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 Tweet # Doppler Effect Introduction: Imagine you're standing on the streets outside of your house or apartment. An ambulance car comes rushing past, and you have to cover your ears to shield them from the loud, piercing sound of the sirens. The term behind this phenomenon is known as the Doppler Effect. The Doppler Effect takes into account the changes in pitch as a vehicle or source of sound waves is approaching, then receding.

The Doppler Effect refers to changes in the frequency of a wave for an observer moving relative to a source. The Doppler Effect can be affected by the motion of the source, the motion of the medium, or the motion of the observer. According to the Doppler Effect, the frequency (or pitch) of a wave decreases if either the receiver or the source moves away from the other.

The Doppler Effect is summarized by the equation below:

$f=({c+v_x}/{c+v_s})f_o$, where c=velocity of waves in the medium, $v_x$=velocity of the receiver relative to the medium, $v_s$=velocity of the source relative to the medium, f=observed frequency, and $f_o$=emitted frequency

The formula for the Doppler Effect typically presumes that the source of the sound either approaches or recedes from the observer of that sound. This equation is not only important to consider in the case of sirens, but also in the case of radar technologies when measuring the velocity of a moving object. This is also used with the Hammond B-3 organ and has applications in astronomy.

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