Phy107Spr07Lect14

Phy107Spr07Lect14 - From Last Time Wave Properties Doppler...

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1 Fri. Feb. 23 Phy107 Spr07 Lect 14 1 From Last Time… Wave Properties Interference: waves can superimpose constructively or destructively • Two speakers can be quieter than one! • Doppler effect – Frequency shift (up or down) from moving source. Fri. Feb. 23 Phy107 Spr07 Lect 14 2 Doppler Effect for a moving source • Source moves toward observer (A): wavelength appears shorter, frequency higher • As the source moves away from the observer (B), the wavelength appears longer and the frequency appears to be lower Fri. Feb. 23 Phy107 Spr07 Lect 14 3 Question A police car is moving toward you at constant speed. You would hear A. A constant pitch B. A pitch increasing in frequency C. A pitch decreasing in frequency D. A pitch moving up and down in frequency Fri. Feb. 23 Phy107 Spr07 Lect 14 4 Shock Waves and Sonic Booms • A shock wave results when the source velocity exceeds the speed of the wave itself • The circles represent the wave fronts emitted by the source Fig 14.1 , p. 439 Slide 15 Fri. Feb. 23 Phy107 Spr07 Lect 14 5 Sonic Boom • Source of sound approaching the listener is equal to or faster than the speed of sound • Each successive wave is superimposed on the previous one • Shock wave results as air compression in crest gets very large Fri. Feb. 23 Phy107 Spr07 Lect 14 6 Breaking the sound barrier No sound received till after the source passes the listener - then a sonic boom - followed by normal sound from the source Conical bow wake from condensed water vapor at high pressure shock wave front.
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2 Fri. Feb. 23 Phy107 Spr07 Lect 14 7 Breaking the ‘sound’ barrier in a canoe! If the canoe moves faster than the water wave velocity, shock wave also builds up where all the crests line up. For water wave velocity ~1 m/s,
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Phy107Spr07Lect14 - From Last Time Wave Properties Doppler...

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