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The following is an archived discussion of a featured article nomination. Please do not modify it. Subsequent comments should be made on the article's talk page or in Wikipedia talk:Featured article candidates. No further edits should be made to this page.

The article was not promoted 00:03, 17 April 2008.

Force

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I'm nominating this article for featured article because it is a core-topic myself and many others have worked very hard on. It is thorough, well-referenced, and represents an article that is better than practically any other I've found in any other encycloepdia. ScienceApologist (talk) 21:32, 8 April 2008 (UTC)[reply]

Comments

Otherwise all the links worked and the sources look good. Ealdgyth - Talk 23:26, 8 April 2008 (UTC)[reply]
I took care of everything but physics post which I think is a good source despite Tab Stevens being somewhat of a low profile and connexions which is a Rice University project and has a high degree of reliability. ScienceApologist (talk) 01:13, 9 April 2008 (UTC)[reply]
Probably want to take those done graphics out, they really bog down the FAC page. Ealdgyth - Talk 01:28, 9 April 2008 (UTC)[reply]

Question: "According to Newton's Second Law, the combination of all forces acting on a body (known as the net force or resultant force) is equal to the product of acceleration and the mass of the body.": can you confirm that in every case "the rate of change of linear momentum" is equivalent to acceleration? I heard that on a quantum/relativistic/modern physics level this needn't be true (I'm asking this because this isn't the way Newton himself proposed the law)? On another note, can the first and second paras of the lead be merged? It would make more sense that way; one para what a force is, the second the history of our understanding of force. There are entire paragraphs in the article without a single citation/reference. Please try to include at least one cite at the end of every paragraph for verifiability. indopug (talk) 03:15, 9 April 2008 (UTC)[reply]

I believe what you may be refering to is the issue with relativistic particles that carry momentum despite the rest mass of such particles being zero. However, if you follow the formulations outlined in our section on special relativity, there is a clear indication of how the idea of "force" can be recast to deal with this. In such a situation the four-acceleration is directly relatable to the rate of change of the four-momentum through some proper time interval. I'll also point out that the way forces behave in quantum dynamics is outlined in the Feynman diagrams section and, for massive particles, always follows the same way. Some paragraphs in the article are basically common knowledge so it is hard to know what to cite. If you can indicate specific examples of facts you want to see cited that aren't, I will try to include them. ScienceApologist (talk) 12:48, 9 April 2008 (UTC)[reply]
  • Comment References could use some formatting clean-up; they're inconsistent at the moment, and there are some random typos/errors that a copyedit would take care of. BuddingJournalist 15:38, 9 April 2008 (UTC)[reply]
  • Comment
    • I think this is a pretty good article for people who are physicists, it definitely needs some work for others to be able to understand. I took college level physics 5 years ago and I am having trouble in certain spots. What level of reader is this article directed at? The article seems to expect a certain level understanding for things like: Simple machines, General relativity, kinematics, momentum and many more.
      • What part of the FAC-criteria are you referring to with this questioning? We try to write a readable article. However, I don't know what is not understandable with the points you outline below. You must explain why you find things confusing or hard to understand or I cannot fix them. ScienceApologist (talk) 18:42, 9 April 2008 (UTC)[reply]
    • Mention that the "Theory of impetus" was a precursor to momentum?
    • "Pre-Newtonian concepts" section only mentions the western world. Were there any notable force discoveries in the east?
    • Please state Newton's laws before discussing them. Right now it launches into discussions of things that the reader are supposed to know beforehand.
    • Awkward sentence "Accelerations can be defined through kinematic measurements while mass can be determined through, for example, counting atoms."
    • The article doesn't clearly divide what is and isn't true anymore. For example impetus is mentioned as a "medieval idea" but it is not clearly refuted.
      • That's because impetus, as an idea, is not clearly refuted. Impetus is considered by some philosophers of science to be nascent inertia/momentum. Others see the mixing of imprecise terminology to be a problem. In any case, we cannot "refute" the idea in main part because medieval thinkers had not fleshed it out enough. That's a discussion for the impetus page. ScienceApologist (talk) 19:03, 9 April 2008 (UTC)[reply]
    • "sometimes called the "second most famous formula in physics"." How is this relevant? Why is it called this? What is the most famous? Also blogs shouldn't be used as sources whenever possible.
      • There are a lot of people who call it this, that's just one example. It's a relevant comment about the equation. The most famous is E=mc2. Blogs are fine when they are written by reliable people with PhDs about the subjects in which they have their PhDs. ScienceApologist (talk) 18:42, 9 April 2008 (UTC)[reply]
    • "which follows as a direct consequence of the caveat in Newton's First Law," which caveat?
    • Doesn't mention to the reader that Newtons laws work on only the macroscopic level.
    • why does this sentence have ticks around it? If it's a quote what's it quoting from? "'When a resultant force acts on an object of constant mass, an acceleration will result with the product of its mass and acceleration equal to the resultant force, the direction of the acceleration being in the same direction as that of the resultant force. F=ma'"
    • Why is there a link for "internal forces" Should that be describe on this page?
    • This sentence is overly complex and could be stated in a simpler manner: "As with other physical concepts (e.g. temperature), the intuitive notion is quantified using operational definitions that are consistent with direct perception, but are more precise and consistent with the conceptual definition of force offered by Newtonian mechanics."
    • I stopped at Descriptions. -Ravedave (talk) 17:29, 9 April 2008 (UTC)[reply]

Most of your comments are ill-posed and not very helpful (that is, they aren't actionable as either I think that they are proposing edits which are problematic or I cannot tell what edits you are proposing). I hope that you can formulate them better as we proceed. Maybe giving some suggested wording, offering some questions, etc. I want the article to be readable, but we need to strike a balance between reaching a broad audience and extensive coverage. The FAC criteria require that we include as much relevant information as possible. That's what I tried to do.

If the article is to confusing to understand, perhaps you could offer some pointers on how to make it more understandable. So far, about six different people have read it and all see problems/solutions in places that are different from each other. I need to know what you are expecting out of a feature article if I am to accommodate your desires.

ScienceApologist (talk) 18:42, 9 April 2008 (UTC)[reply]

Changed from oppose to comment. No thanks.-Ravedave (talk) 21:26, 9 April 2008 (UTC)[reply]
  • Oppose. Abstaining for now. Fails Wikipedia:Explain jargon, which is required for featured articles. Both paragraphs of the lead are unreadable by anyone unfamiliar with physics. Compare with the opening paragraphs of the physics articles on Encarta or Britannica. The lead (at least) should be parsable by someone learning physics (think junior high school), not just people who already understand it and are familiar with the jargon. Kaldari (talk) 19:06, 9 April 2008 (UTC)[reply]
    • As I see it, there are two ways to address this comment. One is to try to rewrite the article explaining all the terminology. The other is to hope that the reader clicks on the wikilinks. If we use your approach, I'm afraid we will bog down the reader immediately. However, I can see why just wikilinking can look overwhelming. Perhaps you would like to propose an alternative wording so I can see what you are talking about? Comparing our introduction to Britannica or Encarta, I see we actually do a better job using precise formulations. Precision versus readability is an old problem at Wikipedia, as is audience determination. How do we make everyone happy? ScienceApologist (talk) 19:09, 9 April 2008 (UTC)[reply]
      • I agree that our lead is far more precise, however, what we gain in precision is small compared to what we lose in readability. Encyclopedia articles do not need to be written to the level of precision of a college textbook or academic paper. For example, in the first couple sentences I would say "an object" or "a body" instead of "a mass", "can cause" instead of "has the capacity to cause", "the acceleration of the body multiplied by the mass of the body" instead of "the product of acceleration and the mass of the body". I have no idea what the 3rd sentence means, so I can't help you with that (and I took college physics and calculus). I would remove the clause "In an extended body" from the 5th sentence (what's an "extended body" anyway?). I would change "intuitive misunderstandings" to just "misunderstandings" (what's an "intuitive misunderstanding"?). The second paragraph of the lead either needs to be less specific or needs a lot more explanation of the terms that are used. I'm a strong believer that the lead section of every article, no matter how technical, should at least be readable by someone in high school. You can get more detailed in the article body, however. And I realize a lot of the information can be parsed by following links, but there's no reason to make the text difficult to read when it doesn't have to be. Kaldari (talk) 19:31, 9 April 2008 (UTC)[reply]
        • I fixed the first paragraph along the lines you propose. Before tackling the second paragraph, could you let me know what you think of the first pass? ScienceApologist (talk) 19:51, 9 April 2008 (UTC)[reply]
          • That is a big improvement already. Now I don't feel completely stupid when trying to read the lead section ;) With a bit more work on "dumbing down" the article text, I think I could change my Oppose to a Support. And by "dumbing down" I just mean using more common language when possible and trying to explain esoteric terms and ideas. Kaldari (talk) 23:36, 9 April 2008 (UTC)[reply]
            • Okay, good. I don't want to get stalled, however. I'm running out of ideas for how to explain these concepts any more clearly. Already I feel as if the discussion of Archimedes is getting redundant. Please help as much as you can. ScienceApologist (talk) 07:07, 10 April 2008 (UTC)[reply]
      • The WP:Explain jargon page offers a potential solution in the form of a glossary at the end of the article. I haven't seen a page that uses this approach, but perhaps that would be beneficial in terms of not bogging down the flow (especially if wikilinks were also used)?—RJH (talk) 20:37, 9 April 2008 (UTC)[reply]
        • Okay, how exactly would a glossary work? Would we link to the glossary from the places in the text where the terminology was used or would we just have a glossary at the end and allow readers to read it there? Let me compare this article to another featured article that passed: redshift. Is that article better than this one? Why or why not? ScienceApologist (talk) 22:42, 9 April 2008 (UTC)[reply]
  • Comment Because of the (admittedly regrettable) colloquial definition of "massive" nowadays, can "massive" be cut from the first sentence to avoid the potential of misleading readers? BuddingJournalist 21:34, 9 April 2008 (UTC)[reply]
    Sure. I'll try to redo it. ScienceApologist (talk) 22:27, 9 April 2008 (UTC)[reply]
  • Oppose Comment I agree with Kaldari - this lead is unreadable. I am working on a PhD in English literature, but I like to read popular science books in my spare time (!). This article, which addresses a key concept in physics, should be able to be understood by someone like myself, who wants to delve deeper into these topics. The lead is very off-putting because of the density of links and jargon. I haven't read the rest of the article, but I will in the next few days. I might note that when I listened to the MIT online physics lectures, this whole concept seemed much clearer. We can surely do better. Awadewit (talk) 21:43, 9 April 2008 (UTC)[reply]
    I agree that the article should be readable by someone like yourself, but I need you to explain what I need to do in order for me to improve it. Please provide any help you can! ScienceApologist (talk) 22:27, 9 April 2008 (UTC)[reply]
    I'm going to read over it and place my thoughts on the article talk page. I'll try to explain how an interested but rather uninformed person like myself reads the article. Awadewit (talk) 18:21, 10 April 2008 (UTC)[reply]
    Exactly the data I need! Thank you so much! ScienceApologist (talk) 18:34, 10 April 2008 (UTC)[reply]
    I'm going to have oppose for now, since the entire article is difficult to understand and the prose is poor in places. However, I have begun placing my comments on the talk page and I am willing to work with the editors to make the page more accessible. Awadewit (talk) 04:02, 11 April 2008 (UTC)[reply]
    Update: I am working with the editors to make the prose more accessible. Awadewit (talk) 17:44, 16 April 2008 (UTC)[reply]
  • Oppose I'm afraid, I'm with Awadewit on this one. I'd like to consider myself a reasonably intelligent layperson, but I couldn't get past the first three sentences. I wanted to dive in and edit, but got stuck. So here's the thing about those first three sentences:
    • Sentence one says: "Force is..." Sentence is about a "combination of forces." Then sentence three says "More precisely, force is..."
    • I would have thought that sentence three follows right on from sentence one. It is (literally) a precision of the opening statement. So I wondered if sentence two a) could be moved to after sentence three or b) could be eliminated altogether. I dived in...
    • ...and this is where I got stuck. I couldn't figure it out. What is the relationship between those three sentences?
  • OK, so if you want, call me a reasonably unintelligent layperson. But then when my eye wandered even further down the lead, the words started blurring before me.
  • (Oh, but I did get an "A" in Physics O-Level, so surely there's hope for me yet?! Help me out!  ;) ) --jbmurray (talk|contribs) 20:39, 14 April 2008 (UTC)[reply]
    • Comment: Wouldn't the second sentence be more comprehensible if it read: "The net effect of all the forces acting on a object divided by the mass of the object is equal to the acceleration of the object."--Grahame (talk) 03:55, 15 April 2008 (UTC)[reply]
      • I don't think the problem is with the individual sentences; it's how they fit together. Does that make sense?
        • I think you are confused with the fact that force is only defined when it is a net force. When the force is balanced with an equal and opposite force, the net force is zero and the situation becomes indistinguishable in a bare mechanics sense from a situation with no forces. However, whether forces exist when they are balanced is a semantics question. They do exist in the sense that the models for such forces follow the same definitions as the models for unbalanced forces and there are predictable results (at least from an engineering standpoint in equilbrium mechanics) as to how such forces interact. Still, it is technically not correct to say that a force must always result in an acceleration. Only unbalanced/net/all the combined forces on an object result in the net acceleration. The situation itself is complicated: complicated enough to confuse those receiving top marks in O-Level physics, I'd say. How we are to rectify this situation while maintaining readability and connection for a wide audience is the question. I understand your frustration, but your comment of "I don't get it" isn't actionable at this juncture. If you can figure out the nuances we need and propose a solution, I'll be happy to implement it or at least consider it. Right now, I'm not sure how to proceed with your criticism. 69.86.169.166 (talk) 05:52, 15 April 2008 (UTC)[reply]
  • OK, I dove in. I'm going slowly, and I'd be happy to do this on the talk page if you think it helps. If you think it doesn't, then so be it. It may be too agonizing for you. I apologize already. But let's try. I've moved on a sentence or two, and came up with the following suggestion for the first part of the lead:
In physics, a force is a push or pull that can cause an object with mass to accelerate.[1] So the key variables in calculating force are mass and acceleration: the combination of all the forces acting on a object is equal to the acceleration of the object multiplied by the mass of the object. More precisely, the force on an object is the amount an object's momentum (mass multiplied by velocity) changes as time elapses.[2] Because one of these key variables, momentum, is a vector (which means that it has direction as well as magnitude), forces must also be vectors.
Forces that act on three-dimensional objects may also cause rotation, deformation, or a change in pressure. Rotational effects are determined by the torques (the rotational equivalent of forces), while deformation and pressure are determined by the stresses that the forces create with respect to certain areas of the object.[3][4]
First, I'd like to know if I've "broken" anything. Have my changes introduced inaccuracies? I fear they might have, and this is why: rotation, deformation, or a change of pressure don't seem immediately to me to be instances of acceleration, and yet we started out defining force solely in terms of mass and acceleration. If these are instances of acceleration, then it might be useful to say so; if they indeed aren't, then the apparent contradiction should perhaps be explained.
Does this make sense? I do feel terribly bad that I am probably asking you to explain things that seem as obvious as saying that the sky is blue. But if you feel at all that we could make progress this way, then I'm happy to be your token idiot on whom to try out new formulations.
I should also say that I'm happy not to understand everything in this article. But I'd like to be able to understand more than I currently do. --jbmurray (talk|contribs) 07:57, 15 April 2008 (UTC)[reply]
Okay, it looks good to me. A few comments:
  1. Should the word "So" begin a sentence?
  2. Yes, rotations, deformations, and changes in pressure are all technically instances of accelerations, though they are rarely demarcated as such. I don't think mentioning this is necessary as by logical construction the reader should be able to figure it out (as you did, in fact. Even though these things didn't seem immediately to you to be accelerations, the prose led you in that direction.)
  3. I changed the bit about momentum and force to more accurately reflect the mathematics of the situation. This was the only technical inaccuracy introduced.
Please do not apologize for your lack of understanding. I am not upset by it in the least and am gratified that someone not understanding the article would want to work on it to make it more understanding to them. I am willing to spend the time it takes. I have been working on this article for over a year, so a few more days/weeks will not hurt. It's just good to get a few more eyes on it -- especially non-physicist ones.
ScienceApologist (talk) 08:12, 15 April 2008 (UTC)[reply]
  • I'm relieved I didn't break anything. I would be happy to continue along these lines, probably better on the talk page, if you find it useful. I am withdrawing my "oppose." But right now, I need to go to bed, so will be back tomorrow. Oh, but I am happy to note that I'm personally fairly cavalier about beginning sentences with conjunctions such as "So." I recognize that others are more concerned about such things. And explicitness, where it does not become to ridiculous, would certainly help me. Thanks for this. --jbmurray (talk|contribs) 08:27, 15 April 2008 (UTC)[reply]
Question: Should it say "the net force on an object is the amount an object's momentum changes as time elapses" or "the net force on an object is equal to the amount an object's momentum changes as time elapses"? Kaldari (talk) 17:28, 15 April 2008 (UTC)[reply]
I don't see a distinction, but your comment made me realize that the wording about the time derivative of momentum was off. I fixed it. ScienceApologist (talk) 18:36, 15 April 2008 (UTC)[reply]
  • Comment This is an excellent article and one I enjoyed reading, but to achieve FA status even more hard work is needed. I know it has been said before, but readabilty will be a problem for many people. The problem begins with the second sentence of the Lead section which sets the tone for the whole article, (with the possible exception of the history). Force is well worthy of publication in a physics text-book, but not an encyclopedia. I feel really bad for being negative about such a good article. GrahamColmTalk 17:50, 15 April 2008 (UTC)[reply]
    Ay ay ay! I wish there was something I could do to make it better! I feel like I'm not being given any pointers in what direction to go. ScienceApologist (talk) 18:36, 15 April 2008 (UTC)[reply]
I have posted my thoughts of a rewritten lead to the talk page (though this had not taken into account Vb's comments below) — BillC talk 21:09, 15 April 2008 (UTC)[reply]
I'm ignoring Vb's comments as being a singular fringe perspective anyway. Emphasizing the fact that there is a degeneracy of definitions between force and inertial mass is not helpful. Trying to remove Newton's second law as a central point misses the very way forces are used in classical physics. ScienceApologist (talk) 21:47, 15 April 2008 (UTC)[reply]
  • Oppose I am very sorry but this article is not really correct and contains contradistinctions. Force is definitively not defined by Newton's second law (even if Landau states so). Though the text explains this in detail ("The use of Newton's second law as a definition of force has been disparaged in some of the more rigorous textbooks,[3][13] because it is essentially a mathematical truism)", this wrong understanding of the concept appeared once again in the lead. The first sentence is correct ("A force, in physics, is a push or pull that can cause an object with mass to accelerate.[1]"). The second one is false ("A more mathematically precise definition is that the combination of all the forces (also known as the net force) acting on an object is equal to the acceleration of the object multiplied by the mass of the object.") The text overtones the difference between the two formulations of Newton's second law F=ma and F=dp/dt. This difference has really nothing to do with the definition of force and, while it should be mentioned, it should not be so often repeated as if it were a common misunderstanding. On the other hand, the concept of mass in Newton's second law is not defined by "counting the atoms" (what is the mass of an atom?) but by the proportionality factor linking force and acceleration (if Newton's second Law is assumed). This is the inertial mass, i.e. a measure of the inertia of the body (that it can be interpreted as a measure of the amount of matter is sommeting utterly indepedent). I am ready to reread this article and maybe support it if:
    1. the concept of force is clearly defined without reference to Newton's second law.
    2. the concept of inertial mass is correctly used in relation with Newton's second law
    3. the difference between F=ma and F=dp/dt is less underlined (e.g. removed from the lead)

Vb (talk) 20:55, 15 April 2008 (UTC)[reply]

  • Sorry, this singular perspective has been advocated from time to time but is not supported by the majority of sources. Certainly the idea that inertial mass is inextricably connected to the definition of force is true, but it is simply not the case that Newton's second law does not define a force. We may not like the way it is defined by the majority of sources, but there you go. We cannot indulge the fantasies of people hoping to excise Newton from the definition of force. Also the distinction between F=ma and F=dp/dt is a perfectly reasonable one to make. One assumes constant mass, the other doesn't. I believe that this comment needs to be ignored. ScienceApologist (talk) 21:45, 15 April 2008 (UTC)[reply]
  • This could all be resolved by editing the Lead, and dumping the second sentence. However, my general comments (above) would still apply. BTW, please do not call rational arguments "fantasies" -it's not helping. GrahamColmTalk 21:59, 15 April 2008 (UTC)[reply]
  • Sorry, Graham, if I came off as abrupt or if my use of the term "fantasies" was too pejorative. We've had some problems at the article with certain people wanting to reformulate definitinos and remove Newton almost entirely from the article on the basis that he is "wrong". This rather strident demand that we demote discussion of Newton because his definition is a truism seems to me to be fairly unbalanced: that almost every introductory text on physics uses Newtonian mechanics and the "truism" definition of force as a definitional framework is undeniable. Sure many texts disparage the concept, but they don't deny its utility and its empirical success. That's what matters here. I guess it was the statement that the article is "not really correct" that got to me. Hey, this sentiment basically flies in the face of the careful exploration and summary that was done of all the available reliable and verifiable sources over the last year in trying to get the article up to FA standard. Part of the reason we introduce Newton so stridently is because that's how force is treated in outside sources. It might be fun to rewrite the story of force so that Newton plays a backseat role, but I'm convinced such a treatment would be essentially original research. So, all I can say is read the archives of the talk page for more. I'll note also that this user struck a similar tone on the article earlier and made comments disparaging Newton -- claiming in fact that Newton knew he was wrong when he wrote down his second law (there's no evidence of this at all). I'll have you know that there is a small but adamant group of "disparage-Newton" activists who seem to think that on Wikipedia we should not use Newton's definitions for forces because they're somehow "wrong" (Despite the verifiability not truth threshhold). Their arguments are sometimes reasonable, sometimes impenetrable. See Talk:Force/Archive_3#Dissident_view, Talk:Force/Archive_3#Correct_definition_of_force, [[1]], and Talk:Force/Archive2#Enormousdude_Violates_WP:3RR.3F for examples. Basically, there are two ways we can handle this: use the traditional way introductory textbooks, encyclopedias, histories of science, or go along with the half-dozen or so people who for about four years have been hoping to get Newton's Laws basically removed from the force article. ScienceApologist (talk) 22:17, 15 April 2008 (UTC)[reply]
No I don't advocate that Newton's second law should be removed from the article. I don't even state that Newton had a false definition of force. I simply say, as many "more rigorous textbooks,[3][13]" that Newton's second law is an empirical law which can be denied by experiment (see e.g. Modified Newtonian Dynamics). If it were a definition it could not. Newton's second law is a law of physics (as the name says) and not a definition of anything: it states that force is proportional to accelaration (if constant mass BTW) and that the proportionality constant is the inertial mass. Since force is a concept which is utterly independent of kinematics this is a law. If it weren't, it would be a truism as clearly said in this article. Vb 06:57, 16 April 2008 (UTC) —Preceding unsigned comment added by 84.175.195.48 (talk) [reply]
You're using MOND to try to make your point? Puh-leeaze. Sure people can ask the question, "what if Newton's second law is wrong?" but so far no one has provided anything more than vague suppositions for it not being so. Trying to force (no pun intended) this issue is a violation of WP:FRINGE and WP:WEIGHT. ScienceApologist (talk) 12:52, 16 April 2008 (UTC)[reply]
To make the point clear. Newton's second law is a bit like Ohm's Law, U=RI. It states that U is proportional to I. Both U and I are independent quantities which can be idependentlymeasured (just like force -with a dynamometer- and acceleration -via kinematic measurements). Ohm's law defines the proportionality factor R. Of course Ohm's Law can be improved. Everybody knows that the law is only valid for a given range of I an U. However Ohm's law is no way a definition of U! What I say here is basic physics and I am very surprised this is open to discussion. A good textbook on the topic is "the evolution of ideas in physics" by Einstein and Infeld where all those concepts are clearly explained from scratch. Vb 07:16, 16 April 2008 (UTC)[reply]
So your real point is that maybe some mass is not "ohmic" in the sense that maybe the acceleration and force are not in a linear regime. Fine. Except, this is a minority opinion -- so minority that it hardly gets mention in the sources. Remember, we are bound by WP:RS and WP:V -- not by technical accuracy. Also, if you believe the equivalence principle -- I mean REALLY believe it -- then Newton's Law regains its status as a flat definition. While theorists play with the equivalence principle a lot, there are no experiments to date which deny this. In fact, the equivalence principle has been tested to such an extent that we might say that it is one of the best measured phenomena in all of physics. ScienceApologist (talk) 12:52, 16 April 2008 (UTC)[reply]
No It is not my point at all. It is a question of principle. Newton's second law is called like it is and not Newton's second definition for a good reason. It is because it is a postulate, an axiom of classical mechanics - which can be tested by experiment. It is not a definition - which

cannot. This is just as Ohm's law is a postulate of linear electrical theory. It is not at all a definition of electric potential! I am not a supporter of MOND theory and I don't want to stress such an exception in this article. There are other examples where the relation between force and acceleration becomes non linear: For example the special relativity still sticks to the concept of force with the same definition as in classical physics even if Newton's second law is not valid in this context. Vb 15:18, 16 April 2008 (UTC) Comment: For ease of reading shouldn't the section on Newton's Third Law state "For every action, there is an equal and opposite reaction", not just express this as a formular.--Grahame (talk) 03:13, 16 April 2008 (UTC)[reply]

  • I thought long and hard on this one. The problem is that we don't define action (physics) in our article due to the fact that we don't delve deeply into Lagrangian/Hamiltonian mechanics. While this statement of Newton's Third Law is technically correct, in terms of forces it is much simpler than that. The problem is that people often misinterpret Newton's third law because the statement you outline as the famous example is missing two important pieces: a discussion of action being a proxy for force and a discussion of the fact that there needs to be two distinct objects in the system before Newton's Third Law applies. These two strict requirements for Newton's Third Law are essential and that's why I didn't include the wording you propose. In point of fact, it is included at the article on Newton's Third Law, but I think for purposes of an article on force we should stick to Newton's Third Law's implications for forces and not be too concerned about the normal wording that people know and love since that isn't directly relevant to the question of forces. If people are confused, let them research Newton's Third Law in more detail. This is my 2 cents. YMMV. ScienceApologist (talk) 12:58, 16 April 2008 (UTC)[reply]

Reluctant oppose I feel bad for having to oppose this article, since the authors clearly lavished a lot of care and thoughtful attention to it, and I agree with many of their perspectives. It's hard, I think, to cover any technical subject completely while keeping the prose intelligible and "brilliant", especially if you're not getting unambiguous suggestions.

The writing seems rough and uneven, although that may be because the authors are having to please too many people; too many cooks and all that. My real worries are that the article does not cover its subject completely/accurately and includes tangential subjects that might be better as a minor subsection. Admittedly, I'm no expert, but here would be my suggestions for improving the article:

  • My impression is that the article would benefit from sticking to one conception/definition of "force", and explain that really well, and not try to cover minor definitions, extensions and other usages of the word "force" in great detail. Specifically, I think the authors should stick to the vector force F = dp/dt used in the classical Newtonian mechanics of particles and rigid bodies. That's hard enough to explain, and provides a natural scope for the article, a bite-size morsel that everyone could digest.
  • As a technical point, I think F = dp/dt is more accurate than F=ma, since it allows the mass of the body to change as well. I say this as someone who just moved a wheelbarrow while it was raining. ;)
  • Remaining for the moment with classical mechanics, I think it's important to note that Newton's vectorial force-momentum approach to classical mechanics is not the only way. As I'm sure you know, there are several alternative approaches — the field of analytical mechanics — that don't use forces, but scalar functions and a variational principle. The principle of least action is maybe the most famous, but there's also several others, such as the Hamilton-Jacobi equation or Gauss' principle of least constraint. The concept of force is not essential to classical mechanics. That said, you might mention the special advantages of the Newtonian approach, e.g., great for frictional forces, usually used for molecular dynamics simulations, etc.
  • Forces seem most appropriate when talking about particles and rigid bodies? For fields, fluids and deformable solids, it seems as though pressure (and, more generally, the stress tensor) are more fundamental than force; well, at least they seem to be the goal of calculations, and the net force is calculated from them. You might consider having a special section devoted to the extrapolation of the force concept to continua via pressure/stresses.
  • The extension of force and acceleration to special relativity is OK, but I'm worried that people are going to think that they actually get used on a regular basis. There's the related problem that people get all confused about what definition of mass to use. I'd just devote a sentence or two to it, mentioning that a four-force can be defined but is rarely used, the four-momentum being preferred.
  • I think the "four fundamental forces" and the Feynman diagrams are misleading and will confuse most lay-readers. As far as I know, vectorial Newtonian forces and accelerations are never used in theoretical quantum field theory or indeed in any form of quantum mechanics. The focus there seems to be on scalar quantities such as energy, or more generally four-momentum. I think that's why scientists seem to prefer to call them "interactions", even if the popular press insists on calling them "forces". Perhaps you could put such non-Newtonian definitions of "force" into a special section?
  • A FA about force should talk about how classical forces are measured experimentally and also how we perceive force (well, actually, pressure) physiologically.
  • The treatment of centripetal force is ambiguously worded and doesn't make clear that the centripetal force is not a physical force in its own right, but rather a force requirement, namely, the force required for a mass m to move at speed v in a circle of radius r. Any physical force can supply the wants of that force requirement; an object can move in that that circle due to a magnetic field force, tension in a string, a spring force, gravity, etc.
  • Consistent with the historical development, I think more attention should be given to the equilibrium of forces and maybe how that led to D'Alembert's principle. That might tie in nicely to the discussion of analytical mechanics?
  • You mention the machines of the ancient world, but it'd be nice to have a whole section on the multiplication of force: you know, how levers work, how pulleys work, how jacks work, etc. Our readers might want to lift a heavy rock out of their garden, or their engine out of their car, or jack up a corner of their house. :) It'd be good to enlighten them on how that works.
  • If you're going to give examples of macroscopic forces, you might consider giving some examples of microscopic or even intermolecular forces, such as van der Waals forces. You could have a cool picture of a gecko climbing up glass as an illustration! :) There are also faux forces that derive at least partly from entropy, such as the elastic force of a rubber band or "hydrophobic forces". of course, it's worth emphasizing that some popular formulae for intermolecular forces/interactions, such as the Lennard-Jones potential, are just approximations of a more complicated quantum-mechanical potential.

I'm sorry that I can't be more supportive, but I'm sympathetic and willing to help, not just make a bazillion criticisms. I really appreciate everyone's hard work on the article, and hope that these comments are somehow helpful. Willow (talk) 14:39, 16 April 2008 (UTC)[reply]

Now, this is something I can sink my teeth into. Maybe the problem is that we have too broad of an article? We might be able to slough off some of the extra ideas into daughter articles. I'm going to think about your organizational suggestions and try to make some grand changes soon. ScienceApologist (talk) 16:13, 16 April 2008 (UTC)[reply]

Comment It might be worth splitting force into Force and Introduction to Force, as has been done with Introduction to quantum mechanics/quantum mechanics. -Ravedave (talk) 16:51, 16 April 2008 (UTC)[reply]

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