One kilogram is equal to about 2. Although both kilograms and pounds are measured with a scale, kilograms are a measure of mass, or the amount of matter in an object.
Pounds are a measure of weight, which is the force of gravity on an object. The mass of an object does not change, while weight is affected by fluctuations in gravity. A 1 kg object on Earth has the same mass but a different weight if it is taken to the Moon. World View. Natural silicon is 92 percent silicon Russian laboratories have provided kilogram quantities of silicon enriched to The surfaces are oxidized. Isotopic analyses by different techniques have produced significantly different results for the composition.
A device called a watt balance, shown here at the National Institute of Standards and Technology, counteracts the gravitational force on an object by electromagnetic induction, and could be used to define the kilogram. The watt balance is predicated on an even more troublesome artifact. Gravitational acceleration is permanently encumbered with a limit of parts-per-billion precision.
The proponents of the watt balance approach admit that the lunar cycle and tides affect their measurements, although the corrections are confidently manageable. Local gravitational acceleration g , not to be confused with the fundamental gravitational constant, G , of course, is also affected by distribution of mass and by geographical location of the apparatus. Earthquakes, volcanic eruptions, and seasonal hydrology have the largest correctional influence.
Also, landmasses rising and falling and ice caps melting with seasonal temperature changes; polar motions; atmospheric pressure; depth of the local water table; and even human activities affect gravitational acceleration. The crustal lithosphere is constantly stirring around. Global climate changes affect sea levels. Gravitational shifts occur on time scales ranging from minutes to years and spatial extents from meters to global.
The BIPM should have been aware of their transgression beforehand. This cogent quote followed an astute observation by Maxwell that seems to have been overlooked by the metrology community:. In and , theoretical physicist Frank Wilczek published a series of brief, thoughtful essays on absolute physical units emphasizing, among other things, relationships among them. Much of his presentation dealt with units of length, time, and mass. Wilczek noted as an illustration that units must be such that one could communicate information, such as body mass, with a correspondent anywhere—on the Moon or even in the Andromeda galaxy—by simply transmitting pure numbers.
No such hypothetical exchange of information on mass would be possible under the BIPM proposal, making it a choice that is uniquely and disadvantageously confined in both geography and time. Furthermore, length the meter , time the second , and mass the kilogram are all comprehensible phenomena to the general public, but the BIPM-proposed kilogram definition is undeniably obtuse, stifling clarity and visualization.
An essential insight with respect to the mass fundamental unit is the following dictum: There is, in practice, absolutely no need for parts-per-billion precision in a macroscopic mass such as embodied in the current standard kilogram.
But in keeping with the philosophy of the meter and second, there is a need for an equivalently precise fundamental mass standard. Fortunately, such a standard can be quite elegantly and simply instituted microscopically, where it is needed, without the ambiguities and complexities inherent in either of the BIPM proposals. Current measurement techniques have yielded better than parts-per-billion precision masses of atoms, and even the electron and the muon, all relative to carbon Measurements can be on one atom at a time.
The mass of carbon is an invariant of nature. Ubiquitous carbon requires no upkeep or security precautions. It would seem, though, that the proposed carbon alternative leaves us with an impractical dilemma: macroscopic mass.
But one mole of carbon atoms has a mass of exactly 12 grams, providing a macroscopic connection to the unified atomic mass. Although somewhat arbitrary, this long-standing dictum is nevertheless an intuitive and understandable option. More problematic, it might initially seem, is the mole. If the atomic weight of an atom of carbon were defined as exactly 12 atomic mass units, this mass could then be related to the kilogram—an approach the author advocates. I have a simple solution.
It is, in the simple scheme of things, the quantitative gauge that links two mass scales, microscopic and macroscopic. The mole does not belong on the list of SI base units for physical quantities and, in fact, was added to that list only in To some, such a suggestion is horrifying, chafing at the drilled-in and deeply entrenched notion that the mole is a physical unit, a must for the chemical amount of substance, rather than a numerical quantity.
The platinum-iridium metal artifact that currently defines the kilogram, along with all its hundred or so near-clones, in this alternative view become secondary global standards, reference materials, precise to better than 0. Certainly, this value is an analog to the definition of a meter as related to the speed of light in a vacuum. In the future, instrumentation connecting time and mass is likely to play a role in the kilogram—mole connection.
The Compton clock, a device taking advantage of atom interferometry, has recently been constructed and successfully operated. Companies bet carbon labels can help the climate. Will consumers catch on? Jessica Wolfrom June 17, Washington Post. Are Cellphones Really a Cancer Risk? Rome Mildred Anna Rosalie Tuker. The Great Events by Famous Historians, v. Montessori Elementary Materials Maria Montessori. One kilogram is equivalent to 2.
Symbol: kg. The base unit of mass in the International System of Units, equal to 1, grams 2. Published by Houghton Mifflin Company.
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