Sound P1.19 - P1.18

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  • SOUND
    • longitudinal wave
      • compressions and rare fractions
      • particles move back and forth
        • parallel with direction of movement
      • direction of energy transfer parallel to vibrations
    • travels through a medium
    • frequency determines pitch
    • Infrasound
      • uses
        • communication between animals
        • detection of animal movement in remote locations
        • detecting the passage of meteors
        • detecting volcano eruptions
          • Volcanic eruptions release infrasound
            • can be detected with sensors
      • sound waves with frequencies less than 20 Hz
        • can't be heard by humans but can be detected using microphones
    • Ultrasound
      • sound waves with frequencies greater than 20 000 Hz
        • can't be heard by humans but can be detected using microphones
      • uses
        • communication between animals
        • sonar
          • loudspeaker on a ship emits a pulse of ultrasound
            • reflected by sea bed
          • distance = speed x time
            • depth is half distance travelled by sound
              • because it has to go and come back
          • used to find depth or detect fish
        • foetal scanning
          • probe emits and receives ultrasound waves
            • machine detects time between sending pulse and receiving echo
          • gel used to stop ultrasound reflecting around the skin
          • ultrasound safer than x ray

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