Chapter 12Chapter 12SoundSound

Section 1Section 1

All sounds are caused by All sounds are caused by vibrationsvibrations

►Sound wavesSound waves formed when a vibrating object formed when a vibrating object

collides with air molecules, collides with air molecules, transferring energy to themtransferring energy to them

►Compressional wavesCompressional waves have two regions, called have two regions, called

compressions and rarefactions, compressions and rarefactions, which push air molecules together which push air molecules together and then spread them apartand then spread them apart

►MediumMedium the type of matter, whether liquid, solid, the type of matter, whether liquid, solid,

or gas; that sound waves travel throughor gas; that sound waves travel through

►A sound wave’s speed depends on the A sound wave’s speed depends on the substance of the medium and whether substance of the medium and whether the medium is solid, liquid, or gas.the medium is solid, liquid, or gas. Sound travels more quickly through solids Sound travels more quickly through solids

and liquids because the individual molecules and liquids because the individual molecules are closer together than the molecules in gas.are closer together than the molecules in gas.

►As a medium’s temperature increases, its As a medium’s temperature increases, its molecules move faster and it conducts molecules move faster and it conducts sound waves faster.sound waves faster.

Section 2Section 2

Properties of SoundProperties of Sound►AmplitudeAmplitude

The amount of energy a wave carries The amount of energy a wave carries corresponds to its amplitudecorresponds to its amplitude

which is related to the density of the particles which is related to the density of the particles in the compressions and rarefactions.in the compressions and rarefactions.

►IntensityIntensity the amount of energy that flows through a the amount of energy that flows through a

certain area in a specific amount of timecertain area in a specific amount of time►LoudnessLoudness

human perception of sound intensityhuman perception of sound intensity►DecibelDecibel

Each unit on a scale that measures sound Each unit on a scale that measures sound intensityintensity

► PitchPitch how low or high a sound seems to behow low or high a sound seems to be

► FrequencyFrequency is the number of compressions or rarefactions of a is the number of compressions or rarefactions of a

sound wave that pass per secondsound wave that pass per second human ears can hear frequencies from ~20 to human ears can hear frequencies from ~20 to

~20,000 Hz~20,000 Hz►Ultrasonic wavesUltrasonic waves

sound frequencies over 20,000 Hz that have medical sound frequencies over 20,000 Hz that have medical and scientific uses.and scientific uses.

► Infrasonic or subsonic wavesInfrasonic or subsonic waves frequencies below 20 Hz usually can’t be heard but frequencies below 20 Hz usually can’t be heard but

may feel like a rumble.may feel like a rumble.►Doppler effectDoppler effect

change in pitch or wave frequency due to a moving change in pitch or wave frequency due to a moving wave sourcewave source

either the source of the wave or the observer can be either the source of the wave or the observer can be movingmoving

Section 3Section 3

►MusicMusic sounds that are deliberately used in a regular patternsounds that are deliberately used in a regular pattern

►Natural frequencyNatural frequency frequency at which the a material vibratesfrequency at which the a material vibrates

►ResonanceResonance the ability of a medium to vibrate by absorbing the ability of a medium to vibrate by absorbing

energy at its own natural frequencyenergy at its own natural frequency

► SoundSound qualityquality differences among sounds of the same pitch and differences among sounds of the same pitch and

loudnessloudness

► Fundamental frequencyFundamental frequency the main tone played and heardthe main tone played and heard

►OvertoneOvertone vibration with a frequency that is a multiple of the vibration with a frequency that is a multiple of the

fundamental frequencyfundamental frequency

►Musical instrumentsMusical instruments devices used to make musical soundsdevices used to make musical sounds

► StringsStrings instruments in which sound is produced by plucking, instruments in which sound is produced by plucking,

striking, or drawing a bow across tightly stretched striking, or drawing a bow across tightly stretched stringsstrings

►BrassBrass andand woodwindswoodwinds air vibration in a air vibration in a resonatorresonator with the pitch determined with the pitch determined

by the length of the vibrating tube of airby the length of the vibrating tube of air

ResonatorResonator►Hollow chamber that amplifies soundHollow chamber that amplifies sound

► PercussionPercussion instrumentsinstruments produce sound by being struck, shaken, rubbed, or produce sound by being struck, shaken, rubbed, or

brushed.brushed.

►BeatsBeats pulsing vibration in loudnesspulsing vibration in loudness

Section 4Section 4

►Uses of soundUses of sound entertainment, warning signals, informationentertainment, warning signals, information

►AcousticsAcoustics study of sound, which can prevent excessive study of sound, which can prevent excessive

reverberation and create good listening environmentsreverberation and create good listening environments

► EcholocationEcholocation process of locating objects by sending out sounds and process of locating objects by sending out sounds and

interpreting the waves reflected backinterpreting the waves reflected back

► SonarSonar uses reflection of underwater sound waves to locate uses reflection of underwater sound waves to locate

objectsobjects

►Ultrasound wavesUltrasound waves used to diagnose, monitor & treat many medical used to diagnose, monitor & treat many medical

conditionsconditions Can produce images of internal structures for detection Can produce images of internal structures for detection

of medical problemsof medical problems Can treat medical problems such as kidney or gallstonesCan treat medical problems such as kidney or gallstones