Space after tabular environement

Question

I want to add a space after a tabular environement. I tried to use the \vspace comand but it does not work, it adds the space between the first and the second line before the table instead of between the first line and the table itself. Any suggestions?

Here is the code:

\begin{tabular}{||m{0.3\textwidth} | m{0.7\textwidth} ||}
    \hline \hline
    Instruments and measure set up & 
    \begin{itemize}
        \item Power supply
        \item Waveform generator ($f=1\mathrm{kHz}, V_{pp}=0.8943\mathrm{V}$) 
        \item Oscilloscope              
    \end{itemize}
    \\
    \hline 
    Measured data &
    \begin{itemize}
        \item Output voltage: $V_o$
    \end{itemize}
    \\
    \hline
    Involved  variables, measured values and procedure & 
    Using \textit{Math Mode}, measure the voltage drop amplitude across the $8\mathrm\Omega$ resistor taking into account the $\frac{1}{\sqrt{2}}$ factor of the RMS.\newline
    Applying the following formula:
    $$ P_o = I\cdot V_{o_{RMS}} =  \frac{V_{o_{RMS}}^{2}}{R_L} 
    = \frac{V_o^{2}}{2\cdot8\mathrm{\Omega}}$$
    we obtain the power delivered by the amplifier to the speaker.
    \\
    \hline \hline       
\end{tabular}
\vspace{1cm}
\noindent
Specification: $1\mathrm{W} \le P_o \le 3\mathrm{W}$\\ \\
Measurements:
\begin{itemize}
    \item $V_o=\frac{V_{pp}}{2}=\frac{7.68\mathrm V}{2}=3.84$V
\end{itemize}
\noindent
\\
{\Large \textbf{Result:} $P_o=0.92$W}  

Answer 1

A little bit more compact. Units and values done with siunitx to ensure they are properly typeset. Changed the width of the second column of the tabular, to account the little space that LaTeX adds at both sides of a column. Removed the vertical lines to make it a bit more smooth. Added package parskip because that seems to be what you actually want here. If this is a homework assignment, no one will argue about it, if this is within a thesis or report, i would reconsider the whole presentation.

\documentclass{article}
\usepackage{array}
\usepackage{geometry}
\usepackage{ragged2e}
\newcommand{\tabitem}{\par\RaggedRight\textbullet~}
\usepackage{siunitx}
\usepackage{booktabs}
\usepackage{parskip}
\begin{document}
\begin{tabular}{m{0.3\textwidth}  m{0.64\textwidth} }
\toprule
    Instruments and measure set up & 
        \tabitem Power supply
        \tabitem Waveform generator ($f=\SI{1}{\kilo\hertz}, V_{pp}=\SI{0.8943}{\volt}$) 
        \tabitem Oscilloscope              
    \\
    \midrule
    Measured data &
        \tabitem Output voltage: $V_o$
    \\
    \midrule
    Involved  variables, measured values and procedure & 
    Using \textit{Math Mode}, measure the voltage drop amplitude across the \SI{8}{\ohm} resistor taking into account the $\sqrt{2}^{-1}$ factor of the RMS.\newline
    Applying the following formula:\par
    $\displaystyle P_o = I\cdot V_{o_\mathrm{{RMS}}} =  \frac{V_{o_{\text{RMS}}}^{2}}{R_L} 
     = \frac{V_o^{2}}{2\cdot\SI{8}{\ohm}}$\par
    we obtain the power delivered by the amplifier to the speaker.
    \\
    \bottomrule
\end{tabular}

\medbreak
Specification: $\SI{1}{\watt} \le P_o \le \SI{2}{\watt}$ 

Measurements:
    \tabitem $V_o=\frac{V_{pp}}{2}=\frac{\SI{7.68}{\volt}}{2}=\SI{3.84}{\volt}$

    {\Large \textbf{Result:} $P_o=\SI{0.92}{\watt}$
\end{document}

Answer 2

I propose to use tabularx to have the exact columnwidths ratio, and a description environment for the vertical spacing after the table, and some other improvements:

\documentclass{article}
\usepackage{array}
\usepackage[showframe]{geometry}
\usepackage{ragged2e}
\newcommand{\tabitem}{\par\RaggedRight\textbullet~}
\usepackage{siunitx}
\usepackage{booktabs, tabularx}
\usepackage{enumitem, nccmath}%
 \renewcommand{\tabularxcolumn}[1]{>{\abovedisplayskip=2pt\belowdisplayskip=5pt\arraybackslash}m{#1}}
\newcolumntype{Y}{>{\hsize=0.6\hsize}X}
\newcolumntype{Z}{>{\hsize=1.4\hsize}X}

\begin{document}

{\centering%}
\begin{tabularx}{\linewidth}{YZ }
\toprule
    Instruments and measure set up &
        \tabitem Power supply
        \tabitem Waveform generator ($f=\SI{1}{\kilo\hertz}, V_{pp}=\SI{0.8943}{\volt}$)
        \tabitem Oscilloscope
    \\
    \midrule
    Measured data &
        \tabitem Output voltage: $V_o$
    \\
    \midrule
    Involved variables, measured values and procedure &
    Using \textit{Math Mode}, measure the voltage drop amplitude across the \SI{8}{\ohm} resistor taking into account the $\sqrt{2}^{-1}$ factor of the RMS.\newline
    Applying the following formula:
    \[ P_o = I\cdot V_{o_\mathrm{{RMS}}} = \frac{V_{o_{\text{RMS}}}^{2}}{R_L}
     = \frac{V_o^{2}}{2\cdot\SI{8}{\ohm}} \]
    we obtain the power delivered by the amplifier to the speaker.
    \\
    \bottomrule
\end{tabularx}
}

\begin{description}[font=\normalfont, leftmargin=0pt]
\item[Specification:] $\SI{1}{\watt} \le P_o \le \SI{2}{\watt}$.
\item[Measurements:]\leavevmode\vspace{-1.5ex}
\begin{fleqn}
\begin{equation*}
\bullet\enspace V_o=\frac{V_{pp}}{2}=\frac{\SI{7.68}{\volt}}{2}=\SI{3.84}{\volt}
\end{equation*}
\end{fleqn}
\end{description}
\vspace*{\topsep}

    {\Large \textbf{Result:} $P_o=\SI{0.92}{\watt}$

\end{document}