Abstract: The relation between nonequilibrium work and free-energy difference, i. e. , the Jarzynski equality is proved by using a forced harmonic oscillator, in wich the free-energy difference between two equilibrium states can be calculated by the exponential averaging of generalized work. This process is performed during a finite time. Moreover, we find a dynamical resonance of average work or dissipative energy can become maximum if the external driving force is regarded as a periodic signal.

Key words: generalized work, free-energy difference, forced oscillator, resonance