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Sound consists of ripples in air pressure that travel out from the source at a speed of about 1100 feet per second. A sound source like a plane that travels at the same speed as the sound it produces (Mach one) creates a sonic boom which consists of all the sound waves it has produced since reaching that speed coming togeter in the same place and reinforcing each other. When the source of sound travels faster than the speed of sound the sonic boom continues to be produced in a cone shaped wave front. The angle of the cone's wave front tells how much faster than the speed of sound the source is going. For example, at twice the speed of sound, the angle the side if the cone makes with the axis of the cone is 45 degrees. Most supersonic planes have swept back wings to keep the wing away from the destructive sound level in the cone's surface of sound reinforcement. An observer on the ground will experience the sonic boom of a supersonic plane as the cone of sound reinforcement sweeps by.

You can see a two dimensional analogy of sonic behavior in the ripples in the surface of a pond. The ripples travel outward from the source at a much lower speed than sound waves, making them easier to observe. A stationary boat bobbing up and down makes ripples that travel outward. As the boat starts to move ahead slowly, the ripples are no longer concentric but are closer spaced in the direction the boat is traveling and spread out away from the direction it is traveling. When the boat reaches the speed of the ripples a bow wave is formed. As the boat travels faster, the bow wave bends back into a V. When the boat is traveling twice the speed of the ripples, the bow wave is at an angle of 45 degrees to the direction of the boat.