Talk:Conservation of mass
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[edit] Merged with "law of conservation of matter"
I redirected the conservation of matter article here, since the article there wasn't so great, and having the two was pretty much redundant. Vastly more articles linked to this article (Conservation of mass) than to the other. The article text is, of course, still preserved in the history of Law of Conservation of Matter.
The Wikipedia entry claims that mass and matter are EQUIVALENT to energy. Hmm. Have a think about that. There is a lot of confusion about Einstein's Law; it is often taken to mean that mass and energy are the same thing, which is not (necessarily) so; its significance is that it links the conservation of mass with the conservation of energy, which before Einstein were thought to be independent. In modern physics we accept that energy is conserved (but may be transferred) and THEREFORE mass is conserved (but may be transferred).
- Well, I don't necessarily disagree, but the conservation of matter (which was taken to mean various kinds of fermions) gave us a chance to talk about the conservation of baryon number and lepton number and so on. You can't just make and destroy these things without their anti-counterparts, so far as we know (or have seen) and so this is something separate than just conservation of mass (which may include all kinds of energy like kinetic energy and photons which are their own antiparticles and may be made and split and whatever). So here was the place to talk about additional conservation laws that had to do with other quantum numbers. But maybe, as you say, it wasn't done so well. Einstein gave us overall mass conservation without the particle conservation. But maybe (and usually) there's something more to it than that. Something in addition. If you blow up a thermonuke, not only doesn't the total mass change (fi you keep the energy in) but the number of baryons and leptons doesn't either. Which is remarkable to me. Sbharris 07:09, 23 May 2006 (UTC)
Well, I'd be for getting rid of the above stub entirely, or else expanding it a LOT.
The problem is the word "matter." It's got problems, as noted above, because it's not total MASS. In relativity, single observers (in single inertial frames) measure momentum, total energy, and a combination of these called invariant mass (mass for short), all to be separately conserved, in reactions in closed systems. Whenever you see somebody talking about conservation of "energy-matter" you know they're really trying to talk about muddy circumstances in which "matter" has somehow been "turned into" energy, but the additive combination is conserved. But in that case, by "matter" they mean "a sum of rest masses of matter particles" which is complicated and somewhat articifical, because it's never what we measure in a system (where those particles are not at rest, and are often subject to terrific potential binding energies). The sum of rest masses is always something we calculate by taking rest masses out of a book and adding them up. You can actually do that to get the active energy released in nuclear reactions, and that's where this whole idea of "sum of mass-energy conservation" comes from. However, it's (as I said) artificial is some ways. By contrast, total momentum, total energy and invariant mass of many systems is measureable directly. If you have a system on scales, its total momentum is zero, the mass is what it weighs, and its total energy is mass times c^2. During a reaction, none of those things change, if you keep the system closed. That's the most simple kind of conservation. Nothing is converted to anything. Mass is conserved, momentum is conserved, and total energy is conserved.
So anyway, all this has to be explained. Some things in physics you should say a lot about, or else nothing at all. In between always gets makes you say something that is wrong. Steve 20:56, 19 June 2006 (UTC)
[edit] Moving "Special Relativity Section"
Conservation of mass, although not exact, is extremely important in sciences that does not deal with relativity (i.e. chemistry) and also physics from a historical perspective.
The section on "Mass conservation in the theory of special relativity" lacks context and overshadows the importance of mass conservation. Rather, it should be short section and linked to "Mass-energy equivalence". Hence it should NOT be merged with "Energy-matter conservation", as the two topics pertains to different scientific fields. Roger (sorry for not signing comment)
- Previous comment is unsigned, however I agree. As a first step, I'm going to move the "historical section" in conservation of mass up front. It's hugely important, and is as approximately true (and as useful) as Newton's law of gravity. But the departures from it, now take up most of the present article. So a bit of rebalancing here needs to be done, with the bulk left to the relativity sections as "main articles". I'll make a first pass and let others have a shot.Steve 06:55, 21 June 2006 (UTC)
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- I also agree. In fact, I have on three separate occasions attempted a rewrite to highlight the importance of conservation of mass in chemistry and de-emphasize special relativity, which does after all have its own article, as you point out. I wasn't happy with my attempts and eventually gave up, but it still needs to be done. -lethe talk + 11:30, 21 June 2006 (UTC)
The whole section "Mass conservation in the theory of special relativity" doesn't seem to fit in the article. For one thing, it's unnecessarily long and convoluted. I suggest that the whole section be rewrittened to be much more concised, and linked off to another article for more information. Any objections? Roger
- Have offloaded it to a separate article. The stuff in it is not completely duplicated in the conservation section in the article on special relativity, so I've merely added links there and here. At least it's not cluttering this one any more. Steve 06:38, 3 July 2006 (UTC)
Excised from introduction a sentence fragment and some redundant text mentioning special relativity: In a strict sense the law of conservation of mass/matter may be viewed as a naive approximation to reality. While conservation of energy equations from special relativity give the more appropriate relationships between energy and mass behavior. Gnixon 04:39, 28 July 2006 (UTC)
- Well, I'm afraid you've managed to muck it up some in the process. Please read the end of the article! The mass of systems (when viewed by a single observer in their center-of-mass frame) IS conserved, even in relativity, and even in nuclear reactions. Yes, that includes alpha, beta, and gamma decay. In all of these, the moving alpha, the moving beta, and the gamma photon all contribute mass to the system, and so long as they remain part of the system, the system mass does not change through the whole process of nuclear decay. Of course it changes when the particle is let out of the system, but you can't expect conservation of mass in a system which isn't closed! Yes, that means that kinetic energy has mass in this context. Yes, that means that massless photons contribute mass in this context. And so on. SBHarris 03:26, 22 August 2006 (UTC)
[edit] Ficks Principle?
I came to wikipedia to look for Ficks principle, and this page is the closest thing to it. Considering I came here looking for info, I probably shouldn't be the person to add a whole page, or a section to this one. Ficks principle roughly states that the amount of a substance that enters a system (e.g. a mass) must equal the amount of that substance that leaves the system. Its used in physiology in measuring things like glomerular filtration rate. Someone should add a quick thing to this page, or add a fick's principle page since this is a pretty common topic. Thanks. Rjkd12 15:52, 28 November 2006 (UTC)
- Fick's principle probably needs its own physiology stub, but it's too arcane to discuss much here. Mass-balance is used in dozens of ways in dozens of fields. Fick's principle is just mass balance, expressed as a time derivative, and as used in biology. I don't even know why it has a special name, except that perhaps physiologists were so excited to discover and use some simple calculus, that they couldn't help themselves. ;) SBHarris 16:15, 28 November 2006 (UTC)
[edit] Merging again from Law of Conservation of Matter
I've redirected Law of Conservation of Matter to here, as there appears to be consensus for merge. Here are the contents of the article which are not in this article. I can't make heads or tails of it:
"The difficulty in stating this law in terms of the word "matter" is that "matter" is not a well-defined word. Most definitions of matter require that it be comprised of ordinary fermionic matter, which is composed of fermionic particles such as neutrons, protons, electrons and positrons. Most definitions of "matter" include neither electromagnetic radiation (such as light or gamma rays) nor do not include forms of potential energy associated with static nuclear or electromagnetic fields. The problem, however, is that scientists now know that such fields represent an appreciable percentage of the mass of ordinary objects, and even of particles themselves when they are compound particles (i.e., hadrons). The kinetic energy of particles in ordinary objects such as the kinetic energy of atoms represented in heat, but also the kinetic energy of subatomic particles contributes to the mass of objects, even though such energies are also not usually considered to be matter."
el:Αφθαρσία της ύλης pl:Prawo zachowania ru:Закон сохранения sl:Zakon o ohranitvi
There was also more in the page history. Kla'quot 09:20, 9 March 2007 (UTC)
- Just as well. The problems were in the definition of the word "matter" which isn't well-defined in science. Thus, the law of conservation of matter should indeed be redirected to the conservation of mass page, and the problems with the world matter continue to be discussed in the matter article. Which is as things now stand. The reason you can't make heads or tails of the above is probably because you're not a native English speaker, and in English, "matter" is not synonymous with "mass." Matter is a lose philosophical word from the old days before relativity, and is probably obsolete, like "phlogiston." Nobody knows or can agree on what it means, really. Mass is much better defined.
[edit] hard to understand!
i dont understand this! —Preceding unsigned comment added by Sarahis1313 (talk • contribs) 21:35, 2 October 2007 (UTC)
[edit] WikiProject class rating
This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:46, 10 November 2007 (UTC)
[edit] Removed a bunch of junk
Article states:
"In special relativity, the conservation of mass can not be cast as a simple statement of conservation of energy. For example, a system of two photons can be massless or have an inertial mass up to 2E/c², where E is each photon's energy (assumed equal), as a function of relative momentum orientation for the photons. However, such a system requires the observer to change. So, independently of the energy content being constant at 2E, the total mass may vary from zero to 2E/c². [1]."
Nowhere does Wheeler say this (quote page, please). The "system" described is not even the same system! A system in which two photons of energy E are going the same direction, cannot be converted to a system in which they are moving in opposite directions, by any change of the observer. They are two separate systems, and why should they have the same mass? As for their energies, you can't simply get system energy by adding up energies of parts of the system. Moving from a system in which photons are going in (almost) the same direction, to a system in which they are going in opposite directions, amounts to changing the observer. Doing this changes the energy of the system unless you change the energy of the photons at the same time. But doing both at once is hardly fair-- why would you expect to have ANYTHING conserved, if you're changing both obsever and photons seen by the previous observer TOO? I took this whole paragraph out, because it describes a series of experiments and observers, not anything held truly constant. Photons of energy E in opposite directios will have MORE energy than 2E for any other observer in which they don't go in opposite directions. Diminishing them so they don't results in a different system. SBHarris 04:30, 24 February 2008 (UTC)
[edit] Law, Oh Really
Shouldn't it be more apparent that more recent scientific theories much advertise against this so called law? Right now It's waaay down. Waaay down. It was on the simpsons by the way. PoorLeno (talk) 13:16, 10 March 2008 (UTC)
