1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution This is one of our past homework assignments with the solution given to us. I'm trying to work my way through each part of this assignment but am getting stuck on a few aspects of the model. My approach: I first set up a FBD modeling each mass in the system and analyzing the forces acting on that mass. So for mass 1 in part a) I would say there is the spring and damping force acting to the left of the mass and another spring force acting to the right of the mass. What I'm having a bit of difficulty understanding is the the displacement of each mass and how its oriented in the diagram. Do we always take the origin at the center of mass for the object? Is it wrong to place the origin at the wall where spring 1 is connected? I'm getting a little confused on such small matters like this but its effecting my ability to move forward. For instance in part b) I'm confused about the 2nd differential equation modeling mass 2. Why are both forces negative?