In most physics or chemistry classes, students learn about the terms "mass," "density" and their relationship. Mass usually refers to the amount of matter in an object, while density is the physical property of matter. By definition, density is mass per unit volume where volume is the space the object occupies. The symbol for density is the Greek letter "rho" or "ρ." Although you can easily find mass from the equation given for density, there are a few rules you need to follow to solve correctly these types of problems.
To find mass from density, you need the equation Density= Mass/Volume or D= M/V. The proper SI units for density are g/cubic cm (grams per cubic centimeters), or you can also express it as kg/cubic m (kilograms per cubic meters).
Use the equation D=M/V to solve for mass "M" in terms of "V" and "D," by multiplying both sides of the equation by "V." That is DxV= (M/V) x V. The 2 Vs cancel each other out on the right side of the equation. The new equation is now in terms of "M" or mass and given by M=DxV.
Practice finding the mass from density using this example. An object in the form of a cube with height, length and width equal to 1 cm has a density of 6 g/cubic cm.
Find the volume to solve for mass (M) by knowing that the formula for the volume (V) of a cube is equal to length x width x height. From Step 3, these are all equal to 1 so volume of the cube is 1cm x1cm x1cm= 1 cubic cm.
Substitute the values for density (D) from Step 3 and the value for volume (V) from Step 4 into the equation M=DxV and multiply to get M= (6 g/cubic cm) x (1 cubic cm) = 6 g. The mass is 6 g. Remember to check your units, as they need to be in the proper SI units.
When you are given a volume in cubic meters and a density in grams per cubic centimeters, you need to convert cubic meters to cubic centimeters (see link in Resources).