It is any phenomenon that involves the propagation in the form of elastic waves (whether audible or not), usually through a fluid (or other elastic means) that is generating the vibratory movement of a body.
It is very important in our life and knowing the way it is propagated to communicate is important, since thanks to this life becomes easy, the waves that must travel to listen for example the voice of our friends or the heartbeat of Someone is very interesting.
Knowing their characteristics makes us differentiate and know why each person's instruments and voice are heard differently.
Sound has many uses, the knowledge acquired by mankind through the work of many personalities, are used today to meet human needs, including mass communication, healthy recreation, health maintenance such as magnetic resonances, and television
The pressure variations of the medium.
In nature there are sounds generated by different sound sources
The smooth running of the water through a tap has the same frequency characteristics
The Iguazu Falls, with its approximately 100 meters high free fall
Some scraped string instrument (violin, cello) are performed "normally" with the bow rubbing the strings or when pressed
The pipe organ (and its electronic copies), the saxophone (also of air, like the organ) and those instruments that, not being of fixed envelope, can easily control this function, such as the flute etc ...
Percussion instruments that form the "drums": drums, cymbals, drummers, tumblers (in this field we must highlight the cymbals, with a long declining time that can be violently cut by the musician) using a pedal or the hand itself.