これは毛細管に吸い上げられた液柱の降下の様子です。
\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}
\fill[top color=white, bottom color=cyan][rounded corners=5pt]
(7.25,-6)--(7.25,-7)--(8.5,-7)--(8.5,-6);
\draw(7.25,-6)--(8.5,-6);
\draw[densely dotted](8,-6)--(9,-4.8) (4,-3)--(5,-1.8);
\draw[{[scale=2.5]<}-{[scale=2.5]>}](8.8,-5.1)--(4.8,-2.1);
\draw(6.8,-3.2)node[scale=2]{$l$};
\draw[-{[scale=2]>}](4.3,-2.9)--(5.7,-4);
\draw(5.1,-3.2)node[scale=1.75]{$v$};
%棒 \fill[ball color=yellow!70!brown!20](3.75,-2.8)--(3.75,-2.7)
%--(2.25,-2.7)--(2.25,-2.8)--(3.75,-2.8);
\draw(3.75,-2.8)--(3.75,-2.7)--(2.25,-2.7)--(2.25,-2.8)--(3.75,-2.8);
\fill[left color=white, right color=lightgray!20!white]
(2.8,-5)--(2.8,1)--(3.2,1)--(3.2,-5);
\fill[left color=white, right color=lightgray!20!white]
(3,1)circle[x radius=0.2, y radius=0.1];
\draw(3,1)circle[x radius=0.2, y radius=0.1];
\draw(2.8,-5)--(2.8,1);
\draw(3.2,-5)--(3.2,1);
\fill[ball color=white](3.25,-2)--(2.75,-2)--(2.75,-2.5)
--(2.5,-2.5)--(2.5,-3)--(2.75,-3)--(2.75,-3.5)--(3.25,-3.5)
--(3.25,-3)--(3.5,-3)--(3.25,-2.5)--(3.25,-2);
\fill[white, opacity=0.85](3.25,-2)--(2.75,-2)--(2.75,-2.5)
--(2.5,-2.5)--(2.5,-3)--(2.75,-3)--(2.75,-3.5)--(3.25,-3.5)
--(3.25,-3)--(3.5,-3)--(3.25,-2.5)--(3.25,-2);
\draw(3.25,-2)--(2.75,-2)--(2.75,-2.5)--(2.5,-2.5)--(2.5,-3)
--(2.75,-3)--(2.75,-3.5)--(3.25,-3.5)--(3.25,-3)--(3.5,-3)
--(3.25,-2.5)--(3.25,-2);
\fill[ball color=yellow!70!brown!20]
(2.25,-2.75)circle[x radius=0.15,y radius=0.15];
\fill[ball color=yellow!70!brown!20]
(3.75,-2.75)circle[x radius=0.15,y radius=0.15];
\draw(2.25,-2.75)circle[x radius=0.15,y radius=0.15];
\draw(3.75,-2.75)circle[x radius=0.15,y radius=0.15];
\fill[ball color=yellow!50!brown!20!]
(3.3,-2)circle[x radius=0.2,y radius=0.15, rotate=250];
\draw(3.3,-2)circle[x radius=0.2,y radius=0.15, rotate=250];
\draw(3.35,-2.1)circle[x radius=0.12,y radius=0.05, rotate=40];
\fill[top color=white, bottom color=gray](3.2,-2.1)
--(3.3,-2.2)--(2.8,-3)--(2.7,-2.9)--(3.2,-2.1);
\draw(3.2,-2.1)--(3.3,-2.2)--(2.8,-3)--(2.7,-2.9)--(3.2,-2.1);
\fill[top color=gray, bottom color=gray]
(2.75,-2.95)circle[x radius=0.07,y radius=0.04, rotate=325];
\draw(2.75,-2.95)circle[x radius=0.07,y radius=0.04, rotate=325];
%管
\fill[top color=white,middle color=lightgray!20!white, bottom color=white]
(8,-6)--(0,0)--(-0.25,-0.25)--(7.75,-6.25);
\fill[top color=white, bottom color=cyan!50!white]
(8,-6)--(4,-3)--(3.75,-3.25)--(7.75,-6.25);
\draw(0.9,0.45)node[scale=2]{$2a$};
\draw(0.35,-0.5)arc[x radius=0.75,y radius=0.75,start angle=200,end angle=120];
\draw[{[scale=1.5]<}-{[scale=1.5]>}](0.52,-0.36)--(0.25,-0.65);
\draw(0,0)--(8,-6);
\draw(-0.25,-0.25)--(7.75,-6.25);
\fill[top color=white, bottom color=cyan](7.875,-6.125)circle[x radius=0.18,y radius=0.1,rotate=45];
\draw(7.875,-6.125)circle[x radius=0.18,y radius=0.1,rotate=45];
\draw(0,0)arc[x radius=0.19,y radius=0.17,rotate=45,start angle=60,end angle=230];
\draw[dash dot dot](8,-6)--(8,1);
\draw(8,-5.5)arc[x radius=0.5,y radius=0.5,rotate=45,start angle=90,end angle=140];
\draw[ultra thick](1,-0.75)--(6,-4.5);
\draw[ultra thick](0.75,-1)--(5.75,-4.75);
\draw(7.6,-5.2)node[scale=2]{$\theta $};
%ビーカー
\draw[rounded corners=5pt](7,-5.8)--(7.25,-5.8)--(7.25,-7)--(8.5,-7)--(8.5,-5.8)--(8.75,-5.8);
%注射器
\fill[ball color=black](1.6,-6.4)--(1.6,-7)--(4.25,-7)--(4.25,-6.4);
\draw(1.6,-6.4)--(1.6,-7)--(4.25,-7)--(4.25,-6.4);
\fill[top color=white, bottom color=gray](2.5,-6)--(2.5,-5)--(3.5,-5)--(3.5,-6);
\draw(2.5,-6)--(2.5,-5)--(3.5,-5)--(3.5,-6);
\fill[top color=white, bottom color=lightgray](2,-5.6)
--(4,-5.6)--(4,-5.4)--(2,-5.4)--(2,-5.6);
\draw(2,-5.6)--(4,-5.6)--(4,-5.4)--(2,-5.4)--(2,-5.6);
\fill[left color=white, right color=lightgray!50!white](2.9,-5.5)
--(2.9,-4.5)--(3.1,-4.5)--(3.1,-5.5);
\draw(2.9,-5.5)--(2.9,-4.5)--(3.1,-4.5)--(3.1,-5.5);
\draw (2.85,-4.65) to[out=90,in=-90] (2.85,-4.49) to[out=135,in=-20,looseness=0.45]
(1,-3.9) to[out=160,in=-45] (-1,-2.5) to[out=135,in=280] (-1.8,-1)
to[out=100,in=180] (-1,0.5) to[out=0,in=140] (0,0);
\draw (3.15,-4.65) to[out=90,in=-90] (3.15,-4.49) to[out=120,in=-20,looseness=0.6]
(1,-3.6) to[out=160,in=-45] (-1,-2.1) to[out=135,in=280] (-1.5,-1.1)
to[out=100,in=180] (-1,0.2) to[out=0,in=140] (-0.25,-0.25);
\draw(2.85,-4.65)--(3.15,-4.65);
\draw(1.5,-6.3)arc[x radius=1,y radius=0.45,start angle=250,end angle=80];
\draw(1.5,-6.2)arc[x radius=1,y radius=0.33,start angle=240,end angle=90];
\draw[thick,white](2.8,-4.435)--(2.8,-4.197);
\fill[top color=white, bottom color=lightgray!20!white](2,-6)
--(1.8,-6.2)--(1.5,-6.2)--(1.5,-6.3)--(1.8,-6.3)--(2,-6.5);
\fill[top color=white, bottom color=lightgray!20!white](4.2,-6.1)
--(4.5,-6.1)--(4.5,-6.4)--(4.2,-6.4);
\fill[top color=white, bottom color=lightgray!20!white](2,-6)
--(4,-6)--(4,-6.5)--(2,-6.5);
\draw(2,-6)--(4,-6);
\draw(2,-6.5)--(4,-6.5);
\fill[top color=white, bottom color=lightgray!20!white]
(4.1,-6.25)circle[x radius=0.1,y radius=0.5];
\draw(4.1,-6.25)circle[x radius=0.1,y radius=0.5];
\draw(4.2,-6.1)--(4.5,-6.1);
\draw(4.2,-6.4)--(4.5,-6.4);
\draw(4.55,-6.25)circle[x radius=0.05,y radius=0.25];
\fill[ball color=lightgray](2.7,-5.95)--(3.3,-5.95)
--(3.3,-6.55)--(2.7,-6.55)--(2.7,-5.95);
\fill[white,opacity=0.1](2.7,-5.95)--(3.3,-5.95)
--(3.3,-6.55)--(2.7,-6.55)--(2.7,-5.95);
\draw(2.7,-5.95)--(3.3,-5.95)--(3.3,-6.55)--(2.7,-6.55)--(2.7,-5.95);
\draw(2,-6)--(1.8,-6.2);
\draw(2,-6.5)--(1.8,-6.3);
\draw(1.8,-6.3)--(1.5,-6.3)--(1.5,-6.2)--(1.8,-6.2);
\draw(2,-6.05)arc[x radius=0.1,y radius=0.225,start angle=120,end angle=240];
%白いネジ
\fill[ball color=white,](3,-5.5)circle[x radius=0.08, y radius=0.42];
\fill[white,opacity=0.9](3,-5.5)circle[x radius=0.08, y radius=0.42];
\draw(3,-5.5)circle[x radius=0.08, y radius=0.42];
\fill[ball color=white,](3,-5.5)circle(0.2);
\fill[white,opacity=0.9](3,-5.5)circle(0.2);
\draw(3,-5.5)circle(0.2);
\fill(2.9,-5.5)circle(0.04);
\fill[ball color=gray!60!white](2.6,-5.2)--(2.8,-5.2)
--(2.8,-5.9)--(2.6,-5.9)--(2.6,-5.2);
\fill[ball color=gray!60!white](3.4,-5.2)--(3.2,-5.2)
--(3.2,-5.9)--(3.4,-5.9)--(3.4,-5.2);
\draw(2.6,-5.2)--(2.8,-5.2)--(2.8,-5.9)--(2.6,-5.9)--(2.6,-5.2);
\draw(3.4,-5.2)--(3.2,-5.2)--(3.2,-5.9)--(3.4,-5.9)--(3.4,-5.2);
%標線{$l_i$}
\foreach \x/\y in {0.9/-0.67, 3.9/-2.9, 0.8/-0.6,2.5/-1.875, 6.3/-4.7, 5.2/-3.9}
\draw[thick] (\x,\y) arc[x radius=0.2, y radius=0.2,
start angle=80, end angle=200];
%ネジ
\fill[top color=white, bottom color=gray](2.7,-2.6)--(2.8,-2.45)
--(3.2,-2.76)--(3.1,-2.9)--(2.7,-2.6);
\fill[top color=white, bottom color=gray](2.9,-2.25)--(3,-2.1)
--(3.4,-2.41)--(3.3,-2.55)--(2.9,-2.25);
\draw(2.9,-2.25)--(3,-2.1)--(3.4,-2.41)--(3.3,-2.55)--(2.9,-2.25);
\draw(2.7,-2.6)--(2.8,-2.45)--(3.2,-2.76)--(3.1,-2.9)--(2.7,-2.6);
\draw(4,-3)--(3.75,-3.25);
\end{tikzpicture}
\end{document}