Motion
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From: Gregory L. Hansen on 20 Sep 2005 22:14 In article <1127237115.004748.182350(a)g44g2000cwa.googlegroups.com>, Don1 <dcshead(a)charter.net> wrote: >Randy Poe wrote: >> Don1 wrote: >> > This is what happens with any >> > vehicle and propellent - why a rocket can't go faster than the >> > propellent is expelled. >> >> Incorrect. A rocket is not limited to its propellant speed. >> >> - Randy > >Well I dont know Randy, is that according to the law of action equals >reaction? After all of the propellant has been exhausted isn't it all >going backward at the same speed as the rocket is going forward? Isn't >that what equilibrium is all about? > >Don Since force equals the exhaust velocity times the rate that propellent is expelled we can write m dv/dt = -v_e dm/dt where v is the rocket velocity and v_e is the exhaust velocity, and the minus sign means the propellant goes one way and the rocket goes the other. Rearrange, dv = v_e dm/m Integrate. v(m) = v_e ln (m_0/m) where m_0 is the initial mass. When m_0/m > 2.72, the rocket can go faster than its exhaust. It's different for a jet airplane which scoops up its propellant from the air it goes through. -- "The ability to quote is a serviceable substitute for wit". --William Somerset Maugham
From: odin on 21 Sep 2005 00:24 > TomGee--Your posts are nothing more than the behavior of a spoiled > brat. When folks offer you some physical insight and guidance, you > play you spoiled brat games. What a waste of your own time. I don't get what his point is.
From: Sam Wormley on 21 Sep 2005 10:14 TomGee wrote: > I was a > school superintendent once and I would have fired you on the spot had > you worked for me then. > > Sam, I'm sure you're a good person, you just have wrong ideas about > reality and you don't show any ambition to learn better. > I pity the school.
From: Randy Poe on 21 Sep 2005 10:35 TomGee wrote: > Randy Poe wrote: > So? Nothing in there about not requiring an energy source to continue > its motion. How can anyone rationally assume that means it needs no > force for it to persevere in a state of rest or of uniform motion. This bothered people in ancient Greece. Nobody exposed to the last couple of millenia of science seems bothered by it. Well, except you. > > (Newton's discussion) > > PROJECTILES persevere in their motions, so far as they are not retarded > > by the resistance of the air, or impelled downwards by the force of > > gravity. A top, whose parts by their cohesion are perpetually drawn > > aside from rectilinear motions, does not cease its rotation, otherwise > > than as it is retarded by the air. > > > > > Here still there is no mention of no force necessary to maintain an > object's motions. So the principle is "anything Newton neglected to mention is assumed to be present"? Internal motive forces, invisible sprites pushing things along, pink unicorns...? Newton mentions the things that affect motion. If an external force is present, the motion is changed. IF AN EXTERNAL FORCE IS ABSENT, THE MOTION IS UNCHANGED. There is no room there for an internal force to have an effect. There is no option left there for "if an external force is present and an internal force is absent" or "if an external force is absent and an internal force is absent". So perhaps your "internal force" is a different kind of thing from what we call forces. It is always there, there is no such thing as "absence of internal force", and therefore there is no experiment which can determine the effect of your "internal force". > > The greater bodies of the planets > > and comets, meeting with less resistance in more free spaces, preserve > > their motions both progressive and circular for a much longer time." > > > > > Nope. Nothing here about that either. Yep, he left it out, so assume its present, along with the sprites and the unicorns. > > I don't know what edition that's from. There were three, from about > > 1687 to 1726. To me it reads exactly the way we all have been > > interpreting it for 300 years. Without the influence of any forces, > > > You see how some people make things up? You did right here. You > interpreted your own quotes to say "without the influence of any > forces", yet that is not what you quoted. "Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon." Unless there are impressed forces, a body will continue at rest or in straight line motion. Read it right there. It will continue unless there are forces. Without forces, it will continue. With forces, it will change. Is there another way to read that? Has the word "unless" taken on a new meaning I was unaware of? "I am going to take the last cookie unless somebody tells me not to." To me, that says that if somebody tells me not to, I will refrain from taking the cookie. But if nobody says anything, I will take it. To you, perhaps it says that I need somebody to give me an order to take the cookie before I decide to take it. "A body continues in a straight line unless a force changes the motion." To me, that says that if a force changes the motion, the body will not continue in a straight line motion. But if no force is present, the body will continue. To you, apparently it says the motion won't continue unless a force is present to continue it. > Nowhere above do you quote such a phrase. Relevent phrase quoted again above. > > body moving in a straight line will continue in a straight line; a body > > rotating will continue to rotate; a body at rest will remain at rest. > > > > > Still nothing about not needing an energy supply to keep going. Do you think an energy supply is needed? What's keeping Voyager going, way out there beyond the solar system, now that its fuel is gone? > > > It's a false model simply because Newton's 1st law was corrupted in its > > > translation > > > > I'm having a little trouble pulling down the Latin on this computer. > > It's a huge PDF and it's choking my computer. I'll post it tomorrow > > to put that little accusation to rest. > > > > > Right. I can wait. Voila. Source: http://burndy.mit.edu/Collections/Babson/Online/Principia/ Scanned copies of each of the three authorized editions. Here is material from the 1726 edition. "LEX I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus illud a viribus impressis cogitur status suum mutare." My latin isn't great, but I get pretty much the same reading from that as the translation above. "Every body perseveres in its state of rest or moving uniformly in a straight line, unless by virtue of an impressed force its state is changed." - Randy
From: TomGee on 21 Sep 2005 11:46
Randy Poe wrote: > TomGee wrote: > > Randy Poe wrote: > > So? Nothing in there about not requiring an energy source to continue > > its motion. How can anyone rationally assume that means it needs no > > force for it to persevere in a state of rest or of uniform motion. > > This bothered people in ancient Greece. Nobody exposed to the > last couple of millenia of science seems bothered by it. > > Well, except you. > > > > (Newton's discussion) > > > PROJECTILES persevere in their motions, so far as they are not retarded > > > by the resistance of the air, or impelled downwards by the force of > > > gravity. A top, whose parts by their cohesion are perpetually drawn > > > aside from rectilinear motions, does not cease its rotation, otherwise > > > than as it is retarded by the air. > > > > > > > > Here still there is no mention of no force necessary to maintain an > > object's motions. > > So the principle is "anything Newton neglected to mention is > assumed to be present"? Internal motive forces, invisible sprites > pushing things along, pink unicorns...? > > No, of course not, but that's what you and everyone else assume. To think that Newton would accidentally neglect to mention such an important factor is ludicrous. Most likely, he did not believe such a thing, as he referred to "an inherent force" of a body that was free to move in a straight line at uniform speed. Why then would he contradict that by saying no inherent force is needed? In science, if something was not said, it cannot be assumed it was meant. > > > Newton mentions the things that affect motion. If an external > force is present, the motion is changed. IF AN EXTERNAL FORCE > IS ABSENT, THE MOTION IS UNCHANGED. There is no room there for > an internal force to have an effect. There is no option left there > for "if an external force is present and an internal force is > absent" or "if an external force is absent and an internal force > is absent". > > Not so. There is pulenty of room there. Just because you say there isn't does not make it so. In fact, the only option is for there to be an internal force as moving with no external nor internal forces constitutes perpetual motion, and surely you don't believe in perpetual motion, do you? > > > So perhaps your "internal force" is a different kind of thing > from what we call forces. It is always there, there is no such > thing as "absence of internal force", and therefore there is > no experiment which can determine the effect of your "internal > force". > > Oh yes there is. Start with E=mc^2+(energy of motion) which states in effect that a given mass has a quantity of energy in it. Go next to kinetic energy, which is the energy that a body or system has due to its motion, which is the energy-of-motion factor noted in my equation above. From there, recall that Newton did not rule out but actually cited "an inherent force" and that without such a force the situation becomes one of perpetual motion, then we can safely and simply assume that my internal force is nothing more than the kinetic energy of the body. My model contends that energy is a force. A force is "power or strength: the power, strength, or energy that somebody or something possesses" Microsoft® Encarta® Reference Library 2005. © 1993-2004 Microsoft Corporation. All rights reserved. When I first said that, some denied it and some derided my claim, and others ignored it. No one, however, was able to argue against it logically. Some ranted and raved, to no avail. They believe in perpetual motion, I take it. My claims are supported also by the fact that momentum is a quantity but it is also a force which is energy conserved. A "quantity" cannot be said to be conserved but mass and energy are said to be conserved. > > > > > The greater bodies of the planets > > > and comets, meeting with less resistance in more free spaces, preserve > > > their motions both progressive and circular for a much longer time." > > > > > > > > Nope. Nothing here about that either. > > Yep, he left it out, so assume its present, along with the sprites > and the unicorns. > > No, why would you do that? It's not a rational act. Neither is your belief that he left it out. Your teachers left it out, and their teachers left it out, and it became a false "fact". Why would anyone support a false fact? The only proper answer is their incapacity to readily absorb change. Many people believe their god is the only true god, and they defend that belief to the death, so it is evident that people do not accept change easily. I did not expect such deep resistance from scientists, however, and I am appalled by it. > > > > > I don't know what edition that's from. There were three, from about > > > 1687 to 1726. To me it reads exactly the way we all have been > > > interpreting it for 300 years. Without the influence of any forces, > > > > > You see how some people make things up? You did right here. You > > interpreted your own quotes to say "without the influence of any > > forces", yet that is not what you quoted. > > "Every body perseveres in its state of rest, or of uniform > motion in a right line, unless it is compelled to change that state by > forces impressed thereon." > > Unless there are impressed forces, a body will continue at > rest or in straight line motion. Read it right there. It will > continue unless there are forces. > > No, it does not say that, but even if it did, that contradicts his statement that a body has an inherent force that keeps it moving in a straight line in uniform motion. Why would he contradict himself? I am trying to tell you he did not, those who read what he said changed it to suit their beliefs and set science back beyond Newton's time. Why do you resist such a revelation so? > > > Without forces, it will continue. > With forces, it will change. Is there another way to read that? > Has the word "unless" taken on a new meaning I was unaware of? > > "I am going to take the last cookie unless somebody tells me > not to." > > To me, that says that if somebody tells me not to, I will refrain > from taking the cookie. But if nobody says anything, I will take it. > To you, perhaps it says that I need somebody to give me an order > to take the cookie before I decide to take it. > > "A body continues in a straight line unless a force changes the > motion." > > Oh, my, now you're leaving out words just to fit your argument. The quote refers to an external force, and you have left the word "external" out. > > > To me, that says that if a force changes the motion, the body will > not continue in a straight line motion. But if no force is present, > the body will continue. > > If no force is present, that constitutes perpetual motion, which does not exist in our universe. How do you overcome that? Do you deny that is perpetual motion? Do you claim that it exists in that one instance? > > > To you, apparently it says the motion > won't continue unless a force is present to continue it. > > Yes, that's correct. > > > > Nowhere above do you quote such a phrase. > > Relevent phrase quoted again above. > > > > body moving in a straight line will continue in a straight line; a body > > > rotating will continue to rotate; a body at rest will remain at rest. > > > > > > > > Still nothing about not needing an energy supply to keep going. > > Do you think an energy supply is needed? What's keeping Voyager > going, way out there beyond the solar system, now that its fuel > is gone? > > Well, it could not be perpetual motion, could it? As I say above, it's momentum keeps it going now, but it won't always. > > > > > > It's a false model simply because Newton's 1st law was corrupted in its > > > > translation > > > > > > I'm having a little trouble pulling down the Latin on this computer. > > > It's a huge PDF and it's choking my computer. I'll post it tomorrow > > > to put that little accusation to rest. > > > > > > > > Right. I can wait. > > Voila. Source: > http://burndy.mit.edu/Collections/Babson/Online/Principia/ > Scanned copies of each of the three authorized editions. Here > is material from the 1726 edition. > > "LEX I: Corpus omne perseverare in statu suo quiescendi vel movendi > uniformiter in directum, nisi quatenus illud a viribus impressis > cogitur status suum mutare." > > My latin isn't great, but I get pretty much the same reading from > that as the translation above. > "Every body perseveres in its state of rest or moving uniformly > in a straight line, unless by virtue of an impressed force its > state is changed." > > I agree with that, but it still does not say what you et al claim it says, namely, that it moves in a straight line w/o an inherent force. If it did, that would constitute perpetual motion. Also, it says that an impressed force will change its state of uniform motion in a straight line, but to do that, the force must be an external force. An inherent force will not change its velocity but will maintain it instead. |