\documentclass{article}
\thispagestyle{empty}
\usepackage{graphicx}
\usepackage{pstcol}
\usepackage{color}
\begin{document}
\thispagestyle{empty}
\begin{figure}[htb!]
%  \begin{minipage}[b]{5cm}
    \centering
\psset{unit=2,dotsize=3pt 1}
    \begin{pspicture}(5,5)
%     \psgrid
\psline[linewidth=4pt](0,3.6)(3.2,2.2)
%\psline[linewidth=4pt](0,3.6)(3.2,2.5)
%\psline[linewidth=4pt](0,2.5)(3,1.5)
\psline[linewidth=4pt](-0.6,2.6)(3,1.2)
\pscircle[linewidth=2pt](4.,1.5){0.5}
\psarc[linecolor=blue]{->}(4.,1.5){0.3}{70}{400}
\uput[45](3.75,1.5){\textcolor{blue}{\Large i}}
\psdots[dotstyle=o](4.19,1.7)(3.8,1.3)
\psline[linewidth=2pt]{->}(4.19,1.7)(4.1,1.6)
\psline[linewidth=2pt,linecolor=red]{->}(3.8,1.3)(4.,1.5)
\qdisk(1.6,2.6){2pt}
\psline[linewidth=2pt]{->}(1.6,2.6)(1.55,2.5)
\psline[linewidth=2pt,linecolor=red]{->}(1.6,2.6)(2.2,2.4)
\psdots[dotstyle=+](1.4,2.2)
\psline[linewidth=2pt]{->}(1.4,2.2)(1.5,2.4)
\psline[linewidth=2pt,linecolor=red]{->}(1.4,2.2)(2.4,1.8)
\uput[45](1.4,2.5){\large f$_r$}
\uput[45]{-25}(2.5,1.8){\Large $B_z -g {dB_z\over dz}$} 
\psline[linewidth=3pt]{->}(1.8,3)(1.95,3.2)
\uput[45](2.1,3.1){\Large net f$_r$}
    \end{pspicture}
%\caption{Deflection in the tilded case}\label{fig3}
%  \end{minipage}%
\end{figure}
\end{document}
