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How does liquid density affect buoyancy?
Question Date: 2015-09-20
Answer 1:

The density of a liquid does significantly impact the buoyancy of an object. The buoyancy of an object is proportional to the difference of the density of the object and the density of a liquid. 𝑭𝒃∝(𝝆𝒐𝒃𝒋𝒆𝒄𝒕−𝝆𝒍𝒊𝒒𝒖𝒊𝒅) In the above equation, Fb is the buoyant force (buoyancy), ρobject is the density of the object, and ρliquid is the density of the liquid. Therefore if we take an object, such as a piece of leather that has a density of 0.79 g/cm3, it will have a different buoyancy when we add it to liquids with different densities.

For example, if we add the leather to a cup of rubbing alcohol (also called isopropanol) the leather will sink, because the leather has a greater density than the alcohol. However, the leather will float in water since it has a larger density than the leather. It will float on the surface of the salt water, but it will be slightly submerged in the fresh water (see image below on the link "Buoyancy"), because the density of the salt water is higher than the density of the fresh water, meaning that the salt water weighs more than the fresh water. The difference in densities of the leather and alcohol or leather and water is calculated below. The tendency of an object of float in a liquid is called buoyancy, and the leather is most buoyant in the salt water and least buoyant in the alcohol.

ρLeather = 0.86,
ρAlcohol = 0.79,
ρFresh Water = 1.00,
ρSalt Water = 1.05

Difference in density(ρ):
(ρLeather – ρAlcohol) = 0.07 (Least Buoyant)
Difference in density(ρ):
(ρLeather – ρFresh Water) = -0.14
Difference in density(ρ):
(ρLeather – ρSalt Water) = -0.19 (Most Buoyant)


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