Waves & the Earth

P1.18 Infrasound
1. frequencies
  1. humans hear between 20Hz-20,000Hz
  2. infrasound - below 20Hz
2. uses
  1. communication between animals
    1. e.g. whales&elephants
  2. detecting animal movement in remote location
  3. detecting volcanoes&meteors
3. calculations
P1.19 Ultrasound
1. frequencies
  1. ultrasound - above 20,000Hz
2. uses
  1. sonar
    1. find depth of water below boat
  2. communication between animals
    1. e.g. bats&dolphins
  3. foetal scanning
3. calculations
P1.20 Seismic Waves
1. P&S waves
  1. caused by earthquakes+explosions
  2. P waves=longitudinal
    1. faster
    2. travel through liquids+solids
  3. S waves=transverse
    1. slower
    2. travel through solids
  4. detected by seismometres
2. reflection&refraction
  1. seismic waves reflected&refracted
    1. at boundaries between crust,mantle+core
P1.22 Detecting Earthquakes
1. hard to predict when
  1. unsure of size of forces acting on tectonic plates
  2. unsure of amount of friction on plates
2. locating earthquakes
  1. 1. many seismometers detect P&S waves
  2. 2. P=faster so arrives first
    1. greater difference in time between waves=greater difference between seismometer+earthquake
  3. 3. scientists work out distance from each seismometer
    1. find out where earthquake happened
  4. at least 3 seismometers used
3. causes of earthquakes
  1. 1. tectonic plates move due to convection currents in mantle
  2. 2. plates slide past each other
  3. 3. friction-don't slide smoothly
  4. 4. forces build up till part of plate breaks
  5. 5. plates move with sudden jerk-earthquake!

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Waves & the Earth

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	Erstellt von larissa.hayden08 vor mehr als 9 Jahre