An F-18 Hornet Breaks the Sound Barrier over the USS Kitty Hawk 

Imagine a rowboat on a lake. Imagine that you are viewing it from above. It is moving forward. It is also making waves as the boat jumps ahead and as the paddles disturb the surface of the water. These waves move much faster than the boat, so what you'll see from above is a slowly moving boat with a bulls eye-pattern of waves expanding from it in all directions. A normal airplane is like our boat, and the sound waves are like the waves on the water. As an airplane moves ahead, it sends out sound waves in  all directions. The waves travel faster than the plane. The sound waves are  like spherical onion-layers which fly outwards from the plane, with the  airplane in the center of the expanding "onion."

If a speedboat travels faster than the speed of water waves, it cannot send out a bulls eye-shaped pattern of ripples. For every ripple it made, the speedboat would plough forward through the ripple, moving faster than the ripple possibly could. Because it oversteps its own ripples, a speedboat instead makes a V-shaped wake on the lake. This wake is like a sonic boom, but it's using water waves rather than sound waves.

When a supersonic aircraft flies faster than the speed of sound, it does not send out normal sound waves. Instead it sends out a V-shaped ripple. Of course its not exactly like the water waves, since air is three-dimensional. A supersonic aircraft sends out a cone-shaped ripple of sound waves as it flys. The aircraft is in the tip of the "cone." This ripple is the sonic boom.

Pilots cannot hear their own sonic boom. If you were Superman and could fly along outside a supersonic aircraft, you would not hear the boom either. This is because for you the "boom" is a region of increased pressure  that follows along with the plane. Superman could stick his hand into the airplane's  one-shaped wake and feel the high pressure there. He could even stick his head into the pressure wake but still would hear no "boom" (although the pressure change might make his ears pop!) A sonic boom is only a "boom" or "crack" sound for people on the ground. As the plane flies along, it drags its cone-shaped pressure wave along the ground like a skirt. As the cone of pressure passes by, we hear it as an explosion. It's very much like the sound-pulse from an explosion, but rather than expanding from a centralized explosion, the wave is being continuously created by the flying plane. Depending on the shape of the plane and its speed, the pressure wave might be thick or thin. If it's thin, it will  sound like a "snap" or a "bang". If its broad, it will sound like a "thump"  or a "boom." Imagine the wave from our speedboat. As the boat passes by, all is quiet on the shore. The wave approaches, then SPLASH! 

The splash of a speedboat wake on the shore is like the "thump" of a supersonic jet's wake when it hits the surface of the land. Pressure waves from supersonic aircraft can be destructive. They can  blow out windows, and even collapse walls and roofs. The higher the plane flies, the wider and weaker the pressure wave becomes. If a supersonic plane flew at rooftop level, the sonic pressure wave might explode buildings like a tornado does. Even if a jet pilot flees high, the cone-shaped wave can  become "kinked" when the plane makes a sudden turn. The pressure wave can be very strong inside the elbow of the "kink" and when it hits the ground it  can cause trouble. The rule for fighter pilots is "Fly high over populated areas, and no high-speed turns!" ill look for more info, but this is pretty good 

ET2 Darren Drake