<P> Sonic booms due to large supersonic aircraft can be particularly loud and startling, tend to awaken people, and may cause minor damage to some structures . They led to prohibition of routine supersonic flight over land . Although they cannot be completely prevented, research suggests that with careful shaping of the vehicle the nuisance due to them may be reduced to the point that overland supersonic flight may become a practical option . </P> <P> A sonic boom does not occur only at the moment an object crosses the speed of sound; and neither is it heard in all directions emanating from the speeding object . Rather the boom is a continuous effect that occurs while the object is travelling at supersonic speeds . But it only affects observers that are positioned at a point that intersects a region in the shape of geometrical cone behind the object . As the object moves, this conical region also moves behind it and when the cone passes over the observer, they will briefly experience the boom . </P> <P> When an aircraft passes through the air it creates a series of pressure waves in front of the aircraft and behind it, similar to the bow and stern waves created by a boat . These waves travel at the speed of sound and, as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of each other's way quickly enough . Eventually they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1, and is approximately 1,235 km / h (767 mph) at sea level and 20 ° C (68 ° F). </P> <P> In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail . Because the different radial directions around the aircraft's direction of travel are equivalent (given the "smooth flight" condition), the shock wave forms a Mach cone, similar to a vapour cone, with the aircraft at its tip . The half - angle between direction of flight and the shock wave α (\ displaystyle \ alpha) is given by: </P>

Why is there a noise when you break the sound barrier
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