# What is "relative density"?

Nov 20, 2016

The density of a material relative to that of a reference substance....

#### Explanation:

....And the reference substance is typically water, for which $\rho = 1 \cdot g \cdot c {m}^{-} 3$.

And thus iron, which has $\rho = 7 \cdot g \cdot c {m}^{-} 3$, has a relative density of..

$\text{Reltive density of iron}$ $=$ $\left({\rho}_{\text{iron")/(rho_"water}}\right) = \frac{7 \cdot g \cdot c {m}^{-} 3}{1 \cdot g \cdot c {m}^{-} 3} = 7$.

The relative density is thus a dimensionless quantity. Given its superior relative density, iron will sink in water as it displaces a volume of water whose mass is LESS than the mass of the iron.