What keeps electrons spinning around their nucleus?
in [Relativity]
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From: Bill Hobba on 28 Mar 2005 17:47 "PD" <pdraper(a)yahoo.com> wrote in message news:1112038910.784307.230090(a)o13g2000cwo.googlegroups.com... > > 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 am with Taylor who believes we should remove force as the starting point entirely - http://www.eftaylor.com/pub/FmaAJPguest5.pdf Fictitious forces of acceleration have an entirely different origin than forces caused by an interaction as is abundantly clear in the lagrangian approach i.e. they are simply an artifact of the fact we are no longer dealing with an inertial frame. The lagrangian simply has extra terms in it due to different coordinates. Thanks Bill > > Saying that centrifugal force is force because it acts like a force > comes at the penalty of losing sight of cause and effect (the > acceleration appears to create the force here) and permits the concept > of a force without an interaction. Someone who knows to attach the > little red flag to this notion while carrying it around can do so with > some finesse, but those who are still learning physics should not be > encouraged to equivocate. > > PD >
From: Daryl McCullough on 28 Mar 2005 17:32 mmeron(a)cars3.uchicago.edu says... >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. To me, the part that is misleading is the treatment of *acceleration*. The use of "inertial forces" amounts to defining acceleration to be the quantity A = e_i d/dt V^i instead of defining it to be A = d/dt (e_i V^i) If you use the first definition of "acceleration", then you have to introduce fictitious forces in order to preserve F = mA. If you use the second definition, then no fictitious forces are needed. I think that for more advanced physics, it is a mistake to equate a vector with its components, which is what is happening in defining acceleration component-wise as A^i = d/dt V^i. -- Daryl McCullough Ithaca, NY
From: Bill Hobba on 28 Mar 2005 17:50 <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. Thanks Bill > > Mati Meron | "When you argue with a fool, > meron(a)cars.uchicago.edu | chances are he is doing just the same"
From: Bilge on 28 Mar 2005 18:01 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.
From: mmeron on 28 Mar 2005 18:29
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. Mati Meron | "When you argue with a fool, meron(a)cars.uchicago.edu | chances are he is doing just the same" |