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~ Nature of Sound ~

~ Nature of Sound ~. 1. What is sound? 2. Human Hearing 3. Properties of Sound 4. Interactions of Sound 5. Sound Quality. I. WHAT IS SOUND?. I. WHAT IS SOUND?. A Sound wave is a LONGITUDINAL WAVE caused by vibrations of particles back and forth through a medium.

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~ Nature of Sound ~

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  1. ~ Nature of Sound ~ 1. What is sound? 2. Human Hearing 3. Properties of Sound 4. Interactions of Sound 5. Sound Quality

  2. I.WHAT IS SOUND?

  3. I. WHAT IS SOUND? • A Sound wave is a LONGITUDINAL WAVE caused by vibrations of particles back and forth through a medium. • Sound waves are mechanical waves and NEED A MEDIUM TO TRAVEL • Sound waves travel in all directions from the source

  4. II. Human Hearing

  5. II.Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea

  6. http://www.hearingusa.com/ears01.mov

  7. III. Properties of Sound

  8. A. SPEED OF SOUND • 345 m/s in air at 20°C • Depends on: • Type of medium • travels better through liquids and solids • can’t travel through a vacuum • Temperature of medium • travels faster at higher temps

  9. http://www.stmary.ws/highschool/physics/home/notes/waves/CharacteristicsPeriodicWaves.htmhttp://www.stmary.ws/highschool/physics/home/notes/waves/CharacteristicsPeriodicWaves.htm

  10. B. PITCH • Pitch • highness or lowness of a sound • depends on frequency of sound wave • human range: 20 - 20,000 Hz ultrasonic waves subsonic waves

  11. C. LOUDNESS • Loudness • volume of sound • depends on energy (amplitude) of sound wave • measured in decibels (dB)

  12. Loudness measured in Decibels DECIBEL SCALE 120 110 100 80 70 40 18 10 0

  13. D. DOPPLER EFFECT • Have you ever noticed how the sound of a police car siren changes as it moves past you? The changes in pitch you hear are due to a phenomenon known as the Doppler effect. Look at the illustration of the police car to answer these questions. • The police car has passed the woman standing on the sidewalk, but has not yet passed the man. Which observer hears the siren at a higher pitch—the woman or the man?

  14. D.DOPPLER EFFECT • Doppler Effect • change in wavelength due to the motion of the source. As the source moves, the waves become bunched up and the pitch (frequency) of the sound changes. • moving toward you - pitch sounds higher • moving away from you - pitch sounds lower

  15. Doppler Effect • http://www.fearofphysics.com/Sound/doppler.html

  16. Doppler Effect • http://www.colorado.edu/physics/2000/applets/doppler.html • http://www.pbs.org/wgbh/nova/universe/moving.html

  17. IV. INTERACTIONS OF SOUND Reflection Interference Resonance

  18. A. REFLECTIONS OF SOUND WAVES • Reflections of sound waves are called echos! • Sound waves reflect best off smooth, hard surfaces • ECHOLOCATION • USE OF REFLECTED SOUND WAVES TO FIND OBJECTS

  19. Medical Imaging SONAR “SoundNavigationRanging” Ultrasonic waves are used to see with sound using reflection! • Ultrasonic waves - above 20,000 Hz

  20. Constructive - louder Destructive - softer B. Interference • Interference • When 2 or more waves overlap

  21. SONIC BOOM • When a jet plane reaches the speed of sound, the sound waves in front of the jet combine by constructive interference. The result is a high density compression (high amplitude) compression called the sound barrier.

  22. WATCH THESE VIDEOS! • http://www.youtube.com/watch?v=-d9A2oq1N38&feature=related • http://www.youtube.com/watch?v=QjpikTn2qAk&feature=related

  23. C. RESONANCE • Forced Vibration • when one vibrating object forces another object to vibrate at the same frequency • results in a louder sound because a greater surface area is vibrating • used in guitars, pianos, etc.

  24. = Resonance = • Resonance • special case of forced vibration • object is induced to vibrate at its natural frequency • http://www.youtube.com/watch?v=17tqXgvCN0E

  25. = Resonance = “Galloping Gertie” The Tacoma Narrows Bridge Disaster http://www.youtube.com/watch?v=j-zczJXSxnw&feature=related Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.

  26. = Resonance = • Beats • variations in sound intensity produced by 2 slightly different frequencies • both constructive and destructive interference occur

  27. V. Sound Quality

  28. A. Music vs. Noise • Music • specific pitches and sound quality • regular pattern • Noise • no definite pitch • no set pattern

  29. Anechoic chamber - designed to eliminate reverberation. B. ACOUSTIC • Acoustics • the study of sound • Reverberation • echo effect produced by the reflection of sound

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