Chapter 26 Sound – conceptual physics. – Flashcards
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a. Distinguish between compressions and rarefactions of a sound wave. b. How are compressions and rarefactions produced?
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a. Compression is a pulse of air. Rarefactions are a pulse of low pressure air. b. A vibrating sense in a medium. rare (scarce) compress (alot)
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Light can travel through a vacuum, as is evidenced when you see the sun or the moon. Can sound travel through a vacuum also? Explain why or why not.
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No. There is no medium for the disturbance to travel through.
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a. How fast does sound travel in dry air at room temperature? b. How does air temperature affect the speed of sound?
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a. ~ 330-340m/s. b. Hot temperatures, the sound waves travel faster.
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How does the speed of sound in air compare with its speed in water and in steel?
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Solid steel is the fastest. Air is the slowest speed of sound. Solids are fastest than liquids and liquids are faster than gases.
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Why does sound travel faster in solids and liquids than in gases?
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The molecules are closer together in solids.
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Is sound intensity subjective or is loudness subjective? Why?
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Loudness is a subjective measure of intensity, which is objectively measured in decibels.
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Why do different objects make different sounds when dropped on a floor?
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Every object has a natural frequency when disturbed.
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What does it mean to say that everything has a natural frequency of vibration?
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Every object is unique. The characteristics of shape, size, and material determine the solids natural frequency.
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Why is sound louder when a vibrating source is held to a sounding board?
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The vibrations are happening in a greater surface area.
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What is the relationship between forced vibration and resonance?
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A forced vibration at an objects natural frequency creates resonance.
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Why can a tuning fork or bell be set into resonance, while tissue paper cannot?
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Tissue paper does not have a natural frequency.
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How is resonance produced in a vibrating object?
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Forced vibration at a natural frequency will create resonance.
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What does tuning in a radio station have to do with resonance?
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You are trying to match your radio to the broadcast frequency to create resonance.
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Is it possible for one sound wave to cancel another? Explain.
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Yes. When a compression and rarefaction line up destructive interference occurs and the wave cancels.
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How does interference of sound relate to beats?
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When the interference pattern from two vibrating sources at different frequencies have a fluctuating frequency to create beats.
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What did Native Americans learn long ago when they put their ears to the ground?
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They could hear the hoofbeats of distant horses through the ground before they could hear then through the air.
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Suppose a ringing bell is places inside a sealed jar filled with air. The air is then removed from the jar, creating a vacuum. Describe the difference in what the person nearby hears before and after the air is removed from the jar.
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The person will hear the bell ringing when the jar is filled with air. When the air is removed, the person will not be able to hear the sound because sound cannot travel through a vacuum.
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Describe how a child's swing illustrates resonance.
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The child pumps the swing or is pushed in rhythm with the natural frequency of the swing, increasing the amplitude of the swing.
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Describe how antinoise technology is used to protect the hearing of jackhammer users.
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Sound compressing (or rarefactions) from the hammer are neutralized by mirror image rarefactions (or compressions) in the users earphones.
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