Talk:Newton's laws of motion/Archive 2

Starting Archive2 for Newton's laws of motion, initially to include threads where the last comment was made before 2008 or not dated. R. Baley (talk) 19:39, 25 January 2008 (UTC)

Mohist's scientific theory

From this referenc article:

2400 years ago, the Chinese Mohist philosophers collected their writings in a book called the Mo Ching. Mohism disappeared, but we can still read this in the Mo Ching:

The cessation of motion is due to the opposing force ... If there is no opposing force ... the motion will never stop. This is true as surely as an ox is not a horse.

Here's a perfectly clear a statement of Newton's first law of motion, 2100 years before Newton's Principia. The Principia was part of a scientific revolution, while the statement in the Mo Ching is largely forgotten.

BE AWARE: The calculation of second law of Newton by Newton is wrong

The theoretical acceleration of a body as per applied force can be only calculated using an altered energy formula $E=1/2mv^{2}$, which is this $F=1/2ma^{2}$. (it would be $F=ma^{2}/200$ when calculated in the units I used.)

In other words: Energy, Time and Force are mathematically more or less on equal footing regards the relationship between mass, acceleration and velocity.

see http://www3.sympatico.ca/slavek.krepelka/ttf2/force1.htm

Hm, when I tried $F=1/2ma^{2}$ on the highway today, the other car got completely wrecked, unfortunately. I never had that problem with $F=ma$. — Shastra 19:22, 12 June 2006 (UTC)

Force can said as dE/dx(E is the energy) not dE/dt. And as far as i know differentiation,d(mv²/2)/dx is mvdv/dx i.e. ma.You cannot directly differentiate you have got to apply the chain rule.Subhash 05:31, 15 August 2006 (UTC)

also i read richard feynman lectures ( the introduction 1963). he says that it is right that the first is easy to understand (newton) but near correct and the second is correct 100% (relativity theory) and it requires more previus knowlage to understand it. and teachers have many dificult moments like this: do to choose the easy but uncoreect that gets the concept or the hard to teach and to understand but correct and up to date.

What happend to the Second Law section, and why is the Second Law Historical development section so apparently out of place?

-Ste|vertigo 20:02, 16 May 2006 (UTC)

The applicability

What I think as far as I have read is that The First Law is the law of inertial reference frames(It defines an inertial frame of reference). It says that an inertial reference frame ithat whose acceleration is zero. The second law defines the force. It says that the force applied on a body is dL/dt.Where L is the linear momentum The third law tells us about the interaction between two bodies. It says that when a body applies a force on another body,the other applies an equal and opposite force on the first body.

All the three laws are applicable only together.One cannot say that Newton's second law is not applicable for an accelerated frame since it is defined only for an inertial frame of reference. I have written this in the discussion because i'm afraid no one will believe me.It is my personal experience.Otherwise why would a law represent a special case of the other law formulated by the same person?If one turns the pages of Newton's principia mathematica the truth can be seen.Subhash 05:26, 15 August 2006 (UTC)

Mergefrom Newtonian mechanics

There was talk of merging Newtonian mechanics into Classical mechanics, but the naysayers seemed more numerous than the proponents (esp. on the Talk:Classical mechanics page). The Newtonian mechanics page offers a very shallow treatment of the subject. I suggest merging that page into this one, and turning Newtonian mechanics into a redirect. --Ling.Nut 13:12, 21 September 2006 (UTC)

Problem with Newton's Law #1

Just thought I'd let whoever it may concern know that Newton's First Law has been changed, so that "Objects Suck Dick to Stay in Motion". Someone may want to change it back to the textbook version.

It is not necessary to point that out. We see the changes in the article just as quickly as we see your message. Please sign your contributions to talk with four tildas ~~~~. Better still you could revert the change yourself. JRSpriggs 04:55, 25 September 2006 (UTC)

Derivative Notation

Newton's second law: historical development

The derivatives should be written in Newton's own method, f'(x), rather than in Liebniz notation. 199.126.237.235 00:49, 27 October 2006 (UTC)

It should also be written in Latin, Newton's own language. Loom91 17:08, 28 October 2006 (UTC)

Something Missing

The first bullet-point that occurs in the section entitled "Newton's first law: law of inertia" ends abruptly. The sentance below is also missing text from the start. 84.65.92.40 19:42, 31 October 2006 (UTC)

I think that you were looking at the article during one of the periods between an act of vandalism and when someone reverts it. It would be more efficient to simply revert the vandalism yourself, rather than telling us about it. We see the vandalism itself as soon as we see your message. JRSpriggs 10:55, 1 November 2006 (UTC)

If you want to try reverting vandalism yourself, please read Help:Reverting. JRSpriggs 08:07, 2 November 2006 (UTC)

Multiple layers of vandalism

Since this article is vandalized with great frequency, it often happens that two or three or more acts of vandalism occurr between reversions. So when you notice vandalism and want to revert it (see Help:Reverting), please check that you are reverting to a version which contains no vandalism. Thank you. JRSpriggs 10:48, 2 December 2006 (UTC)

Simple Introduction

Some other science articles are starting to produce introductory versions of themselves to make them more accessible to the average encyclopedia reader. You can see what has been done so far at special relativity, general relativity and evolution, all of which now have special introduction articles. These are intermediate between the very simple articles on Simple Wikipedia and the regular encyclopedia articles. They serve a valuable function in producing something that is useful for getting someone up to speed so that they can then tackle the real article. Those who want even simpler explanations can drop down to Simple Wikipedia. I propose that this article as well consider an introductory version. What do you think?--Filll 22:43, 12 December 2006 (UTC)

To me, this article seems about as simple as they get. But if you think that you can write something even simplier, then go for it. Put {{seeintro}} at the top of this article and then click on the red-link and start writing. Do not forget to put it in a category. You can copy text from this article and then simplify it, if you wish. JRSpriggs 08:09, 13 December 2006 (UTC)

Isn't momentum version of second law also important in classical mechanics?

The article says:

However, it must be remembered that for Newton, mass was constant and independent of velocity. To take "motion" (motu) as meaning momentum gives a false impression of what Newton believed. Since he took mass as constant (part of the constant of proportionality) it can, in modern notation, be taken to the left of the derivative as $mdv/dt\!$. If $m\!$ is dependent on velocity (and thus indirectly upon time) as we would now hold, then $m\!$ has to be included in the derivative, giving $d(mv)/dt\!$ or $dp/dt\!$.

Using momentum in the terminology (which would never have occurred to Newton) is a latter-day revision of the law to bring it into correspondence with special relativity.

However, I seem to remember from college that using F = dp/dt was necessary for solving problems with classical rockets, because mass changes with time. (The change of mass with respect to time is due to fuel consumption, not to relativistic effects. ;-) Itub 13:17, 13 December 2006 (UTC)

To Itub: You are right of course. The mass must be included within the derivative even non-relativistically. And I remember reading a statement by Petr Beckmann (no friend to relativity) that Newton did in fact include the mass inside the derivative. However, I have not seen Newton's orginal text translated from Latin to English in a reliable source to verify that for myself. Some people seem to be convinced that he excluded it. So I do not know which way to go here. If you have a source confirming Newton's position, please correct the text and add the reference. JRSpriggs 04:35, 14 December 2006 (UTC)

Newton did infact include mass within the derivative, writing dp/dt rather than m dv/dt but at the same time we must also remember that mass is always constant in classical mechanics. Treating rockets as variable mass systems and writing dp/dt = m dv/dt + v dm/dt is a misleading fallacy, albeit unfortunately prevalent among elementary text book writers. The fallacious and misleading nature of this treatment is exposed in detail in Kleppner and Kolenkow's Introduction to Mechanics. Loom91 08:43, 14 December 2006 (UTC)

Thanks, I see the confusion now. I think the typical textbook approach is used because it happens to give the same result for the force (and looks simpler) when the calculation is done from the frame of reference of the rocket (v=0). Itub 16:30, 14 December 2006 (UTC)

K&K demnstrated with a simple example that writing F = m dv/dt + v dm/dt is not only logically wrong, it can also give the incorrect answer. It's always preferable to use a constant mass system and apply conservation of momentum. Loom91 08:02, 15 December 2006 (UTC)

See note "motu" below. For those who don't believe that Newton's formulation is equivalent to "Force = rate of change of momentum", please consult (i) on-line versions of the Principia, paying special attention to Definitions I and II (i.e. the first lines of text in the book) and (ii) if you distrust your ability to understand early-18th century mathematical English (I wouldn't blame you), consult the recent translation by I. Bernard Cohen which is (a) into modern English and (b) scrupuously annotated. PaddyLeahy 19:16, 5 August 2007 (UTC)

In continuum mechanics F = dp /dt is the only known form of Newton's second law (check, for instance, "Vectors, tensors and the basic equations of fluid mechanics" by Rutherford Aris, Dover). Of course, one must be aware of Reynolds transport theorem which is an application of Leibniz's rule to mechanics: the real meaning of (d/ dt) is the time derivative inside your working zone plus the ouflow minus the inflow of any quantity (momentum included). Some authors who are not aware of standard continuum mechanics definitions, tend to replace F = dp / dt by m dv/dt = F - (momentum outflow) + (momentum inflow). It is only the old Reynolds transport theorem (fully Galilean invariant by the way), with momentum flows on the other side of the equal sign.

Vandals

I don't know about other high-schoolers, but I find physics (at the very least) a respectable subject, and often I find it even a little fun, even if it is frustrating.

But I think the vandal problem is starting to show up on this page. I have never heard of the "conservation of butter" before, and I don't think it should even be mentioned in this article.

This article should be closed to general editing (I'm VERY NEW editing wise, so I don't know all of the protocol involved with shutting an article to non-"member" editing). I'll go ahead and remove the little snippet about butter myself... but can this article be locked away from vandals?

Thanks, Nick 04:38, 9 January 2007 (UTC)

What you want is called semi-protected which prevents unregistered users and users registered for less than four days from editing the article. This can only be imposed by an administrator. Unfortunately, their policy is only to impose it in extreme cases and then only for short periods. I think it should be used here, but I am not an administrator. JRSpriggs 09:58, 9 January 2007 (UTC)

I am repeating myself, but see Help:Reverting. JRSpriggs 10:16, 9 January 2007 (UTC)

Well, Nick, it appears that they decided to give us semi-protected status after all, contrary to my expectations. I hope it helps. JRSpriggs 12:06, 12 January 2007 (UTC)

Bad punctuation

In the detailed section on the third law of motion, the third paragraph has this sentence:

Usually the planet is less massive than the star and thus displays greater changes in it's state of motion.

"It's" should read "its"; as "it's" means "it is" or "it has" and is clearly incorrect in this context. —The preceding unsigned comment was added by 68.55.57.57 (talk) 21:35, 25 January 2007 (UTC).

Dumbing down

JRSpriggs, the guideline Wikipedia:Make technical articles accessible specifically states Do Not Dumb Down. In science it is inexcusable to be incorrect in order to be understood. The statements of the laws you are advocating are plain incorrect. These wrong statements are no longer used in modern textbooks. They are of historical importance and may be used in the lower detailed sections. The other change you are advocating (QM is only applicable in microscopic scales) is also wrong. There are many macroscopic phenomena that can not be explained by classical physics. Loom91 14:56, 3 February 2007 (UTC)

It is certainly my intention to follow "Every reasonable attempt should be made to ensure that material is presented in the most widely accessible manner possible." without sacrificing accuracy. Perhaps "dumbing down" was a poor choice of words, but I was trying to convey that I felt your edits were unnecessarily technical and would make it difficult for students to understand the article. I was trying also to preserve as much of the work of earlier editors as possible.

I did NOT say that quantum mechanics does not apply to macroscopic phenomena. I was saying that Newton's laws of motion DO apply to them. Generally, I think that we should leave out any statement of what cannot be done with them, unless it is something to which a reasonable person would otherwise think that they would apply. Every theory has a limited range of application, so it should not be necessary to belabor that fact by listing the infinitude of things to which it does not apply.

Any statement about moving bodies in physics must assume (at least implicitly) a reference frame. So I feel that we should keep the discussion of them to a minimum to avoid distracting people from the three laws themselves. It is not clear to me that the first law alone should carry the entire burden of distinguishing between inertial and non-inertial frames.

We should be talking about "bodies" or "objects" rather than "particles", because a particle is only one very special kind of body and Newton's laws are applied to bodies generally, including celestial bodies which contain an extremely large number of distinct particles.

You took out my sentence "In special relativity, a third factor is included — the Lorentz factor." which seems odd for someone who claims he is concerned about accuracy. I had tried including the Lorentz factor into the mass, making it relativistic mass, but I felt that that was confusing. Including it into the velocity, making it four-velocity, would also be confusing. Since these are after-all NEWTON'S laws and used extensively in classical physics, I feel that we need to begin with the statement that momentum is mass times velocity. But qualify that with my sentence for accuracy.

It is not enough to just say "Every force has an equal and opposite force.", because this does not make it clear that the same two bodies are involved in both forces. That is why I said "Whenever A exerts a force on B, B simultaneously exerts a force on A with the same magnitude in the opposite direction and these two forces act along the same line.". Notice that I incorporated your suggestion about acting along the same line.

Phrases like "Note that in the given interpretation..." are just Boilerplate (text) and should be omitted. Similarly, "This is a subtle point, but can be clarified by rigorously developing a complete mathematical theory of analytical mechanics." adds nothing about Newton's laws.

I tried to save as much of your work as possible. I would appreciate the same courtesy in return. JRSpriggs 12:33, 4 February 2007 (UTC)

Firstly, I reverted your edits not out of any disrespect for you bur because I thought that your edits were not in the best interests of the encyclopedia. We must attempt to be clear, but not when being clear means being wrong.

It is a common misconception that anything that doesn't need a microscope to see can be explained away by Newton's laws, quantum mechanics is not needed. There are many macroscopic phenomena to which Newton's laws don't apply. This is the point I was trying to make.

The point is that Newton's law in its classical form is not correct, it carries implicit assumptions. The modern statement shows that it is in fact a definition rather than a law. It also shows why the first law is NOT a special case of the second law. There are reference frames in which a particle free of forces will be seen to accelerate, and in such frames none of Newton's laws in their classical forms will be valid.

Newton's laws in their native form apply to particles and particles only. Their application to collections of particles (or extended masses) involve many complications because forces can produce two different types of motion in extended bodies. In such cases, the correct way to apply Newton's laws is by integrating over the particles and seeing what the result turns out to be. There are many theorems to simplify this process, but they are theorems and not fundamental laws. Newton's laws are applied to extended bodies sometimes when they are small enough to be considered particles. For example, for many purposes Earth may be considered a particle with respect to the Sun.

I removed your sentence about Lorentz factors because, as you say, discussions of relativity are irrelevant in an article about Newton's laws. Loom91 07:40, 5 February 2007 (UTC)

Why do you think a sentence on relativistic treatment is appropriate in an article about Newton's laws. Loom91 15:34, 6 February 2007 (UTC)

For the same reason you think that "These phenomena are usually explained on the basis of General Relativity and Relativistic Quantum Mechanics." is appropriate in spite of the fact that it is not about Newton's laws of motion. And do you have any evidence that Newton ever mentioned "inertial frame of reference" about which you make such a big deal?

I remember that when I was a child first learning about physics and mathematics, I was frustrated that I was given false information (such as Kinetic energy = (m*v**2)/2) without even being told that it was merely an approximation. I do not want to do that to anyone else.

On the other hand, your approach seems to be that Newton's laws are useless and should be presented merely as a historical mistake which should be dismissed. I, on the contrary, think that they are quite useful even today and we should show how they can be used, even if they are not perfect. JRSpriggs 05:26, 7 February 2007 (UTC)

Newton did not mention anything about inertial reference frames. The father of modern physics, Galileo did. There were flaws in Newton's perception of mechanics which were later corrected by combining Galileo's ideas with his, most importantly the principle of relativity which was later revived in an altered form by Einstein to form the philosophical basis of special relativity. Galileo's other revolutionary work, the Principle of Galilean Equivalence lay practically dormant until Einstein used it as the starting point of GTR.

A modern text on evolution hardly presents the theory of Darwinism exactly in the way Darwin envisioned it. Similarly, we are not bound to repeat the mistakes of Newton in the twenty-first century. That does not take any credit away from Newton however, for each contribution to science must judged in the context of its time. But Newton's laws in the form presented in Principia Mathematica is of purely historical interest, just like Natural Selection as presented in On the Origin of Species by Means of Natural Selection is of purely historical interest from today's perspective.

I do not doubt the enormous practical usefulness of Newton's laws, and with the advent of deterministic chaos they are also of some theoretical interest, but I don't see how that can be a reason for presenting them in a logically incorrect (note: not merely approximate) form. In any case, the laws are perfectly understandable in their modern form. Only a knowledge of what is meant by a frame of reference is required to understand the laws. Loom91 06:17, 7 February 2007 (UTC)

Do you now agree that it is appropriate to mention the Lorentz factor (without going into details beyond the link to the article on it)?

I agree that inertial frames of reference are important to modern physics and should be mentioned. But I think that the mention should be briefer because Newton's laws can be understood and used, as Newton did use them, without considering the possibility of non-inertial frames. As the section stands, they seem to overwhelm the laws themselves, making it harder for novices to read the section.

What do you mean by "presenting them in a logically incorrect form"? Where did I do that? (I certainly would not want to do that.) JRSpriggs 06:40, 7 February 2007 (UTC)

It's not that you presented them in a logically incorrect form. The previously given version of the first law, one still seen in primary level/older texts is logically incorrect. Newton's laws can not be correctly discussed without reference to the concept on inertial reference frames. The first law is the very definition of inertial reference frames.

As an example, consider you are on a car accelerating past a tree. From your reference frame, the tree will have an acceleration that can not be accounted for by considering the physical forces acting on it. Newton's laws in their old form provide no way to resolve this paradox. But the reference frame approach shows that the second law can not be applied here because the reference frame is not inertial, because it does not meet the definition of an inertial reference frame given in the first law. Loom91 06:50, 7 February 2007 (UTC)

One could say that the tree appears to disobey the first law because you are suffering from an illusion — your point of view is not that of the Absolute (God?) which defines absolute rest. In modern language, I said "...there is an inertial frame of reference such that:". Actually, there are forces on the tree, but we suppose that they cancel each other out (if Earth's gravity is taken as a force). I suppose if we really want to be modern we should talk about free-falling frames of reference. But my point is — we cannot use the first law to define inertial frames of reference because no objects exist (near here anyway) which are free of external forces. JRSpriggs 07:30, 7 February 2007 (UTC)

Using free-falling frames of reference would take us into the realm of GTR. We trying to present a modern perspective of Newtonian mechanics, not a modern perspective of physics in general. And the concern you mention is one of application, not theoretical. It is possible to define potential as the work done to bring unit charge from infinity, even if no one is actually going to take a charge to infinity and drag it back. Loom91 05:54, 8 February 2007 (UTC)

I'm confused: 1. "This is a subtle point, but can be clarified by rigorously developing a complete mathematical theory of analytical mechanics." (Addressed briefly, above.) Is this meant to imply that this theory has not yet been developed? I agree that this passage might not be necessary in the summary. 2. On the statement of 3 laws: it looks like there has been plenty of discussion about this section already, but couldn't Laws 1 & 2 be stated in their more introductory forms (object in motion... and F=ma) and then briefly elaborated, as necessary? If I were a high school student looking up these laws, Law 1 especially would look pretty foreign to me. 3. Could the whole "inertial frame" paragraph in Importance/Range be clarified? Zadeez 03:49, 17 February 2007 (UTC)

I've made some changes to the article which I think are self-explanatory. Zadeez, we were taught this versions of the Newton's laws in high-school. It's unfortunate that you are still learning the older definition. Any standard high-school text like Halliday and Resnick discuss why it's necessary to use the newer version. The 'introductory' forms are unfortunately wrong. They can be easily falsified by experiment, see my post above. Your point 1 has been removed. Loom91 15:42, 17 February 2007 (UTC)

Loom91 I applaud your adherence to accuracy and completeness, but I think you have sacrificed clarity in the process and possibly introduced original research. I understand that you are passionate about the subject, but I want you to reconsider your approach. I believe this article should cater to people who just started their first physics class not students of advanced theoretical physics. I hold a BS in Aerospace Engineering and I find your text difficult to read. I honestly don't understand why you introduce quantum mechanics and relativity into a discussion of Newton's Laws of Motion. Newton was unaware of them and users of classical mechanics, such as myself, do not require them. Clearly and concisely stating such concepts at the beginning or end is adequate, anything else is overwhelming to the reader and possibly original research. It might be original research because you are putting newer concepts into a description of the laws themselves without providing a reference. I want to resolve this peacefully, with no hard feelings. So I will delay directly modifying the article for at least 1 week to give you an opportunity to respond to my concerns. David.hillshafer 08:45, 18 February 2007 (UTC)

I have just made some pretty bold changes to the article. I have changed the heading of the first section from "The three laws of motion" to "The three laws--modern interpretation." I have left the formulation of the laws therein largely as written by Loom91, but with some minor simplifications which were an attempt to enhance readability, especially for users without much scientific background (after all, who's likely to be reading an article on Newton's laws?). I moved the last paragraph of the section to a later section ("Importance and range of validity") which seemed more appropriate. This latter section now needs some tightening. Most of the changes have been relocation of content, rather than addition or deletion, so hopefully no one's nose will be too out of joint. Rracecarr 16:55, 19 February 2007 (UTC)

I think that the Lorentz factor should be mentioned somewhere in the article to warn students that F=ma is not true in special relativity. Unfortunately, you chose to take it out. JRSpriggs 06:08, 20 February 2007 (UTC)

I did not take it out. As I stated in the post above, I moved it to the section titled "Importance and range of validity".Rracecarr 14:12, 20 February 2007 (UTC)

Yes. I skimmed that paragraph too quickly and missed it. Sorry. JRSpriggs 05:08, 21 February 2007 (UTC)

No worries. Actually it's a little out of context as it stands, because it refers to "a third factor" but the other two factors are mentioned much earlier in the article.Rracecarr 05:38, 21 February 2007 (UTC)

Let's take the article in a new direction

The more I think about it, the more I think we need a stricter set of guidelines for this article, which should make any controversy disappear. This article is called "Newton's Laws of Motion", but it would be more accurate to call it "Laws of Motion with a splash of Newton, Euler, and Einstein". Right now we have David's, Loom91's, JRSpriggs's, Rracecarr's, etc interpretation of the laws of motion, which is inappropriate. We should be true to the article's title. So this article should focus exclusively on Newton's ideas or we should rename the article. One way or the other, we need a single article on the Laws of Motion that includes all available information, without shuffling it together. So, I think we should break the subjects up. Specifically, we should find and describe original materials from the actual contributors. To my knowledge, there are four main sources. Newton first geometrically describes motion in Principia Mathematica, which is largely incomprehensible to modern day practioners. Euler first analytically derives motion in Mechanica, which is what most people still use. Einstein's relativity added the Lorentz factor, which is mostly limited to scientific work. Finally, several people (including Schroedinger and Bohr) contributed to quantum mechanics, for which I have no idea how the Laws are used (if at all). We might also wish to include pre-Newtonian contributors. So as a team, we should find original documents on the history of the subject and describe who now uses which versions of the Laws and when. David.hillshafer 21:05, 22 February 2007 (UTC)

This article is about Newton's laws of motion, not their history. Newton's original statements are important historically, but the article must also reflect their current forms (which are still called Newton's laws). The statement I gave is not something I cooked up myself, it's given in all standard textbooks on classical mechanics. For example, see Halliday and Resnick. Imagine how it would be if an article on Darwinism strictly confined itself to the Origin of Species. Relativity and QM may enter the article only as passing mentions, they can not have any significant contribution to the subject matter of the article. Loom91 08:09, 23 February 2007 (UTC)

Loom91, there is a difference between Darwinian Theory of Natural Selection and Darwin's Theory of Natural Selection. In the same way there is a difference between Newtonian Laws of Motion and Newton's Laws of Motion. The former uses a significant contributor's name as a modifier. While the latter takes the possesive form, implying that the idea belongs solely to the individual. This article's title takes the latter form, and the article should coorespond with the title. While I appreciate the fact that many (all?) textbooks describe the Laws this way, I'm also well aware that most mathematics, science, and engineering professors who write textbooks are rarely historians of science or interested in remaining true to the original authors. For example, in my philosophy course, we read the original works of people like Plato, Kant, and Hume, whereas in all my technical courses, I never read an original document. I was only exposed to a textbook that paraphrased a current, common understanding of an idea. For the purposes of Wikipedia, who should have greater priority, a textbook author or the originator of an idea? Perhaps we should paraphrase current textbooks because they have a strong influence on how the Laws are currently understood, but this should happen in addition to, not in lieu of, the original author's works. I stick by my asertion that an article on Newton's Laws of Motion should be more limited in its scope, because it gives Newton more credit than he deserves at the expense of people like Euler. David.hillshafer 19:40, 1 March 2007 (UTC)

You raise a valid linguistic point, but the fact remains that no authority calls the laws in their modern form Newtonian laws, rather than Newton's laws. Wikipedia is not the place to change existing conventions, Wikipedia is the place to reflect those conventions. Scientific writing must necessarily give more importance to what we know now rather than what we used to know. This is not simply a matter of how textbooks report those laws. Textbooks (usually) report the views of the leading experts in the field, and that's what's imprtant for wikipedia. There are sections in the article that start discussing the laws from their original latin statements, which is enough emphasis on history for me. It won't do to focus so much on the history and genesis that we lose sight of the present. Loom91 07:42, 2 March 2007 (UTC)

Loom91, "no authority calls the laws in their modern form Newtonian laws"? That is a bold claim that I don't think you can back up. Suppose it is true though, then we should put a caveat in the article explaining the convention versus the meaning of "Newton's". However, this does not address the fact that this article should not be limited to current physics textbooks. Physics textbooks are primarily focused on teaching current concepts necessary to accomplish homework and glossing over other details. For example, in every book I've read on the subject outside of a textbook I've read that Newton did not derive the Laws. The whole reason they are called Laws is because Newton saw them as axioms of physics. Euler derived the first two Laws and didn't even worry about the Third Law. This casts serious doubt on the utility of the Laws as anything but a historical achievement, despite what a textbook might say. More to the point, most textbooks state the Laws and then derive them using Euler's approach. Unfortunately, I cannot verify this because Euler's foundational book "Mechanica" has never been translated from Latin to English. I think that is worth repeating. Euler almost single-handedly developed the modern forumlation of Newtonian Dynamics in a two-volume book that has never been translated into English! This is an article about the Laws, and should not be limited to physics textbooks. More than enough other books and references exist on the subject. David.hillshafer 17:53, 2 March 2007 (UTC)

I don't think you will be able to show me a source that calls the laws Newtonian laws rather than Newton's laws. Though the name Newtonian mechanics is in use. Do not underestimate textbooks, they are the best source to learn a subject from the beginning. Even the most elementary textbooks I've read clearly pointed out that the laws did not have their origin with Newton. You seem to be under the misconception that these laws can be derived. This is not true in classical mechanics, unless you assume some other equivalent principle as an axiom instead of the laws (such as the Principle of Stationary Action), which doesn't change anything.

No one derived these laws. Galileo identified the first two and others such as Hugens the third as fundamental laws of Nature. But Newton first consolidated them as the foundations of mechanics and derived many useful results using them. This is why they are called Newton's laws. I fail to see what casts serious doubts on the utility of these laws. These laws (or various equivalent forms derived from them) are the foundations of ordinary macro-scale engineering even in this twenty-first century. I would consider that to be a lot more than historical interest. They also continue to be of theoretical interest in investigations of deterministic chaos. No textbook 'derives' these laws, using any approach. Almost always it's the other way around: formulations such as Lagrange's equations or the Hamilton-Jacobi equation are derived from these laws. The reverse is of course possible, but that changes nothing. Also, I've never claimed that the article should remove historical material. All this historical material is present in the article, more prominently than the modern material. Loom91 07:11, 5 March 2007 (UTC)

"I don't think you will be able to show me a source that calls the laws Newtonian laws rather than Newton's laws." I don't care because you are the one with the burden of proof. You said, "no authority calls the laws in their modern form Newtonian laws", I made no similar claim. Don't try and transfer your burden of proof onto me merely because I express doubt. "Do not underestimate textbooks, they are the best source to learn a subject from the beginning." Do you work for the textbook industry or is this another sweeping generalization of yours? "... unless you assume some other equivalent principle as an axiom instead of the laws". What I assume is irrelevant. The assumptions underlying the classical mathematical description of motion is relevant. Starting with different assumptions can make a world of difference.

I found an interesting Ph.D. thesis at http://www.pitt.edu/~brh15/chap3.pdf. This is useful because it is a publically available online text. His general argument is that Euler was not a Newtonian and derived much of Newton's work in a Cartesian system, while leaving other parts, like the Third Law in silence. If this thesis is correct, then your statement, "No one derived these laws," is false. If you are correct, on the other hand, then you should submit your objections to his advisor before he is given a Ph.D. for false claims.

"These laws (or various equivalent forms derived from them) are the foundations of ordinary macro-scale engineering even in this twenty-first century." I'm well aware of the implications of classical mechanics, given my BS in Aerospace Engineering. I'm also well aware that Euler did not derive anything FROM Newton's Laws. At best, Euler was inspired by the works of Newton and largely replicated them using analysis. However, Euler seems to downplay this angle and gives more credit to Hermann's "Phoronomia". Euler specifically states that he found Newton's "Principia" to be difficult to extend to other examples not mentioned by Newton.

"No textbook 'derives' these laws, using any approach." There you go again making sweeping statments that you cannot backup. Are you familiar with every textbook ever written? Moreover, if you are right, then shame on every textbook ever written for ignoring the foundational works of Euler.

"Also, I've never claimed that the article should remove historical material." Where did I acuse you of wanting to remove historical references? If I did I'm sorry because that was never my intention. I'm saying we should go beyond the meager amounts of history currently provided. The fascinating story of how modern mechanics came to be is being forgotten. Most importaintly, understanding the history of a concept gives great insight into the concepts themselves. David.hillshafer 22:05, 5 March 2007 (UTC)

Playing with language is not helping the debate. I obviously have not read all textbooks, only a few noted ones. You seem to have some aversion for textbooks, but it is extremely difficult to learn a huge subject like classical mechanics directly from the primary literature.

Starting with different assumptions often make no difference at all. It is entirely immaterial whether you assume the Axiom of Choice or Zorn's lemma, because they are logically equivalent. Newton's laws provide a complete and non-redundant axiomatisation of classical mechanics, so they are equivalent to any other complete axiomatisation.

Have you read that paper entirely? What Euler derived in Mechanica were not Newton's laws, but some of his results. I again repeat, it is not that Newton's laws can not be derived. But to derive them requires the assumption of axioms which can not be stronger than Newton's laws (obviously they can not be weaker either), but are constrained to be logically equivalent because of the mathematical completeness of Newton's system. It does not change anything whether you use Newton's laws to derive Lagrange's equations or the reverse. The latter is done by, for example, Structure and Interpretation of Classical Mechanics.

If you want to write more about the history and genesis of Newton's laws, you are most welcome. However, keep in mind the distinction between history of classical mechanics and the history of Newton's laws. Newton's laws are a specific formulation of classical mechanics, the only formulation covered by this article. By your own claim, Euler took mechanics in a different direction. In that case, his work does not really belong in this article. What does belong is the evolution of the laws themselves. Loom91 07:43, 6 March 2007 (UTC)

Newton's Second Law originated from Christiaan Huygens

In my opinion the first line of the article is only partly correct. The second law of motion was first formulated, in a quadratic form, by Christiaan Huygens. At least he should receive some credit. I would suggest to change the first line into:

Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body. The laws were first compiled by Sir Isaac Newton, but the second law is a reformulation and generalization of a law formulated earlier by Christiaan Huygens.Robvhoorn 15:06, 10 April 2007 (UTC)

Actually none of the laws were formulated by Newton. As far as I know, both the first and the second law were first formulated by Galileo, the father of modern physics. Huygens formulated the third law. The achievement of Newton was recognising that these three laws could provide an axiomatic framework for the entire science of classical mechanics. Loom91 09:35, 11 April 2007 (UTC)

What's wrong with my edit?

I added the following part to the Newton's second law.

On point should be noted is this. Newton's second law is not a discovery of the physical world like the theory of relativity. Newton did not discover the nature of "force", instead he mathematically defined "force". Force is defined as "the rate of change of the momentum of the body" by the second law. Therefore, it is not possible to say this law is false by doing experiment, as it is true by definition. It is the first and only definition of "force" in the history of science.

It is deleted immediately without reasons. What's wrong with my edit? Salt 10:29, 12 April 2007 (UTC)

That's quite a philosophical statement, and it would be better if it had a source. Otherwise you could say the same of most laws of physics. Yes, the laws often look just like definitions, but they weren't definitions that someone just made up; they were definitions that were found to be useful to explain the behavior of the real world. For example, although you can take Newton's second law as the definition of force, the concept of force is integrated with other concepts as well (such as energy, weight, etc.), and what matters IMO is that the whole system works. You could always come up with a different set of axioms and put the definitions in a different place. --Itub 10:53, 12 April 2007 (UTC)

To Salt Young: Your statement is WP:POV and WP:OR. By saying that the second law is merely a definition, you are saying that it is arbitrary and physically meaningless. This is false. The second law was carefully selected to make the third law of motion true; and that gives it physical meaning. It is anything but arbitrary. Otherwise, people could just have stayed with the idea that force is proportional to velocity rather than acceleration. JRSpriggs 11:02, 12 April 2007 (UTC)

Salt Yeung is partially correct. It is possible to construct a mathematically consistent model in which the second law is treated as a definition of force. But Newton's law alone and by itself does not accomplish anything. Only when couple with the force laws of nature (universal gravitation or coulomb) does it allow us to calculate motion. So what the second law really does is provide a cross-platform interface for relating the fundamental interactions to motion. It is equally valid to treat the second law as a definition and the force laws as axioms as the other way around. This is a question of formalism rather than anything physical.

In relativity, one can change Maxwell's equations instead of changing Newtonian mechanics, as it is only the combination that has physically observable effects. Instead of saying force = lambda * ma , one could change coulomb's law to add a lambda factor at the bottom. In that case Newton's law would stay the same, a definition of force, while the actual expression for the force would get changed. However, since the reverse is more conventional and convenient, Salt Yeung's edit is unnecessary and also partially wrong (2nd law is not the only possible definition of force). Loom91 12:42, 12 April 2007 (UTC)

Yes. I would agree with all of you that even though the second law is treated as a definition, it is carefully selected and not arbitary. But what I mean is the same as Loom91. To look at the system as a whole, the second law defines "force" for other force laws. For example, if we put the third law to experiment, we would use the definition of "force" that defined by the second law to check whether third law is true. So what I mean is that, unlike the 1st and 3rd law, which can be falsified by experiment, the 2nd law is true by definition. I totally understand that while it is a definition, it is carefully defined to make the 3rd law true and whole system work. I just wnat to point out that the 2nd law is different in the sense of epistemology.

Anyway, I would agree that it is quite a philosophical agrument, it is better included with a source if we would like to add it.

One more point I would like to clearify. I did not mean it is the possible definition of force. But what I mean is that it is the only mathematical definition of force in the "history of science". The same statement can also be found in the article force. Salt 04:12, 13 April 2007 (UTC)

newtonology!

Newton was a great man who was very clever and created the three laws of motion.Right now in my 6th grade science class we are discussing him.He was very helpful to us although some might not realize it. Thanks Newton!!!

p.s we had to create a game called newtonology in this class —The preceding unsigned comment was added by 76.189.1.232 (talk) 00:12, 26 April 2007 (UTC).

Impacts of Newtons Laws on society

can anyone tell specific impacts on society caused by the discovery of these laws and, if possible, give examples?

Impacts

Can anyone please tell me the impacts of Newton's laws on society and give examples if possible?

Newton's laws form the basis of mechanical engineering, so basically everything around you was made with its help. That's one hell of an impact. Loom91 07:41, 28 June 2007 (UTC)

Modest change

First Law is PROBLEMATIC as stated:

The main problem is one word in the first sentence for both definitions. The word "external" should be replaced by either the word "net" or "total". An "external force" is a force that acts on an object inside the system from some object which is outside of the system (see the physics classic text Keith R. Symon, "Mechanics - 3rd edition", Addison Wesley Longman, 1971, p. 160). If we neglect the Earth's spin and motion about the sun, we normally might think a book resting on a table is subject to Newton's 1st Law. The book is the system. The system is not changing its acceleration and will continue to do so until a NET (or TOTAL) force acts upon the book. However, there are two external forces acting on the book: gravity (from the Earth) and a normal force (from the table). Remember that our system is the book and the Earth and table are outside the system; thus, both of these forces are external forces. Hence, there are external forces acting on the book and by the definition presented by Wikipedia (and the usual definition of an external force) one could not apply Newton's 1st Law to this book. However, most physics texts would apply Newton's 1st Law to this book.

The hockey puck used in the later example has external forces applied to it (gravity from the Earth and a normal force from the ice). Your choice of "external force" would remove any possible example on the Earth because gravity is always applied to any object on the Earth (and in fact the Earth itself from the sun).

The simplest solution that would correct this issue is to simply replace "external force" by "net (or total) force". —Preceding unsigned comment added by Paul Bonneau (talk • contribs)

All physics texts I've seen explicitly make the point that Earth is not an inertial frame and that Newton's first law can NOT be applied to objects in it. Nevertheless, it is used to solve problems, but that's only an approximation. It can be experimentally shown that Earth is not an inertial reference frame. See, for example, Physics by Halliday and Resnick. The correct wording is net external force. Also, please sign your comments using ~~~~ and create new sections when starting ew discussions. Loom91 11:36, 6 July 2007 (UTC)

Modest change

Down toward the bottom, we find this statement: "However, since the speed of rotation and revolution change relatively slowly, the inertial force is tiny." This makes it sound like the CHANGE of "speed" (probably should be frequency) of rotation and revolution is what makes an earth-based frame not inertial, rather than the fact it is rotating and revolving at all. I believe this is wrong, but am a bit reluctant to modify this article due to lack of qualification. Paul Bonneau 18:56, 5 July 2007 (UTC)

I changed it.--Patrick 13:06, 6 July 2007 (UTC)

Motu

I removed the following statement, which is dead wrong:

Newton believed that mass was constant and independent of velocity. To interpret "motion" (motu) as momentum gives a false impression of what Newton believed.

On the contrary, prior to introducing the laws of motion, Newton defines "quantity of matter" (= our mass) and "quantity of motion" as quantity of matter times velocity. So "motu" here means exactly the modern (classical) notion of momentum. I have taken the liberty of reordering the discussion of the second law a bit as well. PaddyLeahy 18:51, 5 August 2007 (UTC)

Definiton of an inertal frame of refrence and the First Law

Hi! I've spotted some problems with some important statements:

From the "Newton's laws of motion":

"First Law

If no net force acts on a particle, then it is possible to select a set of reference frames, called inertial reference frames, observed from which the particle moves without any change in velocity."

From the "Inertial frame of reference" :

"An inertial frame of reference, or inertial reference frame, is one in which Newton's first and second laws of motion are valid. In other words, a reference frame that is neither rotating nor accelerated."

This is a circular definition of an inertial frame of reference. There is a problem with this definition of the 1. Newton's law.

Also, an inertial reference frame is usually defined as one in which the first law is valid, the second law is not mentioned in the definition.

From the "Frame of reference" :

"An inertial frame of reference is defined as one in which Newton's first law holds true. That is, one in which a free particle travels in a straight line (or more generally a geodesic) at constant speed "

Here the first Newton's law is defined differently, in the spirit of general relativity. This inconsistencies are confusing to a student trying to understand the Newton's laws.

Yamps 18:16, 21 August 2007 (UTC)

There are various self-consistent ways of describing Newton's laws and defining "force", "inertial reference frame" etc. The one currently in the article is that favored by User:Loom91. It doesn't necessarily jive with the philosophy of editors of other articles, such as inertial frame of reference. Rracecarr 19:27, 21 August 2007 (UTC)

To clarify Rracecarr, it is possible to give the traditional statement of N1L, in which case it is only valid for a certain class of reference frames and invalid for others (this validity being taken as the definition of an inertial reference frame). It is also possible to give the modern statement of N1L, in which case it is itself a definition of inertial reference frames and ttherefore universally valid (as all definitions must be). This should not be a matter of personal choice. Both viewpoints are equally tenable and both should be mentioned in all articles on the topic. Loom91 19:20, 22 August 2007 (UTC)

Thanks for the response. Valid arguments indeed, but one can easily get confused because of the direct reference from one approach to another. It seems to me now that in the "Inertial frame of reference" article it should be stated to which formulation it refers, or maybe the link to that article should be from the original Newton's formulation. Yamps 21:12, 22 August 2007 (UTC)

Something is wrong...I think

Sorry, but i have learned in class that Newtons first law states that: An object will remain stationary or at a constant velocity unless acted upon by a force...

just thought you guys might want to revise that section if what im saying is correct —Preceding unsigned comment added by 124.180.194.158 (talk) 08:14, 17 September 2007 (UTC)

That's pretty much what it says. Where it says "in motion" that means "stationary or at constant velocity" (stationary is just the special case of the constant velocity being zero). The language probably could be made clearer, but at the moment it's very concise; I'm torn. --Bth 12:01, 19 September 2007 (UTC)

Brief statements of the laws in the intro

I think the laws are ok as stated in the intro. Bth changed NL2 in the intro from f=ma to f=dp/dt. I reverted. I agree that this is a more general definition, but it is probably harder to grasp, and it is not the way most people first hear the law. Someone coming to the article having last heard of Newton in 6th grade is more likely to be confused by the more general form, whereas f=ma might jog the memory. The current statement of NL3 is not very specific either: to every action there is an equal and opposite reaction. I can think of lots more precise ways to word that. But that is the traditional wording, and so I think that's what belongs in the intro. Rracecarr 14:56, 19 September 2007 (UTC)

Vandals at it again...

I'm no expert on Newton's Laws, but I am pretty sure "turdmonkeys" is not a term he would have used. (as seen in the header, "statements of the turdmonkeys") As I'm pretty much a newbie here (and in the middle of doing my Physics homework), I'll leave the actual editing to more experienced persons. Jedikaiti 22:37, 23 October 2007 (UTC) I also fixed some resent vandalism, from Ip 66.83.96.11. This "user" replaced the entire page with jlkjklkjlk. —Preceding unsigned comment added by Digmaster (talk • contribs) 15:38, 1 November 2007 (UTC)

Three statements of the laws?

This article should only need one statement of the laws, however it makes sense to have a brief summary at the top - because that is often what people are looking for. To have the laws stated three times in different ways is a little confusing - and very messy. I tried to rewrite the introductory section a while back - though it was reverted - would anyone object if I tried again to combine the two redundant statements into just one redundant statement?

The main problem seems to be that everyone prefers a different way of saying the laws - which isn't too much of a problem, however it leads to constant re-reversion. As I don't think we will ever get a consensus over the "right" way to state the laws (because the Latin is the only correct version) I think we should at least tidy the article up so that the people changing the introductory statements don't drastically effect the flow of the text.

Anyone have any ideas about the best way to proceed? This topic is of immense importance so we should be aiming for at least a Good article. Conrad.Irwin 21:34, 11 November 2007 (UTC)

My view is that the initial statement of the laws, almost historical, is important as it provides a vital linkage to that which many already know. Personally I would delete the "laws in detail" section but maybe some can see some value that would be lost? Rolo Tamasi 22:00, 11 November 2007 (UTC)

In the interest of accuracy and NPOV, we must give all the different statements. Loom91 (talk) 20:13, 18 November 2007 (UTC)

Layman's terms

I think that many parts of this page are overly complicated for someone who just needs to scan through this for help on a science paper. I’m not saying get rid of all the technical stuff but just add a section with the simpler version of the laws and placed so that they stand out and you don’t have to hunt for them. Crazydjman 02:51, 16 November 2007 (UTC)

4th law

What about the fourth law about superposition of forces? Sevcsik (talk) 16:18, 20 November 2007 (UTC)

A Question relating to the Main Page example - ball in aircraft?

An Observer would like to pose a question relating to an example on the main page, the ball on the floor of the stationary aircraft.

The Observer questions the bracketed statement (i.e. the ball does not remain stationary) because he observes events from a different frame of reference. The Observer explains it this way.

The Observer presumes that the ball rests on the floor of the aisle, only due to Gravity. Without Gravity the ball could be placed stationary, off the floor, where it can have no frictional force act on it.

This clear plexiglass aircraft is open at the rear like a Hercules. The Observer is not inside this plexiglass aircraft, with the stationary zero gravity ball suspended in it. The Observer is observing events from beside the runway, looking directly at the suspended ball.

The aircraft has an accelerating force applied to it and it begins to move. "The ball remains stationary" as it has no accelerating force or frictional force applied to it. If the aircraft had no end on the fuselage, the aircraft would disappear while the ball remained in its' original position, because no accelerating force, no frictional force, was applied to it.

Alternatively, if the Observer accepted that the ball was at rest on the floor he could conclude this from his observation. The ball is attempting to remain staionary, however frictional force from the accelerating aircraft are applied to the circumference of the ball causing it to roll. Any accelerating force on the ball is from friction and is fractional to the accelerating force on the aircraft.

There is a contradiction evident between the bracketed statement (the ball is not stationary) and the Observation as described. To the Observer it appears that events relating to the ball confirm Newton's Law. How does the author of the Main Page reconcile the difference for the Observer?--Layman1 03:25, 1 December 2007 (UTC)

I see no benefit of introducing friction into this already unnecessarily confused area.

As all speed is relative it used to be considered self-apparent that any consideration of speed needs a reference point. It was even more apparent that it would be counterproductive to select a reference point that itself was to undergo any acceleration.

These days we debate inertial frames of reference in greater detail than the significance of the laws.

I agree that the section is confusing. I agree with your objection and I particularly dislike the idea that the passengers are able to perceive forces acting on the ball (or lack of them) and the consequent silence on the observation that, if that confuses them, they must be bewildered by the fact that they can feel a force acting on themselves but they do not accelerate! Why do we have to over analyse the simplest things and make them appear to be a significant conceptual challenge? Rolo Tamasi 22:13, 2 December 2007 (UTC)

Comment

Who here can explain how the perception of attraction can be realised...? My reasoning has anyone that advocates to attraction as a force, simply are over looking how force is reliant on motion for its implied exertion.

And on considering motion is reliant on force it should be obvious Attraction should never be treated as a force but rather a by-product of previous repulsions..

Now somewhere in the main article you all have allowed the inference of magic and or attraction being a force.. Please dont tell me you all advocate to magic?

Cheers, P J Schoen.

Newton's Second Law

I have made some additions to this section. Its is not correct to assume NSL implies F=ma. This formula is only correct on 2 conditions, the mass is constant and SI units are use. If SI usings are not use (eg feet, yards..etc) the constant of proportionality is not unity. In many cases F=ma cannot be used, eg a rocket is burning fuel and it is hence getting less massive. This will cause m to change and F=ma is no longer valid.

-- You are incorrect. The types of units one uses in no way changes the validity of the law in question. The confusion stems from the English units of force and mass. A pound-force and a pound-mass are not identical though they are often used interchangeably in layman's terms and even in many (sloppy) textbooks. Wikipedia has a discussion on this somewhere that I've referred to when teaching this.

Thus, it is completely correct to write: 1 [pound-force] = 1 [pound-mass] * 32.174 [ft/sec^2]. This is correct because 1 pound-force equals just that: the force necessary to accelerate 1 pound-mass at a rate 32.174 ft/sec^2. Or, 1 pound-force is the force (weight) of 1 pound-mass under the influence of Earth's gravitational force field, which, since it is proportional to mass, is taken as an acceleration of 32.174 ft/sec^2 at the surface.

The metric system avoids this confusion with F=ma because it distinguishes between mass [kilograms] and force [N], but you pay for it in other formulae (those involving frequency, for example). In the metric system a mass of 1 kilogram weighs 9.8 Newtons because: 9.8 [Newtons] = 1 [kg] * 9.8 [m/s^2]. Thus, 1 Newton is defined as 1 (kg-m)/s^2.

Your first assertion that mass must be constant is true - sort of. Really, F = d(mv)/dt. That is, Force equals the derivative (rate of change) of momentum (mass*velocity). So either mass, or velocity, or both can change as a result of (or cause) force.

I disagree, F=ma is true at all times and all three can change with time. It is a bit like saying that Distance=Speed x Time is only true if the speed is constant, nonsense. Rolo Tamasi (talk) 00:04, 25 January 2008 (UTC)

Simply put, a change in momentum requires force.68.126.188.170 01:31, 16 January 2007 (UTC)Evilrho

See the discussion below, titled "Isn't momentum version of second law also important in classical mechanics?" for some issues with rockets and other systems with variable mass. Itub 18:26, 16 January 2007 (UTC)

Something's Missing

Is it just me or is Newton's second law gone Xykon 09:16, 31 May 2006 (UTC) Newtons second law is soooooo confusing!!!! im giving up on physics and u should tooo!!!

No momentum in Law II

In the latin sentence as well as in [1] there is no question of momentum or rate of change or neither of a resultant force. So, why say there is?
--Aïki 04:26, 19 January 2006 (UTC)

Disputed section: Paragraphs deleted from Third Law section

I deleted these paragraphs: The forces acting between particles A and B lie along parallel lines, but need not lie along the line connecting the particles. One example of this is a force on an electric dipole due to a point charge, when the dipole points in a direction perpendicular to the line connecting the point charge and the dipole. The force on the dipole due to the point charge is perpendicular to the line connecting them, so there is a reaction force on the point charge in the opposite direction, but these two force vectors are parallel and, even when extended to a line, they never cross each other in space. (Delete this whole Paragrph. This is not true)

For long-range forces such as electricity and gravitation, the third law may cease to apply.(Delete this Sentence, even for long distance forces this law applies equally well)

because discussions should be on the discussion page, not in the article. I'm not expressing a view on which contributor is right. --Heron 12:37, 30 January 2006 (UTC)

Newton's Laws of Motion are not laws of Electicity and Magnetism, and nothing concerning electricity and magnetism should have been here to begin with -- so good riddance to the above comments on this basis, also. Newton's Three Laws of Motion are laws of mechanics, first and foremost, and it is silly to go wandering into other subjects in this article. Furthermore, during the time of Newton, very little was known about electricity and magnetism -- as can be seen from the fact that Benjamin Franklin made very basic discoveries in the field in the mid-1700s, and he was awarded two honorary doctorates from British universities on the basis of his discoveries. See the following comments, also.98.67.166.234 (talk) 00:33, 12 November 2009 (UTC)

Newton's third law limitations

The third law is not always true. It fails to hold for electromagnetic forces, for example, when the interacting bodies are far apart or rapidly accelerated and, in fact, it fails for any force which propagate from one body to another with finite velocities.
Source: Mechanics, by Keith R. Symon, University of Wisconsin, Addison-Wesley Publishing Company, Inc., chap. 1-4

But in situations in which bodies influence each other at a distance, as for example through the long-range forces of electricity or gravitation, Newton's third law may cease to apply.
Source: Physics - A new introductory course, Particles and Newtonian Mechanics, by A. P. French and A. M. Hudson, by the Science Teaching Center at the Massachusetts Institute of Technology, p. 13-8.

with cases of extreme acceleration, problems do not fall under newtonian physics; they are analyzied with reletivistic physics. The claim about gravity is outright false. Indeed, earth is gravitationally drawn towards stars hundreds of light-years away, but since gravity drops off as the inverse square of distance, the force is incredibly minute. I have seen at least 4 physics books and none of them ever mention newton's third law not applying. I'm not sure about the electromagnetic forces, but I know gravity is still equal and opposite even at great distances.

College Physics seventh edition, by Raymond A. Serway, Jerry S. Faughn, Chris Vuille, and Charles A. Bennett (published by Thomson Brooks/Cole) says "an isolated force can never occur in nature" (page 90). --Crucible Guardian 08:47, 17 February 2006 (UTC)

If no valuable counter-references is brought in, the Wikipedia:Neutral point of view official policy will have to be applied.
--Aïki 00:29, 31 January 2006 (UTC)

Newton's third law as formulated by Newton is valid only when for electrostatic force and gravitational force instantaneous action at a distance is assumed.

However, it would be very silly to state that newton's third law is wrong because it fails to be a relativistic law of physics.

It is also extremely silly not to be able to capitalize "Newton".98.67.166.234 (talk) 00:45, 12 November 2009 (UTC)

The demand on a theory of physics is that it forms a self-consistent system, and that it agrees with observation to within the accuracy of available observational data.

On a more abstract level we can see that Newton's third law asserts conservation of momentum. The principle of conservation of momentum is just as important in relativistic dynamics as in newtonian dynamics, so in a more abstract sense Newton's third law is still just as valid. --Cleonis | Talk 14:34, 21 February 2006 (UTC)

Newton's third law does not hold exactly for magnetic forces, even with instantaneous action at a distance. The force between two steady current elements, from the Biot-savart force law, does not obey newton's third law. JohnFlux (talk) 12:49, 23 January 2008 (UTC)

We need to include something about the limitations of the 3rd law. An example of it not holding is two magnetic dipoles pointing in the same direction. If you release them they will begin to rotate in the same direction, i.e. the torques they exert on eachother are not opposite. (Conservation of angular momentum is counter-intuitive to the 3rd law here, it is held because of the angular momentum of the field being opposite that of the dipoles) The way it was explained to me was that the 3rd Law only holds for "central" forces, which are forces that act parallel or anti-parallel to the radial vector between two bodies. 130.64.137.176 (talk) 10:26, 16 December 2008 (UTC)

a question ?

say theres two cars 1 in motion and 1 stationary , the car in motion strikes the stationary car , which car will have the most damage ? would the stationary car absorb the momentum from the car in motion therefore causing more damage to the stationary car? please help me on this one ?

The discussion page is for discussing improvements to the article only.TStein (talk) 20:44, 11 July 2008 (UTC)

Assuming that the cars have the same mass they will sustain similar damage. This regardless of whether they remain welded together or bounce apart. This is most easily seen from the 3rd law 'action and reaction are equal and opposite'. The driver of the moving car sees the other 'approaching' at speed. This is the same in his frame of reference as the driver of the stationary car sees in his. Alacrid 19:32, 15 November 2006 (UTC)

As movement can only every be expressed in relative terms, there is no difference between the stationary car and the moving car. The stationary car is only considered stationary due to the frame of reference. Rolo Tamasi (talk) 18:12, 27 January 2008 (UTC)

Just so there's no misunderstanding, if they remain 'welded' together, then there will be more damage done than if they bounced apart. JohnFlux (talk) 12:42, 23 January 2008 (UTC)

This has the cause and effect backward though. The damage absorbs the energy of impact and keeps it from bouncing. TStein (talk) 20:44, 11 July 2008 (UTC)

Do you have a proof of this theory? Rolo Tamasi (talk) 18:12, 27 January 2008 (UTC)

More Answer: So long as the bodies have the same form and hold the same material properties (say, coefficient of restitution), they will deform identically because, as this is a matter simply of motion in frames of reference, the two bodies are indistinguishable in space. —Preceding unsigned comment added by 130.126.215.2 (talk) 08:45, 27 February 2008 (UTC)