Motion
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From: TomGee on 5 Oct 2005 00:06 Randy Poe wrote: > Randy Poe wrote: > > TomGee wrote: > > > Aren't you the one who said KE is not changed by an external force? > > > > No, I never said such a thing. Can you provide the quote where > > you garbled that inference from? > > > > I think I can save you some work. I said that in the case of > circular motion, the force does not do any work on the object, > and it also does not change the KE. > > And just where did you say that? > > > The reason the force does not do any work in that situation > is that the motion and the force are at right angles. > > When a force does work, it changes the KE. As Tipler says, the > amount of work done is equal to the change in KE. In the case > of circular motion, even though there is an external force, > the amount of work done = 0, and the change in KE = 0. > > As I recall, I brought up this example because you were accusing > somebody else of saying that force never changes KE, and I > was guessing that that person meant circular motion, since > you didn't provide an actual quote to support your accusation. > > I guessed the same thing, but "that person" did not mention circular motion but said instead that "acceleration never changes KE" or something to that effect. "That person" is also one of the correspondents in these ngs who insist that physics is very precise in its use of terms, which I consider to be hogwash going by the way they write and by what I've read.
From: TomGee on 5 Oct 2005 00:35 PD wrote: > 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. > > Crapola. Each applies in a different situation and that's why he did not make it one law but three. > > > So in the classical (3 spatial dimensions) case, Newton's > 2nd law is really three equalities. > > Which are...? > > > Since motion in a circle is planar, > this really reduces to two equalities. > > Which are (ho hum)...? > > > 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, > > I see neither one of those two statements. I see you chose two coordinates, if that's what you mean. > > > 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. > > That's only because you ignore two facts: 1. Newton's 1st law applies to an external net force. You keep leaving out "external" to fudge on your conclusions, thinking everyone is stupid here, but all translations of his 1st law state "external net force" - all 3 terms and no less! Which of course does not rule out an inherent force. 2. In view of the fact that the only way objects could orbit without some external net force acting upon them is by violating his 1st law, you are confusing the tangential force with the em attraction in the case of the electron particle and with the gravitational force in the case of the planet.
From: TomGee on 5 Oct 2005 00:43 Don1, he's either bs'ing you or he's totally confused: As I say in my reply to him about that, he's confused about the right angle force and the tangential force being the same thing..
From: TomGee on 5 Oct 2005 01:02 Randy Poe wrote: > Don1 wrote: > > Your quote of middle school science books constitutes positive proof in > > your mind, and might even stand up in a court of law, but it's a crock. > > Is arithmetic a crock because it is taught at young ages > rather than in college? > > Yet another one of your now infamous inferences. He said nothing about what you inferred, he referred to your buddy PD's quote. Now that we know PD is enrolled in middle school we need only to find out what grade you're in and all will understand yours and his problem with plain English. > > > > When a force acts at right angles to a moving body, the body is turned, > > and curves away from the force; not instantaneously but proportional to > > the magnitude of the force and it's duration. If the body responded > > instantaneously there would be an inward jump instead of a curve, and a > > ratchet effect would result. > > > > Instead, the force displaces the moving body, resulting in elliptical > > curvature. > > So your position is that circular motion is impossible? > > I keep thinking 6th grade, but most 6th graders have learned to better handle the reasoning process involved in reaching an inference than you have.
From: Randy Poe on 5 Oct 2005 01:06
TomGee wrote: > Randy Poe wrote: > > Randy Poe wrote: > > > TomGee wrote: > > > > Aren't you the one who said KE is not changed by an external force? > > > > > > No, I never said such a thing. Can you provide the quote where > > > you garbled that inference from? > > > > > > > I think I can save you some work. I said that in the case of > > circular motion, the force does not do any work on the object, > > and it also does not change the KE. > > > > > And just where did you say that? Here: http://groups.google.com/group/alt.sci.physics/msg/649e92bcc880f13f > > As I recall, I brought up this example because you were accusing > > somebody else of saying that force never changes KE, and I > > was guessing that that person meant circular motion, since > > you didn't provide an actual quote to support your accusation. > > > I guessed the same thing, but "that person" did not mention circular > motion but said instead that "acceleration never changes KE" or > something to that effect. I really doubt that "that person" (it was PD) said anything of the sort. But since you aren't known for backing up your claims of what people said, we'll never know, will we? - Randy |