Abstract
This work reports on a study concerning the behaviour of an elastic system subject to a periodic external excitation. Oscillatory movement is the most common type of mechanical movement found in nature and, of course, in technique. A system executing simple harmonic motion is called harmonic oscillator system. If the harmonic oscillator motion describes a path as the straight line, the harmonic oscillator is called linear harmonic oscillator. Such linear harmonic oscillator is considered an elastic system when the force acts upon it is an elastic one. If in the elastic system dissipative forces are involved then they have the effect of energy losses during oscillation, so that, after a while, the oscillator energy is lost in various forms. To compensate the energy losses of dissipative forces, the oscillator must be driven by a periodic external disturbing force that produces forced oscillations in the elastic systems. If external disturbing force is periodical, the oscillator will run a new type of oscillations called forced oscillations. In this case the period and frequency of forced oscillations of the elastic system will be the same as the period and frequency of disturbing force. In this situation there is a transfer of energy between the two systems. Studying forced vibrations, in terms of energy intake, through excitation forces, are overrun highlight the importance of phase shift between force and oscillator movement. Keywords: harmonic oscillator system, periodic external excitation, phase shift, energy, resonance phenomenon