1. Waves and Sound

2. Waves
Are disturbances that move through an empty space or through medium (atoms and molecules)
Waves transfer energy without transferring matter.
Particles of medium move in simple harmonic motion
Mechanical: Through a medium
Electromagnetic: Through empty space

3. Two types of mechanical waves that require a medium
Caused by a disturbed medium and move by action reaction of particles
ex: water wave, sound
A medium is matter particles like gas (ex. air), liquid (ex. Water), and solid (ex. earth)
Two types of mechanical waves that require a medium
Transverse Wave
Longitudinal Wave

4. Electromagnetic wave: Move through empty space (no medium)
Created by moving electrons
Ex. radio waves, microwaves, light
Types Electromagnetic Waves
Through empty space

5. In order to start and transmit a wave, a source of disturbance (vibration) and a disturbed medium or electron are required.
Mechanical caused by vibrating particles
Electromagnetic by vibrating electrons

6. Section 2: Types of Mechanical Waves
Transverse
Longitudinal

7. Wave particles move perpendicular to the direction the wave travels
Perpendicular to the direction of travel
Direction of travel
Transverse Wave:
Wave particles move perpendicular to the direction the wave travels
Ex. vibrating string of a musical instrument

8. Crest- highest point on a transverse wave
Trough- lowest point on a transverse wave
Equilibrium position- center around which simple harmonic motion occurs
Amplitude- from the equilibrium position to the crest or trough

9. Particles vibrate parallel to the direction the wave travels
Longitudinal Wave:
Particles vibrate parallel to the direction the wave travels
ex. sound wave
Direction of travel
Particles vibrate parallel to the direction of travel

10. Parts of a Longitudinal Wave:
Compression- point where the particles are closest together
Rarefaction- point where the particles are furthest apart
Rarefaction
Compression

11. Intro Questions What do all waves transfer? What don’t waves transfer?
What starts a wave?
Pick between the following choices and answer this correctly:
4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

12. Section 3: Relationship between Wavelength, Frequency and Wave Speed

13. Mechanical wave velocity
The velocity of the wave depends on the material it is traveling through.
For a mechanical wave, which needs a medium, the more elastic the medium the faster the wave.
Slower  Fastest
Gas  liquid  solid

14. Electromagnetic Wave Velocity
The velocity of the wave depends on the material it is traveling through.
For a electromagnetic wave, which can travel without a medium like in space, the more elastic the medium gets in the way and slows down the wave.
Slower  Fastest
No medium (space)  gas  liquid  solid

15. velocity ( v ): speed of the wave.
unit: m/s (meter/second)
frequency ( f ): vibrations per second of the wave
unit: Hz (hertz)
wavelength ( ג ): length of one wave pulse
unit: m (meter)

16. Lets revisit our old equation
What is the velocity of an object that moves 25 meters in 3 seconds?

17. Lets revisit our old equation
What is the velocity of an object that moves 25 meters in 3 seconds?

18. Now lets look at the new equation you can use as well.
old
V= ___ d t
Example what is the velocity of a wave that has a frequency of 3Hz and a wavelength of 5m?

19. Now lets look at the new equation you can use as well
old
V= ___ d t

20. Now lets look at the new equation you can use as well
old
V= ___ d t

21. Now lets look at the new equation you can use as well
old
V= ___ d t

22. Now lets look at the new equation you can use as well
old
V= ___ d t

23. Relationship between frequency and wavelength when wave velocity is the same.
Wavelength and frequency are inversely related
As frequency goes up the wavelength gets shorter (assuming no change in velocity)
Click for animation

24. Period (T) vs. Frequency (f)
Period (T) – seconds for one cycle
(unit s)
Frequency (f) – cycles for one second
(unit Hz)
If you know one you can solve for the other

25. Example 1 Wave Math
The frequency of a wave is 560 Hz. What is its period?

26. The frequency of a wave is 560 Hz. What is its period?

27. Example 2 Wave Math
A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequency b) period

28. A girl floats in the ocean and watches 12 wave crests pass her in 46 s
A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequency b) period

29. Example 3 Wave Math
The period of a wave is 0.044s. How many cycles will the energy source make in 22s?
cycles
second

30. The period of a wave is 0.044s. How many cycles will the energy source make in 22s?

31. Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude?
0.33m
0.24m

32. Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude?
0.33m
0.66m

33. Example 4 Wave Math
A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude?
0.12m
0.24m

34. Example 5 Wave Math
What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

35. Example 5 Wave Math
What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

36. Example 6 Wave Math
You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. What is the frequency? B. What is the period? C. What is the velocity?

37. Example 6 Wave Math
You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. what is the frequency B. What is the period C. Velocity

38. Section 4: The Pendulum

39. Movement from a to c and back to a is one complete cycle or vibration
Pendulum- a weight on a string that moves in simple harmonic motion (swings back and forth).
Movement from a to c and back to a is one complete cycle or vibration
This is the equilibrium position.
decelerating
accelerating

40. Simple harmonic motion- vibration about an equilibrium position
Constant back and forth motion over the same path.
15º is the maximum angle for a pendulum to have simple harmonic motion where our equations work

41. Masses do not effect the period in simple harmonic motion.
What effects the period:
L – length of the string
g – acceleration due to gravity

42. Example 7
A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

43. Example 7
A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

44. Example 8
Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch.

45. Example 8
Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch.

46. Example 9
A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion?

47. Example 9
A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion?

48. Example 10
If a pendulum is shortened, does the period increase or decrease? What about its frequency?

49. Example 10
If a pendulum is shortened, does the period increase or decrease? What about its frequency?
Period decreases
Frequency increases

50. Finish section 4 of the worksheets and turn in your packet today when you are done.
Work on something else quietly while you wait for everyone to complete their work

51. Section 5: Wave Interactions
Reflection
Refraction
Diffraction
Interference

52. Reflection:
The turning back of a wave at the boundary of a new medium (bouncing back)
Ex: light off a mirror, or sound echo
Incident wave- incoming

53. Waves reflected off a fixed boundary are inverted.
A fixed boundary is one not allowed to move

54. Waves reflected off a flexible boundary are upright.
A flexible boundary is allowed to move

55. Angle of reflection of a wave equals angle of incidence θr = θi
Law of Reflection:
Angle of reflection of a wave equals angle of incidence
θr = θi
Normal line – line perpendicular to surface being reflected off of. θi
Normal line θr

56. Example 11
Draw the reflected wave, labeling angles of incidence, reflection, and the normal line
35º

57. Wave front:
Portion of a medium’s surface in which particles are in phase
Particles in phase are in the same stage of their vibration.

58. Refraction:
the bending of a wave path as it enters a new medium obliquely (indirectly)
caused by difference in speed of the new medium
fast to slow – bends toward the normal line
slow to fast – bends away from normal

59. Refraction
Light travels slower in water

60. Example 13
Draw the refracted wave, labeling the normal line, angle of incidence, and angle of refraction.
Normal line θi
Slow θr
Fast

61. Diffraction:
Spreading of waves around edges or through an opening of a boundary
Is greatest when size of opening is smaller than wavelength

62. Principle of Superposition:
Displacement of a medium by two or more waves is the algebraic sum of the displacements of the waves alone

63. Interference:
Result of the superposition of two or more waves
constructive- (crest meets crest or trough meets trough) amplitudes add
destructive – (crest meets trough) amplitudes subtract
Only temporary as paths cross

64. Constructive interference
Only temporary as paths cross

65. Destructive interference
Only temporary as paths cross

66. Constructive and destructive interference in two sine waves

67. Example 14 (finish off the drawings)
Before
During
After
Constructive interference
Destructive interference

68. Wave Fronts Interfering
Nodal line
Lines of destructive
interference
Antinodal line
Lines of constructive
interference

69. Standing wave:
created by waves with same frequency, wavelength, and amplitude traveling in opposite directions and interfering.
consists of nodes (o amplitude) and antinodes (max amplitude)
produced by certain frequencies

70. Standing Waves Being Produced
Antinode
Node

71. Section 6: Sound

72. Sound waves are produced by a vibrating object
Sound waves are longitudinal mechanical waves.

73. Sound Frequency: Determines pitch
20 – 20,000 Hz are audible to an average person
Less than 20 Hz are infrasonic
Greater than 20,000 Hz are ultrasonic
Click for Frequency Modulator

74. Echolocation and Sonar
Sonar is simply making use of
an echo.
An echo is used to locate an
object.
When an animal or machine makes a noise, it sends sound waves into the environment around it.
Those waves bounce off nearby objects, and some of them reflect back to the object that made the noise.
Whales, Dolphins, Bats, and many more organisms use sound for locating prey and predators

75. Less than 20 Hz- Infrasonic

76. Generally between phases vsolids > vliquids > vgases
Sound Velocity
Largely depends on medium elasticity
Solids>liquids>gasses
Then depends on temperature
Faster at higher temperatures
Air (at 0ºC) v = 331 m/s and +/- 0.6 m/s per ºC
Generally between phases
vsolids > vliquids > vgases

77. Sound Velocity Equations
v = Tc
v = d/t
v = fλ

78. Interesting sound facts
Sound travels 15 times faster in the steel from a railroad track.
Sound travels 4 times faster in water
At sea level, the speed of sound is 340 m/s or 760 mi/hr. This is called mach 1.

79. The speed of sound will be the same for all frequencies under the same conditions.
Wavelength and frequency are inversely related
As frequency goes up the wavelength gets shorter 79

80. Example 15
What is the speed of sound at room temperature (22ºC)

81. What is the speed of sound at room temperature (22ºC)

82. Example 16
How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is -6.0 ºC?

83. How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is -6.0 ºC?

84. Example 17
If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

85. Example 17
If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

86. Example 18
A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

87. Example 18
A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

88. Example 19
On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

89. Example 19
On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

90. Section 7: The Doppler Effect

91. Doppler Effect
Change in pitch caused by relative motion of source and observer
Pitch increases as sound and observer approach (and vice versa)

92. Doppler Effect Problems
Frequency rises when its coming closer and lowers when moving away.

93. Example 20
Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

94. Example 20
Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

95. Example 21
Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

96. Example 21
Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

97. Example 22
A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

98. Example 22
A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

99. Intro
You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz.
What frequency would your parent hear you at if he/she could?
What frequency do you hear your parent’s car at?

100. You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz.
What frequency would your parent hear you at if he/she could?

101. You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz.
2. What frequency do you hear your parent’s car at?

102. CW/HW
Section 7 of Worksheet Packet

103. Section 8: Intensity and Perceived Sound

104. The property of sound waves associated with loudness is amplitude
The property associated with pitch is frequency

105. Section 9: Resonance and Music

106. Resonance in Music
Forced Vibration- The vibration of an object that is made to vibrate by another vibrating object.
Sympathetic vibrations- secondary vibrations caused by forced vibration of a first object.
Sounding board- part of an instrument forced into vibration to amplify sound

107. Example of creating forced vibrations to make a sound louder
Sounding board of a musical instrument.
Example: guitar makes a strings vibrations resonate

108. Resonance: Also called sympathetic vibrations
Dramatic increase in the amplitude of a wave when the frequency of an applied force matches the natural frequency of the object.

109. Resonance can be dangerous
Wind caused the Tacoma Narrows suspension bridge to vibrate at its natural frequency.
The amplitude of the vibrations caused too much strain on the bridge until it collapsed.

110. Difference between music and noise
Noise- a random mixture of a large number of sound frequencies
Music- Sound frequency or mixture of frequencies with a pattern

111. Percussion Instrument:
Musical sound produced by striking the object
Frequency depends on the mass of the object.
To raise the pitch- decrease the mass of the object.
Ex- drums, xylophone, bells

112. Stringed Instrument
Musical sound produced by plucking or blowing strings
Frequency depends on four factors
To raise pitch
1. decrease diameter of string
2. increase tension
3 decrease length
4. decrease density of string material
Examples: guitar, violin

113. Wind Instrument Musical sound produced by vibrating air column
Frequency depends mainly on length of air column
To raise pitch- decrease the size of the air column
Examples- oboe, flute

114. Standing Waves are formed in the instrument due to vibrations
When the natural frequency is hit the sound amplifies

115. Open Ended Wind Column Instrument
Must be nodes at both ends

116. Closed Ended Wind Column Instrument
There is an antinode at the closed end.
Count standing waves by including the return trip.

117. Acoustics- field of study related to sound
Acoustic designers try to maximize the quality of sound reaching the audience
Control the size, shape, and material used
They try and control the reflection

118. Two types of reflection with sound
Reverberation- If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged.
Echoes- A perceived second sound that arrives after the first has died out.
Echoes occur when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard.

119. Interference causes beats
Beats occur due to constructive and destructive interference between sounds with close but not exact frequencies.