This week at The Lilac Festival, my mother and I experienced loads of different noises all at the same time. With loads of security, we heard lots of sirens passing us, creating the Doppler Effect. The Doppler Effect is the shift of frequency of a wave when a source moves past.
As a source with sound, such as a police car or security car, moves towards you, the frequency is smaller, which creates more of a high pitched sound. While moving, the frequency then begins to increase and after it passes you, the frequency is larger, making a lower sound.
To the human ear, the frequency increases quickly with the source, so the sound sounds like "neeeowwww." With so much chaos and Doppler Effect at the lilac festival, my mom and I decided to give our ears a break and go home early.