Translated by BabelFish
The disturbances move with the speed of sound A.
v=a sonic flow
v>a supersonic flow
It is understood that the behavior of the waves of disturbances depends on the V/a report/ratio which one calls the Mach number. There is sin(a)=a/V=1/Ma Le cone of Mach is made of a shock wave (zone of stressings of the elementary disturbances where the phenomena are extremely violent one).