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Cecil wrote,
Gene Nygaard wrote: You can, of course, choose not to call this quantity "weight." You can call it mass instead, if you want to. Here's an interesting quote from _University_Physics_ by Young and Freedman: "On the moon, a stone would be just as hard to throw horizontally, but it would be easier to lift." It also says weight is a vector and mass is a scalar. -- 73, Cecil http://www.qsl.net/w5dxp You better watch out, Cecil, Gene is liable to write a scathing indictment of your intelligence, integrity, and job fitness, for quoting that. By the way, what ever happened to the old idea that the attraction between two masses was directly proportional to the size of the two masses multiplied together, and inversely proportional to the square of the distance between them - sort of like positive and negative charge (Coulomb's Law and all that). 73, Tom Donaly, KA6RUH |
Cecil, W5DXP wrote:
"On the moon, a stone would be just as hard to throw horizontally, but it would be easier to lift." The normal forces are different on the earth and moon. But, the physics book statement follows from Newton: F= MA, and M is the same on earth or moon. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote: Cecil, W5DXP wrote: "On the moon, a stone would be just as hard to throw horizontally, but it would be easier to lift." The normal forces are different on the earth and moon. But, the physics book statement follows from Newton: F= MA, and M is the same on earth or moon. I think the point is that the inertia is the same, independent of what the gravity might happen to be, thus demonstrating the most fundamental property and defining feature of mass. 73, Jim AC6XG |
Gene Nygaard wrote:
It doesn't cost you any more to pay attention. Repeat to yourself until you understand it: Weight is an AMBIGUOUS word. IT HAS SEVERAL DIFFERENT MEANINGS. What cause have I given you to write to me in such a manner? The one you cite from the Chemical Rubber Company is, of course, one of those several definitions. If it always meant the same as mass in physics jargon, I wouldn't have to point out to you that this is an ambiguous word, would I? This is the first you've mentioned anything about it being ambiguous. Until now, you've just been belligerent and accusational about it. Didn't you read the message you responded to, especially what immediately followed the sentence you quoted? Didn't you see what NIST and ASTM have to say about this? Look at it again, and read it slowly this time I'm commenting on what you said, Gene. I have no comment on what NIST had to say. Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Examples: the child's weight is 23 kg Learn to evaluate your sources, also. Those sources are more credible than any CRC Handbook on this subject. You need to learn how to attribute yours. I didn't write that. :-) Your definition of weight is not the proper one to use for your body weight in the doctor's office or the gym. I don't write definitions. But the ones I have cited are no less accurate in the doctors office than the physics lab. You can, of course, choose not to call this quantity "weight." You can call it mass instead, if you want to. As I recall, the argument was about whether to call it a mass or a force. It's generally accepted that weight is a force. Problems can arise when someone claims a mass is a force and vice versa. Furthermore, it is not an acceptable option to misinterpret what they are saying, and to misapply an inappropriate definition of weight. It is possible that you are doing some of the misinterpreting. You could, of course, argue that we should all change to your usage. Many people already have, obviously. Reflecting the apparent dichotomy, the CRC defines the pound both ways: "1. A unit of mass equal in the U.S. to 0.45359237 kg. exactly. 2. Specifically, a unit of measurement of the thrust or force of a reaction engine representing the weight the engine can move, as an engine with 100,000 pounds of thrust. 3. The force exerted on a one pound mass by the standard acceleration of gravity." That really shouldn't come as any surprise to you, does it, at this stage of the game? I believe I had stated the same thing in so many words, earlier. Interestingly, they also define poundal, pound mass and pound weight. No mention of pound force. Evidently, that would be redundant. ;-) Have you figured out yet what those poundals are, and how they are used? Were you not able to ascertain that from my earlier post where I referenced the definition in Halliday and Resnick? One thing about the CRC Handbook (which edition?) is that they include stuff put in there over a period of many years, most of it undated. Those "pounds weight" are an obsolete term for what are now called pounds force. So which units of weight do you think we're supposed to use now? 73, Jim AC6XG |
On Tue, 30 Sep 2003 14:21:14 -0700, Jim Kelley
wrote: Gene Nygaard wrote: It doesn't cost you any more to pay attention. Repeat to yourself until you understand it: Weight is an AMBIGUOUS word. IT HAS SEVERAL DIFFERENT MEANINGS. What cause have I given you to write to me in such a manner? The one you cite from the Chemical Rubber Company is, of course, one of those several definitions. If it always meant the same as mass in physics jargon, I wouldn't have to point out to you that this is an ambiguous word, would I? This is the first you've mentioned anything about it being ambiguous. You just haven't been paying attention. Until now, you've just been belligerent and accusational about it. Didn't you read the message you responded to, especially what immediately followed the sentence you quoted? Didn't you see what NIST and ASTM have to say about this? Look at it again, and read it slowly this time I'm commenting on what you said, Gene. I have no comment on what NIST had to say. Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Examples: the child's weight is 23 kg Learn to evaluate your sources, also. Those sources are more credible than any CRC Handbook on this subject. You need to learn how to attribute yours. I didn't write that. :-) There isn't any standard way of handling this, as far as I know. I've seen it done several different ways, none of them completely satisfactory. So I'm open to suggestions, if you can tell us how you think it should be done. Next time I'll mark the end of the quote from an earlier message, as well as the beginning--would that satisfy you? Your definition of weight is not the proper one to use for your body weight in the doctor's office or the gym. I don't write definitions. But the ones I have cited are no less accurate in the doctors office than the physics lab. 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. You can, of course, choose not to call this quantity "weight." You can call it mass instead, if you want to. As I recall, the argument was about whether to call it a mass or a force. You recall incorrectly. 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. All of these sources and many others tell you that weight is an ambiguous word, with several different meanings. Problems can arise when someone claims a mass is a force and vice versa. I agree. Furthermore, it is not an acceptable option to misinterpret what they are saying, and to misapply an inappropriate definition of weight. It is possible that you are doing some of the misinterpreting. You could, of course, argue that we should all change to your usage. Many people already have, obviously. Not very many, surprisingly. It is much more common to find people claiming, erroneously, that there is some error in that usage. Reflecting the apparent dichotomy, the CRC defines the pound both ways: "1. A unit of mass equal in the U.S. to 0.45359237 kg. exactly. 2. Specifically, a unit of measurement of the thrust or force of a reaction engine representing the weight the engine can move, as an engine with 100,000 pounds of thrust. 3. The force exerted on a one pound mass by the standard acceleration of gravity." That really shouldn't come as any surprise to you, does it, at this stage of the game? I believe I had stated the same thing in so many words, earlier. Interestingly, they also define poundal, pound mass and pound weight. No mention of pound force. Evidently, that would be redundant. ;-) Have you figured out yet what those poundals are, and how they are used? Were you not able to ascertain that from my earlier post where I referenced the definition in Halliday and Resnick? No, I couldn't tell one way or the other from your mere statement that the poundal was idenitified in that appendix as a unit of force whether or not you know anything about the system in which they are used. Like slugs, poundals only exist in one limited purpose system of mechanical units, mostly used to simplify calculations. Do you understand how these systems are used, and the difference between them. The part you snipped (the second sentence in the last paragraph of mine quited above) makes it clearer that this is what I was asking about. So tell me now, what is the base unit of mass in the system in which poundals are the derived unit of force? Do you understand that yet? I still don't know. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
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 SysOp: The Lost Chord BBS 607-733-5745 telnet://thelostchord.dns2go.com:6000 |
Gene Nygaard wrote:
"Those "pounds weight are an obsolete term for what are now called pounds force." Spoken like a weight-loss promoter. Good mathematics becomes obsolete very slowly. Archimedes found the approximate value of pi in the 3rd century before Christ. 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. 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. Archimedes was slain in his laboratory by a Roman soldier in spite of orders that he be taken alive and transported to Rome. He was the top Greek war machine designer. Best regards, Richad Harrison, KB5WZI |
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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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. Best regards, Richard Harrison, KB5WZI |
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