\documentclass[tikz]{standalone}

\usepackage{libertine}
\usepackage{pgfplots}
\usepgfplotslibrary{statistics}


\begin{document}

% \begin{tabular}{cc}
  \begin{tikzpicture}[scale=.5]
  \begin{axis}[
    xlabel = {\large time},
    ylabel = {\large Magnitude of velocity},
  ]
  \addplot[color=blue] table [x=t, y=v] {output/figures/fig_5/mass_center_analytical.txt};
  \addlegendentry{\large analytical}
  \addplot[color=red] table [x=t, y=v] {output/figures/fig_5/mass_center_simulated.txt};
  \addlegendentry{\large simulated}
  \end{axis}
  \end{tikzpicture}
  % &
  \begin{tikzpicture}[scale=.5]
  \begin{axis}[
    xlabel = {\large time},
    ylabel = {\large Relative height},
  ]
  \addplot[color=blue] table [x=t, y=h] {output/figures/fig_5/mass_center_analytical.txt};
  \addlegendentry{\large analytical}
  \addplot[color=red] table [x=t, y=h] {output/figures/fig_5/mass_center_simulated.txt};
  \addlegendentry{\large simulated}
  \end{axis}
  \end{tikzpicture}
  % \end{tabular}

\end{document}