The relative density of a substance is the ratio of its density to that of water.
Relative density is a ratio so it has no unit.
`"Relative density" = "density of substance" / "density of water"`
The specific gravity of a substance will let us know if it will float or sink, it gives us the idea about relative mass or relative density. If the specific gravity of a substance is below 1 then it will float and if it is greater than 1 it will sink.
Calculate the density of an object of volume 3 m3 and mass 9 kg. State whether this object will float or sink in water. Give reason for your answer.