Talk:Force

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Earlier talk archive at

• Archive 1
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Article listed at WP:GAR

In response ass

ScienceApologist's note on the GAN talk page, I have removed the current GA hold and instead listed Force at Good article reassessment, where it will receive wider attention from other GA reviewers.

The reasons I have taken this decision are elaborated in more detail on the GAN talk page, but to summarise, ScienceApologist's apparent disagreement with Awadewit's original GA review quick-fail, and the accompanying reversions to both the GA tag and the GA page nomination, would seem to imply that her decision is disputed. I have restored the GA fail tag - this should remain on the article even if it ultimately attains GA status, as it pertains to the article history and development. For future reference, it is also rather frowned upon to revert GAN page removals, since it implies the article was never reviewed and restores the original nom date (a complete re-nomination would have been more appropriate).

Regards, EyeSerene^TALK 10:45, 7 December 2007 (UTC)

I've closed the GAR. The consensus was not to list the article as GA, but to recommend renomination at GAN (as a fresh nomination). I disagree with EyeSerene about the fail tag since it states that "the article was not considered to be a good article at the time" and this had not actually been properly determined. I don't feel strongly about this, however, so if anyone does want to restore the fail tag, or even start an ArticleHistory template, with the GAN and the GAR, I won't complain. Geometry guy 19:58, 18 December 2007 (UTC)

No personal preference here; I was just restoring Awadewit's tag. I'll not quibble though ;) EyeSerene^TALK 08:26, 19 December 2007 (UTC)

GAN review

Resolved

 – All issues have been addressed. ScienceApologist (talk) 20:49, 11 January 2008 (UTC)

I will look at this article again, this is a beginning.

GA review (see here for criteria)

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This is a nice piece of work, but it still has some shortcomings with respect to the good article criteria.

1. It is reasonably well written.

   a (prose): b (MoS):

2. It is factually accurate and verifiable.

   a (references): b (citations to reliable sources): c (OR):

   One source is used over and over. For an article this long, more references should be used.

3. It is broad in its coverage.

   a (major aspects): b (focused):

4. It follows the neutral point of view policy.

   Fair representation without bias:

5. It is stable.

   No edit wars etc.:

6.  Done It is illustrated by images, where possible and appropriate.

   a (images are tagged and non-free images have fair use rationales): b (appropriate use with suitable captions):

7. Overall:

   Pass/Fail:

   Good luck improving the articleSriMesh | talk 02:06, 27 December 2007 (UTC)

some issues addressed, however not all, especially citations. Therefore processed a fail article verdict and removed from on hold status.SriMesh | talk 01:55, 3 January 2008 (UTC)

This again shows, that the GA review process is partially useless for articles about textbook physics. Judging the verifiability level to be "original research" because one standard textbook (by Feynman no less) is given as source is nonsense. In fact any inline references for this stuff is nonsense. This article is textbook physics, because you can go to the library of your physics department and take any textbook on mechanics and you'll find it to agree with the article. This is a level of reliability which cannot be documented by inline references. In fact, if you start to diversify the inline references by attributing different paragraphs to different textbooks this is near tio implying that these textbooks doesn't agree or doesn't give evidence for any chapter. --Pjacobi (talk) 13:16, 3 January 2008 (UTC)

We had this comment about a feature article which recently went under review as it didn't have enough citations to verify notability and needs Substantive reliable coverage. The article was Louis Riel and the review. The same was stated there as above, but in reference to biographies rather then science textbooks...The rationale was given that the bulk of the biography aligns with the consensus in all of the major biographies To preserve its feature status, citations were needed even if they were duh' and in every biography/textbook. If they are in every textbook, cite a few....which is what I am helping out with. SriMesh | talk 02:35, 5 January 2008 (UTC)

At the rate of change that this article is improving, it should soon achieve all comments made at all GAN, and if it is nominated again should pass soon. It was awkward to be processing close to the holiday season, should have extended the hold longer - sorrySriMesh | talk 02:41, 5 January 2008 (UTC)

This article suffers due to a lack of an overview section.

I find that some important aspects of forces have been left out. These relate mainly to the comparsion of the different forces. There is some info provide on this in the intro but it is very sketchy and lacks flow which makes it difficult for the reader to follow.

Some of the basic points I find are missing about forces are:

- some forces like gravity come from particles having quality that comes in one flavor but others like electromagnetic come from qualities that have two flavors resulting in both repulsive and attractive forces.

- some forces like friction and pressure are macro particle results. In other words it takes a bunch of particle working in concert for them to have any meaning.

- some forces like electric charge induce seemly different forces like magnatism when in motion. Others like gravity don't.

I am sure people can come up with others too. Some of these are indeed covered in more specfic sections but I feel that if the reader is to arrive as quickly as possible to a feeling for what forces are they need to be up front.

--RobertJDunn (talk) 19:10, 2 January 2008 (UTC)

Some comments on a paragraph

"In free-fall, this force is unopposed and therefore the net force on the object is the force of gravity. For objects not in free-fall, the force of gravity is opposed by the weight of the object. For example, a person standing on the ground experiences zero net force since the force of gravity is canceled by the weight of the person that is manifested by a normal force exerted on the person by the ground.[1]"

Unless in a vacuum, objects in free fall are usually opposed by aerodynamic drag. Objects not in free fall very often have accelerations that are not only due to gravity. Canceled is an OK term mathematically, but conceptually the reader might envision eliminated not equal and opposed. Ward20 (talk) 05:25, 3 January 2008 (UTC)

This is tricky. In the case of aerodynamic drag, the object is not really undergoing free-fall. Thus, an object that has reached terminal velocity technically is not weightless, for example. "Free" fall implies that there are no external forces other than gravity. You are correct about the problems with the term "canceled" however. I'll change that. ScienceApologist (talk) 19:03, 3 January 2008 (UTC)

After researching free-fall a little more rigorously I agree with you.

However, the Merriam-Webster Dictionary definition has a little ambiguity in it, "1: the condition of unrestrained motion in a gravitational field; 2: the part of a parachute jump before the parachute opens"

And the Wikipedia free fall article is contradictory to this definition and contradicts itself.

Perhaps an included free-fall definition might be helpful to cope with the seemingly widespread misconception that I had. Ward20 (talk) 23:00, 3 January 2008 (UTC)

Referencing

Many of the references are 'shared' between three books, one of which is Sears & Zemansky's University Physics; though the current referencing doesn't show what is referenced to which work. I have a 6th edition of Sears & Zemansky and am proposing to separate out those statements which can be attributed to Sears & Zemansky. — BillC ^talk —Preceding comment was added at 23:09, 3 January 2008 (UTC)

The link to an online copy of Maxwell's A Dynamical Theory of the Electromagnetic Field points to a website run by an over-unity zero-point energy group. Admittedly, they are simply hosting a copy of Maxwell's treatise, but still... bad. I'll see if I can find a better site to link to tonight. At worst, we can remove the links altogether, since it's the book that's the reference, not the website. — BillC ^talk 19:19, 7 January 2008 (UTC)

Good catch, Bill! We should also remove all the links elsewhere at Wikipedia. Here's a place to help us find them all: [1]. ScienceApologist (talk) 19:47, 7 January 2008 (UTC)

Sentence needs re-wording

•  Done As the mathematical formalism for Coulomb's Law, physicists of the eighteenth and nineteenth century became interested in the electric field which could be used to determine the electrostatic force on an electric charge at any point in space.

Very long sentence, doesn't flow from section to section. SriMesh | talk 02:45, 5 January 2008 (UTC)

Skipping GA on to FAC

I think that this article is good enough to skip GA entirely. I posted a peer review request and a copyedit request. Hopefully those are answered within the next few weeks favorably and we can put this article up for featured status. ScienceApologist (talk) 10:59, 11 January 2008 (UTC)

Good idea, with the amount of work you've done, it's sure to be a FA. -- penubag  00:51, 12 January 2008 (UTC)

Comments

Below are some comments in response to SA's review request. I hope they're useful. The current version of the article has a lot of good stuff! Gnixon (talk) 20:23, 12 January 2008 (UTC)

Good comments. I like your ideas on reorganizing especially. I'll be working on these in the next few days. ScienceApologist (talk) 21:32, 12 January 2008 (UTC)

Lead

This is obviously the hardest section to write, and will probably be the last thing to fall into place. Nevertheless, here are some comments:

1st paragraph

• "force is what" is a little awkward.
• Is "lift, push, pull" a standard breakdown of types of forces outside of aerodynamics?

  More or less. Push or pull is the typical breakdown. Lift was added by an aerospace afficionado and it is my opinion that it adds a little bit of conceptual flare. ScienceApologist (talk) 21:23, 12 January 2008 (UTC)

• Maybe consult dictionaries for guidance on defining the term. Always difficult to define such a fundamental, well-known concept in a reasonable way.

  Not only that, it's controversial. We have consulted dictionaries and the problem is that most dictionaries are a bit too imprecise in their formulations. We follow them to the extent that they offer good definitions. ScienceApologist (talk) 21:23, 12 January 2008 (UTC)

• Try to convey that force is a thing that tries to make an object accelerate. (But say it better than that!)

  The problem here is the idea that force is a "thing". It's not really a "thing" in the proper material sense. ScienceApologist (talk) 21:23, 12 January 2008 (UTC)

• Maybe mention Newton's laws or classical mechanics right up front in order to place the concept.
• Suggest moving torque, stress, etc., to a later paragraph in lead.

2nd paragraph

• "is mathematically equal to" is imprecise. Is net force defined this way? Is this paragraph about net force or force in general? Why not identify this statement as Newton's 2nd law?

  The distinction between net force and force is somewhat artificial. It's pedagogically clean, but conceptually it can lead to problems. When a force is balanced by another force, do any forces really exist? How do you know? ScienceApologist (talk) 21:23, 12 January 2008 (UTC)

3rd paragraph

• Last two sentences are a little unwieldy

Possible Reorganization

• 1st paragraph: attempt general definition
• 2nd paragraph: specifics centered on Newton's laws
• 3rd paragraph: rotation, stress, etc.
• 4th paragraph: State the four forces. Say how modern theories have come to use other stuff.
• Suggest leaving history for next section

History

General comments I like the organization: Archimedes, Aristotle, Newton, gravity, other fundamental forces, modern concepts. However, sometimes the explicit focus on the development of the concept is a little distracting. I think it's better to just say what Aristotle and Newton did, if you know what I mean.

1st par

• How about saying how the concept of force "arose"?

  Nobody knows. Forces are associated with machines, that's as good as it gets. ScienceApologist (talk) 21:27, 12 January 2008 (UTC)

2nd par

• Could be simplified with something like "Aristotle further developed the concept of force to explain how objects could be made to deviate from their natural motion (wikilink somewhere)."
• "theory" with its wikilink is a little generous here.
• "These shortcomings..." makes it seem like the ancients recognized the flaw in Aristotle's force. Was that the case?

  Ancients didn't, but pre-Galilean European medieval thinkers found flaws that they couldn't address because Aristotle was Catholic dogma (see impetus for example). Also some Islamic figures seemed to have inertia down pat. We can be clearer on this. ScienceApologist (talk) 21:27, 12 January 2008 (UTC)

• Galileo should get his own paragraph
• Did he actually perform the rolling balls experiments? I may be confused by the Tower of Pisa business.

  Yes, he actually did roll balls down inclined planes. At least, if you believe what he wrote, he did. ScienceApologist (talk) 21:27, 12 January 2008 (UTC)

3rd par

• Prefer to say directly what Newton did, excising "is recognized as", "to argue explicitly", "in essence", "first and only", and other qualifiers. This seems like a tough paragraph to write.

4th par

• Put "gravity" right up front, in the first sentence. It's key to the whole history.

5th par

• Good to discuss how modern theories don't lean on "force" like Newton and Maxwell did. I would be more explicit about it, discuss GR and QM more specifically.
• Should explain role of unifying "forces" in development of physics since Maxwell, particularly 20th century, and mention that unifying GR/QFT is a grand goal.
• Noether's theorem is definitely sexy, but way too technical here.
• Focus on saying that gravity is explained by dealing with energy-momentum; strong/electroweak explained within QFT (hard to do this well).

Descriptions

• Newton's laws need to come before the other stuff.

Organization

Taking a break from specifics and looking over the article, I have a proposal for reorganizing the topics:

1) Lead
2) Pre-Newtonian concepts of force
   2.1) Archimedes
   2.2) Aristotle
   2.3) Galileo
3) Force in Newtonian Mechanics
   3.1) Newton's laws
   3.1.1) Statics
   3.1.2) Dynamics
   3.2) Gravity
   3.3) Electromagnetism
4) Forces in Modern Physics
   4.1) Strong and Weak Nuclear Forces
   4.2) Modern Reformulations
      4.2.1) GR
      4.2.2) QFT
      4.2.3) Unification

History could be woven in throughout, particularly in the intros of Sections 3 and 4, and "four forces" could be mentioned in the Section 4 intro. Possibly Gravity and E&M could go into a "Classical Forces" section, but I think they work in Section 3, where one wouldn't be tempted to delve deeply into QED too early. The current article's content would all fit nicely in these sections.

Rotations and torque

This section is a nice description of the ideal case shown in the animation, but does not state clearly the force of gravity of the ball (which is not massless) and its resulting couples are not shown. Suggest in animation that be explained. Ward20 (talk) 19:19, 26 January 2008 (UTC)

GAN

This article was placed for GA review at Christmas, and my hold could have been extended. As all items are done and attended to, and now there is now another awesome idea on this page...please re-register it for GA review, so it can be passed, as I feel it is at GA IMHO, and let me know, and I'll send it to the GA page. Kind Regards...SriMesh | talk 01:14, 15 January 2008 (UTC)

Do we want to think about implementing Gnixon's peer review comments first? Sadly, it appears ScienceApologist has left the project and will not be here to implement them himself. — BillC ^talk 01:22, 15 January 2008 (UTC)

If nobody else is available, and if nobody objects, I may start trying to do that reorganization. Of course, if others want to do it, even better (and if people object, no problem). I wouldn't likely get to it until next week. Not sure whether I'd officially rate the article "good" just yet, but that's only one opinion. Glad to see there's interest in continuing to improve it. Gnixon (talk) 14:37, 18 January 2008 (UTC)

Defining Force

Two statements:

Definition In physics, force is what causes a mass to accelerate experienced as a push or a pull.

Nuclear forces the weak nuclear force is responsible for the decay of certain nucleons into leptons and other types of hadrons.

I know that these are conventionally unexceptional statements but they have always bothered me both with their apparent mutual inconsistency (accelerate - no - decay) and with the fact that nothing as such is being defined (what IS a force?).

George Berkeley, Newton's contemporary, admirer and critic complained that in making forces central to his analysis of the regularities of motion, Newton had merely replaced one mystery, the will of the spirit, with a multitude of mysteries. (Sorry, can't locate the reference.)

But consider this:

Electromagnetic forces With the development of quantum field theory and general relativity, it was realized that "force" is a redundant concept arising from conservation of momentum (4-momentum in relativity and momentum of virtual particles in Quantum Electrodynamics). The conservation of momentum, from Noether's theorem, can be directly derived from the symmetry of space and so is usually considered more fundamental than the concept of a force. Thus the currently known fundamental forces are considered more accurately to be "fundamental interactions".

Fundamental forces All the forces in the Universe are all based on four fundamental forces.

Am I correct in concluding from these that

• acceleration is caused by the net absorption or emission of gauge bosons bringing in or carrying away momentum from the mass

• forces are mathematical concepts intended solely to assist in analysing the trajectories of accelerated masses

• radioactive decay is, at present levels of knowledge, an uncaused random event in the course of which momentum is redistributed between the decay products through the absorption and emission of gauge bosons

• the mathematical concept which best assists in analysing the trajectories of products of the decay of certain nucleons into leptons and other types of hadrons is termed the weak nuclear force.

If this is correct, I'm sure that the light would click on for a great many people if something to this effect was added, perhaps at the end of the article but referenced as a caveat right at the start. GWHodgson212.67.102.183 (talk) 16:50, 24 March 2008 (UTC)

Thanks for your comments, GWHodgson! You are basically correct in your explanation of the situation. I'll add a bit more to see if that helps matters: The weak nuclear force is, in point of fact, what allows leptons and hadrons to interact. It's both a force of repulsion and attraction just like the electromagnetic force or the color force. Most of the time we see weak nuclear force acting repulsively (which is what radioactive decay is associated with) because it is much more likely to get a single particle to split than it is to get two weakly interacting particles to combine. However, in very high density environments such as those found during the formation of neutron stars, the attractive nature of the weak-nuclear force can cause some amazing effects. So let's workshop here how we can best get this subject across to the lay reader. ScienceApologist (talk) 18:33, 24 March 2008 (UTC)

Okay, so I thought a lot about this issue and thought that having a description of Feynman diagrams may help elucidate the matter. Please tell me what you think of the new section. ScienceApologist (talk) 15:07, 25 March 2008 (UTC)

Yes, I do find the inclusion of the section on Feynman diagrams helpful. The following might complete the job.

I suggest the the first sentence of the article be reworded as:

In physics, force is the perceptible cause of the acceleration of a mass (change in the rate or direction of its motion) and is experienced as a push or a pull.

and, to tie in the concepts, replace the first mention of momentum in the second paragraph with "momentum (quantity of motion)".

I'm speaking as a layman so the use of the imprecise term "motion" might be objectionable in a technical article, but I find it aids understanding. The suggested qualifications remind the unwary that accelerate doesn't just mean go faster and sets up the concept that momentum is something that can be carried.

The second part of the third paragraph usefully puts force into context but I suggest it be reworded slightly as follows:

Following the development of quantum mechanics, it is now understood that momentum is a fundamental property of particles and that, according to the standard model of particle physics, changes in momentum are the consequence of the net emission or absorption by particles of momentum-carrying gauge bosons. Effects which are at the macro level experienced as a "force" are the consequence of the aggregate effect of these boson-mediated fundamental interactions. In modern physics, only four fundamental interactions are known; in order of decreasing strength, they are: strong, electromagnetic, weak, and gravitational.[1] High-energy particle physics observations in 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a unified electroweak interaction. No gauge boson has yet been demonstrated for mediating the gravitational interaction and what is perceived as the "force" of gravity is more accurately attributable to the the effect of distortions by massive bodies of the curvature of spacetime as explicated in Einstein's Theory of General Relativity.

This wording expresses what I would like to be the case, ie that forces are artefacts of perception (which would have resolved Bishop Berkeley's complaint - he thought everything was an artefact of perception). I think this is a valid inference from reading the article in full but, if this is not the accepted view (and the articles on Force Carriers and Gauge Boson both seem to view forces as things which can be carried), then I would have to accept that an encyclopedia entry shouldn't stray too far into the realms of speculation.GWHodgsonSkeptical-H (talk) 11:06, 26 March 2008 (UTC)

Each in turn

1. Suggested: In physics, force is the perceptible cause of the acceleration of a mass (change in the rate or direction of its motion) and is experienced as a push or a pull. instead of In physics, force is what causes a mass to accelerate experienced as a push or a pull.

   The addition of "and" is good. However, a force need not be "perceived" to exist. The definition of "acceleration" is indeed confusing to the lay person, but I think that the wikilink on acceleration covers it. We need to be careful to not go overboard in description in the lead.

2. Provide definition: "momentum (quantity of motion)"

   Hmm, this isn't exactly an accurate definition of momentum since momentum is, in fact, both mass and motion. Again, the wikilink I think should suffice, but maybe we can reword things without providing definitions to make it clearer. I want this to be intelligible, but I'm afraid that including these points might be confusing for many and an annoyance to even more.

3. Following the development of quantum mechanics, it is now understood that momentum is a fundamental property of particles and that, according to the standard model of particle physics, changes in momentum are the consequence of the net emission or absorption by particles of momentum-carrying gauge bosons. Effects which are at the macro level experienced as a "force" are the consequence of the aggregate effect of these boson-mediated fundamental interactions. In modern physics, only four fundamental interactions are known; in order of decreasing strength, they are: strong, electromagnetic, weak, and gravitational.[1] High-energy particle physics observations in 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a unified electroweak interaction. No gauge boson has yet been demonstrated for mediating the gravitational interaction and what is perceived as the "force" of gravity is more accurately attributable to the the effect of distortions by massive bodies of the curvature of spacetime as explicated in Einstein's Theory of General Relativity.

   There is a slight issue here with the sentence: "Effects which are at the macro level experienced as a "force" are the consequence of the aggregate effect of these boson-mediated fundamental interactions." This sentence misses the fact that forces also exist on the micro level. A single boson-mediated fundamental interaction often has a "force" associated with it. For example, an electron accelerates because it emits a photon: this is due to the electromagnetic force acting on the electron. One micro-interaction: still a force since a mass accelerated. Also, the last sentence is debatable: the graviton exists if gravitational waves exist, and the Hulse-Taylor pulsar is strong evidence that gravitational waves exist. Let's just keep the regimes completely separate for the lead, but maybe we can explore this a bit more in our section on gravity. (A link to gravitons is probably appropriate, no?)

I will implement the wording I think is good, but let's keep discussing the problematic wording.

ScienceApologist (talk) 20:49, 26 March 2008 (UTC)

Response to each

1a. A force need not be "perceived" to exist.

Ahh - exist! Yes, I was hoping to sneak in the notion that forces don’t exist as real entities, but working through your point on photon emission (3a. below) has disabused me of that (for the time being - but I see the new reference to string theory in the current version of the article may, in time, vindicate me).

1b. the wikilink on acceleration covers it.

I feel that encyclopedia articles, as opposed to dictionary definitions, are intended for the benefit of the non-expert, so some laxity in terminological rigour, some redundancy in definion, can be tolerated so long as the essence of the subject is conveyed clearly, accurately and usefully. How much, of course, is a matter for editorial judgement. However, excessive rigour can be counter-productive because the student simply is not going to follow up every link and reference to tease out the subtleties and nuances of the terms used (in my case, not least, because on my antiquated setup it takes my browser an age to download and assemble each Wikipedia page).

2. momentum (quantity of motion)

The phrase is there in the momentum article, albeit as an archaic term used before the concept of momentum had been fully worked out. The idea of quantity, as opposed to magnitude, took care of the mass dimension.

I was trying to link in the concepts of force -> acceleration -> momentum -> boson using motion as the hook, but why not do it directly and

• insert at the start of para 2: "Acceleration is simply a change in momentum."
• Alternatively, might it be preferable to ditch acceleration in the definition in favour of change of momentum (pace all the F=ma elementary science teachers out there)?

3a. an electron accelerates because it emits a photon: this is due to the electromagnetic force acting on the electron.

There is another way to tackle this: does the electron accelerate because it emits a photon, in which case, what causes it to emit, or does it emit the photon because it accelerates, if so, why does it accelerate? And do the same considerations apply in the case of absorption?

If we have a). force -> electron -> emission/absorption -> acceleration, then it is the emission or absorption which causes the acceleration while the force provokes the emission or "sets up" the electron to be responsive to absorption. But if it is b). force -> electron -> acceleration -> emission/absorption, then it is force that causes the electron to accelerate and emission or absorption is a book-keeping adjustment, a balancing entry, by the system to conserve momentum.

With a)., a mere capacity to accelerate in response to absorption doesn’t convey the sense of active agency that we expect from force and it would seem that, for acceleration by absorption, the agency of force is redundant, in which case we have instances of acceleration without force. With b)., force is a necessary cause for all cases of acceleration, but then we must ask - who’s keeping the books?

• Assuming b). is rejected, is it possible to include a quantum description of acceleration by gauge boson absorption such that the active agency of a force is required?

3b. the last sentence is debatable: the graviton exists if gravitational waves exist

I wasn’t questioning the possibility of a quantum explanation for gravity, I was, in a way, trying to make even clearer the significance of the reconciliation problem that physics is struggling with. One of the several "aha!" moments I had, reading this article, was your apparently deliberate omision of a mention of this postulated particle, explaining instead gravitational effects such as ballistic trajectory in terms of spacetime. This was the first time I had really felt the weight of the divide between the quantum and relativistic approaches to gravity. My impression up till now was that relativity was defective in the way that Newtonian mechanics was defective, of relevance only for engineers grappling with stellar distances and inconceivable speeds but good for its time until the particle physicists could come up with the truth. I had no idea that relativity could teach me things about the flight of a baseball. That, I think, needs to be preserved, so:

• I wouln’t want to see too much made of the search for the graviton if this were to have the effect of impugning the explanatory power of the General Theory.

3c. Let's just keep the regimes completely separate for the lead

I suggested the rewording because at present we go from the particle level, where forces are gauge boson mediated, to the rest, where, apparently, it’s all spacetime. There’s the level of everyday non-gravitational forces which needs to be accommodated.

• I suggest removing the sentence beginning "On large scales" in para 3 and adding instead to the end of the paragraph (i.e. once gravity has been formally introduced): "The gravitational interaction, perceived as a force, is more accurately attributable to the curvature of spacetime as explicated in Einstein's Theory of General Relativity."

Skeptical-H (talk) 17:40, 28 March 2008 (UTC)

Further interactions

1a. Tabled, for the time being.

1b. we might include a quick description of accelerations somewhere other than the lead. Basically acceleration is a change of velocity. Velocity subsumes both speed and direction. Ergo acceleration is a change in speed and/or direction.

2.The issue is very subtle, if I'm to understand your questions correctly. We are trying to determine, it seems, whether it is acceleration or momentum that is more natural to use as a description of what is involved with forces. It comes down to whether you think mass should be involved in discussions of motion (dynamics) or whether it shouldn't (kinematics). It is generally thought that kinematics is a cleaner introduction to mechanics than dynamics: most people are not prepared to subsume the mysteries of mass into the conceptual rigor required to offer descriptions of motion through space and time. While momentum is a more rigorous approach to force definitions: it defies conceptual simplicity. F=ma, for better or worse, is the second most famous equation in physics and it isn't, in point-of-fact, totally wrong. I think we need to use acceleration and momentum in the order in which they appear, but we can provide conceptual definitions of these terms in an early section.

3a. Forces exist because of the absorption and emission of gauge bosons. In other words, we really have emission/absorption --> force --> acceleration. Force, in such a conceptual framework proceeds from the emission and absorption of particles which in turn is associated with accelerations. One could remove the force altogether. However, I do not see emission/absorption --> acceleration --> force as making much sense. The force is the thing that does the accelerating: and while it is equivalent mathematically to say that an acceleration must have an accompanying force, the acceleration in these situations is a response that occurs due to the conservation of momentum which is directly associated with forces, no acceleration.

3b. Relativity and quantum mechanics both need to be accommodated in a unified theory and it is not clear which one will suffer the most modification in the end.

3c. Your suggested sentence and rewording seems reasonable.

ScienceApologist (talk) 17:46, 29 March 2008 (UTC)

All is now clear

Maybe it's because I've spent the last few days grappling with this subject, and read the article several times, but I don't have problems with acceleration and momentum now.

My confusion was centred on decay, dealt with earlier, and the nature of the force/boson mediation. Your 3a. reply finally cleared things up. I suggest the following be inserted after the end of the first sentence of the Feynman diagrams section: Gauge bosons have momentum. When a particle emits (creates) or absorbs (annihilates) a gauge boson a force is generated which accelerates the particle in response to the momentum of the boson, thereby conserving momentum as a whole. This force is the fundamental force associated with the particle/boson interaction.

Skeptical-H (talk) 21:53, 30 March 2008 (UTC)

done. ScienceApologist (talk) 14:45, 1 April 2008 (UTC)

Comments from a lay reader

I've been reading this article aloud with my roommate, who is a physics major. He thinks the page makes sense if you have taken physics, but not necessarily otherwise. I would have to agree. There are many confusing sections. I know that some, such as "Feynman diagrams", might be out of reach for the lay reader, but there are same basic sections such "Newtonian mechanics", which can be improved. My roommate explained everything to me as we were reading and I kept saying, "Why didn't they just say that?" I am convinced this material can be explained to those of us who want to understand! Here is my list of suggestions and confusions (interspersed are copy editing suggestions):

Questions

• Could we advise readers to read the vector article before reading this one or perhaps offer a one-paragraph introduction to vectors? Vectors seem to be very important to this article.

  Sure! How would we do this? ScienceApologist (talk) 12:17, 13 April 2008 (UTC)

  Which suggestion? Awadewit (talk) 03:28, 14 April 2008 (UTC)

  How do we make a one-paragraph introduction to vectors without it seeming artificial? 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

  Could you integrate a simpler description of vectors into the first few paragraphs of the "Description" section, which already discusses the topic of vectors? Awadewit (talk) 16:37, 16 April 2008 (UTC)

Lead

• According to Newton's Second Law, the combination of all forces acting on a body (known as the net force or resultant force) is equal to the acceleration multiplied by the mass of the object. - The lead should be the simplest part of the article. As such, is it absolutely necessary to include phrases such as "according to Newton's Second Law" and "known as net force or resultant force"? I would try to focus the essentials - the basics - only.

   Done

• Since momentum is a vector physical quantity that has both magnitude and direction, forces must also be vectors. - Sadly, vectors are not something I learned about in high school mathematics - is there any way to make this easier to understand? Any way to avoid clicking?

  Hmm. The idea that force is a vector is so fundamental to the descriptions of forces provided by basically everybody, I think we cannot really avoid discussing it, but maybe we can phrase it in a way that is easier to understand. I'll mull it over. ScienceApologist (talk) 12:17, 13 April 2008 (UTC)

• Rotational effects are determined by the torques (the rotational equivalent of forces), while deformation and pressure are determined by the stresses that the forces create with respect to certain areas of the object. - Save multiple definitions for the article - find the simplest wording for the lead (even if it means saving "torque" for the body of the article!).

  Initially, this was included in the lead to allow us to explain the situations that forces create. Newton's second law is a basic introduction, but torquing, stressing, deforming, and pressuring are all things that people talk about and are all due directly to forces. I think some people use these terms in a colloquial sense without ever thinking about their relation to forces. What do you think? ScienceApologist (talk) 12:17, 13 April 2008 (UTC)

  They use these terms all of the time? Perhaps other people. Perhaps a simplified version of the sentence - maybe just focusing on torque? Awadewit (talk) 03:28, 14 April 2008 (UTC)

  Sure, people use the term "stress", "pressure", "deform" all the time. They often don't even realize that what they are talking about is so closely related to the physical concept of forces and, indeed, has its etymology from classical physics. 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

  Forces acting on three-dimensional objects may also cause them to rotate, deform, or result in a change in pressure. Torque determines rotational effects: the rotational equivalent of forces. Stress forces created within the object determine deformation and pressure. - This is written more simply now, but I'm still not sure all of these things need to be mentioned - if the idea is to say that colloquial ideas like pressure use the idea of force, why not just say that? Also, the writing is very choppy. Awadewit (talk) 16:37, 16 April 2008 (UTC)

Pre-Newtonian

• From antiquity, the concept of force was recognized as integral to the functioning of each of the simple machines. - "From antiquity" or "In antiquity, the concept of force has been recognized..."?

  It's still recognized as such. Maybe "Since" is better? ScienceApologist (talk) 12:17, 13 April 2008 (UTC)

  It would have to be: "Since antiquity, the concept of force has been recognized..." Awadewit (talk) 03:28, 14 April 2008 (UTC)

   Done

• The mechanical advantage given by a simple machine allowed for less force to be used in exchange for that force acting over a larger distance. - "larger" or "greater"?

  Technically either/both, but "greater" might make more sense for the lay reader. ScienceApologist (talk) 12:20, 13 April 2008 (UTC)

  I thought "greater" was used for numbers. Awadewit (talk) 03:28, 14 April 2008 (UTC)

  Well, in physics the "number" and the property are often confused. I see your point, though.  Done 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

  A distance can also be longer. Ward20 (talk) 08:12, 14 April 2008 (UTC)

• Philosophical development of the concept of a force proceeded through the work of Aristotle. - This sentence could be more precise - how did it proceed?

  I'll take a crack. ScienceApologist (talk) 12:20, 13 April 2008 (UTC)

• Aristotle believed that it was the natural state of massive objects on Earth, such as the elements water and earth, to be motionless on the ground and that they tended towards that state if left alone. - I would replace all instances of "massive" in the article with "objects that have mass". "Massive" to me means "enormous".

   Done

• This theory, based on the everyday experience of how objects move, such as the constant application of a force needed to keep a cart moving, had conceptual trouble accounting for the behavior of projectiles, such as the flight of arrows. - This sentence is missing the "because" explanation. I understand what it is driving at, but I've taught freshman composition courses long enough to know that it needs the other half for many students.

  Will do. ScienceApologist (talk) 12:23, 13 April 2008 (UTC)

Newtonian mechanics

• Isaac Newton is recognized as the first person to argue explicitly that a constant force causes a constant rate of change (time derivative) of momentum. In essence, he gave the first, and the only, mathematical definition of force—as the time-derivative of momentum: F = dp / dt. - These sentences are repetitive.

   Done

• In Principia Mathematica, Newton set out three laws of motion which have direct relevance to the way forces are described in physics. - "direct relevance"? What does that mean? I interpreted that mean that they aren't the exact formulas used or something. This caveat needs to be better explained or eliminated if it is not crucial.

   Done

• Newton's first law of motion states that objects continue to move in a state of constant velocity unless acted upon by an unbalanced external force. - "unbalanced"? This was quite confusing. I got a demonstrating using two cups from my roommate. I thought it meant that the force was unbalanced on one "side" - I was very wrong and very silly, apparently. The unbalanced bit either needs to be explained or cut. My roommate was of the opinion that it is probably not crucial in a first order explanation - it is a special case.

  I removed the offending unbalanced bit and kept in "net force". Will this work? 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

  It makes sense to me. Awadewit (talk) 16:37, 16 April 2008 (UTC)

• Newton developed this law as an extension of the work of Galileo that connected the condition of constant velocity, whether it be zero or nonzero, to the concept of a lack of net force (see a more detailed description of this below). - Why do we have describe objects at rest as having "zero velocity"? This is confusing. How much is gained here, in the second sentence explaining Newton's first law?

  There is a very deep connection between realizing that rest and constant velocity are the same situation and the idea that no net force acts on inertial objects. In any case, I tried to rephrase. Tell me what you think. 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

  Since rest is physically indistinguishable from non-zero constant velocity, Newton's first law directly connects inertia with the concept of relative velocities. Specifically, in systems where objects are moving with different velocities, it is impossible to determine which object is "in motion" and which object is "at rest"; it is equivalent to switch between what is called in physics "inertial frames of reference". - Is there any way to make the notion of "relative velocities" clearer? Would an example help here? Awadewit (talk) 16:37, 16 April 2008 (UTC)

• The use of Newton's second law in either of these forms as a definition of force has been disparaged in some of the more rigorous textbooks,[3][13] because this removes all empirical content from the law. In fact, the in this equation represents the net (vector sum) force; in equilibrium this is zero by definition, but (balanced) forces are present nevertheless. Instead, Newton's second law only asserts the proportionality of acceleration and mass to force, each of which can be defined without explicit reference to forces. Accelerations can be defined through kinematic measurements while mass can be determined through, for example, counting atoms. However, while kinematics are well-described through reference frame analysis in advanced physics, there are still deep questions that remain as to what is the proper definition of mass. General relativity offers an equivalence between space-time and mass, but lacking a coherent theory of quantum gravity, it is unclear as to how or whether this connection is relevant on microscales. With rather more justification, Newton's second law can be taken as a quantitative definition of mass by writing the law as an equality, the relative units of force and mass are fixed. - This entire paragraph needs to be rewritten or removed. Basically what I came away with (which was apparently completely wrong), was that Newton was wrong.

  This paragraph has been a real problem for a while. There are two issues: Newtonian definitions of force are not necessarily empirically precise (sayeth Walter Noll) and forces themselves become redundant rather than fundamental concepts when looking at advanced physics. I'll mull it over and see if I can come up with a better way of stating all this. 69.86.169.166 (talk) 12:52, 14 April 2008 (UTC)

• Given the empirical success of Newton's law, it is sometimes used to measure the strength of forces (for instance, using astronomical orbits to determine gravitational forces). Nevertheless, the force and the quantities used to measure it remain distinct concepts. - Perhaps this last bit could be explained better and more examples given? I have found that students learn best from example. It is actually quite hard to learn from the abstract principle.

  I tried to make the astronomical orbits example clearer. Do you need more? ScienceApologist (talk) 19:12, 14 April 2008 (UTC)

  For some reason, I can't find this again. Awadewit (talk) 16:37, 16 April 2008 (UTC)

• This means that systems cannot create internal forces that are unbalanced. However, if objects 1 and 2 are considered to be in separate systems, then the two systems will each experience an unbalanced force and accelerate with respect to each other according to Newton's second law. - I think this could be explained better. I didn't really understand it until I received yet another cup demonstration. Again, I think concrete examples might help the pitiful lay reader such as myself.

  I'll try my best. This is actually a very important concept and we should try to get it right. ScienceApologist (talk) 19:12, 14 April 2008 (UTC)

  This did not help - I really think concrete examples would help here. Most readers are unable to think in the highly abstract terms demanded by the article, especially about an unfamiliar topic. Awadewit (talk) 16:37, 16 April 2008 (UTC)

• Generalizing this to a system of an arbitrary number of particles is straightforward. - I read "straightforward" as meaning easy and scoffed at the article, because, of course, I was struggling to read through something I didn't understand well. Apparently, though, it is trying to say that it is easy to extrapolate to other, more complicated systems - is there a better way to say this?

  Sorry. "Straightforward" is a common word in mathematics and physics but is not so common in other places. It means, roughly, "tedious to derive and based on rules already discussed". What about using the word "possible" instead of "straightforward"? ScienceApologist (talk) 19:23, 14 April 2008 (UTC)

  "possible" sounds good. Awadewit (talk) 16:37, 16 April 2008 (UTC)

Descriptions

• Since I know nothing about vectors, paragraphs 2-4 at the beginning of the "Descriptions" section were near-impenetrable to me. I think this might be a good place for one paragraph on what a vector is. I also think this section could be simplified. Once again, after my roommate explained the free-body diagrams, it all became clear.

  Remanded to the Questions section above. ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

• Organizational issue: It would have been nice to have the "Normal force" and "Friction" sections before the "Equilibria" sections. Would that make sense? Currently, the "Normal force" section repeats what is in the "Statical equilibrium" section.

  I am aware of this issue. This stems from the peculiar situation of trying to give examples of situations where equilibria occur before examples of forces have been given. Should organization proceed as examples then descriptions or descriptions then examples? I also don't think that the normal force is quite an exact repetition of the static equilibrium section. We should dialog a bit more about this. ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

  Examples and then descriptions - concrete followed by the abstract. Although not the most sophisticated or accurate way to learn, this is the most common way to learn. :) Awadewit (talk) 16:58, 16 April 2008 (UTC)

• The "Feynman diagrams" section is not explained well - I don't know if this can be rectified. I have a book that does explain them well for the layperson - Deep Down Things - I'll check and see if it says anything about force.

  Please let us know. I tried my very best to write this section as well as I possibly can. ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

  If you have a chance to look at this book, I think the chapters titled "The Marriage of Relativity & Quantum Theory" and "Physics by Pure Thoughts: Gauge Theory" might help. This is the clearest book on particle physics for the layperson that I have seen (and I have a lot of them!). I was shocked how much I could understand reading this book - it attempted to explain much more than other popular science books on the topic and managed to do so extraordinarily well. Awadewit (talk) 16:58, 16 April 2008 (UTC)

• Can we do anything about the "Special relativity" section? I know many readers who will run away because it is all equations. I don't really understand myself. Would anything from the introduction to special relativity page help?

  I didn't write this section, but I understand it. Maybe a brief introduction could help. I'll have to mull this one over. ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

MOS (since it is up for FAC)

• Be sure that the first example of a word is link.

  I've tried to do this, but if you catch anything please fix it! ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

• Try linking more terms, such as "scalar", "free-fall".

  I believe they are linked, just not every time (only the first time). ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

  I believe in linking when the reader might want to click. :) What do you think? Awadewit (talk) 16:58, 16 April 2008 (UTC)

• Be sure footnotes come after punctuation marks.

   Done

• Be sure there is consistency in century references (I saw some "17th century" and some "seventeenth century", for example).

   Done

I'll finish up my notes later! I hope this helps. Awadewit (talk) 04:00, 11 April 2008 (UTC)

It does, more than I can say. ScienceApologist (talk) 19:32, 14 April 2008 (UTC)

Electromagnetic forces

• Unifying all these observations into one succinct statement became known as Coulomb's Law - This is oddly phrased.

   Done

• Subsequent mathematicians and physicists found the construct of the electric field to be useful for determining the electrostatic force on an electric charge at any point in space. Based on Coulomb's Law, knowing the characteristics of the electric field in a given space is equivalent to knowing what the electrostatic force applied on a "test charge" is. - This needs to be explained - I don't know what an electric field or a test charge is - should I have to click on both? (I'm tired of clicking, by the way!)

  I don't think that there's any way around making these statements. For one, the "test charge" is fundamental to the definition of a magnetic field, but we can try to make the wording more descriptive. ScienceApologist (talk) 21:33, 14 April 2008 (UTC)

  Could we describe them even more? Awadewit (talk) 17:23, 16 April 2008 (UTC)

• Meanwhile, knowledge was developed of the Lorentz force of magnetism, the force that exists between two electric currents. - "knowledge was developed"? - an odd phrase

   Done

• However, attempting to reconcile electromagnetic theory with two observations, the photoelectric effect, and the nonexistence of the ultraviolet catastrophe, proved troublesome. - nonexistence or existence of the catastrophe? also, I would explain the catastrophe

  nonexistence actually. The ultraviolet catastrophe was a theoretical prediction that was not observed. I'll mull over how to explain it succinctly. ScienceApologist (talk) 21:56, 14 April 2008 (UTC)

• It is a common misconception to ascribe the stiffness and rigidity of solid matter to the repulsion of like charges under the influence of the electromagnetic force. - Oh, yes, I do this all of the time! Common to whom? Is this really necessary?

  Well, it is common among middle school science teachers, for example. ScienceApologist (talk) 21:56, 14 April 2008 (UTC)

  Trying to stave off the problems in science education, i see. Well, who am I to argue with that? Is there any way to phrase it better, however?

Nuclear forces

• The strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD)[39]. The strong force is the fundamental force mediated by gluons, acting upon quarks, antiquarks, and the gluons themselves. The strong interaction is the most powerful of the four fundamental forces. - It may be impossible, but could we give readers a hints of what these particles are?

  You mean like, "quarks are the constituents of protons and neutrons, antiquarks are the constituents of antiprotons and antineutrons while gluons are the things that hold the quarks together"? I'm not sure if this will help or not. If it does, let me know and I'll include it. 69.86.169.166 (talk) 05:32, 15 April 2008 (UTC)

  I think it does help. Those other particles are slightly more familiar, especially protons and neutrons. For example, my parents know what protons and neutrons are, but they don't know what the rest are. Awadewit (talk) 17:23, 16 April 2008 (UTC)

• The strong force only acts directly upon elementary particles. However, a residual of the force is observed between hadrons (the best known example being the force that acts between nucleons in atomic nuclei) as the nuclear force. Here the strong force acts indirectly, transmitted as gluons which form part of the virtual pi and rho mesons which classically transmit the nuclear force (see this topic for more). The failure of many searches for free quarks has shown that the elementary particles affected are not directly observable. This phenomenon is called colour confinement. - No idea what is happening here and I even have some vague notion what these particles are supposed to be.

  This is a summary of how the strong nuclear force works. Basically, the gluons "glue" together the 3 quarks per hadron (proton/neutron) However, protons and neutrons are glued together in nuclei of atoms through left-over waveparticles from the gluon that form other bosoms (rho and pi mesons) that are the things that actually transmit forces between nuclei. Quarks individually never appear because gluons make sure that they are always found tied to other quarks. That's my rough translation. Can you suggest anyway to combine these translations together? 69.86.169.166 (talk) 05:32, 15 April 2008 (UTC)

  Trying: "Although the strong force only acts directly upon elementary particles, a residue is observed between hadrons. In hadrons, the strong force acts indirectly, where it is transmitted as gluons. The failure to find free quarks, the particles that make up hadrons, demonstrates that the affected elementary particles are not directly observable, a phenomenon referred to as "colour confinement". [This is important because?] So, how badly did I do? Awadewit (talk) 17:23, 16 April 2008 (UTC)

Non-fundamental forces

• A bit more explanation in the "Continuum mechanics" section might be nice.

   Done

  This is better. I sense this is an area where knowledge of tensors would be helpful? Awadewit (talk) 17:23, 16 April 2008 (UTC)

• Tension forces can be idealized using ideal strings which are massless, frictionless, unbreakable, and unstretchable. - What about "imagined" instead of "idealized"? (Not as precise, I know.)

  The problem with imagined is that it implies that tension forces aren't real (they are). Maybe better to say "modeled"? 69.86.169.166 (talk) 05:34, 15 April 2008 (UTC)

  "Modeled" sounds excellent. Awadewit (talk) 17:23, 16 April 2008 (UTC)

• I'm not sure I understand the difference between "tension" and "elasticity". They sound very similar.

  Tension involves no stretching. Elasticity involves stretching. 69.86.169.166 (talk) 05:34, 15 April 2008 (UTC)

  Springs don't stretch? (Sorry I'm so dense - I often ask very silly questions in my attempts to understand this stuff.) Awadewit (talk) 17:23, 16 April 2008 (UTC)

• This provides a definition for the moment of inertia which is the rotational equivalent for mass. In more advanced treatments of mechanics, the moment of inertia acts as a tensor that, when properly analyzed, fully determines the characteristics of rotations including precession and nutation. - Too advanced for me? :)

  If you thought vectors were difficult, imagine the sort of thing that acts on a vector to yield a totally different vector. Now imagine that this sort of thing has physical significance (relating two seemingly independent physical vectors). That's a tensor. It's so matehmatically complicated that most times it isn't formally introduced until 2nd year physics at the university level. Should we indulge ourselves with an introduction to tensors, or should we allow some mystery in our prose?ScienceApologist (talk) 06:19, 15 April 2008 (UTC)

  Actually, that was an excellent explanation. I'm sure the mathematics isn't that complicated! My roommate tells me nothing is that difficult in physics and math - one just has to think about it for a while. He's usually right about that. Vectors, for example, aren't difficult - I just didn't know anything about them until very recently. :) Why don't you add that little explanation into the article? Physics without the math is nothing, I am told. Awadewit (talk) 17:23, 16 April 2008 (UTC)

• The "Non-conservative forces" section lost me.

  Oh no! This is one of the sections of which I am most proud. Did you follow the beginning at least? Where did we lose you? ScienceApologist (talk) 06:19, 15 April 2008 (UTC)

  For certain physical scenarios (what kinds of physical scenarios?), it is impossible to model forces as being due to gradient of potentials. (I forgot, what is the "gradient of potentials"?) This is often due to macrophysical considerations (What are "macrophysical considerations" - larger than physical?) which yield forces as arising from a macroscopic statistical average of microstates. (What are microstates?) For example, friction is caused by the gradients of numerous electrostatic potentials between the atoms, but manifests as a force model which is independent of any macroscale position vector. (Still lost on gradients; not clear on causation/manifestation distinction) Nonconservative forces other than friction include other contact forces, tension, compression, and drag. However, for any sufficiently detailed description, all these forces are the results of conservative ones since each of these macroscopic forces are the net results of the gradients of microscopic potentials.(So, you add up the tiny forces and you get the "one big force" - this can't be right - I'm missing something) The connection between macroscopic non-conservative forces and microscopic conservative forces is described by detailed treatment with statistical mechanics. In macroscopic closed systems, nonconservative forces act to change the internal energies of the system, and are often associated with the transfer of heat. According to the Second Law of Thermodynamics,(What was that again, that I learned fifteen years ago, I'm asking myself) nonconservative forces necessarily result in energy transformations within closed systems from ordered to more random conditions as entropy increases.

  Here are my thoughts as I read. :) Awadewit (talk) 17:37, 16 April 2008 (UTC)

That's it! Awadewit (talk) 03:20, 14 April 2008 (UTC)

Wave-wave interactions

The article makes no mention of waves, yet a wave has a property analogous to momentum in h/lambda. Do wave-wave interactions result in changes in wavelength, and therefore momentum, and if so is force a necessary, or a meaningful, concept in considering wave-wave interactions? Should this be covered also in the article? Skeptical-H (talk) 00:27, 12 April 2008 (UTC)

Waves allow for the transference of momentum and carry momentum, but the only way to change the momentum of a wave is if the force couples to the energy of the wave. For example, electromagnetic forces affect an electromagnetic wave, but the strong nuclear force does not. ScienceApologist (talk) 12:10, 13 April 2008 (UTC)

Yes, but my question was really about whether the language of the article would apply if the subject of the force were a wave, rather than a particle or other massy object. We can understand pushing and pulling an object because we can envisage where an object begins and ends (it has boundaries), but a wave doesn't have the same tangibility. Take a tsunami, for example. Mid-ocean it has a wavelength of several hundred kilometres and relatively low momentum but on the coast its wavelength is compressed to a few metres with enormous momentum. Now presumably this acceleration is brought about by forces propagated through the water from the sea bed, but on which part of the wave do they operate? The wave is just the surface of the sea. In this case, I suppose, the forces are really acting upon the water molecules, and the wave is just an emergent property of the molecules in aggregate motion, but is this the case for all waves? Are all waves (including electromagnetic waves, for example) merely appearances, their apparent momentum being simply a statistic summarising that of the particles through which they propagate. In other words, is it in fact the case that, in every case, forces act only on particles? Or are there circumstances when forces act directly upon waves as entities in their own right? In which case, and I suppose I'm answering my own question here, does the gauge boson carrying the force effect the acceleration by merging as a wave with the subject wave, frequency modulating the wave as a consequence, and, reciprocally, is such a wave capable of splitting into a gauge boson wave and frequency-modulated daughter wave? If these are correct, would it be useful to include a section to this effect in the article? Skeptical-H (talk) 11:55, 16 April 2008 (UTC)

Waves carry energy. E=mc². Therefore waves carry something like "mass" (at least, the energy of the wave behaves the same way through general/special relativity). That's the easiest way to think about it. In your tsunami example, the wavelength of the tsunami stays the same: only its amplitude changes. There is no acceleration and energy of the tsunami is conserved. Since there is no acceleration, there are no forces. The apparent momentum of an electromagnetic wave is, in the limit where forces are considered, tied up in its individual photons. These photons can exchange momentum with charged objects and, when they do, the forces measured obey Newton's laws even though photons are technically waveparticles. Forces do not act on waves in the same sense because forces are ultimately defined for point-particles which a wave is sort of the opposite of. In order to explain how forces act on "waves" you essentially look at the "particle nature" of your wave and then back-calculate the result. Frequency modulation/ interference/ superposition of two waves is effectively the transfer of momentum, but in order to determine the "force" we must localize the wave into something that approximates a particle. I hope this explanation helps. ScienceApologist (talk) 12:46, 16 April 2008 (UTC)

Force as a concept

One thing that bothers me in the lead is that it may not immediately put in perspective to the lay reader that in physics force is a scientific construct used to help model our universe. The phrase "In physics" succinctly indicates that to those that understand scientific method, but for the wider audience I wonder if needs more explanation. Even on a more advanced level as this article shows, there is ambiguity. I suppose it depends on the level and breadth of audience the article is designed for. Ward20 (talk) 19:16, 13 April 2008 (UTC)

I think if a reader just hung out with the lead, the reader would probably not catch the nuance of what Wilczek is saying. However, without some of the background provided by the rest of the article, it would be inappropriate for us to mention this kind of critique too early. The article as it currently stands strikes a balance in this regard. My opinion, of course. YMMV. ScienceApologist (talk) 14:21, 16 April 2008 (UTC)

potential energy paragraph

In the 'potential energy' paragraph you write that :
"Instead of a force, the mathematically equivalent concept of a potential energy field can be used for convenience."
Then, you write : "Forces can be classified as conservative or nonconservative. Conservative forces are equivalent to the gradient of a potential while non-conservative forces are not."

In the first sentence, it seems all forces are conservative since they are 'equivalent' (why?) to the 'concept of a potential energy field', and 'conservative forces are equivalent to the gradient of a potential'. In the last sentence, you say not all forces are conservative.Randomblue (talk) 02:06, 14 April 2008 (UTC)

Great point. The first sentence is actually wrong. I'll try to reword it. ScienceApologist (talk) 19:10, 14 April 2008 (UTC)

Some ideas for a simplified lead

I have had a go a rewriting the lead following comments on the FAC. I have dropped a few phrases and delinked some terms I thought distracting. It's nothing more than suggestions; see what people think:

A force is a push or pull that can cause an object to accelerate. Force has both magnitude and direction, making it a vector quantity. An object will accelerate in proportion to the net force acting upon it and in inverse proportion to the object's mass. An equivalent definition is that the net force on an object is equal to the rate of change of momentum it experiences. Forces acting on three-dimensional objects may also cause them to rotate, deform, or result in a change in pressure. Torque determines rotational effects: the rotational equivalent of forces. Stress forces created within the object determine deformation and pressure.

Since antiquity, scientists have used the concept of force in the study of stationary and moving objects. These studies culminated with the descriptions made by the third century BC philosopher Archimedes of how simple machines functioned. The rules Archimedes determined for how forces interact in simple machines are still a part of modern physics. Earlier descriptions of forces by Aristotle incorporated fundamental misunderstandings, which would not be resolved until the seventeenth century when Isaac Newton correctly described how forces behaved. Newtonian descriptions of forces remained unchanged for nearly three hundred years.

Current understanding of quantum mechanics and the standard model of particle physics associate forces with the fundamental interactions accompanying the emission or absorption of gauge bosons. Only four fundamental interactions are known: in order of decreasing strength, they are: strong, electromagnetic, weak, and gravitational. High-energy particle physics observations, in the 1970s and 1980s, confirmed that the weak and electromagnetic forces are expressions of a unified electroweak interaction. Einstein in his Theory of General Relativity explained that curvature of space-time is an attribute of gravity, though perceived as a force.

— BillC ^talk 21:07, 15 April 2008 (UTC)

• I support it. Let's see how our lay-readers feel. ScienceApologist (talk) 21:49, 15 April 2008 (UTC)

I'll replace the current lead with it to see if it flys. Cheers! Wassupwestcoast (talk) 21:58, 15 April 2008 (UTC)

• Much better. GrahamColm^Talk 22:03, 15 April 2008 (UTC)

First line

The article begins by stating that force is "A force is a push or pull that can cause an object to accelerate." But the reference given (reference 1) already gives a different definition. I do maths and I am used to the way math people talk, that is, they give the precise definition, no beating around the bush. i guess this article starts by given an approximated definition of force and little by little tries to find a better, more encompassing, defintion. I can see that both approaches have its benefits. To fix the situation, i suggest that instead of starting with "A force is a push or pull that can cause an object to accelerate." it should start like: "As a first approximation, one can thing of force as a push or pull that can cause an object to accelerate or deform."

Though, I would much much perfer to start reading something like: "As a first approximation, force is the way matter can interact with matter. For example, the Earth interacts with the moon causing it to accelerate. This interaction is mediated by the gravitational force. A person throwing or squeazing a ball is an interaction between two pieces of matter that is mediated by a electromagnetic force. Notice, however, that the effects of the interaction between two pieces of matter can be not only an acceleration or a deformation. Indeed, most chemical reactions are the interation of matter having consequences different from a change in velocity or shape. Usualy, chemical reactions are carried out by electromagnetic forces."

... or something similar...

or something like this. Also, the references look quite basic. There is a book called "On the concepts of Force" or something like this that I believe would be a nice reference to quote (this is not the same thing as the article in the reference list that has a similar name). —Preceding unsigned comment added by 155.198.157.118 (talk) 14:01, 16 April 2008 (UTC)

I think you are taking a phenomenological approach to forces rather than a strictly theoretical one. Problem is, forces are much maligned as a concept in the physics community. They are useful conceptually but they have some theoretical problems (we're currently wrestling with them elsewhere). I'm not sure that your proposal for a lead is appropriate because it offers imprecise explanations to very complicated phenomena under the guise of "it's all force!". This is very similar to Feynman's critique in Surely You're Joking, Mr. Feynman of a basic textbook for physical science that explained without so much as a discussion that "energy" was what made plants grow, cars move, the sun shine, etc. Feynman pointed out that by using the idea that "energy does it", the book was missing the full explanations for each of these physical processes that were interconnected and subtle. ScienceApologist (talk) 14:25, 16 April 2008 (UTC)

(1) I agree I'm taking a phenomenological approach. But you have to start somewhere. I believe that is better to start with something more conceptual. Regardless of your criticism, my main objection is still up. The first phrase is misleading. It is too subtle just to say that that force is what can cause acceleration if you want to include in it the fact that forces are used to exmplain the deformation of objects. Also, the weak force is used to explain the decay of some particles. So, saying that force is a push or pull, like the undergrad books do, is at best misleading.

(2) I agree that my tone may lead to the assumption that "all is force". I guess we are two pieces of matter interacting over the internet and to explain this phenomena by evoking forces would be crazy. However, your usage of Feynman's critique is unjust. And, in reality that paragraph I wrote is much based on Feynman's writing. Just read Feynman's QED and you see that what I wrote about chemical reactions is there. Anyway, what Feynman is saying is that the guy wrote a whole book of generic statements. I had only one paragrah! As for detailed description of how forces work, one should check the wiki description of specific forces or take courses in physics...

(3) About the second phrase. Now, that one is really wrong. A vector is NOT something that has magnitude and direction. I read this definition in countless undergrad books - it is annoying to see it repeated here. Best to say that "the properties of forces make them behave like vectors" or something in this vein. and link the word vector the its wiki description.

(4) summing up: I believe the first phrase is a bad one - i guess people are not complaining about it bc it's what everyone read in undergrad years; so, it's wrong but in a familiar way, hence we accept it. If all of you don't like my attempt to fix it, fine. But what should be there instead? Also, second phrase is really bad. 18:05, 16 April 2008 (UTC)