What is the "sonic boom"?

When an aircraft exceeds the speed of sound can be heard a loud noise that physicists have called a sonic boom. The term "wall of sound" is quite old: it was invented to emphasize a limitation of the aviation industry in the early '900. For many years, the technologies used are not allowed to build planes faster than sound. Revealed the source of misunderstanding, the fact remains that when a plane actually exceeds a certain speed can hear distinctly a real bang in the air, but whose origins are very different. The correct word to use here is "supersonic", which literally means "faster than sound (not to be confused with" ultrasonic "that it refers to sound frequencies above those audible to the human ear). Air is composed mainly of nitrogen and oxygen molecules, which move freely in all directions. It will perhaps surprise, but under normal conditions (ie room temperature), the tiny air molecules move on average over 1700 miles per hour. When a plane flies through a layer of air at speeds of several hundred km / h, the molecules have no difficulty in moving and let him pass. If a supersonic jet hurtling through the air at a rate comparable to that of molecules, they are unable to move and accumulate, tablets, on the front of the vehicle, which pushes them forward. We can think of air molecules as a swarm of many small insects: if driving in low speed, we can cross it, and if we travel at high speeds, many animals will crack the windshield. The air that accumulates at the aircraft creates a shock wave, which is basically a noise that propagates in all directions. From the ground we hear a sharp noise and deafening bang is elusive.