The Doppler effect, named after Christian Andreas Doppler, is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves.
The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer.
For more information about the topic Doppler effect, read the full article at Wikipedia.org, or see the following related articles:
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.
Recommend this page on Facebook, Twitter,
and Google +1:
Other bookmarking and sharing tools: