# Homogeneity of Physical Equations

We can only add, subtract, or equate quantities of the same units.

For example, in the following equation

$\displaystyle p+\frac{1}{2}\rho {{v}^{2}}+\rho gh={{p}_{0}}$

The terms p, $\frac{1}{2}\rho {{v}^{2}}$, $\rho gh$ and p0 all have the same unit of pascal.