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Chapter 26 Sound

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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

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Chapter 26 Sound

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  1. Chapter 26Sound Conceptual Physics Hewitt, 1999 Bloom High School

  2. 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 • Infrasonic- frequencies <20 Hertz • Elephants, whales, earthquakes • Ultrasonic- frequencies >20,000 Hertz • Plastic welding, jewelry cleaning, mixing

  3. 26.2 Sound in Air • Sound travels in longitudinal waves • Compression- molecules pushed together represent a crest • Rarefraction- molecules pulled apart represent a trough

  4. Rubens Tubes • Uses 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

  5. 26.3 Media that Transmit Sound • Sound needs something to compress to transmit energy • Gases- air, usually • Liquids- water (whale and dolphin communications) • Solids- earthquakes, railroad tracks • Sound cannot travel in space • Ever hear the Death Star explode?

  6. 26.4 Speed of Sound • Speed of sound is dependant on how close the molecules are • The 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 °C • v=d/t (still and always)

  7. 26.5 Loudness • Loudness- how our anatomy interprets amplitude (volume) • Decibel (dB)- 1/10th of a bel • Each level 10 times as loud as the prior level

  8. 26.6 Forced Vibrations • Forced vibrations- a non-vibrating object that vibrates as a result of other vibrations • Tuning fork alone vs. tuning fork on a tabletop

  9. 26.7 Natural Frequency • Natural frequency- depends on material, elasticity of object, shape of object • Small brass bell vs. large brass bell • Baseball bat vs. wrench dropped on the floor • Champagne glass

  10. 28.8 Resonance • Resonance- when the frequency of a forced vibration matches a natural vibration • Kicking your legs while swinging to go higher • Increase in amplitude (loudness) • Crest overlaps with crest • Tacoma Narrows Bridge Collapse

  11. 26.9 Interference • Interference- waves from two separate sources overlapping • Constructive interference- the crest of one wave overlaps with the crest of another wave • Increases amplitude (loudness) • Destructive interference- the crest of one wave overlaps with the trough of another wave • Decreases amplitude (loudness) • http://www.falstad.com/interference/

  12. 26.10 Beats • Beats- 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

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