1. Vibrations and Waves Vibration—“a wiggle in time”
Wave—“a wiggle in space and time”; a disturbance that travels through a medium from one location to another location
Back and forth vibratory motion = oscillatory motion.
The oscillatory motion of a pendulum is an instance of simple harmonic motion.
Period—the time of a back and forth swing. (Time/vibrations)
Depends only on the length of the pendulum and the acceleration of gravity.
A pendulum makes 20 vibrations in 40 seconds. Calculate its period.
Period for the pendulum
40 seconds / 20 vibrations = 2 seconds

2. Wave Description
A pendulum swinging over a moving piece of paper will trace out a sine curve.
Wavelength—the distance between successive identical parts of the wave (crest to crest, for instance).
Frequency—how frequently a vibration occurs.
A complete back and forth vibration is one cycle.
Hertz (Hz)—the unit of frequency.
One cycle per second = 1 Hz
Two cycles per second = 2 Hz
“home”

3. Wave Motion The source of all waves is something that vibrates
The frequency of the vibrating source and the frequency of the wave it produces is the same.
If the frequency is known, then the period can be determined (and vice versa).
Frequency = 1/period
Period = 1/frequency
Waves transfer energy, not matter between two points.
The energy is carried by a disturbance in the medium, not by matter moving from one point to the other.

4. What do trials 1-5 tell you? What about trials 6-8?
The data convincingly show that wave frequency does not affect wave speed. An increase in wave frequency caused a decrease in wavelength while the wave speed remained constant.
What do trials 1-5 tell you?
What about trials 6-8?

5. Wave Speed
The speed of a wave depends on the medium through which it is moving.
Sound travels through air at ~ 330 m/s
Sound travels 4 times faster in water.
Wave speed = frequency x wavelength
v = fl
If they are produced at the same time, high frequency sounds (small wavelength) reach your ears at the same time as low frequency sounds (large wavelengths).
Wavelength is lamda

6. Wave recap "a wave is a disturbance moving through a medium.“
Medium could be water, air, a rope, a slinky and are distinguished by their properties (material, density, temperature, elasticity, ect)
These properties describe the material not the wave itself
Waves are distinguished from each other based on amplitude, frequency, wavelength

7. Wave speed
wave speed depends upon the medium through which the wave is moving. Only an alteration in the properties of the medium will cause a change in the speed.

8. CYU
TRUE or FALSE:
Doubling the frequency of a wave source doubles the speed of the waves.
FALSE!
The speed of a wave is unaffected by changes in the frequency.

9. Solve for wave speed

10. Solve for wave speed
3.5 m/s
2.5 m/s
2.1 m/s
2.2 m/s

11. CYU
As the wavelength of a wave in a uniform medium increases, its speed will ____
Decrease
Increase
Remain the same
As the wavelength of a wave in a uniform medium increases, its frequency will ____

12. CYU
As the wavelength of a wave in a uniform medium increases, its speed will ____
Remain the same, the speed of a wave is not affected by the wavelength of the wave
As the wavelength of a wave in a uniform medium increases, its frequency will ____
Decrease, wavelength and frequency are inversely proportional to each other

13. The water waves below are traveling along the surface of the ocean at a speed of 2.5 m/s and splashing periodically against Wilbert's perch. Each adjacent crest is 5 meters apart. The crests splash Wilbert's feet upon reaching his perch. How much time passes between each successive drenching? Answer and explain using complete sentences.

14. Answer to previous slide
If the wave travels 2.5 meters in one second then it will travel 5.0 meters in 2.0 seconds. If Wilbert gets drenched every time the wave has traveled 5.0 meters, then he will get drenched every 2.0 seconds.

15. Transverse and Longitudinal Waves
Transverse wave—the motion of the medium is at right angles to the direction in which the wave travels.
Longitudinal wave—the motion of the medium is along the same direction in which the medium travels.

16. Reflection – fixed end
Reflection involves a change in direction of waves when they bounce off a barrier
Boundary behavior—the behavior of a wave upon reaching the end of a medium.
Consider a rope fixed to a heavy object at one end.
The speed of the reflected pulse is the same as the incident pulse.
The wavelength of the reflected pulse is the same as the wavelength of the incident pulse.
The amplitude of the reflected pulse is less than the amplitude of the incident pulse (some of the energy was transferred to the other object).

17. Reflection- free end Consider now a rope that is free at both ends.
The wave is not inverted in free-end reflections.

18. Reflection to a different medium
The transmitted pulse (in the more dense medium) is traveling slower than the reflected pulse (in the less dense medium)
The transmitted pulse (in the more dense medium) has a smaller wavelength than the reflected pulse (in the less dense medium)
The speed and the wavelength of the reflected pulse are the same as the speed and the wavelength of the incident pulse (less dense medium)

19. Reflection to a different medium 2
The transmitted pulse (in the less dense medium) is traveling faster than the reflected pulse (in the more dense medium)
The transmitted pulse (in the less dense medium) has a larger wavelength than the reflected pulse (in the more dense medium)
The speed and the wavelength of the reflected pulse are the same as the speed and the wavelength of the incident pulse

20. Summary of Boundary Behavior
The wave speed is always greatest in the least dense medium,
The wavelength is always greatest in the least dense medium,
The frequency of a wave is not altered by crossing a boundary,
The reflected pulse becomes inverted when a wave in a less dense medium is heading towards a boundary with a more dense medium,
The amplitude of the incident pulse is always greater than the amplitude of the reflected pulse.

21. Ripple Tank and Reflection
The diagram at the right depicts a series of straight waves approaching a long barrier extending at an angle across the tank of water.
The direction that these wavefronts (straight-line crests) are traveling through the water is represented by the blue arrow
A ripple tank?
A ripple tank is a large glass-bottomed tank of water that is used to study the behavior of water waves. A light typically shines upon the water from above and illuminates a white sheet of paper placed directly below the tank. A portion of light is absorbed by the water as it passes through the tank. A crest of water will absorb more light than a trough. So the bright spots represent wave troughs and the dark spots represent wave crests. As the water waves move through the ripple tank, the dark and bright spots move as well. As the waves encounter obstacles in their path, their behavior can be observed by watching the movement of the dark and bright spots on the sheet of paper.

22. The Law of Reflection
The diagram below shows the reflected wavefronts and the reflected ray.
the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier.

23. Refraction
Refraction of waves involves a change in the direction of waves as they pass from one medium to another.
Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

24. Refraction
Waves that pass from deep water into shallow water will refract (bend), slow down, and their wavelength will decrease.
What happens to wavelength as wave speed decreases?

25. Refraction Continued
Light waves also refract when moving into a different medium.

26. Diffraction
Diffraction—a change in direction of waves as they pass through an opening or around a barrier in their path.
The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength.
When the wavelength of the waves are smaller than the obstacle, no noticeable diffraction occurs.
Can really be “seen” with sound waves

27. Interference
More than one vibration or wave can exist at the same time in the same space.
Interference pattern—the pattern produced by overlapping waves.
Constructive interference (reinforcement)—when the crest of one wave overlaps the crest of another.
Destructive interference (cancellation)—when the crest of one wave overlaps the trough of another.

28. Interference
Two overlapping water waves produce an interference pattern.
Areas of constructive interference are produced by waves that are in phase with one another.
Areas of destructive interference are produces by waves that are out of phase with one another.
Heavy lines represent crests, light lines represent troughs.
Which letters represent constructive interference? Which ones destructive interference?

29. Standing Waves
Standing wave—a wave in which the nodes remain stationary.
Standing waves are produced when two waves of equal amplitude and wavelength pass through each other in opposite directions.
The nodes are stable regions of destructive interference.
The positions on a standing wave with the largest amplitudes are antinodes.

30. The Doppler Effect Consider a bug jiggling in water.
The frequency of the waves produced by a stationary bug will be the same at points A and B.
The frequency of the waves produced by a bug moving toward B at a speed less than wave speed will be higher at point B than point A.

31. The Doppler Effect
When a sound source moves toward you, the pitch of the sound is greater.
When a light source moves toward you, the frequency of the light is increased (blue shift)
Light from a source moving away from you is red-shifted.

32. Bow Waves
When the speed of the source in a medium is as great as the speed of the wave it produces, the waves pile up and create a barrier wave.
When the source travels faster than the waves it produces, it outruns the wave crests and creates a V-shaped bow wave.
Boats and supersonic aircraft
create bow waves.

37. Sound

38. The Origin of Sound
All sounds are produced by the vibrations of material objects.
Vibrating material sends a disturbance through a medium (usually air) in the form of a longitudinal wave.
Under normal conditions, the frequency of the source = the frequency of the waves produced.
Pitch—our subjective impression of the frequency of a sound.
People with normal hearing can perceive pitches with frequencies from 20 Hz to 20,000 Hz.
Infrasonic—sound waves with frequencies below 20 Hz.
Ultrasonic—sound waves with frequencies above 20,000 Hz.

39. Sound in Air and Media that Transmit Sound
Compression—a pulse of compressed air.
Rarefaction—a region (pulse) of low pressure air.
Remember: It is the pulse that travels; not the medium.
In general, sound is transmitted faster in liquids than gases, and still faster in solids.
Sound cannot travel in a vacuum.

40. The Sonic Spectrum – all mechanical, longitudinal waves.

41. Sound Ranges Infrasonic – less than 20 Hz
Ultrasonic – more than 20,000 Hz
Range of Human Hearing
20 – 20,000 Hz
0 – 120 dB

42. Driver Type Minimum Frequency Maximum Frequency Subwoofer < 20Hz
300-3kHz
Mid Woofer
3kHz
Midrange
300Hz
Tweeter
1.5kHz
> 20kHz
Super Tweeter
10kHz
30kHz
Typical Loudspeaker Driver Ranges

43. Approximate Range (Hz)
Species
Approximate Range (Hz) 
human
64-23,000
dog
67-45,000 
cat
45-64,000 
cow
23-35,000 
horse
55-33,500 
sheep
100-30,000 
rabbit
360-42,000 
rat
200-76,000 
mouse
1,000-91,000 
opossum
500-64,000 
guinea pig
54-50,000 
hedgehog
250-45,000 
raccoon
100-40,000
ferret
16-44,000 
chinchilla
90-22,800 
bat
2, ,000 
beluga whale
1, ,000
elephant
16-12,000 
porpoise
75-150,000
goldfish
20-3,000 
catfish 
50-4,000 
tuna 
50-1,100 
bullfrog 
100-3,000 
tree frog
canary 
250-8,000 
parakeet 
200-8,500 
cockatiel
owl 
200-12,000 
chicken 
125-2,000 

44. What do these sound like?
We hear from Hz.
Will 2000 Hz sound “high” or “low” pitched?

45. Speed of Sound Distance and time Wavelength and frequency
Characteristics of the material the sound is traveling in

46. Speed of Sound In air, sound travels about 330 meters per second.
Water vapor in the air increases this speed slightly.
Increased temperature also increases this speed.
Each degree increase above 0o C increases the speed of sound by 0.60 m/s.
Sound travels 4 times faster in water than in air and 15 times faster in steel than in air.
Sound travels faster through elastic materials than inelastic materials.
Elasticity—the ability of a material to change shape in response to a force and then regain its initial shape.
Example: Steel
Example of an inelastic material: putty

47. Speed of Sound in Air Sound Travels Faster in Hotter Air

48. At 25°C

49. At -25°C

50. “tubes”

51. Decibels – a measure of the relative intensity of sounds.

52. Normal Conversation – 60 dB

53. 85 decibels - prolonged exposure can cause gradual hearing loss
85 decibels - prolonged exposure can cause gradual hearing loss. 100 decibels - no more than 15 minutes prolonged exposure recommended 110 decibels - regular exposure of more than one minute risks permanent hearing loss without hearing protection.  

54. Loudest Sounds Ever! The Tunguska event 315 June 30, 1908
Space shuttle
blue whale 188
The Tunguska event 315 June 30, 1908
400,000 Watt speakers decibel
fireworks
dragster

55. Important Decibel Ideas
This is a “relative” (comparing) scale.
Humans can distinguish about 1 dB.
10dB higher “sounds” 2x louder.
Logarithmic, not linear.
10x more energy = 10dB higher
100x more energy = 20dB higher
1000x more energy = 30dB higher
10,000,000x more energy = 70dB higher

56. Loudness
The intensity of a sound is proportional to the square of the amplitude of a sound wave.
Decibel (db)—the unit of intensity.
Loudness—a physiological sensation that differs from person to person.
Loudness varies nearly as the logarithm of intensity.
0 db = the lower threshold of hearing for a normal ear.
10 db is 10 x more intense than 0 db.
20 db is 10 x more intense than 10 db and 100 x more intense than 0 db.

57. Beats

58. Two similar sounds played together

59. Resonance

60. Natural Frequency of Vibration
The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object.

61. Chalkboard – Tuning Fork
Forced Vibration
Chalkboard – Tuning Fork

62. Resonance

63. Tacoma Narrows Bridge

64. Resonance Examples Breaking Wine Glass