Torricelli’s experiment & barometers

Some basic diagrams to explain pressure with a Torricelli’s experiment creating vacuum (P = 0), a barometer, and a manometer.
For more related figures, please have a look at the Fluid Dynamics category.

Torricelli’s experiment with water (height h ~ 10 m), creating a vacuum inside the tube:

Barometer (open-ended tube) to measure air pressure:

Manometer (closed tube):

Edit and compile if you like:

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% Author: Izaak Neutelings (November 2020)
\documentclass[border=3pt,tikz]{standalone}
\usepackage{siunitx}
\usepackage{physics}
\usepackage{tikz}
\usepackage[outline]{contour} % glow around text
\usetikzlibrary{patterns,decorations.pathmorphing}
\usetikzlibrary{arrows.meta}
\tikzset{>=latex}
\contourlength{1.1pt}
\colorlet{mydarkblue}{blue!50!black}
\colorlet{myred}{red!65!black}
\colorlet{watercol}{blue!80!cyan!10!white}
\colorlet{darkwatercol}{blue!80!cyan!20!white}
\tikzstyle{piston}=[blue!50!black,top color=blue!30,bottom color=blue!50,middle color=blue!20,shading angle=0]
\tikzstyle{water}=[draw=mydarkblue,top color=watercol!90,bottom color=watercol!90!black,shading angle=5]
\tikzstyle{vertical water}=[water,
  top color=watercol!90!black!90,bottom color=watercol!90!black!90,middle color=watercol!80,shading angle=90]
\def\tick#1#2{\draw[thick] (#1)++(#2:0.1) --++ (#2-180:0.2)}
\begin{document}
% PRESSURE TORRICELLI
\begin{tikzpicture}
  \def\Rx{1.0}
  \def\Ry{0.05*\Rx}
  \def\rx{0.18*\Rx}
  \def\ry{0.06*\rx}
  \def\H{1.0}
  \def\h{0.72*\H}   % water level height
  \def\th{2.7*\H}   % tube height
  \def\ty{0.95*\th} % tube level
  \def\td{0.6*\h}   % tube depth
  \def\N{14}
  
  % WATER + CONTAINER
  \draw[vertical water] %rounded corners=2
    (-\Rx,\h) --++ (0,-\h) arc(180:360:{\Rx} and {\Ry}) --++ (0,\h);
  \draw[water]
 
 
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