# How to ensure horizontal alignment when using overbrace function and split equations?

Happy lockdown. I am currently trying to align three split equations together while using the overbrace function to describe the functions of each section (they are symmetrical but for co-ordinate direction). The current code I have is:

\begin{align}
\label{eqn:mom2}
\begin{split}
&x : \overbrace{\rho \frac{Du}{Dt}}^\text{Convection} = \overbrace{\rho g_x - \frac{\delta p}{\delta x} }^\text{Pressure} + \overbrace{\mu (\frac{\delta^2 u}{\delta x^2} + \frac{\delta^2 u}{\delta y^2} + \frac{\delta^2 u}{\delta z^2}) }^\text{Diffusion}
\\
&y : \rho \frac{Dv}{Dt} = \rho g_y - \frac{\delta p}{\delta y} + \mu (\frac{\delta^2 v}{\delta x^2} + \frac{\delta^2 v}{\delta y^2} + \frac{\delta^2 v}{\delta z^2})
\\
&z : \rho \frac{Dw}{Dt} = \rho g_z - \frac{\delta p}{\delta z} + \mu (\frac{\delta^2 w}{\delta x^2} + \frac{\delta^2 w}{\delta y^2} + \frac{\delta^2 w}{\delta z^2})
\end{split}
\end{align}


If you see the attached, the presence of the overbracket misaligns the first equation line with the other two.

Would appreciate any help massively, causing a big headache!!

• Welcome to TeX.SE. – Mico Mar 29 at 16:22
• I also advise you to fix the round brackets that are too small :-)....and to put a complete code with the packages. Welcome again. – Sebastiano Mar 29 at 16:29
• @Sebastiano - I've updated my answer to incorporte your suggestion. :-) – Mico Mar 29 at 16:32

You were very close! I suggest you encase \text{Convection} in a \mathclap directive, effectively making it have zero width. Separately, I would increase the size of the parentheses in the "diffusion" block. \documentclass{article}
\usepackage{mathtools} % for \mathclap macro; loads 'amsmath' automatically
\begin{document}
\begin{equation}
\label{eqn:mom2}
\begin{split}
{\overbrace{\rho g_x - \frac{\delta p}{\delta x} }^{\text{Pressure}}}
+ {\overbrace{\mu \Bigl(\frac{\delta^2 u}{\delta x^2}
+ \frac{\delta^2 u}{\delta y^2}
+ \frac{\delta^2 u}{\delta z^2}\Bigr)\phantom{x} }^{\text{Diffusion}}}
\\
\rho g_y - \frac{\delta p}{\delta y}
+ \mu \Bigl(\frac{\delta^2 v}{\delta x^2}
+ \frac{\delta^2 v}{\delta y^2}
+ \frac{\delta^2 v}{\delta z^2}\Bigr)
\\