{"id":56937,"date":"2024-01-04T15:42:30","date_gmt":"2024-01-04T15:42:30","guid":{"rendered":"https:\/\/www.africa-press.net\/tchad\/politique\/les-constantes-de-la-physique-imposent-leur-loi-aux-unites-de-mesure"},"modified":"2024-01-04T15:53:55","modified_gmt":"2024-01-04T15:53:55","slug":"les-constantes-de-la-physique-imposent-leur-loi-aux-unites-de-mesure","status":"publish","type":"post","link":"https:\/\/www.africa-press.net\/tchad\/toutes-les-actualites\/les-constantes-de-la-physique-imposent-leur-loi-aux-unites-de-mesure","title":{"rendered":"Les constantes de la physique imposent leur loi aux unit\u00e9s de mesure"},"content":{"rendered":"

Africa-Press – Tchad. <\/strong><\/span>Le 20 mai 2019, apre\u0300s cent trente ans de bons et loyaux services, le Grand K est devenu une pie\u0300ce de muse\u0301e. Ce cylindre de platine et d’iridium, enferme\u0301 dans une chambre forte du Bureau international des poids et mesures, a\u0300 Se\u0300vres (Hauts-de-Seine), e\u0301tait l’e\u0301talon du kilogramme depuis 1889.<\/p>\n

De temps a\u0300 autre, on le sortait pour le nettoyer avec une peau de chamois, avant de le comparer a\u0300 des re\u0301pliques de\u0301tenues dans d’autres pays. Lesquelles voyageaient vers Se\u0300vres dans une valise diplomatique pour e\u0301viter qu’un douanier suspicieux ne les souille. Mais au fil du temps, le Grand K avait maigri. A\u0300 moins que ce ne soit sa centaine de re\u0301pliques qui aient grossi. On ne connaissait donc sa valeur qu’a\u0300 50 microgrammes pre\u0300s. Une incertitude – un vingt-millie\u0300me – insupportable pour la science. Sans compter le risque de vol…<\/p>\n

Faire rentrer dans le rang le kilogramme, le kelvin et l’ampe\u0300re<\/b><\/p>\n

Le syste\u0300me international repose sur sept unite\u0301s, dont de\u0301coulent toutes les autres: le me\u0300tre, la seconde, la candela (intensite\u0301 lumineuse), la mole (nombre d’atomes, d’ions ou de mole\u0301cules), le kilogramme, le kelvin (tempe\u0301rature) et l’ampe\u0300re (intensite\u0301 du courant e\u0301lectrique). Jusqu’alors, seules les quatre premie\u0300res reposaient sur des constantes de la physique: la vitesse de la lumie\u0300re, les constantes de Planck (qui relie l’e\u0301nergie d’une particule de lumie\u0300re a\u0300 sa couleur) et de Boltzmann (qui associe l’e\u0301nergie interne d’un syste\u0300me a\u0300 sa tempe\u0301rature), la charge e\u0301le\u0301mentaire de l’e\u0301lectron et N, le nombre d’Avogadro *.<\/p>\n

La Confe\u0301rence ge\u0301ne\u0301rale des poids et mesures a donc propose\u0301 en 2018 de faire rentrer dans le rang le kilogramme, le kelvin et l’ampe\u0300re, tout en re\u0301visant les de\u0301finitions de la mole et du nombre d’Avogadro. Le kilogramme se de\u0301duit donc de\u0301sormais de la constante de Planck. Avec sa nouvelle de\u0301finition, l’incertitude sur sa valeur est d’un cent-millionie\u0300me. L’ampe\u0300re, lui, repose sur la charge e\u0301lectrique e\u0301le\u0301mentaire de l’e\u0301lectron. Le kelvin est de\u0301sormais relie\u0301 aux constantes de Planck et Boltzmann. Enfin, la mole est maintenant la quantite\u0301 de matie\u0300re d’un syste\u0300me contenant exactement N atomes. Autant de re\u0300gles qui devraient re\u0301sister a\u0300 l’e\u0301preuve du temps.<\/p>\n

Pour plus d’informations et d’analyses sur la Tchad<\/a>, suivez Africa-Press<\/a><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

Africa-Press – Tchad. Le 20 mai 2019, apre\u0300s cent trente ans de bons et loyaux services, le Grand K est devenu une pie\u0300ce de muse\u0301e. Ce cylindre de platine et d’iridium, enferme\u0301 dans une chambre forte du Bureau international des poids et mesures, a\u0300 Se\u0300vres (Hauts-de-Seine), e\u0301tait l’e\u0301talon du kilogramme depuis 1889. De temps a\u0300 […]<\/p>\n","protected":false},"author":82,"featured_media":56936,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22,10],"tags":[37,292,29],"class_list":["post-56937","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-divers","category-toutes-les-actualites","tag-africa-press","tag-africa-press-tchad","tag-tchad"],"yoast_head":"\nLes constantes de la physique imposent leur loi aux unit\u00e9s de mesure - tchad<\/title>\n<meta name=\"description\" content=\"Le 20 mai 2019, apre\u0300s cent trente ans de bons et loyaux services, le Grand K est devenu une pie\u0300ce de muse\u0301e. 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