Sound and Related Sound and Related TopicsTopics

Let’s Let’s HearHear More About It More About It

Sound “ideas”Sound “ideas”

compression -- molecules are squished compression -- molecules are squished together creating areas of high pressure.together creating areas of high pressure.

rarefaction -- molecules are spread apart creating areas of low rarefaction -- molecules are spread apart creating areas of low pressure.pressure.

Compressional wave with air as the mediumCompressional wave with air as the medium

Example:Example:

Sound waves need three Sound waves need three things:things:

A source ; something vibrating.A source ; something vibrating.

A medium; something for the A medium; something for the wave to travel in.wave to travel in.

A receiver; something to A receiver; something to detect the vibration.detect the vibration.

If the vibration is:If the vibration is:

Regular and pleasing, we Regular and pleasing, we call it musiccall it music

Irregular and annoying, we Irregular and annoying, we call it noise.call it noise.

The medium dictates the The medium dictates the velocity:velocity:

Fastest in more dense mediums, Fastest in more dense mediums, and more elastic mediums. and more elastic mediums. [bucket]

~ 760.5 miles/hour~ 760.5 miles/hour

In air sound travels at ~331.5m/s at In air sound travels at ~331.5m/s at 00ooC, and increases with Temperature. C, and increases with Temperature.

In some solids, it can travel at ~5000 m/s.In some solids, it can travel at ~5000 m/s.

TOOLBOXTOOLBOX: Speed of Sound 340 : Speed of Sound 340 m/sm/s

In water it travels at ~ 1500m/s, whileIn water it travels at ~ 1500m/s, while

MACH 1MACH 1

Speed of Sound in Various Speed of Sound in Various MaterialsMaterials

Gases

Material v (m/s)

Hydrogen (0°C) 1286

Helium (0°C) 972

Air (20°C) 343

Air (0°C) 331

LiquidsLiquids

Liquids at 25°C

Material v (m/s)

Glycerol 1904

Sea water 1533

Water 1493

Mercury 1450

Kerosene 1324

Methyl alcohol 1143

Carbon tetrachloride 926

SolidsSolidsSolids

Material v (m/s)

Diamond 12000

Pyrex glass 5640

Iron 5130

Aluminum 5100

Brass 4700

Copper 3560

Gold 3240

Lucite 2680

Lead 1322

Rubber 1600

Sonic BOOMSonic BOOM

A Sonic boom is a noise similar to thunder. It is A Sonic boom is a noise similar to thunder. It is caused by an object moving faster than sound. caused by an object moving faster than sound.

An aircraft traveling through the atmosphere An aircraft traveling through the atmosphere continuously produces waves similar to the continuously produces waves similar to the water waves boat. When the aircraft exceeds the water waves boat. When the aircraft exceeds the speed of sound, these pressure waves combine speed of sound, these pressure waves combine and form shock waves. As an aircraft flies at and form shock waves. As an aircraft flies at supersonic speeds it is continually generating supersonic speeds it is continually generating shock waves, dropping sonic boom along its shock waves, dropping sonic boom along its flight path, similar to someone dropping objects flight path, similar to someone dropping objects from a moving vehicle. If the plane makes a from a moving vehicle. If the plane makes a sharp turn or pulls up, the boom will hit the sharp turn or pulls up, the boom will hit the ground in front of the aircraft.ground in front of the aircraft.

Sonic BOOMSonic BOOM

Sonic BOOMSonic BOOM

Sound Wave Sound Wave Characteristics:Characteristics:

Wavelength:Wavelength:

The distance between 2 successive The distance between 2 successive compressions (or 2 successive compressions (or 2 successive rarefactions).rarefactions).

Amplitude:Amplitude:

Relates to the Relates to the intensity or loudness intensity or loudness of the sound.of the sound. An indication of the energy of the wave.An indication of the energy of the wave.

Amplitude:Amplitude:

Measured in Measured in units called units called decibels (dB’s). decibels (dB’s).

120 dB’s is the 120 dB’s is the human ear’s human ear’s pain thresholdpain threshold

Frequency:Frequency:

Relates to the pitch (or tone).Relates to the pitch (or tone).

The higher the frequency, the higher The higher the frequency, the higher the pitch.the pitch.

The human ear.The human ear.

Very detailed Very detailed construction.construction.

Range is from 20 Range is from 20 hertz to 20,000 hertz..hertz to 20,000 hertz..

Below 20 Hz -- Below 20 Hz -- infrasonic sounds.infrasonic sounds.

Above 20,000 Hz -- Above 20,000 Hz -- ultrasonic,ultrasonic,

Uses of SoundUses of Sound

Infrasonic (Subsonic)Infrasonic (Subsonic)

sound frequencies sound frequencies below 20 Hzbelow 20 Hz

Earthquakes produce Earthquakes produce infrasonic soundinfrasonic sound

Elephants Elephants communicate communicate through infrasonicthrough infrasonic

VERY LOW SOUNDSVERY LOW SOUNDS

UltrasonicUltrasonic

sound frequencies sound frequencies above 20,000 Hzabove 20,000 Hz

Examples: Examples: SONAR SONAR

Examples: Echolocation Examples: Echolocation – Bats, Whales– Bats, Whales

Medical UsesMedical Uses

SONARSONAR

(So)und (Na)vigation (So)und (Na)vigation and (R)angingand (R)anging

Can be used over long Can be used over long distancesdistances

4 sites cover 80% of the ocean4 sites cover 80% of the ocean

Sound sent underwater, Sound sent underwater, bounces backbounces back

RADARRADAR

(Ra)dio (D)etecting (Ra)dio (D)etecting (a)nd (R)anging(a)nd (R)anging

Radio waves – Not Radio waves – Not Sound WavesSound Waves

We’ll come back to this We’ll come back to this topic during EM wavestopic during EM waves

Sound Wave PhenomenaSound Wave Phenomena

Doppler EffectDoppler Effect

A Change in pitch or frequency due to A Change in pitch or frequency due to a moving wave source. a moving wave source.

In front of object: High frequency, In front of object: High frequency, high pitch, short wavelengthhigh pitch, short wavelength

Behind object: Low frequency, low Behind object: Low frequency, low pitch, long wavelength. pitch, long wavelength.

Sound waves get pushed together, or Sound waves get pushed together, or spread out, changing pitchspread out, changing pitch

Doppler EffectDoppler Effect

Doppler Effect AppletDoppler Effect Applet

Resonance:Resonance:

When the vibration of the source matches When the vibration of the source matches the natural frequency of the object, causing the natural frequency of the object, causing it to start resonating (vibrating).it to start resonating (vibrating).

Resonance is Vital to the proper functioning of most Resonance is Vital to the proper functioning of most musical instruments.musical instruments.

All objects have a natural frequencyAll objects have a natural frequency

Resonance:Resonance:

Objects vibrate more and more as they Objects vibrate more and more as they absorb more natural frequency vibrations absorb more natural frequency vibrations (constructive interference). If they (constructive interference). If they absorb enough energy, they will break.absorb enough energy, they will break.

How You HEAR!!How You HEAR!! The outer EarThe outer Ear: Where : Where

sound waves are gatheredsound waves are gathered

-Visible part (pinna)-Visible part (pinna)

-Ear Canal -Ear Canal

-Ear Drum-Ear Drum

Channel sound waves Channel sound waves to eardrum which to eardrum which vibratesvibrates

How You HEAR!!How You HEAR!!

Vibrating ear drum Vibrating ear drum causes 3 tiny bones to causes 3 tiny bones to vibrate, which amplify vibrate, which amplify the sound.the sound.

-Hammer-Hammer

-Anvil-Anvil

-Stirrup-Stirrup

The Middle EarThe Middle Ear : : Sound is amplifiedSound is amplified

How You HEAR!!How You HEAR!! The Inner EarThe Inner Ear: :

Converts vibrations Converts vibrations to nerve impulsesto nerve impulses

--CochleaCochlea

Auditory NerveAuditory Nerve

Semi Circular CanalsSemi Circular Canals

Eustachian TubeEustachian Tube Vibrations from Vibrations from

middle ear vibrate middle ear vibrate the cochlea, which the cochlea, which converts vibrations to converts vibrations to nerve impulsesnerve impulses

How You HEAR!!How You HEAR!!

Hearing ProblemsHearing Problems

Hearing Loss: tiny hairs (cilla) in cochlea Hearing Loss: tiny hairs (cilla) in cochlea are destroyed or damaged, often by loud are destroyed or damaged, often by loud sounds.sounds.

Deafness: Caused by failure of eardrum or Deafness: Caused by failure of eardrum or tiny bones to vibrate. Problems with tiny bones to vibrate. Problems with cochlea.cochlea.

  

Dizziness: Caused by problems with semi Dizziness: Caused by problems with semi circular canals - Vertigocircular canals - Vertigo

Ear Infection – Eustachian tube is close to Ear Infection – Eustachian tube is close to nasal cavitynasal cavity  

MUSICMUSIC

Noise – random waves Noise – random waves frequencies, and pitchesfrequencies, and pitches

Music – sound in a regular patternMusic – sound in a regular pattern

MusicMusic

Every Musical note Every Musical note has a certain has a certain frequency, which frequency, which gives it a distinct gives it a distinct pitch.pitch.

Arrange the Arrange the notes in a notes in a familiar or familiar or pleasing pleasing pattern pattern and……and……

MusicMusic

Musical instruments Musical instruments contain contain stringsstrings, , membranesmembranes, , columns of columns of airair – something that – something that vibrates at a natural vibrates at a natural frequency to create pitch.frequency to create pitch.

RememberRemember Resonance - Musical Resonance - Musical instruments contain a instruments contain a resonator which resonator which amplifies the sound.amplifies the sound.

Fundamentals and Fundamentals and Overtones:Overtones:

Fundamental Fundamental Frequency : The Frequency : The lowest frequency.lowest frequency.

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Overtones: Also called harmonics, Overtones: Also called harmonics, these frequencies are whole number these frequencies are whole number ratios of the fundamentalratios of the fundamental

Sound Quality:Sound Quality:

Quality: differences among sounds Quality: differences among sounds of the same pitchof the same pitch

Middle C for a Flute versus a PianoMiddle C for a Flute versus a Piano

Sound QualitySound Quality

The overall sound “envelop” (the The overall sound “envelop” (the combination of the fundamental and combination of the fundamental and overtones) makes the sounds overtones) makes the sounds distinguishabledistinguishable

Interference;Interference;

When two sound waves meet at When two sound waves meet at the same time and spot.the same time and spot.

The effect is called Beats: A rhythmic The effect is called Beats: A rhythmic variation in amplitude.variation in amplitude.

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Beat Frequency = Difference in the Beat Frequency = Difference in the two frequencies.two frequencies.

The end of the the story .The end of the the story .