Talk:Newton's laws of motion

Statement of the First Law of Motion should be adapted/modified

As was recently reported in Scientific American, the Motte translation of the First Law used in this article is incorrect. Also the "unless" in the paraphrase should be changed to "except insofar as". The original article pointing this out is Hoek 2023. 2001:468:C80:C105:81EA:C534:C0F0:2602 (talk) 15:59, 1 October 2023 (UTC)

Does changing "unless" to "except insofar as" actually change the meaning, or is that a distinction without a difference? Maybe, but as a native English speaker, "except insofar as" just sounds to me like a longer way of saying the same thing. And reading the Hoek article, he presents what he calls his "strong reading" of the first law as something that has "never been clearly articulated or explicitly defended in print." Since we're here to provide the mainstream/consensus view before anything else, I'm wary of changing a prominent part of this article based on a single paper and a pop-science news item about it. Hoek's discussion of why the "weak statement" and "strong statement" aren't logically equivalent involves calling several previous exegeses of Newton wrong (pp. 63–64) and then getting deep into the weeds about the second law and what Newton meant by terminology that is obsolete now anyway. (The Scientific American story, although better than a lot of pop science, doesn't try to summarize all this, so it's not that great of a secondary reference for Hoek's argument.) This could all be interesting in the "History" section of the article, but when we are first introducing the laws, we should explain what they have come to be, rather than what was on Newton's mind in 1687, which didn't even include $F=ma$.

When I first tried accessing Hoek's paper via the SciAm story, I hit a paywall and had to resort to my university library, but there's an arXiv version that appears to be substantially identical. XOR'easter (talk) 16:57, 1 October 2023 (UTC)

For what it's worth, Cohen and Whitman's excellent 1999 translation of the Principia renders the first law as "Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by forces impressed." Generally I think Cohen & Whitman is a better translation than Motte, but in this case I tend to agree with @XOR'easter that there's not a big difference in the meaning of the two English translations. I am neutral as to whether the translation in our article should be changed. CodeTalker (talk) 17:55, 1 October 2023 (UTC)

Wiki Education assignment: 4A Wikipedia Assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 21 August 2023 and 16 December 2023. Further details are available on the course page. Student editor(s): Meme2611 (article contribs). Peer reviewers: Tortuga424, Elkinhernandes.

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

It's probably a bad idea to attempt a significant rewrite of one of the most highly-visible physics articles on Wikipedia without first becoming thoroughly conversant with rules like Wikipedia not being a textbook. Language like Simply put, Understanding Inertia through Everyday Examples, To delver [sic] deeper, let's explore, etc., is suitable for other places, but not here. XOR'easter (talk) 20:19, 15 November 2023 (UTC)

Semi-protected edit request on 24 October 2023

Change "A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force." to "A body remains at rest, or in motion at a constant speed in a straight line, except insofar acted upon by a force. Averroes8 (talk) 23:18, 24 October 2023 (UTC)

 Question: Why? The current phrasing seems far clearer to me – I don't think "except insofar acted upon by a force" is even grammatically correct. Tollens (talk) 00:57, 25 October 2023 (UTC)

@Tollens: look a few sections up. This is a tendentious fork of an open discussion. Astrophobe (talk) 01:43, 25 October 2023 (UTC)

Whoops – should've looked. In that case, not done as there appears to be no consensus for the change. Tollens (talk) 02:00, 25 October 2023 (UTC)

Special relativity

Why my edit has been removed ? All I wrote was clearly cited in sources, correct and used in accelertors physics. It is very usefull to calculate the power radiated by a relativist charge which depend on acceleration magnitude and well kwown since ages. That's too bad that this relativist expression of the second law does not appear in this article. Here is an extract of a french Lecture where all the calculus are detailed and correct. https://physique.cmaisonneuve.qc.ca/svezina/nyc/note_nyc/NYC_XXI_Chap%204.9b.pdf — Preceding unsigned comment added by Jlpons (talk • contribs) 05:23, 5 December 2023 (UTC)

This edit [1] was cited to a non-peer-reviewed arXiv preprint, which is not a suitable source for our purposes. The other added content [2] was not in the source provided. More specifically, the first formula appears on a different page, and the second line doesn't appear anywhere. Page 299 discusses motion in a single spatial dimension, so the statement about the angle between the speed direction and the acceleration direction doesn't make sense. I don't have a fundamental objection in principle to having more formulae in that section, but we'd have to write the treatment very clearly, and at the moment it seems to me that details of that sort are better suited for an article like Relativistic mechanics. XOR'easter (talk) 19:46, 5 December 2023 (UTC)

You're right in [2] for the perpendicular acceleration, the centripetal acceleration is used instead just after. The formulas I wrote are correct and the acceleration magnitude well depend on the angle between acceleration (or force if you prefer) and velocity. This is why, for a same force, a charged particle emits $\gamma ^{2}$ times less when the acceleration and speed are paralell. This is a well know result that you can find in any accelerator physics book.

Unfortunately, this formula is "too obvious" to be fullly developped except in few lectures as i mentionned.

I didn't mentionned that the source from arXiv was not published, to be honest when i read it, I was a bit surprised that such a job could be published as it is already well known.

Do what you want, if want to reaad this formula or not. From my point of view this could be a nice illustration and could show that the second law is still usefull even in special relativity... Jlpons (talk) 20:15, 5 December 2023 (UTC)

Because this is a big-picture kind of article, it might make more sense to say something like, "The relativistic version of Newton's second law is used in accelerator physics, for example" and link to another page for the details. XOR'easter (talk) 20:23, 5 December 2023 (UTC)

If you want to have a look at what we have in accelerator physics books, you can have a look at this one:

https://cds.cern.ch/record/398429/files/p437.pdf

where the underlying calculus are not explicit and you just have the results

In page 3, "Thus, for the same applied force (dp/dt) the power radiated is a factor of γ2 larger than for linear motion" which is a direct consequence of what i cited in my french citation above where all calculus are detailed for student. Jlpons (talk) 20:55, 5 December 2023 (UTC)

A link in english where paralell and perpendicular force are well explained in special relativity. The notations i used are also used in eq (7) and eq (10) and the full Newton second law eq (3) is writen using ${\vec {\beta }}={\vec {v}}/c$ but very easy to replace. This is very very basic stuff.

https://makingphysicsclear.com/force-and-acceleration-in-special-relativity/

The aim of Wikipeida is also education, no ? Jlpons (talk) 10:57, 6 December 2023 (UTC)

Just because Wikipedia aims to educate doesn't mean that we should include every way of writing Newton's laws (or every application of Newton's laws, or every notation for Newton's laws) in this specific article. Unless we take care to organize what we write, we end up with articles jammed with distractions that treat minor details as more important than central ideas, and no one learns anything. Some things belong in Newton's laws of motion, while others fit better into Relativistic mechanics or Larmor formula or Synchrotron radiation. Your first source, the chapter on synchrotron radiation, would by itself suggest that this fits into one of the latter two: it presents the results for a specific application without details of how they were derived. The mindset is "here is the power radiated by a moving electron" rather than "this is the way to think about Newton's second law in special relativity". The second is somebody's personal hobby website, which we have to use with care. (I mean, I'm a physicist and I could make a blog about something I think is interesting, but that by itself wouldn't be reason to justify a section on it in the most visible physics article on Wikipedia.)

Like I said earlier, I don't yet have a firm opinion about whether or how to expand that section. I'm just thinking about what would be most pedagogically useful. XOR'easter (talk) 16:29, 6 December 2023 (UTC)

That's too bad. You have a section "relation to other theories" and this would perfectly fit even without without speaking about synchrotron radiations or Larmor formula or other more complex stuff. Just to say how the special relativity impacts the second law. There are already few nices sentences in the article that could be completed with 2 or 3 formulas and why not a nice plot.

I gave you 2 sources that well explain this and only this with all the derivation fully explained. I agree that my 2 first sources was not very appropirate but it is difficult to find online sources of such basic stuff. Jlpons (talk) 18:15, 6 December 2023 (UTC)

The equation I gave are well detailed in this wiki articleAcceleration_(special_relativity)#Acceleration_and_force

They did a full decomposition for the transverse plane and the longitidinal axis.

I would suggest to rewrite the equation (4b) in the format of this article for better undertsanding and link to the above article section.

What do you think ? Jlpons (talk) 04:15, 7 December 2023 (UTC)