Talk:Kilogram
From Academic Kids
All terms of science, including units of measure, use operational definitions, that is, definitions based on actually performable experiments and observable results. The kilogram is intended to represent the mass of one litre of water (where litre is defined in terms of metre, and metre is defined in terms of the measurable speed of light), but that's a theoretical thing --it's not possible with today's technology (nor was it in the past) to conduct any specific experiment with water to produce this value. The kilogram has always been officially defined in terms of the artifact in Paris (the metre once was as well, but now we have new experiments). There is a movement among some scientists now to redefine it in terms of a new experiment in which measurable electrical potentials move a specific mass, but this is still in the works. --LDC
- The kilogram as = 1 L of water was true between 1901 and 1964 (definition of the Litre; see CGPM).
- Urhixidur 20:29, 2004 Nov 23 (UTC)
I was under the impression that the kilogram had recently been redefined in relation to x moles of a certain isotope, rather than the kilogram at Sèvres. Is that not true? - montréalais
- There are a number of competing plans to redefine the kilogram in terms of something repeatable. No plan has yet been decided on. -- The Anome 22:10 22 Jun 2003 (UTC)
According to the Bureau International des Poids et Mesures, the kilogram is still defined by the international prototype in Paris. Do you think it's fair use to put a picture of it from the BIPM site in the article? Basil Fawlty 15:12 22 Jun 2003 (UTC)
- Seems like it would be fair if the source and a disclaimer tag were included. As the fair use page states, "Unique historical images which we cannot reproduce by other means" can be classified as fair use. The big pic (http://www.bipm.org/en/scientific/mass/pictures_mass/prototype.html) is nice. -- Mjwilco 19:12, 11 Sep 2004 (UTC)
What does this mean: "grain in now obsolete Portuguese spelling"? Is that supposed to imply that the word "gram" comes from obsolete Portuguese? Webster's 1913 says: "F. gramme, from Gr. ? that which is written, a letter, a small weight, fr. ? to write.". Or is it some weird reference to the imperial unit grain, meaning 1/7000 of a pound? -- ESP 05:37 20 Jul 2003 (UTC)
Am I right in assuming that, by E=mc^2, if you heat an object, you will (ever-so-slightly) increase its mass, by adding thermal energy? (according to [[1] (http://www.google.com/search?q=1%20calorie%20in%20grams&ie=UTF-8&oe=UTF-8|google)] to heat 1 gram of water by 1 degree C, requires ~0.465 femtograms of energy. Therefore any atom-based definition of the kilogram will require a temperature reference. CS Miller 11:39, Nov 23, 2004 (UTC)
- You are quite right. In Einsteinian terms, we would refer to the zero K mass as the object's rest mass. Note that the SI definition of the second also takes care to specify that the ground state hyperfine transition used occurs at zero K.
- Urhixidur 20:29, 2004 Nov 23 (UTC)
Kilogram as Base unit?
Has the kilogram always been considered a base unit? If so, why does it have a prefix? Why doesn't the metric system use a basic word for that unit, and instead call the gram milli-whatever? If it wasn't considered a base unit initially, when did it come to be considered the base unit? It has always seemed strange to me that a so-called "base" unit has a prefix Nik42 09:00, 26 Jan 2005 (UTC)
- It really is quite stupid, but its too late to change that now :P. My theory is that the gram initially was the base unit, but people realised that it was smarter to use kg (less room for error when copying the base-sphere, and also derived definitions like the newton make more sense. That and it would be strange to measure the human body in grams "I weigh 75345 g, what do you wheigh?) So they just changed the base and kept the name to avoid confusion. This is my theory anyway Gkhan 04:33, Feb 27, 2005 (UTC)
- Well, the weight thing's not really an issue. That's what prefixes are for anyways :-) I mean, no one would say that two cities were 52,000 meters apart, they'd say they were 52 kilometers apart. Still, kg definitely does make more sense as a basic unit for pretty much any purpose, which is why I find it odd that gram gets the basic name. - Nik42 07:50, 1 Mar 2005 (UTC)
AFAIK there is no atomic definition for kilogram. In 1967 the kilogram[2] (http://physics.nist.gov/cgi-bin/cuu/Value?kgu) was defined as the mass of 5.0188 X 10 (power 25) atoms of the carbon isotope of atomic mass number 12. The experimental uncertainty in the count was about 1 part in 20,000. -- Orionix 03:11, 4 Feb 2005 (UTC)
Clarify changes over the last 100 years
From the article: Although it is accurate to state that all other objects in the universe have gained 50 micrograms per kilogram, this perspective is counterintuitive and defeats the purpose of a standard unit of mass.
This makes no sense to me. If you counted the number of micrograms in a kilogram 100 years ago, you'd get a billion (if my metric conversions are correct). And the article is implying that if you count the number of micrograms in a kilogram today, you'd get 1,000,000,050? Wrong.
Maybe a more clear way to say it would be "It is accurate to state that any object in the universe (other than the reference metal in France) that had a mass of 1 kilogram 100 years ago, and has not changed since then, now is considered to have a mass which is 50 micrograms larger than a kilogram. This perspective is counterintuitive and defeats the purpose of a standard unit of mass, since the standard should not change arbitrarily over time."
--24.29.11.65 11:27, 27 Feb 2005 (UTC)
- How is it known that the standard has lost weight? How can one compare a standard to itself over time? It seems like a paradox to me. Prometheus235 19:03, 16 Jun 2005 (UTC)
- Presumably because you can compare the weight of other objects over time. If you consistently find that items measured 100 years ago appeared to possess slightly greater mass than they do today, the simplest explanation is not that all of those items gained mass, but that the standard lost mass. - Nik42 18:25, 17 Jun 2005 (UTC)
