Chapter 25 Vocab and Chapter review
REVIEW
5 REVIEW
Concept Summary
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Teaching Resources
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The period of a pendulum depends only
on the length of the pendulum and the
acceleration of gravity.
The source of all waves is a vibration.
The energy in waves is carried by a dis-
turbance in a medium.
Calculate the wave speed by multiplying
the wavelength and the frequency.
Waves in the stretched strings of musical
instruments and electromagnetic waves
are transverse. Sound waves are longitu-
dinal.
Interference patterns occur when waves
from different sources arrive at the same
point—at the same time.
A standing wave forms if a multiple of
half a wavelength fits into the length of
the medium.
As a wave source approaches, an observer
encounters waves with a higher fre-
quency. As a wave source moves away, an
observer encounters waves with a lower
frequency.
A bow wave occurs when a wave source
moves faster than the waves it produces.
A shock wave occurs when an object
moves faster than the speed of sound.
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crest (p. 492)
trough (p. 492)
amplitude (p. 492)
wavelength (p. 492)
frequency (p. 492)
hertz (p. 492)
transverse wave
   (p. 497)
longitudinal wave
   (p. 497)
interference
   pattern (p. 498)
constructive
   interference
   (p. 498)
destructive
   interference
   (p. 498)
out of phase (p. 499)
in phase (p. 499)
standing wave
   (p. 500)
node (p. 500)
antinodes (p. 500)
Doppler effect
   (p. 502)
blue shift (p. 503)
red shift (p. 503)
bow wave (p. 504)
shock wave (p. 505)
sonic boom (p. 505)
think! Answers
25.2.1
25.2.1
A 100-Hz wave vibrates 100 times/s.
The period is
 1 vib
0.1 Hz
  1 vib
0.1 vib/s
10 s.
25.4.1 The frequency of the wave is 2 Hz; its
       wavelength is 1.5 m; and its wave speed is
             ƒ(1.5 m) (2 Hz)3 m/s.
25.4.2 The wavelength must be 1 m. Then wave
        speed(1 m) (340 Hz) 340 m/s.
25.8
Yes. This is called destructive interference.
In a standing wave, for example, parts of
the wave have no amplitude—the nodes.
Neither! It is the frequency of a wave that
undergoes a change, not the wave speed.
Key Terms
vibration (p. 490)
wave (p. 490)
period (p. 491)
simple harmonic
   motion (p. 491)
sine curve (p. 491)
25.9
CHAPTER 25
VIBRATIONS AND WAVES
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ASSESS
5 ASSESS
Check Concepts
Section 25.0
••••••
Section 25.3
1. Does a vibration or a wave spread out
   through space?
Section 25.1
8. Does the medium in which a wave travels
   move along with the wave itself? Defend
   your answer.
Section 25.4
2. What is the period of a pendulum that takes
   one second to make a complete back-and-
   forth vibration?
9. How does the speed of a wave relate to its
   wavelength and frequency?
10. As the frequency of sound is increased, does
    the wavelength increase or decrease? Give an
    example.
Sections 25.5 and 25.6
11. Distinguish between a transverse wave and a
    longitudinal wave.
Section 25.7
3. Suppose that a pendulum has a period of
   1.5 seconds. How long does it take to make
   a complete back-and-forth vibration?
4. Is a pendulum with a 1.5-second period
   longer or shorter in length than a pendulum
   with a 1-second period?
Section 25.2
12. Distinguish between constructive interfer-
    ence and destructive interference.
13. Is interference a property of only some
    types of waves or of all types of waves?
Section 25.8
14. What causes a standing wave?
5. How is a sine curve related to a wave?
6. Distinguish among these different parts of
   a wave: amplitude, crest, trough, and wave-
   length.
7. Distinguish between the period and the
   frequency of a vibration or a wave. How do
   they relate to one another?
Section 25.9
15. When a wave source moves toward a receiv-
    er, does the receiver encounter an increase
    in wave frequency, wave speed, or both?
16. Does the Doppler effect occur for only some
    types of waves or all types of waves?
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Section 25.10
17. Compared with the speed of water waves
    how fast must a bug swim to keep up with
    the waves it produces? How fast must a boat
    move to produce a bow wave?
18. Distinguish a bow wave from a shock wave.
Section 25.11
22. Shown below are four different pairs of
    transverse wave pulses that move toward
    each other. At some point in time the pulses
    meet and interact (interfere) with each
    other. Rank the four cases from greatest to
    least on the basis of the height of the peak
    that results when the centers of the pairs
    coincide.
19. a. What is a sonic boom?
    b. How fast must an aircraft fly in order to
       produce a sonic boom?
20. If you encounter a sonic boom, is that
    evidence that an aircraft just exceeded the
    speed of sound to become supersonic?
Think and Rank
••••••
Rank each of the following sets of scenarios in
order of the quantity or property involved. List
them from left to right. If scenarios have equal
rankings, then separate them with an equal sign.
(e.g., A = B)
21. A fire engine’s siren emits a certain
    frequency. Rank from greatest to least the
    apparent frequency heard by the stationary
    listener in each scenario.
(A) The fire engine is traveling toward a
    listener at 30 m/s.
(B) The fire engine is traveling away from a
    listener at 5 m/s.
(C) The fire engine is traveling toward a
    listener at 5 m/s.
(D) The fire engine is traveling away from a
    listener at 30 m/s.
23. All the waves below have the same speed
    in the same medium. Use a ruler and rank
    these waves from greatest to least according
    to amplitude, wavelength, frequency, and
    period.
CHAPTER 25CHAPTER 25
VIBRATIONS AND WAVES 509VIBRATIONS AND WAVES
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Plug and Chug
5 ASSESS
(continued)
Think and Explain
24. The four sets of waves below are a top view
    of circular wave patterns made by a bug
    jiggling on the surface of water. Rank them
    from greatest to least based on the speed of
    the bug.
29. Calculate the speed of waves in water that
    are 0.4 m apart and have a frequency of 2 Hz.
30. The lowest frequency we can hear is about
    20 Hz. Calculate the wavelength associated
    with this frequency for sound that travels at
    340 m/s. How long is this in feet?
Think and Explain
••••••
31. Does the period of a pendulum depend of
    the mass of the bob? On the length of the
    string?
25. The shock waves depicted below are pro-
    duced by supersonic aircraft. Rank them
    from greatest to least based on the speed of
    the aircraft.
32. If a pendulum is shortened, does the fre-
    quency increase or decrease? What about its
    period?
33. Carmelita swings to and fro in a sitting posi-
    tion on a playground swing. William says
    that if she stands while swinging, a longer
    time will occur between back-and-forth
    swings. Carlos says no, that the to-and-fro
    time of the swing will be unaffected. Who, if
    either, do you agree with?
                                                    34. You dip your finger repeatedly into a puddle
                                                        of water and make waves. What happens toPlug and Chug ••••••
                                                        the wavelength if you dip your finger more
26. A nurse counts 76 heartbeats in one minute.
                                                        frequently?
    What are the period and frequency of the
                                                    35. If you double the frequency of a vibrat-
    heart’s oscillations?
                                                        ing object, what happens to its period?
27. New York’s 300-m high Citicorp® Tower
    oscillates in the wind with a period of 6.80 s. 36. How does the frequency of vibration of a
                                                        small object floating in water compare to the
    Calculate its frequency of vibration.
                                                        number of waves passing it each second?
28. Calculate the speed of waves in a puddle
                                                    37. If you triple the frequency of a vibrating
    that are 0.15 m apart and made by tapping
                                                        object, what will happen to its period?
    the water surface twice each second.
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38. Red light has a longer wavelength than vio-
    let light. Which has the greater frequency?
39. How far, in terms of wavelength, does a
    wave travel in one period?
40. If a wave vibrates up and down twice each
    second and travels a distance of 20 m each
    second, what is its frequency? Its wave
    speed? (Why is this question best answered
    by careful reading of the question rather
    than searching for a formula?)
45. In the Doppler effect, does frequency
    change? Does wavelength change? Does
    wave speed change?
46. Can the Doppler effect be observed with
    longitudinal waves, with transverse waves,
    or with both?
47. A railroad locomotive is at rest with its
    whistle shrieking, and then it starts moving
    toward you.
    a. Does the frequency that you hear increase,
       decrease, or stay the same?
    b. Does the wavelength that reaches your ear
       increase, decrease, or stay the same?
    c. How about the speed of sound in the air
       between you and the locomotive?
48. When a driver blows his horn while ap-
    proaching a stationary listener, the listener
    hears an increase in the frequency of the
    horn. Would the listener hear an increase in
    the frequency of the horn if she were also in
    a car traveling at the same speed in the same
    direction as the first driver? Explain.
41. The wave patterns seen in Figure 25.6 are
    composed of circles. What does this tell you
    about the speed of the waves in different
    directions?
42. Sound from Source A has a frequency twice
    as great as the frequency of sound from
    Source B. Compare the wavelengths of
    sound from the two sources.
43. What kind of motion should you impart to
    a stretched coiled spring to produce a trans-
    verse wave? A longitudinal wave?
44. Would it be correct to say that the Doppler
    effect is the apparent change in the speed
    of a wave due to the motion of the source?
    (Why is this question a test of reading
    comprehension as well as a test of physics
    knowledge?)
49. Astronomers find that light coming from
    point A at the edge of the sun has a slightly
    higher frequency than light from point B at
    the opposite side. What do these measure-
    ments tell us about the sun’s motion?
CHAPTER 25
VIBRATIONS AND WAVES
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5 ASSESS
(continued)
50. Does a boat moving through the water
    always produce a bow wave? Defend
    your answer.
51. Whenever you watch a high-flying aircraft
    overhead, it seems that its sound comes
    from behind the craft rather than from
    where you see it. Why is this?
52. How does the angle of the V shape of a
    bow wave depend on the speed of the
    wave source?
53. Why is it that a subsonic aircraft, no
    matter how loud it may be, cannot
    produce a sonic boom?
54. True or false: A sonic boom occurs only
    when an aircraft is breaking through the
    sound barrier. Defend your answer.
55. Consider an earthquake caused by a single
    disturbance, which sends out both trans-
    verse and longitudinal waves that travel with
    distinctly different speeds in the ground.
    How can earth scientists in different loca-
    tions determine the earthquake origin?
Think and Solve
••••••
56. The period of a simple pendulum is given
    by T 2 L , where g is the acceleration ofg
    gravity and L is the length of the pendulum.
    In a lab, you want to double the period of
    a certain pendulum. Your friend says you’ll
    have to make the pendulum twice as long.
    Do you agree with your friend?
57. Maria shows her friends a simple
    31-cm-long pendulum. Her teacher, look-
    ing on, asks if she can predict the period of
    the pendulum before she demonstrates it.
    What’s your prediction?
58. The Foucault pendulum in the rotunda of
    the Griffith Observatory in Los Angeles has
    a 110-kg brass ball at the end of a 12.2-m-
    long cable. What is the period of this pen-
    dulum?
59. You are looking through your grandparents’
    window and notice a hummingbird feeder
    hanging by a rope. You can’t see the top
    of the rope, but you notice that in a gentle
    breeze the feeder moves back and forth with
    a period of 4.0 seconds. You make a calcula-
    tion and announce to your grandparents
    that the rope is 4 m long. Your grandparents
    go outside and measure the rope. Should
    they be impressed with you?
60. For your science fair project you decide to
    make a simple pendulum for a grandfather
    clock, such that the period of the pendulum
    is 2.00 seconds. Show that the length of your
    pendulum should be just slightly less than
    the length of a meterstick. (Use g = 9.8 m/s2
    here.)
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61. Melanie is new to the nursing program.
    With a patient she counts 84 heartbeats in
    one minute. She calculates that the period
    and frequency of the heartbeats are 0.71 s
    and 1.4 Hz respectively. Is she correct?
62. A design engineer figures that a proposed
    new skyscraper will swing to and fro in
    strong winds at a frequency of 0.15 Hz. A
    new assistant asks how much time a person
    in the skyscraper will experience during
    each complete swing. What’s your answer?
63. In lab you strike a tuning fork that has a
    frequency of 340 Hz. For a speed of sound
    of 340 m/s, how does the wavelength of
    the resulting sound wave compare with the
    length of a meter stick?
64. If a wave vibrates back and forth three times
    each second, and its wavelength is 2 meters,
    what is its frequency? Its period? Its speed?
67. Radio waves are electromagnetic waves that
    travel at the speed of light, 300,000 kilo-
    meters per second. What is the wavelength
    of FM radio waves received at 100 mega-
    hertz on your radio dial?
68. The wavelength of red light is about
    700 nanometers, or 7 10–7 m. The fre-
    quency of the red light reflected from a
    metal surface and the frequency of the
    vibrating electron that produces it are the
    same. What is this frequency?
Activity
69. The half-angle of the shock-wave cone
    generated by a supersonic aircraft is 45°.
    What is the speed of the plane relative to the
    speed of sound?
65. While watching ocean waves at the dock
    of the bay, Otis notices that 10 waves pass
    beneath him in 30 seconds. He also notices
    that the crests of successive waves exactly
    coincide with the posts that are 5 meters
    apart. What are the period, frequency, wave-
    length, and speed of the ocean waves?
66. The crests on a long surface water wave are
    20 m apart, and in 1 minute 10 crests pass
    by. What is the speed of this wave?
Activity
••••••
70. Tie a rubber tube, a spring, or a rope to a
    fixed support and produce standing waves,
    as Figure 25.14 suggests. How many nodes
    can you produce? How can you change the
    number of nodes?
Teaching Resources
More Problem-Solving Practice
Appendix F
CHAPTER 25
VIBRATIONS AND WAVES
• Computer Test Bank
• Chapter and Unit Tests
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