text: through the air as a 
  In the 
  series of very weak pressure waves. 
  frequencies, the 
  ordinary 
  range of audible 
  threshold of audibility 
  for intensity of sound 
  is for pressure waves with an approximate 
  R.M.S. value of pressure as low as 0.0000002 
  psf. Within 
  this same range of frequencies, 
  the threshold of feeling for intensity of sound 
  is for pressure values with an approximate 
  R.M.S. value of pressure of 0.2 to 0.5 psf. 
  Continuous sound at the threshold of feeling 
  is of the intensity to cause painful hearing. 
  Thus, the shock waves generated by an air- 
  plane in supersonic flight are capable of creat- 
  ing audible sound and, in the extreme case, can 
  be of a magnitude to cause considerable dis- 
  turbance. Pressure jumps of 0.02 to 0.3 psf 
  have been recorded during the passage of an 
  airplane in supersonic flight. As a result, 
  are the pressure waves 
  the sonic “booms” 
  generated by the shock waves formed on the 
  airplane in supersonic flight. 
  
  The source of sonic booms is illustrated by 
  figure 6.14. When the airplane is in level 
  supersonic flight, a pattern of shock waves is 
  developed which 
  is much dependent on the 
  configuration and flight Mach number of the 
  airplane. At a considerable distance from the 
  airplane, these shock waves tend to combine 
  along two common fronts and extend away 
  from the airplane in a sort of conical surface. 
  The waves decrease in strength with distance 
  away from the airplane but the pressure jump 
  remains of an audible intensity for a consider- 
  If the wave 
  able distance from the airplane. 
  extends to the ground or water surface, it will 