Originally Posted by
nd_eric_77
The sound barrier is also relative to the air around the airplane. In other words, at cruising altitude, a jet would need a ground-speed of 660mph PLUS the speed of any tailwind. (IOW, 550 MPH speed + 120 MPH tailwind = 670 MPH ground speed, but < the 660 MPH sound barrier at that altitude).
I hope this doesn't require too techinical an answer, but why is this? The sound waves don't travel at a different speed depending on the winds, do they? So if, with the wind, the plane is moving 763 mph, isn't it moving faster than the speed of sound relative to the ground? Doesn't this mean that on the ground a sonic boom would be observed?