Key Terms and Matching Definitions
_____ amplitude
_____ beats
_____ bow wave
_____ Doppler effect
_____ forced vibration
_____ frequency
_____ hertz
_____ interference
_____ longitudinal wave
_____ natural frequency
_____ period
_____ refraction
_____ resonance
_____ shock wave
_____ sonic boom
_____ sound wave
_____ standing wave
_____ transverse wave
_____ wave
_____ wave speed
_____ wavelength
1. A disturbance or vibration propagated from point to point in a medium or in space.
2. For a wave or vibration, the maximum displacement on either side of the equilibrium (midpoint) position.
3. The distance between successive crests, troughs, or identical parts of a wave.
4. For a vibrating body or medium, the number of vibrations per unit time. For a wave, the number of crests that
pass a particular point per unit time.
5. The SI unit of frequency. It equals one vibration per second.
6. The time required for a vibration or a wave to make a complete cycle; equal to 1/frequency.
7. The speed with which waves pass a particular point:
Wave speed = frequency × wavelength
8. A wave in which the medium vibrates in a direction perpendicular (transverse) to the direction in which the
wave travels. Light is an example.
9. A wave in which the medium vibrates in a direction parallel (longitudinal) to the direction in which the wave
travels. Sound is an example.
10. A longitudinal vibratory disturbance that travels in a medium, which can be heard in the approximate frequency
range 20–20,000 Hertz.
11. The bending of a wave through either a non-uniform medium or from one medium to another, caused by
differences in wave speed.
12. The setting up of vibrations in an object by a vibrating force.
13. The pattern formed by superposition of different sets of waves that produces mutual reinforcement in some
places and cancellation in others.
14. A stationary wave pattern formed in a medium when two sets of identical waves pass through the medium in
opposite directions.
15. The change in frequency of wave motion resulting from motion of the wave source or receiver.
16. The V-shaped wave produced by an object moving across a liquid surface at a speed greater than the wave
speed.
17. The cone-shaped wave created by an object moving at supersonic speed through a fluid.
18. The loud sound resulting from the incidence of a shock wave.
19. A frequency at which an elastic object naturally tends to vibrate, so that minimum energy is required to produce
a forced vibration or to continue vibrating at that frequency.
20. The response of a body when a forcing frequency matches its natural frequency.
21. A series of alternate reinforcements and cancellations produced by the interference of two waves of slightly
different frequency, heard as a throbbing effect in sound waves.
Review Questions
Special Wiggles–Vibrations and Waves
1. What is the source of all waves?
2. How do frequency and period relate to each other?
Wave Motion–Transporting Energy
3. What is it that moves from source to receiver in wave motion?
4. What is the relationship among frequency, wavelength, and wave speed?
Two Types of Waves–Transverse and Longitudinal
5. In a transverse wave, in what direction are the vibrations relative to the direction of wave travel?
6. In a longitudinal wave, in what direction are the vibrations relative to the direction of wave travel?
Sound Travels in Longitudinal Waves
7. Why will sound not travel in a vacuum?
8. How does the speed of sound in water compare with the speed of sound in air? How does the speed in steel
compare with the speed in air?
Sound Can Be Reflected
9. How does the angle of incidence compare with the angle of reflection for sound?
10. What is a reverberation?
Sound Can Be Refracted
11. What causes refraction?
12. Does sound tend to bend upward or downward when its speed near the ground is greater than its speed at a
higher level?
Forced Vibrations and Natural Frequency
13. Why does a struck tuning fork sound louder when it is held against a table?
14. Give three examples of forced vibration.
Resonance and Sympathetic Vibrations
15. Distinguish between forced vibrations and resonance.
16. When you listen to a radio, why are you able to hear only one station at a time rather than all stations at once?
Interference–The Addition and Subtraction of Waves
17. What kind of waves exhibit interference?
18. Distinguish between constructive interference and destructive interference.
The Doppler Effect–Changes in Frequency Due to Motion
19. In the Doppler effect, does frequency change? Does wavelength change? Does wave speed change?
20. Can the Doppler effect be observed with longitudinal waves, transverse waves, or both?
Wave Barriers and Bow Waves
21. How does the V shape of a bow wave depend on the speed of the wave source?
Shock Waves and the Sonic Boom
22. How does the V shape of a shock wave depend on the speed of the wave source?
23. True or false: A sonic boom occurs only when an aircraft is breaking through the sound barrier.
24. True or false: In order for an object to produce a sonic boom, it must be a sound source.
Exercises
1. If we double the frequency of a vibrating object, what happens to its period?
2. If the frequency of a sound wave is doubled, what change occurs in its speed? In its wavelength?
3. Red light has a longer wavelength than blue light. Which has the greater frequency?
4. You dip your finger repeatedly into a puddle of water and make waves. What happens to the wavelength if you
dip your finger more frequently?
5. How does the frequency of vibration of a small object floating in water compare with the number of waves
passing the object each second?
6. Why will marchers at the end of a long parade following a band be out of step with marchers near the front?
7. What two physics mistakes occur in a science fiction movie that shows a distant explosion in outer space,
where you see and hear the explosion at the same time?
8. A cat can hear sound frequencies up to 70,000 Hz. Bats send and receive ultrahigh-frequency squeaks up to
120,000 Hz. Which hears shorter wavelengths, cats or bats?
9. At the stands of a racetrack, you notice smoke from the starter’s gun before you hear it fire. Explain.
10. Why is it so quiet after a snowfall?
11. Why is the moon described as a “silent planet”?
12. If the speed of sound depended on frequency, how would distant music sound?
13. Why is an echo weaker than the original sound?
14. Would there be a Doppler effect if the source of sound were stationary and the listener in motion? Why or why
not? In which direction should the listener move to hear a higher frequency? A lower frequency?
15. When you blow your horn while driving toward a stationary listener, the listener hears an increase in the horn
frequency. Would the listener hear an increase in the horn frequency if he were in another car traveling at the
same speed in the same direction as you? Explain.
16. Astronomers find that light coming from one edge of the sun has a slightly higher frequency than light from the
opposite edge. What do these measurements tell us about the sun’s motion?
17. What can you say about the speed of a boat that makes a bow wave? How about the speed of an aircraft that
produces a shock wave?
18. What physical principle is used by Manuel when he pumps in rhythm with the natural frequency of the swing?
(Click image to enlarge)
19. A special device can transmit out-of-phase sound from a noisy jackhammer to earphones worn by its operator.
Over the noise of the jackhammer, the operator can easily hear your voice while you are unable to hear his.
Explain.
20. If a single disturbance some unknown distance away sends out both transverse and longitudinal waves that
travel with distinctly different speeds in the medium, such as in the ground during earthquakes, how could the
origin of the disturbance be located?
Problems
1. A weight suspended from a spring bobs up and down over a distance of 20 centimeters twice each second.
What is its frequency? Its period? Its amplitude?
2. A rule of thumb for estimating the distance in kilometers between an observer and a lightning stroke is to divide
the number of seconds in the interval between the flash and the sound by 3. Is this rule correct?
3. In terms of wavelength, how far does a wave travel during one period?
4. From far away you watch a woman driving nails into her front porch at a regular rate of 1 stroke per second.
You hear the sound of the blows exactly synchronized with the blows you see. And then you hear one more
blow after you see her cease hammering. How far away is she?
5. A skipper on a boat notices wave crests passing his anchor chain every 5 s. He estimates the distance
between wave crests to be 15 m. He also correctly estimates the speed of the waves. What is this speed?
6. An oceanic depth-sounding vessel surveys the ocean bottom with ultrasonic sound that travels 1530 m/s in
seawater. How deep is the water if the time delay of the echo from the ocean floor is 6 s?
7. A bat flying in a cave emits a sound and receives its echo 0.1 s later. How far away is the cave wall?
8. What frequency of sound produces a wavelength of 1 meter in room-temperature air?