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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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)

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 H-bar is equivalent to Plank's constant divided by 2 pi. So h-bar multiplied by 2 pi is Plank's constant.