in the early 19th century christian doppler, an austrian physicist, proposed a theory regarding the properties of a moving source of sound. this is now known as doppler’s law or the doppler effect. what does this law state

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Sound wave compression affects the frequency of a moving source of sound. Frequency is greater as it approaches an observer and pitch of the sound also increases. As the object moves past the observer, the frequency decreases and the pitch is now lower. This principle is also used to find the speed of moving bodies as well as in determining approaching or receding stars based on the frequency or color shift of their light emissions.

this is poiselle's equation from fluid mechanic in physics. mech eng

what is the actual question though?