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44. What happens if the source of a sound is moving toward you at a 11. What is an echo?
high rate of speed? 12. Why are fundamental frequencies and overtones also called
a. The sound will be traveling faster than from a stationary source. resonant frequencies?
b. The sound will be moving faster only in the direction of travel.
c. You will hear a higher frequency, but people in the source
will not. FOR FURTHER ANALYSIS
d. All observers in all directions will hear a higher frequency.
45. What happens if you are moving at a high rate of speed toward 1. How would distant music sound if the speed of sound decreased
some people standing next to a stationary source of a sound? with frequency?
You will hear 2. What are the significant similarities and differences between
a. a higher frequency than the people you are approaching will longitudinal and transverse waves? Give examples of each.
hear. 3. Sometimes it is easier to hear someone speaking in a full room
b. the same frequency as the people you are approaching will than in an empty room. Explain how this could happen.
hear.
4. Describe how you can use beats to tune a musical instrument.
c. the same frequency as when you and the source are not moving.
5. Is sound actually destroyed in destructive interference?
d. a higher frequency, as will all observers in all directions.
6. Are vibrations the source of all sounds? Discuss whether this is
Answers
supported by observations or is an inference.
1. b 2. b 3. c 4. d 5. b 6. c 7. c 8. a 9. a 10. c 11. b 12. b 13. c 14. b
7. How can sound waves be waves of pressure changes if you can
15. c 16. d 17. a 18. b 19. a 20. b 21. b 22. d 23. b 24. a 25. c 26. a
hear several people talking at the same time?
27. b 28. a 29. d 30. d 31. c 32. d 33. b 34. c 35. c 36. d 37. d 38. b
8. Why is it not a good idea for a large band to march in unison
39. a 40. c 41. d 42. d 43. b 44. c 45. a
across a bridge?
QUESTIONS FOR THOUGHT
INVITATION TO INQUIRY
1. What is a wave?
Does a Noisy Noise Annoy You?
2. Is it possible for a transverse wave to move through air? Explain.
3. A piano tuner hears three beats per second when a tuning fork There is an old question-answer game that children played that went
and a note are sounded together and six beats per second after like this, “What annoys an oyster?”
the string is tightened. What should the tuner do next, tighten or The answer was, “A noisy noise annoys an oyster.”
loosen the string? Explain. You could do an experiment to find out how much noise it takes
4. Why do astronauts on the Moon have to communicate by radio to annoy an oyster, but you might have trouble maintaining live oys-
even when close to one another? ters, as well as measuring how annoyed they might become. So, con-
5. What is resonance? sider using different subjects, including humans. You could modify
6. Explain why sounds travel faster in warm air than in cool air. the question to “What noise level effects how well we concentrate?”
7. Do all frequencies of sound travel with the same velocity? If you choose to do this invitation, start by determining how you
Explain your answer by using one or more equations. are going to make the noise, how you can control different noise levels,
8. What eventually happens to a sound wave traveling through the air? and how you can measure the concentration level of people. A related
9. What gives a musical note its characteristic quality? question could be, “Does listening to music while studying help or hin-
10. Does a supersonic aircraft make a sonic boom only when it der students?”
cracks the sound barrier? Explain.

PARALLEL EXERCISES

The exercises in groups A and B cover the same concepts. Solutions to group A exercises are located in appendix E.

Group A Group B
1. A grasshopper floating in water generates waves at a rate of three 1. A water wave has a frequency of 6 Hz and a wavelength of 3 m.
per second with a wavelength of 2 cm. (a) What is the period of (a) What is the period of these waves? (b) What is the wave
these waves? (b) What is the wave velocity? velocity?
2. The upper limit for human hearing is usually considered to be 2. The lower frequency limit for human hearing is usually
20,000 Hz. What is the corresponding wavelength if the air considered to be 20.0 Hz. What is the corresponding wavelength
temperature is 20.0°C? for this frequency if the air temperature is 20.0°C?
3. A tone with a frequency of 440 Hz is sounded at the same time as 3. A 520 Hz tone is sounded at the same time as a 516 Hz tone.
a 446 Hz tone. What is the beat frequency? What is the beat frequency?
4. Medical applications of ultrasound use frequencies up to 2.00 × 4. The low range of frequencies used for medical applications is about
7
10 Hz. What is the wavelength of this frequency in air? 1,000,000 Hz. What is the wavelength of this frequency in air?

5-23 CHAPTER 5 Wave Motions and Sound 137