Forced oscillations are oscillations that occur when a periodic driving force is applied to a system that is already undergoing oscillations/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations). The driving force puts energy into the system at a certain frequency, which may not necessarily be the same as the natural frequency of the system/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations). When an oscillator is forced with a periodic driving force, the motion may seem chaotic at first, but after the transients die out, the oscillator reaches a steady state where the motion is periodic/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations). The amplitude of the forced oscillations near resonance is higher when the system has less damping/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations). Resonance occurs when a periodic force drives a harmonic oscillator at its natural frequency/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations). The system is said to resonate, and the amplitude of the oscillations can become very large/Book%3A_University_Physics_I_-Mechanics_Sound_Oscillations_and_Waves(OpenStax)/15%3A_Oscillations/15.07%3A_Forced_Oscillations).

In summary, forced oscillations occur when a periodic driving force is applied to a system that is already undergoing oscillations. The motion of the oscillator may seem chaotic at first, but it eventually reaches a steady state where the motion is periodic. The amplitude of the forced oscillations near resonance is higher when the system has less damping, and resonance occurs when a periodic force drives a harmonic oscillator at its natural frequency.