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From: PD on 26 Sep 2005 14:58 TomGee wrote: > PD wrote: > > TomGee wrote: > > > Well, thanks for your input, Paul. Would you be able to answer my > > > question to Randy? Herman tried but he had no luck with it either. Or > > > maybe you can clarify the question for them as you have clarlfied the > > > equation which Randy claims "relates" to our topic. > > > > First of all, the equation that Randy is citing (F = dp/dt) is correct, > > and it is written in words in Encarta as well, which has been quoted > > back to you. > > > > > So what? It has no relevance to the topic and no one said it isn't > correct, so your "First of all" is not relevant either. > > > > > > Secondly, the *other* equation that Encarta puts in words is p=mv, > > which is not generally correct. > > > > > Encarta said no such thing, AFAIK, so you're lying again, so your > "Secondly" is also not relevant. It doesn't say the following? "3. physics measure of movement: a quantity that expresses the motion of a body and its resistance to slowing down. It is equal to the product of the body's mass and velocity. Symbol p". Microsoft® Encarta® Reference Library 2005. © 1993-2004 Microsoft Corporation. All rights reserved. > > > > > > Finally, as for the "question" you have for them, I'm not sure to what > > you refer. If your question was "What do you mean by F = dp/dt", I have > > only a guess as to what Randy truly means by it. Are you asking what I > > mean by it? Are you asking what physicists in general mean by it? > > > > > I know what it means. Randy's use of it has no relevance to our > discussion so I wanted to find out how he meant it since he gave no > support for his use of it. So you don't want me to clarify it for you either, then. PD
From: Timo Nieminen on 26 Sep 2005 15:40 On Mon, 26 Sep 2005, TomGee wrote: > platopes wrote: >> >> But Tom, we all know why it *does not* stop; there is no force acting >> upon it to make it stop. >> > In the first place, you have no way of knowing whether or not it stops. > And Newton said that an inherent force will keep a body at constant > velocity, but we have not been taught that he said that, and instead we > have been taught that he said something which he never said, namely, > that a body needs no force to maintain constant velocity. That's a misrepresentation of what Newton said. Firstly, a more honest translation into the technical langguage of physics would be that Newton said that the mass of a body will keep it at constant velocity. Newton's "inherent force" is not a force in the modern technical sense of the term, and your use of it above invites it to be mistaken for a force in the modern technical sense. Newton clearly stated that the "inherent force" of a body is nothing more than its mass. Secondly, Newton very clearly and carefully stated that the "inherent force" only acts to resist the effect of an "impressed force" (ie a force in the modern technical sense). Newton therefore stated the opposite of what you claim - in the absence of "impressed force", Newton wrote that the "inherent force" does _noothing_. What Newton wrote is that the inherent force resists changes in motion due to impressed force. And as Newton also wrote that any non-zero total impressed force does produce a change in motion, the inherent force _never_ maintains uniform motion. By all means, disagree with Newton if you want, but making claims that Newton said such-and-such, when he actually (and clearly) said the opposite only hurts your argument, by making it appear that either you don't understand what Newton wrote, or that you are dishonestly putting words in Newton's mouth. You could, perhaps, instead of writing Newton said such-and-such, actually quote Newton, either a reputable translation or the original Latin, with sufficient context. Since you've said you disagree with the translations, the Latin text would be best. -- Timo
From: Randy Poe on 26 Sep 2005 16:23 TomGee wrote: > PD wrote: > > TomGee wrote: > > > Well, thanks for your input, Paul. Would you be able to answer my > > > question to Randy? Herman tried but he had no luck with it either. Or > > > maybe you can clarify the question for them as you have clarlfied the > > > equation which Randy claims "relates" to our topic. > > > > First of all, the equation that Randy is citing (F = dp/dt) is correct, > > and it is written in words in Encarta as well, which has been quoted > > back to you. > > > > > So what? It has no relevance to the topic and no one said it isn't > correct, so your "First of all" is not relevant either. F = dp/dt has no relevance to our discussion of what F = dp/dt means and how you use it to find the effect of a force on an object? > > Finally, as for the "question" you have for them, I'm not sure to what > > you refer. If your question was "What do you mean by F = dp/dt", I have > > only a guess as to what Randy truly means by it. Are you asking what I > > mean by it? Are you asking what physicists in general mean by it? Why guess? How many times to I have to say what I mean by it? > I know what it means. Randy's use of it has no relevance to our > discussion Our discussion is whether force is equal to momentum, or its time derivative. I say force is equal to the time derivative of momentum. I would think the equation F = dp/dt, "force equals time derivative of momentum", has some relevance to that discussion. Are you taking the "it's irrelevant" tack now because the "it's useless to find the effects of force" tack failed? > so I wanted to find out how he meant it since he gave no > support for his use of it. What would constitute "support" in your mind? - Randy
From: TomGee on 26 Sep 2005 20:13 Randy Poe wrote: > TomGee wrote: > > Randy Poe wrote: > > > TomGee wrote: > > > > Randy Poe wrote: > > > It relates force and momentum, i.e., tells you how force and > > > momentum are related, by telling you that force is the time > > > rate of change of momentum. > > > > > No, that is not what it tells you. It is an equation - a math > > construct > > It is a model telling you how the two things called force > and momentum are related. The equation doesn't cause this > relationship, but it is a relationship which is true. > > Still, it does not tell you what you imagined it did. Equation, model, math construct, whatever, it simply states what a force is equal to in this particular case. All else you imagine it tells you is just that - imaginary. It does not imply that in the sense it is a necessary condition for the equation to hold. You can infer what you will from what it says, but at best an inference is still just a guess. > > > > - telling you that the force F is _equal_ to the time rate of > > change of the given momentum, exactly like E=mc^2 tells you not that > > energy is mass, but that the energy E is equal to the given mass > > multiplied by c^2. > > That's a pure semantic point. > > You mean a semantical point. Semantics relates to the conditions in which a system or theory can be said to be true. What conditions do you see in my explanation of E=mc^2 above wherein you can say it is debatable? do you imagine the formula says something different? > > > Mass can be viewed as frozen energy, > > Not according to the formula; it says nothing about "frozen energy". What you infer from it is of your own making and not of mine. Frozen energy indeed. > > > in the amount mc^2, all of which can be recovered in matter- > antimatter interactions. > > We are not talking about energy recovery are we? > > > So in a very real sense, matter IS > energy. You are arguing some fundamental difference between > "is" and "is equivalent to". I don't think it's an important > distinction. > > Yet you think the fundamental difference between force and momentum always holds regardless of the level of notation. You are willing to infer that _in a very real sense_ matter is energy, but you refuse to accept that same sense when it is applied to force and momentum. Is that hyprocrisy or fickleness? I can't tell which. > > > As for the relation between force and momentum, what F = dp/dt > tells you is that if momentum is changing, there is a force > involved, and if there is a force, then momentum is changing. > > Grasping at strawmen, are we? Have you found where your equation above states force and momentum are never equivalent? That was my statement which set you off into arguing they are not and you tried to defend your claim with that equation. You continue to view more into equations than what they actually tell you and that is more likely the source of your confusion about what they actually say and what they mean. > > > The two are inextricably linked. > > So when some scientist says "the force of momentum" he is correct even though he infers from "inextricably linked" that momentum is a force? > > > It is not telling you that > sometimes there is a force but dp/dt is zero, and it is not > telling you that sometimes p can change but F can be zero. > It is telling you that if one is zero, the other is zero, and > if one is nonzero, the other is nonzero. > > No, sorry. Your equation actually says none of those things; they are simply what you infer from its symbols. > > > If you have a body with unchanging momentum but say there is a > force acting on it, you have a nonzero term on the right and > a zero on the left. This equation tells you that is impossible. > > No, you have the wrong equation in mind, like p=mv or something. Actually, you seem to be saying that an "unchanging momentum" = zero momentum which of course it doesn't. You seem to be getting more confused the more you try to defend your silly position. > > > > Here are 3 definitions of momentum, all common terms in use by > > laypersons > > Perhaps. > > and scientists > > Since you have never claimed to have read any scientific source, > I doubt any claim that you know how scientists use any term. > > I got all this learning which you never got from comix. Read enough of them and the probability is high that the TOE will come to you sooner or later. > > > > alike in the various ways it can be defined. > > None of them define it like you do above, but yours is as common and as > > valid as the others as an equation useful for determining the amount of > > force in a given momentum. You cannot avoid seeing that translates > > literally into what I said, that force and momentum are equivalent. > > Certainly I can since that is false. > > No, it's true, not false. > > > > See the F on the one side of the = sign? And the other stuff on the > > other side? That means, simply, that if you calculate everything on > > the right side, it will tell you how much force is involved. > > Yes. Therefore it will tell you right away that force and momentum > are not equivalent, since when you do this calculation you will > find that F is not the same as p. > > No, it does not tell you that at all. You're simply inferring all that from the one little equation. It's all in your mind. > > > > Therefore, if I want to know how much force is involved in a given > > momentum, I have that equation handy. > > Did you forget the d/dt part already? It doesn't tell you how > much force is "involved in a given momentum". It tells you how much > force is involved in a given momentum CHANGE. > > And you're forgetting to add a "p" to your equation above, yet I know just what you mean just like you know exactly what I mean when I leave out the word "change". so find another straw to grab onto. But you said it tells you a bunch of other things which you have inferred from it, and you have not responded to that and a whole bunch of other nonsense you have posted and which I have questioned. How does knowing how much force is involved in a given momentum change tell you force and momentum are not the same thing? (We're back to square one). > > > It doesn't matter whether > the momentum involved is a ping pong ball moving at 1 cm/sec or > an elephant at escape velocity. A given force will translate into > exactly the same momentum change for both, because that equation > tells you that force and momentum change are equal, are equivalent, > are the same thing. > > Yes, that's correct. So your claim that force and momentum are not equivalent but force and the rate of change in momentum is not, is correct. > > > > "1. capacity for progressive development: the power to increase or > > develop at an ever-growing pace > > The project was in danger of losing momentum. > > This is not the meaning of p in any equation. > > That's my point, that your equation is not the-all of the universe. It is only one meaning of force and momentum but there are other valid ways to use the terms, even as being equivalent. > > > > 2. forward movement: the speed or force of forward movement of an > > object > > the momentum gained on the downhill stretches of the course > > I agree that this dictionary definition just said that momentum > is the same as "speed of forward movement" and "force of forward > movement". "Force of forward movement" is not a defined quantity > in physics. When somebody wants to do an analysis, the momentum, > force and speed must be kept separate. > > Again, that's correct. But momentum also validly means forward movement. > > > > 3. physics measure of movement: a quantity that expresses the motion > > of a body and its resistance to slowing down. It is equal to the > > product of the body's mass and velocity. Symbol p". > > There you go. This is a correct classical definition of momentum, > as used in Newton. > > This is a physics definition from Encarta which is about the same as what a college dictionary says, contrary to your claim that Encarta is a worthless source. If you like what it says, it's okay, but if not, it's wrong, eh? I said at the very beginning momentum is a quantity. I said it is also something else as used commonly by both scientists and laypersons alike. > > SNIP > > > Microsoft® Encarta® Reference Library 2005. © 1993-2004 Microsoft > > Corporation. All rights reserved. > > Oh gee, what a surprise. Have you considered looking at a physics > book before declaring what physics books say? > > Why don't you? > > > > Now in 1., above, momentum is used to mean a "power". > > It isn't used to represent a mathematical quantity at all. It's not > a thing that has units or can be measured. > > I didn't say it was or that it's such a thing. You think nothing exists beyond physical definitions, but I'm here to tell you there is a real world out here deeply affected by scientific works that run the range from good to bad. It's important then for scientists to be open to the usage of terms which are based in science and voiced by other scientists and the rest of the world. To deny the existence of various meanings for many terms is to be ignorant of the way of the world, and that's not a good type of ignorance for a scientist to have. > > > > In 2., it is > > used as a force OR a speed, > > Yes, two vaguely defined lay terms are equated. > > Lay terms? I don't think so. > > > > and in 3., it is a quantity, just like in > > your equation. > > It is the quantity mv, and even Encarta says that is the physics > definition and does not pretend that the first two are used in > physics, as you seem to be doing. > > You have jumped to that conclusion all by yourself without any help from me. I did not say the first two are physics terms. My point was that there are other valid definitions for some terms that are used in physics, and they are used by other scientists too. > > > > Here's another definition: A property of a moving body > > that determines the length of time required to bring it to rest when > > under the action of a constant force or moment. > > That doesn't tell me HOW it determines that, so it's useless > as a definition. > > A definition is not supposed to tell you how to determine that; that is what equations are for. > > > It doesn't tell me how to determine if object > A has twice the momentum of object B or only 1.5 times as much. > > It's not supposed to do that; it's only a definition of a physics term, not an equation. > > > > Broadly impetus. That > > too is an explanation of momentum as your equation uses the term. > > But an incomplete one. It is hinting at the existence of the F = dp/dt > relation, but not telling you the relation explicitly. > > That's precisely what you're doing. Your equation hints at the relationship between force and momentum as what you imply from it! When your equation does that, it's good; but when a college dictionary does that, it's bad. How hypocritical is that? > > > Momentum COULD have been defined in terms of force by your 4th > definition, if it said explicitly that momentum is proportional > to force and the time required to bring it to zero. > > So you have more brainpower than those who write for Webster's 9th New Collegiate Dictionary. You really are full of yourself, aren't you? > > SNIP > > > > Yet you dare to say that the only valid way to use the terms force and > > momentum is other than the way they are used in my examples? > > > Yes, I DARE to say that the only way to use force and momentum > in an equation is in the single definition that said it was > the physics definition, the single definition that offered > an equation. > > > So if I dare you to go jump in the lake will you do it? > > > > You claim > > the right to demand the use of those two terms only in the way your > > equation defines it? > > I claim the right to defend the use of those terms in physics > as being the ones that Encarta told you were the physics definitions > of those terms. > > I guess that was a No. > > > > > By the statement F = dp/dt, I mean that force is the time rate > > > of change of momentum. > > > > > > In what way is that not an answer to the question? > > > > > > It is an equation that tells you, given an expression for momentum, > > > how to find out the corresponding force. It tells you, given > > > a force, how to find out its effect on momentum. > > > > > > > > High-sounding words, but they're nonsense. What is "an expression for > > momentum" if not just a quantity? > > It's an expression that tells you momentum as a function of time, > which need not be constant. > > > It does NOT tell you how to find out > > a force's effect on momentum! > > Um, yes it does. It tells you that the force is the time derivative > of the momentum. > > Oh? Does that in your mind mean the same thing as, "how to find out a force's effect on momentum?" > > > That doesn't leave a lot of wiggle room. If I know > how force behaves in time and what my initial momentum is, then > I know precisely what the momentum is at every moment in time that > follows. What else could you mean by "find out a force's effect on > momentum" other than "tell you exactly what the momentum will be > at every time forever and ever as a result of that force?" > > I see. And the relevance of all that to your claim that momentum and force are not equivalent is...? > > Tell us, your Nakedness, just how do we find out a force's effect > > on momentum from F=dp/ dt? You are so funny! > > By integration. Would you care to ask a specific example? That > is sufficient to tell you, for instance, what the effect of > a rocket engine is on a rocket, even though the mass of the > rocket is changing as fuel is burned. > > No thanks. Just tell us how that will show force and momentum are not equivalent in the face of common usage of the two as being equivalent. > > SNIP more straw-grasping and drowning sounds....
From: Paul Stowe on 26 Sep 2005 20:46
On 25 Sep 2005 23:42:46 -0700, "TomGee" <lvlus(a)hotmail.com> wrote: > >Paul Stowe wrote: >> On Sun, 25 Sep 2005 10:50:43 -0400, Traveler <traveler(a)nospam.net> wrote: >> >>> On Sun, 25 Sep 2005 03:22:19 GMT, Paul Stowe <TheAetherist(a)best.net> >>> wrote: >>> >>>> It all stems back to this, >>>> >>>> Randy Poe: >>>> >>>> "That's correct. There is no force that keeps bodies in >>>> motion. Forces only act to change motion." >>>> >>>> True... >>> >>> False. The law of cause and effect requires a cause for every >>> effect. >> >> So? The 'cause' is whatever force generated the motion. However >> cause & effect also says that once 'caused' it cannot change >> without further cause. >> > Izzatso? Let's a reference, please, where "cause & effect" says that. Ummm, Yes... v2 t2 / / dp = m | dv -> ma | dt / / v1 t1 >> Momentum is an inertial process and exists without 'further' >> need for cause. >> > Inertia is not a process; it is resistance to change. Inertia is indeed the observation that mass resists changes in it motion. It is intimately related to force, not momentum... > Momentum is a quantity expressing the motion This much is true... > ... and resistance of a body, Not necessarily true. Let me give you a plausible example. Consider a body (as much mass as you like) 'freely responding to a uniform gravitational potential. It will accelerate the body uniformly, thus there will be a real force defined in any inertial frame as, F = ma However, were you inside the body neither you nor any instrument you could devise could would be able to discern that any force at all were acting. There will be NO! inertia response to said acceleration at all, period. > and it is also a force inherent in a body. This would suggest that what we observe as an inertia response is, in fact a result of non-uniform acceleration (stresses) due to the gravitational equivalence of tidal effcets. >>> Physicists have long assumed that bodies move for no reason, as >>> if by magic. >> >> None that I know of... Every one I know would say bodies move as >> a result of forces acting on them. However, those forces need not >> be constant. Indeed, if they were, we'd have non-linear results. >> >>> This belief is pure superstition. It will go down in history as >>> the most stupid blunder in the history of science, more laughable >>> than the flat earth hypothesis. >>> >>> The logical fact is that motion, like every effect, is caused. >> >> Who's arguing against this??? >> >>> No need to invoke either Newton or Einstein to understand this. >>> Use your own common sense. >> > >> > Motion requires energy >> >> Mass in motion IS, by definition, both momentum and ENERGY, period! >> Qunatified as, >> v2 >> / >> p = m | dv >> / >> v1 >> >> v2 >> / >> E = m | v dv >> / >> v1 >> >> > ... and acceleration requires more energy. >> >> Ah, subtly isn't your strong suite I see... >> >> >"subtlety", "suit". >> >> >> Wrt mass, acceleration >> is associated with the term we call force. It take this acting thru >> a non-zero distance to effect any energy change. >> >> > It follows that we are moving in a highly energetic sea of particles. >> > Why? Because sustained motion is caused by a series of interactions. >> > Motion is thus proof of the aether, not a lumineferous aether for the >> > propagation of waves, but a particulate aether, one which explains >> > phenomena such as the electric and magnetic fields, and gravity. >> >> In your mental concept perhaps. I'll not argue this one way or the >> other, I'll just say that, like the rest frame of the aether, it has >> no observational affect on inertial motion of masses. >> >> > Your claim, "In your mental concept perhaps" is an argument even if > you think not. Your belief that objects get a free ride in space is > based on your belief that space is empty of anything that could offer > resistance to their constant velocity. Me, believe space is empty? Now why would everyone who knows me would think this hilarious? :) > It has long been thought that the "quantum vacuum" is made up of > "fields" and processes that conjure up particles from nothing and > that was the standard model until we were able to see the effects > of what we termed Dark Matter. That shifted our knowledge out of > the box we were in out into a better explanation for the so-called > fields and phantom particles. But some of the heads in the box > find it too difficult to change their minds and so they will > continue to believe in fantastical realms of fields and in the > creation of particles out of nothingness. What does this have to do with momentum being mass in inertial motion? Paul Stowe |