Archimedes' Principle

Archimedes' principle aids in the experimental determination of density by providing a convenient and accurate method for determining the volume of an irregularly shaped object, like a rock.

If an object is massed in air and found to have mass m = grams

and is then submerged in water and found to have apparent mass m' = grams

then it has displaced m - m' = grams of water. Since water has a density of 1 gram/cm3, this implies

Volume of object = V = cm3.
The density of the object is then

How many digits are significant?
Note that in the experimental arrangement, the container of water in which the object is submerged is supported on a platform so that the balance scale does not include the measurement of the mass of the water and its container.

Density and buoyancy in a general fluid


Buoyancy concepts
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