What is the difference between density and relative density?
Please see below.
The density is mass divided by volume and hence it has a unit - say in SI units it is
For example density of water in SI units is
For iron it is
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