The Sonic Boom

A sonic boom occurs whenever an object is moving faster than the speed of sound.  Because an object moving faster than the speed of sound moves ahead of the sound waves it produces, those sound waves cannot move out of the way of each other.  The waves compress together and form a shock wave that sounds like a big boom when it reaches the human ear.  We most commonly associated sonic booms with fighter jets that fly through the air very quickly.

However, a fighter jet is not needed to produce a sonic boom.  A simple bullwhip, similar to the one Indiana Jones used, produces a small sonic boom that you hear as the crack of the whip.  The tip of the whip moves faster than the speed of sound, creating a shock wave.

The big sonic boom misconception is that the sonic boom takes place the moment the object breaks the sound barrier.  This isn't true.  It is true that an object moving at the speed of sound produces a sonic boom, but an object moving faster than the speed of sound also produces a sonic boom.  In other words, an object continually produces a sonic boom as long as it is moving at or faster than the speed of sound.  You only hear it once because that is when the waves hit your ears.  There's no real physical barrier that the fighter jet is breaking through.  It's a simple bunching together of sound waves.