Thus an object moving at Mach 0.7 is traveling at seven-tenths the speed of sound and, at Mach 1.0, it would be moving at the speed of sound. The speed of sound at sea level, in dry air at 32 degrees Fahrenheit, is approximately 741 mph. A sonic boom is a loud noise resembling thunder that is caused by an aircraft moving faster than any vibrations it creates in the air.
Air reacts like a fluid to supersonic objects.
Instead of vibrating molecules, as in the case of thunder, the aircraft actually displaces air, pushing it aside with great force. This forms a pressure, or shock wave, much as a boat or ship pushes up a low wave of water. The base of this cone is dragged across the landscape along the flight path, creating one continuous boom along the full width of the cone's base. It is the sharp release of pressure after the buildup by the shock wave that creates the sonic boom. It is the rate of change, the sudden onset of the pressure change, that makes the sonic boom audible.