Faire de l’eau invisible (avec l’hexafluorure de soufre)
Science | Tags : experience, video Ajouter un commentaireVous connaissez l’eau invisible ?
Dans la vidéo ci-dessous, on voit très clairement un petit bateau d’aluminium flotter doucement au gré de … rien. On a juste l’impression que l’embarcation flotte au-dessus du vide.
Mais comment font-ils ??
En fait il ne s’agit pas de rendre l’eau invisible, mais d’exploiter les propriétés d’un gaz incolore, l’hexafluorure de soufre, qui a la particularité d’être plus lourd et plus dense que l’air.
Comme le gaz est plus lourd que l’air, il va naturellement vers le bas, et comme il est 5 fois plus dense que l’air, il offre suffisamment de résistance pour qu’on puisse y faire flotter des objets légers. En effet, plus un gaz est dense (plus les molécules qui le composent sont rapprochées), plus il offre de la résistance. L’eau, par exemple, offre plus de résistance que l’air car, dans un même espace, il y a plus de molécule d’eau que d’air.
En fait, du point de vue du poids et de la densité, l’hexafluorure de soufre a les propriétés inverse de l’helium : si quelqu’un inhale ce gaz, sa voix devient soudainement plus grave car les ondes sonores se déplacent plus doucement.
Attention, cette pratique est cependant largement déconseillée : le gaz étant lourd, il chasserait les molécules d’air de vos alvéoles pulmonaires, et vous étoufferiez par manque d’oxygène !
Note de service : après plusieurs mois d’inactivité, ce blog semble reprendre un peu de service… Je ne sais pas encore quelle direction il prendra, si ce n’est qu’il restera dans la thématique web / techno / sciences… Wait & see !
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