1キログラムの定義は2019年に原器から物理定数に変わった/enのソースを表示

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{{豆知識
|番号=0024
|本文=<span class="mw-translate-fuzzy">Until May 2019 the kilogram was the mass of the International Prototype Kilogram kept near Paris; it was then redefined using the Planck constant. Japan's prototype (No. 6), kept by AIST, was evacuated to the Kakioka geomagnetic observatory in Ibaraki in 1944 during the war, and became an Important Cultural Property in 2022.</span>
|なぜ=Comparisons with national copies showed that they drifted apart by tens of micrograms over about a century.
|ジャンル=科学・自然
|ファクト度=S
|ファクト度の根拠=Raised from the expected A to S: the change of definition, the size of the drift and the history of Japan's prototype were all confirmed in primary sources (BIPM and AIST)
|ネタ度=S
|ネタ度の根拠=Surprising history: the metal cylinder that was "the kilogram itself" was evacuated in wartime and became a cultural property
|便利度=該当なし
|便利度の根拠=A fact worth knowing for its own sake
|検証ステータス=根拠あり
|根拠1URL=https://www.bipm.org/en/history-si/kilogram
|根拠1要約=BIPM, "History of the kilogram". The 1946 verification showed the masses of the copies diverging from the international prototype; in 1989–91 the median difference was about 25 micrograms
|根拠1格付け=一次
|根拠2URL=https://www.bipm.org/fr/-/2019-wmd-fundamentally
|根拠2要約=BIPM announcement. From 20 May 2019 the International System of Units (SI) underwent one of its most significant changes (the kilogram and other units defined by physical constants)
|根拠2格付け=一次
|根拠3URL=https://unit.aist.go.jp/riem/mass-std/%E6%97%A5%E6%9C%AC%E5%9B%BD%E3%82%AD%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%A0%E5%8E%9F%E5%99%A8%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6%202018_11_18.pdf
|根拠3要約=AIST document "About Japan's national prototype kilogram" (2018). Number 6. Evacuated in 1944 to the Kakioka geomagnetic observatory of the Central Meteorological Observatory in Ibaraki. After the redefinition it is planned to serve as a very good weight for maintaining the mass standard
|根拠3格付け=一次
|根拠4URL=https://unit.aist.go.jp/nmij/news/2022/pdf/kg_prototype.pdf
|根拠4要約=AIST announcement (2022). Japan's prototype kilogram and related standards were added on 22 March 2022 to the Important Cultural Property "standards relating to the Metre Convention and the Weights and Measures Act"
|根拠4格付け=一次
|補足=The drift is relative: one can say the international prototype got lighter or the copies got heavier, and which one changed cannot be determined. How Japan's prototype is used now (since 2019) could not be confirmed; AIST's 2018 document only says it is "planned". The redefinition and the cultural-property designation are also in the Japanese Wikipedia article on the prototype kilogram.
|検証日時=2026-10-29
|検証方式=AI＋人
|本家既出チェック=本家に既出
|本家の該当ページ=https://ja.wikipedia.org/wiki/キログラム原器
|派生元=体重計の数字は緯度が高いほど大きく出る
}}