File:MeasureField01.svg

\documentclass[crop,border=5,tikz,convert={outext=,
  command=\unexpanded{pdf2svg \infile\space\outfile\%02d.svg
    all}},multi=false]{standalone}
\usetikzlibrary{calc,patterns}

\newcommand{\markangle}[6][0.25]{
  \begin{scope}
    \clip (#2)--(#3)--(#4);
    \node (ANG) [draw, circle, minimum size=#5] at (#3){};
  \end{scope}
  \coordinate (E1) at (intersection 0 of ANG and #3--#2);
  \coordinate (E2) at (intersection 0 of ANG and #3--#4);
  \coordinate (EM) at ($ (E1)!0.5!(E2) $);
  \coordinate (EM) at ($ (EM)!#1!(#3) $);
  \node at (EM) {#6};
}

\begin{document}
\begin{tikzpicture}[>=latex,scale=1]
  \coordinate (m) at (-65:3);
  \coordinate (S) at (0,-3);
  \coordinate (F) at ($ (0,0)!1.6!(m) $);
  \coordinate (Fel) at ($ (m)+(2,0) $);
  \coordinate (Fg) at ($ (m)+(0,-2) $);
  \fill[pattern = north east lines] (-1,0) rectangle (1,0.3);
  \fill (0,0) circle (0.5mm);
  \shade[ball color=gray!50!red] (m) circle (2mm)
  node[above,shift={(0.2,0.1)}] {$m$};  \draw[thick] (-1,0)--(1,0);
  \draw[semithick,dotted] (0,0)--(S);
  \markangle{S}{0,0}{m}{79}{\small $\alpha$}
  \markangle{Fg}{m}{F}{60}{\small $\alpha$}
  \draw[thick,black] (0,0)--(m) node[midway,right]{$l$};
  \draw[thick,->,black!50!green] (m)--(F)
  node[right]{$\vec{F}_\mathrm{res}$};
  \draw[semithick,black!50!green,dotted] (m)-|(F)-|(m);
  \draw[thick,->,black!50!green] (m)--($(m)!(F)!(Fel)$)
  node[right,above]{$\vec{F}_{\mathrm{el}}$};
  \draw[thick,->,black!50!green] (m)--($(m)!(F)!(Fg)$)
  node[below,shift={(-0.2,0.1)}]{$\vec{F}_g=m\vec{g}$};
  \draw[<->,thick,red!50!yellow] (m)--($(m)!(S)!(Fel)$)
  node[midway,shift={(0,0.15)},red!50!yellow]{$s$};
  \node[blue!50!black] at (0.2,-3.6)
  {$\tan\alpha = \frac{F_\mathrm{el}}{mg}$};
  \node[blue!50!black] at (1.3,-0.75) {\small $\sin\alpha =
    \frac{s}{l}$};
  \node[blue!50!black] at (-2.4,-3.9){\footnotesize$\alpha\ll 1
    \Rightarrow$};% \sin\alpha\approx\tan\alpha\approx\alpha$};
  \node[blue!50!black,draw] at (-1.8,-4.5){\Large $F_\mathrm{el}
    \approx\frac{mg}{l}\cdot s$};
  \begin{scope}[shift={(-2,-2)},scale=0.1]
    \fill[pattern = north east lines] (-2.5,20) rectangle (2.5,21.5);
    \draw[thick] (-2.5,20)--(2.5,20);
    \coordinate (q) at (1.5,0);
    \draw[] (0,20)--(q)node[midway,right]{\footnotesize $l$};
    \draw[->,black!50!green] (q)--+(4,0) node[midway,above]
    {\tiny $\vec{F}_{\mathrm{el}}$};
    \draw[dotted] (0,-12)--(0,20);
    \draw[dotted] (q)--+(0,-12);
    \shade[ball color=gray!50!red] (q) circle (10mm) node[black!50!red]{\tiny $+$}
    node[left,shift={(-0.05,0)}]{\footnotesize $q$};
    \draw[->,yellow!50!red] (-3,-11)--(0,-11);
    \draw[->,yellow!50!red] (4.5,-11)--(1.5,-11)
    node[midway,above]{\footnotesize $s$};
%    \node at (0.75,-11){\tiny $s$};

    \draw[ultra thick] (-4,-10)--(-4,10);
    \draw[ultra thick] (6,-10)--(6,10);
    \foreach \y in {-9,-6,...,9}{
      \node[red!50!black] at (-5.5,\y){\tiny $+$};
      \node[blue!50!black] at (7.5,\y){\tiny $-$};
    }
  \end{scope}
\end{tikzpicture}

\end{document}