In a vessel with water, two weights of the same mass – porcelain and cast iron – are alternately lowered on a thread. When will the bottom pressure be higher?
Our weights have the same mass, but due to the different specific gravity of these materials (porcelain – 2300 kg / m³, cast iron – 7000 kg / m³), they occupy a different volume. It is this value that determines the value of the buoyancy force acting on a body immersed in a liquid.
It is equal to the weight of the liquid displaced by it, or, in other words, the weight of the liquid that fills the volume occupied by the body immersed in the liquid.
F ext = Vρg, where V is the volume of the body, ρ is the density of the liquid (in our case, water), g is the acceleration of gravity. F vyt directly depends on the volume of the submerged body.
Thus, let us first compare the volume of our weights using the specific density formula – V = m / ρ. As you can see from the formula, with the same masses (as in our example), that weight will occupy a larger volume, whose density will be less. That is, a porcelain weight is more voluminous than a cast iron weight. Consequently, the buoyant force acting on it will be greater, which means its weight in water will be less. Hence the answer: the pressure exerted by the porcelain weight on the bottom of the vessel will be less than the pressure of the cast-iron weight.
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