What phenomenon explains the change in sound frequency related to the motion of a source or observer?

The phenomenon that explains the change in sound frequency related to the motion of a source or observer is the Doppler effect. This effect occurs when a sound source moves relative to an observer, leading to a change in the frequency of the sound waves perceived by the observer. When the source moves toward the observer, the sound waves are compressed, resulting in a higher frequency or pitch. Conversely, when the source moves away from the observer, the waves are stretched, leading to a lower frequency or pitch.

The Doppler effect is a fundamental concept in wave physics and has practical applications in various fields, including astronomy (to determine the motion of stars and galaxies) and radar technology. Understanding the Doppler effect helps explain phenomena like the change in the sound of a passing siren. Other options, such as intensity, frequency modulation, and tone shift, do not directly describe this specific phenomenon related to frequency change due to relative motion.