If there is friction operating, the magnitude of the oscillation decreases with time. The frequency and period of oscillation remains constant. A vibrating system normally vibrates at its natural frequency. The external force interacts with the oscillation and the process is then known as forced. It may be acted on by an external force with a different frequency vibration. The natural frequency of oscillation is the same as that of the damped system in the case of light damping if, If the driving frequency is close to the natural frequency, there is a very strong interaction between the two systems. Metronomes with the same frequency but out of phase. Energy can be transferred through the surface. Mechanical eaves such as water waves and strings and springs. Other types such as sound waves, electromagnetic waves an matter waves. The disturbance is perpendicular to the direction of propagation of the wave.
