Sound Waves Ch. 12 1-Sonic Spectrum Sonic Spectrum: the frequency range for longitudinal waves propagating through an elastic medium. No low limit, upper.

Sound Waves Ch. 12

1-Sonic Spectrum Sonic Spectrum: the frequency range for longitudinal waves propagating through an elastic medium. No low limit, upper limit is for waves with wavelength comparable to the inter-particle spacing of the medium. Sound waves are sonic waves with the frequency range 20Hz-20,000Hz.

2- Sources of Sound Sound is produced by an initial vibration that initiates a series of compressions and rarefactions in the nearby medium. The wave energy is passed along to adjacent particles as the sound travels through the medium. Sound waves are produced by vibrating elements such as : reeds (clarinet, saxophone), strings ( guitar, piano, vocal chords), membranes (drums, loudspeakers) and air columns (organ,flute).

4 The middle of a compression (rarefaction) corresponds to a pressure maximum (minimum).

3-Sound Transmission Sound is transmitted as a longitudinal wave through a medium only. Sound travels faster in solids than in liquids and in liquids than in gases. Ex. Speed of sound in air =346 m/s, in water = 1500 m/s, in steel 5200 m/s. Speed of sound is directly proportional to the elasticity and inversely proportional to the density of the medium. Speed of sound increases with temperature.

6 where T c is the air temperature in  C. For air, the speed of the sound can be found with the expression:

7 Example: Bats emit ultrasonic sound waves with a frequency as high as 1.0  10 5 Hz. What is the wavelength of such a wave in air of temperature 15.0  C? The speed of sound in air of this temperature is 340 m/s.

8 Example: A lightning flash is seen in the sky and 8.2 seconds later the boom of thunder is heard. The temperature of the air is 12.0  C. (a) What is the speed of sound in air at that temperature? The speed of sound in air of this temperature is about 338 m/s. (b) How far away is the lightning strike?

ConcepTest 14.1a Sound Bite I 1) the frequency f 2) the wavelength 3) the speed of the wave 4) both f and 5) both v wave and When a sound wave passes from air into water, what properties of the wave will change?

ConcepTest 14.1a Sound Bite I 1) the frequency f 2) the wavelength 3) the speed of the wave 4) both f and 5) both v wave and When a sound wave passes from air into water, what properties of the wave will change? Wave speed must change (different medium). Frequency does not change (determined by the source). v = f vf Now, v = f and since v has changed and f is constant must also change then must also change. Follow-up: Does the wave speed increase or decrease in water?

We just determined that the wavelength of the sound wave will change when it passes from air into water. How will the wavelength change? 1) wavelength will increase 2) wavelength will not change 3) wavelength will decrease ConcepTest 14.1b Sound Bite II

We just determined that the wavelength of the sound wave will change when it passes from air into water. How will the wavelength change? 1) wavelength will increase 2) wavelength will not change 3) wavelength will decrease The speed of sound is greater in water, because the force holding the molecules together is greater. This is generally true for liquids, as compared to gases. If the speed is greater and the frequency has not changed (determined by the source), then the wavelength must also have increased (v = f ). ConcepTest 14.1b Sound Bite II

1) water 2) ice 3) same speed in both 4) sound can only travel in a gas Do sound waves travel faster in water or in ice? ConcepTest 14.2a Speed of Sound I

1) water 2) ice 3) same speed in both 4) sound can only travel in a gas Do sound waves travel faster in water or in ice? ConcepTest 14.2a Speed of Sound I inertia restoring force However, the force holding the molecules together is greater in ice (because it is a solid), so the restoring force is greater. v =  (force / inertia), greater in ice Speed of sound depends on the inertia of the medium and the restoring force. Since ice and water both consist of water molecules, the inertia is the same for both. However, the force holding the molecules together is greater in ice (because it is a solid), so the restoring force is greater. Since v =  (force / inertia), the speed of sound must be greater in ice !

Do you expect an echo to return to you more quickly or less quickly on a hot day, as compared to a cold day? 1) more quickly on a hot day 2) equal times on both days 3) more quickly on a cold day ConcepTest 14.2b Speed of Sound II

Do you expect an echo to return to you more quickly or less quickly on a hot day, as compared to a cold day? 1) more quickly on a hot day 2) equal times on both days 3) more quickly on a cold day The speed of sound in a gas increases with temperature. This is because the molecules are bumping into each other faster and more often, so it is easier to propagate the compression wave (sound wave). ConcepTest 14.2b Speed of Sound II

If you fill your lungs with helium and then try talking, you sound like Donald Duck. What conclusion can you reach about the speed of sound in helium? 1) speed of sound is less in helium 2) speed of sound is the same in helium 3) speed of sound is greater in helium 4) this effect has nothing to do with the speed in helium ConcepTest 14.2c Speed of Sound III

If you fill your lungs with helium and then try talking, you sound like Donald Duck. What conclusion can you reach about the speed of sound in helium? 1) speed of sound is less in helium 2) speed of sound is the same in helium 3) speed of sound is greater in helium 4) this effect has nothing to do with the speed in helium The higher pitch implies a higher frequency. In turn, since v = f, this means that the speed of the wave has increased (as long as the wavelength, determined by the length of the vocal cords, remains constant). ConcepTest 14.2c Speed of Sound III Follow-up: Why is the speed of sound greater in helium than in air?

You drop a rock into a well, and you hear the splash 1.5 s later. If the depth of the well were doubled, how long after you drop the rock would you hear the splash in this case? 1) more than 3 s later 2) 3 s later 3) between 1.5 s and 3 s later 4) 1.5 s later 5) less than 1.5 s later ConcepTest 14.3 Wishing Well

You drop a rock into a well, and you hear the splash 1.5 s later. If the depth of the well were doubled, how long after you drop the rock would you hear the splash in this case? 1) more than 3 s later 2) 3 s later 3) between 1.5 s and 3 s later 4) 1.5 s later 5) less than 1.5 s later Since the speed of sound is so much faster than the speed of the falling rock, we can essentially ignore the travel time of the sound. As for the falling rock, it is accelerating as it falls, so it covers the bottom half of the deeper well much quicker than the top half. The total time will not be exactly 3 s, but somewhat less. ConcepTest 14.3 Wishing Well Follow-up: How long does the sound take to travel the depth of the well?

Intensity I Intensity: time rate at which the sound energy flows through an unit of area normal to the direction of propagation. Energy Energy Intensity = -------------- ; Power = -------- Time x Area Time Intensity of sound is inversely proportional to the square of the distance to the source. Area A Energy E Intensity Unit: Watt/m 2

Intensity “I” Formula Intensity of a Spherical Wave (like produced by a point source) @ the distance r form the source: r

Example Sound What is the intensity of a sound wave produced by a trumpet at the distance of 3.2 m, if the power output of the trumpet is 0.2 W?

Loudness Loudness: the level of the auditory sensation produced by a sound, as perceived by the human ear. The ear is not equally sensitive to all frequencies (Ex. Midrange louder than bass or treble at same intensity). Relative Intensity: =10 log --- (decibels) 1 decibel = 0.1 bel I I I = 10 W/m -threshold of hearing -12 2

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position? 1) drops to 1/2 its original value 2) drops to 1/4 its original value 3) drops to 1/8 its original value 4) drops to 1/16 its original value 5) does not change at all ConcepTest 14.4a Sound Intensity I

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position? 1) drops to 1/2 its original value 2) drops to 1/4 its original value 3) drops to 1/8 its original value 4) drops to 1/16 its original value 5) does not change at all distance doubles decrease to one-quarter For a source of a given power P, the intensity is given by I = P/4  r 2. So if the distance doubles, the intensity must decrease to one-quarter its original value. ConcepTest 14.4a Sound Intensity I Follow-up: What distance would reduce the intensity by a factor of 100?

1) about the same distance 2) about 3 miles 3) about 10 miles 4) about 30 miles 5) about 100 miles You hear a fire truck with a certain intensity, and you are about 1 mile away. Another person hears the same fire truck with an intensity that is about 10 times less. Roughly, how far is the other person from the fire truck? ConcepTest 14.4b Sound Intensity II

1) about the same distance 2) about 3 miles 3) about 10 miles 4) about 30 miles 5) about 100 miles You hear a fire truck with a certain intensity, and you are about 1 mile away. Another person hears the same fire truck with an intensity that is about 10 times less. Roughly, how far is the other person from the fire truck? ConcepTest 14.4b Sound Intensity II inverse square of the distance Remember that intensity drops with the inverse square of the distance, so if intensity drops by a factor of 10, the other person must be  10 farther away, which is about a factor of 3.

When Mary talks, she creates an intensity level of 60 dB at your location. Alice talks with the same volume, also giving 60 dB at your location. If both Mary and Alice talk simultaneously from the same spot, what would be the new intensity level that you hear? 1) more than 120 dB 2) 120 dB 3) between 60 dB and 120 dB 4) 60 dB 5) less than 60 dB ConcepTest 14.5a Decibel Level I

When Mary talks, she creates an intensity level of 60 dB at your location. Alice talks with the same volume, also giving 60 dB at your location. If both Mary and Alice talk simultaneously from the same spot, what would be the new intensity level that you hear? 1) more than 120 dB 2) 120 dB 3) between 60 dB and 120 dB 4) 60 dB 5) less than 60 dB Recall that a difference of 10 dB in intensity level  corresponds to a factor of 10 1 in intensity. Similarly, a difference of 60 dB in  corresponds to a factor of 10 6 in intensity!! In this case, with two voices adding up, the intensity increases by only a factor of 2, meaning that the intensity level is higher by an amount equal to:  = 10 log(2) = 3 dB. The new intensity level is  = 63 dB. ConcepTest 14.5a Decibel Level I

1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 14.5b Decibel Level II

increase by 10 dB  increase intensity by factor of 10 1 (10) increase by 20 dB  increase intensity by factor of 10 2 (100) increase by 30 dB  increase intensity by factor of 10 3 (1000) 1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 14.5b Decibel Level II Follow-up: What decibel level gives an intensity a million times greater?

Intensity level is given by  = 10 log( I / I 0 ) with I 0 = 10 -12 W/m 2. The usual threshold of human hearing is defined as intensity level of  = 0 dB. What does this actually mean in terms of sound intensity? 1) intensity is undefined at that level 2) intensity is 10 0 W/m 2 3) intensity is 0.0 W/m 2 4) intensity is 10 -12 W/m 2 5) intensity is 1.0 W/m 2 ConcepTest 14.5c Decibel Level III

Intensity level is given by  = 10 log( I / I 0 ) with I 0 = 10 -12 W/m 2. The usual threshold of human hearing is defined as intensity level of  = 0 dB. What does this actually mean in terms of sound intensity? 1) intensity is undefined at that level 2) intensity is 10 0 W/m 2 3) intensity is 0.0 W/m 2 4) intensity is 10 -12 W/m 2 5) intensity is 1.0 W/m 2 In order for  to be equal to zero, the term log( I / I 0 ) must also be zero. This occurs when the argument is 1.0, because log(1.0) = 0. In other words, the value of I must be equal to I 0. ConcepTest 14.5c Decibel Level III

Frequency and Pitch High-pitched sound are of high frequency and low-pitched sounds are of low frequency. Musical terminology: octave: two sounds with “f” in ratio 2:1 Fifth: 3:2 Major third: 5:4 Minor third: 6:5 Major chords (Ex. C-E-G) :“f “ratio 4:5:6

Pitch Pitch is related mainly, although not completely, to the frequency of the sound Pitch is not a physical property of the sound Frequency is the stimulus and pitch is the response –It is a psychological reaction that allows humans to place the sound on a scale

Beats Beats are alternations in loudness, due to interference Waves have slightly different frequencies and the time between constructive and destructive interference alternates The beat frequency equals the difference in frequency between the two sources: Beats: produced by the interference of two waves with slightly different frequencies. Amplitude of resultant wave varies with time. # of beats = difference b/w the frequencies of the component waves.

Pair 1Pair 2 1) pair 1 2) pair 2 3) same for both pairs 4) impossible to tell by just looking The traces below show beats that occur when two different pairs of waves interfere. For which case is the difference in frequency of the original waves greater? ConcepTest 14.10 Beats

Pair 1Pair 2 difference in frequency f beat = f 2 – f 1 Recall that the beat frequency is the difference in frequency between the two waves: f beat = f 2 – f 1 greater beat frequency greater frequency difference Pair 1 has the greater beat frequency (more oscillations in same time period), so Pair 1 has the greater frequency difference. 1) pair 1 2) pair 2 3) same for both pairs 4) impossible to tell by just looking The traces below show beats that occur when two different pairs of waves interfere. For which case is the difference in frequency of the original waves greater? ConcepTest 14.10 Beats

Doppler Effect Sound of a train moving towards us is higher pitched Sound of a train moving away from us is lower pitched Christian Doppler (1803-53)

Doppler Formula-Moving Source f L = f s /(1 - u/v) towards listener L f L = f s /(1 + u/v) away from listener L f L – pitch perceived by listener f S – frequency of sound emitted by source v – speed of sound u- speed of source.

Example Doppler A train is traveling at 44.7 m/s when the engineer is sounding the 415 Hz warning horn. The speed of the sound is 343 m/s. What is the pitch and wavelength of the sound as perceived by a person standing at a crossing if the train is a) approaching, b) leaving the crossing. a) b)

Doppler effect for passing aircraft Aircraft moving at less than speed of soundAircraft moving at the speed of sound

What if aircraft is moving faster than the speed of sound? You would hear a sonic boom

Objects moving towards us appears blue- shifted Objects moving away from us appears red- shifted Doppler Effect for Light

Observers A, B and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points ConcepTest 14.11a Doppler Effect I

Observers A, B and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points observer C The number of wave fronts hitting observer C per unit time is greatest – thus the observed frequency is highest there. ConcepTest 14.11a Doppler Effect I Follow-up: Where is the frequency lowest?

You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear ? 1) lower than f 0 2) equal to f 0 3) higher than f 0 ConcepTest 14.11b Doppler Effect II

You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear ? 1) lower than f 0 2) equal to f 0 3) higher than f 0 approach of the source frequency is shifted higher Due to the approach of the source toward the stationary observer, the frequency is shifted higher. This is the same situation as depicted in the previous question. ConcepTest 14.11b Doppler Effect II

In the previous question, the horn had a rest frequency of f 0, and we found that your friend heard a higher frequency f 1 due to the Doppler shift. The sound from the boat hits the cliff behind your friend and returns to you as an echo. What is the frequency of the echo that you hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 but lower than f 1 4) equal to f 1 5) higher than f 1 ConcepTest 14.11c Doppler Effect III

In the previous question, the horn had a rest frequency of f 0, and we found that your friend heard a higher frequency f 1 due to the Doppler shift. The sound from the boat hits the cliff behind your friend and returns to you as an echo. What is the frequency of the echo that you hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 but lower than f 1 4) equal to f 1 5) higher than f 1 you are now a moving observer approaching the sound wave even higher frequency The sound wave bouncing off the cliff has the same frequency f 1 as the one hitting the cliff (what your friend hears). For the echo, you are now a moving observer approaching the sound wave of frequency f 1 so you will hear an even higher frequency. ConcepTest 14.11c Doppler Effect III

Quality of Sound – Tuning Fork Tuning fork produces only the fundamental frequency

Quality of Sound – Flute The same note played on a flute sounds differently The second harmonic is very strong The fourth harmonic is close in strength to the first

Quality of Sound – Clarinet The fifth harmonic is very strong The first and fourth harmonics are very similar, with the third being close to them

Timbre In music, the characteristic sound of any instrument is referred to as the quality of sound, or the timbre, of the sound The quality depends on the mixture of harmonics in the sound

Standing Waves When a traveling wave reflects back on itself, it creates traveling waves in both directions The wave and its reflection interfere according to the superposition principle With exactly the right frequency, the wave will appear to stand still –This is called a standing wave

Standing Waves, cont A node occurs where the two traveling waves have the same magnitude of displacement, but the displacements are in opposite directions –Net displacement is zero at that point –The distance between two nodes is ½λ An antinode occurs where the standing wave vibrates at maximum amplitude

Superposition of 2 traveling harmonic waves, as a function of time. The period and wavelength are exactly the same. One wave travels to the right, one to the left.

Standing waves: adding waves traveling in opposite directions. The picture above shows a “standing wave”. We will study how we can produce such waves by adding one wave to another. Piano strings, guitar strings, bass strings, all of these make sound using standing waves.

Standing Waves on a String Nodes must occur at the ends of the string because these points are fixed

Standing Wave Plucking the string in the middle, it will vibrate. Note: wavelength in the picture is twice the string length: =2L

Fundamental mode: 1 ST Harmonic

2 nd Harmonic L

3 d Harmonic L

Standing Waves on a String, final The lowest frequency of vibration (b) is called the fundamental frequency The n th harmonic has the frequency f n :

Standing Waves on a String – Frequencies ƒ 1, ƒ 2, ƒ 3 form a harmonic series –ƒ 1 is the fundamental and also the first harmonic –ƒ 2 is the second harmonic Waves in the string that are not in the harmonic series are quickly damped out –In effect, when the string is disturbed, it “selects” the standing wave frequencies

Harmonics-Quality (Timbre) Depends upon the # of harmonics and their relative intensity. Strings-Standing Waves Fundamental Frequency (1st Harmonic “f”) 2nd Harmonic 2f (1st overtone) 3rd Harmonic 3f (2nd overtone) Harmonics: whole # multiples of the fundamental frequency.

String Example A string length of 2.5 m is fixed at both ends. When the string vibrates at 85 Hz, a standing wave with five loops is formed. a) What is the wavelength of the standing wave? L = 5 x λ 5 /2, λ 5 = (2/5) L = (2/5) x 2.5 m = 1 m b) What is the speed of the wave? v = λ 5 f 5 = 1 m x 85 Hz = 85 m/s c) What is the fundamental frequency of this string? f 5 = 5f 1, f 1 = f 5 /5 = 85 Hz/5 = 17 Hz

The Laws of Strings 1. Law of length: the frequency of a string is inversely proportional to its length. The equation is: f/f’=l’/l 2. Law of diameters: f of a string is inversely proportional to its diameter. The equation is: f/f’=d’/d 3. Law of tensions: f is proportional to the sqrt of the tension in the string. The equation is: f/f’=sqrtF/sqrtF’ 4. Law of densities: f is inversely proportional to the sqrt of densities. The equation is: f/f’=sqrtD’/sqrtD

Forced Vibrations. Resonance Forced vibrations occur at a frequency that is different from the natural frequency of the system. A system with a driving force will force a vibration at its own frequency. When the frequency of the driving force equals the natural frequency of the system, the system is said to be in resonance Resonance: vibrations happen at the natural frequency of the system. Transfer of energy is optimal.

An Example of Resonance Pendulum A is set in motion The others begin to vibrate due to the vibrations in the flexible beam Pendulum C oscillates at the greatest amplitude since its length, and therefore frequency, matches that of A

Other Examples of Resonance Child being pushed on a swing Shattering glasses Tacoma Narrows Bridge collapse due to oscillations by the wind Upper deck of the Nimitz Freeway collapse due to the Loma Prieta earthquake

Standing Waves in Air Columns If one end of the air column is closed, a node must exist at this end since the movement of the air is restricted If the end is open, the elements of the air have complete freedom of movement and an antinode exists

Tube Open at Both Ends

Resonance in Air Column Open at Both Ends In a pipe open at both ends, the natural frequency of vibration forms a series whose harmonics are equal to integral multiples of the fundamental frequency

Standing waves in a tube A resonance can be used to set up standing sound waves in a tube –this is a longitudinal standing wave (compared to the transverse standing wave on a string) If both ends are open, the possible set of natural frequencies are (as with the string) :

Vibrating Air Columns in Pipes Open end A N A Fundamental f A N A N A1st overtone 2f A N A N A N A 2nd overtone 3f

An open-open tube of air supports standing waves at frequencies of 300 Hz and 400 Hz, and at no frequencies between these two. The second harmonic of this tube has frequency 1. 800 Hz. 2. 600 Hz. 3. 400 Hz. 4. 200 Hz. 5. 100 Hz.

Standing waves: one closed end

Tube Closed at One End

Resonance in an Air Column Closed at One End The closed end must be a node The open end is an antinode There are no even multiples of the fundamental harmonic

Standing waves in a tube If only one end is open, the following set of resonant frequencies are possible:

Closed End Closed end: A NFundamental f A N 1st overtone 3f (third harmonic) A N A N A N 2nd overtone 5f (fifth harmonic)

Example Closed end Tube Given: v = 340 m/s L = 67.5 cm = 0.675 m Find: f 1 Wavelength = 4 * Length Wavelength = 4 * 0.675 m Wavelength = 2.7 m frequency = v/(4L) frequency = (340 m/s)/(2.7 m) frequency = 126 Hz Find: λ What length of tube will have 126 Hz as the third harmonic?

Example : A tube, open at one end, is cut into two shorter, unequal length pieces. The piece that is open at one end has a fundamental frequency of 675hz, while the piece that is open at both ends has a fundamental frequency of 425hz. What was the fundamental frequency of the original tube?

There are some points on a standing wave that never move. What are these points called? 1. Harmonics 2. Normal Modes 3. Nodes 4. Anti-nodes 5. Interference

Two sound waves of nearly equal frequencies are played simultaneously. What is the name of the acoustic phenomena you hear if you listen to these two waves? 1. Beats 2. Diffraction 3. Harmonics 4. Chords 5. Interference

The various possible standing waves on a string are called the 1. antinodes. 2. resonant nodes. 3. normal modes. 4. incident waves.

The frequency of the third harmonic of a string is 1. one-third the frequency of the fundamental. 2. equal to the frequency of the fundamental. 3. three times the frequency of the fundamental. 4. nine times the frequency of the fundamental.

(1) the long pipe (2) the short pipe (3) both have the same frequency (4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 14.6a Pied Piper I

shorter pipe shorter wavelength frequency has to be higher A shorter pipe means that the standing wave in the pipe would have a shorter wavelength. Since the wave speed remains the same, the frequency has to be higher in the short pipe. (1) the long pipe (2) the short pipe (3) both have the same frequency (4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 14.6a Pied Piper I

A wood whistle has a variable length. You just heard the tone from the whistle at maximum length. If the air column is made shorter by moving the end stop, what happens to the frequency? 1) frequency will increase 2) frequency will not change 3) frequency will decrease ConcepTest 14.6b Pied Piper II

A wood whistle has a variable length. You just heard the tone from the whistle at maximum length. If the air column is made shorter by moving the end stop, what happens to the frequency? 1) frequency will increase 2) frequency will not change 3) frequency will decrease shorter pipe shorter wavelength v = f frequency has to increase A shorter pipe means that the standing wave in the pipe would have a shorter wavelength. Since the wave speed remains the same, and since we know that v = f, then we see that the frequency has to increase when the pipe is made shorter. ConcepTest 14.6b Pied Piper II

If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change? 1) frequency will increase 2) frequency will not change 3) frequency will decrease ConcepTest 14.6c Pied Piper III

If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change? 1) frequency will increase 2) frequency will not change 3) frequency will decrease longer pipe longer wavelength v = f frequency has to be lower By drinking some of the soda, you have effectively increased the length of the air column in the bottle. A longer pipe means that the standing wave in the bottle would have a longer wavelength. Since the wave speed remains the same, and since we know that v = f, then we see that the frequency has to be lower. ConcepTest 14.6c Pied Piper III Follow-up: Why doesn’t the wave speed change?

1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 14.7 Open and Closed Pipes

open pipe1/2 of a wave closed pipe 1/4 of a wave wavelength is larger in the closed pipefrequency will be lower In the open pipe, 1/2 of a wave “fits” into the pipe, while in the closed pipe, only 1/4 of a wave fits. Because the wavelength is larger in the closed pipe, the frequency will be lower. 1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 14.7 Open and Closed Pipes Follow-up: What would you have to do to the pipe to increase the frequency?

When you tune a guitar string, what physical characteristic of the string are you actually changing? 1) the tension in the string 2) the mass per unit length of the string 3) the composition of the string 4) the overall length of the string 5) the inertia of the string ConcepTest 14.8 Out of Tune

When you tune a guitar string, what physical characteristic of the string are you actually changing? 1) the tension in the string 2) the mass per unit length of the string 3) the composition of the string 4) the overall length of the string 5) the inertia of the string changing the tension By tightening (or loosening) the knobs on the neck of the guitar, you are changing the tension in the string. This alters the wave speed and therefore alters the frequency of the fundamental standing wave because f = v/2L. ConcepTest 14.8 Out of Tune Follow-up: To increase frequency, do you tighten or loosen the strings?

The Ear The outer ear consists of the ear canal that terminates at the eardrum Just behind the eardrum is the middle ear The bones in the middle ear transmit sounds to the inner ear

The Ear 1. Outer ear: eardrum (stretched membrane that vibrates) 2. Middle ear:hammer (picks up vibrations from the eardrum), anvil(transmits vibrations from the hammer to the stirrup), stirrup(sets another membrane vibrating). 3. Inner ear: cochlea( the nerve fibers convert movement of liquid into electrical impulses.

Frequency Response Curves Bottom curve is the threshold of hearing –Threshold of hearing is strongly dependent on frequency –Easiest frequency to hear is about 3300 Hz When the sound is loud (top curve, threshold of pain) all frequencies can be heard equally well

12 Interactions of Sound Waves Constructive Interference Destructive Interference Beats Acoustics

Diffraction diffraction is the bending of a wave as it moves past edges or obstacles For sound waves for example, it allows to hear “around the corner”, behind obstacles, etc.

Music Music: 1. Pleasant quality, 2.identifiable pitch, 3. Repeated timing called rhythm. Noise: no pleasing quality, no identifiable pitch, no definite relationship b/w the fundamental tone and the overtones.

Applications of Sound Sonar (Sound Navigation And Ranging). Ex. Ships, commercial fishing, submarines, bats, to find oil and minerals, cameras, cars etc. Ultrasonic Cleaning: vibrations knock the dirt off objects without harming them. Sound and Medicine: sonar technique used to diagnose medical problems.

Sound Waves Ch. 12 1-Sonic Spectrum Sonic Spectrum: the frequency range for longitudinal waves propagating through an elastic medium. No low limit, upper.

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Sound Waves Ch. 12 1-Sonic Spectrum Sonic Spectrum: the frequency range for longitudinal waves propagating through an elastic medium. No low limit, upper.

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Presentation on theme: "Sound Waves Ch. 12 1-Sonic Spectrum Sonic Spectrum: the frequency range for longitudinal waves propagating through an elastic medium. No low limit, upper."— Presentation transcript:

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