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Sound WavesSound Waves
Physics Chapter 13 Section 1Physics Chapter 13 Section 1
I. Production of sound wavesI. Production of sound waves Produced by an object vibrating Produced by an object vibrating
-ex. Tuning fork-ex. Tuning fork Prongs move back and forth pushing the air Prongs move back and forth pushing the air
molecules together or spreading them apartmolecules together or spreading them apart
Compression Compression medium molecules move medium molecules move togethertogether
higher density and pressurehigher density and pressure Rarefaction Rarefaction medium molecules spread apart medium molecules spread apart
lower density and pressurelower density and pressure
Online Tuning ForksOnline Tuning Forks
As the tuning fork vibrates it sends a series of As the tuning fork vibrates it sends a series of compressions and rarefactions that expand out compressions and rarefactions that expand out in all directions.in all directions.
*like pond ripples*like pond ripples
*air molecules vibrate*air molecules vibrate Sound waves are longitudinal waves (particles Sound waves are longitudinal waves (particles
move parallel to wave direction)move parallel to wave direction)
CompresionalCompresional waves video waves video
II. Characteristics of sound wavesII. Characteristics of sound waves
Frequency – number of cycles per unit of timeFrequency – number of cycles per unit of time audible sound waves audible sound waves (humans can hear)(humans can hear)
frequency range 20 Hz to 20,000 Hzfrequency range 20 Hz to 20,000 Hz frequencies < 20 Hz frequencies < 20 Hz infrasonic (very long infrasonic (very long
wavelength) sound waves.wavelength) sound waves. frequencies > 20,000 Hz frequencies > 20,000 Hz ultrasonic (short ultrasonic (short
wavelength) sound waves.wavelength) sound waves.
audible depends on our ability to detect audible depends on our ability to detect factors: age, ear damage due to excessive loud factors: age, ear damage due to excessive loud
noisesnoises
as frequency increases, wavelength decreasesas frequency increases, wavelength decreases frequency determines pitchfrequency determines pitch pitch:pitch: how high or low we perceive a sound to how high or low we perceive a sound to
bebe depending on the frequency of a sound wave. depending on the frequency of a sound wave. low pitch = low frequencylow pitch = low frequency high pitch = high frequencyhigh pitch = high frequency * a perceived measurement** a perceived measurement*
ultrasonic waves produce images of objectsultrasonic waves produce images of objects
short wavelengthshort wavelength
provides medical usesprovides medical uses
- images of internal body structures- images of internal body structures
- waves reflect off small objects of varying- waves reflect off small objects of varying
densitiesdensities
ex. Ultrasounds of fetusesex. Ultrasounds of fetuses Ultrasonic pulses emitted and received as they Ultrasonic pulses emitted and received as they
reflect off of fetal tissuesreflect off of fetal tissues
Ultrasound PicturesUltrasound Pictures ex. Echolocation of dolphins and batsex. Echolocation of dolphins and bats
Speed of sound depends on the mediumSpeed of sound depends on the medium
sound waves can pass through solids,sound waves can pass through solids,
liquids, and/or gases (mechanical waves)liquids, and/or gases (mechanical waves)
Depends on how quickly particles of the Depends on how quickly particles of the medium can transfer the vibrationmedium can transfer the vibration
More dense (particles are closer together) = More dense (particles are closer together) = faster transfer of energyfaster transfer of energy
solids generally conduct sound the fastestsolids generally conduct sound the fastest
gases generally conduct sound the slowestgases generally conduct sound the slowest
Also depends on the temperature of the Also depends on the temperature of the mediummedium
higher temperature = particles of the medium higher temperature = particles of the medium colliding more frequentlycolliding more frequently
faster sound wavesfaster sound waves
Each medium has its own set of values for Each medium has its own set of values for speed of sound (table 13-1 page 482)speed of sound (table 13-1 page 482)
In normal air (25In normal air (25ooC) the speed of soundC) the speed of sound
equals 346 m/sequals 346 m/s
Sound waves spread out (propagate) in 3 Sound waves spread out (propagate) in 3 dimensions in approximately spherical patternsdimensions in approximately spherical patterns
Represented on paperRepresented on paper
in 2-D as concentric in 2-D as concentric
circlescircles
Distance between each adjacent wave front = Distance between each adjacent wave front =
1 wavelength (1 wavelength ()) Rays indicate direction of travel of the wave Rays indicate direction of travel of the wave
frontsfronts Plane wave – a segment of a wave front very Plane wave – a segment of a wave front very
far from the source that appears to be a straight far from the source that appears to be a straight line and parallel to the adjacent wave frontsline and parallel to the adjacent wave fronts
Doppler Effect – frequency shift that is the Doppler Effect – 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
(page 485 figure 13-6)(page 485 figure 13-6)
Doppler effectDoppler effect
linklink
Example: #1Example: #1 A car (train, ambulance) moving A car (train, ambulance) moving toward or away from an observer while blowing the toward or away from an observer while blowing the horn or sirenhorn or siren
Pitch appears to change, but the frequency is not Pitch appears to change, but the frequency is not changingchanging
Frequency of the source remains constantFrequency of the source remains constant
Wave fronts will reach the observer in front of the Wave fronts will reach the observer in front of the moving source more often (with highermoving source more often (with higher
frequency) due to source moving toward thefrequency) due to source moving toward the
observerobserver
Wave fronts “pile up” on each otherWave fronts “pile up” on each other
Pitch of sound gets higherPitch of sound gets higher
Example #2 Example #2 Source moving away from Source moving away from observerobserver
Wave fronts will reach observer behind aWave fronts will reach observer behind a
moving source less often (lower frequency)moving source less often (lower frequency)
due to source moving away from observerdue to source moving away from observer
Wave fronts “spread out”Wave fronts “spread out”
Pitch sounds lowerPitch sounds lower
** Speed of the sound waves does not change** Speed of the sound waves does not change Same will happen with a stationary source and a Same will happen with a stationary source and a
moving observermoving observer Doppler effect occurs whenever there is relative Doppler effect occurs whenever there is relative
motion between an observer and a source of wave motion between an observer and a source of wave frontsfronts
** Most common to sound waves, but happens with ** Most common to sound waves, but happens with all waves all waves
- - Moving faster than the speed of soundMoving faster than the speed of sound
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