A sonic boom is a shockwave that is caused by an object breaking the sound barrier. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion, or thunder. As an object passes through the air, it creates a series of pressure waves in front of it and behind it. These waves travel at the speed of sound, and as the speed of the aircraft increases the waves are compressed because they cannot pass each other, eventually merging into a single shock wave. This speed is known as Mach 1 and is approximately 761 mph at sea level.In smooth flight, the shock wave starts at the nose of the aircraft and moves to the tail. There is a sudden rise in pressure at the nose, causing a negative pressure at the tail, where it suddenly returns to normal. This is known as the N wave because of its shape. The boom is experienced when there is a sudden rise in pressure, so the N-wave causes two booms, one when the initial pressure rise from the nose hits, and another when the tail passes and the pressure suddenly returns to normal. This leads to a double boom from supersonic aircraft. When turning, the pressure changes into different forms, with a U-wave shape. Since the boom is being generated continuously, it traces out a path on the ground following the aircraft's flight path, known as the boom carpet.
The power of the shock wave is dependent on the quantity of air that is being accelerated. As the aircraft increases speed the shocks grow tighter around the craft.. At very high speeds and altitudes the cone does not intersect the ground and no boom is heard. The length of the boom from front to back is dependent on the length of the aircraft. Longer aircraft spread out their booms more than smaller ones, which leads to a less powerful boom. The nose shockwave compresses and pulls the air along with the aircraft so that the aircraft behind its shockwave is in subsonic airflow. However, this means that several smaller shock waves can form at other points on the aircraft, like the leading wing edge and especially the inlet to engines. The later shock waves are faster than the first one. This maximizes both the magnitude and the rise time of the shock which makes the boom seem louder.