{"id":37405,"date":"2023-02-27T23:00:00","date_gmt":"2023-02-27T23:00:00","guid":{"rendered":"https:\/\/www.africa-press.net\/cameroun\/?p=37405"},"modified":"2023-02-21T20:48:29","modified_gmt":"2023-02-21T20:48:29","slug":"pourquoi-leau-chaude-gele-plus-vite-que-leau-froide","status":"publish","type":"post","link":"https:\/\/www.africa-press.net\/cameroun\/toutes-les-actualites\/pourquoi-leau-chaude-gele-plus-vite-que-leau-froide","title":{"rendered":"Pourquoi l\u2019eau chaude g\u00e8le plus vite que l\u2019eau froide ?"},"content":{"rendered":"

Africa-Press – Cameroun. <\/strong><\/span>L\u2019ide\u0301e que l\u2019eau chaude pourrait geler plus vite que l\u2019eau froide semble totalement contre-intuitive. Pourtant le phe\u0301nome\u0300ne a e\u0301te\u0301 observe\u0301 a\u0300 maintes reprises. On peut donc le\u0301gitimement se demander quels sont les principes physiques qui me\u0300nent a\u0300 ce re\u0301sultat.<\/p>\n

Sachez avant tout que ce phe\u0301nome\u0300ne e\u0301trange porte un nom. Les scientifiques parlent d’effet Mpemba, du nom d’un e\u0301tudiant tanzanien qui a relate\u0301 en avoir fait l’expe\u0301rience dans les anne\u0301es 1960. Mais il existe des traces d’observation d’une eau chaude qui ge\u0300le plus rapidement qu’une eau froide — violant ainsi apparemment alle\u0300grement les lois de la thermodynamique — jusque dans les e\u0301crits d’Aristote. Pourtant, les scientifiques qui s’y inte\u0301ressent peinent a\u0300 poser les conditions expe\u0301rimentales qui permettent de de\u0301clencher le phe\u0301nome\u0300ne. Et peinent donc a\u0300 l’e\u0301tudier se\u0301rieusement.<\/p>\n

Certains notent d’ailleurs que l’assertion — \u00ab l’eau chaude ge\u0300le plus vite que l’eau froide \u00bb — est suffisamment floue pour laisser cours a\u0300 toutes sortes de fantasmes. En effet, selon la quantite\u0301 d’e\u0301nergie consacre\u0301e a\u0300 refroidir l’eau en dessous de son point de solidification, il peut e\u0302tre extre\u0302mement aise\u0301 de conclure a\u0300 la re\u0301alite\u0301 de l’effet Mpemba.<\/p>\n

Plusieurs hypothe\u0300ses a\u0300 l’effet Mpemba<\/p>\n

Toutefois, les hypothe\u0300ses pour expliquer ce phe\u0301nome\u0300ne e\u0301trange ne manquent pas. La plus simple voudrait que l’e\u0301vaporation que subit le volume d’eau chaude soit a\u0300 l’origine d’une re\u0301duction de la masse de cette eau versus celle de l’eau froide. Ce qui suffirait a\u0300 tromper son monde. La piste de la surfusion a aussi e\u0301te\u0301 explore\u0301e. Ce phe\u0301nome\u0300ne permet en effet a\u0300 l’eau de rester liquide en dessous de 0 \u00b0C. L’eau chaude y e\u0301tant moins sensible, elle pourrait sembler geler plus vite que l’eau froide.<\/p>\n

En 2012, la Royal Society of Chemistry (Royaume-Uni) a lance\u0301 un concours invitant les chercheurs a\u0300 se pencher se\u0301rieusement sur la question. Le vainqueur, un doctorant croate, conclut que l’effet de convection est l’explication la plus plausible de l’effet Mpemba. Placez un re\u0301cipient d’eau chaude dans un environnement froid et il se cre\u0301era en effet des mouvements qui transporteront la chaleur par convection et permettront de refroidir l’eau plus rapidement. D’ailleurs toutes les expe\u0301riences semblent montrer que l’effet est annule\u0301 lorsque l’on agite l’eau re\u0301gulie\u0300rement pendant le refroidissement, coupant court aux mouvements de convection.<\/p>\n

Le myste\u0300re ne semble pourtant toujours pas entie\u0300rement re\u0301solu. Pour preuve, des scientifiques continuent de pre\u0301senter des hypothe\u0300ses parfois un peu exotiques. Et d’autres avancent me\u0302me que l’effet Mpemba n’existe pas du tout. Affaire a\u0300 suivre…<\/p>\n

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

Africa-Press – Cameroun. L\u2019ide\u0301e que l\u2019eau chaude pourrait geler plus vite que l\u2019eau froide semble totalement contre-intuitive. Pourtant le phe\u0301nome\u0300ne a e\u0301te\u0301 observe\u0301 a\u0300 maintes reprises. On peut donc le\u0301gitimement se demander quels sont les principes physiques qui me\u0300nent a\u0300 ce re\u0301sultat. Sachez avant tout que ce phe\u0301nome\u0300ne e\u0301trange porte un nom. Les scientifiques parlent […]<\/p>\n","protected":false},"author":82,"featured_media":37404,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22,10],"tags":[36,50,49],"class_list":["post-37405","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-divers","category-toutes-les-actualites","tag-africa-press","tag-africa-press-cameroun","tag-cameroun"],"yoast_head":"\nPourquoi l\u2019eau chaude g\u00e8le plus vite que l\u2019eau froide ? - Cameroun<\/title>\n<meta name=\"description\" content=\"L\u2019ide\u0301e que l\u2019eau chaude pourrait geler plus vite que l\u2019eau froide semble totalement contre-intuitive. 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