7
Density and Buoyancy
Either directly or indirectly, the concept of density plays an important role in a
myriad of scientific operations: construction of equipment, preparation of solutions, determination of volumes, accurate weighings, measuring buoyancy of
objects, studying properties of gases, and so on. Density is defined as the mass
per unit volume, or
, .,
mass
,_ ..
density = —-.
(7-1)
volume
In scientific work, the densities of solids and liquids usually are expressed in
grams per cubic centimeter or grams per milliliter, whereas the densities of
gases usually are expressed in grams per liter. In engineering work, densities
customarily are expressed in pounds per cubic foot.
DENSITY OF A LIQUID
The simplest way to determine the density of a liquid is to weigh an empty
vessel of known volume and then weigh it again when it is filled with the liquid.
An approximate value may be determined with a simple graduated cylinder
weighed on a triple-beam balance. Only a crude value can be obtained because
the balance can be read only to the nearest 0.1 g and the cylinder only to the
nearest 0.1 ml.