Question

What is the difference between density and relative density?

Answer 1

Please see below.

Explanation:

The density is mass divided by volume and hence it has a unit - say in SI units it is `(kg)/m^3` and in FPS units it is `(lb)/(ft)^3`.

For example density of water in SI units is `1000(kg)/m^3` and in FPS unit it is `62.42796(lb)/(ft^3`.

For iron it is `7874(kg)/m^3` or `491.55776(lb)/(ft^3`.

Relative density on the contrary is the ratio of the density of certain matter with that of water. Hence, it does not have a unit, but is just a number. As such, it's value will not change when we change units, as both densities are calculated as ratio.

It is obvious that for water it is just `1` and for iron it will always be `7.874` , whatever units one uses.