What keeps electrons spinning around their nucleus?
in [Relativity]
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From: mmeron on 29 Mar 2005 00:24 In article <d2abun$65m$3(a)rainier.uits.indiana.edu>, glhansen(a)steel.ucs.indiana.edu (Gregory L. Hansen) writes: >In article <Rj12e.16030$C7.2138(a)news-server.bigpond.net.au>, >Bill Hobba <bhobba(a)rubbish.net.au> wrote: >> >><mmeron(a)cars3.uchicago.edu> wrote in message >>news:yr02e.13$45.3299(a)news.uchicago.edu... > >>> >Which is just another reason force should be considered as a secondary >>> >concept - the PLA is the primary concept. End of rant. >>> > >>> Oh, the PLA most certainly is ***the*** primary concept. So primary, >>> in fact, that it serves as foundation not only for Newtonian mechanics >>> but (with appropriate generalizations) for most of physics. No >>> argument about it. >>> >>> This said, the fact remains that, for applying the PLA, a level of >>> mathematical knowledge and sofistication is required which is way >>> beyond the capabilities of a beginning (high school) physics student >>> and, in fact, way beyond this that most people ever reach. So, we >>> maintain forces as a crutch to be used till more is learned. That's >>> really their remaining role. >> >>Most certainly. But if we are to use forces then I think we need a >>discussion of what they really mean along the lines of what Feynman did in >>the lectures. In fact I consider that to be compulsory reading even for >>grade 8 students (at least the chapters they have the mathematics to >>understand - other chapters can be added as their mathematical knowledge >>grows). Having understood what Feynman wrote I think a lot of confusion can > >The Feynman lectures? For 8th graders? Aren't the Feynman lectures the >ones based on the college courses he taught that the professors attended >and the freshmen dropped out of? > >>be avoided. In my case I always wondered why a definition could be a law. >>It confused me for many years until I read a rather nifty old book on >>classical mechanics. It clearly explained the real import of Newton's Laws >>was in his third law. That was the start of actually understanding what was >>happening. The full resolution came with Landua - Mechanics. I think it >>would be great if students did not need to go through this process and were >>taught what was happening right form the start - at least as much of it as >>they can initially handle. > >I think a lot of this will be resolved for the person who can accept that >there can be several completely valid ways to approach a subject. The >importance of the PLA (Principle of Least Action, right?) doesn't make >Newton's approach bad, just different. > >One objection I would have in trying too hard to teach it "the right" way, >besides confusing the students, is that too often it denies the things >they know. Everyone knows what centrifugal forces are, nobody is confused >on the fact that you feel it in something that's spinning and you don't >feel it in something that's moving uniformly. And then these eggheads >come along and say centrifugal forces don't actually exist, although the >layman knows those nonexistent forces seem to work pretty well when the >laundry machine hits the spin cycle. And the layman isn't wrong. >Insufficient centripetal force to retain the water and sufficient >centrifugal force to expel the water are separated by a simple >transformation. The layman doesn't think of it in that way, but he knows >that things happen when you spin. Does the egghead actually accomplish >anything by trying to excise the word "centrifugal" from the language? > There is this bit of fun to get from telling people "what you thought to be true is not so, the truth is quite different" (with the implied "I'm smarterr than you're, nah nah nananah":-)). And while, in an honest moment, I'll admit that there is some (albeit low) enjoynment to be derived from this, basing the teaching of a discipline on this is not advised. >Should we skip the chapter on Newtonian gravitation in favor of the >equivalence principle? Good point. Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: mmeron on 29 Mar 2005 00:30 In article <Xns9627C5AEB62D6WQAHBGMXSZHVspammote(a)130.39.198.139>, bz <bz+sp(a)ch100-5.chem.lsu.edu> writes: >mmeron(a)cars3.uchicago.edu wrote in >news:8B12e.18$45.3391(a)news.uchicago.edu: > >> In article <Mo12e.16031$C7.902(a)news-server.bigpond.net.au>, "Bill Hobba" >> <bhobba(a)rubbish.net.au> writes: >>> >>><mmeron(a)cars3.uchicago.edu> wrote in message >>>news:XQ02e.15$45.3352(a)news.uchicago.edu... >>>> >coordinates, but I think what is misleading is to call the correction >>>> >terms "forces". >>>> >>>> Only if you attach more meaning to the term "force" than it deserves. >>> >>>Ahhhhhh. Yes. As Feynman says it is half a law. It gains its full >>>meaning when combined with other laws and/or concepts such as Coulombs >>>law or the introduction of non inertial reference frames. >>> >> Yes, it is a rather complex issue. I wrote some stuff about it in the >> past, here, but I never kept a copy. But it certtainly needs some >> sort of broad framework, to make sense. > >Especially when someone keeps insisting that force is always the result of >acceleration Cause, not result. > and that without acceleration (as for example when a gyro >precesses at a constant rate, or when a mass moves at a constant velocity >because it is overcoming drag or friction) there is no force and no work. > Where there is net force, there is acceleration. The F in Newton's law is the total (i.e.) net force acting. Since forces are vectors, it is perfectly possible to have different non-zero forces to sum up to a zero net force. If I put your finger in a vise and squeeze, your finger is being acted upon by two forces, equal and opposite. The net force is zero and your finger is going nowhere. Which by no means mean that since the net is zero, there are no observable (or, for that matter, audible, i.e. loud screams) effects present. Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: Tom Capizzi on 29 Mar 2005 00:45 "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message news:Xns9627C5AEB62D6WQAHBGMXSZHVspammote(a)130.39.198.139... > mmeron(a)cars3.uchicago.edu wrote in > news:8B12e.18$45.3391(a)news.uchicago.edu: > >> In article <Mo12e.16031$C7.902(a)news-server.bigpond.net.au>, "Bill Hobba" >> <bhobba(a)rubbish.net.au> writes: >>> >>><mmeron(a)cars3.uchicago.edu> wrote in message >>>news:XQ02e.15$45.3352(a)news.uchicago.edu... >>>> >coordinates, but I think what is misleading is to call the correction >>>> >terms "forces". >>>> >>>> Only if you attach more meaning to the term "force" than it deserves. >>> >>>Ahhhhhh. Yes. As Feynman says it is half a law. It gains its full >>>meaning when combined with other laws and/or concepts such as Coulombs >>>law or the introduction of non inertial reference frames. >>> >> Yes, it is a rather complex issue. I wrote some stuff about it in the >> past, here, but I never kept a copy. But it certtainly needs some >> sort of broad framework, to make sense. > > Especially when someone keeps insisting that force is always the result of > acceleration and that without acceleration (as for example when a gyro > precesses at a constant rate, or when a mass moves at a constant velocity > because it is overcoming drag or friction) there is no force and no work. > > When I push my car, I exert a force. If the brake is off, the ground is > level and I push hard enough, the car begins to move. I am doing work as > long as it is moving, even if it has ceased to accelerate, as long as I > must exert force to keep it moving, I am doing work. > > I am having the hardest time getting that point across to someone in > another thread. > > Of course, maybe I am the one that is totally wrong. If so PLEASE tell me. > I know the feeling - I've pushed many a vehicle on streets that weren't always that level. But the work you are doing is expended overcoming the force of friction. On level ground you are doing no work against gravity. People often claim that holding a book at a fixed height off the ground is also work. Here they are in error. There is no motion and no friction. In spite of the fact that your arm gets tired, there is no work being done, unless the book is actually lifted to a higher elevation. > -- > bz > > please pardon my infinite ignorance, the set-of-things-I-do-not-know is an > infinite set. > > bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: mmeron on 29 Mar 2005 00:50 In article <d2ac7c$65m$5(a)rainier.uits.indiana.edu>, glhansen(a)steel.ucs.indiana.edu (Gregory L. Hansen) writes: >In article <slrnd4h9dg.6h5.dubious(a)radioactivex.lebesque-al.net>, >Bilge <cranks(a)fghfgigtu.com> wrote: >> mmeron(a)cars3.uchicago.edu: >> >> >I don't see anything in the formulation of newton's laws saying that >> >forces must be traceable to fundamental interactions. What should be >> >taught is that there are "physical forces" which are, indeed, a >> >measure of interactions between objects, and there may be additional >> >"inertial forces" which are an artifact of the choice of reference >> >frame. But being an artifact, does not mean that they've no >> >> ``Inertial force'' is an oxymoron. If ``inertial forces'' are >>to be considered forces, then the word ``force'' is nothing but >>a placeholder for a noun, since anything is then a force. > >A force makes something accelerate. If you're at rest in an accelerate >frame you might see a ball accelerate spontaneously. If it accelerated, a >force must have acted on it. "Inertial force" might not be the best name >for that because they don't appear in an inertial reference frame. >-- Got a point. Lets call them "non-inertial forces". Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: bz on 29 Mar 2005 04:54
"Tom Capizzi" <etianshrdlu(a)verizon.net> wrote in news:BX52e.46657$db6.1238(a)trndny02: > > "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message > news:Xns9627C5AEB62D6WQAHBGMXSZHVspammote(a)130.39.198.139... >> mmeron(a)cars3.uchicago.edu wrote in >> news:8B12e.18$45.3391(a)news.uchicago.edu: .... > > I know the feeling - I've pushed many a vehicle on streets that weren't > always > that level. But the work you are doing is expended overcoming the force > of friction. On level ground you are doing no work against gravity. Right. but I am still doing work. Tires, etc., have rolling friction. As long as I must exert a force to keep the car moving, I am doing work in the physics sense. > People often > claim that holding a book at a fixed height off the ground is also work. > Here > they are in error. There is no motion and no friction. In spite of the > fact that > your arm gets tired, there is no work being done, unless the book is > actually > lifted to a higher elevation. Right. I understand this. Of course if my muscles tremble slightly and the book moves up and down, oscillating around the fixed height, THEN work is being done, isn't it? -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap |