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Chapter 26 Sound. Conceptual Physics Hewitt, 1999 Bloom High School. 26.1 The Origin of Sound. All sound produced by vibration of an object Strings in instrument, reed in a sax, etc. Pitch - how our anatomy interprets frequency (tone or note) Human range 20-20,000 Hertz - PowerPoint PPT Presentation
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Chapter 26Sound
Conceptual PhysicsHewitt, 1999
Bloom High School
26.1 The Origin of SoundAll sound produced by vibration of an object
Strings in instrument, reed in a sax, etc.
Pitch- how our anatomy interprets frequency (tone or note)Human range 20-20,000 Hertz
Infrasonic- frequencies <20 HertzElephants, whales, earthquakes
Ultrasonic- frequencies >20,000 HertzPlastic welding, jewelry cleaning, mixing
26.2 Sound in AirSound travels in longitudinal wavesCompression- molecules pushed together
represent a crestRarefraction- molecules pulled apart represent a
trough
Rubens TubesUses a flammable gas in a metal tube to show how
frequency and wavelength are related to compressions and rarefractions
http://www.youtube.com/watch?v=FOYXomUFyb8
26.3 Media that Transmit SoundSound needs something to compress to transmit energy
Gases- air, usuallyLiquids- water (whale and dolphin communications)Solids- earthquakes, railroad tracks
Sound cannot travel in spaceEver hear the Death Star explode?
26.4 Speed of SoundSpeed of sound is dependant on how close the
molecules areThe closer they are, the faster the speed
Solids- fastest Liquids- fast Gases- slowest
Temperature dependant- the faster the molecules are moving, the faster the speed of sound
v=330m/s + (T)(0.6m/°Cs)Speed of sound in air, T=temperature in °Cv=d/t (still and always)
26.5 LoudnessLoudness- how our
anatomy interprets amplitude (volume)
Decibel (dB)- 1/10th of a belEach level 10 times as
loud as the prior level
26.6 Forced VibrationsForced vibrations- a non-vibrating object that
vibrates as a result of other vibrationsTuning fork alone vs. tuning fork on a tabletop
26.7 Natural FrequencyNatural frequency- depends on material,
elasticity of object, shape of objectSmall brass bell vs. large brass bellBaseball bat vs. wrench dropped on the floorChampagne glass
28.8 ResonanceResonance- when the frequency of a forced vibration
matches a natural vibrationKicking your legs while swinging to go higherIncrease in amplitude (loudness)
Crest overlaps with crestTacoma Narrows Bridge Collapse
26.9 InterferenceInterference- waves from two separate sources
overlapping
Constructive interference- the crest of one wave overlaps with the crest of another waveIncreases amplitude (loudness)
Destructive interference- the crest of one wave overlaps with the trough of another waveDecreases amplitude (loudness)
http://www.falstad.com/interference/
26.10 BeatsBeats- the periodic variation in loudness
Caused by the interference of two slightly different frequencies
www.sciencejoywagon.com/explrsci/media/tonebeat.htm
Used to tune instruments
C:\Program Files\Wolfram Research\Mathematica Player\7.0\MathematicaPlayer.exe