Talk:Classical mechanics

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I just exchanged 'u' and 'v' under the topic "Velocity" to represent velocities of first (by u) and second car (by v) as 'u' precedes 'v'. A minor change.

Under the topic "Frames of reference", it is stated that "Speed of light is not constant" whereas i believe that it should be "Speed of light is constant". So edited the same.

Sunil 16:29, 6 January 2006 (UTC) sunil

I changed it back to the speed of light is not constant because this article seems to cover pre-special-relativity mechanics, in which case the speed of light is not generally constant. When it comes to relativistic mechanics, the constancy of the speed of light is the difference used to derive the equations of special relativity. DAG 17:16, 19 February 2006 (UTC)

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Gareth, I like some of what you've done, but I'm a bit disappointed with the resulting formatting changes. In previous versions, each concept had a separate, dilineated section with information presented in a concise, organized manner. This was useful for quick reference. Your version is more precise and reads better than earlier versions, but is less useful as a quick reference. My recommendation is to add a separate page titled "Equations of Classical Mechanics" or "Summary of Classical Mechanics", which will basically be a table of the various important equations in classical mechanics.

The page should start with definition equations for the various key parameters (eg. velocity, acceleration, force, work, kinetic energy, momentum, angular momentum, etc...). This section could then be followed by a listing of other useful equations, like x=1/2at²+v₀t+x₀. What do you think?

--Matt Stoker

Thanks for the praise. The "Equations..." page sounds like a really good idea - GWO

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Personally, I would prefer defining force at least initially as, F = m*a, however, if the consensus is that F=d(m*v)/dt is more precise,

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I phrased it like that for a few reasons. Its a more literal "translation" of what Newton said, you do need it for some problems (the pendulum drop sand, rocket burning fuel...) and (last and least) it fits with the concepts of relativistic mechanics (4-momenta and all that) better -- GWO

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would it be preferable to first define momentum as p=m*v and then define force as F=dp/dt?

--Matt Stoker

Yes, it would be better. That way you can keep the same definition of force in relativity.

Could be. Weigh up the addition of some more notation, with the simplification of some of the equations. Would it obscure the logical flow behind F=d(m*v)/dt=m*dv/dt=m*a ? I guess the notation thing is the age-old problem of mathematical writingGWO

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I find the statement that F = m a is the definition of force to be incorrect. This defines the force vector, but it does not define the force; that would be F = G M m/r^2, or F = -k x, or F = m g, etc. This is a common misconception that few professors take the time to explain. F = m a tells you that a mass is being accelerated and that it results from some force. To set up the equations of motion you must substitute the definition fo the force for F, so -k x = m a is the equation of motion.

--George Hrabovsky

Just did a major overhaul of the classical mechanics equations. Mostly I added a few equations here and there, made vector quantities bold, and changed the format to be more friendly with bold vector quantities.

Moved the request: Someone please add the equations for gravitational, electric, and magnetic forces

to this page, and responding. Gravitational may be appropriate, but electrical and magnetic force definitions belong with articles on electricity and magnetism (believe me, they're another whole ball game).

Final note: physicists divide physics in to classical and quantum mechanics. Einstein's relativity is actually lumped in with classical.

I'm not sure it's so cut and dried. I know there are quantum mechanical approximations that are based on "classical mechanics" and then if necessary relativistic corrections are tacked on.--Matt Stoker

On that topic, I came here to find out what the "opposite" of Newtonian Mechanics is so I could link it from Aerodynamics but there seem to be many different fields; now I'm confused. Could someone tell me what the field is when one can no longer assume conservation of mass and conservation of energy? moink 23:04, 26 Dec 2003 (UTC)

You can always assume conservation of energy; however in relativity conservation of mass is an approximation

I tried to address this question in "3 Limits of validity" in the article. There is not exactly an "opposite". In aerodynamics, the fundamentally different physics is mostly electromagnetism. Electromagnetism and classical mechanics were made fully consistent, only with the use of relativity, but I can't think of a way the solution to that problem affects aerodynamics. Classical electromagnetism involves fields and wave, as does classical mechanics, but when the same entity shows both wave and particle properties, as in chemistry or optical shot noise, the relevant physics is quantum mechanics. David R. Ingham 04:14, 18 March 2006 (UTC)

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I've gutted the article and re-written major parts of it. It's still far from complete, but I'm structuring it after quantum mechanics, which I think has a very nice layout. Some of the removed material probably ought to be stuck back in, either here or in a separate article.

Comments are welcome. Hope I haven't ruffled any feathers :-P

Some changes, with reasons:

• Removed the description of SI units. They ought to go into the respective nodes for force, mass, and so forth; in my opinion they are distractions from the presentation of the theory.
• Removed most of the examples, but I want to put them back in somewhere. Some of the examples were rather disorganized, e.g. discussing the effects of gravity without having introduced gravitation. Also, Newton's law of gravitation is quite independent of the formal structure of classical mechanics, and that wasn't coming through properly.

Ultimately, I think we'll want to have links to the important sub-topics of classical mechanics: composite objects, inertial and non-inertial reference frames, oscillations, and so forth. -- CYD

Einstein long ago presented us with a radical new way to view the universe. His mathematical calculations and theories harbored destruction for the current theories of the time. The theories focused on objects such as: Planets, Galaxies, Nebulae, Gravity. Next, came Quantum Physics. These mathematical calculations and theories focused on the tiny world. Atoms, Quarks, Protons, Neutrons, Electrons...

Now, In their own right, each of the theories are correct. But, when the two theories had to be combined mathematically, they were incompatible; the math would spit out nonsense.

Recently, a new theory called string theory has surfaced. The book by Brian Greene, called The Elegant Universe, explains the theory. When positioned "between" these two theories, it can connect the two; making them compatible, and causing another revolution.

Rockets/physics type stuff

Hi, I need a bit o help. See, in my science class we're making rockets (out of pop bottles, but still). We can add wings, weights, etc., and the point (the part we get graded on) is to get them to go up about 20 feet (which I can do) AND to get them to go straight up and straight back down w/in 5 ft. I think of where we launched it from. Any ideas @ all on how to do this? Thanks a bundle! I don't know how often I'll be checking back here, so my e-mail is DFINEDFINE1@aol.com Thanks, much! ~~Taylor

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Could someone explain how a problem involving a changing mass would sound such as decreasing rocket propellant or something like that. I'm just trying to get a feel for this since up till now I've just understood Newton's Second Law as F=ma or F=m(dv/dt). From the Newton's Laws of Motion page I got the equation F=ma+v(dm/dt) for calculating the force with a variable mass, is this right? thanks - James

examples section

It appeared that the examples section had been the result of several clashing writers, so I tried to clean it up and get a good explanation for the galilean transformation, which I think is what was trying to be explained before by the standard two cars example.

Small copyedit

In this sentence, Classical mechanics can be used to describe the motion of human-sized objects (such as tops and baseballs), many astronomical objects (such as planets and galaxies), and certain microscopic objects (such as organic molecules.) ... wouldn't it be better to replace "human-sized objects" without a more accurate, less ambiguous phrase--baseballs are NOT the size of humans. Perhaps we could say something like "objects easily perceived and manipulable on the human scale"...I'm not a great wordsmith, someone help me out 70.57.137.163 04:44, 8 Apr 2005 (UTC)

   I changed it to "macroscopic", which means just that.
   --Jeepien

Tycho ?

The lead sentence names the Classic Three post-Copernican astronomers as founders of classical mechanics. Why is this? Tycho was a superb observational astronomer, but the only thing resembling physics in his work is his abandonment of crytalline spheres for [nothing in particular, so far as I know, but that's better than spheres]. Can someone explain what I've missed here? --Dandrake 19:53, August 1, 2005 (UTC)

ultraviolet catastrophe

Isn't this more a problem of classical electromagnetism? It is the same to quantum mechanics, which includes both, but it seems to make a difference when talking about classical mechanics. --David R. Ingham

I see now that "electrodynamics" is just a redirect.

I think I will move the ultruviolet catastrophy to E&M. --David R. Ingham

Sums of P

I regard that net forces are zero when $\sum P=0$ and are also the oppesite of them. Main,brief reason might be $F={\frac {d(mv)}{dt}}=0$. :)Might be right?

--HydrogenSu 18:07, 2 February 2006 (UTC)

Do not combine Classical Mechanics with Newtonian Mechanics

Newtonian mechanics is a subfield of classical mechanics. Classical mechanics also includes La Grangian mechanics, Hamiltonian mechanics, and continuum mechanics. Newtonian mechanics was the first instance of classical mechanics, but it is not the whole of classical mechanics.

--F3meyer 20:37, 2 April 2006 (UTC)

Do not combine classical with Newtonian

I agree with F3meyer, and would only add that Einstein's theories of special and general relativity are the most obvious example of mechanics which are classical mechanics but not Newtonian. For that reason, I have taken it upon myself to remove the meger recommendation out of the article and put it into this discussion. Tom Lougheed 18:12, 7 April 2006 (UTC)

I also agree with F3, but notice that there is no general agreement that relativistic mechanncs is "classical", see below. Harald88 01:23, 20 May 2006 (UTC)

Redirect Link?

If Newtonian mechanics is different from Classical, "Newtonian Mechanics" shouldn't redirect to this page, right? Scipio Carthage (talk) 15:36, 21 March 2008 (UTC)

Is General Relativity Part of Classical Mechanics?

I am concerned that the partition of Mechanics into Classical Mechanics and Quantum Mechanics is not a generally agreed concenpt in Physics. I do agree that this kind of partition of Mechanics is good, and do not want to remove it from the article. I would just like to know what support there is for including Special and General Relativity as part of Classical Mechanics.

Since first studying Mechanics, I have regarded Special Relativity as a transitional part of physics and General Relativity as modern physics. The development of Quantum Mechanics, Special Relativity, and General Relativity all occured about the same time, about 1920. So there is no basis in chronology for treating General Relativity and Quantum Mechanics separately.

If we take a theoretic approach, Newtonian Mechanics, Lagrangian Mechanics, and Hamiltonian Mechanics have a different axiomatic basis, but they are almost dual in their theorems and to the observational facts to which they are faithful. However Special Relativity is more general in the range of facts to which it is faithful. It also requires a radical new axiom that the speed of light is the same in all inertial frames of reference. General relativity requires several new axioms not included in classical mechanics. General Relativity is faithful to observations involving speeds near the speed of light and involving mases comparable or greater than a solar mass. Newtonian Gravitational theory on the other hand is completely consistent with Newtowniam Mechanics, Lagrangian Mechanics, or Hamiltonian Mechanics. So from a theoretic approach, General Relativity is not part of Classical Mechanics.

Please discuss this topic. If there is a basis for including General Relativity in Classical Mechanics, this article will be better if that basis is referenced.

--F3meyer 23:33, 23 April 2006 (UTC)

I just wanted to start this discussion. All textbooks that I studied (such as by Alonso&Finn) have three groups:

- Classical mechanics - Relativistic mechanics - Quantum mechanics.

Thus it's incorrect to state that classical mechanics includes relativistic mechanics, as this article now does. Harald88 01:27, 20 May 2006 (UTC)

H-bar multiplied by 2 pi ?

The equation in the 'classical approximation to quantum mechanics' section includes the value '${2\pi \hbar }$'. The ${hbar}$ is equivalent to Plank's constant divided by ${2\pi }$. So ${hbar}$ multiplied by ${2\pi }$ is Plank's constant. So there must be a mistake somewhere - why not simply write ${h}$ instead of ${2\pi \hbar }$ ?

Displacement

Should position be changed to displacement because velocity is a vector not a scalar value. I thik it should, while position is correct, displacement is clearer and it implies displacement from an origin which it must be measured from.--James086 12:04, 8 August 2006 (UTC)

I need the (simple version) physics for determining the speed of wind required to topple a vehicle such as a a semi-trailor. I believe there is some ground surface friction to overcome and the density of air must be known as well as the mass of the vehicle. How do these all tie together to move or topple the truck and determine at what wind velocity would this occur?

About the introduction

The article should not start out as it does. It should explain what the topic "classical mechanics" is about. Preferably in general terms that can be understood by non-specialist readers. The advanced taxonomy can be saved for later, and should be moderated (thermodynamics is not a part of classical mechanics, for instance). However interesting, it is unlikely that someone would look up this topic in order to learn about quantum mechanics. Do we need the leading paragraphs at all? Ulcph 01:31, 1 September 2006 (UTC)

Here's what I had in mind: move the concrete description to the top, and save the following for some other time:

Classical mechanics is a branch of physics which studies the deterministic motion of objects. It includes several different branches which represent specialised forms or stages of development:

• Newtonian mechanics
• Lagrangian mechanics
• Hamiltonian mechanics
• Special Relativity
• General Relativity
• thermodynamics
• statistical mechanics
• continuum mechanics
• geometric optics

Most of the above are in some way equivalent, either exactly equivalent or equivalent under special circumstances. For example, Lagrangian mechanics is exactly equivalent to Newtonian mechanics, always, but in its simplest form, Hamiltonian mechanics is only equivalent to the prior two when no frictional or drag forces are present. In other cases, an abovementioned branch of mechanics is a convenient specialised form: Newtonian mechanics can be used to deduce statistical mechanics, and statistical mechanics directly produces, more accurately, all of the results of thermodynamics.

Classical mechanics excludes any physics which involves the uncertainty principle, so quantum mechanics is not "classical", and is sometimes called modern physics by contrast. Some sources also exclude so-called "relativistic physics" from that category. However, a number of sources do include Einstein's mechanics, which in their view represents classical mechanics in its most developed and most accurate form.

It seems to repeat things that are discussed further on anyway. Ulcph 02:28, 1 September 2006 (UTC)

Please note that an intro usually includes a basic summary! The difference in definitions is too important to omit from the intro, so I reinserted that. Apart of that, I agree that most of that text does not need to be in the intro. Harald88 09:06, 1 September 2006 (UTC)

Strangely, looking at my edit it does not appear to have been taken away, and I don't believe I did. So thanks. I only put in a space to set apart the nice hidden science-promo, in HTML-comments. Which is almost too nice to lose? Ulcph 19:55, 1 September 2006 (UTC)

I don't follow what you say...

And I now notice that I omitted by mistake:

"Quantum physics (and more specifically quantum mechanics) refers to developments since approximately 1900, starting with similarly decisive discoveries by Planck, Einstein, and Bohr".

But on second thoughts, it's better to not reinsert that there: an elaboration about quantum-mechanics doesn't really belong in the intro of an article about classical mechanics anyway. Harald88 22:59, 1 September 2006 (UTC)

Just that I did not see that I deleted that sentence - and I tend to agree that it may be rather a distaction at this place. What else I tried to say was that, I found this hidden away:

The notion of “classical“ may be somewhat confusing, insofar as this term usually refers to the era of classical antiquity in European history. While many discoveries within the mathematics of that period remain in full force today, and of the greatest use, the same cannot be said about its "science". This in no way belittles the many important developments, especially within technology, which took place in antiquity and during the Middle Ages in Europe and elsewhere.

However, the emergence of classical mechanics was a decisive stage in the development of science, in the modern sense of the term. What characterizes it, above all, is its insistence on mathematics (rather than speculation), and its reliance on experiment (rather than observation). With classical mechanics it was established how to formulate quantitative predictions in theory, and how to test them by carefully designed measurement. The emerging globally cooperative endeavor increasingly provided for much closer scrutiny and testing, both of theory and experiment. This was, and remains, a key factor in establishing certain knowledge, and in bringing it to the service of society. History shows how closely the health and wealth of a society depends on nurturing this investigative and critical approach.

Certainly gets right to the point - but maybe someone Bowdlerized it. Ulcph 22:42, 8 September 2006 (UTC)

merging classical and Newtonian:calling all mechanicians

Hello,

I see the consensus above that Newtonian mechanics should not be merged with this page. At least to me it seems that you are not basing your arguments upon the actual contents of that Wikipedia article, but on knowledge you have (above & beyond that article) which tells you that the two topics are separate and distinct.

Good.

In my opinion, the contents of that article could very easily be merged into this one. This has nothing to do with the distinctions that you have drawn here on the talk page, and everything to do with the fact that the Newtonian mechanics article offers an extremely brief & surface treatment.

I'm not arguing pro- or anti-merge; I'm asking for help. Would some of you who are knowledgeable in this area please do these two things:

1. either bulk up Newtonian mechanics or delete its contents and turn it into a redirect (a fate it probably doesn't deserve -- with the caveat that it might significantly overlap Newton's laws of motion)
2. remove the merge request from Newtonian mechanics.

The merge request has been sitting there since January, altho it was very recently turned into a "merged disputed" tag.

Could Newtonian mechanics instead be merged with Newton's laws of motion?--Ling.Nut 20:19, 18 September 2006 (UTC)

Many thanks --Ling.Nut 19:08, 18 September 2006 (UTC)

Newtonian Kaons

Here's one I have not seen before:

"Newton's own explanation avoided wave principles and resembled more the explanation for the decay of the neutral Kaons, K0 and K0 bar. That is, he supposed that the light particles were altered or excited by the glass and resonated."

It seems to "explain" something relatively simple in terms of something exceedingly complicated (probably involving the third generation and the Kobayashi-Masakawa matrix). We can do without. Ulcph 17:38, 28 September 2006 (UTC)

History

Needed a remake. Besides the beauty above, it preserves and enhances what was already there. And adds a few niceties. Ulcph 18:55, 28 September 2006 (UTC) Bold text

Simple Introduction

Some other science articles are starting to produce introductory versions of themselves to make them more accessible to the average encyclopedia reader. You can see what has been done so far at special relativity, general relativity and evolution, all of which now have special introduction articles. These are intermediate between the very simple articles on Simple Wikipedia and the regular encyclopedia articles. They serve a valuable function in producing something that is useful for getting someone up to speed so that they can then tackle the real article. Those who want even simpler explanations can drop down to Simple Wikipedia. I propose that this article as well consider an introductory version. What do you think?--Filll 22:45, 12 December 2006 (UTC)

Introduction

The wording is awful. Who wrote this? Special relativity and general relativity have nothing to do with classical mechanics. This is outrageous!!--Filll 22:45, 12 December 2006 (UTC)

Vectors

Do we really need the paragraph describing basic vector addition in the middle there? It's not really on topic. Perhaps someone should write a "vector math for physicists" article and link there. Comments? Aragh 10:45, 18 May 2007 (UTC)

Introduction

"Classical mechanics is used for..." is not a definition. How about: "In physics, classical mechanics is a theory of..."? Saying what something is used for doesn't necessarily tell what it is. - 207.61.202.185 23:46, 26 June 2007 (UTC)

a basic problem

I think there is a mistake .rational continuum mechanics is something different to classical mechanics.The later discuss point mass or rigid body motions,but the former is about construcing a mathemtical structure for mechanics of general deformable bodies.for any infomations ,look at works by Clifford Truesdell. I suggest that this page must completely change because one page for classical mechanics is enough ,but the rational mechanics does not have any pages. —The preceding unsigned comment was added by Aghamoallem (talk • contribs) 14:39, 27 June 2007.

also known as Newtonian mechanics

The phrase (also called Newtonian mechanics) has been added to the start of the lead. Actually it was originally worded "Newton physics", then "Newtonian physics", now "Newtonian mechanics". But is this worth adding at all? The alternative phrasing is already discussed at the end of the lead. —Duae Quartunciae (talk · cont) 13:57, 7 August 2007 (UTC)

Please put them all in brackets to find them directly by its links and its (correct!) different names. - Cf. e.g. Einstein effects and not Einteinian effects; especially Newton already saw light already like a wave and like a "corpuscle" (photon), ok?DeepBlueDiamond 16:51, 8 August 2007 (UTC)

OK. I have put in the correct phrasing for English, which is "Newtonian mechanics". There's nothing to wikilink, however. This is already the page for Newtonian mechanics; that link would just redirect straight back to here! Cheers —Duae Quartunciae (talk · cont) 04:49, 11 August 2007 (UTC)

Data

Notes:

1. The initial inertial velocity is a convention between the different reference frames.

2. The total tensional energy of an isolated system is equal to zero.

3. The total energy of an isolated system is equal to zero.

Sincerely,

Antonio A. Blatter —Preceding unsigned comment added by 216.244.213.251 (talk) 19:25, 11 March 2008 (UTC)

Taylor Expansion ind "The Newtonian approximation to special relativity"

There's an error in the Taylor expansion of the Lorentz Factor

$\gamma ={\frac {1}{\sqrt {1-v^{2}/c^{2}}}}=\left(1-{\frac {v^{2}}{c^{2}}}\right)^{-{\frac {1}{2}}}=\left(1+\left(1-{\frac {v^{2}}{c^{2}}}\right)^{-{\frac {3}{2}}}+...\right)$

in

$p={\frac {m_{0}v}{\sqrt {1-v^{2}/c^{2}}}}=m_{0}v\left(1+\left(1-{\frac {v^{2}}{c^{2}}}\right)^{-{\frac {3}{2}}}+...\right)$,

because that implies

$\gamma =\left(1+\gamma ^{3}+...\right)$,

and that is wrong. Also for $v<<c$ it follows $p=m_{0}v\left(1+1^{3/2}\right)=2m_{0}v$, which, again, is wrong. I will change that to

$p={\frac {m_{0}v}{\sqrt {1-v^{2}/c^{2}}}}=m_{0}v\left(1+{\frac {1}{2}}{\frac {v^{2}}{c^{2}}}+...\right)$

taken from

$\gamma =\left(1+{\frac {1}{2}}\beta ^{2}+...\right)$,

to be found also on the wiki page Lorentz factor.