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Sound

Sound. Ch 13.1 – 13.2. Sound Waves. Sound waves produced by vibrating objects longitudinal mechanical As objects vibrate, a series of compressions and rarefactions are created

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Sound

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  1. Sound Ch 13.1 – 13.2

  2. Sound Waves • Sound waves • produced by vibrating objects • longitudinal • mechanical • As objects vibrate, a series of compressions and rarefactions are created • a compression is the region of a longitudinal wave in which the density and pressure are greater than normal • A rarefaction is the region of a longitudinal wave in which the density and pressure are less than normal

  3. Sound Waves Longitudinal Wave Vibration of Sound Source

  4. Speed of Sound Waves • The speed of a sound waves depends partially on three things: • Material • vair < vhelium < vhydrogen • Phase vsolid > vliquid > vgas • Temperature • vair,0°C < vair, 25°C < vair, 100°C

  5. Speed of Sound in air • vsound= 331.5 + 0.6T T is temp in °C • Example: to find the speed of sound in air at 63°C vsound = 331.5 + 0.6(63) = 369.3 m/s

  6. Example You are in a canyon when you shout your name. You hear an echo 2 s later. If it were 20°C, how far away is the nearest canyon wall?

  7. Sound Waves • audible sound waves are the waves the average human can hear 20 < f < 20,000 Hz • f < 20 Hz are called infrasonic • f > 20,000 Hz are called ultrasonic • pitch is the perceived highness or lowness of a sound • pitch is determined by the freq. of the wave • high freq. = high pitch • low freq = low pitch

  8. Ultrasonic Waves • Medical applications of Ultrasonic Waves • Sonograms • Ultrasonic waves used to produce images of objects inside the body • Break up Kidney stones • vibrations of the waves cause stones to break apart and pass through excretory system

  9. Sound waves • Sound waves propagate in 3D • concentric circles are used to depict the center of compressions (wave front) of a sound wave • the distance between adjacent wave fronts is = to one wavelength

  10. Sound Waves • For a stationary object that is emitting sound waves… The distance between each circle represents the wavelength. Tighter circles means shorter wavelength and higher frequency and pitch

  11. VIDEO 13-1 Doppler Effect Sonic Booms • For a moving object that is emitting sound waves… shorter λ = higher freq. longer λ = lower freq. higher freq. = higher pitch lower freq. = lower pitch Behind In Front

  12. STOP

  13. 13-2 Resonance • Natural Frequencies • Frequency of vibration determined by the physical parameters of the vibrating object • Resonance • a condition that exists when the frequency of a force applied to a system matches the natural frequency of vibration of the system • Increases the intensity & amplitude of the sound

  14. Harmonics • Fundamental Frequency - the lowest frequency of vibration of a standing wave. • Harmonics are multiples of the fundamental frequency

  15. Calculating Harmonic Number In a pipe open at both ends

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