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What is a sound wave?. Mechanical wave – longitudinal A vibration Particles of medium are disturbed Causes a wave. causes. Most common medium is air Can travel through solids and liquids. Sound Interactions. Reflection Echo - when a sound wave reflects off a surface. - PowerPoint PPT Presentation
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What is a sound wave?• Mechanical wave – longitudinal
*A vibration
*Particles of medium are disturbed
*Causes a wave
causes
Most common medium is air Can travel through solids and liquids
Sound Interactions• Reflection– Echo - when a sound wave reflects off a surface.• Harder and smoother the surface the stronger the reflection.
• Diffraction– Through openings (doorways)– Around corners
• Interference– Can be:• Destructive – sound will be fainter• Constructive – sound will be louder
Speed of Sound (SOS)
• 343 m/s – at room temperature through air• Depends on medium sound is traveling
through–3 characteristics of the medium affect SOS:
1. Elasticity2. Density3. Temperature
Elasticity• The ability of a medium to bounce back
after being disturbed.• More elastic medium – the particles
bounce back faster – sound travels faster.• Less elastic medium – the particles bounce
back slowly – sound travels slower.• From faster to slower: solids > liquids >
gases
Density• Sound travels more slowly in
denser mediums• Due to particles not moving as
quickly back to rest position in denser materials (too crowded).
Temperature• Sound travels more slowly
at lower temperatures than higher temperatures.•Because particles move
slower in lower temperatures.
SOS final thoughts• The faster the particles of the medium can
return to rest position – the faster sound will move through medium.– More elastic – faster (bounce back quicker)– Less dense – faster (not as crowded)– Higher temp – faster (particles naturally move faster)
• First person to break sound barrier (go faster than sound) – Chuck Yeager– Flew at higher altitude b/c lower temp = lower SOS
Properties of sound• Loudness – depends on
amount of energy used to create sound (amplitude of wave).• Pitch – depends on frequency
of wave.
Loudness• Depends on 2 things:–The amount of energy it takes to make the
sound.–The distance from the source of the sound.
• Decibel (dB) – unit for loudness of sound• Intensity – The amount of energy a sound
wave carries over a certain amount time in a particular area.
Pitch• How high or low the sound seems• High pitch – high frequency• Low pitch – low frequency• Ultrasound – sound waves with freq. above
normal human hearing. (Usually above 20,000 Hz)
• Infrasound – Below human range of hearing (usually under 20 Hz)
The Doppler Effect• The change in frequency (pitch) as a source
of sound MOVES in relation to the observer.–Pitch increases as source moves toward
observer.–Pitch decreases as source moves away.
• Think of a siren approaching then passing by. It sounds different.
• Can happen with light waves also.