The speed of sound in air, under normal conditions, is 1224 km/h. When this value is exceeded, we say that the sound barrier has been broken.
Sound waves are mechanical waves (which need a propagation medium) that propagate in spherical wave fronts , similar to waves generated in water by a falling object, but in all directions. The propagation speed of these waves in the air, under normal conditions, is approximately 1224 km/h (340 m/s). Therefore, at the moment when a supersonic plane accelerates and reaches that speed, we say that the sound barrier has been reached and, when it exceeds the 1224 km/h mark, the aircraft breaks this barrier.
Mechanical waves, when propagating, transport energy. At the moment of breaking the sound barrier , for example, this energy is manifested. In addition to the intense noise produced, a cloud is formed (as in the image that opens the text) that is the result of the condensation of water vapor due to the extreme pressure variation that occurs around an aircraft, for example. This phenomenon is one face of the manifestation of energy carried by mechanical waves.