I have the infamous triatomic molecule, with two m masses in the extremes and one 2m mass in the middle, joined by two k springs. I have worked all through the problem (found frequencies, normal modes, drawn configurations, initial conditions) with no hindrances, but I can't seem to get the last question. It says: If a harmonic force is applied to one of the masses, to which would it be better to excite better the highest frequency mode? Btw, the highest freq. mode is w^2= 2k/m and it happens with the first and third masses are in phase, with the middle mass in counterphase (1,-1,1) How do I know which mass should I excite? Thanks Sol.