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Chapter 21: Sound

Chapter 21: Sound. Pages 532 - 557. Sound is a form of energy produced by the vibration of matter. Sound is a compressional or longitudinal wave Ex. Spring Sound is transmitted through solids, liquids, and gases. Sound is transmitted better through solids and liquids. Why? More dense

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Chapter 21: Sound

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  1. Chapter 21: Sound Pages 532 - 557

  2. Sound is a form of energy produced by the vibration of matter. • Sound is a compressional or longitudinal wave • Ex. Spring • Sound is transmitted through solids, liquids, and gases.

  3. Sound is transmitted better through solids and liquids. Why? • More dense • Gases transmits sound a lot farther than a solid and liquid. Why? • Less dense; not as many particles to interfere.

  4. Sound • So what causes sounds to travel better through some substances and not others? • The greater the elasticity, the greater the speed. • The greater the density, the slower the speed. • The best conductors of sound are elastic substances.

  5. Sound can not be transmitted through a vacuum. • Sound needs a medium in order for it to be transmitted. • Radio waves can travel through a vacuum; no medium is needed. • This is why astronauts can use radio signals to talk in space.

  6. Speed of Sound • 344 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

  7. Parts of the ear • Outer ear: pinna • Ear canal • Ear drum: tympanum • Vibrates the ear drum

  8. Middle ear: three small bones • Anvil • Hammer • Stirrup • Inner ear • Cochlea: filled with fluid • Hair-like nerve endings • Auditory nerves

  9. Brain • Damage done to the hairs causes permanent hearing loss. The hairs never grow back.

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

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

  12. Ultrasonic: higher than 20,000 Hz Uses: clean jewelry, medical applications Infrasonic: lower than 20 Hz Found: in the atmosphere and in the crust when plates move; also an indication motion sickness Frequencies you cannot hear

  13. Human Hearing • Intensity • volume of sound • depends on energy (amplitude) of sound wave • measured in decibels (dB)

  14. Sound is measured in what? • Above 120 dB can cause hearing loss.

  15. Human Hearing DECIBEL SCALE 120 110 100 80 70 40 18 10 0

  16. Doppler Effect • Doppler Effect • change in wave frequency caused by a moving wave source • moving toward you - pitch sounds higher • moving away from you - pitch sounds lower

  17. Reflection of Sound Waves • Echoes • Echolocation: process using reflected sound waves to find objects • Bats • Whales • SONAR • Ultrasonography

  18. Medical Imaging SONAR “Sound Navigation and Ranging” Seeing with Sound • Ultrasonic waves - above 20,000 Hz

  19. Diffraction • Bends of waves around or through a barrier Examples: • Thunder • Someone in the hallway on the other side and we can hear them.

  20. Constructive - louder Destructive - softer D. Interference • Interference • the ability of 2 or more waves to combine to form a new wave

  21. D. Interference • Beats • variations in sound intensity produced by 2 slightly different frequencies • both constructive and destructive interference occur

  22. Interference • The effects caused by 2 or more waves. • Ex. Several instruments produce interference in a band.

  23. Cool Interference Examples: • The Sound Barrier: the point at which the source of a sound accelerates to the speed of sound • Sonic Booms: the explosive sound heard when a shock wave reaches your ears • 1st time sound barrier broken: Oct. 14, 1947 by Chuck Yeager (speed of sound is called Mach 1); so Mach 6 is going 6 times the speed of sound

  24. Sound Barrier and Sonic Booms

  25. Movie Clip of Breaking the sound barrier

  26. 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.

  27. Resonance • Resonance • special case of forced vibration • object is induced to vibrate at its natural frequency

  28. Harmonics • Fundamental • the lowest natural frequency of an object • Overtones • multiples of the fundamental frequency

  29. Examples • Fundamental – 100 Hz • 1st Overtone – 200 Hz • 2nd Overtone – 300 Hz

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

  31. Interference • Beats • variations in sound intensity produced by 2 slightly different frequencies • both constructive and destructive interference occur

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

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