What keeps electrons spinning around their nucleus?
in [Relativity]
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From: David Cross on 30 Mar 2005 01:40 On Wed, 30 Mar 2005 03:45:34 GMT, "Bill Hobba" <bhobba(a)rubbish.net.au> wrote: >"David Cross" <spamdenied(a)nospam.net> wrote in message >news:co0j41dgr2ekm7opfiej4qqt9h6b5nhv4k(a)4ax.com... >> On Tue, 29 Mar 05 14:12:53 GMT, jmfbahciv(a)aol.com wrote: >> >I always have problems drawing that force diagram. The arrows >> >never "matched" my common sense. And torque always confused me >> >and, as a result, I always reverted to "memorized" formulas >> >whenever I did those problems. >> >> I think I was lucky; I learned about torques after I'd learned how to >apply >> cross products. :) Therefore all I needed was the radial distance away >from >> the center and the applied force. :) > >Having studied physics after completing a math degree I had the same >experience. Trouble is I ran into the problem Feynman alluded to - the math >can hide the physics. What had happened for me was that we were learning about the forces exerted by magnetic fields, and the professor, although he didn't have to, taught the cross-product form of the F = qvB sin theta equation in order to get us to understand the physical significance of the perpendicularity of the force to the velocity and field vectors. As a result, when I came across r x F (that is, rF sin theta), I didn't have to be sidetracked by rather strained explanations for explaining why the units of torque are Newton-meters and why the torque was perpendicular to the force and the radial direction. I just had to skip past all that and realize that the physical significance is the same as that for the qv x B :) Having seen the cross product, it was then child's play to understand the dot product, since the two just express different kinds of directional character to the physical quantities we deal with in mechanics and electromagnetism (although I realize this is lazy speaking when it comes to the dot product since work is a scalar; nonetheless, appreciating that the directional character of the force plays a role in how much work is done is crucial to special cases in mechanics, such as circular motion. :) ). As for force/torque diagrams, I find it helps a lot to have a good physical intuition. That has to be developed; I didn't really start to grasp force diagrams until I did many problems involving friction, statics, net forces, what-have-you. But once you grasp them, it's a short step to automatically using your right hand to work out which way the torque is for conditions where the net torque needs to be zero, or when you know it's rotational mechanics. :-) --- David Cross dcross1 AT shaw DOT ca
From: TomGee on 30 Mar 2005 02:09 Tom Capizzi wrote: > "TomGee" <lvlus(a)hotmail.com> wrote in message > SNIP > > > 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. > > Wrong, Cap, it is you who doesn't recognize the basics staring you in the face. Both are legitimate forces; it depends on which frame you happen to be in. > > > 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. > > If you were to remove that force, would the mass just stop moving? If not, why not? Answer: Law 1. The natural tendency of a moving mass is to continue moving following a straight path at a constant speed whenever there are no external forces acting upon it to cause it to accelerate (or words to that effect). The inertia of a mass works against any external forces working to accelerate it and that inertia is called an inertial force. Pure basics! Centrifugal force is what causes a mass to flee from a centripetal force from the viewpoint of a rotating reference frame, which is no less valid than a non-rotating frame since, under strict definitions like those you impose on centrifugal force, there is no such thing. TomGee TomGee > >
From: TomGee on 30 Mar 2005 02:18 RP, "sub-forces" might be more better since they are not any of the four fundamental forces but are related to them....? TomGee
From: Y.Porat on 30 Mar 2005 02:22 there is a basic particle that do not move in a straight line it moves naturaly in a closed circle see my site its time to refresh your parroting mind in meal all of you guys. Y.Porat ----------------------------
From: TomGee on 30 Mar 2005 02:54
PD wrote: > Harry wrote: > > <mmeron(a)cars3.uchicago.edu> wrote in message > > news:7K52e.21$45.3808(a)news.uchicago.edu... > > SNIP > > > > Right. Active forces (or how to call them, I think Newton called them > > impressed forces) cause acceleration. But a centrifugal force is a > reaction > > force > > Ack! Not in Newton's sense of action and reaction. > Sure it is. It is the inertial force's reaction to the centripetal force of gravitation which can balance out to keep objects in orbit. > > > > to a centripetal force, which is caused by a change in direction. > > Ack! Confusing cause and effect. The force causes the change in > direction, not the other way around. > > Yes, it causes the object to orbit instead of fleeing out and away. > > > > I > > wouldn't describe such as "pseudo force" or "fictional" force, as > that gives > > the wrong impression that no real force is exerted. > > Again, if you consider it carefully, it's not that complicated. If you > are rear-ended in your car, the reason your neck gets hurt is because > your body accelerates forward and your head does not. There is no need > to assert a force exerting backwards on your head to account for this > (although it would appear that there was one in a frame that > accelerates forward in impact). > > PD > > Wrong, PD. The inertial force of your head works against the acceleration caused by the crash since it is loosely connected to your body. If it did not - i.e., if it was frozen to your body - your neck would not get hurt, barring any other harm-causing events. > > > > In reality such forces > > are real enough to break your neck! Newton also didn't call them > "pseudo" or > > "fictional", AFAIK; he just called them innate/inertial forces. > > > > Harald > > Yes, Harald, that is exactly what he called them. TomGee |