Why is there are sonic boom when planes make the sound barrier?

Question

What causes the sound?

Answer 1

A sonic boom is the audible component of a shock wave in air. The term is commonly used to refer to the air shocks caused by the supersonic flight of military aircraft or passenger transports such as Concorde (Mach 2.03, no longer flying) and the Space Shuttle (Mach 27, has only flown once since the 2003 crash). Sonic booms generate enormous amounts of sound energy, sounding much like an explosion; typically the shock front may approach 167 megawatts per square meter, and may exceed 200 decibels.

When an aircraft is near the sound barrier, an unusual cloud sometimes forms in its wake. A Prandtl-Glauert Singularity results from a drop in pressure, because of shock wave formation. This pressure change causes a sharp drop in temperature, which in humid conditions leads the water vapor in the air to condense into droplets and form the cloud

Answer 2

At or above the speed of sound, half the acoustic energy generated by the jet engine is constrained to a 2D surface (usually a plane or cone) which has the effect of concentrating the energy in that space. As this plane/cone passes you, you sample the energy stored on (or in) it for a brief but very intense moment. Ergo you hear a bang.

This is the short answer, real world distortions that in effect complicate the amount of energy accumulated and stored on the 2D surface, and the shape of that surface are (but not limited to):
1) air density gradient from ground level to flight altitude.
2) humidity - humid air converts the acoustic energy to heat more quickly.
3) polar energy dispersion from the power plant. It is not usually spherical and is colored (polar dispersion is frequency dependent)
4) multi path convergences - can form an interference pattern as observed on the ground making the geometric relationship between the ground track projection and observer important to predicting the amplitude of the response.

Answer 3

sound is a compression wave going through matter, in this case air. As the plane reaches the same speed as the compression wave, the waves build up in front of the plane. Then the plane goes through that buildup

Answer 4

the engines...