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BEHAVIOR OF

SOUND-REFLECTION - REFRACTION

-INTERFERENCE - RESONANCE-DOPPLER EFFECT

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REFLECTION OF SOUND

Sound wave bounces whena boundary is met.

A reflection of sound iscalled an echo.

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REFLECTION OF SOUND

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Hard and smooth materials reflectsound better.

Rough and soft materials have greaterability to absorb sound.

REVERBERATIONS multiplereflections

REFLECTION OF SOUND

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REFRACTION OF SOUND

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involves a change in the direction andspeed of waves as they pass from onemedium to another.

Warmer temperature- sound travelsfaster

Colder temperature- sound travelsslower

REFRACTION OF SOUND

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DIFFRACTION

Diffraction of sound is the bendingof sound wave through a small

opening.

Diffraction involves a change indirection of waves as they pass throughan opening or around a barrier in theirpath.

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INTERFERENCE OF SOUND

When two waves meet at a certainpoint.CONSTRUCTIVE INTERFERENCEDESTRUCTIVE INTERFERENCE

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Beats

When 2 tunes of slightly different frequencyare sounded together, fluctuations in theloudness of the combined sound is heard.

Periodic variation in the loudness of sound is

called beats.

Beats are produced due to interference.

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Beats

Constructive interference loud sound

Destructive interference soft sound

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NATURAL FREQUENCY

The frequency or frequencies at which

an object tends to vibrate with when hit,struck, plucked, strummed or somehowdisturbed is known as the naturalfrequency of the object.

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FORCED VIBRATION

The tendency of one object toforce another adjoining or

interconnected object intovibrational motion is referred toas a forced vibration .

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RESONANCE

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Simulation: Sympathetic vibration

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RESONANCE

occurs when two interconnected objectsshare the same vibrational frequency.

When one of the objects is vibrating, itforces the second object into vibrationalmotion.

The result is a large vibration.

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What do you observe in the sound that

you hear when an ambulance passes by?

fire truck train

http://nz.youtube.com/watch?v=imoxDcn2Sgohttp://nz.youtube.com/watch?v=lgKMencd3zEhttp://nz.youtube.com/watch?v=lgKMencd3zEhttp://nz.youtube.com/watch?v=imoxDcn2Sgo

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DOPPLER EFFECT

Waves formed by stationarysource.

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DOPPLER EFFECT

Waves formed by a moving source.

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DOPPLER EFFECT

HIGHFREQUENCY

LOWFREQUENCY

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DOPPLER EFFECT

Apparent change in thefrequency of soundobserved whenever the

source of waves ismoving with respect toan observer.

It was discovered byHans ChristianDoppler.

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Mathematical Proof

Source is moving away toward thelistener:

f = ___f___1- (v s / v)

Where:f= new frequency

f=original frequency of soundvs = Velocity of sourcev = velocity of sound

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Source moving away from the listener:

f = ___f___1+ (v s / v)

Where:f= new frequency f=original frequency of soundvs = Velocity of sourcev = velocity of sound

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SHOCK WAVES

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Shock waves

Are produced if the source actually moves atthe same speed as or faster than the waveitself can move.

Produced by an aircraft moving faster thanthe speed of sound.

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Sonic Boom

If a fast aircraft moves above you, you willhear a sonic boom

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Sonic Boom

The result of the piling up of compressionalwavefronts .These compressional wavefronts

pile up and interfere to produce a very highpressure zone.

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PROBLEM SOLVING

What is the speed of sound when thetemperature is 38 0 C?

Most people can detect frequencies as highas 20 000 Hz. Assuming the speed of soundin air is 345 m/s, determine the wavelength ofthe sound corresponding to this upper rangeof audible hearing.

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On a hot summer day, a pesky little mosquitoproduced its warning sound near your ear.The sound is produced by the beating of its

wings at a rate of about 600 wing beats persecond.a. What is the frequency in Hertz of the soundwave? b. Assuming the sound wave moveswith a velocity of 350 m/s, what is thewavelength of the wave

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Playing middle C on the piano keyboardproduces a sound with a frequency of 256Hz. Assuming the speed of sound in air is 345

m/s, determine the wavelength of the soundcorresponding to the note of middle C.

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Problem-solving

The siren of a police car at rest emits apredominant frequency of 1600 Hz. Whatfrequency will you hear if you are at rest and

the police car moves at 250m/s. a) towardyou b) away from you. If the surrounding airtemperature is 32 deg Celsius?

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