What keeps electrons spinning around their nucleus?
in [Relativity]
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From: mmeron on 29 Mar 2005 18:24 In article <slrnd4jd0e.6h5.dubious(a)radioactivex.lebesque-al.net>, dubious(a)radioactivex.lebesque-al.net (Bilge) writes: > mmeron(a)cars3.uchicago.edu: > >In article <slrnd4h9dg.6h5.dubious(a)radioactivex.lebesque-al.net>, > >dubious(a)radioactivex.lebesque-al.net (Bilge) writes: > >> 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. > >> > >Not "anything". Just anything that can be plugged into f = ma to > >yield equations of motion. > > That would be anything, if you admit ``inertial forces'' to be >forces. ``Fictitious force'' would be a lot more apt. > Nope. > >You can use, say, the Coriolis force in > >this way, but I doubt very much that pepperoni pizza will work. > > Sure I can, just by balancing the electromagnetic force with >the ``force of gravity'' to treat the pizza oven as an inertial >frame when explaining why the pizza is (supposedly) at rest. > The idea was to use the pizza in lieu of force, not test mass. Of course, once you eat it, it is gone either way. 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 18:41 "Gregory L. Hansen" <glhansen(a)steel.ucs.indiana.edu> wrote in message news:d2bom8$ldk$2(a)rainier.uits.indiana.edu... > 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. > I have heard that the evidence for glass flowing is not reliable. It doesn't happen very quickly, so it originally came from examination of old glass. The old glass was found to be thicker at one end. The assumption was that it flowed. However, it was later shown to be an artifact of the way glass used to made, by spinning large sheets of it. Has anyone else heard similar reports? >>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" > > > -- > "No one need be surprised that the subject of contagion was not clear to > our ancestors."-- Heironymus Fracastorius, 1546
From: Puppet_Sock on 29 Mar 2005 18:51 Tom Capizzi wrote: > <puppet_sock(a)hotmail.com> wrote in message > news:c7976c46.0503291409.5e027614(a)posting.google.com... > > 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? > > Electrons don't really have position. They have complex probability > amplitudes. > What do you get when you take the derivative of that? Come on. Review your QM. Position is an observable. Velocity is the time deriv of position. "Don't really have" isn't a sensible statement. What they have is expectation values, Eigen values, etc. So it is perfectly sensible to ask such questions as "if I measure the position of an electron, what is the expected value, and what is the distribution?" Or "if I measure the value now, or in ten minutes, will I get the same result?" Socks
From: Tom Capizzi on 29 Mar 2005 19:00 "TomGee" <lvlus(a)hotmail.com> wrote in message news:1112126318.449947.69940(a)f14g2000cwb.googlegroups.com... > Well, Greg, even PD admits that the centripetal acceleration is a > force, but he does not know the bases of such forces. In the case of > the electron, it is the em force and in the case of his examples, it is > the gravitational force. Obviously, if we decide to not call > centrifugal force a force any longer, the other should not be called > one either. The centripetal force is imposed as an inward pull while > centrifugal force is a function of inertia, which is that tendency of a > body to continue unaccelerated when no net force is acting upon it. > The inertia of a body is what keeps it wanting to leave its orbit but > the pull of gravity keeps it from doing that. > > He has denied that em is the force involved in an atom which binds the > electron into orbitals. He was taught that both centripetal force and > centrifugal force exist, but now he lemmingly goes over the cliff by > discarding centrifugal force but retaining centripetal force without > knowing why. Wormy is doing the same, of course, as a Chief Lemming. > > Is everyone here so full of knowledge that they think the basics no > longer apply? > You don't recognize the basics when you see them. Centripetal force is a legitimate force, centrifugal force is not. By the way, centripetal acceleration is not a force, it is an acceleration caused by centripetal force. When the string breaks the orbiting mass follows a straight line away from the center of rotation. It doesn't take a force to "make" the mass flee the center. It does take a force to restrain the mass from departing. > TomGee >
From: TomGee on 29 Mar 2005 19:12
No, PD, that is a question you did not answer. I answered it. You disagreed with my answer. You could not have disagreed if I did not post an answer, now could you? TomGee |