what is sound? define, define, define!
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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). - PowerPoint PPT PresentationTRANSCRIPT
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)
“If a tree falls in a forest far from any sound detector (human ear,
microphone, etc.), does the tree's fall make any noise?”
Know thy “enemy”
Did you know?
Changes in air pressure perceived as sound are the same as…
Did you know?
Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology
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
So many waves, but which is the one…
Nice animated examples: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l1c.html
Sound - longitudinal
Soundvibrations, vibrations, vibrations
Sound simple harmonic motion
Simple harmonic motion
• Vibrating system• Common property: motion repetitive
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 itself3. Frequency – how often the wave repeats itself during time unit4. Amplitude – how high and low wave oscillations are5. Phase – position of a wave at a certain time
Simple harmonic motion
Refraction wave bends(refracts) around the object
• Obstacle size: smaller than a wavelength
Reflection the wave reflects away from the object
• Obstacle dimensions significantly larger than wavelength
• any change in the medium
Reflection on a string
Reflection within a tube
Superposition waves in a crowd
Standing waves
STRING bound at both ends
Tube closed at both ends
Tube opened at both ends
Tube closed at one ends
Velocity and pressure