Talk:Newton's laws of motion/Archive 5

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References have no numbers

Since the Wiki update, I see no numbers in the reference list after 1, only bullets. Anyone else see this or know why it's happening? I checked the Isaac Newton article and it seems fine. MarcusMaximus (talk) 08:01, 14 May 2010 (UTC)

The first reference contained a numbered list, which seems to be what broke the reference list numbering. I've changed that footnote to use a bullet list and all is fine once more.

I changed back to the old skin (monobook) and the problem was there too, so I'm not clear if this was anything to do with the recent update. I'll see if I can find out whether this is a known problem.

All the best. –Syncategoremata (talk) 09:35, 14 May 2010 (UTC)

Changes May 17, 2010

The article was not well orginized. I moved things around and did not eliminate content. I only eliminated repeated ideas. The article had the issue of having the three laws defined, explained and re-explained in three places: the introduction, the "Definition section", and the "explanation" section. I streamlined all those sections into one introduction and three main sections for each law. I also eliminated the section for the history of the first and second law. There is no point having those titles (note that I did not deleted the content. The article still needs better formating --114.108.192.10 (talk) 09:01, 6 January 2012 (UTC)a--114.108.192.10 (talk) 09:01, 6 January 2012 (UTC)Bold text[[File:[[File:]]]]nd editing of paragraphs to make the paragraphs flow better. ) 00:52, 18 May 2010

I applaud your boldness and I think the article is much improved by your edits. My only complaint, and the others here will tell you that I harp on this a lot, is that it doesn't start with F=ma. In many discussions on this talk page I've expressed my unease about starting with F=dp/dt because it's misleading, but I'll give it a rest for now. MarcusMaximus (talk) 00:00, 21 May 2010 (UTC)

Thanks for your words. I really don't have a strong opinion on dp/dt vs. ma. I only have two reasons why I started with dp/dt: one is because the derivation flows from d(mv)dt to ma, but I guess it can go the other way around; and the other reason because it follows from the modern interpretation of what Newton wanted to say. I will read this talk page and check other arguments. If you want to change the order to ma then dp/dt, I don't have any objection. Cheers. sanpaz (talk) 15:48, 21 May 2010 (UTC)

I just read other sections of the talk page related to dp/dt vs. ma. I hope I did not open pandora's box :). But, here is my take on the the subject complementing my previous comment: the introduction of the article starts with ma and then goes to say dp/dt, which is fine for introducing people into the second law. But in the main section about the Second Law it should be dp/dt first then ma. The section is where you as a reader go to find a more in-depth explanation on the subject, which I think should be in the correct order (dp/dt then ma, which is the way Newton intended). So, the way the article is right now I think is the most appropriate. sanpaz (talk) 21:48, 21 May 2010 (UTC)

Constant mass? Special case?

In various places I have seen a statement to the effect that F=d(mv)/dt accounts for systems of variable mass, while F=ma is only valid for constant mass systems. On the contrary, the law stated in terms of F=ma is true regardless of whether the mass is constant. If you use the d(mv)/dt form, you can get incorrect results for variable mass systems, such as a melting ice cube will accelerate under zero net force.

In fact, the claim that this form of the equation accounts for variable mass systems implies that the consequence of an unforced system gaining or losing mass is a change in velocity, which is flat out wrong. It is actually a change in momentum.

Therefore F=ma is not a special case of d(mv)/dt for "constant mass systems", because F=d(mv)/dt does not correctly account for varying mass; it is valid only for constant mass systems (see reference 22[1] on the main page of this article). F=ma is the correct form of Newton's Second Law for any particle or rigid body with constant or varying mass at any point in time within the speed domain of classical mechanics. I think we need to scrub the articles on classical mechanics topics from this false claim, and maybe even give an explicit statement to the contrary. MarcusMaximus (talk) 05:19, 25 August 2008 (UTC)

I should clarify that I am not opposed to stating the law as F=d(mv)/dt so long as it is made clear that one of the fundamental assumptions of classical mechanics is constant mass. MarcusMaximus (talk) 05:47, 25 August 2008 (UTC)

The melting ice cube doesn't change its mass. Unless you count the liquid water as being no longer part of the body; but this is not the case, because the water will continue to move at the same velocity of the ice (assuming no external force on either water or ice), so, in this case, the body consists of both ice and water.

A better example would be imagining a shopping cart which is moving at constant speed, and you drop something heavy in it. The cart will slow down, as the total (horizontal) momentum will stay constant. (You can say that the body you dropped pushes the cart back, but then you are considering the body as being just the empty cart, and its mass is constant.)

Or, you can think of a jet plane, which accelerates because its mass decreases. (You can also say that the fluid jet pushes the plane, but it's just the different ways you can divide the system. In the first description, the plane including the fluid still in it is a body, and the fluid already ejected is another, and they have both variable mass. In the second description, the plane excluding the fluid is a body, the whole of the fluid (both in the plane and in the jet) is another, they have both constant mass, and they push each other according to the third law.)

Also, F = ma breaks down in special relativity, whereas F = d(mv)/dt doesn't.

As for Newton's wording, he wrote Mutationem motus proportionalem esse vi motrici impressae, and the following part ("If a force generates a motion [...] whether that force be impressed altogether and at once or gradually and successively.") only makes sense if motus is momentum and vis is impulse. --A r m y 1 9 8 7 ! !  19:53, 2 September 2008 (UTC)

"The melting ice cube doesn't change its mass." That's precisely my point: the melting ice cube cannot be correctly treated as a variable mass system using F=d(mv)/dt, because this equation does not correctly account for varying mass. It only works correctly if you keep all the same mass in the system, which is by definition a constant mass system.

Although I agree with your statement about the melting ice cube, I don't agree with your two examples.

• The cart's final velocity depends on the velocity of the heavy object. If the object has the same forward velocity as the cart when you drop it in, there is no change in the speed of the cart. The object brings its own momentum into the system with it.
• A jet airplane does not accelerate because it is losing mass; you must be talking about a rocket. The thrust of jet airplane is produced by injecting energy into the air passing through the jet engine to accelerate the air backward and thereby gain momentum in the opposite direction. The mass of fuel injected into the combustion chamber is negligible compared to the mass of air flowing through the engine. And, by the way, a rocket doesn't gain speed because it is losing mass, it gains speed because it is ejecting mass forcefully.

My only point is that in the realm of classical mechanics, F=ma is always true, regardless of whether the mass of the system is changing, and F=d(mv)/dt is true only for constant mass systems, which makes it misleading and pointless to put the mass inside the differential. In fact, I can show you how F=ma is derived by using conservation of momentum on a variable mass system, if you want. If you're really worried about special relativity, we can state the law as F=$\gamma$ma, which is true even for relativistic varying-rest-mass systems (while the other form is only true for relativistic systems of constant rest-mass), but I'm pretty sure that is beyond the scope of Newtonian mechanics. MarcusMaximus (talk) 02:55, 3 September 2008 (UTC)

(Yes, replace "jet plane" with "rocket" above.) In classical mechanics, there is no way for a body to change its mass unless it expels some matter, or some matters joins it. In that case, in the reference frame in which the expelled/new matter is stationary, F = d(mv)/dt is still valid. Re-read the examples above, explicitly considering the reference frame in which the horizontal momentum of the body dropped in the cart is zero, or the momentum of the fluid expelled by the rocket is zero. You will see that, in that reference frame, if F is 0, d(mv) will be zero but dv won't.

On the other hand, you can consider a body as being always composed by the same matter, and, if you consider "cart + heavy object" to be a body, you'll find that it (or better, its center of mass) doesn't accelerate without external force; if instead you consider "cart" as a body and "heavy object" as another, there is a force from the cart to the object which speeds up the latter, and an opposite force from the object to the cart slowing down the cart. Under this description, m is always constant in classical mechanics, so the whole issue is meaningless.

(As for SR, F = γma is only valid if F and v are perpendicular, otherwhise it is F = md(γv)/dt = m(γ³a_∥ + γa_⊥), where a_∥ is the part of acceleration which is parallel to velocity, and likewise for a_⊥. For the varying-m case, see http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html.)

--A r m y 1 9 8 7 ! !  09:33, 3 September 2008 (UTC)

It is a major weakness of the F = d(mv)/dt formula if it is true only in a special subset of inertial reference frames. Dynamics are supposed to be identical in any inertial reference frame. I don't understand what exactly you are claiming, but I have a feeling it is a pathological case that I examined a few weeks ago that can be better treated using a different (and more general) formula for conservation of linear momentum. Could you elaborate on what you mean by "In that case, in the reference frame in which the expelled/new matter is stationary, F = d(mv)/dt is still valid."? Thanks. MarcusMaximus (talk) 18:05, 3 September 2008 (UTC)

It means that F = d(mv)/dt is valid only if any accreted/expelled matter has zero momentum in the reference frame used. But that what's commonly intended when one says "F = d(mv)/dt is also valid for non-constant m". I think that in most cases, identifying bodies so that each body always consists of the same matter eliminates these confusions. (In the other cases, I'd just use conservation of momentum. Just curious, what was the problem you were examining?) --A r m y 1 9 8 7 ! ! ! 18:47, 3 September 2008 (UTC)

It sounds like you're saying F = d(mv)/dt is not a general formula for the momentum of variable mass systems, that it is restricted only to be used in a privileged set of reference frames that move with the accreted/expelled mass. This is useless for analyzing anything but the most trivial academic problems, because for any system where the mass entering or leaving the system has a nonconstant velocity, you have to continuously change your reference frame.

"Identifying bodies so that each body always consists of the same matter" is impractical for some systems that expel amorphous mass produce force, like rockets and satellites, where it would be overwhelming to track every little $\delta m$ of mass after it leaves the nozzle. I'm sure there are many more examples.

The problem I was examining was the classic problem of finding the force exerted on a fixed platform by a falling chain. It is a pathological case where the mass "leaving" the system (the "system" is the falling portion of the chain) decelerates to zero velocity at the same moment it "leaves" the system, and thus surrenders all of its linear momentum in the form of a force exerted on the platform. I suppose this is as you specified, where the system must be analyzed from a reference frame where the delta-mass has zero momentum. I believe this is a silly restriction that proves the non-generality of the equation.

Why not just use the more general linear momentum formula that correctly models any variable mass system? I'm not just talking about the algebraic conservation of momentum equation. There is a differential equation that looks similar to the equation in question that accounts for momentum change due to both external forces and mass with nonzero velocity entering or leaving the system, taking momentum with it. It is valid in any inertial reference frame. And best of all (in my opinion), it collapses to F=ma in any reference frame for systems of constant or varying mass, and it is correct.

$\mathbf {F} +{}^{N}\!\mathbf {v} ^{\delta m}{\frac {dm}{dt}}={\frac {d}{dt}}(m{}^{N}\!\mathbf {v} ^{CM})$.

where ${}^{N}\!\mathbf {v} ^{\delta m}$ is the velocity in inertial frame N of the mass center of the particles instantaneously entering or leaving the system, and ${}^{N}\!\mathbf {v} ^{CM}$ is the velocity in N of the mass center of the remaining mass. The first term on the left is the external force, and the second term is the momentum carried by any mass entering or leaving the system. This is the full definition of the rate of change of system momentum in non-relativistic mechanics.

Obviously you could choose a reference frame where ${}^{N}\!\mathbf {v} ^{\delta m}$ is zero to get an equation for the special case you talked about. This equation is much more general. If you carry out the chain rule on the right side, then combine the $\scriptstyle {dm/dt}$ terms on the left side, you get the expression for thrust and the correct equation of motion of a varying mass rocket (or an ice cube).

(I also corrected two small italics formatting errors in your post.) MarcusMaximus (talk) 20:44, 3 September 2008 (UTC)

Yes, that's all correct, but I fail to understand how that "collapses to F=ma in any reference frame for systems of constant or varying mass". (Unless you require ^Nv^δm to always equal ^Nv^CM. But, for example, that isn't the case when a bullet penetrates a wooden block...) --A r m y 1 9 8 7 ! ! ! 22:26, 3 September 2008 (UTC)

I should have said any inertial reference frame, since that is one of the restrictions on Newton's 2nd Law. It collapses to F=ma when you consider that, by definition,

$({}^{N}\!\mathbf {v} ^{\delta m}-{}^{N}\!\mathbf {v} ^{CM}){\frac {dm}{dt}}=\mathbf {v} _{exit}{\frac {dm}{dt}}$,

which is a transfer of momentum, or a "thrust" type force, exerted on the "main" mass by the entering/departing mass. If you group it with the other external forces for convenience, you get F=ma. MarcusMaximus (talk) 22:48, 3 September 2008 (UTC)

Ok, now I understand what you mean. I'm adding a clarification in the article. --A r m y 1 9 8 7 ! ! ! 19:33, 4 September 2008 (UTC)

I'm glad we've understood each other. Do you see my point that putting the (necessarily constant) mass inside the differential is pointless and misleading? MarcusMaximus (talk) 08:39, 5 September 2008 (UTC)

Nope. You continue to toss around words like "pointless". You clearly don't stop to think that even if there is some minor difficulty with the equation, it can still produce a very good approximation to what the answer is, in the case where the mass is varying. There is a strong and valuable point to being able to produce good approximations. You don't like approximations? Well every one of the equations on this page and in the article is an approximation. We have on God-like ability to produce exact equations. Even V = IR, Ohm's Law, is an approximation.98.67.166.234 (talk) 07:14, 12 November 2009 (UTC)

Well, among other things, F = dp/dt is closer to the original formulation by Newton (though ∆p ∝ I is even closer), it happens to hold in special relativity, and it is useful in some circumstances (even if in some of them it means an infinitesimal momentum divided by an infinitesimal time, rather than the derivative of momentum seen as a function of time: see, for example, Kinetic theory#Pressure — though it uses deltas rather than d's —, or the solution of your falling chain problem). So I think it should be kept in the article, even if clarified when necessary. --A r m y 1 9 8 7 ! ! ! 10:13, 5 September 2008 (UTC)

I can accept what you're saying about it being closer to Newton's original formulation. I question the value of it holding true in special relativity, because this is an article about classical mechanics. I believe it is of no (or negative) value to consider that it works for "some" variable mass problems, pathological cases, where it just happens to be the equation you end up with by canceling one of the terms in the general equation because you happened to pick a preferred reference frame (like the falling chain problem). This is misleading, and it violates the principle that the laws of dynamics hold identically in any inertial reference frame.

So I think that if we present it in the current form, it needs to be stressed in articles that F=d(mv)/dt is only valid for constant mass systems, particularly because there seems to be a widespread belief to the contrary. MarcusMaximus (talk) 18:19, 5 September 2008 (UTC)

You keep on questioning the use of the equation F = d(mv)/dt in Classical Mechanics (which includes Newtonian Mechanics). However, you are clearly missing the very important principle that ANY equation from Relativity Theory absolutely MUST be valid in Classical Mechanics, too. The people, Einstein and others, have always applied this as a check on their work in developing Relativity Theory. Absolutely, whenever they found that when they took their new equations, and let the velocity tend to zero, and masses and densities become small (in the case of General Relativity), and they did not reduce to the already-known equations of Classical Mechanics, then they had made a mistake and had to go back to the drawing board.

Even if you disregard the fact that Newton stated nearly the same thing (Forget about history!), then the equation F = d(mv)/dt is valid in Classical Mechanics because it has been checked and rechecked 100 times! Sometimes, the equations of Relativity Theory are elegant and compactly-stated, so why not use them, for simple things like the relationship between force and momentum?

Furthermore, quibbling about the "validity" of the equation F = d(mv)/dt in Classical Physics in the case where the mass is allowed to vary (such as with the discharge of propellant), has gotten outrageous. You cannot really expect any of these equations to provide exact answers to problems. That is inherently foolish, because they are all approximations. Everyone of them. The validity of the equation F = d(mv)/dt under changing-mass conditions is just as good as are the approximations that it produces are to the real situations. In one heck of a lot of situations, an answer that within plus or minus 10 percent of the answer is a good one. Furthermore, good approximations can usually be refined to much better ones with the application of more effort to the calculation. For example, if you are going to buy concrete for a project, it is much better to buy 10% more than you really need than 60% more. As for improving approximations, I am an engineer and a mathematician, too, and we both use the method called "successive approximations" to solve problems.

Do not quibble any more about the "validity" of methods of calculations that give good approximations. Go and Sin No More.98.67.166.234 (talk) 06:59, 12 November 2009 (UTC)

I'm not critcizing F = d(mv)/dt because it is only "approximately valid" for varying mass sytems. It is conceptually incorrect. You can use it to prove that a melting ice cube with a tiny bit of initial momentum will accelerate to very high speeds without any external forces. MarcusMaximus (talk) 03:23, 3 July 2010 (UTC)

The mass of a melting ice cube system does not alter - if you seal it in a jar the jar and ice cube will behave consistently whether the ice cube is frozen or completely liquid. The error comes from being inconsistent in what you regard as part of the system - excluding the water after it has melted from the ice cube. That is a modeling error rather than a formulaic one. Crispmuncher (talk) 20:57, 3 July 2010 (UTC)

"The mass of a melting ice cube system does not alter" -- That is exactly the point I'm trying to make throughout this entire discussion. You must use a constant mass system if you use F = d(mv)/dt. As I said above, it is conceptually incorrect to apply it to a varying mass system. MarcusMaximus (talk) 23:00, 11 July 2010 (UTC)

I would suggest on having a look at "standard classical continuum mechanics". F = d(m v) / dt is the only useful formula in that realm (check for instance Navier-Stokes equations). The only point is that ALL TIME DERIVATIVES must be understood in the sense of the Reynolds transport theorem (an application of Leibniz rule to Classical Mechanics). That is to say: time variations of linear momentum really mean time variations inside any considered domain plus the contribution coming from inflows and outflows of linear momentum. So called "thrust forces" in rockets, for any fluid dynamicist, are just a weird (though formally right) rearrangement of flow contributions to Reynolds transport theorem from left hand side to right hand side of the Cauchy momentum equation.

Newton's Third Law

I could not edit this article. However, I would like to add an important point to the "general" description of Newton's third law of motion. It should be:

Every action has a reaction equal in magnitude and opposite in direction, and the action and reaction forces always act on different objects and these forces are of the same type. —Preceding unsigned comment added by Infinte loop (talk • contribs) 21:18, 10 April 2010 (UTC)

If there is an equal force in the opposite direction then the sum of both forces is zero and there is never any change in momentum. This is not logical. —Preceding unsigned comment added by 59.148.242.98 (talk) 02:25, 26 July 2010 (UTC)

This law is about equal and opposite forces acting on different bodies. Of course, if they acted on the same body, they would cancel each other out, but they don't, so momentum changes just fine, and Newton's third law still applies. I suspect this misunderstanding is partly due to the way the law is commonly expressed: To every action there is an equal and opposite reaction." -AndrewDressel (talk) 12:57, 28 July 2010 (UTC)

Newton's Laws in Popular Culture

I think we should make a section called "Newton's Laws in Popular Culture" and compile any references in historical or fictional sources that refer to Newton's Laws ... or also popular misconceptions about his laws.

For example, the Celebrex 2010 ad makes mention of this, and so did Napoleon when he made his comment that a cannonball (not these exact words) tends to stay in motion, but once it stops it tends to stay at rest.24.49.35.99 (talk) 01:32, 15 October 2010 (UTC)

trouble understanding...

in the first line the wording is a little hard to understand. it says "in the absence of a non-zero net force" could this be reworded as: "in the presence of a net force of zero"? —Preceding unsigned comment added by 222.155.135.73 (talk) 06:40, 2 October 2010 (UTC)

About the First Law

I think there ought to be some improvements about the First Law:

1. In our textbooks, the wording is either "a particle with no external force acting on" or "a free particle" instead of "unless it is acted upon by an external unbalanced force". The current wording involves the quantitative definition of force (otherwise you cannot know when the total force is zero), which is the job of Second Law.
2. A dedicated section or subsection under First Law should be written to answer the FAQ why we need the First Law when we can derive it from the Second Law by letting $\mathbf {a} =0$.
3. A common misinterpretation of the applicability of Newton's laws of motion is that none of them are valid when the speed approaches the speed of light. In fact, without the First Law, the wording "inertial frame" in the postulate invariance of speed of light would be undefined. Section Importance and range of validity says nothing wrong, but I think we should emphasize the fact that First Law always holds, except in general relativity.

--Netheril96 (talk) 06:56, 4 October 2010 (UTC)

On "Importance and range of validity"

In that section then mention "In quantum mechanics concepts such as force, momentum, and position are defined by linear operators that operate on the quantum state;" However, in quantum mechanics the concept of force is not defined. Sure we have Ehrenfest theorem in which we can define an equation that resembles Newton's second law. But the concept of force is not defined in this theory. —Preceding unsigned comment added by Sk8hack (talk • contribs) 04:24, 17 November 2010 (UTC)

Derivations?

It would be great if we could see derivations for some of these laws. For example, Feynman derives Newton's second law in "The Feynman Lectures on Physics" Volume 2 (Chapter 19). Hamsterlopithecus (talk) 01:46, 7 December 2010 (UTC)

Laws Of Motion

Excuse me Im Just Trying To Find Out Information About Laws Of Motions . Can You Help Me ? —Preceding unsigned comment added by 206.248.44.63 (talk) 00:39, 15 February 2011 (UTC)

You're in the right place. In fact, just one click away from a huge article with dozens of links to further explanations about the key words and ideas. Click on the "Article" tab at the top of this window to read it (you are posting in the "Discussion" tab, where we discuss how to write the article). DMacks (talk) 01:58, 15 February 2011 (UTC)

I wish we could figure out how some people get directed to talk pages rather than the real thing. Perhaps the whole ARTICLE | TALK | HISTORY | EDIT division could be a much more evident aspect of the page... –SJ+ 05:05, 15 February 2011 (UTC)

car accidents

does newtons law apply when a stationary vehicle is crashed in rear by a moving vehicle —Preceding unsigned comment added by 86.136.133.208 (talk) 11:15, 22 March 2011 (UTC)

Answer is 'Yes, and there are three laws of Newtonian motion.' Charles Edwin Shipp (talk) 23:16, 25 May 2011 (UTC)

Criticism about Newton's first law

In Matter Earth and Sky, Vol. 1, by George Gamow, we read: The first law of Newton was severely criticized some time ago, by the well-known English astronomer Sir Arthur Eddington (1882-1944). He argued, quite correctly, that in general we can only tell if there is a force acting on a given body if it suffers any change in its state of uniform motion or rest. Eddington modified Newton's first law, placing after the comma "... unless it doesn't continue". In fact, Newton's first law should be seen less as a natural law than as the definition of force.

Sorry, I don't have this book in English so I made a poor translation, maybe it's better written in this one:

The British physicist Arthur Eddington criticised Newton’s first law of motion on the grounds that we can tell whether a force is acting on a material body only by the fact that the motion of the body deviates from uniform motion or from a state of rest. He suggests the reformulation: ‘Every body continues in a state of rest or uniform motion in a straight line except insofar as it doesn’t’ [Gamow and Cleveland, 1960, p.35]. Gamow and Cleveland comment ‘Newton’s first law should not be considered so much a law of nature as the definition of a force,’ a view that parallels that of Giere quoted above.". From this site: ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1098&context=pscpapers

José Henrique Campos (talk) 06:48, 23 May 2011 (UTC)

Video demonstrations

MIT prof Walter Lewin has some great course videos on mechanics, some of which would make good additions here. He has given copyright release for some of them; I'll add a couple of them here to see what they look like. –SJ+ 02:22, 29 January 2011 (UTC) (noting that we have incomplete citation style guidelines for video clips!)

The sound of the Newtons second law video is odd, has a few high pitching sounds. I personally found this basic video explaining the laws good (http://www.youtube.com/watch?v=iH48Lc7wq0U&feature=feedwll&list=WL) but have no idea about Wikipedia and its video policy or if I can even post links to youtube at the end of article so I leave it at the discretion of others to add or remove the video. --SkyHiRider (talk) 15:46, 18 February 2011 (UTC)

I'm not quite delighted in the idea, since Wikipedia is an encyclopedia, not a direct learning resource. I would prefer the videos are instead perused in Wikiversity, and I think the videos shouldn't sprinkle the article. Rursus dixit. (^mbork³!) 16:27, 21 May 2011 (UTC)

I agree with Rursus.--Fashionslide (talk) 21:25, 27 August 2011 (UTC)

Anomalies of Newton's first law of motion

First, since the first law doesn't have it's own article, this doesn't deserve one either. I've redirected to this article, but will someone look at it to see if it has any value or is just a hoax (which is what it looks like to me) before redirect thanks! Crazynas ^t 22:48, 11 August 2011 (UTC)

Updated some links

The article had some preexisting links to my own book, Newtonian Physics. I have a new edition with a new title and a different URL, so I've updated the URLs in the article accordingly. I think the edit summaries explain pretty clearly what I did. I thought I should post here to explain, and assert my identity, since the semiprotection on this article suggests that people may be prone to revert.--Fashionslide (talk) 21:29, 27 August 2011 (UTC)

Edit request from , 24 October 2011

The words "action" and "reaction" are extremely misleading and should only be used when necessary due to direct historical translation. More care needs to be shown to emphasize to readers that the forces are inextricably linked and one is not a response to the other.

Thanks! David

Diggitydev (talk) 15:05, 24 October 2011 (UTC)

Not done: please be more specific about what needs to be changed. --Jnorton7558 (talk) 17:45, 24 October 2011 (UTC)

Free Fall

The only force acting on an object is gravity. — Preceding unsigned comment added by 72.161.231.197 (talk) 23:54, 1 November 2011 (UTC)

Indeed. According to the Second Law, that's why free-falling objects accelerate. If you are trying to imply that there's not an equal and opposite reaction, there is: The earth is falling up at you just as you fall down to it. Of course, the earth has a bit more mass and you have a bit less gravity, so the force on the earth is tiny and its acceleration is even tinier. But it's a nice exercise to calculate how far the earth moves. Hint: It's easiest to do this using the First Law: the center of mass of you and the earth doesn't change when you jump. —Ben FrantzDale (talk) 11:42, 2 November 2011 (UTC)

Unamanga — Preceding unsigned comment added by 152.106.99.22 (talk) 16:20, 18 April 2012 (UTC)

Careful, Unamanga. The force upon Earth by you is equal to the force upon you by Earth. It's only because Earth is so much more massive that its acceleration is so much smaller. — Preceding unsigned comment added by 24.223.130.60 (talk) 13:18, 28 April 2012 (UTC)

The extent of which Newton Law of motion applies

Newton Law of motion it’s a theoretical explication of events, and in calculating Force you usually calculate objects whit no shape, atom matrix, atoms and temperature. Furthermore this theory is without real world meaning, only as a tool of mathematics, only through Pressure it gets a more real meaning, calculating Force on to an area (real space), even then you need the details of 3D space matter (shape, atom matrix, atoms and temperature) of the active investigation area, you need all to understand even in calculus the real needs of different materials on impact pressure. Yes it actually can but you also have to include the motin of the person in action . laderrrrrr! (sound it out) Very Important! - This laws can`t be used to calculate pressure, impact or damage. — Preceding unsigned comment added by 109.96.217.180 (talk) 01:28, 1 March 2012 (UTC)

poor quality

It's too bad that such an important subject (rated Top-importance by WikiProject physics) is covered by an article that is of such poor quality (rated C-Class). It's clearly not healthy that the page has been protected or semi-protected for such a long time ... since 2008?? The article has some serious problems in terms of readability by the general reader. Some suggestions: (1) Dump the Latin statements from the Principia and their English translations. Give modern statements of the laws. (2) Dump the calculus. The general reader doesn't know calculus.--75.83.69.196 (talk) 02:16, 4 December 2011 (UTC)

The C rating may or may not be earned. But any weakness in this article is NOT due to either the math or latin. Both can easily be skipped over without affecting the readability of the article. The modern formulation of each law are clearly stated. As far as the semi-protection, the article is clearly better than it was before the semi-protection. TStein (talk) 03:49, 4 December 2011 (UTC)

This article is clearly intended for someone with a background in science. It's not readable for the lay audience. — Preceding unsigned comment added by 68.34.138.122 (talk) 23:12, 4 January 2012 (UTC)

Wikipedia should not be a poor encyclopedia, this article has good level

This article is fine with the latin cites and calculus. STOP the intent to convert Wikipedia in an encyclopedic dictionary or a high school level compendium.

If a layperson is searching for this subject that is because (s)he is interested in science. Moreover, (s)he can learn that differential calculus was the language that allowed to express those laws, differential calculus allow us to express the dynamics of the world.

Wikipedia articles should have a deep insight on each subject.

I agree to have this page protected to prevent unjustified simplification.

Maybe it is time to open a new wiki site, wikicompendium addressed to a high school audience, more similar to an encyclopedic dictionary, or an illustrated dictionary. I have stop to write in wikipedia, because of vandals that erase what I write because they want to oversimplify the content or because they write wrong concepts because they do not know the subject more than is tough in high school.

See other encyclopedias, the old ones printed in paper, to see if they are as simple as some people want to destroy this important effort to have a place to consult all the known to humanity. — Preceding unsigned comment added by 189.140.229.42 (talk) 06:22, 27 July 2012 (UTC)

Newton's Third law and the Buddhism

Buddha says that every action has its own fruit and the doer must receive the fruit of what he has done. Action and reaction. - Pali Canon it's obviously mentioned by Lord Buddha first ,the credits should be gone to the Lord Buddha not Newton for this universal law. — Preceding unsigned comment added by Faulknerck2 (talk • contribs) 13:38, 12 February 2012 (UTC) oh golly you know you have to have the motion included with this there nothing up here that has to do with why he was able to figure this stuff out. — Preceding unsigned comment added by 24.171.168.127 (talk) 17:28, 23 May 2012 (UTC)

Edit request on 29 August 2012 (Second Law)

Replace the follwing:

where, since the law is valid only for constant-mass systems, the mass can be taken outside the differentiation operator by the constant factor rule in differentiation. Thus,

With:

if the system's mass is constant, mass can be taken outside the differentiation operator by the constant factor rule in differentiation. Thus for constant mass,

Reason:

The claims that mass must remain constant are incorrect as that does not apply to rockets which are described by Newton's second law in it's momentum form. In fact, Newton's second law in momentum form is used with variable mass to prove the Tsiolkovsky rocket equation. 184.99.251.11 (talk) 23:30, 29 August 2012 (UTC)

If you assume a time-varying mass and then apply the product rule to Newton's second law $F=d(mV)/dt$ to a rocket of mass $m(t)$ and velocity $V(t)$, you will end up with

$F=m{\frac {dV}{dt}}+V{\frac {dm}{dt}}.$

Compare this to the equation used to derive the Tsiolkovsky equation:

$F=m{\frac {dV}{dt}}+(V-V_{\mathrm {e} }){\frac {dm}{dt}}.$

The two equations are evidently not the same; the latter includes an extra term involving the exhaust velocity. If you attempt to use Newton's second law + product rule to derive the behavior of a rocket you will get the wrong answer. Zueignung (talk) 01:22, 30 August 2012 (UTC)

Not done: as per Zuenignung.

References

Italicse Principia Mathematica in caption

The words "Principia Mathematica" should probably be italicised in the figure caption in the lead section. 203.176.108.99 (talk) 04:39, 31 August 2012 (UTC)

Fixed. Good catch. Zueignung (talk) 04:48, 31 August 2012 (UTC)

Newton's First Law Of Motion Needs a Refinement

It has been pointed out by Hasmukh K. Tank, (Ref: www.physforum.com, New Theories, A refinement of Newton's First Law of Motion), that: since every object has some 'mass' and 'energy', there is always a 'gravitational-potential-well' around it; so when it tries to move in any direction, it has to 'climb' its own 'gravitational-potential-well', so it experiences a constant deceleration. Decelerations experienced by the Pioneer-10, Pioneer-11, Galileo and Ulysses space-probes, of the order of 10^-10 meter per seconds-square were beceuse of this, due to their own 'gravitational-potential-well'. Even the linear-part of 'cosmological-red-shift', is because of the photon's own 'gravitational-potential-well'. Receeding galaxies too experience this deceleration, because, it is shown that: the globular-clusters, the spiral-galaxies, and the galactic-clusters, have self-gravitational-deceleration at their "surfaces" of the value equal to the decelerations of the four space-probes and the inter-galactic-photons.49.213.52.32 (talk) 11:45, 4 September 2012 (UTC) th — Preceding unsigned comment added by 14.96.165.21 (talk) 08:49, 9 September 2012 (UTC)

There is nothing there to discuss. That is not a peer reviewed paper reflecting any form of scientific consensus or even legitimate diverging opinion - it is a user post to a bulletin board and has already been debunked there. To that debunking I will add that if true this would break the law of conservation of momentum, the law of conservation of energy, and imply the existence of a frame of absolute rest. Those are pretty big barriers to overcome that any legitimate theory would need to convincingly address. It doesn't touch upon them in the slightest. This is no different to any of countless other self-published scientific "revelations" written without a basic grounding in the subject matter at hand that are nothing more than a waste of everyone's time. Crispmuncher (talk) 18:55, 9 September 2012 (UTC).

Newton's Third Law Can't Be This Terrible... Can it?

The current version on the article states the following: "Third law: When two bodies interact by exerting force on each other, these forces (termed the action and the reaction) are equal in magnitude, but opposite in direction."

In otherwords this is saying "When 2 bodies are exerting ANY force on each other even if they're different, these forces are equal yet opposite". Either Newton was an idiot or someone made a grave error. Zoele (talk) 21:05, 9 September 2012 (UTC)

I changed it. Better, or still unclear? Zueignung (talk) 21:51, 9 September 2012 (UTC)

I think the OP was challenging the theory, not the notation - "When 2 bodies are exerting ANY force on each other even if they're different" implies a grave error indeed, but on on the part of the asker - the two forces are always the same which is the crux of the third law. Using mathematical notation in place of prose in text like that does not strike me as being an improvement. Crispmuncher (talk) 05:42, 10 September 2012 (UTC).

You are free to revert it if you don't like it. I can sort of imagine situations where the previous wording of the third law could cause confusion; since the previous wording only talks about the two bodies "exerting force" on each other, one might be tempted to pick out two different forces that aren't part of an action-reaction pair (for example, if the two bodies are both massive and charged, then the gravitational force that body 1 exerts on body 2 is not necessarily equal in magnitude to the electromagnetic force that body 2 exerts on body 1). Zueignung (talk) 15:16, 10 September 2012 (UTC)

Edit request on 1 February 2013

Please add Greek language link at the sidebar. Pargpapadopoulos (talk) 11:05, 1 February 2013 (UTC)

Can you post the link here? I don't know what the article is called in Greek. — HHHIPPO 11:43, 1 February 2013 (UTC)

 Done el:Νόμοι κίνησης του Νεύτωνα -- Dianna (talk) 03:18, 2 February 2013 (UTC)

Edit request on 11 February 2013

JFB80 (talk) 20:29, 11 February 2013 (UTC)

Not done: please be more specific about what needs to be changed. — HHHIPPO 21:01, 11 February 2013 (UTC)

Deleted section, -CLARIFICATION- to which extend this laws can apply

I had a section here which is no longer, so I post something similar, please give a reason for deletion this time. This laws pertain to mathematics which are not real in universal law, only in philosophy, or our head. in this universe there is no equality between anything even atoms are different so you can`t have 1+1 since 1 doesn't =1, of course laws can get wary close, for example the 3 Newtonian law can calculate theoretical impact, but for true impact its required details of matter, which newton NEVER calculated, so I ask again , PLEASE SPECIFY FOR THE "INNOCENT" OF THIS WORLD THAT THIS IS FAR AWAY OF CALCULATING IMPACT. Because some think because Newton, that Pressure its only for gas, and water makes same damage as iron. — Preceding unsigned comment added by 46.251.100.132 (talk) 21:41, 23 November 2012 (UTC)

What?Spirit469 (talk) 16:48, 26 February 2013 (UTC)

Simple summaries: Style and WikiProject Mathematics guidelines

I came quickly to consult on these laws and was taken aback by their "summarized" form. Surely simpler summaries could be used?

Firstly, a summary, by definition in my opinion, cannot be exact. Secondly, surely Netwon's Law's are those laws that Newton devised rather that the modern refinements and developments of them. These refinements and devlopments should in my opinion be articulated in the body of the article, to avoid the historical reality of the Laws being disappeared in current expression.

The summary of the first law introduces the concept of velocity vs. speed which seems an unnecessary complication in a summary. Could the law not be simply summarised as:-

An object will remain at rest or at a constant speed and direction unless
it is acted upon by an external force.  

This could then be expanded upon as necessary in the body of the article to detail the refinements that have been made over the centuries and the current expression of the Law (if indeed there is one).

The second law could be summarised as:-

A body acted upon by a force will accelerate in line with that force at a rate which 
is proportional to the force and inversely proprtional to the object's mass.

I cannot see why the summary of the third law given is considered a better summary than the "standard" one I remember from school:-

For every action there is an equal and opposite reaction. 

This law is perhaps the best known of all but the summary of it given in the artcile makes it seem opaque to the point of being almost incomprehensible to a casual reader.

--LookingGlass (talk) 15:09, 27 November 2012 (UTC)

I have no problem with the first two summaries, although the mathematical statements should also be included; e.g., at the end of the 2nd law summary, put "Mathematically, F = ma". The third summary is a popular one, although I can't figure out why: it's completely opaque and sounds like some kind of metaphysical woo-woo about karma. It's the sort of sentence you expect to occur in the same paragraph as the Rule of Three. "Action" and "reaction" are not common terms for forces, and this is made worse by the fact that "action" has a different, more common meaning in physics, and "reaction" is a word everyone associates (in a physical-sciences context) with chemical reactions. Zueignung (talk) 17:12, 27 November 2012 (UTC)

The "style guidance" given in [Wikipedia:WikiProject Mathematics] reads: "if it makes sense, add a very quick (and naive) explanation/description" and I don't see that a "naive" summary needs to include a mathematical formula. Surely those come in the more detailed sections that follow? Again from the WikiProject page: "A general approach is to start simple, then move toward more abstract and general statements as the article proceeds." The "action and reaction etc" came from my schooling so no "woo-woo" in there :D I don't believe that the universal statement: "everyone associates (reaction) with chemical reactions", holds, as engineers, of all kinds, mechanical, electrical, structural, automotive, etc, use the words action/reaction routinely in describing forces. Perhaps it could be expanded a little into something like: "When a force is exerted on an object the reaction that results is equal and opposite to it"? However in any case, the far more confusing issue that arises from the law is impression that the two forces magically cancel each other out so that no motion ever can result, so there inevitably arise issue that cannot be addressed in any summary.

--LookingGlass (talk) 22:38, 27 November 2012 (UTC)

Zueignung, would this address the issue of woo-woo, and summarise for all audiences the third law: "For every force that an object exerts there exists simultaneously an equal and opposite force"? --LookingGlass (talk) 11:50, 28 November 2012 (UTC)

Yes, I think this is a good summary. I still don't agree with taking the mathematics out of the lead, since the lead is supposed to serve as a summary of the entire article—one should not "tease" the reader by suppressing important facts. Writing out the second law as a mouthful of words about proportionality and inverse proportionality is fine as a non-mathematical summary, but it just begs to be followed up by the concise mathematical statement F = ma.

In fact, given the advice of WP:LEAD, it probably makes sense to expand the lead to one smallish paragraph for each law. The topic sentence can be the prose summary, and the remaining sentences can contain more precise information. Zueignung (talk) 18:23, 28 November 2012 (UTC)

Sounds good to me Zueignung LookingGlass (talk) 09:18, 29 November 2012 (UTC)

Always being challegened in light in "New Town" incident. I suppose it's a good thing, perhaps the only good thing. Mapsurfer49 (talk) 22:46, 18 December 2012 (UTC)

In the caption for "An illustration of Newton's third law in which two skaters push against each other", the phrase

"... exerts a force −F on the skater on the right."

should read

"... exerts a force −F on the skater on the left."

98.224.91.10 (talk) 07:35, 21 December 2012 (UTC)

I fixed the description of that photo. I also did away with the signs, since the forces are equal in magnitude. There is no such thing as an objectively "negative force". The sign of a force only depends on your reference frame, and what you have decided to be the "positive" direction. --Spirit469 (talk) 16:51, 26 February 2013 (UTC)

Edit request on 13 May 2013

I request that this:

"Second law: The acceleration of a body is directly proportional to, and in the same direction as, the net force acting on the body, and inversely proportional to its mass. Thus, F = ma, where F is the net force acting on the object, m is the mass of the object and a is the acceleration of the object."

...be changed to this:

"Second law: The net force acting on a body is directly proportional the body's rate of change of momentum with respect to time. When the mass is contant, the equation reduces to F = ma, where a is the acceleration of the object, F is the resultant (net) force and m is the mass."

MessiersAndromeda (talk) 21:27, 13 May 2013 (UTC)

Not done: please provide reliable sources that support the change you want to be made.- Camyoung54 ^talk 21:36, 13 May 2013 (UTC)

Walter Lewin - Issac Newton 3-1, ridiculous!

For what reason are there 3 video of Walter Lewin in the article about Newton's laws? I see just one picture with Newton. Is professor Lewin the greatest promoter of Newtonian Mechanics of all times? Lewin should disappear from the article. This is abusive self promotion. His teaching style is nothing exceptional. Many high school teachers are doing a better job in explaining Newton's laws than Lewin who gesticulates, moves a lot and often consults a written material, which is somehow distracting for students and Wikipedia readers.

Since we don't have video of Newton himself teaching these laws, Lewin will have to do. If you have a personal issue against him, the videos can be removed if you can provide an equally valid replacement. — Reatlas (talk) 04:56, 4 September 2013 (UTC)

1st Law

Although I may be wildly incorrect, or this may have been discussed many times before, isn't the inclusion of the phrase 'external force' key in the 1st law?

I thought I was always taught that the distinction between an object being acted on by a force, and being acted on by an external force was important? — Preceding unsigned comment added by 76.104.134.119 (talk) 03:39, 4 September 2013 (UTC)

• edit* apologies, I should also confirm that I am referencing only the summarised section at the top of the article. — Preceding unsigned comment added by 76.104.134.119 (talk) 03:41, 4 September 2013 (UTC)

The lead now says external force. — Reatlas (talk) 04:56, 4 September 2013 (UTC)

translation

wouldn't it be more accurate something like Mathematical Principles on Natural Philosophy or Natural Philosophy with Mathematical Principles? — Preceding unsigned comment added by ΘωμάςΧ (talk • contribs) 16:31, 20 October 2013 (UTC)

Noether and conservation of momentum

Conservation of momentum is derived via Noether from translation invariance, not Galilean invariance as stated. 46.65.117.250 (talk) 21:42, 26 October 2013 (UTC)

Second law of motion

This article makes many gross errors about the second law.

The second law, as Newton stated it, is that force equals to the derivative of momentum.

Is wrong to assume that mass is constant. For example, a water tank dropping water does not have a constant mass, but a mass which varies with time, thus the derivative dm/dt is not zero.

This text is particularily wrong: "Since the law is valid only for constant-mass systems,[16][17][18] " Is wrong because the law d(m.v)/dt=F is valid also for non constant mass, like the dropping tank, rockets, general fluid mechanics, ans many important systems under Newtonian mechanics. — Preceding unsigned comment added by 186.59.1.82 (talk) 04:44, 15 January 2014 (UTC)

Take it up with the authors of those physics texts listed in References 16, 17, and 18. Admittedly, there are situations where the ejecting or accreting mass has zero velocity in some well-chosen reference frame, so some terms drop out of the equation. In such a case you will get the same result as if you naively use the F=dp/dt formula and treat mass as a variable. But that is just the result of good fortune, it's not a physically sound way to analyze variable mass systems. MarcusMaximus (talk) 01:42, 9 February 2014 (UTC)

I am well and truly baffled by the number of people who read that sentence, ignore the three references provided, and then jump onto the talk page with a facile comment that asserts F = d(mv)/dt simply must be true for variable-mass systems. You don't even have to dig into the source material; the choice quotes are already reproduced in each footnote. Perhaps that sentence should be expanded to really drill into the reader what's going on? Zueignung (talk) 17:58, 22 February 2014 (UTC)

Mistreatment of variable-mass systems

We have been over this issue several times before, but it has crept in again. The recently revised and extended section on variable-mass systems, which purports to derive the equation of motion of a rocket from the form F=dp/dt, has some problems.

• First, it restricts itself to the physically nonsensical situation where the force of the exhaust is applied instantaneously (impulsively) to the rocket. For any real rocket this assumption is false, yet real rockets still obey Newton's second law. So we need a derivation that does not rely on this assumption.
• Second, it attempts to change reference frames halfway through the derivation, but applies it incorrectly. The derivation begins in an inertial reference frame with velocities V for the rocket and v_e for the exhaust gas. Then in order to justify dropping the Vdm/dt term, it changes to a reference frame in which V=0 (i.e. moving with the rocket) yet it retains the dV/dt term. Either this new frame is an inertial reference frame and the equation becomes invalid the instant the rocket starts moving (V≠0), or this is a non-inertial reference frame that moves with the rocket and therefore dV/dt must also be zero, creating a trivial equation saying the exhaust force is zero. (Also note that in a non-inertial reference frame, Newton's second law doesn't apply unless you add fictitious forces, which is not done here.)

Clearly, this is the wrong way to treat a variable mass system. It gets the right answer only by making two errors that allow dropping inconvenient terms. On the other hand, what was there before was correct. I propose we change it back. MarcusMaximus (talk) 02:21, 9 February 2014 (UTC)

I agree. The section as written is uncited and (as you've pointed out) makes several dubious assumptions. Zueignung (talk) 23:24, 22 February 2014 (UTC)

Ok, I have changed it back. Hopefully I didn't screw anything up. MarcusMaximus (talk) 21:48, 5 March 2014 (UTC)

MarcusMaximus: "First, it restricts itself to the physically nonsensical situation where the force of the exhaust is applied instantaneously (impulsively) to the rocket. For any real rocket this assumption is false, yet real rockets still obey Newton's second law. So we need a derivation that does not rely on this assumption."

Kmarinas86: Newton's Third Law was not "derived" in my version of this section, and nor is it derived in the present one. It was taken as a given from the start of it. The assumption that the force of the exhaust is applied instantaneously is required if one wishes to assert $\mathbf {F} +\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}=m{\mathrm {d} \mathbf {v} \over \mathrm {d} t}$ as obeying Newton's Third Law of Motion. It is also the same assumption required to assert the validity of the Tsiolkovsky rocket equation.

MarcusMaximus: "Second, it attempts to change reference frames halfway through the derivation, but applies it incorrectly. The derivation begins in an inertial reference frame with velocities V for the rocket and v_e for the exhaust gas. Then in order to justify dropping the Vdm/dt term, it changes to a reference frame in which V=0 (i.e. moving with the rocket) yet it retains the dV/dt term.[....]"

Kmarinas86: dV/dt is acceleration, not velocity, which is why it is kept even though the frame of reference is changed.

MarcusMaximus: "[....]Either this new frame is an inertial reference frame and the equation becomes invalid the instant the rocket starts moving (V≠0)[....]"

Kmarinas86: Yes.

MarcusMaximus: "[....]or this is a non-inertial reference frame that moves with the rocket and therefore dV/dt must also be zero, creating a trivial equation saying the exhaust force is zero. (Also note that in a non-inertial reference frame, Newton's second law doesn't apply unless you add fictitious forces, which is not done here.) Clearly, this is the wrong way to treat a variable mass system. It gets the right answer only by making two errors that allow dropping inconvenient terms."

Kmarinas86: The force is instantaneous and is evaluated as a function of terms calculated in the instantaneous inertial frame of reference of the rocket. However, you're right. At a different time t when the rocket is faster, $v_{e}$ of past exhaust in the new rocket frame continues to change, which requires reinstating the term that was dropped. If you attempted to integrate the instantaneous force equation without this term in order to obtain the momentum of the rocket, you would indeed get an error. Also the frame of reference of the rocket continues to move away from the system center of momentum frame, so treating all the forces in the rocket frame does require a non-inertial treatment whose effect increases with the momentum gained by the rocket. Such requires another term that will take have take into account fictitious forces which when integrated provide the necessary correction for the momentum of the system to be "conserved" in the rocket's point of view as the rocket goes from instantaneous inertial frames at time t, t+ε, etc..

As much as I disagree with some of your former reasons for reverting my contribution, I do agree with your latter reasons. Therefore, I do not contest the revert.siNkarma86—Expert Sectioneer of Wikipedia
^{86 = 19+9+14 + karma = 19+9+14 + talk} 00:39, 6 March 2014 (UTC)

Kmarinas86: The assumption that the force of the exhaust is applied instantaneously is required if one wishes to assert $\mathbf {F} +\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}=m{\mathrm {d} \mathbf {v} \over \mathrm {d} t}$ as obeying Newton's Third Law of Motion. It is also the same assumption required to assert the validity of the Tsiolkovsky rocket equation.

MarcusMaximus reply: I don't see why the above equation requires any assumption about instantaneous forces. It can be derived using a control-volume approach as is common in fluid dynamics. The additional term on the left hand side is the momentum flux due to advection through the surface of the control volume, i.e. into or out of the system. In other words, dp/dt of the system is not only due to external forces, but also to momentum carried out of the system by some of the material.

Kmarinas86: dV/dt is acceleration, not velocity, which is why it is kept even though the frame of reference is changed.

MarcusMaximus reply: If you are changing to another inertial reference frame, which allows you to keep dV/dt unchanged, you can't then drop the Vdm/dt from the equation because V is, in general, not equal to zero (as you acknowledge in the subsequent Q and A).

Kmarinas86: ... At a different time t when the rocket is faster, $v_{e}$ of past exhaust in the new rocket frame continues to change, which requires reinstating the term that was dropped. If you attempted to integrate the instantaneous force equation without this term in order to obtain the momentum of the rocket, you would indeed get an error.

MarcusMaximus reply: Two points: First, if a differential equation can't be integrated to describe the motion, it is not an equation of motion. Second, forget about the center of momentum frame. If you use this equation, $\mathbf {F} +\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}=m{\mathrm {d} \mathbf {v} \over \mathrm {d} t}$, where u is the relative velocity of the exhaust compared to the rocket mass center, you have the equation of motion in an inertial frame and you don't have the issue of fictitious forces. It can be directly integrated.

I'm glad we can find common ground on the article contents. MarcusMaximus (talk) 08:36, 9 March 2014 (UTC)

MarcusMaximus: "If you use this equation, $\mathbf {F} +\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}=m{\mathrm {d} \mathbf {v} \over \mathrm {d} t}$, where u is the relative velocity of the exhaust compared to the rocket mass center, you have the equation of motion in an inertial frame and you don't have the issue of fictitious forces."

Kmarinas86 reply: I figure by $\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}$ that all the "extra" force is assumed to be carried in the form of momentum advected away from the rocket "volume", excluding any forces applied by the exhaust once outside the volume. Or if possible, external forces by the exhaust on the rocket would probably be included in $\mathbf {F}$ if they were significant. If not included in $\mathbf {F}$, I would expect a term like $\sum \mathbf {m} _{i}{\frac {\mathrm {d} u_{i}}{\mathrm {d} t}}$, but that is of course very complicated for the purpose of this article. If as you said, "We have been over this issue several times before, but it has crept in again." then perhaps what follows from this could be narrowed down in the section. Maybe something like $\mathbf {F} _{distant}+\mathbf {F} _{advected}=m{\mathrm {d} \mathbf {v} \over \mathrm {d} t}$ where $\mathbf {F} _{advected}=\mathbf {u} {\frac {\mathrm {d} m}{\mathrm {d} t}}$ just to make it clear to those doubtful of the expression that it is indeed correct?siNkarma86—Expert Sectioneer of Wikipedia
^{86 = 19+9+14 + karma = 19+9+14 + talk} 13:05, 10 March 2014 (UTC)

While I agree with what you've written, I'm in favor of keeping it as simple as possible. I think we should do our best to avoid adding multiple subscripted terms, because that gives the impression to the reader that what we are discussing lacks generality. F includes all external forces impressed, including the pressure and shearing of the (now external) exhaust gas. The advective term describes only the momentum transported through the surface of the control volume. I think it would be ok to add some statement like that to the text. MarcusMaximus (talk) 23:57, 10 March 2014 (UTC)

                      "WHAT IS VELOCITY"  ♥  — Preceding unsigned comment added by 70.88.31.58 (talk) 18:23, 19 March 2014 (UTC) 

Walter

Walter Lewin has appeared in the article. — Preceding unsigned comment added by 123.222.200.230 (talk) 11:07, 2 April 2014 (UTC)

Derivation of one Law from another?

There is a misconception that it is possible to derive Newton's First Law from the Second Law, or vice versa. However, if one Law was a corollary of another, it can no longer be stated as an independent Law, and that cannot be true since, in that case, we would have only two Newton's Laws of Motion. Could someone please mention this is the article and explain exactly why the first two laws are independent? I find myself incapable of providing a convincing explanation. Yetanotherwriter (talk) 05:29, 11 April 2014 (UTC)

mass?

define mass? — Preceding unsigned comment added by 39.52.2.184 (talk) 09:45, 13 April 2014 (UTC)

See the "mass" article. That term is a clickable link the very first time it's used in this article too. DMacks (talk) 16:36, 13 April 2014 (UTC)

History of first law

The part of the article concerning the history of the first law about Aristotle's view of motion contradicts the text quoted in the article on Parmenides:

"no one could say why a thing once set in motion should stop anywhere; for why should it stop here rather than here? So that a thing will either be at rest or must be moved ad infinitum, unless something more powerful get in its way." (Reference given: Aristotle, Physics Book IV, 6,8 - an online source with this text is http://classics.mit.edu/Aristotle/physics.4.iv.html)

Here, where Aristotle is talking about motion in a void, his views coincide with the first law. True, Aristotle got it wrong in more complex situations such as movement in air, where he thought the air could push back harder than the projectile pushing the air away, but it seems he started thinking along the lines that ultimately led to the first law many centuries later. — Preceding unsigned comment added by Bargedweller (talk • contribs) 18:00, 22 April 2014 (UTC)

Troubling phrasing of 3rd law in intro, the others too.

"When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body."

As this is a paraphrase presumably of some source, generally we would need to cite that source. Without a citation, this (and the others w/o citations) is OR. It's almost even "primary" given that we see the 3rd law not as "secondary sources to be paraphrased", but rather as some grand law out there in knowledge-space that just exists and we are going to explain it. That's primary sourcing, OR, and it's disallowed. What is needed here is cited sources.
Unfortunately, there's an infinity of rephrasings of these laws in an infinity of sources, some better than others, many of them awful. Which one? I don't know. Pick one, or a number of them (many of them conflict!), then knowledgeable editors will judge their reliability. But, we need them. The next paragraph down, I see a very nice reference to that beautiful translation. The phrasing for the 3rd law doesn't seem to be too related to that source, also the source should be cited inline right where the paraphrasing is given.

So in particular, this wording of the 3rd law is problematic because it only strictly applies to static systems (where no masses are accelerating). Many of the better phrasings of the 3rd law refer to "actions" where actions are rates of change of momentum (dP/dt) in addition to just forces. This phrasing needs to admit dP/dt in addition to "force", or restrict its application to systems without accelerating masses (static systems). See the 5th and 6th entries at http://zonalandeducation.com/mstm/physics/mechanics/forces/newton/waysToSay/waysToSayThird.html (click on the "More" buttons) for some nice smooth explanatory candy.

Cheers,
Montyv (talk) 03:34, 6 June 2014 (UTC)

Montyv, are you saying the Third Law as worded only applies to static systems, or are you saying the Third Law truly only applies to static systems? I am not sure I agree with either of those statements, but I would like to know which you mean.

If you mean the latter, could you please explain in more detail? I have never encountered a statement like yours before, and in my engineering experience we use the Third Law for all systems, static or dynamic. I admit only a layman's understanding of general relativity if that is relevant to your point. MarcusMaximus (talk) 21:02, 7 June 2014 (UTC)

As worded.
Don't forget that I'm also saying the source of the wording is unclear. I.e. it looks like it's an editor's interpretation, which is OR. It needs a citation for the source of the wording.
The 3rd law definitely doesn't apply only to static systems. The 3rd law more originally used the word "action". "Actions" can be rates of change of momentum as well as forces (though you need to take the negatives of the dP/dt's). As worded, "force" is ambiguous, and depending on its meaning the wording can be true for all systems or true only for static systems. If "force" means "forces and pseudoforces", then the wording is true for dynamic as well as static systems. The "pseudoforce" introduced in a frame accelerating along with a mass is exactly equal to -ma (or -dP/dt), so most people consider it proper to call -ma a pseudoforce. The negatives of rates of change of momentum are pseudoforces in the vastly most common way of looking at the matter. Given that, the word "force" in casual usage can easily (and often does) mean "forces and pseudoforces". That's why (I think) 3rd law rewordings get away with converting "action" to "force" -- because in casual ways of thinking, "force" may include pseudoforces. The trouble with casually mixing pseudoforce in with "force" is that in many other contexts, "force" strictly means a real force, i.e. a fundamental force, i.e. any force that is not a pseudoforce. It's our obligation to not repeat careless wordings from otherwise-reliable sources. We should find sources of wordings that state the 3rd law correctly and unambiguously.
Montyv (talk) 08:08, 12 June 2014 (UTC)

I have always understood Newton's laws to be stated with respect to an inertial reference frame. In that case I don't think pseudoforces are relevant. MarcusMaximus (talk) 05:59, 13 June 2014 (UTC)

Newton's first law

I believe the mathematical expression representing the first law could be improved by using an equivalence arrow symbol (tex: \Leftrightarrow) since the reverse is also true? 85.230.140.118 (talk) 23:08, 28 July 2014 (UTC)

Done Anon126 (notify me of responses! / talk / contribs) 21:17, 9 August 2014 (UTC)

Third Law Latin translation

I think it would make a lot more sense if "partes contrarias" were translated as "opposing places" rather than "contrary parts". That is, translate as "To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to opposing places." A more natural translation would read "in opposite directions", but the original translator of this seems to want to stick very closely to the Latin. — Preceding unsigned comment added by Smaug123 (talk • contribs) 11:06, 28 September 2014 (UTC)

SI units on Newton's Second Law

Hey Andrew,

You reverted my edit: https://en.wikipedia.org/w/index.php?title=Newton%27s_laws_of_motion&oldid=629291389&diff=prev

I am not sure I agree with your reasoning as of yet, for three reasons. The reasoning you gave was, "It is true in any consistent system of units. No need to mention a favorite here."

1) The units I mentioned are the standard SI units. SI units are the ones used around the world. It is not that the units are my favorites but that they are the ones universally accepted.

2) The second law is not true if the units are changed. For instance if the second law is given in terms of Newtons, meters per second squared, and grams, it is no longer true. Units give physical meaning to a law and insight into what the law is saying.

3) In practice calculations involving the second law always involve units. It seems appropriate to mention units in a section about the second law because the second law is always used with units.

I would be interested in hearing what you have to say.

P.S. This point may not be worth mentioning. I mean, it's not my main argument, but that we would leave this statement, "Thus, the net force applied to a body produces a proportional acceleration. In other words, if a body is accelerating, then there is a force on it," which was adjacent to the statement I made about units, which you removed, but then remove a statement about units, really boggles my mind. It seems much more relevant to me to mention that there are units in which the force, mass and acceleration are mentioned than the restate the law in a sentence when it has already been stated as a formula. Just making the point that it is not like we're in dire need to save space. Units are so inherent in any calculations or understanding involving the second law that it seems strange to mention the law without mentioning units, and since SI units are the universally accepted system of units, those are the ones to go with. makeswell (talk) 03:50, 13 October 2014 (UTC)

The truth of Newton's second law is independent of any system of units, and can just as easily be calculated correctly in US customary units, where force is in pounds, mass is in slugs, and acceleration is in ft/s^2. As your example in item 2 demonstrates, simply using SI units is not sufficient to be successful. It is always necessary to be aware of the units going into a formula in order to know what units come out of a formula and to make conversions when necessary. My objection was not specifically with providing an example calculation with units, but to the implied assertion that the law is only true if the correct units, or SI units, or even N, m, and kg, are chosen. Finally, the second law is not always used with units. Plenty of analyses are performed that incorporate the second law and many other laws to produce algebraic or unit-less results. After all, Newton published his laws in 1687, and the forerunner to SI units wasn't implemented until the 1790s. Let's continue this conversation on the article talk page. -AndrewDressel (talk) 21:33, 13 October 2014 (UTC)

Okay, so let's mention units in the article. As AndrewDressel said, "It is always necessary to be aware of the units going into a formula," and as I said, "Units give physical meaning to a law."

I didn't think the way I phrased my edit implied that the law was only true when the SI units N, m and kg were chosen but I do see the main point that AndrewDressel is making, that the law is true with a variety of units. The units are somewhat arbitrary, and an infinite number of different unit types could hypothetically be substituted while the law remains true.

I think it seems most logical to mention the systems of units that are most commonly found in practice. I know the metric system is very common. AndrewDressel mentioned US customary units. I see no harm in mentioning both pounds, slugs and foot per second and also newtons, seconds, meters and kilograms.

What do other editors think of the proposal to mention both the US and SI units? makeswell (talk) 01:19, 14 October 2014 (UTC)

P.S. We could probably write an example with units which would also improve upon the current rephrasing of the second law, which I quoted in the P.S. of my previous comment in this section of the Talk page (please let me know if it is not clear what quoted portion of the article I'm referring to). Something like, "The second law implies that a spaceship traveling through space and accelerating 60 meters per second squared and weighing 5 megagrams [or some realistic mass] would require a force of 300,000 newtons." Would that be a better edit? That way we would mention units, give an example of how the second law is applied, and improve upon what's currently there by making it more concrete. makeswell (talk) 09:39, 14 October 2014 (UTC)

The equation F = ma is true only in certain unit systems (e.g., SI and US), just as the equation F = q₁q₂/r² is only true in certain unit systems (e..g, Gaussian). Otherwise, a proportionality constant is needed. Zueignung (talk) 20:55, 7 November 2014 (UTC)

Isaac Newton published book called Philosophiae Naturalis Principia Mathematica, which means Mathematical Principles of Natural Philosophy with all his discoveries — Preceding unsigned comment added by 86.30.132.252 (talk) 15:40, 18 January 2015 (UTC)

Semi-protected edit request on 5 March 2015

Add Baruch Spinoza in his Ethics chapter 2 as another philosopher who formulated a law of inertia before Newton. 2601:8:A900:1300:D4F3:8CED:CD:5A43 (talk) 18:30, 5 March 2015 (UTC)

Not done: please provide reliable sources that support the change you want to be made. — {{U|Technical 13}} (e • t • c) 22:30, 5 March 2015 (UTC)

External Force for Newton's Second

An acceleration to a body only occurs in proportion to the external forces acting on that body. This is not stated in this articles formulation of it. It is not clear F=ma only applies to forces external to the system (however that is defined). REF. "Classical Mechanics" 3rd ed. Goldstein, Poole and Safko Page 5 (esp EQ 1.22). Kq6up (talk) 23:21, 18 March 2015 (UTC)

newtons laws

the worst thing ever — Preceding unsigned comment added by 208.54.218.106 (talk) 20:32, 2 March 2015 (UTC)

The reason why many people have problems with Newton's physics are not the mathematical formulas, but the fact that Newton's force never moves! It is a completely static force, and once you know that, you gonna understand all the formulas very easily. And you'll see that the real moving force is the momentum or the energy with squared velocity. And although Newton's force is mathematically explainable with the derivation of velocity, it is in fact nothing else than weight! Static weights and counterweights, that's all what Newton is about. All explanations with falling apples and other crap are simply wrong. Cheers, 81.6.59.42 (talk) 12:16, 22 June 2015 (UTC)

Edit request to correct a many centuries old explanation error

There it is (to be inserted into https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Impulse):

However, and rather easier to understand, an impulse J also occurs when a force F acts over an interval of space Δs, and it is given by

$\mathbf {J} =\int _{\Delta s}\mathbf {F} \,\mathrm {d} s.$

Since force is the space derivative of momentum, it follows that

$\mathbf {J} =\Delta \mathbf {p} =m\Delta \mathbf {v} .$

The first relation suggests that Newton's force can also be seen as the derivation of space and not time (or acceleration) from the momentum. This formula also shows clearly that Newton's force is a completely static force and newer moves, while the moving forces are the momentum and the energy.

Cheers, 81.6.59.42 (talk) 12:36, 22 June 2015 (UTC)

Newton's unfaithful first law - better explained

There is the explanation:

The first law states that if the net force (the vector sum of all forces acting on an object) is zero, then the momentum of the object is constant. Momentum is mass times velocity, with the mass derived from density times volume, while velocity is an vector quantity which expresses both the object's speed and the direction of its motion; therefore, the statement that the object's momentum is constant is a statement that its mass, speed and the direction of its motion are constant.

The first law can subsequently be stated mathematically as

$\sum \mathbf {F} =0\;\Leftrightarrow \;{\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} s}}=0.$

Consequently,

• An object that is at rest will stay at rest unless an external force acting upon it is strong enough to move the objects mass.
• An object that is in motion will not change its momentum unless it changes its mass or an external force acts upon it.

Cheers, 81.6.59.42 (talk) 13:08, 22 June 2015 (UTC)

Videos on page

In light of MIT removing the videos of Professor Lewin from the OCW site, the links don't work, and this page would do well to remove them, or link to other locations on the web where these videos may reside.

As the removal from the MIT website prompted an investigation into the nature of the 'serious matter' described, I learned of things not related to physics.

Thank you, CLK — Preceding unsigned comment added by 205.166.161.61 (talk) 19:52, 1 October 2015 (UTC)

Limitation

The limitations section does not say whether Newton's laws are applicable to cases where acceleration is measured relative to a rotating frame of reference, as for example in the derivation of the "Coriolis force". g4oep — Preceding unsigned comment added by 77.96.58.212 (talk) 09:27, 7 November 2015 (UTC)

Newton's Second Law

More appropriate definition of this law is: "rate of change of momentum is directly proportional to applied resultant (vector sum) force and occurs in the direction of this force". This rather than the current defition which involves acceleration since acceleration was simply derived form of this law. — Preceding unsigned comment added by Hedgehogguy (talk • contribs) 03:02, 12 May 2016 (UTC)

Newton's first law

Proposed update to wording: Currently: Newton's first law currently says "When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force." Suggested change: add "net" -- "When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force."

This change is important because forces CAN be applied to an object without changing its velocity. — Preceding unsigned comment added by Nscozzaro (talk • contribs) 18:58, 23 May 2016 (UTC)

Semi-protected edit request on 22 May 2016 (reference for Descartes's formulation of the First Law)

This edit would add a reference for Descartes's formulation of the First Law.

Text in article: The 17th century philosopher and mathematician René Descartes also formulated the law, although he did not perform any experiments to confirm it.

Reference: Cohen, I. B. Science and the Founding Fathers: Science in the Political Thought of Jefferson, Franklin, Adams and Madison. New York: W.W. Norton, 1995. Page 117.

NB: Cohen cites Descartes's Principia philosophiae (Principles of Philosophy).

-- 50.53.46.136 (talk) 06:22, 22 May 2016 (UTC)

Here is Descartes's text in English (37. The first law of nature ... and 37. The first law of nature ...) and in Latin (XXXVII. Prima lex natura ...). --50.53.46.136 (talk) 07:58, 22 May 2016 (UTC)

Here is a secondary source relating the first laws of Newton and Descartes in more detail:

Cohen, I. B. The Newtonian Revolution: With Illustrations of the Transformation of Scientific Ideas. Cambridge [England]: Cambridge University Press, 1980. Pages 183-4.

--50.53.36.227 (talk) 17:28, 22 May 2016 (UTC)

Looking into this now. I think the Princeton userpage reference cannot be used. Allow me 10 minutes. — Andy W. (talk · ctb) 21:20, 26 May 2016 (UTC)

Done — Andy W. (talk · ctb) 21:37, 26 May 2016 (UTC)

Thanks, Andy. As for the primary source, a See also link to Descartes's Principles of Philosophy might be useful. --50.53.55.41 (talk) 22:58, 27 May 2016 (UTC)

Newton's first law

Proposed update to wording:

Currently: Newton's first law currently states, "When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force."

Suggested change: add "net" -- "When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force."

This change is important because forces CAN be applied to an object without changing its velocity (ie, forces that cancel). Nscozzaro (talk) 19:00, 23 May 2016 (UTC)

I agree with your suggestion. However, Wikipedia has an article on Resultant force and another on Net force. At first glance I can't see what difference is implied in the content of these two articles. We should add the word net or resultant after first determining which one is more appropriate. Dolphin (t) 11:39, 24 May 2016 (UTC)

"Net force" is correct. "Resultant force" is the net force vector placed representatively on an image of the object such that it also produces the correct torque. Nscozzaro (talk) 01:57, 26 May 2016 (UTC)

I mildly dissent from the proposed addition of "net". In classical mechanics there is no such thing as a "net force" which can act on an object, it is a mathematical abstraction. The fact that forces can be applied which have exactly zero net contribution is a degenerate case, and a detail that we don't need to cover in the short intro definition. It seems analogous to saying "No object can change temperature unless it experiences a change in its thermal energy" should be changed to "No object can change temperature unless it experiences a net change in its thermal energy." Technically true but a bit pedantic and distracting. Just my opinion. MarcusMaximus (talk) 20:47, 1 June 2016 (UTC)

What is "correct" is what the cited sources say. If they disagree, then say so. --50.53.53.81 (talk) 08:41, 2 June 2016 (UTC)

Marion (2nd ed.) does not use the word "net". Symon (3rd ed.) does not use the word "net", but he uses "forces" (plural). Goldstein (2nd ed.) does not mention the first law. --50.53.53.81 (talk) 09:00, 2 June 2016 (UTC)

Newton doesn't use the word "net" either. See the article. --50.53.53.81 (talk) 09:16, 2 June 2016 (UTC)

Semi-protected edit request on 3 December 2016

The last sentence of the section titled "Newton's first law" reads: "Newton's laws are valid only in an inertial reference frame."

It should read "Newton's first two laws are valid only in an inertial reference frame." 27.32.243.188 (talk) 02:43, 3 December 2016 (UTC)

Thanks for that suggestion. I have made the change; see my diff. Do you have a reliable published source I can cite to allow independent verification of my change? Dolphin (t) 11:22, 3 December 2016 (UTC)

I would contend that Newton's 3rd Law also applies only in an inertial reference frame. In a non-inertial reference frame there are all kinds of fictitious forces that have no equal and opposite counterpart. MarcusMaximus (talk) 02:56, 5 December 2016 (UTC)

No reliable published source has yet been supplied to support the statement put in place on 3 December. Can you supply a citable source to support the opposite view? Dolphin (t) 03:56, 5 December 2016 (UTC)

Vector presentation

The current article mentions that there have been a number of formulations of Newton's laws, and presents them with a vector notation that is in common use today. I'm not sure of the timeline, but I was under the impression that vectors weren't in wide use at the time of Newton, and thus Newton's actual formulation of the laws wouldn't have been in a vector framework. I don't expect this article to develop Newton's original formulation, however, assuming I'm correct, it could be misleading to not speak to the idea of the original formulation not being in vector form. Is there a good article that explains the various formulations? Am I correct about the original formulation? 75.139.254.117 (talk) 04:28, 28 December 2016 (UTC)

Problematic claim

"The discovery of the second law of thermodynamics by Carnot in the 19th century showed that every physical quantity is not conserved over time, thus disproving the validity of inducing the opposite metaphysical view from Newton's laws. Hence, a "steady-state" worldview based solely on Newton's laws and the conservation laws does not take entropy into account."

This seems like a personal conclusion from a writer. It presents no citations. In particular the claim "showed that every physical quantity is not conserved over time" sounds particularly disingenuous, I doubt entropy was the first 'physical quantity' that isn't conserved. I suspect minimization or maximization principles are much older, for example the Principle of Least Action traces back to the 1600s with Fermat.

200.100.104.225 (talk) 09:34, 26 December 2016 (UTC)

It sounds like a particular point is being attempted to be made about the thinking about conservation laws. It does sound a little suspect, as I'm not sure it's clear that entropy is a fundamental physical entity. It certainly has been given physical interpretations, but that's not the same thing. 75.139.254.117 (talk) 04:36, 28 December 2016 (UTC)

And I think that the author meant "that not every physical quantity is conserved over time". The current statement makes no sense. — Preceding unsigned comment added by 185.147.13.130 (talk) 15:54, 3 March 2017 (UTC)

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First Law/First Video

I'm a Physics flunky. So I have difficulty understanding the first video. I get the part where he is talking about hopping on his horse and accelerating; it stands to reason he would feel force in the form of a kind of "push" which he indicates at his back. No problem there.

Then he suggests that we (the students) are coming toward him, but we feel no force. But if we are coming toward him, given he is accelerating, we would have to accelerate also (I think, but maybe this is where I am confused). Since our mass is not changing (I think this is safe to assume here), it must be our velocity that changes in order to "catch up" with him. Thus, force occurs for us as we approach him.

Now, if he had said we remain sitting in our seats as he rides toward us on his horse (or whatever conveyance), then I would agree there is no force being exerted upon us students. That would make sense to me.

I am worried that someone will suggest that I am taking matters too "literally" or something to that effect. I'm just trying to understand physics, and such responses will not help in my understanding. I'm fine with the analogy, it is simply that the analogy is not working for me.Henryxmartin (talk) 21:54, 18 July 2017 (UTC)

Thank you for your serious responses. Help me turn this flunky around!

I haven't seen the video but I do understand Newton's laws of motion. Perhaps he is saying the students are stationary and he is moving towards them on (or in) a vehicle such that the gap is closing and they appear to him to be accelerating towards him. Dolphin (t) 21:46, 18 July 2017 (UTC)

Thanks, Dolphin. As I said above, if we had remained sitting, then yes, it is all understandable. But in the video, the professor suggests (if I am hearing it accurately -- my sense of hearing is not good due to a condition, and the video's sound quality is not the best either) that the students are coming toward him, I think in the context of while he is still accelerating (or maybe he has achieved constant velocity, but it sounds like he is saying he is moving relative to us).Henryxmartin (talk) 21:54, 18 July 2017 (UTC)

At about 3 minutes in, he says he is accelerating toward us and we are coming toward him. But he adds that we are being accelerated toward him -- I wonder if he means that we appear to be accelerating toward him. But, if so, then this is not clear by his words alone. — Preceding unsigned comment added by Henryxmartin (talk • contribs) 22:05, 18 July 2017 (UTC)

Yes, most likely. The body of students and the lecturer both appear to be accelerating towards each other, but it is only the lecturer on his horse who is experiencing an unusual force, and therefore only the lecturer who is experiencing a genuine acceleration. This is explained by noting that the lecturer's acceleration is apparent to all observers at rest in inertial (or unaccelerated) frames of reference. In contrast, the lecturer and his frame of reference are accelerating so it is not an inertial frame of reference and he must expect that his observations will be unreliable.

The body of students are rotating with the Earth's surface, once every 24 hours, so it is a rotating frame of reference and therefore not truly inertial but in the timescale of observing the man on his horse, the error is negligible. (See Foucault's pendulum.)

When I select the MIT Physics video lecture I get an error message saying "Page not found". Does anyone have any suggestion as to how to see it? Better still, erase the dead URL and replace with an active link to the lecture. Dolphin (t) 05:02, 19 July 2017 (UTC)

I'd hope it was obvious by now that I am clear on the concept once the problem with the lecturer is addressed. The rest of it all follows. The problem here is the video, with the lecturer stating something he might not have meant. But being he is the expert, and I the student, I am still not 100% certain. If we agree that the prof has made an error, then what follows might make sense to me. Maybe get a better set of videos -- maybe ones with better audio also?Henryxmartin (talk) 23:45, 19 July 2017 (UTC)

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Semi-protected edit request on 17 February 2018

the newton laws of motion is based on apple which broken from tree — Preceding unsigned comment added by 103.207.173.30 (talk) 03:17, 17 February 2018 (UTC)

Sigh

I remember learning these laws as:

• A body in motion tends to stay in motion, and a body at rest tends to stay at rest.
• The acceleration of a body is proportional to the forces acting on it (or something like that; I don't remember the exact phrasing).
• Every action has an equal and opposite reaction.

Does anyone else recall this classical phrasing of the laws, and where it came from? It might be useful to quote it in the article somewhere. Eleuther (talk) 18:09, 20 June 2018 (UTC)

Newton published his famous laws in a document written in Latin. When translated to English his laws appear to modern readers to be verbose and lacking clarity. Consequently, authors of introductory physics books mostly present the laws in their own words, each one striving for maximum clarity. The same is true for many teachers of the subject. There is no classical or preferred wording of the laws in English. Dolphin (t) 18:29, 20 June 2018 (UTC)

"Preferential"?

The article as it stands now (2018-07-31) states the 1st law using the phrase "preferential reference frame". I've never heard of a "preferential" reference frame, and the phrase is neither explained in the article nor is it linked to some other article. What is a "preferential" reference frame? Imerologul Valah (talk) 20:17, 31 July 2018 (UTC)

Юридической силы не имеют!

Следовательно - отсебятина ! Маало-ли кто што понапишет !! ))) 85.140.25.142 (talk) 12:42, 30 September 2019 (UTC)

They have no legal force!

Therefore - a gag!

- signed Whoever writes this!

So, no change necessary Andy Dingley (talk) 12:53, 30 September 2019 (UTC)

Just an idea

For any object in space– omitting gravity, IMPOV

An object of any mass (continuous) irrespective of size can be pushed or pulled without any resistance - Right?

It is the gravitating mass, due to which a falling mass shows resistance because of its weight against another force. For Example an object on earth. If this is true then shouldn’t the definition or the concept of inertia, which means resistance, needs revising.

No idea id someone agrees with the following but

An object is said to be in a state of a well-balanced condition if its centroid or center of mass (c.o.m) locates itself at its spontaneous strategic position if left on its own accord. An undisturbed mass at rest is always in well-balanced condition.

An aforementioned object is said to be in a state of an unbalanced condition if its c.o.m off its strategic position due to any means. The course of the shifting of the centroid, which is under duress due to an unbalanced condition, not only moves the object forward but also guides the direction of its motion. A disturbed mass is always at unbalanced condition - Motion. Thus

An object is said to be at rest if its c.o.m remain at its original position.

An object is said to be in a state of motion if its c.o.m off its original position.

An object may spin about its undisturbed c.o.m in the direction of applied force when only a part of the mass is disturbed.

A mass may spin and move if its c.o.m and a part of the mass are disturbed.

An object may also be found at fully or partially disturbed and undisturbed conditions

Let A and B are two spherical objects of masses M and m at rest such that A > B and therefore M > m. Ca and Cb are the center of masses of A and B respectively.

Both A and B maintain their state of rest if Ca and Cb maintain their original position – Undisturbed state

Both A and B lose their state of rest if Ca and Cb loss their original position respectively - Disturbed state

Now, assume A is disturbed and moves with velocity V while B is undisturbed. Following is one of the possible conditions when A collides with B.

A pushes B in front of it in its original direction of momentum until both gains V1.

Here B never offers any resistance to A rather it takes the momentum from A – total momentum of the system still remains the same. Let "a" and "b" are the jitters/impulses (shock waves) produced within A and B respectively due to their collision. Cb shifts away from its original position when “b” passes through it, which makes B unstable. Similarly, Ca also shifts towards its original position when “a” passes through it, which makes A less unstable than before.

Although both A and B osculate (juxtaposed) each other but exert no further force on each other after when both masses attains V1. Both Ca and Cb off center, therefore, A is under reduced momentum of while B gained a momentum.

A or B spins if the line action of "a" and "b" are truncated – not passes through the centroid.

Push or pull is considered a force. A pushes B due to its momentum, therefore, momentum is a Force F.

So force which is a push or pull depends upon on both moving mass and its final velocity, not acceleration.

Addendum: It is said all the laws of physics remain the same in every inertial frame if moving with constant speed. This is true only if the inertial frame is moving in earth’s (or any other celestial’s) atmosphere due to its smooth ride on equipotential lines (same elevation).

No celestial gravity’s atmosphere means no smooth ride on the equipotential lines of gravity and hence all the objects in a spaceship if not attached to each other are considered individual object including spaceship.

Therefore a person (if not fasten) in a spaceship and a spaceship are two different objects in space therefore initially when a spaceship accelerates from rest and then gains constant speed, all objects (if not attached to the spaceship) within the spaceship are still at rest. This means the back of the cockpit moves towards a person who is still at rest while the front of spaceship moves away from the said person. Finally, the rear cockpit reaches a person and a person is pushed by the rear cockpit in forwarding direction of the spaceship when it catches/hit a person.

So the above statement might not hold true for space due to the lack of celestial gravity. — Preceding unsigned comment added by 2001:56A:739C:D300:2503:4AE4:B7:5558 (talk) 19:04, 21 April 2019 (UTC)

For any object in space – considering gravity

As said, it is the gravitating mass, due to which a falling mass shows resistance because of its weight against another force, therefore the heavier the mass the greater will be its gravity or resistance due to gravity (all particles of the object fall towards the c.o.m of that object) or the greater the mass the greater the force will be required to displace its c.o.m, therefore, a tiny apple can’t change the strategic position of c.o.m of earth.

The c.o.m of falling mass is below its original position while the c.o.m of flying object is above its original position

The collision effect of the aforementioned A and B depends upon the size, shape, density, and velocity, etc therefore both "a" and "b" may or may not reach the center of mass of A and B respectively. The two outer particles of A and B, which collide with other, start exerting a force on the neighboring particles, the said neighboring particles pass "a" or "b" to the next connected particles closely and so on and this is how shock wave passes through A or B.

Both "a" and "b" depend upon the mass below, above, right, left, back and in front and how their elasticity or interlocking system etc is.

It is said that all objects fall at the same rate if this is true then why the damaging/penetrating effect of the same mass is different if fall (at the same rate) from different heights on the ground.

This means force is directly proportional to the mass of the falling object and its final velocity (not acceleration)

Therefore Force F = MV but not F = ma or mg where g=GM/d^2 or 9.8 m/s/s.

Similarly, addition (unless totaling) or multiplication of two or more things of different types (e.g. goats and trees) has no useful meaning in mathematics, therefore, I don’t understand why mass and velocity (or ma) are in the multiplication form in the formula of momentum. For Example

We get the following when 3 goats are multiplied with 5 trees

= 3 (goats) x 5 (trees) = 15 goat.tree

Likewise, the momentum of a mass of 3 kg when moving with a velocity of 5 m/s can be calculated as follows

Momentum = mv = 3 (kg) x 5 (m/s) = 15 Kg.m/s

Although we are so used to with kg.m/s and others similar multiplication in science that we accept them religiously but to be very honest, both goat.tree and kg.m/s, etc have no useful meaning - (m/s has meaning).

Why not momentum = M+V if the multiplication of MV is allowed. And the same is applied to all similar mathematical equations.

Anyway, shouldn’t force be measured relative to the displacement of c.o.m of moving mass as explained above and or indirectly via relative to standard penetration on the ground or any standard surface? 2001:56A:739C:D300:6144:2EAE:B584:322A (talk) 04:01, 7 April 2019 (UTC)Eclectic Eccentric Kamikaze

• Inertia is not "resistance". In the idealised "Newtonian pool table" that we're taught at school there is no "resistance" (i.e. no friction) as this would make things too hard to comprehend. However there is still inertia and gravity.

An object of any mass (continuous) irrespective of size can be pushed or pulled without any resistance - Right? is true if there's no resistance, i.e. there's inertia, but there's no friction and no gravity acting upon it in the direction of movement. So in the simplest case, "an ant can push the Earth", just very, very slowly.

You have to be very careful with terminology here. "Inertia" is inertia, not resistance. "Momentum" is momentum, not force. It might give rise to a force, or more carefully worded it might give a force for a limited time, or it might give rise to an impulse. But to say therefore, momentum is a Force is just wrong (that "is" implies a definition, not just a correlation) and thinking that will make all your subsequent reasoning go adrift. Andy Dingley (talk) 10:07, 7 April 2019 (UTC)

You may be right but inertia is a resistance according to the a definition of Wikipedia. Neither an apple nor earth shows resistance when they feel the same amount of force pulling each other together. its just a proposal. — Preceding unsigned comment added by 2001:56A:739C:D300:6D17:A780:4BAC:2A63 (talk) 19:43, 7 April 2019 (UTC) So if an object of any mass (continuous) irrespective of size can be pushed or pulled without any resistance (true - you said) then this means all objects of different masses can be accelerated at the same rate with the application of the same amount of force. — Preceding unsigned comment added by 2001:56A:739C:D300:7CC1:E023:1A7:BE51 (talk) 14:36, 10 April 2019 (UTC)

Newton didn't first proposed laws of motion

Kanada (Indian philosopher) had first described laws of motion in Sanskrit (Ancient Indian language) around 600 BCE.

This has been recently verified too.

This should be updated 2409:4064:2211:7794:541C:1972:FB76:2CE6 (talk) 15:02, 12 July 2019 (UTC)

• Source?

Also, he didn't invent "Newton's laws of motion". Nor has anyone ever claimed that "laws of motion" of motion were Newton's invention. Even at Newton's time there were other theories for this, such as impetus. However's Newton's were the ones which worked.

AIUI, Kanada had a number of interesting theories, although there's very little known about his personal life, including an uncertainty over his date of nearly 500 years! So even though many of his theories, which overlap with Classical Greek thought, may be original and might even have influenced the Greeks, it's pretty certain that the Greeks had these ideas long before him and he may even have been influenced by the Greeks himself. His "four atoms" theory of classical elements is widespread throughout the ancient world and Aruni, another Vedic thinker was much earlier than Kanada.

His mechanics though, as much as I've read, was non-Newtonian. He had a concept of 'mass' and of 'weight' and gravity (I don't know how clear his distinction between them was), but he did not make Newton's connection to inertia. His thoughts on motion were thus like the impetus theories: the impelling force was related to the velocity, not (as Newton realised) to the change in velocity, i.e. acceleration. Andy Dingley (talk) 15:59, 12 July 2019 (UTC)

I agree with Andy Dingley. Newton’s Laws of Motion, published in 1687, were founded on the excellent work of Copernicus (1543), and subsequent work by Galileo, Johannes Kepler, Tycho Brahe and others. Newton’s Laws were effectively the result of collaboration of a number of leading thinkers and writers from 1543 until Newton’s time. I don’t doubt that prior to 1543 others speculated on the nature of motion but those speculations are not in the same class as the collaboration that led to Newton’s Principia. Dolphin (t) 23:08, 12 July 2019 (UTC)

Reply to user:Dolphin51

You should start reading properly. I hadnt said that kanada had INVENTED.

Source is Internet archive- Link of his 36 volumes-https://archive.org/details/RigvedaSamhithaAsthanaMahavidvanHPVenkataRao

Lines from his VOLUMES-

वेगः निमित्तविशेषात कर्मणो जायते | Translation : Change of motion is due to impressed force. (The law stated that an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.)

वेगः निमित्तापेक्षात कर्मणो जायते नियतदिक क्रियाप्रबन्धहेतु | Translation : Change of motion is proportional to the impressed force and is in the direction of the force.

वेगः संयोगविशेषविरोधी | Translation : Action and reaction are equal and opposite.

AND THIS IS PRESERVED IN ENGLAND. And he PROPOSED this even if with the uncertainty of 500 years then it is (600BCE + 500 years) or (600BCE - 500 years)

Even if we go against kanada then too its about 100BCE. Still before than NEWTON. And what role do personal life plays here? And there is no proof or pointing evidence that Greeks had first discovered

But

This confirms that kanada did proposed earlier than newton So this article needs an update. — Preceding unsigned comment added by Unitorimus (talk • contribs) 14:58, 13 July 2019 (UTC)

Constant mass

Hi all,

In "Newton's second law" part, it doesn't make sense to first write f=d(mv)/dt and afterwards say that it only applies to constant mass (by citing Plastino at al) and take the mass out of the derivative.

What Plastino et al explain is that f=d(mv)/dt shouldn't be written right from the beginning. The only correct expression in classical mechanics is f=ma. So that form should appear (and in the introduction as well!).

Therefore it is not really needed to give a comment on the constancy of the mass. But for completeness one could add the correct expression of the force when the mass is variable (which is given in Plastino at al).

Thanks! G — Preceding unsigned comment added by GreyClock (talk • contribs) 11:25, 6 November 2019 (UTC)

Unusual updates

Hi all,

Can the three edits on 12 July 2019‎ be reverted? They only add confusion. — Preceding unsigned comment added by 104.193.185.2 (talk) 00:19, 2 December 2019 (UTC)

Semi-protected edit request on 21 June 2020

Please take a look at section Laws, subsection Newton's first law, the 4th paragraph. There the penultimate sentence reads:
"if A verified the first law, then B will verify it too."
I request the 1st letter in this sentence to be changed to a capital letter (in agreement with general capitalization rules), so that the sentence will be:
"If A verified the first law, then B will verify it too."
Thank you for considering my request. 77.253.24.92 (talk) 14:15, 21 June 2020 (UTC)

 Done Danski454 (talk) 14:28, 21 June 2020 (UTC)

Semi-protected edit request on 24 June 2020

We can write the laws in a much more understandable ways, as such 1st law can be written as, "Until an unbalanced force is applied on it, the bodies at rest remain stationary and bodies in motion continue to move at uniform velocities."and there are much easier ways of writing others too. I think that you will consider this and reduce the protection so that we could edit it and make it easier thanks. 43.250.243.193 (talk) 05:38, 24 June 2020 (UTC)

 Not done: requests for decreases to the page protection level should be directed to the protecting admin or to Wikipedia:Requests for page protection if the protecting admin is not active or has declined the request. JTP ^{(talk • contribs)} 06:05, 24 June 2020 (UTC)

Verifying axioms?

The writers of this article seem to be unaware that Newton's laws are axioms; that is, he postulated them first and then drew conclusions from them. Saying that "Newton's laws were verified by experiment and observation for over 200 years" is not exactly right. You can't verify an axiom; you can only see if the conclusions drawn from it lead to a contradiction. (For instance, the show Mythbusters once ran an experiment to see if a feather and a hammer would fall at the same rate in a vacuum. Apparently they didn't realize that a negative result would have destroyed all of classical mechanics.) Still, I understand that the laws are now considered valid only within a certain range of conditions, so it's more complicated than simply declaring them to be axioms. I don't know enough about this subject to revise the article, but I believe this point should be addressed. Wgrommel (talk) 14:10, 5 November 2020 (UTC)

I think the physical world is not subject to humankind’s axioms, and I don’t think of Newton’s laws of motion as axioms. Can you cite a reliable published source that supports the idea that they are axioms? Dolphin (t) 19:16, 5 November 2020 (UTC)

Semi-protected edit request on 22 December 2020

In the section on Newton's First Law, please change "this is equivalent to saying that is the net force" to "this is equivalent to saying that if the net force". This will change the word "is" to "if" and make the sentence both correct and more readable. 2601:5CD:C280:CBD0:2D1B:D7C7:164D:3FCF (talk) 19:56, 22 December 2020 (UTC)

 Done, thanks! ‑‑ElHef (Meep?) 20:09, 22 December 2020 (UTC)

figure skaters and 3rd law comment

I second the concern of the above post. The diagram is not accurate. 'Normal' forces do not demonstrate the third law. Just as a block resting on a table does not demonstrate the third law regarding normal forces. It would be better to say that when a single skater pushes against a wall, the skater is pushed back (i.e. the skater's own body experiences a force being applied to it). If we consider a block resting on a table, the 3rd law force corresponding to the weight of the block is not the normal force that the table exerts on the block. It is the gravitational force that the block exerts on the earth. — Preceding unsigned comment added by 2001:8003:6D09:5A01:A978:4311:4348:4A15 (talk) 11:15, 29 January 2021 (UTC)

Semi-protected edit request on 27 June 2021

Fake deepak (talk) 05:34, 27 June 2021 (UTC) newton has eight law but no one tell you about this it is a clear offence newton discover many laws but some of laws are discribed more clearley but some are not

 Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate. Living Concrete (talk) 06:45, 27 June 2021 (UTC)

Figure skaters and 3rd law

hi, I wonder if the figure skater diagram is optimal? It doesn't indicate any forces: are they holding hands while spinning? are they (about) to push apart? Are there any forces at all involved?

Also, the key 3rd law concept is that of opposite laws: An ideal diagram would show one person pushing the other, and experiencing a force back into their body (the opposite reaction, and also the correct image for a free body diagram...— Preceding unsigned comment added by Tim bates (talk • contribs) 20:20, 26 January 2012 (UTC)

Removal

I removed the following as the conservation of energy article disproves it: Conservation of energy was discovered nearly two centuries after Newton's lifetime, the long delay occurring because of the difficulty in understanding the role of microscopic and invisible forms of energy such as heat and infra-red light.— Preceding unsigned comment added by Narssarssuaq (talk • contribs) 11:46, 22 August 2012 (UTC)

Newton's 3rd law actually discovered by Leonardo da Vinci

I can't seem to edit the article... can someone add that Newton's 3rd law was actually discovered by Leonardo da Vinci? Just google 'da vinci 3rd law' for a bunch of sources— Preceding unsigned comment added by Bpg609 (talk • contribs) 05:41, 25 January 2016 (UTC)

Action and reaction with velocity

Newton's original Latin reads:

Hisce volui tantum ostendere quam late pateat, quamq; certa sit Lex tertia motus. Nam si aestimetur Agentis actio ex ejus vi et velocitate conjunctim; et Resistentis reactio ex ejus partium singularum velocitatibus et viribus resistendi ab earum attritione, cohaesione, pondere et acceleratione oriundis; erunt actio et reactio, in omni instrumentorum usu, sibi invicem semper aequales. Et quatenus actio propagatur per instrumentum et ultimo imprimitur in corpus omne resistens, ejus ultima determinatio determinationi reactionis semper erit contraria.

from Philosophiae Naturalis Principia Mathematica, Axiomata, sive Leges Motus, P.24

https://la.wikisource.org/wiki/Philosophiae_Naturalis_Principia_Mathematica_-_Axiomata,_sive_Leges_Motus

Translated to English, this reads:

I was only willing to show by those examples the great extent and certainty of the third Law of motion. For if we estimate the action of the agent from its force and velocity conjunctly, and likewise the reaction of the impediment conjunctly from the velocities of its several parts, and from the forces of resistance arising from the attrition, cohesion, weight, and acceleration of those parts, the action and reaction in the use of all sorts of machines will be found always equal to one another. And so far as the action is propagated by the intervening instruments, and at last impressed upon the resisting body, the ultimate determination of the action will be always contrary to the determination of the reaction.— Preceding unsigned comment added by Mugenzero255 (talk • contribs) 09:39, 29 March 2017 (UTC)

The role of the 3rd law in self-consistency with respect to scaling up from subsystem to system

The question of what Newton's laws actually apply to (fundamental bodies or extended systems) should be addressed. Definitions I and II in the Principia characterize bodies as extended objects whose mass and momentum are (what we in the current era would call) the volume integrals respective of density and density multiplied by velocity; and Definition IV described the force applied to the body as the total external force (or "impressed" force) applied to its parts.

It needs to be noted that this raises the issue of self-consistency: does a system, whose parts each satisfy Newton's laws, also satisfy those laws, and if so, what mass, momentum, position and velocity is to be ascribed to the system that the laws are to be taken with respect to.

In this context, (1) the first law can also be characterized as a "no self-force" law; (2) the underlying additivity assumption for mass, mass moment, momentum and force needs to be noted (with references to relevant parts of the Principia), (3) the role should also be noted that the third law plays for self-consistency with respect to scaling up from subsystems to systems, by ensuring that the internal forces within a system do not produce a net self-force (so that the only force that acts on the system is the sum of the "impressed" forces), (4) that the requirement of self-consistency also implies the third law and (5) the first law becomes a special case of the third law, when the latter is generalized to also include the case where the two bodies in question are one and the same. (It's not entirely clear whether the original wording of the third law already does so or not.)

Finally, there is the ambiguity inherent in Third Law's statement: is it meant to also assert that the forces acting between two subsystems act along the line separating the two. The wording in the Principia (particularly with the examples raised), tends to suggest this but leaves the issue open. It is required for self-consistency with respect to the matter of angular momentum and self-torques (which in turn has a bearing on Kepler's law of Area, which Newton used as one of the motivations for his work).

The question of ambiguity of the Third Law has been noted in the literature. References to the different interpretations should be provided, and at the very least, a distinction should be noted between a "strong" form of the Third Law (equal, opposite and directed toward or away from each other) versus the "weak" form (equal, opposite, but not necessarily directed toward or away from each other). It hinges partly on whether the extra clause "et in partes contrarias dirigi" ("directed to contrary parts") in the Third Law is meant as "directed toward or away from each other" or not. A possible reference on this may be V. F. Lenzen, Isis, Vol. 27, No. 2 (Aug., 1937), pp. 258-260; though I don't have access to it.— Preceding unsigned comment added by 65.28.164.71 (talk • contribs) 20:54, 27 March 2019 (UTC)

Semi-protected edit request on 12 October 2021

Newton’s first law: the law of inertia Newton’s first law states that if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force. In fact, in classical Newtonian mechanics, there is no important distinction between rest and uniform motion in a straight line; they may be regarded as the same state of motion seen by different observers, one moving at the same velocity as the particle and the other moving at constant velocity with respect to the particle. This postulate is known as the law of inertia. 122.173.171.187 (talk) 11:19, 12 October 2021 (UTC)

 Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate. ScottishFinnishRadish (talk) 11:28, 12 October 2021 (UTC)

Semi-protected edit request on 2 January 2022

For the first law the equation right now says

F = 0 <-> dv/dt = 0

This should be changed to

F = 0 <-> dv/dt = constant

because, by applying the another derivative to dv/dt = d2v/dt2 = 0 <-> F = 0 68.2.232.101 (talk) 22:58, 2 January 2022 (UTC)

 Not done. You have not provided reliable sources which demonstrate that the change should be made. Separately, I don't follow your reasoning. You're arguing that, if ${\frac {d\mathbf {v} }{dt}}$ is constant, then ${\frac {d^{2}\mathbf {v} }{dt^{2}}}=0$, and that therefore acceleration is zero. But all that ${\frac {d^{2}\mathbf {v} }{dt^{2}}}=0$ means is that acceleration is constant. If you want acceleration to be zero, you want the statement that's in the page right now: ${\frac {d\mathbf {v} }{dt}}$ is acceleration, so when ${\frac {d\mathbf {v} }{dt}}$ is zero, acceleration is zero too (and therefore so is force, as the page claims). I think you may be reading the equation as the derivative of position with respect to time rather than the derivative with velocity with respect to time. Velocity is the first derivative of position with respect to time. The first derivative of velocity with respect to time is acceleration, whereas the second derivative of velocity with respect to time is jerk. Having constant jerk does not necessarily mean that there is no force, it just means that whatever net force is being applied cannot be varying. - Astrophobe (talk) 01:39, 3 January 2022 (UTC)