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What is sound? define, define, define! Changes in air pressure Perception of the changes We can hear from about 15 changes per second to 20000 changes per second (Hz)
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“If a tree falls in a forest far from any sound detector (human ear, microphone, etc.), does the tree's fall make any noise?”
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Know thy “enemy”
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Did you know? Changes in air pressure perceived as sound are the same as…
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Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology
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Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology Difference? Weather – greater magnitude, and change far more slowly
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So many waves, but which is the one… Nice animated examples: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l1c.html
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Sound - longitudinal
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Sound vibrations, vibrations, vibrations
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Sound simple harmonic motion
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Simple harmonic motion Vibrating system Common property: motion repetitive
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1.Period – time between two repetitions (duration of one cycle) 2.Wavelength – the distance between corresponding points, from cycle to cycle as the wave repeats itself 3. Frequency – how often the wave repeats itself during time unit 4. Amplitude – how high and low wave oscillations are 5. Phase – position of a wave at a certain time Simple harmonic motion
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Refraction wave bends(refracts) around the object Obstacle size: smaller than a wavelength
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Reflection the wave reflects away from the object Obstacle dimensions significantly larger than wavelength any change in the medium
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Reflection on a string
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Reflection within a tube
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Superposition waves in a crowd
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Standing waves
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STRING bound at both ends
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Tube closed at both ends
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Tube opened at both ends
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Tube closed at one ends
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Velocity and pressure
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