Sound Barrier (disambiguation).
In aerodynamics, the sound barrier usually refers to the point at which an aircraft moves
from transonic to supersonic speed. The term came into use during World War II when a
number of aircraft started to encounter the effects of compressibility, a grab-bag of unrelated
aerodynamic effects. The term fell out of use in the 1950s when aircraft started to routinely
"break" the sound barrier. Refer to the speed of sound for the science behind the velocity
referred to as the sound barrier.