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# Density as mass over volume

The density ($\rho$) of an object is its mass $\Tred{(m)}$ divided by its volume $\Tblue{(V)}$.$$\rho = \frac{\Tred{m}}{\Tblue{V}}$$

The symbol $\rho$ comes from the Greek alphabet and is called 'rho'. It should not be confused with $p$ from the Latin alphabet.

A $1 \ucm^{3}$ piece of lead is heavier than a $1 \ucm^{3}$ piece of plastic because lead is denser than plastic.

The SI unit of density is $\text{kg/m}^{3}$.

A person has a mass of $55 \text{ kg}$ and a volume of $0.05 \text{ m}^{3}$. Their density is $$\rho = \frac{\Tred{55 \text{ kg}}} {\Tblue{0.05 \text{m}^{3}}} = 1100 \text{kg/m}^{3}$$

The table below shows the density of some well-known materials at room temperature.
 Material Density ($\text{kg/m}^{3}$) Helium Air Water (liquid) Gold $0.18$ $1.29$ $1,000$ $19,300$
Gold has a very high density.