Talk:Classical mechanics

I started this too late and when tired so it's got a lot of work to do! Also didn't start at the start...

My plan is roughly

Newtonian Mechanics

Motion (Introducing velocity, acceleration etc.)

Newton's Laws of motion (introducing force and mass also applications)

Work,Kinetic Energy,Potential Energy and Conservation

Momentum, Impulse and Collisions

Rotation of rigid bodies and dynamics of rotational motion

Equlibrium and elasticity

Gravitation

Periodic motion

Fluid Mechanics

I see this page leading people to a lot of other pages which will have the more modern and in depth stuff. At university this was the introductory stuff in first year leading on to everything else in quantum mechanics. --Alex MacDonald 17:54, 11 August 2007 (CDT)

I'd add classical electrodynamics (Maxwell's equations) - they are a part of classical mechanics. Anthony Argyriou 14:01, 14 August 2007 (CDT)

Wouldn't this be better as individual articles or are you just intending a general overview? There are a huge number of concepts to be covered in a single article and it will be extremely long. I disagree that classical EM should be included: this is really a separate subject to classical mechanics and there are already easily enough topics in the list above to make this a very long article. Roger Moore 16:51, 11 November 2007 (CST)

Latin laws?

Are the original Latin forms of the laws really relevant to the subject? I feel that Latin is not the best way to present the laws, since most people (even physicists) do not speak Latin. Perhaps the Latin form could be linked to or put in a footnote, if you feel it is relevant to the reader. I think the English translation should be at the top in any case. This is comparable to presenting the work of Einstein and Gödel in German. Johan A. Förberg 22:13, 10 March 2010 (UTC)

Does this article really benefit from the "Inertial propulsion" section?

This article has a sub-section devoted to the subject of "inertial propulsion" or "reactionless propulsion". Although I did edit that section to improve the English, I am finding it difficult to believe that the section serves any purpose as part of this Classical mechanics article. After all, it is not classical mechanics.

We already have the Reactionless propulsion article and a section of the Perpetual motion machine article, both devoted to the subject of inertial propulsion and it strikes me that those two are enough. What do you think? Should that section about "inertial propulsion" be removed from this Classical mechanics article?

What do others think?? Milton Beychok 01:56, 17 March 2010 (UTC)

I agree with Milton, "inertia propulsion" (that, as far as I understand Dmitrii, is a hoax) is a very specific subject that is out of place in a broad review, as this article should be. I would also not write about perpetual motion machines in an article of this kind. --Paul Wormer 06:42, 17 March 2010 (UTC)

Agree. The inertial propulsion is just a specific case of the perpetual motion; it does not deserve a section; one wikilink at the preamble is sufficient. I suggest: "The range of applicability of the non-relativistic Newtonian mechanics refers to harge values of action (much bigger that the Planck contant and the small speed (much smaller than speed of light). Within this area, the attempts to bypass the Laws of Mechanics refer to science-fiction and frauds. The most often attempts of such by-pass refer to the realizations of the Perpetual motion machine (which break the Law of conservation of Energy) or the inertioids (which break the Law of conservation of momentum and are equivalent of the perpetual motion due to the principle of ralativity."

How do you like this? Dmitrii Kouznetsov 08:10, 17 March 2010 (UTC)

I suppressed the gravitsapa and add the range of applicability instead. The copyedit may be required. Also, the derivation of the laws of conservation from the Laws of Newton may be included. And other staff mentioned by Alex. Dmitrii Kouznetsov 10:59, 17 March 2010 (UTC)

Dmitrii, you are quite right about your additions needing copy editing. I corrected about 45 or so spelling errors. However, the English construction and structure also needs copy editing ... but I will leave that for others to do. I don't have the time to undertake that.

I still believe that all mention of the "gravitsapa" and the "inertioid" should be completely removed from this article. It is completely out of place in this article. Milton Beychok 15:50, 17 March 2010 (UTC)

Thanks for the corrections.

I agree about the gravitsapa: No gratitsapa in this article! But I still think, If the section tells about conservation of momentum and that of energy, then it should have wikilink to the inertioid and that to the perpetual motion.

The same applies to the relativistic mechanics. The section that postulates the maximal speed, should it finger to the faster-than-light spacecrafts? For example, many physicians used to watch some Star war, but how many of them know anything about Physics?

What do colleagues think? Dmitrii Kouznetsov 00:38, 18 March 2010 (UTC)

Dmitrii, I repeat that I believe all mention of "gravitsapa", "inertioid" or "perpetual motion" or "fraud" or "hoax" should be removed from the Main Article. Those are completely out of place in this seriously technical article about classical mechanics. The Related Articles subpage could have wiki links to the Reactionless propulsion and the Perpetual motion machine articles ... and that should be enough. As for physicians watching Star Wars, I very much doubt that any serious articles in any medical journals discussed Star Wars. Milton Beychok 04:36, 18 March 2010 (UTC)

Milton, I found another argument in favor of your point of view: the article becomes long. I removed the inertioids. I simplified the preamble, moving the last paragraph into a special section. Dmitrii Kouznetsov 17:43, 18 March 2010 (UTC)

Dmitrii, thanks very much for deleting all mention of "gravitsapa", "inertioid" or "perpetual motion" or "fraud" or "hoax". Regards, Milton Beychok 21:59, 18 March 2010 (UTC)

Font for vectors

In the physics journals, often vectors are denoted with bold Roman letters, for example F. With HTML, we could make them bold Italics, for example F . Should we do it through the article, or it is better to keep all vectors "bold Roman"? (This case is easier to realize with environment "math" for complicated formulas with vectors) Dmitrii Kouznetsov 07:58, 19 March 2010 (UTC)

If they are in the text, then I usually use bold italic Roman letters, for example F or v. Milton Beychok 14:48, 19 March 2010 (UTC)

Shouldn't they be the same in the test and in the excluded formulas? Dmitrii Kouznetsov 05:27, 23 March 2010 (UTC)

As far as I can remember, I always saw Roman bold if bold was used for vectors. (This is rarely done in mathematics, but frequently in applications.) Probably bold italics would be more consistent since variables are in italics, but I don't remember to have seen it. In old books Fraktur was used, but this is no longer usual. In any case, on this wiki the choice is restricted. F is not bold italics, it is bold slanted, and I do not expect the TeX of "math" to support either bold slanted or italics. Thus I suggest to use bold Roman consistently in text and in math mode. --Peter Schmitt 13:31, 23 March 2010 (UTC)

Peter, thank you for the explanation. Hence, we should replace F to F for any vectorial F through the classical mechanics and, perhaps, other articles. Could you do this authomatically with some bot? Dmitrii Kouznetsov 03:03, 25 March 2010 (UTC)

The Royal Society recommends bold italic/slanted, but bold roman/upright is common. One reason for this that needs to be considered here is this. Would the slanted bold be clearly distinguishable from slanted nonbold on people's computers? Peter Jackson 09:57, 25 March 2010 (UTC)

Dmitrii, a bot cannot decide if a use of slanted belongs to a formula. Moreover, I do not think that there should be strict rules (only suggestions).

Peter, my answer was "theoretical". From a practical view (of which you remind me) it probably is different: how well F, F, F and F can be distinguished may depend on the browser. Thus it may best to avoid using the same letter in two versions ... and if there have to be two then F and F are best to distinguish. Mathematicians and scientists will not be confused by TeX formulas using another font, and non-experts probably will not notice it, anyway. (It is a pity that TeX in text does not work well). --Peter Schmitt 23:19, 25 March 2010 (UTC)

Newtonian mechanics

The article Classical mechanics appears to suggest that this subject is co-extensive with Newtonian mechanics. That omits the later formulations of Hamiltonian mechanics and Lagrangian mechanics. These articles have yet to be written, but this one is misformulated. John R. Brews 17:21, 7 January 2011 (UTC)

I have to retract this statement: the section Classical_mechanics#Formalization_of_the_classical_mechanics_and_the_extensions does mention these formulations. John R. Brews 17:23, 7 January 2011 (UTC)

Some Comments

I have some thoughts:

I think the lead paragraph focuses excessively on the limitations of classical mechanics, as compared to relativistic and quantum mechanics. It almost sets it out to be a dead science, which it is not. I think it would be better to more thoroughly outline the scope of classical mechanics, and simply note that there are applications which require different mechanics.

The picture at the top is great.

The disposition could be improved. I think the article should begin with a statement of the Laws (from which everything else can be derived) and a thorough explanation of their implications. The vector notation is compact and practical for us that know our linear algebra in and out, but not strictly necessary for understanding most of the results. Perhaps we can save the vector calculus for later in the article? Also, I think many results can be explained with just Euclidean coordinates, so perhaps the cylindrical coordinates should be saved for later as well?

This is not a textbook where we have the luxury of defining our concepts and deriving all results from postulates. We need to go straight at it and explain what mechanics is really about. We must also be careful not to assume too much mathematical knowledge in our readers. Many results in mechanics can be understood without much mathematical discussion.

The part about uniform circular motion is great, and a very important example. It shows that circular motion requires constant acceleration. Since we have already introduced the idea of different coordinate systems, we might say something about the centrifugal force and the Coriolis effect (when a rotating system is chosen as a frame of reference).

The `Range of validity' chapter is intriguing, but perhaps we could trim it down a bit and move some of the material to the respective articles? We should not dwell too much on the limitations I think — even if classical mechanics is not the mechanics of stars and elementary particles, it is very much the mechanics of trains, buildings, bridges and everyday life. Johan Förberg 00:53, 23 December 2011 (UTC)