Talk:Dynamics (mechanics)

From Wikipedia, the free encyclopedia
  (Redirected from Talk:Dynamics (physics))
Jump to: navigation, search
WikiProject Physics (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 

causes of motion[edit]

external causes or internal or both? 91.51.206.181 (talk) 23:40, 22 March 2010 (UTC)

This is an interesting question. What would constitute an internal cause of motion? Or in what context? In other words, can you be more specific or give an example? Then maybe this question could be answered. Other than that, personally, I can only percieve external causes all the way down to the sub atomic level. Steve Quinn (formerly Ti-30X) (talk) 01:50, 23 March 2010 (UTC)

Expansion request[edit]

Kinetics (dynamics) is currently a redirect back to this article, which is quite annoying if you are trying to navigate there. -- Beland 07:59, 10 July 2005 (UTC)

State of this article[edit]

I came across this page and was very surprised to see that so little has been written about this topic. I've rated it as a stub article of top importance, considering that undergraduate entry level physics always starts with a semester of dynamics. Since there are many good physics articles, I would imagine it won't be too hard to piece together something that is at least B class. EMBaero (talk) 03:30, 9 December 2007 (UTC)EMBaero

How to fix the articles about Dynamics???[edit]

The current state of all articles related to Dynamics is not the best. I have encountered many pages that talk about the same thing or are related to each other and are not organized in a structured and logical manner. These are: Dynamics, kinetics, Kinematics, Equations of motion, SUVAT_equations, Displacement (vector), Acceleration, Velocity, Speed, Relative velocity, Rigid body dynamics, rigid body, Uniform circular motion, Centripetal force, Centrifugal force, Circular motion, Simple Harmonic Motion, Harmonic oscillator, Vibration, Damping, Damping ratio, Pendulum (mathematics), Rotational speed, Angular acceleration, Angular velocity, Angular frequency, Angular displacement, Rotational motion, Coriolis, Momentum, Angular momentum, Newton's law of motion, D'Alembert's principle, Virtual work, Friction, Mechanical work, Kinetic energy, Potential energy etc... (more need to be found). My proposal is to start from the Dynamics Page and structured the whole topic around this article. In this article the terms of Kinematics and Kinetics are explained and links to their corresponding sub-pages are provided (Particle Kinematics and Kinetics, and Rigid body kinematics and kinetics). Comments Sanpaz (talk) 20:54, 13 February 2008 (UTC)

A good proposal, but a big project. Brews ohare (talk) 00:07, 5 June 2008 (UTC)

Study vs "branch"[edit]

Thanks for the nice revisions, Brews ohare. I'll rewrite the opening statement to be: "Dynamics is the study of ...," and move the "branch" talk to history section. (Similar treatment can be applied to kinetics.) Hope this can emphasis on the common use today while preserving historic context. Sillyvalley (talk) 05:59, 18 September 2008 (UTC)

Hi Sillyvalley: I believe three editors were editing the article at the same time. So I may have lost some of your changes inadvertently. Brews ohare (talk) 17:08, 18 September 2008 (UTC)

I'm just glad that the article is active, doing more diligence. I disagree that the foundation of dynamics is postulated laws, unless we are talking purely about analytical dynamics - I can't imagine the two as equivalent. This is the same problem (more serious one) I have with the current electrodynamic article. Analytical dynamics (or anything else for that matter) is effectively theoretical. It cannot be the whole of dynamics. Sillyvalley (talk) 06:24, 19 September 2008 (UTC)

Kinematics[edit]

I have rewritten the article to be briefer and to eliminate what I found to be somewhat misleading or even erroneous remarks about kinematics. It also appears that definitions from dictionaries and encyclopedias are to be avoided, as they do not reflect technical usage. It is preferable to refer to texts on the subject for definitions. Thus, the reference to the definition in Encyclopedia Brittanica is deleted as erroneous. Brews ohare (talk) 17:05, 18 September 2008 (UTC)

In the section "Dynamics and its relation to kinetics and statics" one idea is missing, which was there before: That Classical mechanics was considered divided into Dynamics and Statics, as suggested by Timoshenko, Hibbler, Beer and Johnston, etc; with Dynamics being divided into Kinematics and Kinetics. Sanpaz (talk) 17:13, 18 September 2008 (UTC)
The article states: In a still earlier point of view, dynamics was comprised of statics (the study of equilibrium and its relation to forces) and kinetics (the study of motion and its relation to forces). That seems to be a bit different. Should that combination be included too? Brews ohare (talk) 17:26, 18 September 2008 (UTC)
Not really. Your statement says Dynamics=statics+kinetics. But what the books I am referencing say is Mechanics=Statics+Dynamics(Kinematics, kinetics). I am just trying to include all definitions in the literature. If I am missing your point please let me know. Sanpaz (talk) 17:29, 18 September 2008 (UTC)
I guess we were editing at the same time, so I replied to your previous comment, which you just changed a bit. So, yes, I think that combination Mechanics=Statics+Dynamics(Kinematics, kinetics) should be included and referenced to Timoshenko for example. Sanpaz (talk) 17:38, 18 September 2008 (UTC)
- "another approach separated statics, and combined kinetics and kinematics under the rubric dynamics" - This statement does not describe the division of mechanics as clearly. Such historic discussions are not made elsewhere in Wikipedia, so it's important to paint a clear picture.
- "One approach combined statics and kinetics under the name dynamics, which became the branch dealing with determination of the motion of bodies resulting from the action of specified forces" - This statement still lacks reference? Again, it's better to spell out the "implied" other branch of mechanics.Sillyvalley (talk) 10:33, 19 September 2008 (UTC)
I took a stab at it. Take a look. Brews ohare (talk) 18:00, 18 September 2008 (UTC)
Excellent! Sanpaz (talk) 19:37, 18 September 2008 (UTC)
Thanks for adding reference to the static+kinetic=dynamics view. Sillyvalley (talk) 19:35, 20 September 2008 (UTC)

Dynamics vs analytical dynamics[edit]

A quick view of Greenwood 1977 convinced me that this is clearly a treatment of analytical dynamics alone, even though its title is "classical dynamics"; it is classical in the Hamiltonian/Lagrangian sense, not in the physics sense. Without a qualifier, dynamics concerns physics, which is based on empirical laws despite of application of mathematical models. I know that the difference between "empirical" and "postulated" can sometimes border on being philosophical, but a die-hard physicist wouldn't take a pure analytical approach. As long as it has not been disproved by empirical data and as long as the possibility exists for empirical data to disprove it, it is an empirical law. (Think Aristotle and Galileo.) But I don't have a suitable text at hand to make revisions. Hope some die-hard physicist can jump in. Sillyvalley (talk) 06:47, 19 September 2008 (UTC)

Made some effort to integrate previous revisions. I revived the structure set up in http://en.wikipedia.org/w/index.php?title=Dynamics_(physics)&oldid=239231754. Here are some of the considerations:

  1. Dynamics is used very widely in physics today. A generalized view suits an encyclopedia. An alternative statement could be "in physics, dynamics has a wide range of meanings. The focus of ..."
  2. Classical dynamics supercedes dynamics without qualifier, due to the latter's diminishing popularity.
  3. I realize that dropping "study" in the generalized explanation was a mistake because even with qualifiers, 'ics's are still studies.
  4. Eletrodynamics and thermodynamics are grouped together because "field" view and particle view are distinct in classical physics. Field view needs to be represented. —Preceding unsigned comment added by Sillyvalley (talkcontribs) 09:18, 19 September 2008 (UTC)
  5. Analytical dynamics is discussed separately, as it is really mathematical physics. The postulated laws doesn't really take the place of empirical laws; they are merely hypotheses that can correctly be transformed to "prove" empirical laws, whence gaining legitimacy' in physics.
  6. Historical discussions are pushed behind fundamental principles, as I hope to extend the principles section to contain a one-line description of each item. History must not distract content.

Otherwise new materials are largely left unchanged. If you folks agree, the dispute template can be removed. Sillyvalley (talk) 09:11, 19 September 2008 (UTC)

If you are concerned about the general meaning of the term "dynamics" a disambiguation page should be set up. It could refer to electrodynamics, thermodynamics, fluid mechanics and so forth, as well as analytical dynamics. The present page is in fact about analytical dynamics, in the sense of the preeminent source Whittaker. You seem to be worried that the article over stresses "mathematical physics" at the expense of empirical law. However, the subject is mathematical physics, though, as with all mathematical physics, the examples are related to empirical matters, such as planetary motion, precessing tops, and so forth. However, no attempt is made in this field to actually discuss any details of physical observation or experiment, experimental errors, experimental design etc. That fact of mathematical physics (and this article) need raise no fears about confusing hypothesis with empirical law. Brews ohare (talk) 15:53, 19 September 2008 (UTC)
In fact, it seems a disambiguation page like this is Dynamics, and does distinguish between the various meanings referring to the pages mentioned above. Therefore I have removed the lead-in sentence on dynamics as a general matter. Brews ohare (talk) 16:11, 19 September 2008 (UTC)
Well, looks like a good solution is to set up a Dynamics (mathematical physics) page, and add an entry to Dynamics disambiguation. After all, this page is titled "Dynamics (physics)", not "Dynamics (mathematics). Would this work? Sillyvalley (talk) 05:02, 20 September 2008 (UTC)

Proposed merger with kinetics[edit]

Opposed I see no advantage in merging these topics; the distinction between the two topics is more readily grasped if they are kept in separate articles. As a matter of usage, the engineering and physics communities seem to view the two topics differently. Brews ohare (talk) 17:16, 19 September 2008 (UTC)

Opposed That difference in usage is what I've been seeing lately with this discussion about Statics/Dynamics/kinetics/kinematics. From an engineering perspective, we are taught with the view of Dynamics=Kinematics+Kinetics, and statics being the other branch of mechanics. Only now, with this discussion, is that I found out about these different approaches from books on Classical Mechanics (physics approach) and books on Engineering Mechanics. But the question now is: How to deal with this two points of view? How do we structure the topics about mechanics? I say leave the kinetics article as long as both articles have the explanation on the different meaning of Dynamics (The engineering and the physics meaning). Perhaps the engineering books are behind in the correct treatment of the topic...I don't know.
I have a question for physicist: Is there another term for Kinetic energy? or why is the word kinetic still being used in this term and not in Dynamics? - Sanpaz (talk) 19:35, 19 September 2008 (UTC)
Accepted. I initially omitted the engineering context of the kinetics page. After recent rounds in dynamics page, a merger is now inappropriate. We can move that page to Kinetics (engineering), and give some history of the terminology in physics, so "Kinetics (physics)" redirection can receive a proper context. This method, though, has some problem with the use of kinetics in physical chemistry, as the word is used in a physics sense in that discipline. Another possible way to handle this is to keep the title, but emphasize that the term is still widely used in engineering (as is statics). The current state of the article kind of fall into the latter but can be improved. Sillyvalley (talk) 05:10, 20 September 2008 (UTC)

Factual accuracy[edit]

What exactly are the facts disputed on this page? Brews ohare (talk) 18:35, 19 September 2008 (UTC)

That dynamics equates analytical dynamics is disputed. (In physics, any way. See above section) Analytical dynamics is really mathematical physics, and not physics. Physics deals with empirical phenomena, whereas mathematical physics deals with postulations and their consequences. Hamilton himself in effect states that "s = 1/2 g t2" (Galileo) is dynamics, "f = m dv/dt" (Newton) is also dynamics. Sillyvalley (talk) 04:57, 20 September 2008 (UTC)
I am unclear about your view. The Dynamics page makes clear that there are many meanings for dynamics in physics. There is little doubt that one of the meanings is analytical dynamics. That point is made very clear in the Dynamics page and in the intro to Dynamics (physics). So I think it all looks just fine.
There is, however, a Mathematical physics page, and it lays claim to Hamiltonian mechanics.
So it appears to me that you are really proposing a rather large scale restructuring of the mathematical physics area, with a math phys disambiguation that would lead to quantum mechanics, stat mech, fluid mech, special relativity, and who knows what. The standard format would then suggest that Hamiltonian mechanics for example becomes Mathematical physics (Hamiltonian mechanics). Yeah, sure.
Inasmuch as dynamics in the meaning of analytical mechanics is common usage, it will still appear on the disambiguation list at dynamics page as Mathematical physics (dynamics). The present article that is now Dynamics (physics) will become this new Mathematical physics (dynamics). The page Dynamics (physics) then becomes an overview article leading into who knows what, exactly. It will need a total rewrite, as nothing in it as it exists right now is about the general subject.
I suggest you lay out a plan for this total re-arrangement before hacking away at it piecemeal. I don't have this kind of ambition, and would let sleeping dogs lie. Brews ohare (talk) 12:36, 20 September 2008 (UTC)

Maybe an approach is to rename this page Analytical dynamics, add it to the disambiguation Dynamics page and delete Dynamics (physics)? Brews ohare (talk) 15:37, 20 September 2008 (UTC)

I see your point about the revelations being too ambitious. But given the rich history and influence of dynamics in physics, it wouldn't be prudent to delete dynamics (physics) all together. (Disambiguation page is too limited for the purpose of presenting evolution and diversity of views, which is still important in an encyclopedia.) Here's a proposal that is moderate and manageable in scope: Keep the page's title, but structure it as the following.
== Dynamics in MathPhys ==
  • Analytical dynamics commonly associated with dynamics (no qualifier), based on postulated principles, characterized by Lagrangian/Hamiltonian formulations, etc.
== Dynamics in physics (empirical) ==
  • Original (Galilean/Newtonian) dynamics (no qualifier, sometimes classical dynamics) still one pillar of classical mechanics and the term widely taught in general physics, though significance as a standalone study has diminished. Proliferation of all kinds of active dynamics' in physics. History of semantics and role of dynamics.
== Fundamental principles ==
  • Empirical, analytical, philosophical, and so on
== ... ==
The order between analytical dynamics and classical dynamics is based on a perceived concurrent consensus that dynamics (no qualifier) is more commonly associated with the former. Whereas this can still be disputed, it can be revised later when more citations are available.
My concern is not about you and me - trained physicists, engineers, mathematicians always (or should) view encyclopedic presentations with a grain of salt. But Wikipedia has gained such momentum that (fortunately and unfortunately) a high school student (or worse, a law maker:-) can easily come to "the Web" for an authoritative answer, even for academic consultation. At its current state, one can easily leave with the impression that physics is a bunch of theories and math, even though Physics page may say otherwise. (As I mentioned, the current electrodynamics page is worse.)
Will this work? I can hack away a sandbox if you think it's worth a try, so you can preview and comment. Sillyvalley (talk) 19:35, 20 September 2008 (UTC)
Your proposal does not appeal to me. The proposed Dynamics (physics) page is becoming extremely broad. It is ranging into the area of philosophy of science, which is outside its scope. On such a page the present discussion of analytical dynamics is far too detailed, and should be put on an Analytical dynamics page instead. Brews ohare (talk) 15:39, 21 September 2008 (UTC)

Moment of inertia[edit]

Moment of inertia is not an essential concept as mass. It is introduced to simplify motion of a rigid body so we can compose motion using the moment (of center of mass) and a rotational moment. At its bottom, Newton's law is at work. After adding the effect of all (infinitesimal) forces on all (infinitesimal) particles, there is no need for moment of inertia but that's a lot more labor.

When the geometric relationship among the particles is no longer constant (non-rigid), moment of inertia loses its convenience. So in places like elastic mechanics, fluid mechanics, and continuum mechanics in general, this concept is not used. Sillyvalley (talk) 05:37, 20 September 2008 (UTC)

I wouldn't argue about the fundamental ranking of mass vs. moment of inertia. But what is meant by bringing up moment of inertia is the issue of things related to orientation of the body, like rotational motion, for example. Mentioning only mass tend to focus the mind on point particles, and to push the big topic of rigid body motion into the background. As chapters on rigid body motion are found in every text, this topic deserves some presence here. Brews ohare (talk) 12:14, 20 September 2008 (UTC)
Let's think about a better way to introduce moment of inertia, angular momentum, torque, etc. (Maybe in the "Dynamics in (empirical) physics" section.) As Lagrangian/Hamiltonian principles are also used in continuum mechanics, placing moment of inertia right beside mass could easily be confusing. If I understand it correctly, Lagrange and Hamilton didn't limit themselves to rigid body, and did not concern themselves with specialized concepts in formulating their equations. Sillyvalley (talk) 19:35, 20 September 2008 (UTC)
The analytical dynamics discussion should not include an "empirical physics" section. The allusion to moment of inertia is not intended as part of an all-inclusive list, nor to exclude other matters. It is just to widen the reader's perspective a little by suggesting more than dynamics of partilce is involved.
I find that your concept of this page is not compatible with a discussion of analytical dynamics, so I'd recommend moving all the present material onto a new Analytical dynamics page, and rewriting the dynamics (physics) page with a banner
For dynamics as discussed in analytical dynamics, see Analytical dynamics.
. Brews ohare (talk) 15:47, 21 September 2008 (UTC)

Relativistic dynamics[edit]

I was mistaken in referencing the Relativistic dynamics page. But there is actually a citation in the disambiguation page in support of the view that some consider the simple application of special theory of relativity to classical dynamics as relativistic dynamics. This page shares the responsibility to elaborate these views. It is not an unnecessary repetition. Sillyvalley (talk) 19:35, 20 September 2008 (UTC)

Reorganization[edit]

Please see new page Analytical dynamics and revision of Dynamics disambiguation page. Brews ohare (talk) 15:59, 21 September 2008 (UTC) hinlih fgfceyl98nn/ —Preceding unsigned comment added by 121.246.146.226 (talk) 04:33, 9 June 2009 (UTC)

Merger Analytical dynamics and Dynamics[edit]

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section. A summary of the conclusions reached follows.
The result of this discussion was no consensus.

I know this comes from a previous discussion, but I do not see the need for having two separate articles about Dynamics and Analytical dynamics. They are very much about the same thing, which is the motion of bodies as forces are applied to them. Perhaps the initial intent of the article Dynamics (physics) was for it to be of a general nature, trying to describe how the word dynamics was used in all branches of physics. However, that is not the case. The article currently is about mechanics. I suggest leaving the article Dynamics_(physics) (I would even change the name to Dynamics_(mechanics)) and simply stating in it what anaylitical dynamics is. sanpaz (talk) 19:35, 31 May 2010 (UTC)

I think it would be great if someone could sort out the wider mess that we've got into with these articles! I think before starting this, we need to have a consensus view on how the topic should be arranged, and what articles we should have. Several articles suggest that some authors split classical mechanics into three areas:
  1. equilibrium and its relation to forces (statics)
  2. motion and its relation to forces (kinetics)
  3. implications of observed motions without regard for its causes (kinematics)
but most modern authors treat 2 and 3 as a single area (dynamics). (Of course as you note there's the added complication that most of these words are also used to mean other things - e.g. reaction kinetics, molecular dynamics, dynamics as a general word for the time-evolution of physical processes, kinematics in the sense used in biomechanics, etc.) I would be in favour of having articles on statics and dynamics (probably under the name "Dynamics (mechanics)") and having kinetics and kinematics both redirect to dynamics. (So to finally answer your question, my !vote is merge.)
Alternatively, how about merging all of them into Classical mechanics?
Either way, I think it's then necessary to stop well-intentioned people from recreating the problem - we have gone round this loop before - see Dynamics (physics) from December 2008. Djr32 (talk) 22:31, 31 May 2010 (UTC)
I realized awhile back that this situation is not easy to sort out. First, allow me to present an argument stated in one section of the Analytical dyanmics article. Clicking on that link will bring you to the relevant section. Here is the argument:
"Today, dynamics and kinematics continue to be considered the two pillars of classical mechanics. Dynamics is still included in mechanical, aerospace, and other engineering curriculums because of its importance in machine design, the design of land, sea, air, and space vehicles and other applications. However, few modern physicists concern themselves with an independent treatment of "dynamics" or "kinematics", nevermind "statics" or "kinetics". Instead, the entire undifferentiated subject is referred to as classical mechanics. In fact, many undergraduate and graduate text books since mid-20th century on "classical mechanics" lack chapters titled "dynamics" or "kinematics" .[3][10][11][12][13][14][15][16][17] In these books, although the word "dynamics" is used when acceleration is ascribed to a force, the word "kinetics" is never mentioned. However, clear exceptions exist. Prominent examples include The Feynman Lectures on Physics".
To me the title of this section states it even more succinctly - "Fundamental importance in engineering, diminishing emphasis in physics".
In any case, I think merging all of these into the article "Classical mechanics" is the best solution. This way all the caveats to naming conventions can be in one article, besides the valuable content itself. Truthfully, sometimes this set of articles seem almost indistinguishable to me. In addition, all these concepts sometimes appear to be just another way of discussing Newtonian mechanics. Hence, all the more reason to merge all of them into one article, and edit from there. I am mostly relying on memory here, from editing and attempts at editing a few of these articles. So, I vote, merge all into Classical mechanics. ----Steve Quinn (formerly Ti-30X) (talk) 03:11, 1 June 2010 (UTC)
I do agree with merging it to Classical Mechanics. Now that we are on this subject I think the whole set of classical mechanics articles, starting with the main article, need to be improved substantially. I think we can agree that the whole set of classical mechanics articles (just see the navigation panel for classical mechanics, and all the articles I have been collecting) is in disarray. It is not a criticism of the content but on the organization and the repetition of content. To give you an example: see the merging tag of circular motion and non-inertial reference frame a placed in those articles. There is a lot of repetition. And let's not talk about fictitious forces, and how many articles include a whole section of that. What has happened, I think is that a lot of those articles started in isolation, without a context. Angular velocity is a concept, so somebody created an article about it; however, Angular velocity is not something that requires a whole article. The only article that should exist would be Rotational motion, or may be circular motion (that is another discussion), and the concepts of angular velocity, angular acceleration etc would be included in it.
I would like to start a conversation (more like a task) in the classical mechanics talk page (I'll do that later today), about this issues. I have been thinking about this for a long time (see discussion on this talk page of Dynamics above from 2008 I think). It is a big task to streamline all these articles. But, I think by working from the top of the hierarchy of articles (classical mechanics, Kinematics, dynamics (mechanics), Inertial reference frames, etc) things can improve little by little.
I think we need to work together on this. I know that many of you guys are very interested in classical mechanics, and would like to have a great set of articles that are as good or better than a regular text book. (This last inspirational segment was for free :) ).
I would like to see your take on this or if you guys have more ideas. sanpaz (talk) 14:52, 1 June 2010 (UTC)
I think sanpaz has a really good idea here. And the "merger proposal" tag in circular motion only underscores the need for an improvement project such as this one. This would be an opportunity for a "team" of editors to streamline, or merge articles. It is also an opportunity to remove repetitious material. In addition, I think the idea of working from the top down would probably be an effective approach. I think your example of "Rotational motion", or "circular motion" and the concepts of angular velocity, angular acceleration etc is a good illustration of the issue at hand. And of course, hopefully, effective editing can be accomplished with these articles as well. ----Steve Quinn (formerly Ti-30X) (talk) 17:17, 1 June 2010 (UTC)

Hi! guys I see you all have a good point of view however let me say mine. When we (engineers/engineering professors) refer to dynamics few things come to mind: dynamics as in rigid body motion and dynamics as in vibration. Another name for vibration is structural dynamics. Another name for rigid body motion is analytical dynamics. Therefore dynamics in general should include both analytical dynamics and strutural dynamics. My suggestion is to edit the pages to reflect this. I prefer to have three pages one discussing dynamics and another two one discussing analytical and another for structural. I would redirect structural dynamics and/or vibration one to the other. The same for rigid body dynamics and/or analytical dynamics. I do not know how to direct or have more than one keyword to direct for a specific page.Dr eng x (talk) 04:50, 2 September 2010 (UTC)


The above discussion is preserved as an archive. Please do not modify it. Subsequent comments should be made in a new section.