Chapter 16 - Sound  Sound waves are longitudinal waves with rarefaction and compression.  As an object’s vibration moves toward air it creates a compression  As the object moves away from air it creates a partial vacuum (rarefaction)

 Sound travels faster through solids and liquids than through air.  Sound can only travel as fast as the air molecules. (about 340 m/sec)  Will sound travel faster in hot or cold air? (Why?)

 The amplitude of a sound wave (the amount of compression) determines the loudness of the sound  Loudness is measured in decibels (dB) Whisper 20 dB Loud conversation dB Loud music dB hearing damage starts Jackhammer 120 dB pain starts

 The wavelength (or frequency) of a sound wave determines the pitch.  The higher the frequency the shorter the wavelength (more energy) High frequency Low frequency wavelength

 Doppler effect – the change in pitch resulting from a moving sound source (like a siren moving past you) The frequency changes as an object moves past you. Higher pitch – moving towards you Lower pitch – moving away from you

 When something moves faster than sound, sound waves pile up and create a shock wave. (sonic boom) Shock Wave

 Sonar – uses the time it takes for a sound wave to bounce back to determine distance. (a depth finder)  Echolocation uses sonar to locate object (Dolphins, whales and bats use echolocation)