\begin{eqnarray}
\Delta y
\end{eqnarray}
is the variation of each spring, and k is the resort constant,, and I'm sorry, y_1 is the solution, it is my mistake.
I need to find the differential equations for each mass. ##y_1## is the equilibrium position, and ##y_2## is the second equilibrium position for each mass.
I was thinking consider the next sistem:
\begin{eqnarray}
k\Delta y-mg&=&m\frac{d^2 y_2}{dt^2}
\\ -2k\Delta y_1 -k\Delta y_2 -2mg...