Coulomb force

Coulomb forces between point charges.

Edit and compile if you like:

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% Author: Izaak Neutelings (July 2018)
\documentclass[border=3pt,tikz]{standalone}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{physics}
\tikzset{>=latex} % for LaTeX arrow head
%\usepackage{xcolor}
%\colorlet{force}{orange!80!black}
\tikzstyle{charge}=[thin,top color=red!50,bottom color=red!70,shading angle=20]
\tikzstyle{charge+}=[thin,top color=red!50,bottom color=red!90!black,shading angle=20]
\tikzstyle{charge-}=[thin,top color=blue!50,bottom color=blue!80,shading angle=20]
\tikzstyle{force}=[->,very thick,orange!80!black]
\tikzstyle{vector}=[->,very thick,green!45!black]
\def\a{2.5}
\def\R{0.33}
\def\F{1.8}
\begin{document}
\Large
% REPELLING CHARGES +q +q
\begin{tikzpicture}
  \coordinate (L) at (-\a,0);
  \coordinate (R) at (+\a,0);
  
  % FORCES
  \draw[force] (L) ++ (-\R,0) --++ (-\F,0) node[left] {$\mathbf{F}_{21}$};
  \draw[force] (R) ++ (+\R,0) --++ (+\F,0) node[right] {$\mathbf{F}_{12}$};
  
  % POSITION VECTOR
  \draw[vector] (L) --++ (0.4*\a,0) node[right=-2] {$\vu{r}_{21}$};
  
  % CHARGES
  \draw[charge+] (L) circle (\R) node[scale=1.2] {$+$};
  \draw[charge+] (R) circle (\R) node[scale=1.2] {$+$};
  \draw[<->]     (L)++(\R,-1.1*\R) --++ (2*\a-2*\R,0) node[midway,below] {r};
  \node[above] at (-\a,\R) {$q_1=+q_0$};
  \node[above] at (+\a,\R) {$q_2=+q_0$};
 
 
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