%
% pendel.tex -- mathematisches Pendel
%
% (c) 2021 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschule
%
\documentclass[tikz]{standalone}
\usepackage{amsmath}
\usepackage{times}
\usepackage{txfonts}
\usepackage{pgfplots}
\usepackage{csvsimple}
\usetikzlibrary{arrows,intersections,math,calc}
\begin{document}
\def\skala{1}
\begin{tikzpicture}[>=latex,thick,scale=\skala]

\definecolor{darkgreen}{rgb}{0,0.7,0}

\def\winkel{25}

\fill[color=red!20] (0,0) -- (0,-2) arc (-90:{-\winkel}:2) -- cycle;

\node at ({0.5*(-90-\winkel)}:1) {$\vartheta$};
\draw[color=red,shorten >= 0.25cm] (0,0) -- ({-\winkel}:3);
\node[color=red] at ({-\winkel}:1.5) [above right] {$l$};

\draw[->] (0,3.1) -- (0,-3.5) coordinate[label={left:$x$}];
%\draw[->] (-3.1,0) -- (3.5,0) coordinate[label={$y$}];

\draw[color=blue] (0,0) -- (0,{-3*sin(\winkel)})
	-- ({3*cos(\winkel)},{-3*sin(\winkel)});

\fill[color=white] (0,0) circle[radius=0.05];
\draw (0,0) circle[radius=0.05];

\draw[line width=0.2pt] (0,0) circle[radius=3];

\node at ($({-\winkel}:3)+(0.1,0)$) [below right] {$P$};

\draw[->,color=darkgreen]
	({-\winkel}:3) -- ($({-\winkel}:3)+(0,-3)$);
\draw[->,color=darkgreen]
	({-\winkel}:3) -- ($({-\winkel}:3)+({-\winkel-90}:{3*cos(\winkel)})$);
\draw[line width=0.3pt,color=darkgreen]
	($({-\winkel}:3)+(0,-3)$)
	-- ($({-\winkel}:3)+({-\winkel-90}:{3*cos(\winkel)})$);

\node[color=darkgreen] at ($({-\winkel}:3)+(0,-2)$) [right] {$g$};

\definecolor{darkred}{rgb}{0.6,0,0}
\fill[color=darkred] ({-\winkel}:3) circle[radius=0.25];
\draw[color=red] ({-\winkel}:3) circle[radius=0.25];
\node[color=white] at ({-\winkel}:3) {$m$};

\node at (0,0) [left] {$O$};

\end{tikzpicture}
\end{document}