pressure values, one position peak to the next (condensation to condensation) anywhere along the path of the wave. The
words per second are omitted but understood in referring to frequency so that the frequency is expressed only in cycles.
Sometimes cps (cycles per second) is used. The time required for one cycle to occur is called the period of the wave.
Cycles per second is the American unit of measurement for frequency while Hertz (Hz) is the international unit of
measurement. (1 Hz = 1 cps). Initially, cycles or cps will be used in this text; however, later the term Hertz will be used.
On the left hand side of the graft you can recognize the zero axis--the value of the wave measured from the zero axis to
the maximum value of the wave is called the "amplitude." The expressed value of the amplitude of the wave depends
upon the units used to measure the relative compression of the particles or their effect.
Velocity and Wavelength.
a. Velocity. The length of time required for sound to travel from one point to another is called speed or velocity.
In air at 0€ C (32€ F) the velocity of sound waves is about 1,090 feet per second. As the temperature rises so does the
speed of sound. At 20€ C (69€ F) the velocity of sound is about 1,130 feet per second. As the medium increases in
density the velocity increases. For example, in water, sound travels at 4,700 feet per second. In solids, sound velocity is
usually many times greater than in air. Light waves and electromagnetic waves travel much faster than sound, 186,000
miles per second which is about 700,000 times faster than sound. You can readily recognize this difference in velocity if
you recall that you see the lightning flash before you hear the report. At ordinary speaking distances the time required for
sound to travel from one person to another is too short to be of any consequence. However, it can be quite disturbing
when the distance separating the speaker from the listener is relatively great, such as a large auditorium or a stadium.
b. Wavelength. A sound wave, like a light wave or electromagnetic wave, may be identified by its wavelength.
The wavelength is the distance between successive condensations or successive rarefactions, along the path of the sound.
In figure 3, the wavelength is the distance covered by that portion of the wave designated as one cycle. The wavelength
of a soundwave can be calculated by using the formula: