%% Circular differential elements and a ring opened into its matching strip.

\documentclass[tikz,border=7mm]{standalone}
\usepackage{tikzphysics}

\begin{document}
\begin{tikzpicture}[font=\small]
  \node[polar element,
    element inner radius=16mm,
    element radial thickness=3mm,
    element start angle=20,
    element delta angle=38,
    show dimensions] (P) at (0,0) {};
  \node[below=8mm] at (P.south) {polar element};

  \node[differential sector,
    element outer radius=19mm,
    element start angle=20,
    element delta angle=38,
    show dimensions] (S) at (6,0) {};
  \node[below=8mm] at (S.south) {differential sector};

  \pic (D) at (11.5,0) {differential ring diagram={
    element inner radius=1cm,
    element radial thickness=2mm
  }};
  \node[below=12mm] at (D-strip.south)
    {ring element opened into a $2\pi r$ by $d\!r$ strip};
\end{tikzpicture}
\end{document}