From: Ray ®	09/11/2001 17:19:43
Subject: re: AVIATION FAQ	post id: 490480
Why don't most planes fly faster than the speed of sound? Subsonic aircraft are much more efficient and less expensive. If you were sitting in an aeroplane that was travelling faster than the speed of sound, would you be able to hear yourself or anyone else speak? ? From: OP (Avatar) Unlike light, the speed of sound is relative to the speed of the medium in which it travels. (Not the speed of the particles, but the average velocity of the particles, ie the mass speed). As far as the air in the plane is concerned, the passengers are stationary, and can talk as normal. What causes the sonic boom when a plane goes supersonic? [The shockwave generated by air particles colliding.] From: Pete A sonic boom is a shock wave which propagates from an aircraft or other object which is going faster than sound through the air (or other medium). In subsonic flight air is deflected smoothly around the wings. In supersonic flight this cannot happen because the effect of the aircraft wings pushing the air ahead cannot travel faster than sound. The result is a sudden pressure change or shock wave which propagates away from the aircraft in a cone at the speed of sound.