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Richard Harrison wrote: There was a PBS special here today on "The Method" one of the books written by Archimedes, a copy of which was recently sold at auction for 2 million dollars. Very interesting program. Archimedes apparently developed an elementary calculus involving infinity 300 years before Jesus was born. -- 73, Cecil http://www.qsl.net/w5dxp Aristotle wrote that the Greek mathematicians didn't have any need for infinity and never used it. Archimedes said that his "Method" wasn't a proof but a means of mathematical exploration. He also said that Democritus used infinitesimal methods before he did. Democritus was born around 460 B.C. The Babylonians... aw, forget it. 73, Tom Donaly, KA6RUH |
On Wed, 1 Oct 2003 00:36:15 -0500 (CDT),
(Richard Harrison) wrote: Gene Nygaard wrote: "What is the relevant factor here -- that it is pressing down with a force due to gravity of 9000 pounds due to gravity of 9000 pounds force? Or that it has a mass of 9000 pounds? The tonnage of a ship is the weight of the water it displaces. The force pressing down (normal force) in mechanical problems is significant when friction is involved. Force equals mass time acceleration. So, the mass opposes and increases the force required to get an object moving, or slowed, for that matter. That includes a ship. It has inertia and requires force to change its velocity. Drag is imposed on the submerged portion of the hull, especially when coated with barnacles. I shipped out of Long Beach in WW-2 on the LSM 472. I returned to San Francisco on the LSM 94. I was transferred to the LST 604 to take it up river to Stockton to be decomissioned and scrapped. While at the ship yard there I witnessed a curious sight. A large merchant vessel was moved from one berth to another using a small boat with an outboard motor as the tow boat. River current in the basin was almost nil, yet it took several hours to move that large ship with the power of only an outboard motor. It worked! There must have been nothing more powerful available and there must have been no rush to get the berth swap made. Point is that it is likely that neither mass nor weight is as important as current in many situations. How soon you can get up to speed depends a lot on mass as Newton predicts. That motorboat would have done its thing much more quickly with a waterskier in tow than it did with a big merchant ship in tow. So what is the SI equivalent of those 27,561 tons deadweight for that U.S. Navy ship? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
Here I thought Arkie was a fundamentalist/traditionalist who fatfingered in
CCCLV divided by CXIII and CXCIII by LXXI on his GO34 in order to insert constants into his equations. 73, Dave, N3HE "Richard Harrison" wrote in message ... SNIP Archimedes inscribed the largest regular polygon ithat would fit inside a circle. Next he drew outside the circle a similar regular polygon touching the circle on all sides and having its sides parallel to the polygon sides inside the circle. Then he increased the number of sides of his polygons until they totaled 96. He decided a 96-side, equal-sided, figure was close enough to a circle for practical purposes. He also knew that a real circle would have a circumference somewhere between the circumferences of his inside and outside polygons. Also, the circumferences of his inside and outside figures were very nearly the same anyway. The tape measure must not have yet been invented, so Archimedes must have measured the sides of his figures with a straight ruler. He used the sums of the polygon sides to arrive at the circumference of his figures. From these constructions and measurements, Archimedes arrived at a figure of 3.1416 for the ratio of circumference to the diameter of a circle (pi). That`s still close enough for most purposes to this very day. SNIP Best regards, Richad Harrison, KB5WZI |
Gene wrote,
So what is the SI equivalent of those 27,561 tons deadweight for that U.S. Navy ship? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ I asked first. Why are you spamming the newsgroup with off-topic posts? 73, Tom Donaly, KA6RUH |
On 01 Oct 2003 14:59:45 GMT, (Tdonaly) wrote:
Gene wrote, So what is the SI equivalent of those 27,561 tons deadweight for that U.S. Navy ship? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ I asked first. Why are you spamming the newsgroup with off-topic posts? You seem to be operating under several delusions. I'm not spamming. I didn't start this discussion. The discussion I entered was not off topic here. You yourself, while you have contributed to the on-topic discussion, have also been responsible for more thread drift in this thread than anyone else. Democritus? Good grief! There wasn't anything on-topic in the message in which you brought him up. What connection do you find between him and the definition of ohms, and the inaccurate analogy using faulty defintions of pounds that lead to my entry into the discussion? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
On Wed, 01 Oct 2003 08:54:56 GMT, Gene Nygaard
wrote: On Wed, 1 Oct 2003 00:36:15 -0500 (CDT), (Richard Harrison) wrote: Gene Nygaard wrote: "What is the relevant factor here -- that it is pressing down with a force due to gravity of 9000 pounds due to gravity of 9000 pounds force? Or that it has a mass of 9000 pounds? The tonnage of a ship is the weight of the water it displaces. The force pressing down (normal force) in mechanical problems is significant when friction is involved. Force equals mass time acceleration. So, the mass opposes and increases the force required to get an object moving, or slowed, for that matter. That includes a ship. It has inertia and requires force to change its velocity. Drag is imposed on the submerged portion of the hull, especially when coated with barnacles. I shipped out of Long Beach in WW-2 on the LSM 472. I returned to San Francisco on the LSM 94. I was transferred to the LST 604 to take it up river to Stockton to be decomissioned and scrapped. While at the ship yard there I witnessed a curious sight. A large merchant vessel was moved from one berth to another using a small boat with an outboard motor as the tow boat. River current in the basin was almost nil, yet it took several hours to move that large ship with the power of only an outboard motor. It worked! There must have been nothing more powerful available and there must have been no rush to get the berth swap made. Point is that it is likely that neither mass nor weight is as important as current in many situations. How soon you can get up to speed depends a lot on mass as Newton predicts. That motorboat would have done its thing much more quickly with a waterskier in tow than it did with a big merchant ship in tow. So what is the SI equivalent of those 27,561 tons deadweight for that U.S. Navy ship? Let me open it up to everyone, and make it a multiple choice: 1. 245.19 MN 2. 245.19 hectopascals 3. 2.5003 x 10^7 kg 4. 28.003 Gg 5. 2.1892 x 10^8 newtons 6. 28 003 metric tons 7. 25 003 metric tons force 8. to have five significant digits, it depends on the latitude of the ship 9. all of the above 10. none of the above Does your answer fit in with Richard Harrison's description above? Does it fit with what any shipbuilder or any navy uses? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
Gene wrote,
You seem to be operating under several delusions. I'm not spamming. I didn't start this discussion. The discussion I entered was not off topic here. You yourself, while you have contributed to the on-topic discussion, have also been responsible for more thread drift in this thread than anyone else. Democritus? Good grief! There wasn't anything on-topic in the message in which you brought him up. What connection do you find between him and the definition of ohms, and the inaccurate analogy using faulty defintions of pounds that lead to my entry into the discussion? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ Nope, you're spamming. The subject you keep harping on has very little to do with antennas. Evidently, it's so overwhelmingly important to you that you're willing to hand out gratuitous insults and a never-ending series of posts to those you perceive as not agreeing with your narrow understanding of the subject. I'm reminded of Samuel Johnson's friend who only had one idea in his head, and that a wrong one. While you're not alone here in being possessed of an overwhelming obsession, at least the obsessions of the others bear some relation to antenna and transmission line theory. Personally, I don't much care what you do, but I'm curious as to why you do it. How can such a small idea trigger such a large obsession? 73, Tom Donaly, KA6RUH |
Raymond Sirois wrote:
"A 60-pound object on earth will have a weight of 10 pounds on the moon." That`s about right. Gravitational force on the moon is about 0.16 times that on earth. If a mass of 60 pounds is suspended from a weight scale on earth, the force on the scale registers 60 pounds. As Cecil noted, gravitational force is a vector. Its direction is toward the center of the mass that exerts the attraction. A spring scale free to align itself will measure 60 pounds tension no matter where the 60-pound pul on it comes from. On the moon the object with a 60-pound attraction to the earth only exerts a 9.6-pound pull on the spring scale. The object did not change. The spring scale did not change. The mass of the moon is much smaller than that of the earth, so its attraction is proportionally less. A weight balance scale would behave differently from the spring balance scale. The balance weights and positions would be almost unaffected by the change in gravitaional force because the forces on both scale and balance weights change in the same proportion. A weight balance scale would usually employ a balancing weight much smaller than 60 pounds to balance a weight of 60 pounds. The balance is struck with a smaller weight through leverage..It`s a teeter-totter with the measured quantity getting the short end of the stick. Balance remains at the same spot regardless of the gravitational pull on both ends of the balance beam. It`s the torques which balance. When we change the gravitational force, we multiply both sides of the balance equation by the same factor. The spring balance is calibrated for the force of gravity on a mass residing near the earth`s surface. The weight balance is calibrated for the same gravitational attraction on earth. On the moon the spring scale indicates about 10 pounds for an earth weight of 60 pounds. On the moon, the weight balance scale still indicates 60 pounds, though the gravitational pull is only about 10 pounds. Best regards, Richard Harrison, KB5WZI |
Gene Nygaard wrote:
They are incorrect in the doctor's office, and even more incorrect in the supermarket or the jewelry store. Like I said, you don't have to call the quantities used there "weight"--but if you do call them weight, use the definition which is correct in that context. Don't misinterpret what is being used there. Do you know what you're talking about Gene? Cuz I sure don't. It's generally accepted that weight is a force. I've shown in this thread from the experts in the field, including NIST (the U.S. national standards agency) and ASTM (an industry standards agency) and NPL (the U.K. national standards agency) and the Canadian Standard for Metric Practice, that this is false. I don't agree. All of these sources and many others tell you that weight is an ambiguous word, with several different meanings. What physical quantity do you think a grocery store scale measures? Problems can arise when someone claims a mass is a force and vice versa. I agree. And so a torque wrench has what kind of units printed on its scale - mass and distance, or force and distance? You could, of course, argue that we should all change to your usage. Many people already have, obviously. Not very many, surprisingly. Just the ones who write physics books maybe? It is much more common to find people claiming, erroneously, that there is some error in that usage. You're the first guy I've ever seen making claims about errors in usage. Like slugs, poundals only exist in one limited purpose system of mechanical units, mostly used to simplify calculations. But you'd like us to believe the unit of mass in that system is ubiquitous and universal, and that everybody is wrong! 73, Jim AC6XG |
On Wed, 01 Oct 2003 10:32:56 -0700, Jim Kelley
wrote: Gene Nygaard wrote: They are incorrect in the doctor's office, and even more incorrect in the supermarket or the jewelry store. Like I said, you don't have to call the quantities used there "weight"--but if you do call them weight, use the definition which is correct in that context. Don't misinterpret what is being used there. Do you know what you're talking about Gene? Cuz I sure don't. It's generally accepted that weight is a force. I've shown in this thread from the experts in the field, including NIST (the U.S. national standards agency) and ASTM (an industry standards agency) and NPL (the U.K. national standards agency) and the Canadian Standard for Metric Practice, that this is false. I don't agree. All of these sources and many others tell you that weight is an ambiguous word, with several different meanings. What physical quantity do you think a grocery store scale measures? You can probably figure that out for yourself, if you stop to think about how they are tested and certified. Especially if you have enough common sense to figure out that when we buy and sell goods by weight, we wouldn't want to measure some quantity that varies with location. Another big clue is the units in which that quantity is measured; grams in most of the world, and at least on prepackaged goods in the United States. In that regard, you might also consider how the law defines a pound (i.e., 0.45359237 kg), and then ask youself why in the world the law bothers defining a pound in the first place. When I was a kid, almost all the scales in the grocery stores were balances. You do understand what Richard Clark, among others, has told us about what we measure with those balances, don't you? Sure, they had evolved to the point where you didn't have to place loose, individual weights on a pan to get them to balance. The store we used most often had one with a dial readout, and a computing scale listing total price based on various prices per pound, but it prominently displayed the company motto on the side facing the customer: HONEST WEIGHT NO SPRINGS That scale wouldn't give you any different reading atop Mt. Chimborazo or at the North Pole than it did in the store in which it was used. Now, after the invention of the microprocessor, we have other options with reasonable cost and performance to accomplish the same thing. Problems can arise when someone claims a mass is a force and vice versa. I agree. And so a torque wrench has what kind of units printed on its scale - mass and distance, or force and distance? Once again, it doesn't cost you any more to pay attention. Like I told you a long time ago, my torque wrench has "meter kilograms" on it. What does that tell you? Why didn't you answer me then? Message-ID: Date: Fri, 26 Sep 2003 23:35:11 GMT Though I have had mine for several years, such torque wrenches, of course, are still readily available. http://jcwhitney.com/webapp/wcs/stor...&storeId=10101 They are units of force and distance, if you can't figure it out, just as the "foot pounds" which are the other units on my wrench are. But just as the existence of the kilogram force does not prove that pounds are not units of mass, the existence of pounds force does not prove that pounds are not units of mass. You could, of course, argue that we should all change to your usage. Many people already have, obviously. Not very many, surprisingly. Just the ones who write physics books maybe? It is much more common to find people claiming, erroneously, that there is some error in that usage. You're the first guy I've ever seen making claims about errors in usage. Like slugs, poundals only exist in one limited purpose system of mechanical units, mostly used to simplify calculations. But you'd like us to believe the unit of mass in that system is ubiquitous and universal, and that everybody is wrong! The pound, of course, like the foot and the second, predates that system, and those units are all used in many other systems as well as outside any such specialized system. IIRC, there is only at most one unit in any of the commonly used specialized systems of English mechanical units that was invented specifically for use in that system: the poundal in the absolute fps system, the slug in the gravitational fps system, the slinch in the gravitational inch-pound-second system. The old metric cgs systems have two mechanical units with special names that aren't in other systems, the dyne and the erg, and of course they also have various names in the different flavors of cgs for electrical and magnetic units, quantities that have never been measured in English units. Of course, you also have combinations involving those units, such as foot-poundals. That the poundal system is much older than the slug system is merely one of the many clues as to which is older, the pound mass or the pound force. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
On Wed, 01 Oct 2003 03:42:41 GMT, KU2S wrote:
On Tue, 30 Sep 2003 14:17:53 GMT, Gene Nygaard wrote: On Mon, 29 Sep 2003 23:38:14 -0500 (CDT), (Richard Harrison) wrote: Gene Nygaard wrote: "Look in the textbooks you used, and see if the authors have any footnotes citing the authority for whatever definition they use. My Random House American College Dictionary (circa 1950) says: "kilogram, n. Metric System. a unit of mass and weight, equal to 1000 grams and equivalent to 2.2046 pounds avoirdupois. For pounds, the same dictionary says: "Pound. 1. a unit of weight and of mass, varying in different periods and countries. Pounds and kilograms are different units for the same things, force and weight. Still haven't figured out that your claims that both kilograms and pounds are names of both a unit of mass and a unit of force is at odds with what Dave Shrader and Richard Clark have been telling us, have you? Okay people.... before this thread goes any further wrong than it already has.... Kilograms (base unit of measurement, the gram) are units of MASS. This is a measure of the amount matter in an object... Pounds are a unit of force, a measurement of the gravitational attraction a body has relative to another, reference, body. A 2 kilogram object will have the same mass on the earth as it does on the moon. A 60 pound object on the earth will have a weight of 10 pounds on the moon. If you kiddies are going to argue physics, you really SHOULD get your terms straight. God, pseudo-intellectuals really do begin to wear thin quite quickly... Raymond Sirois KU2S So what about those "meter kilograms" on my torque wrench? What's a poundal? Did NIST get it wrong, in what I pointed out in response to Richard Clark's challenge? http://physics.nist.gov/Pubs/SP811/appenB8.html#P To convert from to Multiply by pound (avoirdupois) (lb) 23 kilogram (kg) 4.535 924 E-01 pound (troy or apothecary) (lb) kilogram (kg) 3.732 417 E-01 [The 23 is a reference to a footnote in the printed and pdf versions, a note on a separate page in html] http://physics.nist.gov/Pubs/SP811/footnotes.html#f23 23 The exact conversion factor is 4.535 923 7 E-01. All units in Sec. B.8 and Sec. B.9 that contain the pound refer to the avoirdupois pound. How is the pound officially defined in Canada (Weights and Measures Act of 1953), in the United Kingdom (Weights and Measures Act of 1963), in South Africa, in New Zealand, in Australia, in Ireland and in other places as well as the United States, whose definition you can read at http://www.ngs.noaa.gov/PUBS_LIB/Fed...doc59-5442.pdf http://gssp.wva.net/html.common/refine.pdf But since you are so convinced that this is a "physics" problem, let's just review the last of the examples I quoted earlier from the textbook authors recommended by Dave Shrader. Francis Weston Sears and Mark W. Zemansky, University Physics, Addison-Wesley, 4th ed., 1970. [page 232] The quantity of heat per unit mass that must be supplied to a material at its melting point to convert it completely to a liquid at the same temperature is called the heat of fusion of the material. The quantity of heat per unit mass that must be supplied to a material at its boiling point to convert it completely to a gas a the same temperature is called the heat of vaporization of the material. Heats of fusion and vaporization are expressed in calories per gram, or Btu per pound. Thus the heat of fusion of ice is about 80 cal g^-1 or 144 Btu lb^-1. The heat of vaporization of water (at 100°C) is 539 cal g^-1 or 970 Btu lb^-1. Some heats of fusion and vaporization are listed in Table 16-2. Now, it doesn't take a whole lot of genius to figure out what the quantities are which are measured in those units with the -1 exponents, does it? But you don't even have to guess. Sears and Zemansky come right out and tell you. For you and some of the other slow-witted folks in this thread, here's a hint: Look for the seventh word in each of the first two sentences, that little word sandwiched in between the words "unit" and "that." Did you find it? ****************** That's as far as I went last time around. But this time we are dealing with real deep-rooted stoooopid, so I can't leave anything to the intelligence of the intended reader. That seventh word which I'm pointing out to you is spelled m-a-s-s. Do you see it now, Raymond? That's "mass," right? Now, let's compare the parallels in the construction here. In terms of the quantities being measured, this is expressed as quantity of heat per unit of mass and in terms of the units used to measure these quantities, it is expressed this way Btu lb^-1 Now, let's match them up: o The "quantity of heat" is measured in the units "Btu" o The "per" corresponds to the superscript -1 (that Btu lb^-1 could also be written as Btu/lb where the slash would correspond to "per") o The quantity "mass" is measured in the units "lb"; now that is the abbreviation, from one of its Latin names, for the units which Sears and Zemansky call pounds. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ Gentlemen of the jury, Chicolini here may look like an idiot, and sound like an idiot, but don't let that fool you: He really is an idiot. Groucho Marx |
Gene Nygaard wrote: What physical quantity do you think a grocery store scale measures? You can probably figure that out for yourself, if you stop to think about how they are tested and certified. You misunderstand, Gene. It's not at all clear what _you_ think they measure. I'm not asking about the units displayed on them. What physical quantity do you think is actually being measured? And so a torque wrench has what kind of units printed on its scale - mass and distance, or force and distance? Once again, it doesn't cost you any more to pay attention. They are units of force and distance, There's the point. That the poundal system is much older than the slug system is merely one of the many clues as to which is older, the pound mass or the pound force. Ah, older. So that means.........what? 73, Jim AC6XG |
On Thu, 02 Oct 2003 09:25:38 -0700, Jim Kelley
wrote: Gene Nygaard wrote: What physical quantity do you think a grocery store scale measures? You can probably figure that out for yourself, if you stop to think about how they are tested and certified. You misunderstand, Gene. It's not at all clear what _you_ think they measure. I'm not asking about the units displayed on them. What physical quantity do you think is actually being measured? I think that is probably obvious to anybody with half a brain. But it really doesn't matter, that shouldn't be any impediment to your telling us where my clues have led you. Where are you trying to lead me? Maybe you have some strange notion of what the verb "to measure" means? It wouldn't hurt you to stop and reflect on that for a moment, and answer it at least to yourself, before you get to the "Open mouth, insert foot" stage. And so a torque wrench has what kind of units printed on its scale - mass and distance, or force and distance? Once again, it doesn't cost you any more to pay attention. They are units of force and distance, There's the point. Why are you still refusing to deal with the "meter kilograms" on my torque wrench, even going so far as to dishonestly snip that out from the middle of what you quoted, in between your own comments, without telling us that you were doing so? Since this involves only force and distance, what could it possibly tell you about the existence of a unit of mass called a kilogram? Since this involves only force and distance, what could it possibly tell you about the existence of a unit of mass called a pound? That the poundal system is much older than the slug system is merely one of the many clues as to which is older, the pound mass or the pound force. Ah, older. So that means.........what? Let's not overlook the obvious. Perhaps most the most important thing for your education, and that of several other fools in this thread as well, that it exists. That's something you weren't willing to admit in the beginning. But if it didn't exist, we certainly wouldn't be able to say that it is older. (A corollary, of course, is that if pound force didn't exist, there would be nothing for these units to be older than.) Thus, what you quoted from the appendix of Halliday and Resnick (1981) was incorrect. Do you agree? That it is legitimate. Conversely, that it is the pound force that is the ******* child. This is also one important factor in the usage rules as spelled out by the ASTM and followed by NIST, the U.S. national standards laboratory, and the National Physical Laboratory, the U.K. national standards laboratory. That is indeed one reason why this unit gets to use the unadorned name "pound" and the original symbol "lb," while the newer spinoff needs to be identified as a "pound force" and use the symbol "lbf" to distinguish itself. That the troy pounds, in terms of which the avoirdupois pound was defined for centuries, are units of mass. This doesn't tell you that they have never spawned units of force of the same name; you have to figure that fact out by other means. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
Gene Nygaard wrote:
"Why are you still refusing to deal with the "meter kilograms" on my torque wrench---?" Multiply the meters by 3.28 and multiply the kilograms by 2.2, and you will have torque in their product computed in foot pounds. Or, just multiply the dial reading by 7.22 for ft.lbs. Torque is the product of force and distance. Weight is a force produced by gravity on a particular mass. The indication on a torque wrench is muscle force times lever length. It directly has little relation to gravity in most torque wrench applications. Weight is the easy way to determine mass. Computing mass from collection of acceleration data would be more complicated. M = F/A Best regards, Richard Harrison, KB5WZI |
On Thu, 2 Oct 2003 15:24:23 -0500 (CDT),
(Richard Harrison) wrote: Gene Nygaard wrote: "Why are you still refusing to deal with the "meter kilograms" on my torque wrench---?" Multiply the meters by 3.28 and multiply the kilograms by 2.2, and you will have torque in their product computed in foot pounds. Or, just multiply the dial reading by 7.22 for ft.lbs. Torque is the product of force and distance. It's no surprise that you don't have any problem with this. Don't you remember when I told you that your views were at odds with those of Jim Kelley (and half a dozen others in this thread as well)? It's Jim Kelley who is having great difficulty dealing with these "meter kilograms." Their existence demolishes one of his major arguments. Will he, or any of the others making similar foolish arguments, ever address this? I don't think it's that you understand all this a whole lot better than those others. Rather, you are more like those rocket scientists who blissfully get specific impulse in "seconds" by using pounds mass to cancel out pounds force. In SI, the units of specific impulse are N·s/kg, or the equivalent m/s. Weight is a force produced by gravity on a particular mass. One definition of weight, yes. The indication on a torque wrench is muscle force times lever length. It directly has little relation to gravity in most torque wrench applications. I don't understand why you think that's even something worth bothering to point out. Do you think this would have some bearing on the fact that both Jim and I have characterized torque as "force times distance"? How? The word "weight" didn't enter into those discussions of torque, as far as I can remember. Or are you just pointing out the unrelated (at least in the sense that it wasn't part of our discussion of torque) fact that pounds force are often used for things that are never called "weight," so identifying them as "units of weight" is pretty stupid? At least, compared to the identification of pounds mass as "units of weight" since in the definition of weight as a synonym for the "mass" of physics jargon, that's what mass units such as troy ounces or avoirdupois pounds or kilograms are always used for--something that can be called "weight"? Weight is the easy way to determine mass. Computing mass from collection of acceleration data would be more complicated. M = F/A Principle of equivalence. Look that up. OTOH, computing force due to gravity with a balance is not merely "more complicated," it is impossible without additional information you don't get from the process of weighing it with the balance. For example, suppose I have a bar of gold that weighs 401.23 troy ounces on my balance. How much force does it exert due to gravity, at my location on Earth? Use any force units you choose--poundals, newtons, kilograms force, sthenes, whatever--just remember that troy ounces are not units of force. Now suppose I take the whole works to the middle of the Sea of Tranquillity on the Moon, and weigh it again. It weighs 401.25 troy ounces. How much force is it exerting due to gravity now? Once again, any units of force will be fine. Now, I'm also sure that you are well aware that we call what we measure with a balance "weight," aren't you? Can you tell me why so many science textbook authors appear to be unaware of this commonly known fact? (They aren't really, it is a sham in most cases, and others try to weasel out of it by imagining some "error" is that usage.) Would you suppose that this might have something to do with the great emphasis some of them place on the operation of a spring scale, going into great detail about how they work, while ignoring the only weighing devices anybody had ever used for the 7000 years or so that people had been weighing things, before those spring scales first appeared in the 19th century? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
Gene Nygaard wrote: It's Jim Kelley who is having great difficulty dealing with these "meter kilograms." Their existence demolishes one of his major arguments. Will he, or any of the others making similar foolish arguments, ever address this? If you have a point, sir, I think it's time you should make it. If your intent is nothing more than to blither inanities, then when will you have your fill? 73 de ac6xg |
Gene Nygaard wrote: So my followup to you is along the same lines: Do you claim that those "meter kilograms" prove that kilograms are not units of mass? Not a very difficult question to answer, is it, Jim? Nope. As I recall, the reason it came up was that you were denying that pounds were a unit of force. I cited the torque wrench, and you pointed out that kg-f are also units of force. I still think you lose on that account. Don't you? 73 ac6xg |
On Fri, 03 Oct 2003 11:01:09 -0700, Jim Kelley
wrote: Gene Nygaard wrote: It's Jim Kelley who is having great difficulty dealing with these "meter kilograms." Their existence demolishes one of his major arguments. Will he, or any of the others making similar foolish arguments, ever address this? If you have a point, sir, I think it's time you should make it. If your intent is nothing more than to blither inanities, then when will you have your fill? You can be pretty dense when you want to be. Here's what you, Jim Kelley, wrote earlier in this thread: Date: Fri, 26 Sep 2003 15:44:09 -0700 Message-ID: Why do you think torque wrenches have the unit 'foot-pounds' printed on them if the pound is a unit of mass? Date: Wed, 01 Oct 2003 10:32:56 -0700 Organization: University of California, Irvine Lines: 53 Message-ID: And so a torque wrench has what kind of units printed on its scale - mass and distance, or force and distance? What was your point in asking these questions? Quite simple. You were offering those "foot-pounds" as proof of the supposed fact that pounds are units of force and not units of mass. In fact, you specifically claimed, by asking a rhetorical question in last Friday's message, that torque wrenches would not have these units on them if a pound is a unit of mass. So my followup to you is along the same lines: Do you claim that those "meter kilograms" prove that kilograms are not units of mass? Not a very difficult question to answer, is it, Jim? Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
On Fri, 03 Oct 2003 11:54:00 -0700, Jim Kelley
wrote: Gene Nygaard wrote: So my followup to you is along the same lines: Do you claim that those "meter kilograms" prove that kilograms are not units of mass? Not a very difficult question to answer, is it, Jim? Nope. As I recall, the reason it came up was that you were denying that pounds were a unit of force. Then why did you claim something entirely different--not that this proved that pounds force exist, but rather that it proved that pounds could not be units of mass? That official definition of a pound as a unit of force still remains an elusive little devil, however. Don't you agree? Or are you good enough to find it? I cited the torque wrench, and you pointed out that kg-f are also units of force. I still think you lose on that account. Don't you? Certainly not. Thanks for correcting your earlier claims. You are making progress, now admitting both that pounds are units of mass, and that kilograms force exist just as well as pounds force do. Have you realized yet that you are now aligning yourself with me, rather than with fools like Richard Clark and KU2S, Raymond Sirois. With me, and with the younger Resnick and Halliday (1960) that I quoted, not with the fools you quoted, Halliday and Resnick (1981 appendix, and appendix of most or all later editions). Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
Supporting theory that Antennas "Match" to 377 Ohms (Free space)
The reason we don't match the antennas to the impedance of free-space is very simple, it all has to do with Industry standards, manufacturing, and application. If you increase the impedance of the coax to match a 377Ω antenna and transceiver, the design of the coax would demand that you increase the dielectric diameter ≈ 230 times in order to preserve the current capacity of the center conductor.
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Supporting theory that Antennas "Match" to 377 Ohms (Free space)
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Supporting theory that Antennas "Match" to 377 Ohms (Free space)
On 07/21/2017 05:32 PM, wrote:
The reason we don't match the antennas to the impedance of free-space is very simple, it all has to do with Industry standards, manufacturing, and application. If you increase the impedance of the coax to match a 377Ω antenna and transceiver, the design of the coax would demand that you increase the dielectric diameter ≈ 230 times in order to preserve the current capacity of the center conductor. Hello, and I think you're confusing the intrinsic impedance of free space (377 ohms) with the feedpoint impedance of an antenna, which depends on frequency, physical dimensions, and construction materials of the antenna. It's the antenna feedpoint impedance that we match our RF source to, not the free space impedance. Sincerely, and 73's from N4GGO, -- J. B. Wood e-mail: |
Supporting theory that Antennas "Match" to 377 Ohms (Free space)
There are lots of opinions here .. but looking carefully at the equations which determine the impedance of free space, these are related to c. (C0 to be correct)
Importantly so is the wavelength of a specific frequency, and from that the physical antenna length required to give good radiation. So .. when you choose the antenna dimension to be a multiple or sub multiple of the wavelength, it is this that matches to the impedance of free space.. Importantly, the antenna changes the mode of transmission from a waveguide, coax, twin or other, to the ejection of electrons into free space, i.e. no longer constrained by a waveguide unless and until some group of these electrons meet a new resonant waveguide in their path. Matching the radiator element to its reference plane, as Richard Harrison mentions, is a separate issue. We generated an AC electrical signal with reference to a ground or balanced opposite. The antenna is part of that AC circuit, and the AC pulses must feel the same medium (impedance) all the way to the point where the energy is released into free space. There are various simulation videos on youtube showing that it is at the peak gradient of the antenna waveform when the electrons are accelerated enough to escape their waveguide, and it is the exposed resonant element which facilitates this change of propagation mode. So in summary .. the choice of antenna length is related to signal wavelength, which is related to C, which also determines the impedance of free space. And this length is what matches to free space (if one must refer to matching here). The matching of feed line to a balanced or ground referenced radiator is entirely separate. It is standard AC and transmission line theory, of which a radiator is matched to its opposite or reference conductor. BR Tom Importantly On Monday, 24 July 2017 at 16:53:44 UTC+2, J.B. Wood wrote: On 07/21/2017 05:32 PM, wrote: The reason we don't match the antennas to the impedance of free-space is very simple, it all has to do with Industry standards, manufacturing, and application. If you increase the impedance of the coax to match a 377Ω antenna and transceiver, the design of the coax would demand that you increase the dielectric diameter ≈ 230 times in order to preserve the current capacity of the center conductor. Hello, and I think you're confusing the intrinsic impedance of free space (377 ohms) with the feedpoint impedance of an antenna, which depends on frequency, physical dimensions, and construction materials of the antenna. It's the antenna feedpoint impedance that we match our RF source to, not the free space impedance. Sincerely, and 73's from N4GGO, -- J. B. Wood e-mail: |
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