Demos Vernier microphone, logger pro, physics with computers, voice program measure voice, chilandi...
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Transcript of Demos Vernier microphone, logger pro, physics with computers, voice program measure voice, chilandi...
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 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
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)
Sound Waves
• pressure/density waves
• compressions
• rarefactions
• reflects
• refracts (similar to light)
• diffracts (bends around corners)
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
density
stiffnessv
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
Sound Intensity Level
2 :amplitude of square to
alproportion isIntensity
AI
hearing of threshold theis W/m10 where
logdB10 Level Sound
212-0
0
I
I
I
Example: Intensity
• point source of sound, 0.010 watts
• I at 10 meters: = power/area
= 0.010watts/(4102m2)= 7.96x10-6 watt/m2.
• = 10log(7.96x10-6/10-12) = 69dB
Beats
21 :sfrequencie sound
in two difference isfrequency Beat
fff
Excel file example of beat frequencies
Beat frequencies are heard up to about 15 Hz
21 fff
Doppler Effect
10
ss
oo f
vv
vvf
source offrequency
source of speed
observer of speed
waveof speed
observedfrequency
s
s
o
o
f
v
v
v
f
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)
Using Doppler Equation
11
Hzfvv
vvf s
s
oo 436400
10343
20343
m/s. 343 vSound observer. toward10m/sat moving is
h siren whic 400Hz toward20m/sat drivesObserver
If observer is moving toward source +voIf observer is moving away from source –vo
If source is moving toward observer –vsIf source is moving away from observer +vs
Hzfvv
vvf s
s
oo 411400
10343
20343
observer. fromaway 10m/sat moving is
h siren whic 400Hz toward20m/sat drivesObserver
Summary
• Sound waves and spectrum
• Sound speed and material parameters
• Sound Intensity Level
• Beats
• Doppler Effect
13
Height vs. Time
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25
Time (s)
Y (
m)
values of “A” and “f”?
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 PhenomenaIf 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.