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Energy transmitted through matter BUT no transport of matter !

  • Period (t): time that one wavelength (l) needs to pass one point [s]
  • Frequency (n): number of wavelengths per unit time = 1 / t [s-1]
  • Wave speed (v): distance a wave point travels per unit time [m s-1]
    • Deep-water waves, z > ½ l -->  v = l / t    
    • Shallow-water waves, z < 1/20 l --> v = 3.1 x SquareRoot(z)
Making waves...
  • Wind deforms water surface and creates small ripples (Wavelength l < 1.7 cm; capillary waves)
  • Ripples offer more troughs to catch wind, more energy is transferred into the water
  • Bigger waves with l > 1.7 cm develop – gravity waves
  • Wind energy increases wave height, length, speed
  • Wave height increases faster than wave length, crests become pointed and troughs rounded; if wind speed = wave speed, then no net energy exchange, wave has reached maximum size and speed
  • Waves break in open ocean when steepness = height/wave length = 1/7 
  • Factors that determine wave energy: (a) wind speed; (b) duration of wind; (c) wind fetch = distance of water over which wind blows in the same direction
Orbital movements in waves

  • Deep water: orbital movement stops at z = ½ l, particle movement decreases exponentially with depth
  • Shallow water: particles move on very flat ellipses. Particle movement remains the same over the entire water depth

  • Long waves move out and ahead of storm area
  • Their speed is faster than wind speed outside the storm area
  • Wave steepness decreases: swell
  • Run over long distance with minimum energy loss
  • Eventually form groups or trains of waves, which travel at ½ speed of individual waves
  • Because it takes time and energy to cause the water to oscillate, the first wave disappears but new wave forms at the end of  group
  • Waves slow down when they come in contact with bottom
  • If waves arrive at an angle different of  90°, the near-shore part ‘feels’ bottom first and slows down
  • Thereby, wave fronts turn towards the coast and all waves arrive 90°