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Doppler Shift Contents: What it is Moving Source Moving observer Whiteboards

Doppler Shift Contents: What it is Moving Source Moving observer Whiteboards. Doppler Shift. Demo/examples: race cars, bells at RR crossing Frequency: (Key to understanding this) Higher approaching Lower receding Moving source/moving observer. TOC. Doppler Shift - moving source.

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Doppler Shift Contents: What it is Moving Source Moving observer Whiteboards

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  1. Doppler Shift • Contents: • What it is • Moving Source • Moving observer • Whiteboards

  2. Doppler Shift • Demo/examples: race cars, bells at RR crossing • Frequency: (Key to understanding this) • Higher approaching • Lower receding • Moving source/moving observer TOC

  3. Doppler Shift - moving source Sitting Still TOC

  4. Moving to the right Doppler Shift - moving source Source creates smaller wavelengths in front, longer in back Demo - Doppler applet TOC

  5. Doppler Shift - moving source • Derivation: ’ =  + usT • f’ = shifted frequency • f = source frequency • us = speed of source • v = speed of sound • When do you use + and - in the denominator? TOC

  6. Observer Doppler Shift - moving observer Motion of the source makes you experience different frequencies TOC

  7. Doppler Shift - moving observer • Derivation:f = v/, f’= (v + uo)/ • f’ = shifted frequency • f = source frequency • uo = speed of observer • v = speed of sound • When do you use + and - ? TOC

  8. Doppler Shift Moving source - approach – f’ Moving source - recede – f’ Moving observer - recede – f’ Moving observer - approach – f’ Moving observer - approach – f Moving source - recede – f Be sure to do at least one of the last two… TOC

  9. A car with a 256 Hz horn approaches you at 40.0 m/s. What frequency do you hear? (3) (use v sound = 343 m/s) • Source – approaching • f = 256 Hz, us = 40.0 m/s, v = 343 m/s, and - W 290. Hz

  10. A man wearing a pointy hat screams at a perfect 1000. Hz while running away from you at 9.5 m/s. What frequency do you hear? (use v sound = 343 m/s) • Source – receding • f = 1000. Hz, us = 9.5 m/s, v = 343 m/s, and + W 973. Hz

  11. Your father is nagging you at a pitch of 85.0 Hz, and you ride your motorized “Hello Kitty” skateboard away from him at 14.0 m/s. What frequency do you hear? (use v sound = 343 m/s) • Observer, receding • f = 85 hz, uo = 14 m/s, v = 343 m/s, and - W 81.5. Hz

  12. You are running toward the Jo-Jo man with a quarter and a dime at 6.7 m/s. If the music from the truck is at a frequency of 2013 Hz, what is the frequency you hear? (use v sound = 343 m/s) • Observer, Approaching • f = 2013 hz, uo = 6.7 m/s, v = 343 m/s, and + W 2052.3 Hz

  13. Duggan is playing the National Anthem on the electric guitar at the senior assembly. You are late, so you are running toward him at 11.2 m/s. If you hear his last note as an A 440 Hz, what is the real frequency he is making? (use v sound = 343 m/s) • Observer, Approaching • f’ = 440 hz, uo = 11.2 m/s, v = 343 m/s, and + W 426 Hz

  14. A group of students wearing pointy hats is riding Ducati motorcycles (The “Hello Kitty” limited edition) and chanting “Respectful, Responsible, Safe” driving away from you at 34 m/s. You hear them at a pitch of 512 Hz, what pitch are they really making? (use v sound = 343 m/s) • Source – receding • f’ = 512 Hz, us = 34 m/s, v = 343 m/s, and + W 562.8 Hz

  15. Solving for us or uo problems (optional)

  16. What speed in what direction is the same car (f = 256 Hz) moving if you hear 213 Hz (use v sound = 343 m/s) • Moving source • lower frequency • f’ = f{ v } • {v + us } • f’ = 213 Hz, f = 256 Hz, v = 343 m/s, and + W 69.2 m/s away from you

  17. A running person who is late for a concert hears the concertmaster who is playing an A 440. Hz. How fast and in what direction are they running if they hear a frequency of 463 Hz. (use v sound = 343 m/s) • Moving observer • higher frequency • f’ = f{v ± uo} • { v } • f = 440.0 Hz, f’ = 463 Hz, v = 343 m/s, and + W 17.9 m/s

  18. You are driving on a road, and a car coming the other way has a horn with a frequency of 256 Hz. The oncoming car is going 20.0 m/s toward you, and you are going 60.0 m/s toward them. What frequency do you hear? • Moving source, then moving observer • higher frequency, higher frequency • f’ = f{ v } • {v + us } • f = 256 hz, us = 20.0 m/s, v = 343 m/s, and - • f’ = f{v ± uo} • { v } • f = f’ from before, uo = 60.0 m/s, v = 343 m/s, and + W 319.4 Hz

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