Motion
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From: Herman Trivilino on 18 Sep 2005 17:28 "Don1" <dcshead(a)charter.net> wrote ... >> > 3) Resultant motion is the algebraic sum of inertial motion and forced >> > displacement, and can be written mathematically as d/t=l/t + s/t; or as >> > d/t=l/t + (a/2)t^2: Do you not see that d/t and l/t are terms that have units of velocity, and (a/2)t^2 is a term that has units of distance?! >> I thought my example of the motion of the Plymouth Prowler made it clear >> to >> you that this formulation gives results that don't match the way cars >> really >> move. > These motions are just the basic premises, or postulates. I don't understand the relevance of this statement. Are you saying that, since they are just basic premises or postulates, they don't need to match what's observed? > All actual > motion is affected by various forces such as the power source and all > kinds of friction. That's why a formulation such as yours is not relevant to these cases. > Not to mention that the Prowler is a unique automobile. But, you did mention it, didn't you? And, in regards to the context in which I brought it up, it is in fact not at all unique. Most, if not all, automobiles speed up with an acceleration that is larger in the beginning of the time interval in which they speed up, and smaller towards the end. Therefore, anyone who attempted to use your formulation to describe their motion would get results that are, to a very large extent, wrong. Wrong, that is, in the sense that the distance travelled by them would be, to a very large extent, larger than the distance calculated using your formula. Apart from fixing the mistakes I mentioned above with the units, you might consider adding a third order term. It would get you closer to agreement with what's observed, assuming that's your goal. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =----
From: TomGee on 18 Sep 2005 17:46 It? It's a "them", fool, not an "it"!
From: Randy Poe on 18 Sep 2005 17:57 TomGee wrote: > Sam Wormley wrote: > > Newton is much more precise > > http://scienceworld.wolfram.com/physics/NewtonsLaws.html > > > > 1. (Law of inertia): A body at rest remains at rest and a > > body in motion continues to move at a constant velocity > > unless acted upon by an external force. > > > > > Well, well, Worms, you're starting to support your beliefs with actual > excerpts from your websites! Very good, keep it up. No matter what well-known fact you choose, somewhere on the internet is somebody who disbelieves in it and writes volumes on his (occasionally her) disbelief. > According to your buddy PD, though, the 1st law includes a claim that > the body has no internal force to keep it in motion. Did you leave > that out, or don'tcha agree with PD? That's correct. There is no force that keeps bodies in motion. Forces only act to change motion. > > 2. A force F acting on a body gives it an acceleration a > > which is in the direction of the force and has magnitude > > inversely proportional to the mass m of the body: F = ma . > > > > Here F is the applied force, m is the mass of the particle, > > and a = dv/dt is the particle's acceleration, with v being > > the particle's velocity. This equation, together with the > > principle that bodies act symmetrically on one another > > (Newton's third law--so that the force particle A feels > > from particle B is equal to the force B feels from A--is > > the basis for understanding particle dynamics". > > > > > PD claims such accelerations do not amount to a change in kinetic > energy. Do you agree or disagree? You are misreading something. A change in speed constitutes a change in kinetic energy. Perhaps you garbled a description of circular motion, in which the force acts perpendicular to the velocity. In that case, the acceleration results in a change of direction, but not of speed, and the kinetic energy is constant. > > 3. Whenever a body exerts a force on another body, the latter > > exerts a force of equal magnitude and opposite direction > > on the former. This is known as the weak law of action and > > reaction. > > > > "Newton's [second] law completely describes all the phenomena > > of classical mechanics...." > > > So the force in 2. above is different from the force of bodies striking > each other? When bodies strike each other, the forces obey Newton's laws, including the third law. > In 2., the force makes a body move in the same direction > of the force, The acceleration is in the direction of the force. That may or may not cause motion toward the force. Generally not. If something is moving past you and you give it a kick as it goes by, it won't change direction and start going straight out from the direction of your kick. It will still have a component due to the original motion. > but in 3., the force of one body makes the other move > away from it. No. That is really garbled. If A pulls on B, then A gives an acceleration of B toward A. That's law number 2. At the same time, A is pulled toward B. That's law number 3. The fact that A is pulled toward B does not contradict the fact that B is pulled toward A. If you hit a piece of wood with your fist, you might dent the wood (law #2). That does not prevent the wood from denting your hand at the same time (law #3). - Randy
From: tadchem on 18 Sep 2005 18:51 "oriel36" <geraldkelleher(a)yahoo.com> wrote in message news:1127066684.790359.49960(a)g44g2000cwa.googlegroups.com... > To Sam et al. > > What have I told you before. > > Newton worked off mean Sun/Earth distances and concentrated on > variations from the mean distances rather than mean motions along the > orbits as Kepler did *. As Newton concocted a geocentric/heliocentric > orbital equivalency cut from the cloth of Flamsteed's axial > rotation/stellar circumpolar equivalency you can get the stretching of > distances alright but you cannot fit the sidereal format which > facilitates the geocentric/heliocentric equivalency into a Keplerian > framework. > > http://www.pfm.howard.edu/astronomy/Chaisson/AT401/IMAGES/AACHCIR0.JPG > > Go ahead,under the Newtonian scheme,a constant .986 degree orbital > displacement in an elliptical framework generates the unsightly > spectacle of the Earth moving faster at the aphelion and slower at the > perihelion.You get the correct stretching of distances but the rest is > nothing but a giant fudge . Your ignorance is exceeded by your obsession to flaunt it. Newton developed the concept of momentum, including *angular momentum*, which is the basis for Kepler's Third Law (the so-called "Harmonic Law"). Newton also showed that his inverse-square law of gravitation means that the closer a body is to the center of force, the *faster* it moves, regardless of the shape of its orbit. You are making too much out of a single diagram concocted for a freshman course constructed as a survey of astronomy for non-scientists. The diagram *assumes* a *circular* orbit. The 0.986 degree per day figure is an *approximation.* The actual *average* angular velocity of earth in its orbit is the sidereal year in days (365.2564) divided into 360 degrees: 0.9856090 degrees per day. In 1665, based on the best available information about the size of the earth, the acceleration of gravity at the earth's surface, and the distance to the moon in multiples of the radius of the earth, Newton calculated the acceleration of the moon's orbit. His calculations gave a value that was unacceptably low, and he abandoned his theory - temporarily. In 1671 Picard measured the length of one second of arc along a meridian in France and improved the accuracy of the size of the earth. His value increased earth's radius by 16% over the old value. A recalculation of Newton's work using the improved value for earth's radius helped establish the correctness of his theory of gravitation. In addition to showing that his theory of gravitation was consistent with known data about celestial mechanics, Newton also investigated the inverse problem of what orbit were required by his theory. He established that any orbit following his law of gravity *must* be a conic section: circle, ellipse, parabola, or hyperbola. The only 'fly in the ointment' was the orbit of Mercury, which had a 'drift' that Newtonian gravitation could not account for of 42.84 +/- 0.41 arc-seconds per century. Only Einstein was able to improve on this result with GR. He successfully accounted quantitatively for the drift of the orbit. Tom Davidson Richmond, VA
From: Don1 on 18 Sep 2005 19:22
Sam Wormley wrote: > Don1 wrote: > > Sam Wormley wrote: > > > >>Newton is much more precise > > > > Snip< > > > >> "Newton's [second] law completely describes all the phenomena > >> of classical mechanics...." > > > > > > I don't think so. > > > > Don > > > > How so? A simple question, but a book would be required to answer it. Don |