1. The problem statement, all variables and given/known data Hello everyone, i'm a bit stuck on this particular problem and i was hoping somebody could give me a couple tips or hints! "consider a linear monoatomic chain where all atoms have a mass M except one which has a small mass m. The force constant is C." First i'm asked to write the equation of motion for the relevant atoms. Then, i'm asked to solve it assuming a displacment function for atom n in the form of Un = Aexp(-ax)exp(i((omega)t - Kx)) Let the chain be: vs-2 -- vs-1 --- u --- vs --- vs+1 where u is the impurity 3. The attempt at a solution I'm currently lost at the beginning of the problem, finding the equation of motion. What i first thought was to treat this almost like it were the case of a diatomic chain. Mdvs/dt = C(vs+1 + u - 2vs) mdu/dt = C(vs-1 + vs - 2u) however, upon continuing in the problem i'm not sure that this is correct. Could anyone offer any advice as to how i should start this problem?