What keeps electrons spinning around their nucleus?
in [Relativity]
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From: mmeron on 28 Mar 2005 16:11 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:-) Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: RP on 28 Mar 2005 16:27 PD wrote: > TomGee wrote: > >>David, >>No one said em interaction _causes_ the electron to move around the >>nucleus. The question was "What binds the electron to the atom"? >>TomGee > > > That was NOT the question. The question was: > "More imporatant is what sustains them in their perpetual motions?" > which I guess you now admit is a question you did not answer. > > PD Conservation of momentum. Richard Perry
From: PD on 28 Mar 2005 16:25 RP wrote: > PD wrote: > > TomGee wrote: > > > >>David, > >>No one said em interaction _causes_ the electron to move around the > >>nucleus. The question was "What binds the electron to the atom"? > >>TomGee > > > > > > That was NOT the question. The question was: > > "More imporatant is what sustains them in their perpetual motions?" > > which I guess you now admit is a question you did not answer. > > > > PD > > Conservation of momentum. > > Richard Perry And THAT is a much better answer. PD
From: Gregory L. Hansen on 28 Mar 2005 16:41 In article <pWY1e.114757$Ze3.29554(a)attbi_s51>, Sam Wormley <swormley1(a)mchsi.com> wrote: >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. > > An TomGee thinks this Newtonian perspective has something to do with > the quantum mechanical behavior of electrons... Is he right? > I like to give a charitable interpretation when I can. I'm sure you remember working out the classical two-body problem by reducing it to a one-dimensional problem in r, and using the angular momentum to define a centrifugal term. Then the sum of gravitational attraction and centrifugal repulsion forms a potential well V(r) that the particle oscillates in. That's working the problem in an accelerated frame, although a poorly defined accelerated frame since the transverse motion isn't discussed. But without the centrifugal term (or inertia) the particle would go straight into the center. That's an adequate treatment for a planet orbiting the Sun, or for a classical picture of the atom sans radiation. I think TomGee must have had a classical picture in mind. Bilge gave the real answer when he said that velocity is not an observable in quantum mechanics. An electron in an S state has no orbit, it has an orbital. The velocity expectation values are zero. Not enough energy to escape, no lower energy states to fall into. We can imagine a hydrogen atom where the electron is given a wavepacket with some centroid that orbits the nucleus in a classical sense. But the wave packet would evolve, and the electron would quickly either fly away or radiate and find its ground state. That might make for an interesting computer animation. -- "When the fool walks through the street, in his lack of understanding he calls everything foolish." -- Ecclesiastes 10:3, New American Bible
From: Daryl McCullough on 28 Mar 2005 17:23
mmeron(a)cars3.uchicago.edu says... >There is ***nothing*** wrong with centrifugal force. The term >"fictitious" is misleading. True, it doesn't stem from interaction, >just from choice of reference frame. So? It is quite often convenient >to deal with a problem in an accelerated frame, rather than transform >to an inertial frame and back. And when you want to deal with a >problem in the accelerated frame and still use Newton's laws, you >include inertial forces (i much prefer the term "inertial" than the >misleading "fictitious"). I don't think that there is anything wrong with using noninertial coordinates, but I think what is misleading is to call the correction terms "forces". I know that's just terminology, but the way I see it, inertial forces result from using noninertial coordinates, but *pretending* that they are inertial. What I mean is this: Noninertial coordinates mean that your basis vectors e_i are not constant. So if you define the acceleration vector A to be the time derivative of the velocity vector V, you get A = d/dt V = d/dt (V^i e_i) = e_i (d/dt V^i) + V^i (d/dt e_i) The use of "fictitious forces" amounts to pretending that the second term is a *force* term, rather than what it really is, an *acceleration* term. If we start with F = m A and move the second term to the other side of the equation, we get F - m V^i (d/dt e_i) = e_i (d/dt V^i) and then the extra acceleration term looks like an extra force term, if we define F_inertial = - m V^i (d/dt e_i) So, while I agree with you that using noninertial coordinates can be convenient, there really is no *convenience* benefit to treating the extra term as a fictitious force, instead of what it is, an acceleration term. -- Daryl McCullough Ithaca, NY |