1. WAVES
Chapter 20 p

2. Section 1

3. Objectives 1. Explain the relationship among waves, energy, and matter
2. Describe the difference between transverse waves and compressional waves

4. A. Waves Carry Energy
Waves (rhythmic disturbances that carry energy without carrying matter) can carry energy by itself or with matter
Example – if a boat makes waves, then just energy is moving through the wave in an outward motion, but if you throw a ball, the energy is traveling in the direction of the ball along with the matter of the ball

5. But how does a wave carry energy without transporting matter?
If a line of students were standing shoulder to shoulder and passing a ball to each other without moving their feet and only their hands (ball is being passed side to side) then the ball is not actually moving, but the people are. The energy is traveling through the students, not the ball. Would the ball be able to move without the students? But the ball can represent the motion of the energy that is being moved. So… what do the people represent if the ball represents energy?
Answer:
Waves!

6. B. Wave Motion! Ever wondered how the waves move the way they do?
Ever been in a pool or the lake and you bobbed up and down instead of moving forward or backward?
Water molecules actually move in a circular motion which causes that bobbing motion rather than a distinct forward or backward motion. The molecules will bump into each other and transfer the energy from one to another.
It depends on the amount of energy exerted that determines on the strength and size of the wave
Any type of energy will cause a wave to move outward, but if there isn’t enough energy it won’t be strong enough to actually move or carry matter.

8. C. What do you think?
How can being near a source of deep, loud sounds, such as heavy machinery or the subwoofer of a stereo, demonstrate that waves carry energy???
Answer:
Try this: With a partner, turn to each other and take turns saying hello in a deep voice. You can actually feel and hear the vibration coming from their voice.
You can feel the vibrations as well as hear
the sound!

9. D. Mechanic Waves
Mechanical waves (use matter to transfer energy) travel through matter called mediums
In an example of ripples on a pond, what would be the medium?
Answer:
The mechanical wave travels as energy is transferred from particle to particle in the medium which can be liquid, solid or gas.
You would not be able to hear a sound wave if it weren’t for air in which the air molecules transfer the energy to your ear.
Water!

10. E. What do you think?
Why do you think the word mechanical is appropriate for waves that need matter to move?
Hint: think about what a machine does…. Think about why your mechanical pencil is called “mechanical” instead of just “pencil”.
Answer:
One definition of a machine is: a device that
transmits energy. In a mechanical wave, matter
transmits energy.

11. F. Transverse Waves
Transverse wave (a type of mechanical wave that the wave energy causes the matter in the medium to move up and down or back and forth at right angles to the direction the wave travels)
Example: a rope tied to the wall and you moving it up and down. Watch as the rope appears to move away from you but it is not. The wave is what is moving away.
The high points of the waves are called crests
The low points of the waves are called troughs

12. Diagram of a wave

13. G. Compressional Waves
Compressional wave (a type of mechanical wave in which matter in the medium moves forward and backward in the same direction that the wave travels)
Example: Imagine holding a slinky in both hands with them stretched apart. You move one hand and a wave is sent to the other end. The slinky did not leave your hand and travel with the wave. Instead the part of the slinky that moved like a wave bounced back and forth until it was at its origin in a resting position

14. Slinky Waves

15. H. Sound Waves A type of compressional wave
Example: your voice is created when your vocal cords move in which you feel a vibration same as if you were to touch the speaker on a stereo when music is playing
All waves are produced by something that vibrates

16. I. Making Sound Waves
When something is producing sound it actually touches some of the air molecules around it in which those air molecules carry the energy that travels to your ear
But from the beginning source of the sound, the medium pushes the air molecules making them squeeze together
Compression (the group of molecules that are squeezed together)

17. When the medium moves downward during the vibration, the molecules have space to move away from each other
Rarefraction (a place where molecules are far apart)

18. J. Electromagnetic Wave
Electromagnetic wave (a wave that does not require matter to carry energy)
These are transverse waves that are produced by the motion of electrically charged particles
Can travel through mediums that are solid, liquid or gas just like what?
Answer:
Example: Radio waves. They don’t stop when they reach your house. They travel right through it.
Mechanical Waces!

19. Unlike mechanical waves, electromagnetic waves can travel through space or a vacuum where no matter exists
What is another type of wave, other than a radio wave, that can travel through space?
Answer:
Light wave!

20. But wait! There’s more! Other waves that travel through space include:
INFRARED

21. VISIBLE

22. ULTRAVIOLET

23. Another type of electromagnetic wave: X-RAY
This is actually
Mr. DiFabio’s elbow!

24. X-rays don’t just help medically, but also security!

25. Review!
1. What is a wave?
Rhythmic disturbances that carry energy without carrying matter
2. What type of mediums can both mechanical and electromagnetic wave travel through?
Solid, liquid, or gas
3. What type of waves causes the matter to move up and down or back and forth at ninety degree angles?
Transverse wave

26. 5. What are all waves produced from?
4. What type of wave only carries the energy forward and backward in the same direction the wave travels?
Compressional wave
5. What are all waves produced from?
vibrations
6. What is it called when the molecules are squeezed together?
Compression
7. What is it called when the molecules are far apart?
rarerefraction
8. What type of wave doesn’t need matter as a medium?
Electromagnetic wave
9. What are types of waves that can travel through space?
Light, infrared, visible, radio, ultraviolet

27. Section 2
Wave Properties

28. Objectives
1. describe the relationship between the frequency and wavelength of a wave
2. Explain why waves travel at different speeds

29. A. Amplitude
The amplitude of a transverse wave is (half the distance between a crest and a trough)

30. In a compressional wave, the amplitude is greater when the particles of the medium are squeezed together in each compression and spread farther apart in each rarefraction

31. B. Amplitude and Energy
A wave’s amplitude is related to its energy that the wave carries
Example: a bright light has greater amplitude than a dim light same a loud sound has greater amplitude than a soft sound and same with energy carried

32. Tsunami
A tsunami is created by underwater earthquakes along fault lines in the ocean floor and result in a huge wave onto land. Some waves reach up to 30 meters (100 feet) but there was one recently in Japan that reached 40 meters. The energy a tsunami carries above shore creates much damage to property and people zU

33. C. Wavelength
Transverse Waves Wavelength (the distance from the top of one crest to the top of the next crest or the bottom of one trough to another trough
Another way to describe a wave
Compressional Waves Wavelength (the distance between the center of one compression and the next or the center of one rarefraction to the next

34. Wavelengths are different depending on type of light such as a red light has a wider wavelength than a green light
It is the wavelength of visible light that determines its color

36. D. Frequency
Frequency (the number of wavelengths that pass a given point in 1 second)
The unit of frequency is the # of wavelengths/s (per second) or hertz (Hz)
All waves are produces by?
Answer:
Vibrations

37. The faster the vibration is, the higher the frequency

38. Ready to hear it??
VIDEO WARNING: you won’t hear anything at first but at some point it will begin to hurt ears so do not play all the way through… may need to stop around 1100 Hz
**PLEASE ASK STUDENTS IF ANYONE HAS EAR PROBLEMS**
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39. Hearing test! How old are yours ears??
Everybody put your head down and one hand up. When you stop hearing the sound, put your hand down.
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Let’s watch it again, this time with your head up and watching the screen.

40. Here are some more!
This one shows different age groups and what they should be able to hear!
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This one shows the wave frequency with the Hertz and has an extra special one
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41. E. Color and Pitch
Frequency and Wavelength are related which means either one will determine the color of a light wave meaning blue light has a larger frequency and a shorter wavelength than a red light
In a sound wave, either the wavelength or frequency determines the pitch (the highness or lowness of a sound)

42. F. Wave Speed
During a thunderstorm, do you hear the thunder first or do you see the lightening first?
Answer:
Light travels quicker than sound.
It depends on the distance of the
lightening. The further away it is, the
more likely you are to see the lightening
before you hear the thunder.

43. Electromagnetic waves travel faster in gases than in solids or liquids
Sound travels faster in solids than in liquids and faster in liquids than in gases
This is because atoms are closer to each other in a solid than in a liquid, and closer together in a liquid than in a gas
Electromagnetic waves travel faster in gases than in solids or liquids
Example: you can get to your next class quicker if the hallways were empty same as electromagnetic waves
If many atoms are in the medium, then they are slowed down

44. Review! 1. What is amplitude?
2. Do loud sounds or soft sounds carry more energy?
3. What is wavelength?
4. Why is wavelength an important characteristic of a wave?
5. What is the measurement used for wave frequency?

45. More Review! 6. What two characteristics are related?
7. If a wavelength is longer, what happens to the frequency?
8. Which travels faster: light or sound?
9. What kind of mediums do electromagnetic waves travel faster in?

46. Review Answers
1. one-half the distance between the crest and the trough
2. loud
3. the distance from the top of the crest to the top of the next crest or the bottom of one trough to the next trough

47. 4. Because it determines what type of wave it is such as what color a light will be
5. Hertz (Hz)
6. Frequency and wavelength
7. The frequency decreases
8. light
9. Ones with fewer atoms in the medium, such as gases

48. Section 3
Wave Behavior

49. Objectives 1. Explain how waves can reflect from some surfaces
2. Explain how waves change direction when they move from one material into another
3. Describe how waves are able to bend around barriers

50. A. Reflection
Reflection (occurs when a wave strikes an object or surface and bounces off)
Example: an echo is a reflected sound
Sound is actually reflected off of all surfaces, but most surfaces absorb it which is why you don’t always hear an echo

51. Your reflection in the mirror happens because light waves produced by a light source bounce off of your face, strike the mirror or shiny surface, and reflect back into your eyes
The smoother and shinier the surface, the more reflection you will see. The more rough spots or uneven a surface is, the light bounces off in an scattered way causing the reflection to be less likely

52. B. Refraction
Refraction (the bending of a wave as it moves from one medium into another)
Have you ever dropped something in the water and tried grabbing for it but missed? That’s because the light rays from the object changed direction as they passed from the water into the air

53. C. Refraction and Wave Speed
The speed of a wave can be different in different materials
Example: light waves travel faster in air than in water
Refraction occurs when the speed of a wave changes as it passes from one substance to another

54. A line perpendicular to the water’s surface is called the “normal”
When a light ray passes from air into water, it slows down and bends toward the normal, but when the light ray passes from water to air, it speeds up and bends away from the normal
The larger the speed change of the light wave, the larger the change in the direction
Example: shine a flashlight into water and the light

57. What is happening here?

58. D. Color from Refraction
Refraction causes prisms to separate sunlight into many colors and produces rainbows too
What produces a rainbow?
Answer:
Sunlight refracts as it enters
raindrops, reflects from the far
inside surfaces of the drops, and
refracts as it leaves the drops.

61. E. Diffraction Diffraction (the bending of waves around a barrier)
Not the same bending as refraction which is when waves change speed through a medium
Example: hearing music from another room because the sound waves bend around the door and down the hallway, but the speed of the sound waves remain the same

62. F. Diffraction of Light Waves
Light waves do not diffract as much as much as sound waves
Think about it: you can’t see inside the classroom playing music before you enter it, but you can hear it
Light waves do diffract at an extremely small amount

63. Think about it: you can see light under a closed door because the light waves are diffracting around the edges but not at the same amount that is inside the room
The diffraction of light waves is too small for you to see around a corner.
How cool would that be if you could though?

64. G. Diffraction and Wavelength
Light waves have a wavelength between 400 and 700 billionths of a meter
Sound waves that you can hear have wavelengths between a few millimeters and about 10 meters
A wave is diffracted more when its wavelength is similar in size to the barrier or opening
In other words… the light wave is too small

65. H. When Waves Meet
Waves pass right through each other and continue moving as though the other wave never existed

66. I. Wave Interference
Interference (the ability of two waves to combine and form a new wave when they overlap)
Constructive interference (the crest of one wave overlaps the crest of the other)
The amplitudes of these combine make a larger wave while they overlap

67. Destructive interference (occurs when the crest of one wave overlaps the trough of another wave)
When they combine, the amplitude is smaller
If the two waves have equal amplitudes and meet crest to trough, they cancel each other out during the overlap
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68. J. Reducing Noise
Too much expose to loud noises can damage your hearing
Protective ear wear absorbs some of those loud sounds to prevent your ear/hearing from being damaged
While you can keep those noises out, you can also keep them in

69. Review! 1. What is reflection?
2. What is a sound wave example of a reflection? Light wave?
3. What is refraction?
4. What causes an object to appear in a different location under water than where it actually is located?

70. 5. When does refraction occur?
6. How is a rainbow produced?
7. What is diffraction?
8. How is diffraction different from refraction?
9. What diffracts more than a light wave?
10. When is a wave diffracted more?
11. Why can we hear sounds down the hall but not see what is happening inside of a room down the hall?

71. 12. What happens when two waves meet?
13. What is interference?
14. What is the difference between constructive interference and destructive interference?
15. What happens to the wave amplitude during constructive interference? Destructive interference?
16. What happens when two waves meet and have them same amplitude?