Modelová Otázka ID 3228 - 
Máme 3 nádoby naplněné do stejné výšky vodou. První nádoba má tvar válce, druhá nádoba tvar komolého kužele a třetí nádoba má tvar kužele. Mají‑li podstavy všech 3 nádob stejný poloměr, které z následujících tvrzení správně popisuje tlakovou sílu, kterou voda působí na dno nádob?
Správná odpověď je: C
Jestliže mají nádoby stejný obsah podstav a volná hladina kapaliny je ve všech nádobách ve stejné výšce nad dnem nádoby, je tlaková síla působící na dno všech nádob stejná. Tento jev se nazývá hydrostatický paradox (hydrostatické paradoxon) a je důsledkem závislosti hydrostatické tlakové síly na hydrostatickém tlaku a ploše povrchu, na nějž síla působí. Tento vztah lze zapsat jako 
. Pro hydrostatický tlak v dané hladině pod povrchem kapaliny platí vzorec 
, ve vzorci pro hydrostatickou tlakovou sílu 
tedy spolu s hustotou kapaliny a tíhovým zrychlením figurují pouze plocha dna nádoby a hloubka dna pod volnou hladinou kapaliny.
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