Density is the amount of mass per volume. In order to measure it, you
would need to find the mass of the object and how much space it
For liquids, you would find the mass of a graduated
cylinder. Then add the liquid in the graduated cylinder and weigh the
graduated cylinder with the liquid. You would subtract the mass of the
graduated cylinder from this value to find the mass of the liquid.
Since you are using a graduated cylinder, you can find the volume of
the liquid by measuring it with the graduated cylinder.
solids, weigh the solid to find the mass. If the solid is a shape like
a cube or a rectangle, it will be easy to find the volume of the solid.
If the object is an irregular shape, first place water in a container
where you can measure the volume of the liquid. Then place the object
in the water and find the change in the volume of the liquid. This
change in volume is the volume of the solid.
For gases, it's
much harder to make the measurements directly by weighing, because the
densities are low. If you have the right equipment, you can weigh a
container with a known volume of the gas, then remove almost all the
gas with a vacuum pump and weigh the empty container. Often, you know
enough about the gas (what types of molecules it's made of, what its
temperature and pressure are, and how the density varies with
temperature and pressure) to figure out what its density is without
having to directly measure it.
(republished on 07/17/06)