Talk:Momentum

message: The introductory paragraph is somewhat obscure and is not meaningful from a lay perspective; this section should give a good physical insight into momentum and why it is important, not simply give a mathematical definition and some scientific statements which happen to be true. Metsfanmax (talk) 18:59, 2 July 2009 (UTC)
replies: text: I agree. The first paragraph of an article should be comprehensible to someone with with minimal experience reading descriptions of mathematical concepts. Otherwise we risk discouraging people from learning about this, an article that's very important to WikiProject Mathematics. Saprophage (talk) 17:12, 15 May 2010 (UTC)

text: I agree. This is a regular problem throughout the science and mathematics articles in Wikipedia. It should be possible for someone doing their high-school homework to look up a subject and get a comprehensible explanation. Although the present policy in WP is purist and technically impeccable, these articles are virtually useless for all but the cognescenti. JMcC (talk) 09:58, 22 July 2012 (UTC)
replies: text: I agree too. I have noticed a tendency in articles in the physical sciences for a useful, clear and simple introduction to evolve, suitable for teenagers and the uninitiated; and then someone comes along and inserts a statement about relativity, or the speed of light, or quantum mechanics. This statement is technically correct (as far as I can tell) but arguably inappropriate in the introduction. The best defence we have against this tendency appears to be WP:Make technical articles understandable so I guess we need to wield that as effectively as possible so these articles have something useful for the uninitiated. Dolphin (t) 12:56, 22 July 2012 (UTC)
thread_title:  Introduction 

message: We had a complaint at WikiProject Physics (see Simple explanations, please) that this article is not easy for someone with no background in physics to read. There are some good efforts in this article to explain things simply, but often they come after more difficult concepts like frame dependence or Noether's theorem. I am reorganizing the article to put more difficult material later. RockMagnetist (talk) 16:27, 22 July 2012 (UTC)
replies: text: There may have been a thread called Simple explanations, please at some time in the past, but it isn't there now. I suggest you find a diff or two to show Users exactly what was said in the complaint. Dolphin (t) 11:59, 23 July 2012 (UTC)
replies: text: Sorry, the link should have been to the talk page. It is fixed now. RockMagnetist (talk) 05:53, 24 July 2012 (UTC)

text: Why isn't there a section somewhere explaining the core idea itself simply in plain text?  — Preceding unsigned comment added by Bearsca (talk • contribs) 01:24, 1 August 2015 (UTC)

text: The first couple of paragraphs in the lede give a simple explanation in plain language. Remember Wikipedia is an encyclopedia, not a text book. I think the lede is appropriately introductory for an encyclopedia. Dolphin (t) 06:11, 1 August 2015 (UTC)
thread_title:  Accessibility 

message: The section Momentum#History of the concept has the appearance of original research, with many judgements stated without backing by an independent source. That is particularly true of the discussion of Newton's mechanics, with statements like this: "The extent to which Isaac Newton contributed to the concept has been much debated. The answer is apparently nothing, except to state more fully and with better mathematics what was already known. ". There is a lot of good material here, and I hope someone can find suitable third-party sources for it. RockMagnetist (talk) 16:44, 30 July 2012 (UTC)
replies: text: In its current state it may be incomplete, the talkheader items above show how. However, I don't see any justification for the OR tag right now so removing it. 76.180.168.166 (talk) 18:46, 14 February 2013 (UTC)
replies: text: I gave specific reasons just above your comment. You should discuss them before deciding that the tag is not justified. RockMagnetist (talk) 19:00, 14 February 2013 (UTC)
replies: text: I only quickly read the section, so I don't wanna judge if it still contains OR, but the particular passage you quoted above is not in the article any more. Maybe you want to check it again. — HHHIPPO 19:18, 14 February 2013 (UTC)
replies: text: True, I hadn't noticed that passage was missing. I remember finding that not all the qualitative statements were really backed up by the references, but I'm not sure which were at fault. I'll go ahead and remove the tag. RockMagnetist (talk) 19:28, 14 February 2013 (UTC)
thread_title:  Original research 

message: I removed the section on analogies with mass and heat transfer. It is misleading, because the viscosity law of a Newtonian fluid is not an equation for momentum transfer, although it does contribute to the equation for conservation of momentum. Similarly, the relevant analogues for heat and mass are also conservation equations. RockMagnetist (talk) 16:57, 4 August 2012 (UTC)
thread_title:  Analogies 

message: In the animation, the top "box" covers more ground than the bottom one does.  Further, shouldn't they always meet in the middle?  I was lost for a second trying to figure out just what was trying to be taught to me because of this.  I'd propose the v's be the same, top and bottom, and that the boxes on the bottom start at far left and far right so that they meet at the same place as the collision on the top.
Tgm1024 (talk) 13:32, 9 September 2012 (UTC)
replies: text: What I'd like to see is the right box starting at rest in both frames and the other two boxes starting from the left with the same speed. However, these graphics were made by someone in Germany in 2006, so anyone wanting to change them will probably have to start from scratch. RockMagnetist (talk) 15:24, 10 September 2012 (UTC)
thread_title:  Elastic Collisions animation not quite right? 

message: I made a first pass at writing a section on variable mass systems. Possible issues:
* I didn't really put in much of a derivation of the variable-mass formula since this is already done at variable-mass system (and also Tsiolkovsky rocket equation, though this is not linked in the section).
* I avoided the phrase variable-mass system since the "system" essentially gets redefined halfway through the derivation. It seems confusing to talk about "variable-mass system" this and "variable-mass system" that, and then say "just kidding, here's the real system we need to analyze". Zueignung (talk) 03:32, 11 September 2012 (UTC)
replies: text: I like it! I agree that there is no need to derive the formula here. RockMagnetist (talk) 06:09, 11 September 2012 (UTC)
replies: text: Yea just about to say the same. Good work! Maschen (talk) 06:10, 11 September 2012 (UTC)
thread_title:  Variable mass 

message: This article says that momentum is a vector. But is not it really a covector? At least generalized momentum   p_j = \frac{\partial \mathcal{L} }{\partial \dot{q}_j} looks like covector to me.  --Alexei Kopylov (talk) 21:52, 23 May 2014 (UTC)
replies: text: I think physicists don't generally distinguish between vectors and covectors. Certainly, it would only cause confusion in the earlier parts of this article that are (intentionally) written at a level that a high school student would understand. RockMagnetist (talk) 17:09, 24 May 2014 (UTC)
replies: text: I agree that we should not scare high school students with words such as covector. But should at least mention it somewhere? I'm not sure what is appropriate place for this.Alexei Kopylov (talk) 09:08, 27 May 2014 (UTC)
replies: text: The section on relativistic momentum already has a passing mention of position as contravariant and momentum as covariant. (Actually, it said momentum is contravariant, so it's just as well you drew this to my attention!) The books I have read (like Goldstein's Classical Mechanics) call both vectors (contravariant and covariant), rather than calling one a vector and the other a covector. But we could add a footnote mentioning the alternative terminology. Is there some area of physics where you see it used? RockMagnetist (talk) 16:03, 27 May 2014 (UTC)
replies: text: I'm not a physicist, I'm a mathematician.  I was confused, and I'm afraid someone else would be confused. But I'm not familiar with standard physics terminology, so I don't know how to change the article. Alexei Kopylov (talk) 05:47, 29 May 2014 (UTC)

text: Because a Minkowski space (or more generally a pseudo-Riemannian manifold) has a metric tensor defined on it, the covariant and contravariant vector spaces are dual spaces, so it's always possible to express any 4-vector as either a contravariant or covariant vector, by raising or lowering the index as needed.  However, any particular 4-vector is typically more naturally expressed as one or the other, and I believe you're right, canonical momenta at least are more naturally expressed as covectors.  But what trumps any discussion of naturalness is that equations have to at least be correct, and not mix contravariant and covariant vectors as if it didn't matter which of those a vector is.  Elementary vector analysis can get by with just ignoring the difference between contravariant and covariant vectors, because when using a standard basis or some other orthonormal basis on a Euclidean space, the components of the metric tensor are just the identity matrix, so the components of the contravariant and covariant versions of a vector are identical.  But you can't get by with ignoring the distinction on a Minkowski space.  (It isn't possible to define an orthonormal basis on a Minkowski space, because the metric isn't positive definite.)  Red Act (talk) 00:40, 7 August 2014 (UTC)
replies: text: For Minkowski space we have metric, but what about generalized momentum? Alexei Kopylov (talk) 20:33, 13 August 2014 (UTC)
replies: text: Ah.  When I wrote the above, I had just edited the "Four-vector formulation" section, so I was thinking about the relativistic version of momentum.  But the same thing applies with Newtonian momentum, except with the Euclidean metric instead of the Minkowski metric.  Newtonian momentum can be expressed as either a contravariant or a covariant vector, by raising or lowering the index as needed with the Euclidean metric.  Red Act (talk) 16:22, 14 August 2014 (UTC)
thread_title:  Is momentum a vector or covector? 

message: The article on the quantum momentum operator states "As it is known from classical mechanics, the momentum is the generator of translation," and "momentum" in that sentence is a link to this article.  However, this momentum article does not cover the concept of "generator of translations". It would be good if someone could add this.  Tpellman (talk) 01:55, 18 May 2015 (UTC)
replies: text: At this time the article mentioned that momentum conservation is connected to the symmetry of translation, but I agree that concisely describing momentum as the generator of translations would be helpful (it is not only true in QM, but classical mechanics also). M∧Ŝc2ħεИτlk 07:06, 10 June 2016 (UTC)
thread_title:  Generator of translation? 

message: There is a link to angular momentum but do we need a hat note to it since this article is specifically linear momentum?  RJFJR (talk) 20:04, 7 June 2016 (UTC)
replies: text: I think a hat note would be a good means to clarify the distinction between the two concepts. Dolphin (t) 20:43, 7 June 2016 (UTC)

text: I agree. RockMagnetist(talk) 21:13, 7 June 2016 (UTC)
replies: text: I have inserted a hatnote. See my diff. Dolphin (t) 04:22, 10 June 2016 (UTC)
thread_title:  Angular momentum 

message: One of the equations in this article has been revised multiple times recently. The main issue is whether  should be represented by a slash,
\gamma = \frac{1}{\sqrt{1-\left(v/c\right)^2}},
or as a vertical fraction:
\gamma = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}
or
\gamma = \frac{1}{\sqrt{1-\frac{\textstyle v^2}{\textstyle c^2}}}
Those in favor of the first version are trying to maximize the size of the characters; an IP editor claims this is arbitrary and has expressed a distaste for slashes. I have two comments:
# The Physical Review style guide recommends using slashes in the numerator and denominator of fractions "except where excessive bracketing would obscure your meaning or slashing would interfere with continuance of notation."
# I think a non-arbitrary criterion for the size of characters is that, if possible, they should all be the same size (and here I am including numbers).
Thus, I favor the first version. The third isn't bad, but requires rather more TeX commands than a simple equation like this should need. What is your preference ? RockMagnetist(talk) 15:28, 29 June 2016 (UTC)
replies: text: Fourth version preferred, immediately followed by third version. First and second versions rather not. - DVdm (talk) 15:36, 29 June 2016 (UTC)

text: With the addition of \textstyle, the size of the text/variables is as before any changes were made. 87.254.76.130 (talk) 15:39, 29 June 2016 (UTC)

text: I too prefer the fourth version narrowly over the first. RockMagnetist(talk) 15:40, 29 June 2016 (UTC)

text: "The third isn't bad, but requires rather more TeX commands than a simple equation like this should need." Please could you elaborate on what the correct number of LaTeX commands that an equation should need? 87.254.76.130 (talk) 15:55, 29 June 2016 (UTC)
replies: text: My point is that a given article should have a consistent style, but many people contribute to this article, so conforming to that style should be as easy as possible. And there is no question that the fourth equation is easier to format than the third. RockMagnetist(talk) 16:31, 29 June 2016 (UTC)
replies: text:  Could you be more specific about the difficulties in the two different forms of LaTeX? Would you like me to prepare further options for making things as easy as possible, as I can see other possibilities if this is an issue? I note that I am asking such a question. 87.254.76.130 (talk) 16:49, 29 June 2016 (UTC)
replies: text: Mainly I object to using \textstyle inside an expression. That is quite technical and unorthodox; it shouldn't ever be necessary to mix textstyle with displaystyle in the same equation. Please do feel free to suggest other ways of formatting this equation. RockMagnetist(talk) 16:59, 29 June 2016 (UTC)
thread_title:  Formatting an equation 

message: I scanned for British spellings "our" and "ise", and came up empty. "Generalize" is used frequently, therefore I conclude the article is already in American English. JustinTime55 (talk) 14:39, 11 August 2016 (UTC)
thread_title:  English variety 

message: In the "other units" section of the information box, the article lists "ft/s" as a unit of momentum. This seems like an error; ft/s stands for feet per second, which is a unit of speed and velocity (not momentum, at least as far as I am aware). Furthermore, the text links to the page for feet per second, which makes no mention whatsoever of momentum. Should this be changed, or is there something I'm missing here? 108.20.171.228 (talk) 22:51, 17 October 2016 (UTC)
replies: text: You are indeed missing something. The ft/s is multiplied by a slug, which is a unit of mass, so the product is in units of momentum. RockMagnetist(talk) 01:18, 18 October 2016 (UTC)
thread_title:  Listed alternate units 

message: Don’t declaration and acceleration produced during the infinitesimal contact period of time in collision affects the transfer of momentum (final velocities) of objects after collision2001:56A:7399:1200:3078:21D0:B447:EDC6 (talk) 05:24, 31 March 2017 (UTC)
thread_title:  Transfer of momentum  

message: Please, add "kinetic momentum" to the synonyms in first line.  — Preceding unsigned comment added by 81.40.235.248 (talk) 18:51, 31 August 2020 (UTC)
replies: text: I think that would be confusing because it is a type of momentum, not momentum in the broad sense. It is already mentioned in the third paragraph of the lead. I think that changing that mention to boldface would be justified, though, as there is a redirect here. RockMagnetist(talk) 14:35, 1 September 2020 (UTC)
thread_title:  Section: Kinetic momentum 

message: Change "In Hamiltonian mechanics, the Lagrangian (a function of generalized coordinates and their derivatives)" to "In Hamiltonian mechanics, the Lagrangian (a function of time, generalized coordinates and their derivatives)" 178.23.234.209 (talk) 20:38, 27 October 2020 (UTC)
replies: text: Not done: please provide reliable sources that support the change you want to be made. Goldsztajn (talk) 22:16, 27 October 2020 (UTC)
thread_title:  Semi-protected edit request on 27 October 2020 

message: There is discussion in Talk:Hamiltonian on where Hamiltonian should be directed. It seems now to direct to the classical version of Hamiltonian mechanics. Yet more often now, it is likely that the quantum mechanics version is meant. It then occurred to me that most likely momentum would direct to the classical explanation and not the quantum version, and it does seem that we have Momentum operator for the quantum version. (I might wonder why it isn't Momentum (quantum mechanics), but otherwise.) Without actually suggesting it, should all the quantum version be in its own article, with only classical here? Gah4 (talk) 12:20, 1 November 2020 (UTC)
replies: text: My feeling is that a discussion of the quantum version belongs in this article, with perhaps a more extensive discussion elsewhere (I agree with you about the name, but that's best discussed at Talk:Momentum operator). We already have Newton, relativistic and generalized momentum, and it's useful to have the different approaches beside each other for comparison. RockMagnetist(talk) 23:09, 1 November 2020 (UTC)
thread_title:  Hamiltionian 

message: "Momentum is also conserved in special relativity (with a modified formula)".
This phrase misleading, it is not the momentum that has been defined in previous paragraph the one that is conserved, but the spatial components of the four-momentum. 
To be clarified.  — Preceding unsigned comment added by 81.40.239.244 (talk) 12:43, 28 November 2020 (UTC)
thread_title:  Relativistic 

message: The article says:  when bodies come in contact there is always some dissipation.  Classically, it is hard to avoid some dissipation, but in quantum systems, there can only be dissipation if there are states available for energy to go into. When atoms in a gas collide, there is not normally enough energy to get one to the next available energy state.  Or, one might say that atoms never collide, but instead there is repulsion from the electron cloud. But it is Fermi exclusion more than electron repulsion that keeps atoms apart. In any case, in quantum systems there is not always some dissipation. Gah4 (talk) 18:35, 16 June 2021 (UTC)
thread_title:  '' when bodies come in contact there is always some dissipation'' 

message: On my iPhone 11, the introduction says "then the object's momentum p is", then shows the billiard balls with caption, then the formula floating all by itself below.  If it's possible, if someone could get the formula to stick with the paragraph it would be easier to follow.  Thanks.  
Pbackstrom (talk) 13:53, 30 December 2021 (UTC)
thread_title:  Format Introduction for iPhone 

message: following is for editing "Momentum" Page on Wikipedia.org:
NOTE : Recent research findings reported a novel equation for Momentum, which is NOT based upon  mass and velocity of the body under motion but, it is based upon the mass and "frequency" of the  particle under motion. You could find that research work at the DOI given below. This work is available online, for your kind information.
Research Article Title: "Kinetic Energy of a Particle Independent of its Mass & Velocity"; DOI:10.9790/4861-1501013441
So, I request you to kindly update this novel equation and derivation on Wikipedia for the benefit of the wide readers of Wikipedia.
Thank you
PS: I am suggesting the following edits for addition [from START to END, present below] into the "Momentum" Page of Wikipedia; you could add more if you wish. Related novel equation for kinetic energy is also discovered in that research work at the above DOI document. You could update it as well on the Kinetic energy page of Wikipedia.
---START of EDIT---
Novel equation for "Momentum" recently discovered by research and reported in the scientific literature is given below. This discovery was done by the Indian researcher Mr. Bhargava R. Kotur, as recorded in the above DOI document.
p = sqrt (h. n . m) 
In the above equation, p - stands for the Momentum, f - is the frequency of the body or particle under motion, m - is the mass of the body, and h - is the famous Planck's constant, sqrt - stands for the mathematical function "square root";
The derivation of the above work could be found at the DOI already mentioned earlier.
 --- END of EDIT --- Ganesh Siva75 (talk) 19:28, 10 February 2023 (UTC)
thread_title:  Novel Equation for Momentum - Reg;