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17.4 Sound and Hearing
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Sound Waves Longitudinal waves
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Properties of Sound Waves
Speed Intensity & loudness Frequency & Pitch
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At 200C the speed of sound is 342 m/s
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Varies based on the medium (phase & temp.) Fastest in solids
Speed Varies based on the medium (phase & temp.) Fastest in solids Depends on density and elasticity of medium
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Intensity and loudness
Intensity = rate wave’s energy flows through area
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Intensity and loudness
Depends on amplitude and distance from source
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Which wave is the loudest?
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Measured in decibels (dB)
Intensity Measured in decibels (dB) 0 dB = barely can be heard 15-20 dB = whisper 40-50 = normal conversation 120 = threshold of pain in humans = jet engine taking off
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Physical response to intensity Varies based on physical factors
Loudness Physical response to intensity Varies based on physical factors
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As intensity increases, loudness increases.
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Pitch is frequency as you perceive it.
Frequency & Pitch Pitch is frequency as you perceive it. Remember: long wavelength = low frequency
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High frequency sounds have a high pitch.
Frequency & Pitch High frequency sounds have a high pitch. Low frequency sounds have a low pitch.
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Which wave has the highest pitch?
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Which wave is the loudest? Which wave has the highest pitch?
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Sound People can hear between 20 and 20,000 Hz. Infrasound is lower than people can hear. Ultrasound is higher than people can hear.
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Used in sonar and ultrasound imaging.
Sonar- determines distance to an object underwater
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Ultrasound Ultrasound imaging
Most people hear sounds between 20 Hz and 20,000 Hz. Infrasound- sound at frequencies below what people can hear. Ultrasound is higher than what people can hear. Sonar- technique for determining the distance to an object under water. Ultrasound imaging
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Ultrasound Imaging Ultrasound pulses are sent into a patient
Each pulse is short (1/8000 second) Pulses are too short for the reflection to interfere with the next pulse Reflected pulses make a detailed map of structures/organs inside the body
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Ultrasound Imaging
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Fetal Ultrasound Face
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Kidney Ultrasound
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Heart Ultrasound
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Change in frequency caused by motion of the source, listener, or both.
Doppler Effect Change in frequency caused by motion of the source, listener, or both.
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The Doppler Effect
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Higher frequency when approaching Lower frequency when moving away
Doppler Effect Higher frequency when approaching Lower frequency when moving away
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The Ear 3 parts: Outer Middle Inner
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Parts of the Ear
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Gathers and focuses sound into middle ear About 2.5 cm long
Outer Ear Gathers and focuses sound into middle ear About 2.5 cm long
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Outer Ear
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Receives and amplifies sound vibrations Contains 3 bones:
Middle Ear Receives and amplifies sound vibrations Contains 3 bones: Hammer, anvil, & stirrup
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Middle Ear
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Inner Ear Uses nerve endings to sense vibrations and send signals to the brain Made up of the cochlea- spiral shaped canal filled with fluid and lined by thousands of nerve cells with tiny hair-like projections
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Inner Ear
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Hearing Sound is funneled by the outer ear It hits the eardrum
The eardrum vibrates at the same frequency as the sound waves hitting it. The vibration is transferred to the hammer The hammer hits the anvil The anvil moves the stirrup back and forth Vibrations then enter the cochlea
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Hearing The hair-like projections in the cochlea sense vibrations
The nerve cells send electrical impulses to the brain
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Reproducing Sound Sound waves are converted into electronic signals that can be processed and stored. To hear the sound, the electronic signals are converted back into sound waves.
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Recreating Sound Electronic signals vibrate a magnet that is attached to a membrane. The membrane sends sound waves through the air. The reverse process is used to record sound.
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Resonance Response of a standing wave to another wave of the same frequency Depends on interference (constructive or destructive)
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