1. Section 1 The Nature of Sound
Chapter 11 Sound
Section 1 The Nature of Sound

2. What causes sound? Every sound is produced by an object that vibrates
Example: Your voice
Your vocal cords make a vibration

3. Sound Waves These are compressional waves
Remember, in these types of waves there are both compressions and rarefactions
Figure 1 p. 322

4. The Speed of Sound
Sound waves can travel through a solid, liquid, or a gas
Sound waves cannot travel through empty space
For example: This is why on the Moon, astronauts must talk to each other via electronic communication equipment.

5. The Speed of Sound Sound waves cannot travel through empty space
For example: This is why on the Moon, astronauts must talk to each other via electronic communication equipment.

6. The Speed of Sound Air: 347 m/s Water: 1,498 m/s Aluminum: 4,877 m/s
Which do they travel through the fastest?

7. The Speed of Sound
Sound travels the fastest in solids b/c the particles are so close together.

8. Human Hearing
Your ears and brain work together to make sense of the different sound waves.
Involves four stages

9. How you hear:
Step 1:
Ear gathers the compressional waves

10. How you hear:
Step 2: The ear amplifies the waves

11. How you hear:
Step 3: The waves are converted to nerve impulses that travel to the brain

12. How you hear:
Step 4: The brain decodes and interprets the nerve impulses

13. Human Ear
Three sections: Outer ear, middle ear, and inner ear

14. Outer Ear Visible part of ear, ear canal, and eardrum
Visible part of ear: shaped to help catch sound waves

15. Outer Ear
Ear canal: 2-3 cm long; size of index finger; sound waves travel through here to eardrum
Eardrum: tough membrane; 0.1 mm thick
When sound waves hit the eardrum they cause it to vibrate.

16. Outer Ear Eardrum: tough membrane; 0.1 mm thick
When sound waves hit the eardrum they cause it to vibrate.

17. Middle Ear
What are the three tiny bones in your middle ear?

18. Middle Ear What are the three tiny bones in your middle ear? Stirrup
Anvil
Hammer

19. Middle Ear
These make a system that multiplies the force and pressure on a sound wave
This causes the sound wave to amplify and causes the “oval window” to vibrate.

20. Inner Ear
Contains the cochlea: spiral-shaped structure that contains liquid and tiny hair cells
The hair cells in the cochlea begin to vibrate and send nerve impulses through the auditory nerve to the brain.

21. Hear loss
When the tiny hair cells are damaged or destroyed your hearing will become damaged.
New research suggests that these hair cells may be able to repair themselves.

22. Section 2 Properties of Sound
Chapter 12 Sound
Section 2 Properties of Sound

23. Amplitude in Compressional Waves
Related to density of compressions and rarefactions

24. Low Amplitude Sound Waves
The particles are less compressed in a compression
The particles are less spread out in a rarefaction

25. High Amplitude Sound Waves
Particles are more compressed in a compression
Particles are more spread out in a rarefaction

26. Loud and Quiet Sounds
Loud sound waves carry more energy than quiet sound waves

27. Intensity
The amount of energy that passes through a certain area in a certain time

28. Intensity
When you turn down the volume on your radio the amount of energy is , meaning the intensity is also

29. Intensity
Determines how far away a sound can be heard

30. Intensity Low intensity = short distance
High intensity = long distance

31. Losing Intensity Farther a wave travels the less intense it becomes
Loses energy
*Think of a basketball after you drop it

32. Loudness
Human perception of intensity

33. Loudness and Intensity
Loud sounds have a high intensity
Quiet sounds have a low intensity

34. Loudness and Intensity
High intensity waves cause your eardrum to move back and forth farther
Also causes increased movement of the hair cells in inner ear
Result: You hear a loud sound!

35. How Loud is too Loud??
People have different loudness perceptions

36. Decibel Scale Unit for measuring sound intensity dB *p. 329
Faintest Sound = 0 dB (Whisper)
Pain Threshold = 120 dB (Rock Concerts)

37. Decibel Scale Faintest Sound = 0 dB (Whisper)
Pain Threshold = 120 dB (Rock Concerts)

38. Pitch
How high or low a sound seems
Related to the frequency of a wave

39. Pitch & Frequency High Frequency = fast vibrations = high pitch
Low Frequency = slow vibrations = low pitch

40. Ultrasonic Waves Sound frequencies above 20,000 Hz are ultrasonic
Humans can hear waves from frequency of 20 Hz- 20,000 Hz

41. Ultrasonic Waves Used in medical diagnosis and treatment
Used to locate underwater objects
Dogs can hear up to 35,000 Hz
Bats can hear higher than 100,000 Hz

42. Infrasonic Waves Frequencies below 20 Hz
You may feel these even though you cannot hear them
Examples:
Wind, Heavy Machinery, Earthquakes

43. Doppler Effect Change in pitch or frequency due to a moving object
Example: Racetrack
The car sounds louder as it approaches you and quieter as it moves away from you.

44. Chapter 12 Sound
Section 3 Music

45. Music vs. Noise Noise has random patterns and pitches
Music has specific patterns and pitches

46. Music
Sounds are deliberately placed in a certain, regular pattern

47. Natural Frequencies
Every material or object has a set of frequencies at which it vibrates
Called its
“natural frequency”

48. Natural Frequencies Depends on: Thickness 2. Length 3. Material
4. How tightly its stretched

49. Music and Resonance Sound of instrument is amplified by resonance
This causes the instrument to absorb energy and vibrate at its
natural frequency
Air makes the sound louder

50. Sound Quality
Differences among sounds of the same pitch and loudness

51. Sound Quality
Object could be made to vibrate at frequencies other than their natural frequency.
Makes sound waves with more
than one frequency.

52. Overtones You only hear one of many frequencies made by an instrument.
Not all frequencies are
the same intensity.

53. Overtones
Vibration whose frequency is a multiple of the fundamental frequency (the main tone played and heard)

54. Musical Instruments
What are some examples of musical instruments?

55. Musical Instruments
Strings: These instruments contain resonators (hollow chamber) to amplify the sound.

56. Musical Instruments Brass and Woodwinds
*Rely on vibration of air to make music
*Length of the vibrating tube of air determines the pitch of the sound

57. Musical Instruments Percussion
*Consists of a membrane that is stretched over a resonator.
*When membrane is struck, it causes the air inside to vibrate.
* Makes sound

58. Beats
These occur when sound waves of different frequencies combine.

59. Chapter 11 Sound
Section 4 Using Sound

60. Reverberations
Echoing effect
Produced by reflections
of sound

61. Reverberations Could ruin a concert or musical performance
Concert halls must be
designed to reduce the
effect of this

62. Acoustics The study of sound
Scientists and engineers who specialize in this design concert halls

63. Reducing Reverberation
Soft, porous materials reduce reverberation
Example:
Drapes, carpet, cushioned seats

64. Echolocation
Using sounds and sound waves to determine the location of an object
What animal uses echolocation?

65. Sonar
System that uses underwater sound waves to detect objects

66. Sonar
In 1988 this was used to locate the Central America, a ship that had disappeared 140 years ago in a hurricane near South Carolina’s coast. It contained gold estimated to be worth $1 billion dollars. It was found 2,400 m under water.

67. How Sonar Works First: Sound pulse is sent to bottom of ocean
Second: Sound wave is reflected when it hits something solid
Third: Underwater microphone ( hydrophone) picks up signal

68. How Sonar Works Finally: Speed of sound in water is known.
Distance of object is calculated by measuring time between when signal was sent and when it was received back.

69. Use of Ultrasonic Waves
Break up dirt build up in jewelry
Clean glassware in
chemistry
3. Medicine

70. Ultrasound in Medicine
Name one thing ultrasonic waves are used for in medicine.

72. Ultrasound Imaging
The ultrasonic sound waves are reflected off the targeted organs or tissues and they are used to produce electrical signals.
A computer converts these signals into video images (sonograms).

73. Ultrasound Imaging This type of imaging only works on soft tissue.
Hard tissue, bones, and air absorb the ultrasonic waves.

74. Treating with Ultrasound
Physicians now use ultrasonic sound waves to break up kidney stones.