Original source : http://www.scientificamerican.com
Posted : March 2002
Author : Tobias Rossmann
What is the sound barrier?
The sound barrier, in aerodynamics, is the point at which an
object moves from transonic to supersonic speed. The term, which occasionally
has other meanings, came into use during World War II, when a number of
aircraft started to encounter the effects of compressibility, a collection of
several unrelated aerodynamic effects that "struck" their aircraft
like an impediment to further acceleration. By the 1950s, new aircraft designs
routinely "broke" the sound barrier
(http://en.wikipedia.org)