Chapter 21: Sound

Chapter 21: SoundPages 532 - 557Sound is a form of energy produced by the vibration of matter.Sound is a compressional or longitudinal waveEx. SpringSound is transmitted through solids, liquids, and gases.Sound is transmitted better through solids and liquids. Why?More denseGases transmits sound a lot farther than a solid and liquid. Why?Less dense; not as many particles to interfere.

SoundSo what causes sounds to travel better through some substances and not others?The greater the elasticity, the greater the speed.The greater the density, the slower the speed.The best conductors of sound are elastic substances.Sound can not be transmitted through a vacuum.Sound needs a medium in order for it to be transmitted.Radio waves can travel through a vacuum; no medium is needed.This is why astronauts can use radio signals to talk in space.

Speed of Sound344 m/s in air at 20CDepends on:Type of mediumtravels better through liquids and solidscant travel through a vacuumTemperature of mediumtravels faster at higher temps

Parts of the earOuter ear: pinnaEar canalEar drum: tympanumVibrates the ear drum

Middle ear: three small bonesAnvilHammerStirrupInner earCochlea: filled with fluidHair-like nerve endingsAuditory nerves

BrainDamage done to the hairs causes permanent hearing loss. The hairs never grow back.

B. Human Hearing

sound wavevibrates ear drumamplified by bonesconverted to nerve impulses in cochlea Human HearingPitchhighness or lowness of a sounddepends on frequency of sound wavehuman range: 20 - 20,000 Hz

ultrasonic wavessubsonic wavesFrequencies you cannot hearUltrasonic: higher than 20,000 HzUses: clean jewelry, medical applicationsInfrasonic: lower than 20 HzFound: in the atmosphere and in the crust when plates move; also an indication motion sickness Human HearingIntensityvolume of sounddepends on energy (amplitude) of sound wavemeasured in decibels (dB)

Sound is measured in what?Above 120 dB can cause hearing loss.

Human Hearing

70801001101204018100DECIBEL SCALEDoppler EffectDoppler Effectchange in wave frequency caused by a moving wave sourcemoving toward you - pitch sounds highermoving away from you - pitch sounds lower

Reflection of Sound WavesEchoesEcholocation: process using reflected sound waves to find objectsBatsWhalesSONARUltrasonographySeeing with SoundUltrasonic waves - above 20,000 Hz

Medical Imaging

SONARSound Navigation and RangingDiffractionBends of waves around or through a barrierExamples:ThunderSomeone in the hallway on the other side and wecan hear them.

Constructive - louder

D. InterferenceInterferencethe ability of 2 or more waves to combine to form a new wave

Destructive - softerD. InterferenceBeatsvariations in sound intensity produced by 2 slightly different frequenciesboth constructive and destructive interference occur

InterferenceThe effects caused by 2 or more waves.Ex. Several instruments produce interference in a band.

Cool Interference Examples:The Sound Barrier: the point at which the source of a sound accelerates to the speed of sound Sonic Booms: the explosive sound heard when a shock wave reaches your ears1st time sound barrier broken: Oct. 14, 1947 by Chuck Yeager (speed of sound is called Mach 1); so Mach 6 is going 6 times the speed of soundSound Barrier and Sonic Booms

Movie Clip of Breaking the sound barrierResonanceForced Vibrationwhen one vibrating object forces another object to vibrate at the same frequencyresults in a louder sound because a greater surface area is vibratingused in guitars, pianos, etc.

ResonanceResonancespecial case of forced vibrationobject is induced to vibrate at its natural frequency

HarmonicsFundamentalthe lowest natural frequency of an objectOvertonesmultiples of the fundamental frequency

ExamplesFundamental 100 Hz1st Overtone 200 Hz2nd Overtone 300 Hz

Music vs. NoiseMusicspecific pitches and sound qualityregular patternNoiseno definite pitchno set pattern

InterferenceBeatsvariations in sound intensity produced by 2 slightly different frequenciesboth constructive and destructive interference occur

AcousticsAcousticsthe study of soundReverberation echo effect produced by the reflection of sound

Anechoic chamber - designed to eliminate reverberation.