What keeps electrons spinning around their nucleus?
in [Relativity]
|
From: Bill Hobba on 29 Mar 2005 17:34 <mmeron(a)cars3.uchicago.edu> wrote in message news:ox12e.17$45.3415(a)news.uchicago.edu... > In article <Rj12e.16030$C7.2138(a)news-server.bigpond.net.au>, "Bill Hobba" <bhobba(a)rubbish.net.au> writes: > > > ><mmeron(a)cars3.uchicago.edu> wrote in message > >news:yr02e.13$45.3299(a)news.uchicago.edu... > >> In article <hT%1e.15978$C7.12491(a)news-server.bigpond.net.au>, "Bill Hobba" > ><bhobba(a)rubbish.net.au> writes: > >> > > >> ><mmeron(a)cars3.uchicago.edu> wrote in message > >> >news:4q_1e.11$45.3008(a)news.uchicago.edu... > >> >> In article <1112038910.784307.230090(a)o13g2000cwo.googlegroups.com>, > >"PD" > >> ><pdraper(a)yahoo.com> writes: > >> >> > > >> >> >Gregory L. Hansen wrote: > >> >> >> In article <1112035436.549412.84900(a)z14g2000cwz.googlegroups.com>, > >> >> >> PD <pdraper(a)yahoo.com> wrote: > >> >> >> > > >> >> >> >TomGee wrote: > >> >> >> >> Wormy, Bilge, PD, and all you other lemmings, > >> >> >> >> > >> >> >> >> you cannot understand that it is the _measurement_ of the force > >> >> >which > >> >> >> >> is fictional and not the feeling of being pulled out as a > >carousel > >> >> >> >> spins. > >> >> >> > > >> >> >> >Nope. You feel the force pulling you *in*, which is a force you are > >> >> >> ... > >> >> >> >Let me ask you another question. As an elevator suddenly starts to > >> >> >> >descend, you feel lighter. Are you in fact lighter? Why should > >> >> >Earth's > >> >> >> ... > >> >> >> >Let me ask you another question. You are on a road making a > >circular > >> >> >> >bend left in your car. What force acting on the car enables you to > >> >> >> > >> >> >> Reference frames, Paul. TomGee feels, TomGee is in, TomGee turns... > >> >> > > >> >> >> Who's making the measurement? A hypothetical 2nd observer > >stationary > >> >> >with > >> >> >> respect to the Earth, or TomGee? > >> >> >> > >> >> >> In those three situations, TomGee is in an accelerated frame. If > >> >> >TomGee > >> >> >> is pushed to the left against a wall, there's an inertial force > >> >> >pushing > >> >> >> him to the left. A 2nd, inertial observer might say no, TomGee is > >> >> >REALLY > >> >> >> being pushed to the right, but so what? He's not in the car. He's > >> >> >just > >> >> >> asserting that there's something special about his reference frame > >> >> >such > >> >> >> that he can make valid observations but TomGee can't, and pretending > >> >> >> there's no valid way to transform between them. > >> >> >> > >> >> >> Centrifugal force is called a force because it acts like a force. > >It > >> >> >will > >> >> >> cause something to accelerate relative to the stationary observer > >> >> >who's > >> >> >> already pinned against the wall. The stationary observer is, of > >> >> >course, > >> >> >> spinning madly about if viewed by the hypothetical 2nd observer > >who's > >> >> > > >> >> >> at rest relative to the Earth, but so what? There's nothing special > >> >> >about > >> >> >> the Earth frame, nothing wrong with the accelerated frame. If > >TomGee > >> >> >is > >> >> >> pinned to the wall of a centrifuge, then TomGee is still at rest > >with > >> >> > > >> >> >> respect to himself and he can define a reference frame from his > >> >> >> perspective. > >> >> >> -- > >> >> > > >> >> >Yeah, but I'm opposed to this kind of presentation, especially to the > >> >> >uneducated. I really believe that forces should be taught as being > >> >> >characterized by interactions between two objects, and those > >> >> >interactions should be traceable to one of the four (or less) > >> >> >fundamental interactions, and that forces are the cause and > >> >> >accelerations are the effect. > >> >> > > >> >> 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 > >> >> observable effects on motion relative to said reference frame. I see > >> >> no reason to treat it as some sort of a dangerous knowledge that > >> >> should be kept away from the uninitiated, else their mind may > >> >> explode:-) > >> > > >> >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 > >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. > > > Well, here is the rub, how much they can initially handle. For most > of them the answer is "not too much". Keep in mind that education is, > by and large, a processes involving quite average students being > taught by quite average teachers. True. > I've no doubt that if you'll pick > the cream of the crop of high school students, top 1-2%, and hand them > to a teacher of Feynman's caliber, you'll see some truly amazing > results. Unfortunately, you cannot use this as a general purpose > model:-( Hmmmmm. I think this is something we need to address in education. Perhaps we need a model more aligned to each individual students requirements rather than a class where the same information is given to every student. The current system encourages it to be dumbed down to even lower than what the average student can understand - after all only 50% of students will be average or above. I always rather liked what was done in the later years of uni. We had class material worth a certain percentage of the exam and assignments and projects worth so much. Perhaps we could encourage interested students to see teachers with questions they could investigate as part of optional assignments for extra credit? And yes my experience is most students simply do not ask the type of questions I do so basing circulum on the problems I had is not a good choice. > > That said, there is certainly room to analyze the way things are being > taught. The natural tendency is to teach things in the historic order > in which they were developed (an educational equivalent of "ontogeny > recapitulates philogeny"). That may not necessarily be the best > course of action. Having read the replies by yourself, Gregory and PD I relise in suggesting that I had forgetten one of the things I emphasize in education. It must actually be tested rather than be based on what I or others may think belongs in a course. Thanks Bill > > Mati Meron | "When you argue with a fool, > meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: Gregory L. Hansen on 29 Mar 2005 17:40 In article <c7976c46.0503291409.5e027614(a)posting.google.com>, <puppet_sock(a)hotmail.com> wrote: >dubious(a)radioactivex.lebesque-al.net (Bilge) wrote in message >news:<slrnd4dc08.n0h.dubious(a)radioactivex.lebesque-al.net>... >> Nick: >> >What is the velocity of an electron in a shell? >> >> Velocity isn't a quantum mechanical observable. > >Of course it is. What ever do you think you get when you take >the time derivative of position? >Socks Phase velocity? -- "In any case, don't stress too much--cortisol inhibits muscular hypertrophy. " -- Eric Dodd
From: Gregory L. Hansen on 29 Mar 2005 17:43 In article <d2cjmo0g7s(a)drn.newsguy.com>, Daryl McCullough <stevendaryl3016(a)yahoo.com> wrote: >Gregory L. Hansen says... > >>Daryl McCullough <stevendaryl3016(a)yahoo.com> wrote: > >>>I'm not exactly sure what you are arguing here. There is an >>>operational way to perform parallel transport of vectors. Yes, >>>you are right, that if there is an unknown force acting on our >>>measurement devices, then that will screw things up. But so what? >> >>So you're arguing against the notion of inertial forces. > >I'm arguing against *calling* them inertial forces. Instead, they >are connection coefficients, which are part of the *acceleration* >vector. Well, I argue against calling them inertial forces because they appear in non-inertial frames. > >>>Inertial frames are special any way you look at it. Either they >>>are the frames with no fictitious forces, or they are the frames >>>in which the connection coefficients are all zero. >> >>Or they're frames whose inertial forces exactly cancel out the Coriolis >>and centrifugal forces? > >I'm not exactly sure what you mean here. I thought the Coriolis and >centrifugal forces *were* the inertial forces. I'm talking about calling the rotating frame the natural case, just arbitrarily. > >Somebody quoted something that Einstein wrote about the equivalence >principle. He said that what was special about the freefalling frame >in the presence of gravity is that the inertial force due to acceleration >downwards (which would tend to throw you towards the top of a downwardly >accelerating rocket) is exactly cancelled by the force of gravity. I >think that's a confusing way to look at it. Me, too. But that's something like what I had in mind. -- "Are those morons getting dumber or just louder?" -- Mayor Quimby
From: mmeron on 29 Mar 2005 17:45 In article <d2bom8$ldk$2(a)rainier.uits.indiana.edu>, glhansen(a)steel.ucs.indiana.edu (Gregory L. Hansen) writes: >In article <RD52e.20$45.3912(a)news.uchicago.edu>, > <mmeron(a)cars3.uchicago.edu> wrote: >>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: > >>>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":-)). > >I think exactly that every time I see "glass is a liquid" come floating >around. Glasses tend to be harder, stiffer, and more creep resistant >than most crystalline solids, and without the redeeming quality of >(eventually) dripping through a funnel. But long after the words "solid" >and "liquid" were defined based on bulk properties, atoms were discovered >and then it was noticed that glass isn't crystalline, and ever since, >weenie egghead wanna-be's have been spouting "Glass is a liquid, what you >thought was true is wrong, I'm smarter than you are, nah nah nananah!" >Thereby sharing with people the factoid that glassy materials lack >long-range order, but otherwise mystifying the process of science. > Yes, yes, exactly. A perfect example. Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: Bill Hobba on 29 Mar 2005 17:50
"Gregory L. Hansen" <glhansen(a)steel.ucs.indiana.edu> wrote in message news:d2abun$65m$3(a)rainier.uits.indiana.edu... > In article <Rj12e.16030$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? Yes. But not all chapters are of the same difficulty. Some of the early chapters of volume one are I think quite suitable for 8th graders. In fact a popular book of some of them was produced called (I think) six easy pieces. But point taken. It would need to be tested on the students first to see if they could grasp it. > > >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. Ohhhhh of course. Newton's approach has problems when looked at carefully. But in modern treatments those problems can all be removed without resorting to the PLA. The reason I like the PLA as a basis is it is the natural language for explaining Noethers important discoveries. Also the physical basis of the PLA exists without much further ado - Feynmans sum over histories approach to QM. > > 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? Hmmmm. Interesting point. What I think it accomplishes is allowing the thinking students who see problems with the usual presnetiaon to understand what is happening. But those students are the rarity. Perhaps as I suggested in other posts we need a system more tailored to the requirements of each student? > > Should we skip the chapter on Newtonian gravitation in favor of the > equivalence principle? No. Thanks Bill > > > -- > "'No user-serviceable parts inside.' I'll be the judge of that!" |