The amplitude of vibration is strongly dependent on the frequency of excitation, and on the properties of the springmass system.
To see this mathematically, note that the solution has the form . Observe that is the amplitude of vibration, and look at the preceding section to find out how the amplitude of vibration varies with frequency, the natural frequency of the system, the damping factor, and the amplitude of the forcing. The formulae for are quite complicated, but you will learn a great deal if you are able to sketch graphs of as a function of for various values of .