Question

Why is relative density required to show whether an object floats and sinks? Can't we just simply take the density of the object and see if it is more or less than that of water?

Answer 1

Good question. But remember that relative density is just a single number which can tell you whether the object will float or sink.

If you take the densities of two different objects, what are actually doing is comparing them and thus in that case too, you are finding a relation between them. Hence, knowing the densities separately, or knowing the relative density will amount to doing the same thing.