1. Waves

2. Waves Definition of wave
A disturbance that transfers energy through matter or space
“Disturbance”-a change from a normal state

3. Periodic or Harmonic Motion
Motion that repeats itself in the same amount of time
One repetition of motion called a cycle
Examples?
What does graph look like?

4. Periodic or Harmonic Motion
Amount of time to complete cycle called a period (T)
Frequency (f) is how many complete cycles occur in one second
T = 1/f or f =1/T
Amplitude is the amount of displacement from rest

5. Graphing harmonic motion

6. Graphing Harmonic Motion

7. Homework
Complete Harmonic Motion Worksheet

8. Waves demonstrate harmonic motion
Wave movement through matter
Particles move
Particles return to original position (location)

9. Types of Waves Based on particle motion in wave 2 types Transverse
Longitudinal

10. Wave Type-Transverse Particle motion perpendicular to wave direction

11. Wave Type-Transverse Particle motion perpendicular to wave direction

12. Parts of a Transverse Wave

13. Examples of Transverse Waves
Shaking a string
Ocean waves
Ripples on a pond
“Stadium” or human wave
Electromagnetic (radio, light, micro ect…)

14. Wave Type-Longitudinal
Particle motion in direction of wave

15. Wave Type-Longitudinal
Particle motion in direction of wave

16. Parts of a Longitudinal Wave
Particle motion in direction of wave

17. Examples of Longitudinal Waves
Sound waves
Oscillating springs

18. Sound waves are longitudinal waves

19. Represent longitudinal waves as transverse waves
Particle displacement in a longitudinal wave can be graphed as a transverse wave
Particle motion from rest graphed as amplitude

20. Sound Waves Sound waves move vibrational energy through matter
Sound waves are longitudinal waves

21. Wave Properties Common Characteristics of Wave
Length
Height
Frequency (how often they occur)
Period (how long to make 1 cycle)
Speed
All Characteristics of Waves Can Vary

22. Wave Characteristics
Wavelength (λ)-the distance between repeating parts of a wave
Trough to trough
Peak to Peak
Rarefaction to Rarefaction
Compression to compression
- Or any other repeating part

23. Wave Characteristics
Wave amplitude (height)-the maximum displacement from the undisturbed position of the medium to the top of a crest or bottom of a trough

24. Check Your Understanding Transverse Waves
The wavelength of the wave in the diagram above is given by letter ______.
The amplitude of the wave in the diagram above is given by letter _____.

25. Check Your Understanding Transverse Waves
Indicate the interval which represents one full wavelength.

26. Wave Characteristics
The frequency (f) of a wave is the number of complete waves (cycles) that pass the observer in a given time.
Hertz is the unit of frequency, and just means how many cycles (peaks) per second.

27. Wave Characteristics
The period (T) of a wave is the time for a wave to make one complete cycle (peak to peak).
The period is related to the frequency by the following equation f=1/T

28. Wave Characteristics
The speed (v) of a wave is the how fast the wave is moving
distance the wave travels in a certain amount of time.

29. Wave Characteristics
The relationship between the speed, frequency, period and wavelength
Example:
2 waves each second (i.e. frequency = 2 Hz)
the period is equal to 1/f = ½ second
the distance between the waves as 25 cm: this is the wavelength.
In 0.5 s, waves move 25 cm, so we can find the speed using:
speed= v = λ x f = 25 x 2 = 50 cm/sec OR
speed = v = λ x 1/T = 25 x (1÷ ½) = 50 cm/sec

30. Homework
Complete Wave Worksheet

31. Factors Affecting the Speed of Sound
Sound waves require matter to travel
No particles to compress = no waves = no sound
Speed of sound depends on matter or medium
Speed does not depend of the source
Factors that affect the speed of sound include:
Temperature of medium
Elasticity of medium
Density of medium

32. Speed of Sound Temperature Affects
Temperature changes affect sound speed more in gases than solids or liquids
Particles spaced apart in gases
Temperature affects spacing of particles in gases (Charles & Boyles Gas Laws)
Temperature
High temperature air = higher sound speed
Low temperature air = lower sound speed
Heat and sound = kinetic energy

33. Speed of Sound Elasticity
Elasticity = The tendency of an object to return to its original shape once the forces are no longer applied.
Phases of matter have great effect on elasticity of matter
Greater elasticity = Greater speed of sound
vsolids > vliquids > vgases

34. Speed of Sound Density Less effect on speed of sound than elasticity
Within a single phase of matter = greater impact
Density = mass/volume
Within a single phase of matter
Greater density = lower speed of sound
Mass of heavier particles are harder to move
Greater density = Greater inertia

35. Speed of Sound Materials Material Speed of Sound (m/s) Iron 5890 Lead
The speed of sound varies through different materials
Material
Speed of Sound (m/s)
Iron
5890
Lead
1960
Water
1479
Ice
3980
Air
330

36. Sonic Boom
When an object travels faster than the speed of sound it breaks the “sound barrier”
Waves all traveling at same speed, pile up on each other as plane pushes them together
Result is a “sonic boom”

37. Properties of Sound Intensity-measure of sound’s amplitude
Related to loudness, but loudness is subjective
Intensity measured in decibels (dB)
Increase in 10 dB results in sound that is twice as loud
Source
Intensity Level (dB)
Threshold of hearing (TOH)
Rustling leaves 10
Whisper 20
Normal conversation 60
Busy street traffic 70
Vacuum cleaner 80
Rock concert
110
Threshold of pain
130
Military jet takeoff
140
Eardrum perforation
160

38. Properties of Sound Frequency and Pitch
Frequency is number of waves in a certain amount of time
Frequency is measured in Hertz (Hz)
Pitch is related to frequency, describes how high or low the sound is. Pitch is subjective.
Pitch is the sensation of frequencies
High frequency = high pitched sounds
Low frequency = low pitched sounds

39. Human Hearing and Frequency
Humans can hear frequencies ranging from 20-20,000 Hz
Ultrasound are sound waves with frequencies above the human hearing range

40. Properties of Sound Sound Quality is referred to Timbre
Differences in timbre allow listeners to hear not only the difference between an oboe and a flute, but also the difference between two different flutes, even if both flutes are playing notes at the same frequency and amplitude

41. Properties of Sound Descriptions related to timbre Warm Mellow
Resonant
Dark or Bright
Heavy or Light
Flat
Having much, little, or no vibrato
Descriptions related to timbre
Reedy
Brassy
Clear
Rounded
Piercing
Strident
Harsh

42. Properties of Sound Doppler Effect
The observed effect between an observer and a sound source when one is moving relative to another
distance decreasing → perceived frequency (pitch) is increased
distance increasing → perceived frequency (pitch) is decreased

43. Doppler Effect Examples
(visual)
(visual and audio)

44. Wave Interactions
What is the result of collisions between waves and other waves or objects?
Waves transfer energy
Collisions results in energy transfer
Lose or gain energy

45. Wave Interactions Wave colliding with other waves cause interference
Principle of Superposition
Waves add (subtract) amplitudes (energy)
Two kinds of interference
Constructive (add)
Destructive (subtract)

46. Sound Wave Interactions
Interference
Constructive = increase in intensity
Destructive = decrease in intensity

47. Wave Interactions Constructive Interference
waves add to produce a new wave with larger peaks than either of the two original waves

48. Wave Interactions
Constructive interference

49. Wave Interactions Destructive Interference
waves add to produce a new wave with smaller peaks than either of the two original waves

50. Sound Wave Interactions
Interference

51. Phase shifts of waves
The phase shift tells an observer how out of sync two or more waves are
It gives the offset of the two waves
In phase = constructive interference
Out of phase = destructive interference

52. In phase and out of phase waves
Waves are completely out of phase
– destructive interference
Waves are completely in phase
– constructive interference

53. Sonic Boom Constructive interference of waves = sonic boom
Crack of a bull whip = sonic boom

54. Standing waves on a string

55. Harmonics of Standing Waves

56. Harmonics of standing waves

57. Homework
Complete Sound and Standing Waves Worksheets

58. Sound Wave Interactions
Resonance
Is the vibration of an object at its natural frequency
This frequency depends on the length of the object

59. Sound Wave Interactions
Resonance
Tuning forks and bells vibrate at their natural frequency
All objects have a frequency that they resonate at
When waves bounce back and forth on themselves within the object and constructively interfere, we call it resonance.

60. Sound Wave Interactions
Resonance Examples
(Movie of Tacoma Narrows Bridge)

61. Wave Interactions
Wave colliding with objects have following 3 outcomes
Refraction
Reflection
Diffraction

62. Wave Interactions REFLECTION
Reflection is when waves bounce from a surface back toward the source.
A mirror reflects the image of the observer.
None of the characteristics of a wave are changed by reflection.
No change-wavelength, frequency, period
Change-wave direction

63. Wave Interactions REFLECTION Law of Reflection
Angle of Incidence = Angle of Reflection

64. Sound Wave Interactions
Reflection
When a sound wave in air reaches the surface of another material, some of the sound is reflected off the surface and some passes into the material (transmitted)

65. Sound Wave Interactions
Reflection
Smooth surfaces best
more sound will be reflected from a smooth wall made of mud than a pile of dirt
reason is that the rough or porous surface allows for many reflections, resulting in more absorption and less reflection

66. Sound Wave Interactions
Reflections
Echoes
When sound reflects off a smooth flat surface, an echo or reproduction of the sound can be heard.
Echoes are more noticeable if the surface is far enough away to allow for a time-lag between when the sound is made and when it is hear. (~0.1 seconds)

67. Echo Problem
If the speed of sound in air is 340 m/sec and you hear an echo 1 sec after you yell, how far away is the reflector?
Remember that that the sound wave has to travel there and back so
V=total distance/time
340m/sec= total distance/1 sec
Total distance = 340 m/sec x 1 sec
= 340 m
Distance to reflector = total distance ÷ 2
= 170 m

68. Wave Interactions DIFFRACTION
Diffraction is the bending of waves when they collide with the edges of objects.
All waves diffract.
We can hear around a corner because of the diffraction of sound waves.

69. Sound Wave Interactions
Diffraction
Because sound waves diffract, you can hear around corners and from behind obstacles

70. Wave Interactions REFRACTION
Refraction is when waves are deflected when passing from one medium to another
The wave generally changes direction.

71. Sound Wave Interactions
Refraction is the bending of waves when they enter a medium where their speed is different.

72. Sound Wave Interactions
Refraction-Effect
Cool air-lower speed, Warm air-higher speed
Normally, only the direct sound is received. But refraction can add some additional sound, effectively amplifying the sound. Natural amplifiers can occur over cool lakes.

73. Homework
Complete Wave Interactions Worksheet

74. The End