demos Vernier microphone logger pro physics with computers

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.

Thanksgiving Week • Ch. 12 Problem 33 a-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 5 pm

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

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

Speed of 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

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

Sound Intensity Level

Example: Intensity • point source of sound, 0. 010 watts • I at 10 meters: = power/area = 0. 010 watts/(4 p 102 m 2) = 7. 96 x 10 -6 watt/m 2. • b = 10 log(7. 96 x 10 -6/10 -12) = 69 d. B

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

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) 10

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 11

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

values of “A” and “f”? 13

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.

14. 6 Musical Instruments and Sound Characteristics The pitch of woodwind instruments can be varied by covering and uncovering holes in the tube.

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:

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.

14. 6 Musical Instruments and Sound Characteristics The sum of the fundamental frequency and the overtones gives the final waveform.