Chapter 21probe


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Chapter 21probe

  1. 1. Chapter 21: Sound Pages 532 - 557
  2. 2. • Sound is a form of energy produced by the vibration of matter. • Sound is a compressional or longitudinal wave • Sound is transmitted through solids, liquids, and gases.
  3. 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. 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. 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. 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. 7. The denser the medium, the faster sound will travel. The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound. Sound travels through different media. We hear sound which usually travels through air. Sound travels through other media as well, such as water and various solids. Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas.
  8. 8. Parts of the ear • Outer ear: pinna • Ear canal • Ear drum: tympanum –Vibrates the ear drum
  9. 9. • Middle ear: three small bones –Anvil –Hammer –Stirrup • Inner ear –Cochlea: filled with fluid •Hair-like nerve endings •Auditory nerves
  10. 10. Brain • Damage done to the hairs causes permanent hearing loss. The hairs never grow back.
  11. 11. B. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
  12. 12. 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
  13. 13. FREQUENCIES YOU CANNOT HEAR •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
  14. 14. Human Hearing • Intensity – volume of sound – depends on energy (amplitude) of sound wave – measured in decibels (dB)
  15. 15. Human Hearing 70 80 100 110 120 40 18 10 0 DECIBEL SCALE Above 120 dB can cause hearing loss
  16. 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. 17. What is the Doppler Effect? The Doppler Effect is the apparent change in frequency detected when the sound is moving relative to the hearer.
  18. 18. Reflection of Sound Waves • Echoes • Echolocation: process using reflected sound waves to find objects – Bats – Whales – SONAR – Ultrasonography
  19. 19. Seeing with Sound • Ultrasonic waves - above 20,000 Hz Medical Imaging SONAR “Sound Navigation and Ranging”
  20. 20. What is sonar? Sonar is a system that uses the reflection of underwater sound waves to detect objects. This has been used to find sunken ships and schools of fish.
  21. 21. Diffraction • Bends of waves around or through a barrier Examples: 1. Thunder 2.Someone in the hallway on the other side and we can hear them.
  22. 22. Constructive - louder D. Interference • Interference – the ability of 2 or more waves to combine to form a new wave Destructive - softer
  23. 23. D. Interference • Beats – variations in sound intensity produced by 2 slightly different frequencies – both constructive and destructive interference occur
  24. 24. Interference –The effects caused by 2 or more waves. •Ex. Several instruments produce interference in a band.
  25. 25. 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
  26. 26. Sound Barrier and Sonic Booms
  27. 27. 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.
  28. 28. Resonance • Resonance – special case of forced vibration – object is induced to vibrate at its natural frequency
  29. 29. Harmonics • Fundamental – the lowest natural frequency of an object • Overtones – multiples of the fundamental frequency
  30. 30. • Examples –Fundamental – 100 Hz –1st Overtone – 200 Hz –2nd Overtone – 300 Hz
  31. 31. Music vs. Noise • Music – specific pitches and sound quality – regular pattern • Noise – no definite pitch – no set pattern
  32. 32. Acoustics • Acoustics – the study of sound • Reverberation – echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.
  33. 33. Acoustics