What phenomenon do traffic police use to measure the speed of cars based on wave interference?

Traffic police utilize the phenomenon of beats to measure the speed of cars through the principle of wave interference. Beats occur when two sound waves of slightly different frequencies interfere with each other, creating a pattern of alternating constructive and destructive interference that manifests as variations in loudness.

In the context of traffic monitoring, police may use radar guns that emit radio waves which reflect off moving vehicles. As the speed of the car changes, the frequency of the returned waves also changes due to the Doppler effect. By analyzing these frequency variations and the resulting beat frequencies, officers can calculate the speed of the vehicles accurately. This method leverages the properties of wave interactions, particularly how superimposed waves can result in observable changes in sound intensity, allowing for precise speed measurements on the roads.

Although waves, interference patterns, and frequency are all related concepts in wave physics, the specific application of measuring speed through the interaction of different wave frequencies leading to beats makes it the most relevant choice in this scenario.