= Mixed-axis trajectory of a prestressed spring pair
{title2=$X/\epsilon=\cos(\sqrt2\omega_y t),\quad Y/\epsilon=\cos(\omega_y t)$}
Two equal <masses> linked in a line by three identical <springs>, each stretched to twice its natural <length>, have longitudinal <stiffness matrix> $k\begin{pmatrix}2&-1\\-1&2\end{pmatrix}$ and transverse matrix half as large. Equal displacements of both <masses> select the symmetric modes. Equal longitudinal and transverse release <amplitudes> produce the title trajectory. It is not closed after one transverse <period> because the two mode <frequencies> have irrational ratio $\sqrt2$. Higher-order geometric terms are neglected in this small-displacement solution.
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