20:10, 23 July 2023 (UTC)

The subsection on centripetal force seemed like it belonged with the other examples, so I split it out and did some rearranging. XOR'easter (talk) 23:03, 23 July 2023 (UTC)

All much better.

Resolved

Johnjbarton (talk) 23:17, 23 July 2023 (UTC)

Pauli repulsion "force"

In Normal force we say: When their electron clouds overlap, Pauli repulsion (due to fermionic nature of electrons) follows resulting in the force that acts in a direction normal to the surface interface between two objects. The sentence has a reference I don't have access to.

Similarly: All other forces in nature derive from these four fundamental interactions. For example, friction is a manifestation of the electromagnetic force acting between atoms of two surfaces, and the Pauli exclusion principle,.. has a reference to Pauli repulsion which does not mention friction.

IMO if we want to say these things we need better references and a clear section on Pauli exclusion as/related Force. Or at least as section, if in fact "clear" is too much to ask.

As far as I know, Pauli repulsion is more of a miracle than a "Force". Pauli exclusion principle never mentions "force" or "friction". To be sure, the things I've read seem to dance around the "repulsion" issue. Johnjbarton (talk) 23:12, 25 July 2023 (UTC)

Ok I found a great article by EH Lieb on the stability of bulk matter refed from one of the other wikipedia pages.

I boiled down the article to two sentences. The Pauli part is solid, but Lieb did not express the uncertainty principle part cleanly (He does say uncertainty and he does work on hydrogenic atoms and concludes: An electron is like a rubber ball, or a fluid, with an energy density proportional to $\rho ^{5/3}$. It costs energy to squeeze it and this accounts for the stability of atoms.)

Please review the last paragraph in QM section in this article. Johnjbarton (talk) 03:36, 26 July 2023 (UTC)

The reference used for the normal force can be found from the archive.org: [5], but it is an undergraduate textbook which does not say anything about electrons, only makes an analogy between the springs of a mattress and 'atomic springs'. A better reference would be preferable. The article by Lieb does not say anything about normal force, and is not as useful in this case. As far as I know, for normal force, there should be some reference to the solidity of the objects. Jähmefyysikko (talk) 08:05, 26 July 2023 (UTC)

Thanks for that reference. I will keep that reference for normal force but change the text to match it. The "normal force" seems to me to be just the reaction of a solid to the normal component of the gravitational force. But it is in engineering focused books. Anyway its a classical thing and no Pauli is called for.

I think solidity of objects is simply postulated for classical physics, eg Rigid body, so we don't need to explain it.

I think I fixed the normal force section. Johnjbarton (talk) 14:04, 26 July 2023 (UTC)

@Jähmefyysikko I notice that you added a bit about electron degeneracy pressure. Can we find a reference for that part?

The article on electron degeneracy pressure cites Lenard and Dyson's paper on "Stability of Matter", but they never mention degeneracy pressure. Lieb's papers which review and build on Lenard and Dyson don't use that term either. My specific concern is the word "pressure" or the combination "degeneracy pressure". Pressure implies force.

This call comes back to whether Pauli exclusion and confinement uncertainty are "forces" or not. These constraints are built into the mechanics so they don't get listed with the 4 Forces. Seems nutty to me, but hey no one asked me. I guess the classical mechanics analogy might be to say torque or rolling constraints: the rigidity of the bodies involved in rotation or rolling are "given" or idealized so we can focus on modeling the motion.

In addition both Pauli exclusion and the uncertainty effect are involved in stability. Since the refs for electron degeneracy are incorrect I don't know what it includes. Fun! Johnjbarton (talk) 14:28, 26 July 2023 (UTC)

I added Griffiths as a reference to establish this terminology. The references do not state this very clearly, but one can calculate the degeneracy pressure as a thermodynamic pressure via the definition P=-dF/dV at fixed particle number and at zero temperature. F is the free energy of the Fermi gas (internal energy at T=0).

I would not call Pauli exclusion a microscopic 'force' but I don't see a problem with it giving rise to macroscopic forces either. After all, one can define conservative forces as F=-dU/dx regardless what the source of the energy U is. Of course, there must also be some other force involved at the boundary of the system which confines the Fermi gas inside the volume, and this the force that the piston or the wall of the system feels. Jähmefyysikko (talk) 18:53, 26 July 2023 (UTC)

Thanks! I think the Force article is decent shape. Your edit lead me to electron degeneracy pressure, Thomas-Fermi model, Fermi gas, Degenerate matter and so on, all of which have issues ;-).

Resolved

Johnjbarton (talk) 23:50, 26 July 2023 (UTC)

Newton's first law or Galilean relativity?

The section on Newton's first law seems to be about relativity?

FWIW, Feather says the first law is essential a definition of what a Force does (see also our lead sentence). Johnjbarton (talk) 22:19, 27 July 2023 (UTC)

I agree. The current version of the section on the first law does not fare well when assessed using the principles at WP:Make technical articles understandable. The section should be reworked to make it more appropriate to an article on the topic of force. Dolphin (t) 22:30, 27 July 2023 (UTC)

Well, the first law is about relativity—Galilean relativity. XOR'easter (talk) 17:22, 28 July 2023 (UTC)

Someone fixed this. The current revision shrinks the relativity bit appropriate to an article on force.

Resolved

Johnjbarton (talk) 21:55, 28 July 2023 (UTC)

"this has been disparaged"

The Second law section has this teaser: Some textbooks use Newton's second law as a definition of force, but this has been disparaged in other textbooks. I think the first half is ok, but the second half is (unfairly) vague. It leaves the reader wondering if the second law is wrong or what.

Feynman's objection is to "definition" as an operating principle in physics: "we cannot ... make mechanics a mathematical theory". It seems to me that Feynman would not object to using F=ma as establishing the meaning of force for the collection of scenarios typical of classical mechanics.

Similarly the second sentence refs Noll, who ends with a comment about fundamental interactions and says: I am not aware of any general axiomatic mathematical framework that would encompass all of these kinds of non-classical forces as special cases.

So the issue is questions of clear scope rather than definition.

I think we should move this paragraph and expand it with such quotes, so as to make the content transparent, or delete it despite the 7 references.

Thoughts? Johnjbarton (talk) 22:37, 28 July 2023 (UTC)

Some quotes:

${\vec {F}}=m{\vec {a}}$ is probably the most useful equation in all of physics. But what does it mean? To understand Newton's second law, we need to answer the questions: What is force? What is mass? Both of these quantities appear in the equation along with acceleration, which we already understand. In the years since Newton, philosophers have debated these questions at great length. Even though Newton explained what he meant by mass, some people think that mass is a quantity which is defined by this equation. If you know the magnitude of the force acting on an object, measure the magnitude of the resulting acceleration; then the mass of the object is $m=F/a$. Other people think that the second law is a definition of force. Knowing the mass of an object, measure its acceleration, and the applied force can be found.... Now, if the second law is a definition of either mass or force, it is not a deep discovery in physics; it is simply a definition. But if the equation is used to define two of the three quantities which appear in it, then it has no meaning at all. Can it be that Newton's famous second law is meaningless?

The way to understand what ${\vec {F}}=m{\vec {a}}$ means is by making use of it. Through applications to specific problems, such as those given throughout this chapter, we can see how it works and understand how it organizes the world. Sometimes it is used to determine a mass. Once determined, the response of that mass to various different forces can be studied. Sometimes ${\vec {F}}=m{\vec {a}}$ is used to determine a force, whose effect on various different masses is then studied. In many cases $m$ and ${\vec {F}}$ are known independently and ${\vec {F}}=m{\vec {a}}$ successfully predicts the motion. Though the precise logical status of Newton's second law may pose a recondite philosophical question, in practice simple, workable determinations of ${\vec {F}}$ and $m$ exist which lead to consistent results over the enormous range of phenomena described by classical physics.

Frautschi, Steven C.; Olenick, Richard P.; Apostol, Tom M.; Goodstein, David L. (2007). The Mechanical Universe: Mechanics and Heat (Advanced ed.). Cambridge [Cambridgeshire]: Cambridge University Press. p. 134. ISBN 978-0-521-71590-4. OCLC 227002144.

Although it is interesting and worthwhile to study the physical laws simply because they help us to understand and to use nature, one ought to stop every once in a while and think, “What do they really mean?” The meaning of any statement is a subject that has interested and troubled philosophers from time immemorial, and the meaning of physical laws is even more interesting, because it is generally believed that these laws represent some kind of real knowledge. The meaning of knowledge is a deep problem in philosophy, and it is always important to ask, “What does it mean?”

Let us ask, “What is the meaning of the physical laws of Newton, which we write as $F=ma$? What is the meaning of force, mass, and acceleration?” Well, we can intuitively sense the meaning of mass, and we can define acceleration if we know the meaning of position and time. We shall not discuss those meanings, but shall concentrate on the new concept of force. The answer is equally simple: “If a body is accelerating, then there is a force on it.” That is what Newton’s laws say, so the most precise and beautiful definition of force imaginable might simply be to say that force is the mass of an object times the acceleration. Suppose we have a law which says that the conservation of momentum is valid if the sum of all the external forces is zero; then the question arises, “What does it mean, that the sum of all the external forces is zero?” A pleasant way to define that statement would be: “When the total momentum is a constant, then the sum of the external forces is zero.” There must be something wrong with that, because it is just not saying anything new. If we have discovered a fundamental law, which asserts that the force is equal to the mass times the acceleration, and then define the force to be the mass times the acceleration, we have found out nothing. We could also define force to mean that a moving object with no force acting on it continues to move with constant velocity in a straight line. If we then observe an object not moving in a straight line with a constant velocity, we might say that there is a force on it. Now such things certainly cannot be the content of physics, because they are definitions going in a circle. The Newtonian statement above, however, seems to be a most precise definition of force, and one that appeals to the mathematician; nevertheless, it is completely useless, because no prediction whatsoever can be made from a definition. One might sit in an armchair all day long and define words at will, but to find out what happens when two balls push against each other, or when a weight is hung on a spring, is another matter altogether, because the way the bodies behave is something completely outside any choice of definitions.

For example, if we were to choose to say that an object left to itself keeps its position and does not move, then when we see something drifting, we could say that must be due to a “gorce”—a gorce is the rate of change of position. Now we have a wonderful new law, everything stands still except when a gorce is acting. You see, that would be analogous to the above definition of force, and it would contain no information. The real content of Newton’s laws is this: that the force is supposed to have some independent properties, in addition to the law $F=ma$; but the specific independent properties that the force has were not completely described by Newton or by anybody else, and therefore the physical law $F=ma$ is an incomplete law. It implies that if we study the mass times the acceleration and call the product the force, i.e., if we study the characteristics of force as a program of interest, then we shall find that forces have some simplicity; the law is a good program for analyzing nature, it is a suggestion that the forces will be simple.

Feynman, Richard P.; Leighton, Robert B.; Sands, Matthew L. (1989) [1965]. The Feynman Lectures on Physics, Volume 1. Reading, Mass.: Addison-Wesley Pub. Co. ISBN 0-201-02010-6. OCLC 531535. section 12-1

[I]f we observe that an air track rider of mass $m$ starts to accelerate at rate ${\vec {a}}$, it might be tempting to conclude that we have just observed a force $F=ma$. Tempting, but wrong. [...] Newton’s third law is essential if the second law is to be meaningful: without it, there would be no way to know whether an acceleration results from a real force, or is merely an artifact of being in a non-inertial system. If the acceleration is due to a force, then somewhere in the universe there must be an equal and opposite force acting on some other body.

Kleppner, Daniel; Kolenkow, Robert J. (2014). An introduction to mechanics (2nd ed.). Cambridge: Cambridge University Press. pp. 54–55. ISBN 978-0-521-19811-0. OCLC 854617117.

These laws are so familiar that we sometimes tend to lose sight of their true significance (or lack of it) as physical laws. [...] The definition of force becomes complete and precise only when "mass" is defined. Thus the First and Second Laws are not really "laws" in the usual sense; rather, they may be considered definitions. Because length, time, and mass are concepts normally already understood, we use Newton's First and Second Laws as the operational definition of force. Newton's Third Law, however, is indeed a law. It is a statement concerning the real physical world and contains all of the physics in Newton's laws of motion. [Footnote: *The reasoning presented here, viz., that the First and Second Laws are actually definitions and that the Third Law contains the physics, is not the only possible interpretation. Lindsay and Margenau (Li36), for example, present the first two Laws as physical laws and then derive the Third Law as a consequence.]

Thornton, Stephen T.; Marion, Jerry B. (2004). Classical Dynamics of Particles and Systems (5th ed.). Thomson Brooks/Cole. pp. 49–50. ISBN 0-534-40896-6.

The two principles are equivalent to Newton's three laws of motion, which in their usual formulation involve a number of logical difficulties that the present treatment tries to avoid. For instance, Newton's first law, which states that a particle moves with constant velocity in the absence of an applied force, is incomplete without a definition of force and might at first seem to be but a special case of the second law. Actually it is an implicit statement of Principle 1 [existence of inertial reference frames] and was logically necessary for Newton's complete formulation of mechanics. Although such questions would seem to arise in understanding Newton's laws, we should remember that it is his formulation that lies at the basis of classical mechanics as we know it today. The two principles as we have given them are, in fact, an interpretation of Newton's laws. This interpretation is due originally to Mach (1942). Our development is closely related to work by Eisenbud (1958).

It is interesting that Eq. (1.20), Newton's second law, is now a definition of force, rather than a fundamental law. Why, one may ask, has this definition been so important in classical mechanics? As may have been expected, the answer lies in its physical content. It is found empirically that in many physical situations it is $m{\vec {a}}$ that is known a priori rather than some other dynamical property. That is, the force is what is specified independent of the mass, acceleration, or many other properties of the particle whose motion is being studied. Moreover, forces satisfy a superposition principle: the total force on a particle can be found by adding contributions from different agents. It is such properties that elevate Eq. (1.20) from a rather empty definition to a dynamical relationship.

José, Jorge V.; Saletan, Eugene J. (1998). Classical dynamics: A Contemporary Approach. Cambridge [England]: Cambridge University Press. ISBN 978-1-139-64890-5. OCLC 857769535.

As with the other branches of theoretical physics, our exposition makes no use of the historical approach. From the very beginning it is based on the most general principles: Galileo's principle of relativity, and Hamilton's principle of least action. Only with this approach, indeed, can the exposition form a logical whole and avoid tautological definitions of the fundamental mechanical quantities.

Landau, Lev D.; Lifshitz, Evgeny M. (1969). Mechanics. Course of Theoretical Physics. Vol. 1. Translated by Sykes, J. B.; Bell, J. S. (2nd ed.). Pergamon Press. p. vii. ISBN 978-0-080-06466-6.

XOR'easter (talk) 23:49, 28 July 2023 (UTC)

I've moved that teaser to the end of the section and expanded the latter part, as it had been bothering me for a while. XOR'easter (talk) 00:32, 29 July 2023 (UTC)

Nice work, looks good. I think the various attitudes towards force are interesting for reflection, but the level of this article wants to be "behold force", not "consider here that which some call force".

Resolved

Johnjbarton (talk) 20:43, 29 July 2023 (UTC)

Newton or Noether?

In the third we say: Combining Newton's Second and Third Laws, it is possible to show that the linear momentum of a system is conserved.

And yet elsewhere, Noether's theorem we say it is consequence of "uniformity of space distance-wise"

I will add some qualification to the statement (and avoid Noether in this article) Johnjbarton (talk) 23:30, 28 July 2023 (UTC)

Your first quotation correctly implies that the concept of conservation of linear momentum is best understood by a reader who already has some understanding of Newton’s laws of motion. That is most reasonable.

Your second quotation implies that conservation of linear momentum is best understood by a reader who already has some understanding of “uniformity of space distance-wise” or Noether’s theorem. That implication is unreasonable in an article such as this article on Force, in an encyclopaedia such as this one which caters for a general readership. Space distance (whatever that is) and Noether’s theorem are much more advanced than Newton’s Laws. WP:Make technical articles understandable is relevant. Dolphin (t) 07:04, 29 July 2023 (UTC)

My question was not about appropriateness but about correctness. I corrected the sentence, please check it. Johnjbarton (talk) 13:54, 29 July 2023 (UTC)

The section on the Third law has been in error for a while because it says the momentum of a system is conserved. That is incorrect because it is only closed systems whose linear momentum is conserved. That is why closed systems are important and Wikipedia has an article dedicated to them.

On 28 July you amended the sentence so that it now says “... in systems where Newton’s laws apply.” I’m not aware of any systems, closed or not, in which Newton’s laws don’t apply. I haven’t seen any mention of such systems on Wikipedia. If you know of such a mention please let me know on this Talk page.

I think you should remove your mention of “systems where Newton’s laws apply” and, instead, insert the blue link to Closed system. Dolphin (t) 12:49, 30 July 2023 (UTC)

Go ahead an fix what you think is wrong here. My only concern was the claim the Newtons laws show linear momentum is conserved, which we now have two different issues with. I also think you could simply delete the paragraph. This is not an article on conservation of momentum but it is an article which is very long. Johnjbarton (talk) 20:27, 30 July 2023 (UTC)

I have amended the sentence. See my diff. Dolphin (t) 13:05, 1 August 2023 (UTC)

I was puzzled by this discussion earlier. I stumbled upon this sentence in the sadly unreferenced Causality (physics)

Rather, Newton's Second Law can be derived from the conservation of momentum, which itself is a consequence the spatial homogeneity of physical laws.

Deriving conservation from Newton's empirical law of course works, but it could be seen as running backwards.

This just FYI, I'm posting this for interest; I still don't think Noether belongs in this Force article. Johnjbarton (talk) 23:51, 10 August 2023 (UTC)

I agree. It would be backwards to use momentum conservation to derive Newton’s laws. The sections on Newton’s laws in this article on force would not be improved by any mention of Noether. Dolphin (t) 01:12, 11 August 2023 (UTC)

Presentation order

With such a sprawling article, it is difficult to find a best possible order for the presentation. Currently I am bugged by the fact that quantum field theory is presented before classical fields (which are discussed in the section Fundamental interactions#Electromagnetic). Somehow this should be organized so that Maxwell's theory would act as a conceptual bridge to QFT, which elaborates on the nature of the fields and the interaction process. Then the logic of QFT would not seem like such a huge jump. Jähmefyysikko (talk) 13:24, 30 July 2023 (UTC)

I think the electromagnetic and gravitation sections are doing two things: 1) discussing classical force 2) discussing fundamental interaction. I think the bulk of the material in each of these two sections should be moved up to Examples of forces, leaving just the modern fundamental action info in the current location. Johnjbarton (talk) 14:15, 30 July 2023 (UTC)

Ok I carried out my proposal, I think this solves the issue @Jähmefyysikko raised.

Both the gravity and em sections were too long. They are still too long, esp. the one in the Examples section. It should be condensed IMO. Johnjbarton (talk) 20:22, 30 July 2023 (UTC)

Bibliography / Further reading

A recent edit by @ActivelyDisinterested changed "Further reading" to "Bibliography", but we already have "References". The edit seems to be motivated by a desire to signal that the items in the list are also references and should not be deleted without manual checking.

I think a better solution is to move all of the Harvard style citations into the Further reading list. That way the References section is one consistent style of citation and moreover changes to the items on the Further reading list are decoupled from the references. As a bonus the Harvard style entries in the Further reading list will call out those books as both referenced and recommended for further references. Johnjbarton (talk) 15:07, 9 August 2023 (UTC)

That would seem to run counter to MOS:FURTHER. There would also be some technical difficulties. The Harvard references will be collected by the {{reflist}}, it's not possible to change this behaviour. Other styles of references can be separated out, but that would require every other reference (including any future references) to have a correct |group= setup in the reference header. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 15:18, 9 August 2023 (UTC)

Thanks! However as suggested in MOS:FURTHER, I think this is a case of " References section is too long for a reader to use as part of a general reading list." IMO the current solution is fragile and looks bad.

I think we could define the items like Cutnell in a ref= list in the reflist like:Help:Cite_errors/Cite_error_references_no_text#Overview. Then we could ref from both places?

This way the fixes you recently applied will be less likely to be needed. What do you think? Johnjbarton (talk) 15:33, 9 August 2023 (UTC)

That should work, but it would be confusingly at odds with how nearly every other article is setup. The relevant part of MOS:FURTHER is This section is not intended as a repository for general references or full citations that were used to create the article content, these are citations used to support the articles content. Rather than something additional to the content. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 15:55, 9 August 2023 (UTC)

Having both a References and a Bibliography seems confusing to me. "Further reading" is exactly what we want in this case. We want a list of the best material for additional reading and some of those items we used in as references in the article -- because they were the best material.

I think the full article Wikipedia:Further_reading clearly covers our case here. The only real issue is the technology. I will investigate if the ref= approach works. Johnjbarton (talk) 16:19, 9 August 2023 (UTC)

But these are not additional reading, there are required parts of referencing. However I won't stand in the way of how you want to setup the details in this article. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 16:31, 9 August 2023 (UTC)

Sorry if I was not clear: I want the References list to be 100% solid. My proposal was an attempt to make the Further reading list to include some short entries that were then referenced into that 100% solid reference list.

But the technology thing I wanted does not work. It seems that any ref name=Foo after the References section fails? So a short entire in the Further reading can't be referenced.

I think the best solution would be to simply duplicate the cite templates in the Further reading. That is, get replace the harvb templates in the body with cite templates and dupe the ones we want in Further reading.

Then the items in Further reading are independent of references. Deleting a Further reading will not damage the references list. Johnjbarton (talk) 16:44, 9 August 2023 (UTC)

I changed the Feynman v1 reference to the duplicated form as a trial. I think the references are better, the Further reading is slightly better, deletions in Further reading (for Feynman v1) don't affect references, and we don't have two citation techniques in one article.

(BTW I think Further reading should be shorter)

@XOR'easter @Jähmefyysikko are you ok with this direction? Johnjbarton (talk) 17:31, 9 August 2023 (UTC)

Not all of the inline citations to the Feynman Lectures are to chapter 12. XOR'easter (talk) 18:34, 9 August 2023 (UTC)

Yes all references after the reflist fail. You could replace all the Harvard references with the cites from the Further reading section. If you do so though you should remove them entirely from the Further reading section, as it's not meant to hold duplicates. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 17:32, 9 August 2023 (UTC)

I guess it depends on what one thinks "Further reading" accomplishes. I do not agree with the lack of duplication in an article as extensive as Force.

One can take "Further reading" to mean "A well-curated list of sources of broad scope and general interest, some of which are also listed as references". That is the topical, balance, neutral, and limited criteria in Wikipedia:Further_reading.

Or one can take "Further reading" to mean "Some sources not important enough to reference in the article but listed here for reasons unclear to many." ;-)

IMO at this point we could delete the current list and improve the article.

Johnjbarton (talk) 19:14, 9 August 2023 (UTC)

Based on the above reasoning, I went ahead and removed the rest of the Further reading. At this point it had only three entries left. Jähmefyysikko (talk) 19:39, 9 August 2023 (UTC)

You could replace the Harvard references with the full cites and remove them from the Further reading section, as that would standardise the references in the article. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 15:27, 9 August 2023 (UTC)

• Can I suggest anyone working with short form references turn on the associated error messages, details can be found in Category:Harv and Sfn template errors. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 17:45, 9 August 2023 (UTC)

  Thanks! I would prefer to stop using the short form and especially not mix them. Johnjbarton (talk) 18:41, 9 August 2023 (UTC)

  The article should have a consistent referencing style, but the error messages will make it easier to make sure you remove them all. -- LCU ActivelyDisinterested ∆transmissions∆ °co-ords° 19:25, 9 August 2023 (UTC)

  Ok I'm trying the script, thanks. Johnjbarton (talk) 21:30, 9 August 2023 (UTC)

Derivatives of Force

@Johnjbarton is of the opinion that any mention to Yank and other derivatives of Force should not be reported on Wikipedia even if they are provided with sources. It's obvious that this concepts are used just in very few publications and, in general, this type of lexicon is really facetious, but I don't think that it can't even be mentioned on the article. How we should manage this topic? FootKalos1597 (talk) 08:03, 12 April 2024 (UTC)

Velocity and acceleration are obviously highly important. The next derivative, jerk, is much less important; and subsequent derivatives are only relevant in a small number of highly specialized areas. My view is that jerk and higher derivatives, if they appear in this article, are more likely to confuse and demotivate than to be beneficial.

The higher derivates are well covered at Fourth, fifth, and sixth derivatives of position. I think it will be sufficient if this article is listed at Force#See also. Dolphin (t) 12:49, 12 April 2024 (UTC)

We are talking about YANK, not jerk. There's no such page for dynamic quantities, but just for kinematic quantities. So you're proposing to create a new page like Fourth, fifth, and sixth derivatives of position also for dynamic quantities or to unify both less common dynamic and kinematics quantities in the same page? FootKalos1597 (talk) 13:45, 12 April 2024 (UTC)

I’m not proposing a new page within this topic; I am opposed to an extra page. I am suggesting inserting Fourth, fifth, and sixth derivatives of position into See also in the article Force and ending there.

I don’t know what you mean by a page for dynamic quantities. I doubt it is sufficiently notable to warrant a separate page on Wikipedia. If you think it is notable enough you might explain what would be in this page for dynamic quantities. Dolphin (t) 14:15, 12 April 2024 (UTC)

I mean that jerk, snap, crackle etc. are derivatives of position, so they're used in Kinematics, the branch of physics that describe motion. Otherwise yank, tug, snatch etc. are derivatives of linear momentum, therefore they're formally included in Dynamics, the branch of physics that roughly describes the causes of motion. Conceptually, even if really related, they're two different group of quantities. FootKalos1597 (talk) 16:20, 12 April 2024 (UTC)

@FootKalos1597 Your comment on my revert is not correct. My edit summary was

• "A primary reference is no sufficient for new concepts, please see WP:PSTS"

I did not remove Yank nor did I claim "that any mention to Yank and other derivatives of Force should not be reported on Wikipedia".

I specifically removed the higher derivatives for the reason I listed. It is now up to you to build consensus to include that content. Please see WP:BURDEN. Johnjbarton (talk) 15:52, 12 April 2024 (UTC)

The reason you listed didn't correspond to the actual status of my last edit. We are in presence of concept that in their nature they're not new at all (is trivial to make derivatives of a quantity). The problem here is that the use (therefore the name given to) this quantities is very specific and circumscribed. So in my opinion is totally legit to just mention their existence, without any further interpretation. In order to do it according to Wikipedia rules I cited 4-5 articles where this quantity were effectively used. I don't know why this work should not be considered enough. I can't understand why you also decide to revert at all my edit, removing also totally legit sources instead of simply removing any sentence you personally judged "too much".FootKalos1597 (talk) 16:27, 12 April 2024 (UTC)

I agree completely with your point:

• "We are in presence of concept that in their nature they're not new at all (is trivial to make derivatives of a quantity)"

and as pointed out by @Dolphin51, maybe the best course is to not include the topic.

However, these are not criteria for wikipedia. Notability requires secondary references. If we have secondary refs we can argue about whether to still exclude the topic because it is trivial. But without a secondary ref there is no reason to discuss it.

(to be sure we are on the same page, I am not arguing against "yank" content that exists, only against additional higher derivatives.)

Maybe we can find someway of combining jerk/yank and all the higher exotica in one page? That would seem to me to match the topic best. Johnjbarton (talk) 17:51, 12 April 2024 (UTC)

We could think about a page titled Higher kinematics and dynamics derivatives with this type of partition:

• Kinematic quantities
  • jerk
  • snap

etc.

• Dynamic quantities
  • yank
  • tug

etc.

What do you think? FootKalos1597 (talk) 19:39, 12 April 2024 (UTC)

The problem here is sourcing, and the sourcing bar is even higher for creating a new article. In this case I doubt it is workable. MrOllie (talk) 19:52, 12 April 2024 (UTC)

So what should be the best option in order to don't throw away the baby with the bathwater? FootKalos1597 (talk) 20:13, 12 April 2024 (UTC)

At some point one has to accept that Wikipedia doesn't cover absolutely everything. MrOllie (talk) 20:14, 12 April 2024 (UTC)

I don't agree that this is the case, considering that we're are talking of an edit that was barely a mention on a wider page and not a full article on a ultra specific topic. In my opinion it's something that can be cited somewhere with the sources provided. FootKalos1597 (talk) 20:26, 12 April 2024 (UTC)

We need secondary sources for something like this. Ideally we'd see definitions in something like a textbook for terminology like this. If we don't have the required level of sourcing that means we leave it out - not that we compromise on sourcing standards to include it anyway. MrOllie (talk) 20:29, 12 April 2024 (UTC)

A lot of things in science are not included in textbooks. It can't be a principle applied with any type of exception. By the way this is my opinion and it seems that I'm part of the minority here FootKalos1597 (talk) 20:34, 12 April 2024 (UTC)

That's OK. Wikipedia doesn't include a lot of things in science, by design. MrOllie (talk) 20:35, 12 April 2024 (UTC)

I added a textbook reference. That's all that is needed here. Johnjbarton (talk) 02:31, 13 April 2024 (UTC)