Motion
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From: TomGee on 4 Oct 2005 21:22 Here's the context of circular motion, PD: 1. How can the orbital electron rotate permanently without energy supply? Here's your answer: Newton's first law. Now show us where his 1st law says anything about circular motion.
From: PD on 4 Oct 2005 22:19 TomGee wrote: > Here's the context of circular motion, PD: > 1. How can the orbital electron rotate permanently without energy > supply? > > Here's your answer: > Newton's first law. > > Now show us where his 1st law says anything about circular motion. I don't know why you think that a law has to include in its statement all the places where it applies. A theory is precisely powerful precisely because it can be extended to places not originally anticipated. PD
From: platopes on 4 Oct 2005 22:49 PD wrote: > TomGee wrote: > > Here's the context of circular motion, PD: > > 1. How can the orbital electron rotate permanently without energy > > supply? > > > > Here's your answer: > > Newton's first law. > > > > Now show us where his 1st law says anything about circular motion. > > I don't know why you think that a law has to include in its statement > all the places where it applies. A theory is precisely powerful > precisely because it can be extended to places not originally > anticipated. > > PD You mean no unbalanced force is observed to be acting on the electron, so no continuous energy supply is necessary for its movement? http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1d.html#balanced I guess there's no scenario wherein the electron...uh..."starts up"? Thanks for all the great words... p
From: PD on 4 Oct 2005 23:32 platopes wrote: > PD wrote: > > TomGee wrote: > > > Here's the context of circular motion, PD: > > > 1. How can the orbital electron rotate permanently without energy > > > supply? > > > > > > Here's your answer: > > > Newton's first law. > > > > > > Now show us where his 1st law says anything about circular motion. > > > > I don't know why you think that a law has to include in its statement > > all the places where it applies. A theory is precisely powerful > > precisely because it can be extended to places not originally > > anticipated. > > > > PD > > You mean no unbalanced force is observed to be acting on the > electron, so no continuous energy supply is necessary for its movement? One of the great things about Newton's laws (or, equivalently, the law of conservation of momentum) is that they apply separately in each dimension. So in the classical (3 spatial dimensions) case, Newton's 2nd law is really three equalities. Since motion in a circle is planar, this really reduces to two equalities. I'm certainly free to choose any coordinate system that spans this 2-space, so I'll choose radial and tangential coordinates. Now we have two statements of Newton's 2nd law, one for the radial direction and one for the tangential motion. In the tangential direction there is no net force on the orbiting object, and so Newton's second law and first law both say there will be no change in the speed in that direction. All of this could also be said using the conservation of mechanical energy. The orbiting body has a constant radius in a central field, so its potential energy is constant. The work-energy theorem then says that any other force acting in the direction of the displacement will contribute (perhaps positively, perhaps negatively) to the kinetic energy. However, there is no force acting in the direction of the displacement; the two are perpendicular to each other. Thus the kinetic energy remains the same. PD > > > http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1d.html#balanced > > I guess there's no scenario wherein the electron...uh..."starts up"? > Thanks for all the great words... > > p
From: TomGee on 4 Oct 2005 23:34
S--t, PD, you don't even know what you done wrong! How does the 1st law apply with its precise power to circular motion and how does it extend to circular motion? |