The illustrates the approximation of the wavefronts that are ahead of the moving sound source. This plane travels at the same speed as sound, so we see that it travels at the same speed as the waves it produces. As a consequence of this wavefront formation we have the Doppler effect and its result is a loud bang . The formation of wave fronts can also be called shock waves .
According to the figure, we see that, when the speed of sound is reached, all the wavefronts are concentrated in a single point, in this case the point represented is point F . It is exactly at this point that the amplitudes are added, making the intensity of the sound wave very high. Thus, at that point there is a sudden increase in pressure in the region.
The wavefronts represented in the figure above are compression fronts whose resulting effect is a formidable boom. Right behind there is a superposition of refraction fronts and, in this case, as seen in the photo at the beginning of this chapter, the effect is different.
The sudden and intense reduction in pressure causes the condensation of the water vapor contained in the air in this region and gives rise to the cloud that is observed around the plane. We have to pay attention to the fact that the plane does not cross the cloud, it creates it. In the figure below we can see that for an airplane that flies faster than the speed of sound, the wave crests form a series of arranged circles. We have the formation of a sound cone when we draw tangent lines to the circles.
Shock waves produced by an airplane flying faster than the speed of sound.
For an observer who is situated at a point outside the region covered by the circles, no sound will be detected. But when the region that encompasses the circles passes by the observer, he will feel a sudden change in pressure, as if it were a small explosion, or a shock wave.