"Kg" beralih ke halaman ini. For other uses, see Kg (disambiguation) . Untuk kegunaan lain, lihat Kg (disambiguasi) .
 | |
| Standard: Standar: | SI base unit Unit dasar SI |
| Quantity : Quantity : | Mass Massa |
| Symbol: Simbol: | kg kg |
| Expressed in: Disajikan dalam: | 1 kg = 1 kg = |
| Natural units Alam unit | 4.594 6 7(23) × 10 7 Planck masses 4,594 6 7 (23) × 10 7 Planck massa |
| Energy Energi | 1.356 3 92 7 33(68) × 10 50 hertz [ Note 1 ] 1,356 3 92 7 33 (68) × 10 50 hertz [Catatan 1] |
| 89,875,517,873,681,764 joules (precisely) 89.875.517.873.681.764 joule (tepatnya) | |
| US customary US adat | ≈ 2.204 6 22 6 22 pounds - avoirdupois ≈ 2,204 6 22 6 22 pound - avoirdupois |
In everyday usage, the mass of an object, which is measured in kilograms, is often referred to as its weight . Dalam penggunaan sehari-hari, massa dari sebuah obyek, yang diukur dalam kilogram, sering disebut sebagai yang berat . However, the term weight in strict scientific contexts refers to the gravitational force of an object. Namun, istilah bobot dalam konteks ilmiah yang ketat mengacu pada gravitasi kekuatan sebuah obyek. Throughout most of the world, force is measured with the SI unit newton and the non-SI unit kilogram-force . Di sebagian besar dunia, kekuatan diukur dengan unit SI newton dan non-SI unit kilogram-force . Similarly, the avoirdupois (or international ) pound , used in both the Imperial system and US customary units , is a unit of mass and its related unit of force is the pound-force . Demikian pula, avoirdupois (atau internasional) pon , yang digunakan baik dalam sistem Imperial dan adat unit AS , adalah satuan massa dan unit terkait gaya adalah pound-force . The avoirdupois pound is defined as exactly 0.453 5 92 3 7 kg , [ 2 ] making one kilogram approximately equal to 2.2046 avoirdupois pounds. Pound avoirdupois didefinisikan sebagai persis 0,453 5 92 3 7 kg, [2] membuat satu kilogram kira-kira sama dengan 2,2046 £ avoirdupois.
Many units in the SI system are defined relative to the kilogram so its stability is important. Banyak unit dalam sistem SI didefinisikan relatif terhadap kilogram sehingga stabilitas adalah penting. After the International Prototype Kilogram had been found to vary in mass over time, the International Committee for Weights and Measures (known also by its French-language initials CIPM) recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature. [ 3 ] No final decision is expected before 2011. [ 4 ] Setelah Prototipe Kilogram Internasional telah ditemukan untuk berubah dengan massa dari waktu ke waktu, itu Komite Internasional untuk Berat dan Ukuran (dikenal juga dengan inisial bahasa Perancis-nya CIPM) yang direkomendasikan pada tahun 2005 bahwa kilogram didefinisikan ulang dalam hal konstanta fundamental alam. [3] Tidak ada keputusan akhir diharapkan sebelum 2011. [4]
Sifat massa
See also: Mass versus weight Lihat juga: Massa versus berat
While the weight of matter is entirely dependent upon the strength of gravity, the mass of matter is invariant. [ Note 5 ] Accordingly, for astronauts in microgravity , no effort is required to hold objects off the cabin floor; they are “weightless”. Sedangkan bobot materi sepenuhnya tergantung pada kekuatan gravitasi, massa materi invarian. [Catatan 5] Oleh karena itu, untuk astronot di gayaberat mikro , tidak ada upaya yang dibutuhkan untuk menjaga benda-benda dari lantai kabin, mereka adalah "ringan". However, since objects in microgravity still retain their mass and inertia, an astronaut must exert ten times as much force to accelerate a 10‑kilogram object at the same rate as a 1‑kilogram object. Namun, karena benda-benda di gayaberat mikro masih mempertahankan massa dan inersia, astronot harus mengerahkan kekuatan sepuluh kali banyak untuk mempercepat objek 10-kilogram di tingkat yang sama sebagai objek 1-kilogram.
On earth, a common swing set can demonstrate the relationship of force, mass, and acceleration without being appreciably influenced by weight (downward force). Di bumi, sebuah ayunan umum dapat menunjukkan hubungan antara gaya, massa, dan percepatan tanpa appreciably dipengaruhi oleh berat (gaya ke bawah). If one were to stand behind a large adult sitting stationary in a swing and give him a strong push, the adult would accelerate relatively slowly and swing only a limited distance forwards before beginning to swing backwards. Kalau orang untuk berdiri di belakang orang dewasa yang besar duduk diam dalam ayunan dan memberikan dorongan yang kuat, orang dewasa akan mempercepat ayunan yang relatif lambat dan hanya terbatas jarak ke depan sebelum mulai ayunan mundur. Exerting that same effort while pushing on a small child would produce much greater acceleration. Mengerahkan upaya yang sama saat mendorong pada anak kecil akan menghasilkan percepatan yang jauh lebih besar.
[ edit ] History [ sunting ] Sejarah
[ edit ] Early definitions [ sunting ] definisi Awal
For more on the history of the kilogram, see grave (mass) . Untuk informasi lebih lanjut tentang sejarah kilogram, lihat kuburan (massa) .
On 7 April 1795, the gram was decreed in France to be equal to “the absolute weight of a volume of water equal to the cube of the hundredth part of the meter, at the temperature of melting ice.” [ 5 ] The concept of using a specified volume of water to define a unit measure of mass was first advanced by the English philosopher John Wilkins in 1668. [ 6 ] [ 7 ] Pada tanggal 7 April 1795, para gram itu diputuskan di Perancis untuk menjadi sama dengan "berat mutlak dari volume air yang sama dengan kubus bagian keseratus meter, pada suhu saat es mencair." [5] Konsep menggunakan volume tertentu air untuk menentukan ukuran unit massa pertama kali maju oleh filsuf Inggris John Wilkins di 1668. [6] [7] Since trade and commerce typically involve items significantly more massive than one gram, and since a mass standard made of water would be inconvenient and unstable, the regulation of commerce necessitated the manufacture of a practical realization of the water-based definition of mass. Sejak perdagangan dan perdagangan biasanya melibatkan barang secara signifikan lebih besar dari satu gram, dan karena standar massa yang terbuat dari air akan menjadi nyaman dan tidak stabil, peraturan perdagangan mengharuskan pembuatan sebuah realisasi praktis air berbasis definisi massa. Accordingly, a provisional mass standard was made as a single-piece, metallic artifact one thousand times more massive than the gram—the kilogram. Dengan demikian, standar massa sementara dibuat sebagai bagian-tunggal, logam artefak kilogram seribu kali lebih besar daripada-gram ini.
At the same time, work was commissioned to precisely determine the mass of a cubic decimeter (one liter ) of water. [ Note 6 ] [ 5 ] Although the decreed definition of the kilogram specified water at 0 Pada saat yang sama, kerja ditugaskan untuk tepat menentukan massa sebuah decimeter kubik (satu liter ) air. [Catatan 6] [5] Meskipun definisi dekrit dari kilogram yang ditetapkan air pada 0 °C—its highly stable temperature point—the French chemist, Louis Lefèvre-Gineau and the Italian naturalist, Giovanni Fabbroni after several years of research chose to redefine the standard in 1799 to water's most stable density point: the temperature at which water reaches maximum density, which was measured at the time as 4 ° C-suhu yang sangat stabil titik-ahli kimia Perancis, Louis LeFevre-Gineau dan naturalis Italia, Giovanni Fabbroni setelah beberapa tahun penelitian memilih untuk mendefinisikan standar pada 1799 kepadatan titik paling stabil's air: suhu di mana air mencapai maksimum kepadatan, yang diukur pada saat itu sebagai 4 °C. [ Note 7 ] [ 8 ] They concluded that one cubic decimeter of water at its maximum density was equal to 99.9265% of the target mass of the provisional kilogram standard made four years earlier. [ Note 8 ] [ 9 ] That same year, 1799, an all-platinum kilogram prototype was fabricated with the objective that it would equal, as close as was scientifically feasible for the day, the mass of one cubic decimeter of water at 4 ° C. [Catatan 7] [8] Mereka menyimpulkan bahwa salah satu decimeter kubik air pada kepadatan maksimum sama dengan 99,9265% dari target massa standar kilogram sementara membuat empat tahun sebelumnya. [Catatan 8] [9] Hal yang sama tahun 1799, sebuah kilogram platinum semua prototipe itu dibuat dengan tujuan bahwa hal itu akan sama, sedekat secara ilmiah layak untuk hari itu, massa dari satu decimeter kubik air di 4 °C. ° C. The prototype was presented to the Archives of the Republic in June and on 10 Prototipe yang telah disampaikan kepada Arsip Republik pada bulan Juni dan pada tanggal 10 December 1799, the prototype was formally ratified as the Kilogramme des Archives (Kilogram of the Archives) and the kilogram was defined as being equal to its mass. Desember 1799, prototipe secara resmi disahkan sebagai Kilogramme des Archives (Kilogram dari Arsip) dan kilogram didefinisikan sebagai sama dengan massa. This standard stood for the next ninety years. Standar ini berdiri selama sembilan puluh tahun ke depan.
[ edit ] International Prototype Kilogram [ sunting ] Internasional Prototipe Kilogram
Since 1889, the SI system defines the magnitude of the kilogram to be equal to the mass of the International Prototype Kilogram , [ 1 ] often referred to in the professional metrology world as the “IPK”. Sejak 1889, para SI sistem mendefinisikan besarnya dari kilogram yang akan sama dengan massa dari International Prototype Kilogram, [1] sering disebut di profesional metrologi dunia sebagai "IPK". The IPK is made of a platinum alloy known as “Pt‑10Ir”, which is 90% platinum and 10% iridium (by mass) and is machined into a right-circular cylinder (height = diameter) of 39.17 Para IPK terbuat dari platina paduan dikenal sebagai "Pt-10Ir", yang merupakan 90% platinum dan 10% iridium (oleh massa) dan mesin menjadi-lingkaran silinder kanan (tinggi = diameter) dari 39,17 millimeters to minimize its surface area. [ 10 ] The addition of 10% iridium improved upon the all-platinum Kilogram of the Archives by greatly increasing hardness while still retaining platinum's many virtues: extreme resistance to oxidation , extremely high density , satisfactory electrical and thermal conductivities , and low magnetic susceptibility . milimeter untuk meminimalkan area permukaannya. [10] Penambahan% iridium 10 perbaikan pada-Kilogram platinum semua Arsip dengan amat meningkatnya kekerasan sementara masih mempertahankan banyak kebajikan's platinum: ketahanan ekstrim untuk oksidasi , sangat tinggi kepadatan , memuaskan listrik dan termal konduktivitas , dan rendah suseptibilitas magnetik . The IPK and its six sister copies are stored at the International Bureau of Weights and Measures (known by its French-language initials BIPM) in an environmentally monitored safe in the lower vault located in the basement of the BIPM's House of Breteuil in Sèvres on the outskirts of Paris (see External images , below for photographs). Para IPK dan enam salinan adik disimpan di Biro Internasional Berat dan Ukuran (dikenal dengan berbahasa Perancis inisial nya BIPM) di lingkungan dipantau aman di lemari besi yang lebih rendah yang terletak di basement dari BIPM House of Breteuil di Sèvres pada pinggiran Paris (lihat Gambar eksternal , di bawah ini untuk foto). Three independently controlled keys are required to open the vault. Tiga kunci dikontrol secara independen diperlukan untuk membuka lemari besi. Official copies of the IPK were made available to other nations to serve as their national standards. salinan resmi IPK dibuat tersedia bagi negara lain untuk melayani sebagai standar nasional mereka. These are compared to the IPK roughly every 50 years. Ini adalah dibandingkan dengan IPK sekitar setiap 50 tahun.The IPK is one of three cylinders made in 1879. Yang IPK adalah satu dari tiga silinder yang dibuat pada tahun 1879. In 1883, it was found to be indistinguishable from the mass of the Kilogram of the Archives made eighty-four years prior, and was formally ratified as the kilogram by the 1st CGPM in 1889. [ 10 ] Pada 1883, telah ditemukan untuk bisa dibedakan dari massa Kilogram Arsip dibuat dari delapan puluh empat tahun sebelumnya, dan secara resmi disahkan sebagai kilogram oleh 1 CGPM tahun 1889. [10]
Modern measurements of Vienna Standard Mean Ocean Water , which is pure distilled water with an isotopic composition representative of the average of the world's oceans, show it has a density of 0.999 9 75 ± 0.000 0 01 kg/L at its point of maximum density (3.984 °C) under one standard atmosphere (760 torr ) of pressure. [ 11 ] Thus, a cubic decimeter of water at its point of maximum density is 25 parts per million less massive than the IPK. pengukuran Modern Vienna Standard Mean Ocean Water , yang merupakan air suling murni dengan isotop mewakili komposisi rata-rata dunia lautan, menunjukkan ia memiliki kepadatan 0,999 9 75 ± 0,000 0 01 kg / L pada titik kepadatan maksimum ( 3,984 ° C) dalam satu atmosfer standar (760 torr ) dari tekanan. [11] Dengan demikian, decimeter kubik air pada titik kepadatan maksimum adalah 25 bagian per juta lebih besar dari IPK tersebut. This small difference, and the fact that the mass of the IPK was indistinguishable from the mass of the Kilogram of the Archives, speak volumes of the scientists' skills over 211 years ago when making their measurements of water's properties and in manufacturing the Kilogram of the Archives. Perbedaan kecil, dan fakta bahwa massa IPK tidak bisa dibedakan dari massa Kilogram dari Arsip, berbicara banyak keterampilan para ilmuwan lebih dari 211 tahun yang lalu ketika melakukan pengukuran mereka sifat air dan di manufaktur Kilogram dari Arsip.
[ edit ] Stability of the International Prototype Kilogram [ sunting ] Stabilitas International Prototype Kilogram
Note that none of the replicas has a mass precisely equal to that of the IPK; their masses are calibrated and documented as offset values. Perhatikan bahwa tidak ada replika memiliki massa tepat sama dengan yang dari IPK; massa mereka dikalibrasi dan didokumentasikan sebagai nilai offset. For instance, K20, the US's primary standard, originally had an official mass of 1 kg − 39 micrograms (µg) in 1889; that is to say, K20 was 39 Misalnya, K20,'s primer standar AS, pada awalnya memiliki massa resmi 1 kg - 39 mikrogram (ug) pada tahun 1889, yang mengatakan, K20 adalah 39 µg less than the IPK. ug kurang dari IPK tersebut. A verification performed in 1948 showed a mass of 1 kg − 19 µg. The latest verification performed in 1999 shows a mass precisely identical to its original 1889 value. Sebuah verifikasi dilakukan pada tahun 1948 menunjukkan massa 1 kg - 19 ug. Verifikasi terbaru dilakukan pada tahun 1999 menunjukkan massa justru identik dengan nilai 1889 yang asli. Quite unlike transient variations such as this, the US's check standard , K4, has persistently declined in mass relative to the IPK—and for an identifiable reason. Cukup berbeda dengan variasi transient seperti ini, AS itu standar pemeriksaan , K4, telah terus menerus menurun di massa relatif ke IPK-dan karena alasan yang dapat diidentifikasi. Check standards are used much more often than primary standards and are prone to scratches and other wear. Periksa standar digunakan jauh lebih sering daripada standar primer dan rentan terhadap goresan dan mengenakan lainnya. K4 was originally delivered with an official mass of 1 kg − 75 µg in 1889, but as of 1989 was officially calibrated at 1 kg − 106 µg and ten years later was 1 kg − 116 µg. Over a period of 110 years, K4 lost 41 K4 awalnya disampaikan dengan massa resmi 1 kg - 75 ug pada tahun 1889, namun pada 1989 secara resmi dikalibrasi pada 1 kg - 106 ug dan sepuluh tahun kemudian adalah 1 kg - 116 ug. Selama periode 110 tahun, K4 hilang 41 µg relative to the IPK. [ 13 ] ug relatif terhadap IPK tersebut. [13]
Beyond the simple wear that check standards can experience, the mass of even the carefully stored national prototypes can drift relative to the IPK for a variety of reasons, some known and some unknown. Di luar memakai standar sederhana yang dapat memeriksa pengalaman, massa nasional bahkan prototipe disimpan dengan hati-hati bisa hanyut relatif terhadap IPK untuk berbagai alasan, beberapa dikenal dan belum diketahui. Since the IPK and its replicas are stored in air (albeit under two or more nested bell jars ), they gain mass through adsorption of atmospheric contamination onto their surfaces. Karena IPK dan replika yang disimpan di udara (walaupun di bawah dua atau lebih nested stoples bel ), massa mereka peroleh melalui adsorpsi kontaminasi atmosfer ke permukaan mereka. Accordingly, they are cleaned in a process the BIPM developed between 1939 and 1946 known as “the BIPM cleaning method” that comprises lightly rubbing with a chamois soaked in equal parts ether and ethanol , followed by steam cleaning with bi- distilled water, and allowing the prototypes to settle for 7–10 days before verification. [ Note 12 ] Cleaning the prototypes removes between 5 and 60 Oleh karena itu, dibersihkan dalam proses BIPM dikembangkan antara 1939 dan 1946 yang dikenal sebagai "metode pembersihan BIPM" yang terdiri ringan menggosok dengan chamois basah di bagian yang sama eter dan etanol , diikuti oleh uap membersihkan dengan bi- suling air, dan memungkinkan yang prototipe untuk menyelesaikan selama 7-10 hari sebelum verifikasi. [Catatan 12] Membersihkan prototipe menghilangkan antara 5 dan 60 µg of contamination depending largely on the time elapsed since the last cleaning. ug kontaminasi sebagian besar tergantung pada waktu yang telah berlalu sejak terakhir pembersihan. Further, a second cleaning can remove up to 10 Lebih lanjut, membersihkan kedua dapat menghapus hingga 10 µg more. ug lebih. After cleaning—even when they are stored under their bell jars—the IPK and its replicas immediately begin gaining mass again. Setelah dibersihkan-bahkan ketika mereka disimpan dalam kendi bel mereka-IPK dan replika yang segera mulai mendapatkan massa lagi. The BIPM even developed a model of this gain and concluded that it averaged 1.11 The BIPM bahkan mengembangkan model keuntungan ini dan menyimpulkan bahwa rata-rata 1,11 µg per month for the first 3 months after cleaning and then decreased to an average of about 1 ug per bulan untuk 3 bulan pertama setelah dibersihkan dan kemudian menurun menjadi rata-rata sekitar 1 µg per year thereafter. ug per tahun setelahnya. Since check standards like K4 are not cleaned for routine calibrations of other mass standards—a precaution to minimize the potential for wear and handling damage—the BIPM's model of time-dependent mass gain has been used as an “after cleaning” correction factor. Sejak memeriksa standar seperti K4 tidak dibersihkan untuk kalibrasi rutin lain-tindakan pencegahan standar massa untuk memperkecil potensi untuk dipakai dan model penanganan kerusakan-the BIPM's keuntungan massa bergantung waktu telah digunakan sebagai "setelah dibersihkan" faktor koreksi.
What is known specifically about the IPK is that it exhibits a short-term instability of about 30 Apa yang dikenal secara spesifik tentang IPK adalah bahwa hal itu menunjukan ketidakstabilan jangka pendek dari sekitar 30 µg over a period of about a month in its after-cleaned mass. [ 18 ] The precise reason for this short-term instability is not understood but is thought to entail surface effects: microscopic differences between the prototypes' polished surfaces, possibly aggravated by hydrogen absorption due to catalysis of the volatile organic compounds that slowly deposit onto the prototypes as well as the hydrocarbon -based solvents used to clean them. [ 17 ] [ 19 ] ug selama sekitar sebulan setelah dibersihkan di massanya. [18] Alasan yang tepat untuk jangka pendek ketidakstabilan tidak dipahami namun diperkirakan memerlukan efek permukaan: perbedaan mikroskopik antara 'dipoles permukaan prototip, mungkin diperburuk oleh hidrogen untuk penyerapan karena katalisis dari senyawa organik yang mudah menguap yang perlahan deposit ke prototipe serta hidrokarbon berbasis pelarut-digunakan untuk membersihkan mereka. [17] [19]
Scientists are seeing far greater variability in the prototypes than previously believed. Para ilmuwan melihat variabilitas jauh lebih dalam prototipe dari yang dipercayai sebelumnya. The increasing divergence in the masses of the world's prototypes and the short-term instability in the IPK has prompted research into improved methods to obtain a smooth surface finish using diamond-turning on newly manufactured replicas and has intensified the search for a new definition of the kilogram. Penyimpangan peningkatan massa prototipe dunia dan ketidakstabilan jangka pendek di IPK telah mendorong penelitian metode yang sudah diperbaiki untuk mendapatkan menyelesaikan permukaannya halus menggunakan berlian menyalakan replika yang baru diproduksi dan telah menggiatkan mencari definisi baru kilogram. See Proposed future definitions , below. [ 20 ] Lihat Usulan definisi masa depan , di bawah ini. [20]
[ edit ] Importance of the kilogram [ sunting ] Pentingnya kilogram
Because the magnitude of many of the units comprising the SI system of measurement is ultimately defined by the mass of a 131-year-old, golf ball-sized piece of metal, the quality of the IPK must be diligently protected to preserve the integrity of the SI system. Karena besarnya banyak unit yang terdiri dari sistem pengukuran SI pada akhirnya ditentukan oleh massa sepotong, golf 131 tahun ukuran bola-logam, kualitas rajin IPK harus dilindungi untuk menjaga integritas SI sistem. Yet, in spite of the best stewardship, the average mass of the worldwide ensemble of prototypes and the mass of the IPK have likely diverged another 5 Namun, meskipun pelayanan terbaik, massa rata-rata dari seluruh dunia ansambel prototipe dan massa dari IPK mungkin telah menyimpang lain 5 µg since the third periodic verification 21 ug sejak verifikasi periodik ketiga 21 years ago. [ Note 16 ] Further, the world's national metrology laboratories must wait for the fourth periodic verification to confirm whether the historical trends tahun yang lalu. [Catatan 16] Selanjutnya, nasional laboratorium metrologi dunia harus menunggu verifikasi periodik keempat untuk mengkonfirmasi apakah historis tren persisted. bersikeras.
Fortunately, definitions of the SI units are quite different from their practical realizations . For instance, the meter is defined as the distance light travels in a vacuum during a time interval of 1 ⁄ 299,792,458 of a second. Untungnya, definisi dari unit SI sangat berbeda dari mereka realisasi praktis . Sebagai contoh, meter didefinisikan sebagai jarak perjalanan cahaya di dalam vakum selama selang waktu 1 / 299792458 detik. However, the meter's practical realization typically takes the form of a helium-neon laser, and the meter's length is delineated —not defined—as 1,579,800.298 7 28 wavelengths of light from this laser. Namun, yang praktis realisasi meter biasanya mengambil bentuk-neon laser helium, dan meter yang panjang itu digambarkan -tidak didefinisikan-seperti 1,579,800.298 7 28 panjang gelombang cahaya dari laser ini. Now suppose that the official measurement of the second was found to have drifted by a few parts per billion (it is actually exquisitely stable). Sekarang anggaplah bahwa pengukuran resmi kedua ditemukan telah hanyut oleh beberapa bagian per miliar (itu sebenarnya indah stabil). There would be no automatic effect on the meter because the second—and thus the meter's length—is abstracted via the laser comprising the meter's practical realization. Tidak akan ada efek otomatis pada meteran karena kedua sehingga meteran yang panjang-adalah diabstraksikan melalui laser terdiri's praktis realisasi meter. Scientists performing meter calibrations would simply continue to measure out the same number of laser wavelengths until an agreement was reached to do otherwise. Para ilmuwan melakukan kalibrasi meter hanya akan terus mengukur jumlah yang sama panjang gelombang laser sampai dicapai kesepakatan untuk melakukan sebaliknya. The same is true with regard to the real-world dependency on the kilogram: if the mass of the IPK was found to have changed slightly, there would be no automatic effect upon the other units of measure because their practical realizations provide an insulating layer of abstraction. Hal yang sama berlaku berkaitan dengan dunia nyata ketergantungan pada kilogram: jika massa IPK ditemukan telah berubah sedikit, tidak akan ada efek otomatis pada unit lain diukur karena realisasi praktis mereka memberikan lapisan isolasi dari abstraksi. Any discrepancy would eventually have to be reconciled though because the virtue of the SI system is its precise mathematical and logical harmony amongst its units. Perbedaan apapun akhirnya harus berdamai meskipun karena kebajikan dari sistem SI adalah tepat harmoni yang matematis dan logis di antara unit tersebut. If the IPK's value were definitively proven to have changed, one solution would be to simply redefine the kilogram as being equal to the mass of the IPK plus an offset value, similarly to what is currently done with its replicas; eg, “the kilogram is equal to the mass of the IPK + 42 parts per billion ” (equivalent to 42 Jika nilai IPK yang telah definitif terbukti telah berubah, salah satu solusi adalah dengan hanya mendefinisikan kilogram sebagai sama dengan massa IPK ditambah dengan nilai offset, sama dengan apa yang sedang dilakukan dengan replika-nya, misalnya, "adalah kilogram sama dengan massa + IPK 42 bagian per miliar "(setara dengan 42 µg). ug).
The long-term solution to this problem, however, is to liberate the SI system's dependency on the IPK by developing a practical realization of the kilogram that can be reproduced in different laboratories by following a written specification. Solusi jangka panjang untuk masalah ini, bagaimanapun, adalah untuk membebaskan ketergantungan pada sistem SI IPK dengan mengembangkan realisasi praktis dari kilogram yang dapat diperbanyak di laboratorium yang berbeda dengan mengikuti spesifikasi yang tertulis. The units of measure in such a practical realization would have their magnitudes precisely defined and expressed in terms of fundamental physical constants. Satuan ukuran sedemikian realisasi praktis besaran mereka akan didefinisikan secara tegas dan dinyatakan dalam bentuk konstanta fisika dasar. While major portions of the SI system would still be based on the kilogram, the kilogram would in turn be based on invariant, universal constants of nature. Sedangkan bagian utama dari sistem SI masih akan didasarkan pada kilogram, kilogram yang pada gilirannya akan didasarkan pada invarian, konstanta universal alam. While this is a worthwhile objective and much work towards that end is ongoing, no alternative has yet achieved the uncertainty of a couple parts in 10 8 (~20 Walaupun ini merupakan tujuan yang berharga dan bekerja ke arah yang lebih akhir ini berkelanjutan, belum ada alternatif mencapai ketidakpastian dari beberapa bagian di 10 8 (~ 20 µg) required to improve upon the IPK. ug) yang diperlukan untuk memperbaiki IPK tersebut. However, as of April 2007 [update] , the US's National Institute of Standards and Technology (NIST) had an implementation of the watt balance that was approaching this goal, with a demonstrated uncertainty of 36 Namun, per April 2007 [update] , di AS yang Institut Nasional Standarisasi dan Teknologi (NIST) yang merupakan implementasi dari saldo watt yang mendekati tujuan ini, dengan menunjukkan ketidakpastian 36 µg. [ 21 ] See Watt ug. [21] Lihat Watt balance , below. keseimbangan , di bawah ini.
[ edit ] Proposed future definitions [ sunting ] Usulan definisi masa depan
- In the following section, wherever numeric equalities are shown in 'concise form'—such as 1.854 8 7(14) × 10 43 —the two digits between the parentheses denote the uncertainty at 1σ standard deviation (68% confidence level) in the two least significant digits of the significand . Pada bagian berikut, mana kesamaan-kesamaan numerik yang ditampilkan dalam "ringkas form'-seperti 1,854 8 7 (14) × 10 43-dua digit antara tanda kurung menyatakan ketidakpastian di 1σ deviasi standar (68% tingkat kepercayaan) dalam dua paling signifikan digit dari significand .
[ edit ] Atom-counting approaches [ sunting ] Atom pendekatan penghitungan
[ edit ] Carbon-12 [ sunting ] Karbon-12
Though not offering a practical realization, this definition would precisely define the magnitude of the kilogram in terms of a certain number of carbon‑12 atoms. Meskipun tidak menawarkan realisasi praktis, definisi ini justru akan menentukan besarnya kilogram dalam hal sejumlah karbon-12 atom. Carbon‑12 ( 12 C) is an isotope of carbon. Karbon-12 (12 C) adalah isotop karbon. The mole is currently defined as “the quantity of entities (elementary particles like atoms or molecules) equal to the number of atoms in 12 grams of carbon‑12.” Thus, the current definition of the mole requires that 1000 ⁄ 12 (83⅓) moles of 12 C has a mass of precisely one kilogram. The mol saat ini didefinisikan sebagai "jumlah entitas (partikel dasar seperti atom atau molekul) sama dengan jumlah atom dalam 12 gram karbon-12 demikian.", definisi saat mol mengharuskan 1000-1012 (83 ⅓) mol dari 12 C memiliki massa tepat satu kilogram. The number of atoms in a mole, a quantity known as the Avogadro constant , is experimentally determined, and the current best estimate of its value is 6.022 1 41 7 9(30) × 10 23 entities per mole ( CODATA , 2006). Jumlah atom dalam mol, sebuah kuantitas yang dikenal sebagai tetapan Avogadro , adalah eksperimental ditentukan, dan perkiraan nilai terbaik saat ini adalah 6,022 1 41 7 9 (30) × 10 23 entitas per mol ( CODATA , 2006). This new definition of the kilogram proposes to fix the Avogadro constant at precisely 6.022 1 41 7 9 × 10 23 with the kilogram being defined as “the mass equal to that of 1000 ⁄ 12 · 6.022 1 41 7 9 × 10 23 atoms of 12 C.” Definisi baru dari kilogram mengusulkan untuk memperbaiki konstanta Avogadro tepat 6,022 1 41 7 9 × 10 23 dengan kilogram didefinisikan sebagai "massa sama dengan 1000 / 12 ° 6,022 1 41 7 9 × 10 23 atom dari 12 C. "The accuracy of the measured value of the Avogadro constant is currently limited by the uncertainty in the value of the Planck constant —a measure relating the energy of photons to their frequency. Keakuratan nilai diukur dari konstanta Avogadro saat ini terbatas oleh ketidakpastian dalam nilai konstan Planck -ukuran yang berhubungan dengan energi foton terhadap frekuensi mereka. That relative standard uncertainty has been 50 Bahwa ketidakpastian baku relatif telah 50 parts per billion (ppb) since 2006. bagian per miliar (ppb) sejak 2006. By fixing the Avogadro constant, the practical effect of this proposal would be that the uncertainty in the mass of a 12 C atom—and the magnitude of the kilogram—could be no better than the current 50 Dengan memperbaiki Avogadro konstan, efek praktis dari proposal ini adalah bahwa ketidakpastian dalam massa sebuah atom C-12 besar dan dari kilogram-bisa tidak lebih baik daripada 50 saat ini ppb uncertainty in the Planck constant. ppb ketidakpastian dalam konstanta Planck. Under this proposal, the magnitude of the kilogram would be subject to future refinement as improved measurements of the value of the Planck constant become available; electronic realizations of the kilogram would be recalibrated as required. Dalam proposal ini, besarnya kilogram akan dikenakan perbaikan masa depan sebagai pengukuran peningkatan nilai konstanta Planck menjadi tersedia; realisasi elektronik kilogram akan dikalibrasi ulang seperti yang diperlukan. Conversely, an electronic definition of the kilogram (see Electronic approaches , below), which would precisely fix the Planck constant, would continue to allow 83⅓ moles of 12 C to have a mass of precisely one kilogram but the number of atoms comprising a mole (the Avogadro constant) would continue to be subject to future refinement. Sebaliknya, definisi elektronik kilogram (lihat pendekatan Elektronik , di bawah), yang justru akan memperbaiki Planck konstan, akan terus memungkinkan 83 ⅓ mol 12 C untuk memiliki massa tepat satu kilogram tetapi jumlah atom yang terdiri dari tahi lalat ( yang Avogadro konstan) akan terus menjadi subyek perbaikan masa depan.
A variation on a 12 C-based definition proposes to define the Avogadro constant as being precisely 84,446,886 3 (≈ 6.022 1 40 9 8 × 10 23 ) atoms. Sebuah variasi pada definisi berbasis C-12 mengusulkan untuk mendefinisikan konstanta Avogadro sebagai tepatnya 84.446.886 3 (≈ 6,022 1 40 9 8 × 10 23) atom. An imaginary realization of a 12-gram mass prototype would be a cube of 12 C atoms measuring precisely 84,446,886 atoms across on a side. Sebuah realisasi imajiner gram massa prototipe-12 akan menjadi kubus dari 12 atom C pengukuran tepat 84.446.886 atom di sisinya. With this proposal, the kilogram would be defined as “the mass equal to 84,446,886 3 Dengan proposal ini, kilogram akan didefinisikan sebagai "massa sebesar 84.446.886 3 × 83⅓ atoms of 12 C.” The value 84,446,886 was chosen because it has a special property; its cube (the proposed new value for the Avogadro constant) is evenly divisible by twelve. ⅓ × 83 12 atom C. "Nilai 84.446.886 dipilih karena memiliki properti khusus; kubus nya (nilai baru yang diusulkan untuk tetapan Avogadro) secara merata dibagi dua belas. Thus with this definition of the kilogram, there would be an integer number of atoms in one gram of 12 C: 50,184,508,190,229,061,679,538 atoms. [ 22 ] [ Note 17 ] Jadi dengan definisi kilogram, akan ada nomor integer dari atom dalam satu gram dari 12 C: 50.184.508.190.229.061.679.538 atom. [22] [Catatan 17]
[ edit ] Avogadro project [ sunting ] Proyek Avogadro
Experiments are being performed on the Avogadro Project's silicon spheres to determine whether their masses are most stable when stored in a vacuum, a partial vacuum, or ambient pressure. Eksperimen sedang dilakukan pada silikon Proyek Avogadro bola untuk menentukan apakah mereka massa paling stabil bila disimpan dalam vakum, sebuah vakum parsial, atau tekanan ambien. However, no technical means currently exist to prove a long-term stability any better than that of the IPK's because the most sensitive and accurate measurements of mass are made with dual-pan balances like the BIPM's FB‑2 flexure-strip balance (see External links , below). Namun, tidak berarti teknis saat ini ada untuk membuktikan panjang stabilitas jangka lebih baik dibandingkan dengan IPK itu karena sensitif dan akurat pengukuran sebagian besar massa yang dibuat dengan dual-pan saldo seperti itu FB-BIPM 2 lentur-strip keseimbangan (lihat Eksternal link , di bawah). Balances can only compare the mass of a silicon sphere to that of a reference mass. Saldo hanya dapat membandingkan massa bola silikon dengan seorang massa referensi. Given the latest understanding of the lack of long-term mass stability with the IPK and its replicas, there is no known, perfectly stable mass artifact to compare against. Single-pan scales , which measure weight relative to an invariant of nature, are not precise to the necessary long-term uncertainty of 10–20 parts per billion. Mengingat pemahaman terbaru dari kurangnya massa stabilitas jangka-panjang dengan IPK dan replika tersebut, tidak ada dikenal, massa artefak stabil sempurna untuk membandingkan melawan. Single-pan timbangan , yang mengukur berat relatif ke invarian alam, tidak tepat untuk ketidakpastian jangka panjang diperlukan antara 10-20 bagian per miliar. Another issue to be overcome is that silicon oxidizes and forms a thin layer (equivalent to 5–20 silicon atoms) of silicon dioxide ( quartz ) and silicon monoxide . masalah lain yang harus diatasi adalah bahwa silikon mengoksidasi dan membentuk lapisan tipis (setara dengan 5-20 atom silikon) dari silikon dioksida ( kuarsa ) dan silikon monoksida . This layer slightly increases the mass of the sphere, an effect which must be accounted for when polishing the sphere to its finish dimension. Lapisan ini sedikit meningkatkan massa bola, efek yang harus dipertanggungjawabkan ketika polishing dimensi bola untuk menyelesaikan nya. Oxidation is not an issue with platinum and iridium, both of which are noble metals that are roughly as cathodic as oxygen and therefore don't oxidize unless coaxed to do so in the laboratory. Oksidasi bukan merupakan masalah dengan platinum dan iridium, keduanya merupakan logam mulia yang kasar sebagai katodik sebagai oksigen dan karena itu tidak mengoksidasi kecuali dibujuk untuk melakukannya di laboratorium. The presence of the thin oxide layer on a silicon-sphere mass prototype places additional restrictions on the procedures that might be suitable to clean it to avoid changing the layer's thickness or oxide stoichiometry . Adanya lapisan oksida tipis di lingkup massa prototipe-silikon tempat batasan-batasan tambahan pada prosedur yang mungkin cocok untuk membersihkannya untuk menghindari perubahan ketebalan lapisan's atau oksida stoikiometri .
All silicon-based approaches would fix the Avogadro constant but vary in the details of the definition of the kilogram. Semua pendekatan berbasis silikon akan memperbaiki tetapan Avogadro, tetapi bervariasi dalam rincian definisi kilogram. One approach would use silicon with all three of its natural isotopes present. Salah satu pendekatan akan menggunakan silikon dengan tiga isotop alami sekarang. About 7.78% of silicon comprises the two heavier isotopes: 29 Si and 30 Si. Sekitar 7,78% dari silikon terdiri dari dua isotop yang lebih berat: 29 dan 30 Si Si. As described in Carbon‑12 above, this method would define the magnitude of the kilogram in terms of a certain number of 12 C atoms by fixing the Avogadro constant; the silicon sphere would be the practical realization. This approach could accurately delineate the magnitude of the kilogram because the masses of the three silicon nuclides relative to 12 C are known with great precision (relative uncertainties of 1 Seperti dijelaskan dalam karbon-12 di atas, metode ini akan menentukan besarnya kilogram dalam sejumlah tertentu dari 12 atom C dengan menetapkan konstan Avogadro; lingkup silikon akan realisasi praktis. Pendekatan ini dapat secara akurat menggambarkan besarnya kilogram karena massa silikon tiga nuklida relatif terhadap 12 C dikenal dengan tepat (ketidakpastian relatif 1 ppb or better). ppb atau lebih baik). An alternative method for creating a silicon sphere-based kilogram proposes to use isotopic separation techniques to enrich the silicon until it is nearly pure 28 Si, which has a relative atomic mass of 27.976 9 26 5 325(19) . Sebuah metode alternatif untuk menciptakan sebuah bola yang berbasis silikon kilogram mengusulkan untuk menggunakan pemisahan isotop teknik untuk memperkaya silikon sampai hampir murni 28 Si, yang memiliki massa atom relatif 27,976 9 26 5 325 (19). With this approach, the Avogadro constant would not only be fixed, but so too would the atomic mass of 28 Si. Dengan pendekatan ini, konstanta Avogadro tidak hanya akan tetap, namun demikian juga akan massa atom 28 Si. As such, the definition of the kilogram would be decoupled from 12 C and the kilogram would instead be defined as 1000 ⁄ 27.976 9 26 5 325 Dengan demikian, definisi kilogram akan dipisahkan dari 12 C dan kilogram, bukan akan didefinisikan sebagai 1000 / 27,976 9 26 5 325 · · 6.022 1 41 7 9 × 10 23 atoms of 28 Si (≈ 35.743 7 40 4 3 fixed moles of 28 Si atoms). 6,022 1 41 7 9 × 10 23 atom sebesar 28 Si (≈ 35,743 7 40 4 3 mol tetap sebesar 28 atom Si). Physicists could elect to define the kilogram in terms of 28 Si even when kilogram prototypes are made of natural silicon (all three isotopes present). Fisikawan bisa memilih untuk mendefinisikan kilogram dalam hal 28 Si bahkan ketika prototipe kilogram terbuat dari silikon alami (semua tiga isotop sekarang). Even with a kilogram definition based on theoretically pure 28 Si, a silicon-sphere prototype made of only nearly pure 28 Si would necessarily deviate slightly from the defined number of moles of silicon to compensate for various chemical and isotopic impurities as well as the effect of surface oxides. [ 23 ] Bahkan dengan definisi kilogram berdasarkan teoritis murni 28 Si, sebuah bola terbuat dari silikon prototipe hanya hampir murni 28 Si tentu akan menyimpang sedikit dari jumlah yang ditetapkan mol silikon untuk mengimbangi berbagai bahan kimia dan kotoran isotop serta pengaruh permukaan oksida. [23]
[ edit ] Ion accumulation [ sunting ] Ion akumulasi
Another Avogadro-based approach, ion accumulation, since abandoned, would have defined and delineated the kilogram by precisely creating new metal prototypes on demand. Lain berbasis pendekatan Avogadro, ion akumulasi, sejak ditinggalkan, akan didefinisikan dan dibuat batasnya kilogram dengan tepat menciptakan prototipe logam baru sesuai permintaan. It would have done so by accumulating gold or bismuth ions (atoms stripped of an electron) and counted them by measuring the electrical current required to neutralize the ions. Itu akan melakukannya dengan mengumpulkan emas atau bismut ion (atom kehilangan elektron) dan menghitung mereka dengan mengukur arus listrik yang dibutuhkan untuk menetralkan ion. Gold ( 197 Au) and bismuth ( 209 Bi) were chosen because they can be safely handled and have the two highest atomic masses among the mononuclidic elements that is effectively non-radioactive (bismuth) or is perfectly stable (gold). See also Table of nuclides . [ Note 19 ]With a gold-based definition of the kilogram for instance, the relative atomic mass of gold could have been fixed as precisely 196.966 5 687 , from the current value of 196.966 5 687(6) . As with a definition based upon carbon‑12, the Avogadro constant would also have been fixed. The kilogram would then have been defined as “the mass equal to that of precisely 1000 ⁄ 196.966 5 687 · · 6.022 1 41 7 9 × 10 23 atoms of gold” (precisely 3,057,443,620,887,933,963,384,315 atoms of gold or about 5.077 0 03 7 1 fixed moles).
In 2003, German experiments with gold at a current of only 10 µA demonstrated a relative uncertainty of 1.5%. [ 24 ] Follow-on experiments using bismuth ions and a current of 30 mA were expected to accumulate a mass of 30 g in six days and to have a relative uncertainty of better than 1 part in 10 6 . [ 25 ] Ultimately, ion‑accumulation approaches proved to be unsuitable. Measurements required months and the data proved too erratic for the technique to be considered a viable future replacement to the IPK. [ 26 ]
Among the many technical challenges of the ion-deposition apparatus was obtaining a sufficiently high ion current (mass deposition rate) while simultaneously decelerating the ions so they could all deposit onto a target electrode embedded in a balance pan. Experiments with gold showed the ions had to be decelerated to very low energies to avoid sputtering effects—an phenomenon whereby ions that had already been counted ricochet off the target electrode or even dislodged atoms that had already been deposited. The deposited mass fraction in the 2003 German experiments only approached very close to 100% at ion energies of less than around 1 eV (<1 km/s for gold). [ 24 ]
If the kilogram had been defined as a precise quantity of gold or bismuth atoms deposited with an electric current, not only would the Avogadro constant and the atomic mass of gold or bismuth had to have been precisely fixed, but also the value of the elementary charge ( e ) , likely to 1.602 1 76 4 87 × 10 −19 C (from the present 2006 CODATA value of 1.602 1 76 4 87(40) × 10 −19 ). Doing so would have effectively defined the ampere as a flow of 1 ⁄ 1.602 1 76 4 87 × 10 −19 (6,241,509,647,120,417,390) electrons per second past a fixed point in an electric circuit. The SI unit of mass would have been fully defined by having precisely fixed the values of the Avogadro constant and elementary charge, and by exploiting the fact that the atomic masses of bismuth and gold atoms are invariant, universal constants of nature.
Beyond the slow speed of making a new mass standard and the poor reproducibility, there were other intrinsic shortcomings to the ion‑accumulation approach that proved to be formidable obstacles to ion-accumulation-based techniques becoming a practical realization. The apparatus necessarily required that the deposition chamber have an integral balance system to enable the convenient calibration of a reasonable quantity of transfer standards relative to any single internal ion-deposited prototype. Furthermore, the mass prototypes produced by ion deposition techniques would have been nothing like the freestanding platinum-iridium prototypes currently in use; they would have been deposited onto—and become part of—an electrode imbedded into one pan of a special balance integrated into the device. Moreover, the ion-deposited mass wouldn't have had a hard, highly polished surface that can be vigorously cleaned like those of current prototypes. Gold, while dense and a noble metal (resistant to oxidation and the formation of other compounds), is extremely soft so an internal gold prototype would have to be kept well isolated and scrupulously clean to avoid contamination and the potential of wear from having to remove the contamination. Bismuth, which is an inexpensive metal used in low-temperature solders, slowly oxidizes when exposed to room-temperature air and forms other chemical compounds and so would not have produced stable reference masses unless it was continually maintained in a vacuum or inert atmosphere.
[ edit ] Electronic approaches
[ edit ] Watt balance
The watt balance requires exquisitely precise measurement of gravity in a laboratory (see “FG‑5 absolute gravimeter” in External images , below). For instance, the NIST compensates for earth's gravity gradient of 3.09 µGal per centimeter when the elevation of the center of the gravimeter differs from that of the nearby test mass in the watt balance; a change in the weight of a one-kilogram test mass that equates to about 3.16 µg/cm.
In April 2007, the NIST's implementation of the watt balance demonstrated a combined relative standard uncertainty (CRSU) of 36 µg and a short-term resolution of 10–15 µg. [ 21 ] [ Note 20 ] The UK's National Physical Laboratory's watt balance demonstrated a CRSU of 70.3 µg in 2007. [ 27 ] That watt balance was disassembled and shipped in 2009 to Canada's Institute for National Measurement Standards (part of the National Research Council ), where research and development with the device could continue.
With the watt balance, the kilogram would be redefined and internationally recognized in terms of two invariants of nature: the speed of light ( c ) and the Planck constant ( h ), which is a measure that relates the energy of photons to their frequency. The Planck constant would be fixed; for example, to h = 6.626 0 68 9 6 × 10 −34 J·s (from the 2006 CODATA value of 6.626 0 68 9 6(33) × 10 −34 J·s ). [ Note 21 ] The kilogram would relate to these two fundamental constants of nature via the formula 1 kg = c 2 / h = f , which is to say, the mass of the kilogram would be equivalent to the square of the speed of light divided by the Planck constant, where the defined amount of energy is expressed as a simple frequency. The kilogram would thus be defined as “the mass of a body at rest whose equivalent energy equals the energy of photons whose frequencies sum to ( 299,792,458 2 ⁄ 6.626 0 68 9 6 × 10 −34 ) hertz .” [ 28 ] [ Note 22 ] This quotient is approximately 1.356 3 92 7 33 × 10 50 hertz (symbol = Hz), which is expressed here at a precision of better than one part per billion—better precision than the watt balance will be able to operate at for the foreseeable future.
By fixing the value of the Planck constant and defining the kilogram in terms of its equivalent energy, the magnitude of the kilogram is being measured in terms of Albert Einstein's famous equation E = mc 2 , which holds that mass can be expressed in terms of energy and vice versa. Due to the way the SI system of measurement is logically structured, E = mc 2 means one kilogram is precisely equivalent to an energy of 89,875,517,873,681,764 joules , which is the square of the speed of light in meters per second (299,792,458 2 ) , or as stated above, this energy in joules can be divided by the Planck constant to express the energy as a sum of photon frequencies. Regardless of the units of measure employed, one kilogram has an exceedingly great deal of equivalent energy; it is comparable to that released in the explosion of a fairly powerful hydrogen bomb : a yield of approximately 21 megatons . At a slower rate, the largest electric power-producing facility in the United States, Grand Coulee Dam , would typically require over 14 months to generate nearly 90 quadrillion joules of energy. In terms of a collection of photons that have a total energy equivalent to one kilogram, the approximately 5.95 × 10 35 near‑infrared photons from the above-mentioned chemical oxygen-iodine laser, which is a weapon system intended for destroying intercontinental ballistic missiles, would require a beam length that could reach beyond any of the 200 stars nearest the sun; with a beam intensity of one megawatt per square centimeter and a diameter of 3.6 centimeters, it would have a length of 280 light‑years .
The virtue of electronic realizations like the watt balance is that the definition and dissemination of the kilogram would no longer be dependent upon the stability of kilogram prototypes, which must be very carefully handled and stored. It would free physicists from the need to rely on assumptions about the stability of those prototypes, including those that would be manufactured under atom-counting schemes. Instead, hand-tuned, close-approximation mass standards would simply be weighed and documented as being equal to one kilogram plus an offset value. With the watt balance, the kilogram would not only be delineated in electrical and gravity terms, all of which are traceable to invariants of nature; it would be defined in electrical terms in a manner that is directly traceable to just two fundamental constants of nature. Mass artifacts—physical objects calibrated in a watt balance, including the IPK—would become transfer standards .
Scales like the watt balance also permit more flexibility in choosing materials with especially desirable properties for mass standards. For instance, Pt‑10Ir could continue to be used so that the specific gravity of newly produced mass standards would be the same as existing national primary and check standards (≈21.55 g/ml). This would reduce the relative uncertainty when making mass comparisons in air . Alternately, entirely different materials and constructions could be explored with the objective of producing mass standards with greater stability. For instance, osmium -iridium alloys could be investigated if platinum's propensity to absorb hydrogen (due to catalysis of VOCs and hydrocarbon-based cleaning solvents) and atmospheric mercury proved to be sources of instability. Also, vapor-deposited, protective ceramic coatings like nitrides could be investigated for their suitability to isolate these new alloys.
The challenge with watt balances is not only in reducing their uncertainty, but also in making them truly practical realizations of the kilogram. Nearly every aspect of watt balances and their support equipment requires such extraordinarily precise and accurate, state-of-the-art technology that—unlike a device like an atomic clock—few countries would currently choose to fund their operation. For instance, the NIST's watt balance used four resistance standards in 2007, each of which was rotated through the watt balance every two to six weeks after being calibrated in a different part of NIST headquarters facility in Gaithersburg, Maryland . It was found that simply moving the resistance standards down the hall to the watt balance after calibration altered their values 10 ppb (equivalent to 10 µg) or more. [ 30 ] Present-day technology is insufficient to permit stable operation of watt balances between even biannual calibrations. If the kilogram is defined in terms of the Planck constant, it is likely there will only be a few—at most—watt balances initially operating in the world.
[ edit ] Ampere-based force
Effectively, this would define the kilogram as a derivative of the ampere rather than present relationship, which defines the ampere as a derivative of the kilogram. This redefinition of the kilogram would specify elementary charge ( e ) as precisely 1.602 1 76 4 87 × 10 −19 coulomb rather than the current 2006 CODATA value of 1.602 1 76 4 87(40) × 10 −19 . Effectively, the coulomb would be the sum of 6,241,509,647,120,417,390 elementary charges. It would necessarily follow that the ampere (one coulomb per second) would also become an electrical current of this precise quantity of elementary charges per second passing a given point in an electric circuit.
The virtue of a practical realization based upon this definition is that unlike the watt balance and other scale-based methods, all of which require the careful characterization of gravity in the laboratory, this method delineates the magnitude of the kilogram directly in the very terms that define the nature of mass: acceleration due to an applied force. Unfortunately, it is extremely difficult to develop a practical realization based upon accelerating masses. Experiments over a period of years in Japan with a superconducting , 30 g mass supported by diamagnetic levitation never achieved an uncertainty better than ten parts per million. Magnetic hysteresis was one of the limiting issues. Other groups are continuing this line of research using different techniques to levitate the mass. [ 31 ]
[ edit ] SI multiples [ sunting ] SI kelipatan
Because SI prefixes may not be concatenated (serially linked) within the name or symbol for a unit of measure, SI prefixes are used with the gram , not the kilogram, which already has a prefix as part of its name. [ 32 ] For instance, one-millionth of a kilogram is 1 mg (one milligram), not 1 µkg (one microkilogram).| Submultiples Submultiples | Multiples Kelipatan | |||||
|---|---|---|---|---|---|---|
| Value Nilai | Symbol Simbol | Name Nama | Value Nilai | Symbol Simbol | Name Nama | |
| 10 −1 g | dg dg | decigram decigram | 10 1 g | dag dag | decagram | |
| 10 −2 g | cg cg | centigram sentigram | 10 2 g | hg hg | hectogram hektogram | |
| 10 −3 g | mg mg | milligram miligram | 10 3 g | kg kg | kilogram kilogram | |
| 10 −6 g | µg ug | microgram (mcg) | 10 6 g | Mg Mg | megagram ( tonne ) | |
| 10 −9 g | ng ng | nanogram | 10 9 g | Gg Gg | gigagram | |
| 10 −12 g | pg pg | picogram | 10 12 g | Tg Tg | teragram | |
| 10 −15 g | fg fg | femtogram | 10 15 g | Pg Pg | petagram | |
| 10 −18 g | ag ag | attogram | 10 18 g | Eg Misalnya | exagram | |
| 10 −21 g | zg | zeptogram | 10 21 g | Zg Zg | zettagram | |
| 10 −24 g | yg yg | yoctogram | 10 24 g | Yg | yottagram | |
| Common prefixes are in bold face. [ Note 23 ] | ||||||
- When the Greek lowercase “µ” (mu) in the symbol of microgram is typographically unavailable, it is occasionally—although not properly—replaced by Latin lowercase “u”.
- The microgram is often abbreviated “mcg”, particularly in pharmaceutical and nutritional supplement labeling, to avoid confusion since the “µ” prefix is not well recognized outside of technical disciplines. [ Note 24 ] Note however, that the abbreviation “mcg”, is also the symbol for an obsolete CGS unit of measure known as the “millicentigram”, which is equal to 10 µg.
- The unit name “megagram” is rarely used, and even then, typically only in technical fields in contexts where especially rigorous consistency with the units of measure is desired. For most purposes, the unit “ tonne ” is instead used. The tonne and its symbol, t, were adopted by the CIPM in 1879. It is a non-SI unit accepted by the BIPM for use with the SI. According to the BIPM, “In English speaking countries this unit is usually called 'metric ton'.” [ 33 ] Note also that the unit name “megatonne” or “megaton” (Mt) is often used in general-interest literature on greenhouse gas emissions whereas the equivalent value in scientific papers on the subject is often the “teragram” (Tg).
[ edit ] Glossary [ sunting ] Istilah
- Abstracted : Isolated and its effect changed in form, often simplified or made more accessible in the process.
- Artifact : A simple human-made object used directly as a comparative standard in the measurement of a physical quantity.
- Check standard :
- A standard body's backup replica of the International Prototype Kilogram (IPK).
- A secondary kilogram mass standard used as a stand-in for the primary standard during routine calibrations.
- Definition : A formal, specific, and exact specification.
- Delineation : The physical means used to mark a boundary or express the magnitude of an entity.
- Disseminate : To widely distribute the magnitude of a unit of measure, typically via replicas and transfer standards.
- IPK : Abbreviation of “International Prototype Kilogram” ( CG image ), the mass artifact in France internationally recognized as having the defining mass of precisely one kilogram.
- Magnitude : The extent or numeric value of a property
- National prototype : A replica of the IPK possessed by a nation.
- Practical realization : A readily reproducible apparatus to conveniently delineate the magnitude of a unit of measure.
- Primary national standard :
- A replica of the IPK possessed by a nation
- The least used replica of the IPK when a nation possesses more than one.
- Prototype :
- A human-made object that serves as the defining comparative standard in the measurement of a physical quantity.
- A human-made object that serves as the comparative standard in the measurement of a physical quantity.
- The IPK and any of its replicas
- Replica : An official copy of the IPK.
- Sister copy : One of six official copies of the IPK that are stored in the same safe as the IPK and are used as check standards by the BIPM.
- Transfer standard : An artifact or apparatus that reproduces the magnitude of a unit of measure in a different, usually more practical, form.
Catatan
- ^ One kilogram at rest has an equivalent energy equal to the energy of photons whose frequencies sum to this value.
- ^ The spelling kilogram is the modern spelling used by the International Bureau of Weights and Measures (BIPM), the US National Institute of Standards and Technology (NIST), the UK's National Measurement Office, National Research Council Canada, and Australia's National Measurement Institute. The traditional British-English spelling kilogramme is sometimes also used.
- ^ Also known by its French-language name Le Grand K .
- ^ In professional metrology (the science of measurement), the acceleration of earth's gravity is taken as standard gravity (symbol: g n ), which is defined as precisely 9.806 6 5 meters per square second (m/s 2 ). The expression “1 m/s 2 ” means that for every second that elapses, velocity changes an additional 1 meter per second. In more familiar terms: an acceleration of 1 m/s 2 can also be expressed as a rate of change in velocity of precisely 3.6 km/h per second (≈2.2 mph per second).
- ^ Matter has invariant mass assuming it is not traveling at a relativistic speed with respect to an observer. According to Einstein's theory of special relativity , the relativistic mass (apparent mass with respect to an observer) of an object or particle with rest mass m 0 increases with its speed as M = = γ m 0 (where γ is the Lorentz factor ). This effect is vanishingly small at everyday speeds, which are many orders of magnitude less than the speed of light . For example, to change the mass of a kilogram by 1 μg (1 ppb , about the level of detection by current technology) would require moving it at 0.0045% of the speed of light relative to an observer, which is 13.4 km/s (30,000 mph). As regards the kilogram, relativity's effect upon the constancy of matter's mass is simply an interesting scientific phenomenon that has zero effect on the definition of the kilogram and its practical realizations.
- ^ The same decree also defined the liter as follows: “Liter: the measure of volume, both for liquid and solids, for which the displacement would be that of a cube [with sides measuring] one-tenth of a meter.” Original text: “ Litre , la mesure de capacité, tant pour les liquides que pour les matières sèches, dont la contenance sera celle du cube de la dixièrne partie du mètre.”
- ^ Modern measurements show the temperature at which water reaches maximum density is 3.984 °C. ° C. However, the scientists at the close of the 18th century concluded that the temperature was 4 °C. ° C.
- ^ The provisional kilogram standard had been fabricated in accordance with a single, inaccurate measurement of the density of water made earlier by Antoine Lavoisier and René Just Haüy , which showed that one cubic decimeter of distilled water at 0 °C had a mass of 18,841 grains in France's soon-to-be-obsoleted poids de marc system. The newer, highly accurate measurements by Lefèvre‑Gineau and Fabbroni concluded that the mass of a cubic decimeter of water at the new temperature of 4 °C—a condition at which water is denser—was actually less massive , at 18,827.15 grains, than the earlier inaccurate value assumed for 0 °C water. France's metric system had been championed by Charles Maurice de Talleyrand‑Périgord . On 30 March 1791, four days after Talleyrand forwarded a specific proposal on how to proceed with the project, the French government ordered a committee known as the Academy to commence work on accurately determining the magnitude of the base units of the new metric system. The Academy divided the task among five commissions. The commission charged with determining the mass of a cubic decimeter of water originally comprised Lavoisier and Haüy but their work was finished by Louis Lefèvre‑Gineau and Giovanni Fabbroni.
Neither Lavoisier nor Haüy can be blamed for participating in an initial—and inaccurate—measurement and for leaving the final work to Lefèvre‑Gineau and Fabbroni to finish in 1799. As a member of the Ferme générale , Lavoisier was also one of France's 28 tax collectors. He was consequently convicted of treason during the waning days of the Reign of Terror period of the French Revolution and beheaded on 8 May 1794. Lavoisier's partner, Haüy, was also thrown into prison and was himself at risk of going to the guillotine but his life was spared after a renowned French naturalist interceded. - ^ Prototype No. 8(41) was accidentally stamped with the number 41, but its accessories carry the proper number 8. Since there is no prototype marked 8, this prototype is referred to as 8(41).
- ^ The other two Pt‑10Ir standards owned by the US are K79, from a new series of prototypes (K64–K80) that were diamond-turned directly to a finish mass, and K85, which is used for watt balance experiments (see Watt balance , above).
- ^ Extraordinary care is exercised when transporting prototypes. In 1984, the K4 and K20 prototypes were hand-carried in the passenger section of separate commercial airliners.
- ^ Before the BIPM's published report in 1994 detailing the relative change in mass of the prototypes, different standard bodies used different techniques to clean their prototypes. The NIST's practice before then was to soak and rinse its two prototypes first in benzene , then in ethanol, and to then clean them with a jet of bi-distilled water steam.
- ^ Note that if the ∆ 50 µg between the IPK and its replicas was entirely due to wear, the IPK would have to have lost 150 million billion more platinum and iridium atoms over the last century than its replicas. That there would be this much wear, much less a difference of this magnitude, is thought unlikely; 50 µg is roughly the mass of a fingerprint. Specialists at the BIPM in 1946 carefully conducted cleaning experiments and concluded that even vigorous rubbing with a chamois—if done carefully—did not alter the prototypes' mass. More recent cleaning experiments at the BIPM, which were conducted on one particular prototype (K63), and which benefited from the then-new NBS‑2 balance, demonstrated 2 µg stability. Many theories have been advanced to explain the divergence in the masses of the prototypes. One theory posits that the relative change in mass between the IPK and its replicas is not one of loss at all and is instead a simple matter that the IPK has gained less than the replicas. This theory begins with the observation that the IPK is uniquely stored under three nested bell jars whereas its six sister copies stored alongside it in the vault as well as the other replicas dispersed throughout the world are stored under only two. This theory is also founded on two other facts: that platinum has a strong affinity for mercury, and that atmospheric mercury is significantly more abundant in the atmosphere today than at the time the IPK and its replicas were manufactured. The burning of coal is a major contributor to atmospheric mercury and both Denmark and Germany have high coal shares in electrical generation. Conversely, electrical generation in France, where the IPK is stored, is mostly nuclear. This theory is supported by the fact that the mass divergence rate—relative to the IPK—of Denmark's prototype, K48, since it took possession in 1949 is an especially high 78 µg per century while that of Germany's prototype has been even greater at 126 µg/century ever since it took possession of K55 in 1954. However, still other data for other replicas isn't supportive of this theory. This mercury absorption theory is just one of many advanced by the specialists to account for the relative change in mass. To date, each theory has either proven implausible, or there are insufficient data or technical means to either prove or disprove it.
- ^ Even well respected organizations incorrectly represent the relative nature of the mass divergence as being one of mass loss, as exemplified by this site at Science Daily, and this site at PhysOrg.com, and this site at Sandia National Laboratories. The root of the problem is often the reporters' failure to correctly interpret or paraphrase nuanced scientific concepts, as exemplified by this 12 September 2007 story by the Associated Press published on PhysOrg.com . In that AP story, Richard Davis—who used to be the NIST's kilogram specialist and now works for the BIPM in France—was correctly quoted by the AP when he stated that the mass change is a relative issue. Then the AP summarized the nature of issue with this lead-in to the story: “A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight — if ever so slightly.” Like many of the above-linked sites, the AP also misreported the age of the IPK, using the date of its adoption as the mass prototype, not the date of the cylinder's manufacture. This is a mistake even Scientific American fell victim to in a print edition.
- ^ The mean change in mass of the first batch of replicas relative to the IPK over one hundred years is +23.5 µg with a standard deviation of 30 µg. Per The Third Periodic Verification of National Prototypes of the Kilogram (1988–1992) , G. Girard, Metrologia 31 (1994) Pg. 323, Table 3. 3. Data is for prototypes K1, K5, K6, K7, K8(41), K12, K16, K18, K20, K21, K24, K32, K34, K35, K36, K37, K38, and K40; and excludes K2, K23, and K39, which are treated as outliers. This is a larger data set than is shown in the chart at the top of this section, which corresponds to Figure 7 of G. Girard's paper.
- ^ Assuming the past trend continues, whereby the mean change in mass of the first batch of replicas relative to the IPK over one hundred years was +23.5 σ 30 µg.
- ^ The uncertainty in the Avogadro constant narrowed since this proposal was first submitted to American Scientist for publication. The 2006 CODATA value for the Avogadro constant has a relative standard uncertainty of 50 parts per billion and the only cube root values within this uncertainty must fall within the range of 84,446,889.8 ±1.4; that is, there are only three integer cube roots (…89, …90, and …91) in this range and the value 84,446,886 falls outside of it. Unfortunately, none of the three integer values within the range possess the property of their cubes being divisible by twelve; one gram of 12 C could not comprise an integer number of atoms. If the value 84,446,886 was adopted to define the kilogram, many other constants of nature and electrical units would have to be revised an average of about 0.13 part per million. The straightforward adjustment to this approach advanced by the group would instead define the kilogram as “the mass equal to 84,446,890 3 × 83⅓ atoms of carbon‑12.” This proposed value for the Avogadro constant (≈ 6.022 1 41 8 4 × 10 23 ) falls neatly within the 2006 CODATA value of 6.022 1 41 7 9(30) × 10 23 and the proposed definition of the kilogram produces an integer number of atoms in 12 grams of carbon‑12 (602,214,183,858,071,454,769,000 atoms), but not for 1 gram or 1 kilogram.
- ^ The sphere shown in the photograph has an out-of-roundness value (peak to valley on the radius) of 50 nm. nm. According to ACPO, they improved on that with an out-of-roundness of 35 nm. nm. On the 93.6 mm diameter sphere, an out-of-roundness of 35 nm (undulations of ±17.5 nm) is a fractional roundness (∆ r / r ) = 3.7 × 10 −7 . Scaled to the size of earth, this is equivalent to a maximum deviation from sea level of only 2.4 m. m. The roundness of that ACPO sphere is exceeded only by two of the four fused-quartz gyroscope rotors flown on Gravity Probe B , which were manufactured in the late 1990s and given their final figure at the WW Hansen Experimental Physics Lab at Stanford University . Particularly, “Gyro 4” is recorded in the Guinness database of world records (their database, not in their book) as the world's roundest man-made object. According to a published report ( 221 kB PDF, here ) and the GP‑B public affairs coordinator at Stanford University, of the four gyroscopes onboard the probe, Gyro 4 has a maximum surface undulation from a perfect sphere of 3.4 ±0.4 nm on the 38.1 mm diameter sphere, which is a ∆ r / r = 1.8 × 10 −7 . Scaled to the size of earth, this is equivalent to an undulation the size of North America rising slowly up out of the sea (in molecular-layer terraces 11.9 cm high), reaching a maximum elevation of 1.14 ±0.13 m in Nebraska, and then gradually sloping back down to sea level on the other side of the continent.
- ^ In 2003, the same year the first gold-deposition experiments were conducted, physicists found that the only naturally occurring isotope of bismuth, 209 Bi, is actually very slightly radioactive , with the longest known radioactive half-life of any naturally occurring element that decays via alpha radiation —a half-life of 19 ± 2 × 10 18 yr . As this is 1.4 billion times the age of the universe, 209 Bi is considered a stable isotope for most practical applications (those unrelated to such disciplines as nucleocosmochronology and geochronology ). In other terms, 99.999 9 99 9 83 % of the bismuth that existed on earth 4.567 billion years ago still exists today. Only two mononuclidic elements are heavier than bismuth and only one approaches its stability: thorium . Long considered a possible replacement for uranium in nuclear reactors, thorium can cause cancer when inhaled because it is over 1.2 billion times more radioactive than bismuth. It also has such a strong tendency to oxidize that its powders are pyrophoric . These characteristics make thorium unsuitable in ion-deposition experiments. See also Isotopes of bismuth , Isotopes of gold and Isotopes of thorium .
- ^ The combined relative standard uncertainty (CRSU) of these measurements, as with all other tolerances and uncertainties in this article unless otherwise noted, have a 1σ standard deviation, which equates to a confidence level of about 68%; that is to say, 68% of the measurements fall within the stated tolerance.
- ^ The Planck constant's unit of measure “joule-second” (J·s) may be more easily understood when expressed as a “ joule per hertz ” (J/Hz). Universally, an individual photon has an energy that is proportional to its frequency. This relationship is 6.626 0 68 9 6(33) × 10 −34 J/Hz and 1.509 1 90 4 5(8) × 10 33 Hz/J .
- ^ The SI unit, hertz (the reciprocal second) cannot normally be used as a measure of energy. When referring to a watt balance-based definition of the kilogram, the disciplines of professional metrology and physics customarily refer to the quotient of E/h (energy divided by a factor relating the energy of photons to their frequency) as a frequency, f , and add a crucial caveat in prose explaining that the unit of measure, hertz, represents an energy equivalent to that of photons whose frequencies sum to the stated value. However, even authoritative sources will, when communicating to a general-interest audience, sometimes state that one kilogram is equivalent to 1.356 3 92 7 33(68) × 10 50 Hz and attach no explanation (other than displaying the formula c 2 /h ) that the true measure is a corresponding energy, as exemplified here at the NIST's Fundamental physical constants: “Energy Equivalents” calculator.
- ^ Criterion: A combined total of at least 250,000 Google hits on both the modern spelling (‑gram) and the traditional British spelling (‑gramme).
- ^ The practice of using the abbreviation “mcg” rather than the SI symbol “µg” was formally mandated for medical practitioners in 2004 by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) in their “Do Not Use” List: Abbreviations, Acronyms, and Symbols because hand-written expressions of “µg” can be confused with “mg”, resulting in a thousand-fold overdosing. The mandate was also adopted by the Institute for Safe Medication Practices.
