03-12-08 - sound
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TRANSCRIPT
SOUNDSOUND a range of a range of compressioncompression
wavewavefrequencies to which thefrequencies to which thehuman earhuman ear is sensitive is sensitive
TheThe audio spectrumaudio spectrumextends from approximatelyextends from approximately
20 Hz20 Hz toto 20,000 Hz20,000 Hz..
Sounds are produced bySounds are produced byvibrating mattervibrating matter
1. reedsreeds
2. stringsstrings
3. membranesmembranes
4. air columnsair columns
Sound is a Sound is a mechanical wavemechanical wave (longitudinal). (longitudinal). It will It will notnot travel through a vacuum. travel through a vacuum.
Sounds possess the Sounds possess the characteristicscharacteristics
and and propertiesproperties that thatare common to allare common to all
waves.waves.
Just like all longitudinal (compression)Just like all longitudinal (compression)waves, sound waves possess awaves, sound waves possess a
velocityvelocity, , frequencyfrequency, , wavelengthwavelength,,phasephase, , periodperiod, and , and amplitudeamplitude..
Sound waves also Sound waves also reflectreflect, , refractrefract,,diffractdiffract, and , and interfereinterfere..
The velocity of sound in air The velocity of sound in air dependsdepends
on the air temperature. The speed on the air temperature. The speed ofof
sound in dry air is sound in dry air is 331.5 m/s331.5 m/s at at 0 0 ººCC.. This speedThis speed
increasesincreaseswith with
temperature: temperature: about about 0.6 m/s0.6 m/sfor every 1 for every 1 ººC C increase in increase in
temperature.temperature.
Sound generally travels Sound generally travels fastestfastest
in solids and slowest in in solids and slowest in gases,gases,
but there are some but there are some exceptions.exceptions.
Medium Velocity (m/s) Medium Velocity Medium Velocity (m/s) Medium Velocity (m/s)(m/s)
Air 330 Carbon dioxide 260Air 330 Carbon dioxide 260
Helium 930 Hydrogen 1270Helium 930 Hydrogen 1270
Oxygen 320 Water 1460Oxygen 320 Water 1460
Sea water 1520 Mercury 1450Sea water 1520 Mercury 1450
Glass 5500 Granite 5950Glass 5500 Granite 5950
Lead 1230 Pine wood 3320Lead 1230 Pine wood 3320
Copper 3800 Aluminium 5100Copper 3800 Aluminium 5100Sound waves travel faster in solids and liquidsThe speed of sound in solids (earth) is 3,350 m/sThe speed of sound in liquids (water) is 1,525 m/s
The human ear relatesThe human ear relatesamplitudeamplitude to to
loudnessloudnessandand
frequencyfrequency to topitchpitch..
Listen to various sound frequencies Listen to various sound frequencies here and mixtures of sound waves here.and mixtures of sound waves here.
Click Click here to make your own sound waves.You should hear that frequencyYou should hear that frequency
relates to pitch and amplitude relatesrelates to pitch and amplitude relatesto loudness (for a given frequency).to loudness (for a given frequency).
Sound waves refract.Sound waves refract.
Click Click here to view a simulationof the refraction of sound of the refraction of sound
waves.waves.
The The interferenceinterference of sound of soundwaves can cause “beats”waves can cause “beats”
Click Click here and here to run computersimulations of interfering sound wavessimulations of interfering sound waves
that result in discernable beats.that result in discernable beats.
View interference “beats” View interference “beats” here and here.
What are evidences of What are evidences of reflectionreflectionand the and the diffractiondiffraction of sound? of sound?
All objects have a naturalAll objects have a natural
frequency of vibration.frequency of vibration.
ResonanceResonance - the inducing- the inducingof vibrations of a naturalof vibrations of a naturalrate by a vibrating sourcerate by a vibrating source
having the same frequencyhaving the same frequency
““sympathetic vibrations”sympathetic vibrations”
Famous Bridge Collapses:Famous Bridge Collapses:Evidences of Resonance?Evidences of Resonance?
Tacoma Narrows link Tacoma Narrows link Others linkOthers link