SM_PDF_chapter13

# SM_PDF_chapter13 - Mechanical Waves CHAPTER OUTLINE 13.1...

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361 Mechanical Waves CHAPTER OUTLINE 13.1 Propagation of a Disturbance 13.2 The Wave Model 13.3 The Traveling Wave 13.4 The Speed of Transverse Waves on Strings 13.5 Reflection and Transmission of Waves 13.6 Rate of Energy Transfer by Sinusoidal Waves on Strings 13.7 Sound Waves 13.8 The Doppler Effect 13.9 Context Connection Seismic Waves ANSWERS TO QUESTIONS Q13.1 To use a slinky to create a longitudinal wave, pull a few coils back and release. For a transverse wave, jostle the end coil side to side. Q13.2 From v T = µ , we must increase the tension by a factor of 4. Q13.3 It depends on from what the wave reflects. If reflecting from a less dense string, the reflected part of the wave will be right side up. Q13.4 The section of rope moves up and down in SHM. Its speed is always changing. The wave continues on with constant speed in one direction, setting further sections of the rope into up-and-down motion. Q13.5 As the source frequency is doubled, the speed of waves on the string stays constant and the wavelength is reduced by one half. Q13.6 As the source frequency is doubled, the speed of waves on the string stays constant. Q13.7 Higher tension makes wave speed higher. Greater linear density makes the wave move more slowly. Q13.8 As the wave passes from the massive string to the less massive string, the wave speed will increase according to v T = µ . The frequency will remain unchanged. Since v f = λ , the wavelength must increase. Q13.9 Amplitude is increased by a factor of 2 . The wave speed does not change. Q13.10 Sound waves are longitudinal because elements of the medium—parcels of air—move parallel and antiparallel to the direction of wave motion.

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362 Mechanical Waves Q13.11 We assume that a perfect vacuum surrounds the clock. The sound waves require a medium for them to travel to your ear. The hammer on the alarm will strike the bell, and the vibration will spread as sound waves through the body of the clock. If a bone of your skull were in contact with the clock, you would hear the bell. However, in the absence of a surrounding medium like air or water, no sound can be radiated away. A larger-scale example of the same effect: Colossal storms raging on the Sun are deathly still for us. What happens to the sound energy within the clock? Here is the answer: As the sound wave travels through the steel and plastic, traversing joints and going around corners, its energy is converted into additional internal energy, raising the temperature of the materials. After the sound has died away, the clock will glow very slightly brighter in the infrared portion of the electromagnetic spectrum. Q13.12 The frequency increases by a factor of 2 because the wave speed, which is dependent only on the medium through which the wave travels, remains constant. Q13.13 When listening, you are approximately the same distance from all of the members of the group. If different frequencies traveled at different speeds, then you might hear the higher pitched frequencies before you heard the lower ones produced at the same time. Although it might be
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• Fall '07
• MahaAshour-Abdalla

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