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SOUND. SOUND. KEY TOPICS NATURE OF SOUND AUDIO SPECTRUM RESONANCE & FORCED VIBRATION INTERFERENCE REFLECTION & REFRACTION. SOUND. SOUND ANIMATION DEMO. SOUND. LONGITUDINAL WAVES ON A SLINKY DEMO. SOUND.

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SOUND

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SOUND


SOUND

  • KEY TOPICS

    • NATURE OF SOUND

    • AUDIO SPECTRUM

    • RESONANCE & FORCED VIBRATION

    • INTERFERENCE

    • REFLECTION & REFRACTION


SOUND

  • SOUND ANIMATION

  • DEMO


SOUND

  • LONGITUDINAL WAVES ON A SLINKY

  • DEMO


SOUND

  • SOUND IS THE COHERENT VIBRATIONS OF ATOMS OR MOLECULES IN SOLIDS, LIQUIDS AND GASSES.

  • INCOHERENT VIBRATIONS ARE CALLED HEAT.


ACTIVITY

  • SOURCES OF SOUND

  • SOUND MEDIA


SOUND

SOUND SPECTRUM

INFRASOUND < 20 HZ

  • AUDIBLE SOUND > 20 HZ

    • AND < 20 KHZ

DEMO

ULTRASOUND >20 KHZ


SOUND

  • The PHET simulator “SOUND” can be used to demonstrate sounds up to 1kHz.


ACTIVITY

  • HARRY’S SOUND SORT

  • SORTING SOUNDS


SOUND

  • THE SPEED OF SOUND IN AIR IS APPROXIMATELY

    • 330 m/s

    • 1000 ft/sDEMO

  • THIS IS ALSO DESIGNATED MACH 1

  • THE SPEED DEPENDS ON TEMPERATURE, PRESSURE AND HUMIDITY


SOUND

  • IF ONE SEES A LIHTNING FLASH AND 15 SECONDS LATER, HEARS THE THUNDER, THEN THE DISTANCE TO THE FLASH IS _______ MILES.

  • A. 3

  • B. 15

  • C. 1

  • D. 30


RESONANCE

  • VIBRATING AT A NATURAL FREQUENCY

  • ENERGY CAN BE TRANSFERRED EFFICIENTLY TO A VIBRATING OBJECT VIA RESONANCE.

    DEMO


RESONANCE

  • The Tacoma Narrows bridge collapse is one of the most dramatic examples of resonance.

  • DEMO


RESONANCE

  • RESONANCE IS USED TO PRODUCE MUSICAL NOTES WITH A DEFINITE FRQUENCY.

  • EXAMPLES OF VIBRATING OBJECTS

    • STRINGS

    • AIR COLUMNS

    • SURFACES (DRUMS)DEMO


ACTIVITY

  • Singing Rod

  • Wine Glass

  • Corrugated Horn


ACTIVITY

  • RUBBER BAND GUITAR

  • CHANGES IN FREQUENCY

  • CLIP NOTES


FORCED VIBRATION

  • VIBRATING AT A NON-RESONANT FREQUENCY

  • IT IS OFTEN APPLIED TO THE AMPLIFICATION OF SOUND


ACTIVITY

  • CHICKEN CLUCKER


MUSICAL SOUNDS

  • DIATONIC SCALE

    • POPULAR IN EARLY WESTERN EUROPEAN MUSIC (VOCAL)

    • AN OCTAVE CONTAINED THE FAMILIAR PATTERN OF

      • DO RE ME FA SO LA TI DO

      • C D E F G A B C

      • THE DO AT THE END OF THE OCTAVE HAD TWICE THE FREQUENCY OF THE DO AT THE BEGINNING

      • FREQUENCIES ARE WHOLE NUMBER RATIOS OF EACH OTHER


MUSICAL SOUNDS

  • EQUITEMPERED SCALE

    • THE FREQUENCY OF EACH NOTE IS OBTAINED FROM THE NEXT SMALLER NOTE BY MULTIPLYING BY THE TWELTH ROOT OF TWO (1.059463)

    • EACH OCTAVE HAS THIRTEEN NOTES

    • THE NOTES ARE

      • C C# D D# E F F# G G# A A# B C

      • THE SHARPS ARE THE BLACK KEYS ON A PIANO


ACTIVITY

  • NOTE BEATERS


SOUND INTERFERENCE

  • The PHET simulator “SOUND” can be used to show the superposition of sound from two different sources.


BEATS

  • THE INTERFERENCE OF SOUND FROM TWO DIFFERENT SOURCES

  • IT IS MOST NOTICEABLE WHEN THE FREQUENCY AND LOUDNESS OF THE SOUNDS ARE SIMILAR

  • THE BEAT FREQUENY IS CALCULATED BY TAKING THE DIFFERENCE BETWEEN THE TWO FREQUENCIES

    fb = fl - fs


ACTIVITY

  • BEATS WITH TWO TUNING FORKS


QUALITY

THE QUALITY OF A SOUND IS DETERMINED BY THE INTENSITY OF THE HARMONICS PRESENT.


QUALITY

The PHET simulator “FOURIER: MAKING WAVES” can be used to show how the quality can be changed by varying the harmonics present.


PITCH

  • THE AUDITORY PERCEPTION OF FREQUENCY


REFLECTION OF SOUND

  • REVERBERATION

    • RE-REFLECTED SOUND THAT OCCURS IN CONFINED AREAS SO THAT THE REFLECTED SOUND CAN NOT BE DISTINGUISHED FROM THE SOURCE

    • EXAMPLE - EMPTY ROOM


REFLECTION OF SOUND

  • ECHO

    THE SOUND IS THAT NORMALLY REFLECTED OUTSIDE OR IN LARGE ENCLOSED AREAS SO THAT THE REFLECTED SOUND CAN BE DISTINGUISHED FROM THE SOURCE.


SOUND REFRACTION

  • THE CHANGE IN THE DIRECTION OF TRAVEL OF A SOUND WAVE DUE TO CHANGES IN ITS SPEED.

  • IT IS OFTEN CAUSED BY TEMPERATURE DIFFERENCES IN THE AIR.


TOYS WITH SOUND

  • CAN YOU EXPALAIN HOW MUSICAL TOYS OR NOISE MAKERS PRODUCE OR CONTROL SOUND?


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