(a) and (b) are the time-response of the one-mode model to frictional excitation ( = 0.1 m.s⁻¹ and F_N = 1 N). (c) and (d) are the time response of the four-mode model (modes 1, 4, 7 and 8) to the same excitation. The orange lines correspond to the speed of the finger, the blue lines correspond to the resonator’s movement. (a) and (c) are phase diagrams, corresponding to speed versus displacement of the contact point C of the resonator; the red crosses show the starting point of the simulation: resonator at rest. (b) and (d) are speed versus time graphs, the vertical black lines correspond to the first instant where the speed of both resonator and finger are identical, the red curves correspond to approximately 1 period of the periodic regime. The seven instants (A–F) in (a) are the same as the Figures 4b, 4c and 4d.