SOUND WAVESSOUND WAVES

PRODUCTIONPRODUCTION Vibrating prongs set Vibrating prongs set

the air molecules in the air molecules in motionmotion

Top: molecules closer Top: molecules closer together high air together high air pressure pressure ((compression)compression)

Bottom: molecules Bottom: molecules spread apart low air spread apart low air pressure pressure ((rarefaction)rarefaction)

The crests The crests correspond to correspond to compressionscompressions

The troughs The troughs correspond to correspond to rarefactionsrarefactions

Sound is a Sound is a longitudinal wavelongitudinal wave

Sine curve is air Sine curve is air pressurepressure

CHARACTERISTICSCHARACTERISTICS Frequency Frequency

determines pitchdetermines pitch Frequency of a sound Frequency of a sound

wave the pitch wave the pitch rises (vise versa)rises (vise versa)

Frequency can be Frequency can be measuredmeasured

Pitch refers to how Pitch refers to how different different ff are are perceived by the perceived by the human earhuman ear

Ultrasonic WavesUltrasonic Waves

Can be used to Can be used to produce images produce images inside the bodyinside the body

Short wavelengths Short wavelengths are easily reflected off are easily reflected off small objects (no small objects (no audible or infrasonic)audible or infrasonic)

must be about the must be about the same size or smaller same size or smaller than the objectthan the object

Sounds waves can Sounds waves can travel through solids, travel through solids, liquids, and gasliquids, and gas

Closer molecules are Closer molecules are together, faster the together, faster the sound travelssound travels..

Waves consist of Waves consist of particle vibrations particle vibrations solid faster than gassolid faster than gas

Doppler EffectDoppler Effect The The ff of a sound remains constant of a sound remains constant Which wave front reaches the observers more Which wave front reaches the observers more

often?often? Speed of the sound waves does not changeSpeed of the sound waves does not change ff can be less than or more than the source can be less than or more than the source

DefinitionDefinition

Doppler effectDoppler effect A frequency shift that is the result of relative A frequency shift that is the result of relative

motion between the source of waves and an motion between the source of waves and an observerobserver

Can happen when:Can happen when:• 2 objects are moving2 objects are moving• The source is stopped and the observer is movingThe source is stopped and the observer is moving• Both sounds are movingBoth sounds are moving

Sound IntensitySound Intensity

Sound waves travel outward from their source, Sound waves travel outward from their source, energy is transferred from 1 air molecule to the energy is transferred from 1 air molecule to the nextnext

What is the intensity of the sound What is the intensity of the sound waves produced by a trumpet at a waves produced by a trumpet at a distance of 3.2 m when the power distance of 3.2 m when the power output of the trumpet is 0.20 W?output of the trumpet is 0.20 W?

P = 0.20 WP = 0.20 W r = 3.2mr = 3.2m Intensity = P/4Intensity = P/4ππrr22

Intensity = 0.20 W / (4Intensity = 0.20 W / (4ππ(3.2(3.222)))) Intensity = 0.00155 W/mIntensity = 0.00155 W/m22

Intensity and FrequencyIntensity and Frequency

Intensity and Frequency determine which Intensity and Frequency determine which sounds are audiblesounds are audible

Softest sounds that can be heard by the Softest sounds that can be heard by the avg. human ear occur at 1000Hz and an avg. human ear occur at 1000Hz and an intensity of 1.0 x 10intensity of 1.0 x 10-12-12

Loudest sounds (threshold of pain) occur Loudest sounds (threshold of pain) occur at an intensity of 1.0 W/mat an intensity of 1.0 W/m22

This can cause immediate damage to the ear This can cause immediate damage to the ear even if no pain is felteven if no pain is felt

Intensity is measured in decibelsIntensity is measured in decibels Relating the intensity of a sound wave to Relating the intensity of a sound wave to

the intensity at the threshold of hearingthe intensity at the threshold of hearing• How does the intensity of a sound wave How does the intensity of a sound wave

compare to what you can hear? compare to what you can hear? • The higher the decibel the louder it sounds The higher the decibel the louder it sounds

to youto you An increase in 10 dB means that the An increase in 10 dB means that the

sound is twice as loudsound is twice as loud

Natural frequencyNatural frequency: causes an object to : causes an object to vibratevibrate

ResonanceResonance: when the frequency of a : when the frequency of a force applied to a system matches the force applied to a system matches the natural frequency of vibration of the natural frequency of vibration of the systemsystem

http://www.youtube.com/watch?v=j-zczJXSxnw&eurl=http://video.aol.com/video-detail/humber-bridge-part-1moving-road-deck-in-high-winds/99945219