Find the observed frequency from a moving source as it approaches and recedes.
The Doppler effect is the change in the observed frequency of a wave when the source and observer move relative to each other. As a source approaches, its waves bunch up and the frequency rises; as it moves away, the waves stretch out and the frequency drops. This is why a passing siren shifts from a high to a low pitch.
Enter the frequency emitted by the source, the speed of the source, and the speed of the wave in the medium (343 m/s for sound in air). The calculator returns the frequency heard while the source approaches and while it recedes. The same physics explains the redshift of light from distant galaxies.
While approaching, waves are compressed, raising the frequency. After it passes, the waves are stretched, lowering the frequency, producing the familiar drop in pitch.
Yes. Moving light sources show redshift when receding and blueshift when approaching, which astronomers use to measure the motion of stars and galaxies.