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# Sound part 2

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• Have formulas in book that calculate this exactly, will not cover in class, but will use for a conceptual problem.
• v (light) = 300000000 m/s v (sound) = 343 m/s (light is just about instantaneous) one mile = 1.6 x 10 3 m v = del(x) / t t = del(x) / v = 1.6 x 103 m / 343 m/s = 5 sec so for every 5 sec, the lightning is 1 mile away.
• Fig 16.32
• Fig 16.32 observed wavelength changes
• ### Sound part 2

1. 1. Sound Part 2Sound Part 22/21/20132/21/2013
2. 2. What is sound?What is sound? Any change in air pressureAny change in air pressure The molecules in the air exerts a pressure ofThe molecules in the air exerts a pressure ofover 1 ton per square foot on our earsover 1 ton per square foot on our ears Must be a rapid change in sound pressure toMust be a rapid change in sound pressure tobe heard, a small rapid change will createbe heard, a small rapid change will createnoisenoise Travels as sound wavesTravels as sound waves
3. 3. Tone and NoiseTone and Noise Tuning fork – pure tone andTuning fork – pure tone andrelated frequenciesrelated frequencies We cannot see the tinesWe cannot see the tinesmoving back and forthmoving back and forthbecause they are moving backbecause they are moving backand for the too quickly. Two-and for the too quickly. Two-hundred cycles a second is toohundred cycles a second is toofast to see.fast to see. Noise – random frequenciesNoise – random frequencies
4. 4. Noise travels through a mediumNoise travels through a medium A vibrating object creates a disturbanceA vibrating object creates a disturbancethat travels through a mediumthat travels through a medium A train’s noise can travel through the steelA train’s noise can travel through the steeltracks by creating sound wavestracks by creating sound waves The vibrations of a speaker creates soundThe vibrations of a speaker creates soundwaveswaves Frequency is the number of complete backFrequency is the number of complete backand forth vibrations per secondand forth vibrations per second
5. 5. Noise travelNoise travel Vibrational motion of the medium is set upVibrational motion of the medium is set upby the object.by the object. The vibrations set the molecule of the mediumThe vibrations set the molecule of the mediuminto motion.into motion. The motion of the molecule in the mediumThe motion of the molecule in the mediumsets the molecule next to it, in motion.sets the molecule next to it, in motion. The transfer of energy continues as theThe transfer of energy continues as thevibration of one molecule sets the nextvibration of one molecule sets the nextmolecule into motion.molecule into motion.
6. 6. Sound wave is a pressure waveSound wave is a pressure wave Thus an instrument can be used toThus an instrument can be used tomeasure the oscillations of high and lowmeasure the oscillations of high and lowpressure variations in the pressure.pressure variations in the pressure. These oscillations are shown as theThese oscillations are shown as thetypical sine wave that you may have seentypical sine wave that you may have seen
7. 7. WavelengthWavelength Distance which a disturbance travelsDistance which a disturbance travelsalong the medium in one complete wavealong the medium in one complete wavecycle.cycle. Measured from one wave trough or crest toMeasured from one wave trough or crest tothe next wave trough or crest, in a transversethe next wave trough or crest, in a transversewave. It is from one wave compression to thewave. It is from one wave compression to thenext wave compression in a longitudinal wavenext wave compression in a longitudinal wave With a pressure wave it is from one highWith a pressure wave it is from one highpressure region to the next high pressurepressure region to the next high pressureregionregion
8. 8. Standing sine wave patterns of air vibrating in aStanding sine wave patterns of air vibrating in aclosed tube. Note the node at the closed end and theclosed tube. Note the node at the closed end and theantinode at the open end. Only odd multiples of theantinode at the open end. Only odd multiples of thefundamental are therefore possible.fundamental are therefore possible.
9. 9. Speed of SoundSpeed of Sound Sound waves are pressure disturbancesSound waves are pressure disturbancestraveling through a medium by means oftraveling through a medium by means ofparticle interactionparticle interaction How fast the disturbance is passed fromHow fast the disturbance is passed fromparticle to particle determines the speed ofparticle to particle determines the speed ofsound.sound. How easily the medium transfers theHow easily the medium transfers thedisturbance determines the speed, which isdisturbance determines the speed, which ismeasured in meters per second (m/s)measured in meters per second (m/s)
10. 10. The Speed of SoundThe Speed of SoundThe speed of sound depends onthe materialthat the sound is traveling in.For air, the speed of sound is 343 m/s (767 mph).Usually, the speed of sound in a liquid is greaterthan the speed of sound in a gas.Usually, the speed of sound in a solid is greaterthan the speed of sound in a liquid.
11. 11. IntensityIntensity Inverse square relationshipInverse square relationship The mathematical relationship of intensity andThe mathematical relationship of intensity andthe distance from the sourcethe distance from the source As you move away from the source (largerAs you move away from the source (largerdistance) the area gets larger and thedistance) the area gets larger and theintensity will decrease.intensity will decrease. If the distance from a source doubles the intensityIf the distance from a source doubles the intensitywill decrease by a factor of 4.will decrease by a factor of 4.
12. 12. LoudnessLoudness Loudness of a noise is a more subjectiveLoudness of a noise is a more subjectiveresponse. Factors that affect theresponse. Factors that affect theperception of loudness includes age andperception of loudness includes age andfrequencyfrequency
13. 13. LoudnessLoudnessloudness: a subjective evaluation of a sound. Most closelyrelated to the pressure amplitude of a sound.pressure amplitude: the change in pressure from acondensation to a rarefaction.A typical pressure amplitude for human speech is 0.03 Pa.Typical air pressure is 101,000 Pa. The eardrum is a verysensitive instrument.A sound with a big pressure amplitude is interpreted as aloud sound.
14. 14. Sound RangesSound RangesA typical young human hears sounds in the rangefrom20 Hz to 20,000 Hz (20 kHz)infrasonic: sounds below the range of humanhearing(with frequencies less than 20 Hz)ultrasonic: sounds above the range of humanhearing(with frequencies more than 20 kHz)
15. 15. Speech frequenciesSpeech frequencies Speech frequencies: generally regardedSpeech frequencies: generally regardedto be 500 to 3000 hertzto be 500 to 3000 hertz Frequency range of perceivable sound:Frequency range of perceivable sound:20 Hz to 15,000 to 20,000 Hertz.20 Hz to 15,000 to 20,000 Hertz. Tuning forksTuning forks
16. 16. FrequencyFrequency && PitchPitchJust as the amplitude of a sound wave relates to itsloudness, the frequency of the wave relates to its pitch.The higher the pitch, the higher the frequency. Thefrequency you hear is just the number of wavefronts thathit your eardrums in a unit of time. Wavelength doesn’tnecessarily correspond to pitch because, even if wavefrontsare very close together, if the wave is slow moving, notmany wavefronts will hit you each second.Frequency ↔ PitchAmplitude ↔ Loudness
17. 17. PitchPitchpitch: a subjective evaluation of a sound. Mostclosely related to the frequency of the sound.A sound with a high frequency will sound like a highpitch.
18. 18. Changing PitchChanging Pitch Lungs: Air From theLungs: Air From thelungs rushes up thelungs rushes up thetracheatrachea Vocal Cords: which areVocal Cords: which arelocated in your voicelocated in your voicebox, orbox, or larynxlarynx vibratevibrateas air rushes pass themas air rushes pass them Sound: Sound wavesSound: Sound wavesproduced by theproduced by thevibrating vocal cordsvibrating vocal cordscome out through thecome out through themouthmouth
19. 19. Changing PitchChanging Pitch Pitch is an important property of musicPitch is an important property of music To change pitch, you use the muscles inTo change pitch, you use the muscles inyour throat to stretch and relax your vocalyour throat to stretch and relax your vocalcordscords When your vocal cords stretch they vibrateWhen your vocal cords stretch they vibratemore quickly, which creates higher-frequencymore quickly, which creates higher-frequencysound waves with a higher pitchsound waves with a higher pitch When you vocal cords relax they vibrateWhen you vocal cords relax they vibrateslower, which creates lower-frequency soundslower, which creates lower-frequency soundwaves with a lower pitchwaves with a lower pitch Musical instruments can also change pitch!Musical instruments can also change pitch!
20. 20. Thunder and LightningThunder and LightningIf you see a flash of lightning,and count the number of seconds until you hear the thunder,you can figure out how far away the lightning is.How?
21. 21. The Human EarThe Human EarThe exterior part of the ear (the auricle, or pinna) is made of cartilageand helps funnel sound waves into the auditory canal, which has waxfibers to protect the ear from dirt. At the end of the auditory canal liesthe eardrum (tympanic membrane), which vibrates with the incomingsound waves and transmits these vibrations along three tiny bones(ossicles) called the hammer, anvil, and stirrup (malleus, incus, andstapes). The little stapes bone is attached to the oval window, amembrane of the cochlea.The cochlea is a coil that converts the vibrations it receives intoelectrical impulses and sends them to the brain via the auditory nerve.Delicate hairs (stereocilia) in the cochlea are responsible for this signalconversion. These hairs are easily damaged by loud noises, a majorcause of hearing loss!The semicircular canals help maintain balance, but do not aid hearing.
22. 22. The Human EarThe Human Ear
23. 23. Range of Human HearingRange of Human HearingThe maximum range of frequencies for most people is from about20 to 20 thousand hertz. This means if the number of high pressurefronts (wavefronts) hitting our eardrums each second is from 20 to20 000, then the sound may be detectable. If you listen to loudmusic often, you’ll probably find that your range (bandwidth) willbe diminished.Some animals, like dogs and some fish, can hear frequencies that arehigher than what humans can hear (ultrasound). Bats and dolphinsuse ultrasound to locate prey (echolocation). Doctors make use ofultrasound for imaging fetuses and breaking up kidney stones.Elephants and some whales can communicate over vast distanceswith sound waves too low in pitch for us to hear (infrasound).
24. 24. EchoesEchoes && ReverberationReverberationAn echo is simply a reflected sound wave. Echoes are morenoticeable if you are out in the open except for a distant, largeobject. If went out to the dessert and yelled, you might hear adistant canyon yell back at you. The time between your yelland hearing your echo depends on the speed of sound and onthe distance to the to the canyon. In fact, if you know thespeed of sound, you can easily calculate the distance just bytiming the delay of your echo.Reverberation is the repeated reflection of sound at closequarters. If you were to yell while inside a narrow tunnel, yourreflected sound waves would bounce back to your ears soquickly that your brain wouldn’t be able to distinguish betweenthe original yell and its reflection. It would sound like a singleyell of slightly longer duration.
25. 25. SonarSonarSOund NAvigation and RangingIn addition to locating prey, bats and dolphins use sound wavesfor navigational purposes. Submarines do this too. Theprinciple is to send out sound waves and listen for echoes. Thelonger it takes an echo to return, the farther away the object thatreflected those waves. Sonar is used in commercial fishing boatsto find schools of fish. Scientists use it to map the ocean floor.Special glasses that make use of sonar can help blind people byproducing sounds of different pitches depending on how close anobstacle is.If radio (low frequency light) waves are used instead of soundin an instrument, we call it radar (radio detection and ranging).
26. 26. Sonic BoomsSonic BoomsWhen a source of sound is moving at thespeed of sound, the wavefronts pile up ontop of each other. This makes theircombined amplitude very large, resulting ina shock wave and a sonic boom. Atsupersonic speeds a “Mach cone” is formed.The faster the source compared to sound, thesmaller the shock wave angle will be.
27. 27. Resonancethe frequency of sound wavesexactly matches the natural frequencyof an object.
28. 28. The Doppler EffectThe Doppler EffectThe Doppler Effect is the change in frequency (pitch) of thesound detected by an observer because the sound sourceand the observer have different velocities with respect to themedium of sound propagation.The Doppler Effect describes why the pitch of a siren that isapproaching you sounds higher than the pitch of a siren thatis moving away from you.
29. 29. The Doppler EffectThe Doppler EffectMoving SOURCEApproaching observerIf the source of the sound (the fire truck, for example) ismoving towards an observer, the sound waves “bunch up” infront of the source, causing the wavelength observed by astationary person to shorten.(Smaller wavelengths, bigger frequency.)Receding from observerBehind the source, the sound waves “stretch out”, and thewavelength observed by a stationary person lengthens.(Bigger wavelength, smaller frequency.)
30. 30. Doppler EffectDoppler EffectA tone is not always heard at the same frequency at which it isemitted. When a train sounds its horn as it passes by, the pitch ofthe horn changes from high to low. Any time there is relativemotion between the source of a sound and the receiver of it, there isa difference between the actual frequency and the observedfrequency. This is called the Doppler effect. Click to hear effect:The Doppler effect applied to electomagnetic waves helpsmeteorologists to predict weather, allows astronomers to estimatedistances to remote galaxies, and aids police officers catch youspeeding.The Doppler effect applied to ultrasound is used by doctors tomeasure the speed of blood in blood vessels, just like a cop’s radargun. The faster the blood cell are moving toward the doc, the greaterthe reflected frequency.