2. Chapter: Waves Section 1: What are waves? Section 2: Wave Properties
Table of Contents
Chapter: Waves
Section 1: What are waves?
Section 2: Wave Properties
Section 3: Wave Behavior

3. What are waves? 1
What is a wave?
When you are relaxing on an air mattress in a pool and someone does a cannonball dive off the diving board, you suddenly find yourself bobbing up and down.

4. What are waves? 1
What is a wave?
The up-and-down motion was caused by the peaks and valleys of the ripple that moved from where the splash occurred.
These peaks and valleys make up water waves.

5. What are waves? 1
Waves Carry Energy
Rhythmic disturbances that carry energy without carrying matter are called waves.
You can see the energy of the wave from a speedboat traveling outward, but the water only moves up and down.
If you’ve ever felt a clap of thunder, you know that sound waves can carry large amounts of energy.

6. What are waves? 1
A Model for Waves
Passing a ball down a line of people is a model for how waves can transport energy without transporting matter.
Even though the ball has traveled, the people in line have not moved.

7. What are waves? 1
A Model for Waves
Think about the ripples on the surface or a pond. The energy carried by the ripples travels through the water.
In a water wave, water molecules bump each other and pass energy from molecule to molecule.

8. What are waves? 1
Mechanical Waves
Waves, which use matter to transfer energy, are called mechanical waves.
The matter through which a mechanical wave travels is called a medium.
For ripples on a pond, the medium is the water.

9. What are waves? 1
Mechanical Waves
A mechanical wave travels as energy is transferred from particle to particle in the medium.
For example, a sound wave is a mechanical wave that can travel through air, as well as solids, liquids, and other gases.

10. What are waves? 1
Transverse Waves
In a mechanical transverse wave, 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.
You can make a model of a transverse wave.
Stretch a long rope out on the ground. Hold one end in your hand.

11. Transverse Waves 1 Now shake the end in you hand back and forth.
What are waves? 1
Transverse Waves
Now shake the end in you hand back and forth.
The high points on the waves are called crests and the low points are called troughs.

12. What are waves? 1
Compressional Waves
Mechanical waves can be either transverse or compressional.
In a compressional wave, matter in the medium moves forward and backward along the same direction that the wave travels.

13. What are waves? 1
Compressional Waves
You can make a compressional wave by squeezing together and releasing several coils of a coiled spring toy.

14. Sound Waves 1 Sound waves are compressional waves.
What are waves? 1
Sound Waves
Sound waves are compressional waves.
If you touch a stereo speaker while it’s playing, you can feel it vibrating.
All waves are produced by something that is vibrating.

15. Making Sound Waves 1 Look at the drum shown.
What are waves? 1
Making Sound Waves
Look at the drum shown.
When you hit the drumhead it starts vibrating up and down.

16. What are waves? 1
Making Sound Waves
As the drumhead moves upward, the molecules next to it are pushed closer together.
This group of molecules that are closer together is a compression.

17. What are waves? 1
Making Sound Waves
When the drumhead moves downward, the molecules near it have more room and can spread farther apart.
This group of molecules that are farther apart is a rarefaction.

18. What are waves? 1
Making Sound Waves
As the drumhead vibrates up and down, it forms a series of compressions and rarefactions that move away and spread out in all directions.
This series of compressions and rarefactions is a sound wave.

19. Electromagnetic Waves
What are waves? 1
Electromagnetic Waves
Waves that can travel through space where there is no matter are electromagnetic waves.

20. Electromagnetic Waves
What are waves? 1
Electromagnetic Waves
There are different types of electromagnetic waves, including radio waves, infrared waves, visible light waves, ultraviolet waves, x rays, and gamma rays.
These waves can travel in matter or in space.

21. Radiant Energy From the Sun
What are waves? 1
Radiant Energy From the Sun
The sun emits electromagnetic waves that travel through space and reach Earth.
The energy carried by electromagnetic waves is called radiant energy.
Almost 92 percent of the radiant energy that reaches Earth from the Sun is carried by infrared and visible light waves.

22. Section Check
Section Check 1
Question 1
A rhythmic disturbance that carries energy but not matter is known as a _______.
A. electron
B. matter
C. volcano
D. wave

23. Section Check 1
Answer
The correct answer is D. Think of the wave that you send across a bed sheet by shaking one end. Matter does not move across the bed sheet, only energy.

24. Section Check 1
Question 2
The sound of someone clapping their hands is a wave. Can you explain how?
Answer
Energy from the clap moves out through the air; it is a rhythmic disturbance that travels away from the source.

25. Section Check 1
Question 3
Why wouldn’t a drum solo sound good in outer space?
Answer
You wouldn’t be able to hear a drum in outer space. Where there’s no air, there can be no compression and rarefaction, and thus no sound waves.

26. Wave Properties 2
Amplitude
How high the wave rises above, or falls below, the normal level is called the wave’s amplitude.
The amplitude of a transverse wave is one-half the distance between a crest and a trough.

27. Wave Properties 2
Amplitude and Energy
A wave’s amplitude is related to the energy that the wave carries.
For example, the electromagnetic waves that make up bright light have greater amplitudes than the waves that make up dim light.

28. Wave Properties 2
Amplitude and Energy
Tsunamis are huge sea waves that are caused by underwater earthquakes along faults on the seafloor.
The movement of the seafloor along a fault produces the wave.
The tremendous amounts of energy tsunamis carry cause great damage when they move ashore.

29. Wave Properties 2
Wavelength
For a transverse wave, wavelength is the distance from the top of one crest to the top of the next crest, or from the bottom of one trough to the bottom of the next trough.

30. Wave Properties 2
Wavelength
For a compressional wave, the wavelength is the distance between the center of one
compression and the center of the next compression, or from the center one rarefaction to the center of the next rarefaction.

31. Wave Properties 2
Wavelength
Electromagnetic waves have wavelengths that range from kilometers, for radio waves, to less than a diameter of an atom, for X rays and gamma rays.
This range is called the electromagnetic spectrum.

32. Wave Properties 2
Frequency
The frequency of a wave is the number of wavelengths that pass a given point in 1 s.
The unit of frequency is the number of wavelengths per second, or hertz (Hz).
The faster the vibration is, the higher the frequency is of the wave that is produced.

33. Wave Properties 2
A Sidewalk Model
For waves that travel with the same speed, frequency and wavelength are related.
To model this relationship, imagine people on two parallel moving sidewalks in an airport.

34. A Sidewalk Model 2 One sidewalk has four travelers spaced 4 m apart.
Wave Properties 2
A Sidewalk Model
One sidewalk has four travelers spaced 4 m apart.
The other sidewalk has 16 travelers spaced 1 mile apart.
When people are father apart on a moving sidewalk, fewer people pass the pillar every minute.

35. Frequency and Wavelength
Wave Properties 2
Frequency and Wavelength
Smaller frequencies result in longer wavelengths.
Higher frequencies result in shorter wavelengths.
This is true for all waves that travel at the same speed. As the frequency of a wave increases, its wavelength decreases.

36. Wave Properties 2
Color and Pitch
Because frequency and wavelength are related, either the wavelength or frequency of a light wave determines the color of the light.
Either the wavelength or frequency determines the pitch of a sound wave.

37. Color and Pitch 2 Pitch is how high or low a sound seems to be.
Wave Properties 2
Color and Pitch
Pitch is how high or low a sound seems to be.
Wavelength and frequency are also related for sound waves traveling in air.
As the frequency of sound waves increases, their wavelengths decrease.

38. Wave Properties 2
Color and Pitch
This figure shows how the frequency and wavelength change for notes of a musical scale.

39. Wave Properties 2
Wave Speed
Light travels through air at about 300 million m/s. Sound travels through air at about 340 m/s.

40. Wave Properties 2
Wave Speed
The speed of any wave can be calculated from this equation.
In this equation, the wavelength is represented by the symbol, λ, which is the Greek letter lambda.

41. Wave Properties 2
Wave Speed
When mechanical waves, such as sound, and electromagnetic waves, such as light, travel in different materials, they change speed.
Mechanical waves usually travel faster in solids, and slowest in gases.
Electromagnetic waves travel fasted in gases and slowest in solids.

42. Question 1 2 What is represented by letter C in this illustration?
Section Check
Section Check 2
Question 1
What is represented by letter C in this illustration?
A. amplitude
B. crest
C. rest position
D. trough

43. Section Check 2
Answer
The answer is A. The amplitude of a transverse wave is a measure of how high the crests are or how deep the troughs are.

44. Section Check 2
Question 2
The amplitude of a transverse wave is _______ the distance between a crest and a trough.
A. one-eighth
B. one-fourth
C. one-third
D. one-half

45. Section Check 2
Answer
The answer is D. The amplitude of a transverse wave is one-half the distance between a crest and a trough.

46. Section Check 2
Question 3
If a wave has a frequency of 550 Hz and a wavelength of 90 m, what is its speed?
Answer
The wave speed is 49,500 m/s. Wave speed is calculated by multiplying frequency times the wavelength.

47. Wave Behavior 3
Reflection
Reflection occurs when a wave strikes an object or surface and bounces off.
Sound reflects from all surfaces.
Your echo bounces off the walls, floor, ceiling, furniture, and people.

48. Wave Behavior 3
Reflection
You see your face in a mirror or a still pond because of reflection.
Light waves produced by a source of light such as the sun or a lightbulb bounce off your face, strike the mirror, and reflect back to your eyes.

49. Wave Behavior 3
Reflection
When a surface is smooth and even, the reflected image is clear and sharp.
When light reflects from an uneven or rough surface, you can’t see a sharp image because the reflected light scatters in many different directions.

50. Wave Behavior 3
Refraction
The bending of a wave as it moves from one medium into another is called refraction.

51. Refraction and Wave Speed
Wave Behavior 3
Refraction and Wave Speed
Refraction occurs when the speed of a wave changes as it passes from one substance to another.
A line that is 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.

52. Refraction and Wave Speed
Wave Behavior 3
Refraction and Wave Speed
When the ray passes from water into air, it speeds up and bends away from the normal.

53. Refraction and Wave Speed
Wave Behavior 3
Refraction and Wave Speed
Refraction makes the fish appear to be closer to the surface and farther away from you than in really is.

54. Wave Behavior 3
Color from Refraction
When sunlight passes through a prism, refraction occurs twice: once when sunlight enters the prism, and again when it leaves the prism and returns to the air.
Violet light has the shortest wavelength and is bent the most.
Red light has the longest wavelength and is bent the least.

55. Wave Behavior 3
Color from Refraction
Refraction produces a rainbow when light waves from the Sun pass into and out of water droplets.
The colors you see in a rainbow are in order of decreasing wavelength: red, orange, yellow, green, blue, indigo, and violet.

56. Wave Behavior 3
Diffraction
Why can you hear music from the band room when you are down the hall?
Sound waves bend as they pass through an open doorway.
Diffraction is the bending of waves around a barrier.

57. Diffraction 3 Light waves do bend around the edges of an open door.
Wave Behavior 3
Diffraction
Light waves do bend around the edges of an open door.
However, for an opening as wide as a door, the amount the light bends is extremely small.

58. Diffraction and Wavelength
Wave Behavior 3
Diffraction and Wavelength
Light waves have wavelengths between about 400 and 700 billionths of a meter, while the width of a doorway is about one meter.
Sound waves that you can hear have wavelengths between a few millimeters and about 10 m. They bend more easily around the corners of an open door.

59. Diffraction of Water Waves
Wave Behavior 3
Diffraction of Water Waves
When water waves strike obstacles such as islands, they don’t stop moving.
If the size and spacing of the islands is not too different from the wavelength of the water waves, the water waves bend around the islands, and keep on moving.
If the islands are much larger than the water wavelength, less diffraction would occur.

60. What happens when waves meet?
Wave Behavior 3
What happens when waves meet?
Do waves collide like billiard balls and change direction?
Waves behave differently from billiard balls when they meet.
Waves pass right through each other and continue moving.

61. Wave Behavior 3
Wave Interference
While two waves overlap a new wave is formed by adding the two waves together.
The ability of two waves to combine and form a new wave when they overlap is called interference.

62. Wave Behavior 3
Wave Interference
Sometimes when the waves meet, the crest of one wave overlaps the crest of another wave.
This is called constructive interference.
The amplitude of these combining waves adds together to make a larger wave while they overlap.

63. Wave Behavior 3
Wave Interference
Destructive interference occurs when the crest of one wave overlaps the trough of another wave.
The amplitudes of the two waves combine to make a wave with a smaller amplitude.
Click image to view movie.

64. Wave Behavior 3
Waves and Particles
Like waves of water, when light travels through a small opening, such as a narrow slit, the light spreads out in all directions on the other side of the slit.
If small particles, instead of waves, were sent through the slit, they would continue in a straight line without spreading.

65. Wave Behavior 3
Reducing Noise
Loud sounds have waves with larger amplitudes and carry more energy than softer sounds.
Damage to the ear from loud sounds can be prevented by reducing the energy that reaches the ear.

66. Section Check
Section Check 3
Question 1
When a wave strikes a surface and bounces off, you have a _______.
A. compression
B. rarefaction
C. reflection
D. wavelength

67. Section Check 3
Answer
The answer is C. You are used to visual reflections, but an echo is also a reflection—of a sound wave.

68. Section Check 3
Question 2
Explain the difference between reflection and refraction.
Answer
Reflection is the bouncing of a wave off a surface. Refraction is the bending of a wave as it moves from one medium to another.

69. Section Check 3
Question 3
The larger the change in the speed of a light wave passing from one medium to another, the larger the _______.

70. Section Check 3
Answer
The answer is change in direction. Light passing out of water into air speeds up and is refracted away from the normal.

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