Example: Windshield wiper

% Windshield wiper - drawing for calculating the area swept by the blade
% Author: Jimi Oke
\documentclass{article}
\usepackage[margin=2cm]{geometry}
\usepackage{tikz}
\usetikzlibrary{fadings}
\begin{document}
\begin{tikzpicture}[>=latex]
    \tikzfading[name=fade out, inner color=transparent!0,
         outer color=transparent!100]

    % dimensions and angle
    \draw[|<->|, xshift=0.1cm,yshift=-0.4cm] 
    (15:0) -- (15:6) node[fill=white, midway,sloped] {36 in} ;

    \draw[|<->|, xshift=-0.15cm,yshift=-0.4cm] 
    (155:0) -- (155:2) node[fill=white, midway,sloped] {12 in} ;

    \draw[<-] (15:.6) arc (15:155:.6) ;
    \node at (45:1.1) {$0.8\pi$} ;

    % background/shading
    \fill [gray, path fading=fade out] (-8,-2) rectangle (9,8);

    % sweep area
    \filldraw[gray!50,left color=blue!25, right color=blue!30, middle color=white] 
    (15:2) arc (15:155:2) -- (155:2) -- (155:6) arc (155:15:6) -- (15:2) ;

    \draw[dashed] (15:0) -- (15:2) ;
    \draw[dashed] (155:0) -- (155:2) ;
    
    % wiper blade
    \filldraw(0,0) circle (.08cm) ;
    \filldraw[very thick,black,double distance=1pt] (92:0) -- (92:2.2) ;
    \draw[ultra thick] (90:2) -- (90:6) ;
    \draw[fill=gray!90!blue] (90.5:2.2) -- (94:2.2) -- (91.5:5.5) --
    (90.5:5.5);
    \draw[fill=gray!90!blue]  (90:5.5) -- (91:5.5) -- (90.5:6) --
    (90:6); 
\end{tikzpicture}
\end{document}