I have never used this before, so please bear with me. I am trying to label parts of the flow conservation equation for momentum with braces, which I have done before. However, I can't figure out how to add appropriate line breaks in the label. Here's an example:
\begin{equation*}
\underbrace{\oiiint\limits_V \rho\vec{F}_b\:\mathrm{d}V}_{\text{Body forces (acceleration, emf, etc.)}}
\end{equation*}
Ideally, I would like for there to be a line break between "Body Forces" and "(acceleration, emf, etc.)". These equations get long for those familiar, and having huge labels just distorts the equation by adding extraneous space (and making it go off of the page in some cases). Does anyone know how to do this? I have tried adding all of the following where I would like the line break, to no avail:
\linebreak
\newline
\\
When I add the first two, it appears to just remove the space after compilation. When I try the last one, it won't compile at all. The \text command is from AMSMath, though I can't find any documentation on how to add in line breaks. Any thoughts?
Edit: Below is the entire equation that I am trying to label.
\begin{equation*}
\overbrace{\underbrace{\oiiint\limits_{\vol} \rho \vec{f}_b\diff \vol}_{\text{Body forces (acceleration, emf, gravity, etc.)}}-\underbrace{\oiint\limits_SP\diff S}_{\text{Pressure forces}}+\underbrace{\phantom{\intup\limits_l}\vec{F}_\mu\phantom{\intup\limits_l}}_{\text{Viscous forces}}}^{\vec{F}}=\overbrace{\underbrace{\oiint\limits_S\left(\rho\vec{v}\cdot\mathrm{d}S\right)\vec{v}}_{m\frac{\dd v}{\dd t}}+\underbrace{\frac{\partial}{\partial t}\oiiint\limits_{\vol}\rho \vec{v}\diff \vol}_{\vec{v}\frac{\dd m}{\dd t}}}^{\frac{\dd}{\dd t}\left(m\vec{v}\right)}
\end{equation*}
As you can see, the underbraces and subsequently the terms of the equation are spread out quite a bit. The idea is to condense those into a multi-line solution when they exceed the width of the term (the width of the underbrace itself). The Body Forces, Viscous forces, and probably the Pressure forces labels are the ones that would be affected by the solution for which I am looking. The right side of the equation would be unaffected due to the labels being smaller than the underbraces itself.
Here is the relevant information that needs to be in the preamble in order to print properly (I have more packages in my document, but I think these are the only ones necessary to print that line):
\usepackage{stix2}
\usepackage{amsmath}
\newcommand{\vol}{\makebox[0pt][l]{\ooalign{\hfil$V$\hfil\cr\kern0.09em--\hfil\cr}}}
The \vol is a command that I found on this site and modified to my liking. It would be nice to have a solution that includes both an overbrace and underbrace option, but I am not sure something like this exists. Thank you all for the help so far!
Another edit: I guess I don't understand what MWE means, so maybe below is what you're looking for? With the \begin{document} and such?
\documentclass[10pt,twoside,letterpaper,titlepage]{article}
\usepackage{amsmath}
\usepackage{stix2}
\newcommand{\vol}{\makebox[0pt][l]{\ooalign{\hfil$V$\hfil\cr\kern0.09em--
\hfil\cr}}}
\newcommand{\diff}{\,\mathrm{d}}
\newcommand{\dd}{\mathrm{d}}
\begin{document}
\begin{equation*}
\overbrace{\underbrace{\oiiint\limits_{\vol} \rho \vec{f}_b\diff \vol}_{\text{Body forces (acceleration, emf, gravity, etc.)}}-\underbrace{\oiint\limits_SP\diff S}_{\text{Pressure forces}}+\underbrace{\phantom{\intup\limits_l}\vec{F}_\mu\phantom{\int\limits_S}}_{\text{Viscous forces}}}^{\vec{F}}=\overbrace{\underbrace{\oiint\limits_S\left(\rho\vec{v}\cdot\mathrm{d}S\right)\vec{v}}_{m\frac{\dd v}{\dd t}}+\underbrace{\frac{\partial}{\partial t}\oiiint\limits_{\vol}\rho \vec{v}\diff \vol}_{\vec{v}\frac{\dd m}{\dd t}}}^{\frac{\dd}{\dd t}\left(m\vec{v}\right)}
\end{equation*}
\end{document}
\oiiint
defined?