Sound Ch 13.1 – 13.2

Sound Waves Sound waves mechanical 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

Sound Waves Longitudinal Wave Vibration of Sound Source

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

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

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?

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

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

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

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

13-1 Doppler Effect For a moving object that is emitting sound waves… 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 In Front Behind

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13-2 Resonance 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

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

Calculating Harmonic Number In a pipe open at both ends fn = n v n = 1, 2, 3, . . . 2L Frequency = harmonic number x (speed of sound in the pipe) (2)(length of vibrating air column)