Sounds are often described as loud or soft; high-pitched or low-pitched. These words are commonly used to describe, or characterize, how sounds are perceive. Scientists, on the other hand, describe sounds with characteristics that can be measured using instruments. Scientists measure intensity and amplitude, which can be related to the common words loud and soft. Scientists also measure frequency, which can be related to the common word pitch.
|Perceived Characteristic||Physical Characteristic|
Sound travels in a wave, as commonly illustrated below. However, it is important to remember that in a sound wave, the particles move back and forth rather than up and down, as this picture might seem to suggest.
The picture below shows what the particles are doing - when the pressure is high, the particles are squashed together (compressed under high pressure) and when the pressure is low, the particles are pulled apart (expanding under low pressure). The image below is commonly used to illustrate a waveform, which shows the change in pressure as a sound wave moves past a fixed location.
Another important characteristic of a sound is the wavelength, which is the distance from the top of one wave to the top of the next wave. Although you can see the wavelength of a water wave, you cannot see the wavelength of a sound wave. Scientists can calculate the wavelength of a sound from the measured frequency of the sound and the speed of sound in seawater in that medium.
Another important characteristic of a sound wave is phase. Phase specifies the location of a point within a wave cycle of a repetitive waveform. When two sound waves interact, the difference between the phases of the two waves is important in determining the resulting waveform.
The following sections provide more information on how sound is characterized and discuss the sound characteristics that are related to this picture of a wave: