Shock Waves

http://hypertextbook.com/physics/waves/shock/
When the speed source exceeds the speed of sound, the waves form a barrier that cannot be heard.
-Sound Barriers first came into the English language during WWII.
-The people flying the planes felt a strange pull when getting close to or exceeding the speed of -sound, because that's what a sonic boom is.
-When the wave exceeds speed of sound, the shape of the sound waves form a cone.
-the amplitude of the wave is called a 'shock wave.'
-How fast a wave goes depends on the length of amplitude.
-When a shock wave is as fast as the normal speed, then the shock wave dies and becomes just a sound wave.

Image link= http://www.madsci.org/posts/archives/1997-12/877005226.Ph.1.jpg