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~ Sound ~ The Nature of Sound Speed of Sound Human hearing Doppler effect “Seeing” with sound
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Speed of Sound 344 m/s in air at 20°C Depends on: Type of medium travels better through liquids and solids can’t travel through a vacuum Temperature of medium travels faster at higher temps
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Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
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Human Hearing Pitch highness or lowness of a sound depends on frequency of sound wave human range: 20 - 20,000 Hz ultrasonic waves subsonic waves
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Human Hearing Intensity volume of sound depends on energy (amplitude) of sound wave measured in decibels (dB)
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Human Hearing 70 80 100 110 120 40 18 10 0 DECIBEL SCALE
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Doppler Effect change in wave frequency caused by a moving wave source moving toward you - pitch sounds higher moving away from you - pitch sounds lower
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“Seeing” with Sound Ultrasonic waves - above 20,000 Hz Medical Imaging SONAR “Sound Navigation Ranging”
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Sound Problems v s = D ÷ T where v s = speed of sound 344 m/s D = distance in m T = time in s v s = f x λ, just like a wave problem!
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Ex #1: Find the wavelength of a 200 Hz sound. GIVEN: v s = 344 m/s f = 200 Hz λ = ? WORK: v s = f x λ λ = v s ÷ f λ = 344 m/s ÷ 200 Hz λ = 1.7 m
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Ex #2: If you hear a sound 3 s after you see the motion, how far away is it? GIVEN: v s = 344 m/s T = 3 s D = ? WORK: v s = D ÷ T D = v s x T D = 344 m/s x 3 s D = 1032 m
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~ Music ` Music vs. Noise Resonance Harmonics Interference Acoustics
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~ Music vs. Noise ` Music specific pitches and sound quality regular pattern Noise no definite pitch no set pattern
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= Resonance = Forced Vibration when one vibrating object forces another object to vibrate at the same frequency results in a louder sound because a greater surface area is vibrating used in guitars, pianos, etc.
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= Resonance = Resonance special case of forced vibration object is induced to vibrate at its natural frequency
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= Resonance = “Galloping Gertie” The Tacoma Narrows Bridge Disaster Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.
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} Harmonics } Fundamental the lowest natural frequency of an object Overtones multiples of the fundamental frequency
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Constructive - louder | Interference | Interference the ability of 2 or more waves to combine to form a new wave Destructive - softer
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= Resonance = Beats variations in sound intensity produced by 2 slightly different frequencies both constructive and destructive interference occur
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_ Acoustics _ Acoustics the study of sound Reverberation echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.
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