Answer:
The wave phenomenon that you are describing is known as the Doppler effect. The Doppler effect occurs when a wave, such as a sound wave, passes by an observer and the pitch of the wave seems to change. This is because the frequency of the wave changes as it moves closer to or farther away from the observer. The pitch of a sound wave is directly related to its frequency, so when the frequency of the wave changes, the pitch will also change. This effect is commonly observed with sound waves, but it can also occur with other types of waves, such as light waves.