oscillations when the driving frequency is close to either of these two normal fre-quencies. This is indeed the case. We can explore forced oscillations by considering the arrangement of two masses connected by springs as shown in Figure 4.15. This is similar to the arrangement shown in Figure 4.10 but now the end s of one of the outer springs is moved harmonically as ξ = a cosωt. The displacements ξ,xa
and xb of the masses from equilibrium are shown in Figure 4.15 at some instant