DENSITY OF LIQUIDS
 

The density of a liquid is defined in three ways: mass density, weight density, and particle density. The difference between these quantities might seem theoretically subtle, but in practical situations, the difference becomes apparent.
Mass density is defined in terms of the number of kilograms per meter cubed (kg/m³) in a sample of liquid. Weight density is defined in newtons per meter cubed (N/m³) and is equal to the mass density multiplied by the acceleration in meters per second squared (m/s²) to which the sample is subjected. Particle density is defined as the number of moles of atoms per meter cubed (mol/m³), where 1 mol ≈ 6.02 × 10²³. Let dm be the mass density of a liquid sample (in kilograms per meter cubed), let dw be the weight density (in newtons per meter cubed), and let dp be the particle density (in moles per meter cubed). Let m represent the mass of the sample (in kilograms), let V represent the volume of the sample (in meters cubed), and let N represent the number of moles of atoms in the sample. Let a be the acceleration (in meters per second squared) to which the sample is subjected. Then the following equations hold:
d_m = m/V
d_w = ma/V
d_p = N/V
Alternative definitions for mass density, weight density, and particle density use the liter, which is equal to a thousand centimeters cubed (1000 cm³) or one-thousandth of a meter cubed (0.001 m³), as the standard unit of volume. Once in awhile you’ll see the centimeter cubed (cm³), also known as the milliliter because it is equal to 0.001 liter, used as the standard unit of volume.
These are simplified definitions because they assume that the density of the liquid is uniform throughout the sample.