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Adv Physics

Adv Physics. Chapter 14 Sections 1,2,5. Longitudinal Wave. Motion of material is parallel to direction disturbance/energy travels Compression – region in a longitudinal wave where the density and pressure is greater than normal

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Adv Physics

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  1. Adv Physics Chapter 14 Sections 1,2,5

  2. Longitudinal Wave • Motion of material is parallel to direction disturbance/energy travels • Compression – region in a longitudinal wave where the density and pressure is greater than normal • Rarefaction – region in a longitudinal wave where the density and pressure is less than normal

  3. How is sound produced? • Sound is produced by a vibrating object • The frequency of the source is the same as the frequency of the sound produced • Once a sound wave is created its frequency can NEVER change

  4. Sound Waves • Audible – sound waves with frequencies in the range of human hearing (20 – 20000 Hz) • Infrasonic – sound waves with frequencies below the range of human hearing • Ultrasonic – sound waves with frequencies above the range of human hearing • By age 70 most people can’t hear above 8000 Hz

  5. Pitch • perceived highness or lowness of a sound - determined by frequency http://edu.larc.nasa.gov/connect/machine.swf - higher the frequency the higher the pitch - subjective

  6. Loudness • Volume - determined by energy wave carries http://edu.larc.nasa.gov/connect/machine.swf - larger the amplitude, the louder it sounds

  7. Speed of Sound • Depends on medium and temperature • Medium – in solids particles are closer together so easier and quicker to pass on disturbance • Temperature – as material warms up the particles collide more frequently so disturbance is passed on more quickly

  8. Speed of Sound v in air at 0 degrees C is 331 m/s (740 mi/h) v increases by 0.6 m/s for every 1 degree Celsius increase in temperature • In a solid the change in speed is less dramatic with temperature because the particles are already very close

  9. Doppler Effect • Change in pitch or frequency detected by an observer due to the motion of the source and/or the receiver • http://www.ecocardiografia.info/Doppler_effect.swf

  10. Doppler Effect

  11. Source Toward Stationary Observer • Observer will receive a higher frequency and higher pitch if car is approaching • Observer will receive a lower frequency and lower pitch if car is leaving

  12. Doppler Effect • How does the speed of the source effect your results? • http://www.upscale.utoronto.ca/GeneralInterest/Harrison/Flash/ClassMechanics/DopplerWaveFronts/DopplerWaveFronts.swf • The faster the source moves, the greater the change in frequency

  13. Source Toward Stationary Observer f’ = f / (1 – vs/v) where f’ - perceived frequency f - actual frequency vs - speed of source v - speed of sound Note – faster source moves the greater the change in frequency

  14. Source Moving Away From Stationary Observer f’ = f / (1 + vs/v) where f’ - perceived frequency f - actual frequency vs - speed of source v - speed of sound

  15. Sample Problem A high speed train is traveling at 44.7 m/s when the engineer sounds the 415 Hz warning horn. The speed of sound is 343 m/s. What are the frequency and wavelength of the sound as perceived by a person at the crossing who the train is approaching? Leaving?

  16. Observer Toward Stationary Source f’ = f (1 + vo/v) where f’ - perceived frequency f - actual frequency vo - speed of observer v - speed of sound

  17. Observer Away From Stationary Source f’ = f (1 - vo/v) where f’ - perceived frequency f - actual frequency vo - speed of observer v - speed of sound

  18. Both Moving - If moving toward each other f’ = f [ (1 + vo/v) / (1 – vs/v) ] - If moving away from each other f’ = f [ (1 - vo/v) / (1 + vs/v) ]

  19. Doppler Effect with Light • Red shift – decrease in perceived frequency of light due to source and observer moving apart • Blue shift – increase in perceived frequency of light due to source and observer moving toward each other

  20. Sample Problem An ambulance travels down a highway at a speed of 33.5 m/s. Its siren emits a sound at a frequency of 400 Hz. What is the frequency heard by a passenger in a car traveling at a speed of 24.6 m/s in the opposite direction as the car approaches the ambulance and as the car moves away from the ambulance?

  21. Sample Problem Standing at a crosswalk, you hear a frequency of 560 Hz from the siren on an approaching police car. After the police car passes, the observed frequency of the siren is 480 Hz. Determine the car’s speed from these observations.

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