The siren has a lower pitch as it moves away because crests of the sound are farther apart. Details about sound waves can be found below.
What is a sound wave?
Sound wave is thee longitudinal wave of pressure that is transmitted through any plastic material.
A sound wave like every other type of wave posseses wave like features such as wavelength, period etc.
According to this question, as a siren moves away, the pitch gets lower. This can be attributed to the distant crest of the sound wave.
Learn more about sound waves at: https://brainly.com/question/11797560
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