SOUND WAVES

PRODUCTION  Vibrating prongs set the air molecules in motion  Top: molecules closer together high air pressure (compression)  Bottom: molecules spread apart low air pressure (rarefaction)

 The crests correspond to compressions  The troughs correspond to rarefactions  Sound is a longitudinal wave  Sine curve is air pressure

CHARACTERISTICS  Frequency determines pitch  Frequency of a sound wave the pitch rises (vise versa)  Frequency can be measured  Pitch refers to how different f are perceived by the human ear

Ultrasonic Waves  Can be used to produce images inside the body  Short wavelengths are easily reflected off small objects (no audible or infrasonic)  must be about the same size or smaller than the object

 Sounds waves can travel through solids, liquids, and gas  Closer molecules are together, faster the sound travels.  Waves consist of particle vibrations solid faster than gas

Doppler Effect  The f of a sound remains constant  Which wave front reaches the observers more often?  Speed of the sound waves does not change  f can be less than or more than the source

Definition  Doppler effect A frequency shift that is the result of relative motion between the source of waves and an observer A frequency shift that is the result of relative motion between the source of waves and an observer Can happen when: Can happen when: 2 objects are moving2 objects are moving The source is stopped and the observer is movingThe source is stopped and the observer is moving Both sounds are movingBoth sounds are moving

Sound Intensity  Sound waves travel outward from their source, energy is transferred from 1 air molecule to the next

What is the intensity of the sound waves produced by a trumpet at a distance of 3.2 m when the power output of the trumpet is 0.20 W?  P = 0.20 Wr = 3.2m  Intensity = P/4 πr 2  Intensity = 0.20 W / (4 π(3.2 2 ))  Intensity = W/m 2

Intensity and Frequency  Intensity and Frequency determine which sounds are audible  Softest sounds that can be heard by the avg. human ear occur at 1000Hz and an intensity of 1.0 x  Loudest sounds (threshold of pain) occur at an intensity of 1.0 W/m 2 This can cause immediate damage to the ear even if no pain is felt This can cause immediate damage to the ear even if no pain is felt

 Intensity is measured in decibels Relating the intensity of a sound wave to the intensity at the threshold of hearing Relating the intensity of a sound wave to the intensity at the threshold of hearing How does the intensity of a sound wave compare to what you can hear?How does the intensity of a sound wave compare to what you can hear? The higher the decibel the louder it sounds to youThe higher the decibel the louder it sounds to you An increase in 10 dB means that the sound is twice as loud An increase in 10 dB means that the sound is twice as loud

 Natural frequency: causes an object to vibrate  Resonance: when the frequency of a force applied to a system matches the natural frequency of vibration of the system  zczJXSxnw&eurl= o-detail/humber-bridge-part-1moving-road- deck-in-high-winds/ zczJXSxnw&eurl= o-detail/humber-bridge-part-1moving-road- deck-in-high-winds/ zczJXSxnw&eurl= o-detail/humber-bridge-part-1moving-road- deck-in-high-winds/