# Tag Info

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The Kelvin temperature scale is an absolute temperature scale. That is 0 K is absolute zero. It also has the property that temperature intervals on the Kelvin scale are the same as on the Celsius scale. That is a decrease or increase of one degree Kelvin is the same as a decrease or increase of one degree Celsius. To meet these two requirements it is ...

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The Weights and Measures Act (the origin of the Imperial Units) does not speak of temperature. It was intended to create a uniform system for trade. You don't sell temperature, in the way you sell a pint of milk or a yard of cloth. And frankly, when it was first conceived (before Magna Carta, which already stated: "There shall be but one Measure ...

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According to the wiki page on Imperial and US customary units Fahrenheit is part of both the Imperial and US customary system. I can't think of any reason it wouldn't be included in the Imperial system. Note that in the wiki page on Imperial units it is mentioned that the weight's and measures act (which defined the Imperial system) explicitly used the ...

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In the US, if you purchase a balance or set of reference weights (masses) or a scale for scientific purposes, you can also purchase with it a certificate of traceability. This is a document that states how your device was compared to a reference, and how that reference was traceably compared to an even better reference, and so on, up to the standard kilogram ...

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When the I nternational prototype kilogram (IPK) was created, copies were made and sent to the most important countries in the world and are kept in a protected environment. Periodically they are returned to France, checked and compared and, surprisingly enough, their masses do not match anymore. Factories that produce these items have access to them or ...

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The number of atoms or molecules is not dimensionless, it is the way we "count" the matter. Here are some examples to illustrate the fundamental importance of the amount of substance: While $E = m c^2$, you will not extract the same total energy if your fission process is done with 1 atom or with 1 mole of $^{235}U$. Consider the other basic law $PV=nRT$: ...

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So, here's the thing. The chemistry that underlies molar mass ratios dates back at least to 1805. We've known that if you divide by a certain "relative mass" number you can get whole-number ratios for atoms in a pile of stuff, for that long. It took us about 60 more years to get a handle on how large atoms were with the estimations of Loschmidt, who worked ...

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Weighing matter isn't the only way to account for how much mass you have, counting the number of fundamental particles g hat comprise it is equally legitimate. Moles , slugs, grams are all units that account for the dimensional quality of mass. Counting moles for that matter is a more precise unit of measure.

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I'd like to add a bit more to Adam Davis's concise answer. Newton's Sphere Production Method Firstly, note that the lathing process shown in The video that Adam Davis's Answer links to with the sphere rotated and an oscillating abrasive cup sliding over its surface about pseudo-random rotation axes is the standard technique invented by Isaac Newton that ...

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Another reason that nobody David Richerby mentioned in a comment, is durability. The corner of a cube would be easy to accidentally break because a small force on it would equate to a large pressure (its area gets smaller as the shape of the cube gets more accurate). In fact I think it would be likely to break during machining, resulting in truncated corners ...

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If you know the diameter of the sphere, you know everything you need to know about the dimensions. It all comes down to one single value. Any other shape requires multiple dimensions and thus multiple values. Further, measuring a cube or another shape for accuracy is harder than measuring a sphere. Making very accurate spheres is not as difficult as you ...

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There is a nice article in the New Scientist that describes how these spheres were made. Sphere can be made very precisely (and their shape measured accurately) simply because of their symmetry - and therefore their volume can be determined most accurately. The video clip in the above article shows this in detail. Of course a sphere also has the lowest ...

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A sphere might be harder to machine, but easiest to verify the accuracy of, especially when accounting for slight changes due to temperature. It should be noted that any standard like this must not only have a mass of 1 kg (or whatever) but also have some secondary method of verifying mass, in this case, being able to count (to some accuracy) the number of ...

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