ABSTRACT
Sound waves behave like ripples on a pond. Sound waves behave in a very similar way to these ripples. There are several points to observe. Like the ripples, sound waves move away from the source at a constant speed. Like the ripples on the pond, sound waves simply pass through the atmosphere by exchange of momentum. In the atmosphere, of course, the pattern is three-dimensional and the sound waves are spherical. The speed of sound in air varies slightly with temperature and humidity, but is independent of frequency. Most sources of sound which peopel encounter are due to some mechanical vibration such as the vibration of a panel covering a machine. The motion of vibrating systems such as parts of machines, and the value of sound pressure with time is often said to be simple harmonic. Such acoustic wave motion in a straight duct is one-dimensional, like the wave motion on a long string under tension.
