Doppler Effect
DETAILS/DESCRIPTION: Sound from a moving object rises in pitch if the object is approaching, and fall if the object is departing. This is due to the fact that sound waves from an approaching soirce “bunch up” at the listener’s ear, and “bunched up” waves arrive with greater (higher) frequency. The reverse is true for waves coming from a departing object. This effect was first discovered by Christian Doppler*
The Doppler effect also works with light. When a luminous object (such as a celestial body) is moving away from us, the frequency of its light waves is decreasing. This causes its color to appears more red and the phenomenon is known as ‘red shift.’ Light from an approaching light-source rises in frequency and causes a ‘blue shift.’
Radar devices used by police to track the speed of moving automobiles operate on the Doppler effect, as do medical applications, including radiology, echocardiography, and ultrasonography, all of which utilize the behavior of ultrasonic waves.
ONELINER: The Doppler effect
OTHER CONNECTIONS: None
BIBLIOGRAPHY:
“Doppler Effect.” Gale Encyclopedia of Science. 2nd ed. 6 vols. Gale Group, 2001. Reproduced in Student Resource Center. Detroit: Gale, 2003.
http://0-galenet.galegroup.com.mill1.sjlibrary.org:80/servlet/SRC
“Christian Johann Doppler.” World of Scientific Discovery, 2nded. Gale Group, 1999. Reproduced in Biography Resource Center. Farmington Hills, Mich.: The Gale Group. 2003. http://0-galenet.galegroup.com.mill1.sjlibrary.org:80/servlet/BioRC**
Doppler Effect. Encyclopaedia Britannica. Retrieved December 8, 2003, from Encyclopaedia Britannica Online