SOUND SOUND

intro

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Remember:Remember: Waves Waves

transport transport ENERGYENERGY

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Sound WavesSound Waves•Sound Waves are Compressional

waves.• The vibrations of the molecules are

parallel to the direction of the wave.

•Produced by the compressions and rarefaction of matter.

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Sound Wave Propagation

•Sound is produced by a Sound is produced by a vibrating object.vibrating object.

• As one individual particle is disturbed, it transmits the disturbance to the next interconnected particle.

• This disturbance continues to be passed on to the next particle.

• The result is that energy is transported without the actual transport of matter.

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Clip

• When a sound wave reaches the ear, a series of high and low pressure regions hit the eardrum.

• The arrival of a compression or high pressure region pushes the eardrum inward; the arrival of a low pressure regions serves to “pull” the eardrum outward.

• The continuous arrival of high and low pressure regions sets the eardrum into motion. Video

ClipEardrum

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Frequency and Frequency and PitchPitch•The frequency of a sound

wave determines the pitch.

•Pitch is the highness or lowness of a sound.

•The higher the frequency…the higher the pitch.

• Clip

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• Sound waves below 20 Hz are called infrasonic.

• Sounds waves above 20,000 Hz are called ultrasonic.

• Range of Human Hearing is from about 20 Hz –20,000 Hz

Low PitchLow Pitch

High High PitchPitch

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BioacousticsBioacoustics • is a branch of science concerned

with the production of sound and its effects on living systems.

• Animals that generate “infrasound” include elephants, whales, alligators, hippos, rhinos, giraffe, lions, tigers and several birds. (whale)

• Animals that generate “ultrasound” include Dolphins, bats, many birds and insects.

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EcholocationEcholocation•Bats send out sound waves using their mouth or nose.  

•When the sound hits an object an echo comes back.

•They can the distance between themselves and the object  

•They can identify an object by the sound of the echo.

• They can even tell the size, shape and texture of  a tiny insect from its echo.  

•Most bats use echolocation to navigate in the dark and find food. VIDEO

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Animal Animal CommunicatioCommunication With Soundn With Sound

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Other uses of sound wavesSonar

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Speed of SoundSpeed of Sound•Speed depends upon how fast

one particle can transfer its motion to another particle.

•Remember: Sound waves are mechanical waves.

•Speed of sound depends on the –medium–Temperature

•Why?

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•Video Clip

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Faster in denser materials

LoudnessLoudness• Depends on the amplitude.

Larger A means more pressure.• Remember: A is measure of the

amount of energy in the wave.• Sound level is measured in

Decibels.

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Common Sounds in DecibelsSound Decibel Level

Listener's Perception

Whisper 10 Barely Audible

Quiet Conversation 30 Faintly Heard

Average Office 50 Moderate Level

Summer Nocturnal Insects

60 Moderate Level

Noisy Office 70 Loud

Average Street Traffic 85 Very Loud

Jackhammer 100 Extremely Loud

Jet Aircraft Taking Off 120 Physical Pain

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Sound Activity

• All sound consists of a waves.• If you add 2 waves together that

are going in the same direction, and if those waves are in phase--that is, the peaks and valleys of the waves line up--then the amplitude or height of the waves will double.

• Constructive InterferenceConstructive Interference

Wave Interactions2323

• If you add 2 waves that are going in the same direction, and if those waves are completely out of phase--that is, the peaks of one line up with the valleys of the other--then the amplitude or height of the waves cancel each other out.

• Waves out of phase will cancel each other

Destructive InterferenceDestructive Interference

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Video Video ClipClip

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Echo vs. Reverberation • Sound waves

can be reflected• A reverberation

is perceived when the reflected sound wave reaches your ear in less than 0.1 second after the original sound wave.

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Tacoma Tacoma Narrows Bridge Narrows Bridge

CollapseCollapse

(Nov.7th 1940)

Galloping Galloping GertieGertie On a day of rather high winds, Gertie took on a 30-hertz transverse vibration (like sending waves down a rope by moving the end up and down) with an amplitude of 1½ feet! It later took on a twisting motion of about 14 hertz and quickly tore itself in two.

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Doppler Doppler EffectEffect• Variation in the

perceived pitch of a sound due to a moving sound source.

• “bunches up “ in front of the source

• Spreads out behind the source

Website

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Web Site Website

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•a "sonic a "sonic boom" is the boom" is the sudden onset sudden onset and release of and release of pressure after pressure after the buildup by the buildup by the shock the shock wavewave

•ExampleExample

Sonic BoomSonic Boom3030

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Click on the Picture3232

This picture shows a sonic boom created by the THRUST This picture shows a sonic boom created by the THRUST SSC team car as it broke the land speed record (and also SSC team car as it broke the land speed record (and also

broke the sound barrier on land).broke the sound barrier on land).

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““What’s wrong What’s wrong (or right) with (or right) with

these movies?”these movies?”

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Thanks to:• http://asa.aip.org/

• http://www.animalvoice.com/Links.htm

• http://www.indiana.edu/~emusic/acoustics/frequency.htm

• http://www.museumca.org/caves/onli_echo.html • http://www.everythingdolphins.com/SoundsPG.htm

• http://electron9.phys.utk.edu/phys135d/modules/m10/sound.htm