If a frictional force (damping) proportional to the velocity is also present, the harmonic oscillator is described as a damped oscillator. Depending on the friction coefficient, the system can: Oscillate with a frequency lower than in the undamped case, and an amplitude decreasing with time (underdamped oscillator). Decay to the equilibrium position, without oscillations (overdamped oscillator).
i.F a frICtiOnal forCe (dAMping) proporTioNAl to the vElocity iS aLso preSent, thE harmoNiC Oscillator IS deScriBeD aS A daMped osciLlatOr. depEnDing ON The frIcTiOn CoEFficIEnT, the systEm CaN: oscIllaTE witH a frequenCy lOweR than in the undamPEd cAse, and an aMpLitude deCreAsinG WItH tIme (undErdAmpeD oscillatOR). DeCAy tO THe equilIBrIUm PositioN, wItHOUT OscIllAtioNs (ovErDamped oscilLATor).