\documentclass[convert=true,convert={convertexe={convert},density=1200,outext=.png}]{standalone}

\input{figsDefs.tex}

\begin{document}
	
\begin{tikzpicture}%
	% origine
	\path (-.5,-.1) node[coordinate] (O) {};
	% vecteurs
	\path (0,-1.5) node[coordinate] (Fn) {};
	\draw[->,>=latex,thick,forceCol] (O) -- +(Fn) node[left,pos=0.8] {$\vec{F}_n$};%
	% surface
	\draw[-,fill=black!10] (-2,-.5) -- (1,-.5) -- (2,.5) -- (-1,.5) -- cycle;
	\path (-1.3,-.2) node {$S$};
	% vecteurs
	\draw[->,>=latex,thick,forceCol,dashed] (O) -- +(Fn);%
	
	% \'{e}l\'{e}ment de surface
	\draw[-,fill=black!10,xshift=1cm,yshift=0cm] (-.2,-.05) -- (.1,-.05) -- (.2,.05) -- (-.1,.05) -- cycle;
	\path (0.5,0.2) node {$\Delta S$};
	
	\begin{scope}[xshift=1.5cm,yshift=-0.5cm]
		\draw[-,fill=black!10,xshift=1cm,yshift=0cm] (-.2,-.05) -- (.1,-.05) -- (.2,.05) -- (-.1,.05) -- cycle;
		\path (0.5,0.2) node {$\Delta S$};
		\draw[->,>=latex,thick,forceCol,xshift=1cm,yshift=0cm] (0,0) -- +(0,-.5) node[left] {$\Delta\vec{F}_n$};%
	\end{scope}
	
\end{tikzpicture}%
\end{document}