Powerpoint on the Origin of Sound

7/30/2019 Powerpoint on the Origin of Sound

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Origin of SoundNature of Sound in Air

Media that Transmit SoundSpeed of Sound in Air

RefractionEnergy in Sound WavesForced VibrationsNatural FrequencyResonanceInterferenceBeatsRadio Broadcasts



Sound...

...a longitudinal wave in air caused by a vibrating object.



Origin of Sound

infrasonic

frequencies < 20 Hz

ultrasonic

frequencies > 20,000 Hz

human hearing range

frequencies between 20 Hz and 20,000 Hz



Nature of Sound in Air

Sound requires a medium.

solid, liquid or gas

Will a bell ring in a evacuated Bell Jar?

Sound waves have compression and rarefaction regions.



Speed of Sound in Air

340 meters/second

760 miles/hour

Mach 1



increases with humidityincreases with temperatureincreases with density

How it varies:

SPEED OF SOUND



What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder?

Lightning and Thunder



What is the approximate distance of a thunderstorm when you note

a 3 second delay between the flash of the lightning and the

sound of the thunder?

Answer: 3 seconds 340 meters/second

= 1020 meters



Acoustics...

...the study of sound properties.

When a sound wave strikes a surface it can be.

(a) reflected.

(b) transmitted.

(c) absorbed.

(d) all of these.



Acoustics...

...the study of sound properties.

When a sound wave strikes a surface it can be.

(a) reflected.

(b) transmitted.

(c) absorbed.

(d) all of these.



Reflection of Sound

e.g. an echo

Reverberation - re-echoed sound, multiple reflections ofsound waves from walls

Compare reflections from a hard wall with that from a carpet wall.



Refraction of Sound

Refraction - the bending of a wave

Sound travels faster in warm air than in cool air.

Sound waves bend toward cooler air.





Subsonic - slower than the speed of sound

Supersonic faster than the speed of sound

Mach Number =speed of sound

speed of object

Speed of Sound



Forced Vibrations/Resonance

the setting up of vibrations in an object by a vibrating force.

Examples of Forced Vibration:

A tuning fork touching a wood surfaceSounding boards for stringed instruments

Matching tuning fork boxes



During forced vibration sound is intensified because a larger su rface

area is available to vibrate air molecules.



Resonances



Sound Interference

Overlapping compressions of a sound wave will result in

constructive interference.

and a louder sound.

Overlapping a compression and a rarefaction results in...destructive interference.

and a softer sound.





Constructive Interference Destructive Interference



Sound Interference

Noise reduction headphones

Echo cancellation



Beats - the periodic variation in loudness of two sounds played together

The beat frequency is equal to the difference in the frequency of the

two sounds.

What is the beat frequency when a 262 Hz and a 266 Hz tuning forkare sounded together?

Beats





Electromagnetic Radiation

Radio Transmission and Reception



Electromagnetic Radiation

Interrelated electric and magnetic fields traveling through space

All electromagnetic radiation travels at c = 3 108 m/s in vacuum the cosmicspeed limit!



Electromagnetic Waves



Examples of Electromagnetic Radiation

AM and FM radio waves (including TV signals)

Cell phone communication links

Microwaves

Infrared radiation

Light

X-rays

Gamma rays

What distinguishes these from one another?



Uses of Electromagnetic Waves

Communication systems

One-way and two-way

Radar

Cooking (with microwaves)

Medical Imaging (X rays)Night Vision (infrared)

Astronomy (radio, wave, IR, visible, UV, gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiation And much, much more!



Encoding Information on Radio Waves

What quantities characterize a radio wave?

Two common ways to carry analog information with radio waves

Amplitude Modulation (AM)

Frequency Modulation (FM): static free



Radio Broadcasts

Modulation - an impression of the sound wave on a higher frequency radiowave

AM

Amplitude Modulation

535 kHz to 1605 kHz

FM

Frequency Modulation

88 MHz to 108 MHz



AM Radio

Amplitude Modulation (AM) uses changes in the signal strength to conveyinformation

pressure modulation(sound)

electromagneticwave modulation



FM Radio

Frequency Modulation (FM) uses changes in the wave s frequency toconvey information

pressure modulation(sound)

electromagnetic

wave modulation



What affects propagation of radio waves?

Absorption

by ground, terrain

Loss of energy density with distance

weak far away

Scatteringreflections: especially off metals

leads to multi-path effects



Class Problem

Suppose at a concert a singer'svoice is radio broadcast all theway around the world beforereaching the radio you hold to

your ear. This takes 1/8 second. If

you're close you hear her voice inair before you hear it from the

radio. But if you are far enoughaway, both signals will reach youat the same time. How manymeters distant must you be for this

to occur?



Class Problem

If you sit 42.5 meters away fromthe singer, both the sound fromthe radio that is broadcast all theway around the world and that

through the air will reach you in

the same 1/8 second. Distance inair = speed of sound x time in air =

340m/s x 1/8s = 42.5m.If you sitfarther back, you'll hear the radiosignal before you hear the soundsignal!



Class Problem

Does the wind affect the pitch ofthe factory whistle you hear on awindy day?

If so, why?

If not, why?



Class Problem

No, the wind does not affect the pitch.The wind does affect the speed ofsound because the medium thatcarries the sound moves. But thewavelength of the sound changesaccordingly, which results in no

change in frequency or pitch. This canbe seen by analogy:

Suppose a friend is placing packageson a conveyor belt, say at a"frequency" of one each second. Thenyou, at the other end of the belt, takeoff one package each second.

Suppose the speed of the beltincreases while your friend still placesone package per second on the belt.Can you see that the packages(farther apart now) will still arrive toyou at the rate of one per second?



Class Problem

A train whistle at rest has a frequency of 3000 Hertz. If you are standingstill and observe the frequency to be 3010 Hertz, then you can concludethat...

a) the train is moving away from you.

b) the train is moving toward you

c) the sound from the whistle has echoed

d) not enough information is given



Class Problem

A train whistle at rest has a frequency of 3000 Hertz. If you are standingstill and observe the frequency to be 3010 Hertz, then you can concludethat...

a) the train is moving away from you.

b) the train is moving toward you

c) the sound from the whistle has echoed

d) not enough information is given



What dictates the frequency of a sound wave?

(a) wavelength

(b) medium

(c) source of the sound

(d) speed

(e) amplitude



What dictates the frequency of a sound wave?

(a) wavelength

(b) medium

(c) source of the sound

(d) speed

(e) amplitude



When you move away from a fixed source of sound, the frequency ofthe sound you hear

(a) is greater than what the source emits

(b) is less than what the source emits

(c) is the same as what the source emits



When you move away from a fixed source ofsound, the frequency of the sound you hear

(a) is greater than what the source emits

(b) is less than what the source emits

(c) is the same as what the source emits



Sonic booms from a plane are produced

(a) because the plane breaks through the sound barrier

(b) when the plane reaches the speed of sound

(c) by the plane traveling faster than the speed of sound

(d) by the plane traveling slower than the speed of sound



Sonic booms from a plane are produced

(a) because the plane breaks through the sound barrier

(b) when the plane reaches the speed of sound

(c) by the plane traveling faster than the speed of sound

(d) by the plane traveling slower than the speed of sound



For the same temperature for air, does sound travel faster in humidGalveston or in dry El Paso?

(a) Galveston

(b) El Paso

(c) same speed in either city



For the same temperature for air, does sound travel faster in humidGalveston or in dry El Paso?

(a) Galveston

(b) El Paso

(c) same speed in either city



The bending of sound through air of uneven temperature is called

(a) reflection

(b) refraction

(c) interference

(d) reverberation

(e) resonance



The bending of sound through air of uneven temperature is called

(a) reflection

(b) refraction

(c) interference

(d) reverberation

(e) resonance



Lightning is seen, then ten seconds later thunder is heard.Approximately , how far away in meters is the thundercloud?

(a) 10,500 m

(b) 5280 m

(c) 1050 m

(d) 3400 m

(e) 680 m



Lightning is seen, then ten seconds later thunder is heard.Approximately , how far away in meters is the thundercloud?

(a) 10,500 m

(b) 5280 m

(c) 1050 m

(d) 3400 m

(e) 680 m



A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating neareach other. How many beats per second are heard?

(a) 255

(b) 510

(c) 10

(d) 250

(e) 260



A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating neareach other. How many beats per second are heard?

(a) 255

(b) 510

(c) 10

(d) 250

(e) 260





Noise Versus Music

What is the difference between noise and music?

Answer: The appearance of the waveform.

Mac Mic



NOISE VERSUS MUSIC



Pitch...

is the "highness" or "lowness" of a tone.

Pitch corresponds to frequency.

Concert A on the Musical Scale has a frequency of 440 Hertz.



Same Note - Different Instrument



Harmonica partial tone that is an integer multiple of the fundamentalfrequency

Fundamental Frequency

the lowest frequency of vibrationa.k.a. the first harmonic









BackBack



Sound Intensity and Loudness

Intensity of Sound

refers to the amplitude of the pressure variations in the sound wave



Loudness

the physiological sensation directly related to the sound intensity

measured in bels

1bels = 10 decibels



Loudness

A sound of 10 decibels is or 101 or 10 times as intense as 0decibels.

20 decibels is 102 or 100 times the intensity 0 decibels.

How much more intense is sound at 100 dB than sound at 50 dB?

Answer: 100000 times



Source of Sound Loudness (db)

Threshold of Hearing 0

Conversation 60

Ear Damage Begins 85

Amplified Music 110Jet Airplane at 30 meters 140



Common Sound Intensities

Source of Sound Intensity (W/m2) Sound Level (db)

Jet 30 m away 102

140

Air-raid siren, nearby 1 120

Disco music, amplified 10-1 110

Riveter 10-3 90

Busy street traffic 10-5 70

Conversation in home 10-6 60

Quiet radio in home 10-8 40

Whisper 10-10 20

Rustle of leaves 10-11 10

Threshold of hearing 10-12 0

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Powerpoint on the Origin of Sound