Draw a longitudinal vibrational mode in a one-dimensional system, with a node at the center of the system and with a wavelength twice the nominal length of the system. Show that the instantaneous length of the system is a linear function of the instantaneous amplitude of this mode. What is the order of magnitude of the wavelength if the system is macroscopic and if the wavelength is measured in dimensionless units (i.e., relative to interatomic lengths)?