Animation of a shock wave propagating from an object travelling at the speed of sound. The object compresses the air immediately in front and creates a shock wave where the waves expand outwards at the same speed as the object moves. Consequently, the wave front concertina together at the front of the object. This wall of compression that cannot escape is the sound barrier. If the object exceeds the speed of sound it breaks through the sound barrier and becomes supersonic creating a conical shock wave (Mach cone).