Which of the following is NOT an application of the Doppler shift principle?

The principle of the Doppler shift, which describes how the frequency of waves (such as sound or light) changes in relation to an observer moving relative to the source of the waves, has specific applications. It is primarily used to determine speed and direction based on the change in frequency or wavelength of emitted signals.

Measuring the distance to a sonar contact does not directly rely on the Doppler effect. Sonar systems typically work by emitting sound waves and listening for their echo after they bounce off an object. The time it takes for the sound waves to return is used to calculate distance, independent of the principles of frequency change associated with Doppler shift.

In contrast, measuring the speed of a moving car involves analyzing the change in frequency of sound waves from the car as it approaches or moves away, thus employing the Doppler effect. Similarly, determining whether a star is moving toward or away from Earth leverages the redshift and blueshift of its light, again an application of the Doppler principle. Lastly, finding the direction of motion of a submarine uses sonar technology that can also be influenced by the Doppler effect, particularly when considering the frequency shifts of sounds from the submarine as it moves.