# tikz extending spring with constant number of segments

Is there as simple way to create a pdf animation with tikz of an oscillating mass attached to a spring which extends and compresses as the mass oscillates. The number of "spring elements" should be constant during the oscillation.

I came up with this pretty solution so far. However, I do not quite understand how to chose the right units for the segment length parameter:

\documentclass[tikz]{standalone}
\usepackage{tikz}

\begin{document}

\def\frames{50}
\def\amplitude{1.5}
\def\z0{3.0}
\def\nloops{5.0}

\foreach \n in {0, 1, ..., \frames}
{
\begin{tikzpicture}[x=1cm, y=1cm]

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% calculations
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\pgfmathsetmacro{\height}{\amplitude * cos(2.0 * pi * \n / \frames r) - \z0};
\pgfmathsetmacro{\seglength}{(-\amplitude * cos(2.0 * pi * \n / \frames r) + 3.0) / \nloops * 1cm};

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% help lines
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\draw[color=white,fill=white] (-1.70, 0.4) rectangle (2.00, -6.0);

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% the scene
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% the ceiling
\draw[color=black!70, line width=2.0pt, line cap=round] (-1.70, 0) -- (1.70, 0);
\foreach \x in {-1.60, -1.20, ..., 2.0}
{
\draw[color=black!70, line width=1.00pt, line cap=round] (\x, 0) -- ++ (0.35, 0.4);
}
\draw[color=black!70, line width=2.00pt, line cap=round] (-0.5, 0) -- +(0.0, -0.2);
\draw[color=black!70, line width=2.00pt, line cap=round] (+0.5, 0) -- +(0.0, -0.2);

% the mass
\draw[ball color=orange!90!black!70, rounded corners=1ex] (-1.0, \height) rectangle +(2.0, -0.75);
\draw[color=black!70, line width=2.00pt, line cap=round] (-0.5, \height) -- +(0.0, 0.2);
\draw[color=black!70, line width=2.00pt, line cap=round] (+0.5, \height) -- +(0.0, 0.2);

% the spring
\draw[decorate, color=red!70, line width=2.00pt, line cap=round, decoration={coil, amplitude=0.25cm, segment length=\seglength}] ($(-0.5, \height) + (0, 0.2)$) -- (-0.5, -0.2);

\end{tikzpicture}
}
\end{document}


To the spring should have a minimum extension of 1.5 cm and a maximum extension of 4.5 cm. Here is an image of the spring at minimum extension:

Can someone point me into the right direction?

• – Torbjørn T. Jun 8 '13 at 18:19
• – cjorssen Jun 8 '13 at 22:14
• thanks for the links. the examples illustrate pretty much what I want as the final figure. However, my biggest problem is that the automatic calculation of the segment length seems to give the correct result when I print it but when I use it as an argument in "segement length=\seglength" it behaves inconsistently. I suppose that has to di with the fact that \seglength does not have cm units? – Daniel Jun 9 '13 at 0:21

Thanks for the links to the related question. By studying these really nice solutions I could modify my figure. The result is not as sophisticated as the other solutions but much shorter. Thus, I thought I share it with you.

\documentclass[tikz]{standalone}
\usepackage{tikz}

\begin{document}

\def\frames{50}
\def\r{0.5cm}

\foreach \n in {0, 1, ..., \frames}
{
\begin{tikzpicture}

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% calculations
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\pgfmathsetlengthmacro{\height}{1.5cm * cos(2.0 * pi * \n / \frames r) - 2.9cm};
\pgfmathsetlengthmacro{\seglength}{(-1 * \height - 0.4cm) / 4};

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% the frame
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\draw[color=white,fill=white] (-1.70, 0.4) rectangle (2.00, -6.0);

% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% the scene
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% the ceiling
\draw[color=black!70, line width=2.0pt, line cap=round] (-1.70, 0) -- (1.70, 0);
\foreach \x in {-1.60, -1.20, ..., 2.0}
{
\draw[color=black!70, line width=1.00pt, line cap=round] (\x, 0) -- ++ (0.35, 0.4);
}
\draw[color=black!70, line width=2.00pt, line cap=round] (0.0, 0.0) -- +(0.0, -0.2);

% the mass
\draw[ball color=orange!90!black!70, rounded corners=1ex] ($(0.0, \height) - (0.0, \r)$) circle[radius=\r];
\draw[color=black!70, line width=2.00pt, line cap=round] (0.0, \height) -- +(0.0, 0.2);

% the spring
\draw[decorate, color=black!70, line width=2.00pt, line cap=round, decoration={zigzag, amplitude=0.25cm, segment length=\seglength}] ($(0.0, \height) + (0, 0.2)$) -- (0.0, -0.2);

\end{tikzpicture}
}
\end{document}


The animation looks like this