What is a sonic boom? Before you understand what a sonic boom is, it is important to understand what a shock wave is since these are closely related.
We start though by showing you the differences between a bow wave and a shock wave. This will help you quickly understand what a shock wave is.
Having said that, what is a sonic boom? Air usually gets out of the way
of an aircraft when the speed of the aircraft is less than that of
sound. However, when an aircraft is traveling at a speed greater than
that of sound, air cannot get out of the way fast enough. This will
cause a sudden increase in air pressure behind the aircraft. This air
pressure looks like a three-dimensional shock wave as shown above in the figure.
When the shock wave reaches the ground, people near by the wave will
hear a sudden explosive noise. This noise is called a sonic boom. In the
figure above, the guy on the right has already heard the sonic boom.
However, the guy on the left will hear it shortly.
Notice that the overlapping spheres will indeed create a cone. May be you wondering at this point why the wave is made by spheres instead of circle.
To see a real life example of what a sonic boom is , I encourage you to check this video. You will see the cone shape behind the aircraft after it passed the speed of sound.
When a lion tamer cracks a whip, the tip of the whip will travel faster than the speed of sound. As a result, you hear a sonic boom as well.
In summary, when a plane is traveling faster than the speed of light, a shock wave will form behind the airplane. The shock wave creates a sonic boom. However, to hear the sonic boom, the shock wave has to reach your ear.
Hopefully by now, you clearly understand what a sonic boom is.