Waves and Sound

What are waves?• Wave – – a disturbance that transfers energy from a disturbance that transfers energy from

place to place.place to place.• Medium – – the material thru which a wave passesthe material thru which a wave passes• Waves travel trough the medium without actually Waves travel trough the medium without actually

moving the medium with it.moving the medium with it.

Types of Waves:• Transverse Waves: waves that move the waves that move the

medium at right angles to the direction in which medium at right angles to the direction in which the waves are traveling.the waves are traveling.

• Longitudinal Waves: move particles parallel to move particles parallel to the direction the wave is moving, the direction the wave is moving, ““push-pullpush-pull” ” waves.waves.

• Waves travel trough the medium without actually moving Waves travel trough the medium without actually moving the medium with it. Basically the medium stays put while the medium with it. Basically the medium stays put while the wave moves some distancethe wave moves some distance

Wave Particle Movement

Compression Wave

Transverse Waves

Properties of Waves

• Amplitude – – in a transverse wave in a transverse wave – – the height the height away from the away from the ““restrest” ” position. The amplitude in a position. The amplitude in a longitudinal wave is the measure of how longitudinal wave is the measure of how compressed or rarefied the medium becomes.compressed or rarefied the medium becomes.

• Wavelength – – the distance between two the distance between two corresponding parts of a wave.corresponding parts of a wave.

• Frequency – – the number of complete waves that the number of complete waves that pass a given point in a certain period of time. pass a given point in a certain period of time. Frequency is measured in Frequency is measured in Hertz; one ; one HzHz is a is a wave that occurs once every second.wave that occurs once every second.

• Speed (meters/sec)= wavelength x frequency (meters/sec)= wavelength x frequency• Frequency (Hz = 1/sec)= speed / Wavelength (Hz = 1/sec)= speed / Wavelength• WavelengthWavelength (meters) = speed / Frequency (meters) = speed / Frequency

(Designated by Greek letter lambda )(Designated by Greek letter lambda )

Speed, Frequency, and Wavelength

Speed

Wavelength x frequency

S

x f

S = x f = 1.5 m x 280 Hz = 420 m/s

= S / f = 5.0 m/s / 2.5 Hz = 2 m

Interactions of Waves• Refraction – – The bending of a wave due to the The bending of a wave due to the

wave moving from one type of medium into wave moving from one type of medium into another.another.

• Reflection – – Bounce back waveBounce back wave– Angle of Incidence is the angle of the wave coming into the is the angle of the wave coming into the

object reflecting the wave.object reflecting the wave.– Angle of Reflection is the angle bouncing off and going is the angle bouncing off and going

away from the object.away from the object.

• Diffraction – – Wave passing a barrier or Wave passing a barrier or going through a hole in a barrier bends going through a hole in a barrier bends and causes the wave to wrap around the and causes the wave to wrap around the barrierbarrier

Interactions of Waves

• Interference – when two or more waves meet, they interact. – when two or more waves meet, they interact. This interaction is called interference.This interaction is called interference.– 1. 1. Constructive Interference – the combining of waves to cause higher – the combining of waves to cause higher

amplitude of any of the original waves.amplitude of any of the original waves.

– 2. 2. Destructive Interference – when the combining of the waves produce – when the combining of the waves produce a new wave with a smaller amplitude than the beginning wavesa new wave with a smaller amplitude than the beginning waves

Interactions of Waves

Standing Waves• Standing Waves – – the combining of the incoming and the combining of the incoming and

reflected wave so that the resultant appears to be standing reflected wave so that the resultant appears to be standing stillstill

• Node – – the point where Constructive Interference and the point where Constructive Interference and Destructive Interference cause an amplitude of zero on the Destructive Interference cause an amplitude of zero on the standing wave.standing wave.

• Antinode – – the point where Constructive Interference and the point where Constructive Interference and Destructive Interference of a standing wave are represented Destructive Interference of a standing wave are represented by the crest and the trough.by the crest and the trough.

• Resonance – – the point where vibrations traveling thru and the point where vibrations traveling thru and object matches the natural vibrations of an object. I.e. an object matches the natural vibrations of an object. I.e. an opera singer hitting a note and shattering a crystal glass.opera singer hitting a note and shattering a crystal glass.

Seismic Waves• Seismic Waves – – waves caused by waves caused by

the release of energy due to the release of energy due to earthquakes composed of earthquakes composed of – P - primary wavesP - primary waves– S - secondary wavesS - secondary waves– L - surface wavesL - surface waves

P Waves• P waves –- –- Primary waves are pPrimary waves are pressure ressure

waves & waves & are the fastest moving waves, are the fastest moving waves, they travel thru solids and liquids, Push-they travel thru solids and liquids, Push-Pull Waves AKA Longitudinal wavesPull Waves AKA Longitudinal waves

S Waves• S WavesS Waves – – Secondary Waves are slower Secondary Waves are slower

than primary waves, they cannot travel than primary waves, they cannot travel thru liquid and are Transverse Waves.thru liquid and are Transverse Waves.

L Waves• L Waves (last waves) Surface waveL Waves (last waves) Surface wave – – the the

combination on the Earthcombination on the Earth’’s surface of Primary s surface of Primary and Secondary waves. and Secondary waves. – The rolling chaotic movement of the surfaceThe rolling chaotic movement of the surface– Cause the most damage of the seismic wavesCause the most damage of the seismic waves

Sound• Sounds are longitudinal waves that require a Sounds are longitudinal waves that require a

medium to travel caused by the vibrations of an medium to travel caused by the vibrations of an object.object.

• Speed of Sound – on average:Speed of Sound – on average:– Air is 767 mph (343 m/s) – about 1 mile every 5 secAir is 767 mph (343 m/s) – about 1 mile every 5 sec

– Water is 3,315 mph (1,482 m/s)Water is 3,315 mph (1,482 m/s)

– Steel is 13,330 mph ( 5,960m/s)Steel is 13,330 mph ( 5,960m/s)

• The speed of sound depends on the elasticity, The speed of sound depends on the elasticity, density and temperature of the medium.density and temperature of the medium.

Sonic Boom follows

Sound Waves

A sound wave is a wave of alternating high-pressure and low-pressure regions of air.

The Wavelength of Sound

The Doppler Effect

• The shift in frequency caused by motion is called the Doppler effect.

• It occurs when a sound source is moving at speeds less than the speed of sound.

Speed of Sound• Speed of Sound: depends on the depends on the elasticity, density and and temperature.

• Elasticity – – the ability of an object to bounce back to its original the ability of an object to bounce back to its original shape. Sound travels faster in more elastic objects. Typically gasses shape. Sound travels faster in more elastic objects. Typically gasses are the least elastic, liquids are next and solids are the most elastic.are the least elastic, liquids are next and solids are the most elastic.

• Density – – generally speaking, in material of the same state of matter generally speaking, in material of the same state of matter (solid, liquid or gas) (solid, liquid or gas) the denser the medium the slower the sound the denser the medium the slower the sound travelstravels. Sound travels slower in lead than it does in steel.. Sound travels slower in lead than it does in steel.

• Temperature – – generally speaking generally speaking the the higher the temperature the faster the speed of sound. the speed of sound.

The Speed of Sound• We use the term supersonic to describe motion at

speeds faster than the speed of sound.• A shock wave forms where the wave fronts pile up. • The pressure change across the shock wave is what

causes a very loud sound known as a sonic boom.

Breaking the Sound Barrier• Chuck Yeager – – first man to fly faster first man to fly faster

than the speed of soundthan the speed of sound• Andy Green – – first man to drive a land first man to drive a land

vehicle faster than the speed of sound.vehicle faster than the speed of sound.

October 14, 1947 – in X1 “Glamorous

Glennis”

October 15, 1997 – in SuperSonic Car

“Thrust SSC”763 MPH

Properties of Sound• Intensity – – the amount of energy the wave carries per the amount of energy the wave carries per

second per meter squaredsecond per meter squaredintensity = Watts / m2

• Loudness – – sound level is measured in sound level is measured in decibels (dB) (dB)

Common Sounds and their Loudness

Loudness

Every increase of 20 dB, means the pressure wave is 10 times greater in amplitude.

Logarithmic scale

Linear scale

Decibels (dB) Amplitude

0 1

20 10

40 100

60 1,000

80 10,000

100 100,000

120 1,000,000

Frequency & Pitch• Frequency – the number of vibrations per second – the number of vibrations per second

– Human Hearing – between 20 Hz – 20,000 HzHuman Hearing – between 20 Hz – 20,000 Hz

• Below 20 Hz is called infrasoundBelow 20 Hz is called infrasound

• Above 20,000 Hz is called ultrasoundAbove 20,000 Hz is called ultrasound

• Pitch - dependent of frequency - dependent of frequency

– high frequency yields high pitch soundshigh frequency yields high pitch sounds

– Low frequency yields low pitchLow frequency yields low pitch

• Resonance – when the frequency of sound matches the natural – when the frequency of sound matches the natural frequency of an objectfrequency of an object

Tacoma Narrows Bridge collapse

The Frequency of Sound

• We hear frequencies of sound as having different pitch.

• A low frequency sound has a low pitch, like the rumble of a big truck.

• A high-frequency sound has a high pitch, like a whistle or siren.

• In speech, women have higher fundamental frequencies than men.

Hearing – Human SoundNeed to know these structures & their function: Outer Ear, Middle Ear, Inner Ear, Need to know these structures & their function: Outer Ear, Middle Ear, Inner Ear,

Pinna, Auditory canal, Tympanum, Malleus, Incus, Stapes, Oval Window, Pinna, Auditory canal, Tympanum, Malleus, Incus, Stapes, Oval Window, Cochlea, Auditory Nerve, Semicircular Canals, Eustachian TubeCochlea, Auditory Nerve, Semicircular Canals, Eustachian Tube

Outer Ear• Pinna-- (the ear flap aka (the ear flap aka

auricle), used to focus the ), used to focus the sound waves into the ear sound waves into the ear canalcanal

• External Auditory Meatus – the “hole through the – the “hole through the temporal bone that opens the temporal bone that opens the space for the ear canal, the space for the ear canal, the middle & inner earsmiddle & inner ears

• Auditory Canal – (ear – (ear canal), focuses the sound canal), focuses the sound onto the ear drumonto the ear drum

• Tympanic membrane – – (ear drum), end of the outer (ear drum), end of the outer ear, beginning of the middle ear, beginning of the middle ear. Sound starts the ear ear. Sound starts the ear drum vibrating.drum vibrating.

Middle Ear• Tympanic membrane

vibrates, causing the 3 smallest vibrates, causing the 3 smallest bones in to vibrate, one after bones in to vibrate, one after the nextthe next– Malleus (hammer) is (hammer) is

touching the ear drum & touching the ear drum & vibrates firstvibrates first

– Next is the Next is the Incus (anvil) (anvil) – Last is the Last is the Stapes

• Eustachian Tube: tube that : tube that connects the middle ear w/ the connects the middle ear w/ the pharynx. This allows the pharynx. This allows the pressure on both sides of the pressure on both sides of the ear drum to equalize. ear drum to equalize.

Inner EarThe Stirup vibrates the oval window of the cochlea. Cochlea is a long, fluid-filled tube, folded in half and the coiled up like a snail shell. The entire inner surface is lined w/ cilia.. Attached to the cilia is a nerve fiber. Once cilia are vibrated, the attached nerves are stimulated and they send a signal to the brain.

Balance is achieved by the semicircular canals, three canals which help us determine our body’s position in space.

Recording Sound

A common way to record sound starts with a microphone. A microphone transforms a sound wave into an electrical signal with the same pattern of oscillation.

Recording Sound

In modern digital recording, a sensitive circuit converts analog sounds to digital values between 0 and 65,536.

Recording Sound

Numbers correspond to the amplitude of the signal and are recorded as data. One second of compact-disk-quality sound is a list of 44,100 numbers.

Recording Sound

To play the sound back, the string of numbers is read by a laser and converted into electrical signals again by a second circuit which reverses the process of the previous circuit.

Recording Sound

The electrical signal is amplified until it is powerful enough to move the coil in a speaker and reproduce the sound.

Music• The pitch of a sound is how high or low we hear its frequency. Though pitch and frequency usually

mean the same thing, the way we hear a pitch can be affected by the sounds we heard before and after.

• Rhythm is a regular time pattern in a sound.

• Music is a combination of sound and rhythm that we find pleasant.

• Most of the music you listen to is created from a pattern of frequencies called a musical scale.

Consonance, Dissonance, and Beats

• Harmony is the study of how sounds work together to create effects desired by the composer.

• When we hear more than one frequency of sound and the combination sounds good, we call it consonance.

• When the combination sounds bad or unsettling, we call it dissonance.

Consonance, Dissonance, and Beats

• Consonance and dissonance are related to beats.

• When frequencies are far enough apart that there are no beats, we get consonance.

• When frequencies are too close together, we hear beats that are the cause of dissonance.

• Beats occur when two frequencies are close, but not exactly the same.

Harmonics and Instruments

• The same note sounds different when played on different instruments because the sound from an instrument is not a single pure frequency.

• The variation comes from the harmonics, multiples of the fundamental note.

Application: Sound from a Guitar

Vocabulary to help you out(REEEALLY great test items)