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 Automatic translation  Automatic translation Category: light and photons
Updated April 03, 2022
  shock wave in the air

Image: The Mach cone is a relevant image of the concept of shock wave and sound barrier. When the plane exceeds Mach 1, the waves fall into a cone with the plane as its apex. The boundary between the mach cone and the exterior forms a hyperbola that advances with the plane. The intensity of the bang is the result of the abrupt change in pressure when the air pressure suddenly returns to its natural average balance. This implosion of the wave on itself causes the bang. Credit: FA-18 Hornet breaking the sound barrier on July 7, 1999 by Ensign John Gay, US Navy

  Cherenkov effect or light

Image: The bluish luminosity of the water in the spent fuel cooling pools of nuclear power plants is generated by the Cherenkov effect.
The speed of light in vacuum (299792 km/s) is the maximum speed of energy movement. But the speed of light in water (225563 km/s) can be exceeded, which makes the Cherenkov effect possible.
Credit: Cherenkov radiation in the core of the Advanced Test Reactor, Idaho National Laboratory.

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Mach cone

When an aircraft exceeds the speed of sound (≈340 m/s), it leaves behind all spheres of sound disturbance. These waves are all tangent to a cone called the Mach cone.
At this moment, an important sound energy is concentrated on this border. The acoustic waves emitted meet, add up and cause the double bang perceived only in the cone. The zone outside the cone is a zone of silence.