# Equations on motion for spring

1. May 8, 2012

1. The problem statement, all variables and given/known data

hi,
the question asks for me to find the normal mode of the oscillator shown below
where k1=3nm-1 k2=7.5 k3=39nm-1

im having difficulty setting it up with gravity being the main problem

diagram below

2. Relevant equations

3. The attempt at a solution

equation of motion

where m1 is the 2kg mass and m2 the 6kg mass

m1$\ddot{y1}$=m1g-k1y1 + k2(y1-y2)

m2$\ddot{y2}$=m2g-(k2+k3)y2

i think my equations of motion are wrong, hence why im not able to get the right matrices, im not exactly sure what though, im missing something elementary