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9.5 The Doppler Effect. The Doppler Effect. Apparent change in frequency of a sound relative to the object’s motion. As the source moves closer , observed frequency increases . As the source moves away , observed frequency decreases . Can occur when
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The Doppler Effect • Apparent change in frequency of a sound relative to the object’s motion. • As the source moves closer, observed frequency increases. • As the source moves away, observed frequency decreases. • Can occur when • Source is moving relative to a stationary observer • Observer is moving relative to a stationary source
Stationary Source & Observer Moving Source http://www.fisica.uniud.it/~deangeli/applets/Multimedia/Waves_java/Doppler/doppler.htm
Example 1 You are standing at a railway crossing. A train approaching at 125 km/h sounds its whistle. If the frequency of the whistle is 442 Hz and the air temperature is 20.0°C, what frequency do you hear when the train approaches you? When the train has passed you?
Supersonic Travel Subsonic speed: less than the speed of sound in air Mach number: Mach = speed of object speed of sound Supersonic speed: when Mach > 1 http://www.fisica.uniud.it/~deangeli/applets/Multimedia/Waves_java/Doppler/doppler.htm
Sound barrier: high pressure region produced when plane approaches Mach 1 A shock wave is produced when the place “breaks” through this barrier.
Sonic boom • Explosive sound that radiates from aircraft travelling at supersonic speeds • Caused by constructive interference of spheres of sound waves that are left behind the aircraft The space shuttle, on re-entry: http://www.youtube.com/watch?v=lNL4HHFG8H4 http://www.youtube.com/watch?v=Oo_1HeravCY&feature=related http://www.youtube.com/watch?v=a1CU6VVE0AA&feature=related If time, Mythbusters: http://www.youtube.com/watch?v=GvtAElaDVz8
Homework 9.5 Practise #1, 2 pg 435 9.5 Questions #2-6 pg 435