SoundSound

Sound WavesSound Waves

The Production of Sound WavesThe Production of Sound Waves

Sound waves are caused by vibrationsSound waves are caused by vibrations– The vibrating object has regions of air with The vibrating object has regions of air with

relatively high density and low density around relatively high density and low density around itit

High density areas – compressionsHigh density areas – compressions

Low density areas – rarefactionsLow density areas – rarefactions

Sound waves are longitudinal wavesSound waves are longitudinal waves– They have compacted areas (compressions) They have compacted areas (compressions)

and expanded areas (rarefactions)and expanded areas (rarefactions)

The Production of Sound WavesThe Production of Sound Waves

The Production of Sound WavesThe Production of Sound Waves

Characteristics of Sound WavesCharacteristics of Sound Waves

Humans can hear in a limited frequency range – Humans can hear in a limited frequency range – between 20 and 20,000Hzbetween 20 and 20,000Hz– Audible sound wavesAudible sound waves

Infrasound – any sound consisting of waves with Infrasound – any sound consisting of waves with frequencies lower than 20Hzfrequencies lower than 20Hz

Ultrasound – any sound consisting of waves with Ultrasound – any sound consisting of waves with frequencies higher than 20,000Hzfrequencies higher than 20,000Hz

Characteristics of Sound WavesCharacteristics of Sound Waves

Pitch – the perceived highness or lowness Pitch – the perceived highness or lowness of a sound, depending on the frequency of of a sound, depending on the frequency of sound wavessound waves

Faster vibrations lead to higher pitchFaster vibrations lead to higher pitch

Higher frequency equals higher pitchHigher frequency equals higher pitch

Characteristics of Sound WavesCharacteristics of Sound Waves

Ultrasound is used in sonar systems for boats Ultrasound is used in sonar systems for boats and bats and bats – Can produce an imageCan produce an image

Sonar – a system that uses reflected sound Sonar – a system that uses reflected sound waves to determine the distance to and location waves to determine the distance to and location of objectsof objects– Uses the formula distance = speed * timeUses the formula distance = speed * time

d=vtd=vt

Ultrasound is also used in medicineUltrasound is also used in medicine– Sonograms to look inside a body to view internal Sonograms to look inside a body to view internal

organsorgans– Don’t harm living cells like X-raysDon’t harm living cells like X-rays

Characteristics of Sound WavesCharacteristics of Sound Waves

Speed of sound depends on the mediumSpeed of sound depends on the medium

Sound travels fastest through solidsSound travels fastest through solids

Sound travels slowly through gasesSound travels slowly through gases

Sound travels faster in hot temperatures than in Sound travels faster in hot temperatures than in cold temperaturescold temperatures

Difference is due to ease of particle collisions in Difference is due to ease of particle collisions in solids at high temperaturessolids at high temperatures

Certain solids slow down sound wavesCertain solids slow down sound waves– RubberRubber

Characteristics of Sound WavesCharacteristics of Sound Waves

Characteristics of Sound WavesCharacteristics of Sound WavesSound waves propagate (spread) in all Sound waves propagate (spread) in all directions, three-dimensionally, from the directions, three-dimensionally, from the source of the vibrationssource of the vibrations– Centers of compression surrounding the Centers of compression surrounding the

source are called wave frontssource are called wave fronts– Radial lines perpendicular to the wave fronts Radial lines perpendicular to the wave fronts

are called raysare called raysIndicate direction of wave motionIndicate direction of wave motion

At large distances, spherical wave fronts At large distances, spherical wave fronts appear to be located on a single planeappear to be located on a single plane– Plane wavesPlane waves

Characteristics of Sound WavesCharacteristics of Sound Waves

The Doppler EffectThe Doppler Effect

Frequencies change when the source of the Frequencies change when the source of the wave is movingwave is movingDoppler effect – a frequency shift that is the Doppler effect – a frequency shift that is the result of relative motion between the source of result of relative motion between the source of waves and an observerwaves and an observer– Frequency and pitch increase when the source is Frequency and pitch increase when the source is

closercloserBlue shiftBlue shift

– Frequency and pitch decrease when the source is Frequency and pitch decrease when the source is further awayfurther away

Red shiftRed shift

Present in all wavesPresent in all waves

The Doppler EffectThe Doppler Effect