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Physics with Computers: Sound Waves and Spectrum

Explore sound waves, spectrum, intensity, beats, and the Doppler effect in physics using Vernier microphones and logger pro. Learn about musical instruments and sound characteristics.

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Physics with Computers: Sound Waves and Spectrum

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  1. demos • Vernier microphone, logger pro, physics with computers, voice program • measure voice, chilandi plates, tuning forks, anyone with perfect pitch, meter stick? • Open/closed tubes • Take data on chilandi plates, compare to sand patterns with wave driver applied.

  2. Thanksgiving Week • Ch.12 Problem 33a-c, 35 • No labs this week • Wed. assignment handout today will go over in class on Monday • Test 2 is in testing center until Wed. Nov. 25 at 5pm

  3. 12 Sound • Homework • Problem 33a-c, 35 • Sound waves and spectrum • Sound speed and material parameters • Sound Intensity Level • Beats and Doppler Effect • (omit sections 4, 5, 6, 9)

  4. Sound Waves • pressure/density waves • compressions • rarefactions • reflects • refracts (similar to light) • diffracts (bends around corners)

  5. Speed of Sound Sound speed increases when stiffness increases. Sound speed decreases when density increases. Exs: Aluminum 5100 m/s, Water 1500 m/s, Air 343 m/s

  6. Sound Spectrum • ultrasonic (f > 20kHz) • (human) audible (20Hz < f < 20kHz) • infrasonic (f < 20Hz) • dogs, cats (50Hz < f < 45kHz) • bats up to 120kHz • elephants as low as 5Hz

  7. Sound Intensity Level

  8. Example: Intensity • point source of sound, 0.010 watts • I at 10 meters: = power/area = 0.010watts/(4p102m2) = 7.96x10-6 watt/m2. • b = 10log(7.96x10-6/10-12) = 69dB

  9. Beats Excel file example of beat frequencies Beat frequencies are heard up to about 15 Hz

  10. Doppler Effect Motion of a sound source causes higher frequency of waves on front side (and lower frequency on back side) applet Motion of an observer toward a sound source causes observer to hear a higher frequency (motion away causes lower frequency)

  11. Using Doppler Equation If observer is moving toward source +vo If observer is moving away from source –vo If source is moving toward observer –vs If source is moving away from observer +vs

  12. Summary • Sound waves and spectrum • Sound speed and material parameters • Sound Intensity Level • Beats • Doppler Effect

  13. values of “A” and “f”?

  14. 14.6 Musical Instruments and Sound Characteristics Standing waves can also exist in tubes or pipes, such as woodwind and brass instruments. Organ pipes are fixed in length; there is one (or more) for each key on the keyboard.

  15. 14.6 Musical Instruments and Sound Characteristics The pitch of woodwind instruments can be varied by covering and uncovering holes in the tube.

  16. Sound Phenomena If two sounds are very close in frequency, we perceive them as “beats”—variations in sound intensity. The beat frequency is the difference of the two frequencies:

  17. 14.6 Musical Instruments and Sound Characteristics In general, the way we perceive sound is related to its physical properties, but depends on other factors as well.

  18. 14.6 Musical Instruments and Sound Characteristics The sum of the fundamental frequency and the overtones gives the final waveform.

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