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Earth Science: 16.2A Waves. Waves. Waves. Waves: The movement of ocean waters is a powerful thing. Waves created by storms release energy when they crash along a shoreline. Sometimes the energy of water movement can be harnessed and used to generate electricity.

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waves
Waves

Waves:

  • The movement of ocean waters is a powerful thing.
  • Waves created by storms release energy when they crash along a shoreline.
  • Sometimes the energy of water movement can be harnessed and used to generate electricity.

Proposed wave power systems

waves1
Waves
  • Ocean waves are energy traveling along the boundary between ocean and atmosphere.
  • Waves often transfer energy from a storm far out at sea over distances of several thousand kilometers.
waves2
Waves
  • That’s why even on calm days the ocean still has waves that travel across it’s surface.
  • The power of waves is most noticeable along shorelines, the area between land and sea where waves are constantly rolling in and breaking.
waves3
Waves
  • Sometimes waves are low and gentle.
  • Other times waves can be powerful as they pound the shore during a storm and create damage.
  • When you make waves by tossing a pebble in a pond or blowing wind across a pool you are giving energy to the water.
waves4
Waves
  • The waves you see are just the visible evidence of the energy passing through the water.
  • When watching ocean waves, remember that you are watching energy move through a medium; in this case water.
waves5
Waves

Wave characteristics:

  • Most ocean waves obtain their energy and motion from the wind.
  • When a breeze is less than 3 kilometers per hour, only small waves appear.
waves6
Waves

Wave characteristics:

  • At greater wind speeds, waves gradually form and grow larger with increasing wind speeds.
  • Hurricane winds can produce enormous waves as the wind energy transfers to the water through friction as the high winds drive the waves into the land.
wave characteristics
Wave Characteristics
  • The anatomy of an ocean wave can be seen in the illustration at right.
  • The tops of the waves are crests, which are separated by troughs.
  • Halfway between the troughs and the crests is the calm sea level or still water level, which is the level that the water would occupy if there were no waves.
wave characteristics1
Wave Characteristics
  • The vertical distance between the trough and crest is called the wave height.
  • The horizontal distance between two successive crests is called the wavelength.
  • The time it takes one full wave, one wavelength, to pass a fixed position is the wave period.
wave motion
Wave Motion
  • Wave energy can travel great distances across ocean basins.
  • In one study, waves generated near Antarctica were tracked as they crossed through the Pacific Ocean basin.
  • After more than 10,000 kilometers, the waves finally expanded their energy a week later along the shoreline of the Aleutian Islands of Alaska.
  • The water itself does not travel the distance but the energy of the wave does.
wave motion1
Wave Motion
  • As a wave travels, the water particles pass the energy along by moving in a circle.
  • This movement is called circular orbital motion.
wave motion2
Wave Motion
  • Observations of a floating object reveals it moves not only up and down but also slightly forward and backward with each successive wave.
  • This movement results in a circle that returns the object to essentially the same place in the water.
wave motion3
Wave Motion
  • Circular orbital motion allows energy to move forward through the water while individual water particles that transmit the wave energy move around in a circle.
  • The energy contributed by the wind to water is transmitted not only along the surface of the sea but also downward.
wave motion4
Wave Motion
  • However, beneath the surface, the circular wave motion rapidly diminishes until (at a depth equal to one-half the wavelength measured from still-water level) the movement of wave particles become negligible.
  • This dramatic decrease in wave energy with depth is shown by the rapidly decreasing diameters of the wave particle orbits shown at right.
breaking waves
Breaking waves
  • As long as a wave is in deep water, it is unaffected by water depth.
  • However, when a wave approaches the shore, the water becomes shallower and influences the waves behavior.
  • The wave begins to “feel the bottom” at a water depth equal to half it’s wavelength.
  • Such depths interfere with water movement at the base of the wave and slow it’s advance.
breaking waves1
Breaking waves
  • As a wave advances toward the shore, the slightly faster waves farther out to sea catch up and decrease the wavelength.
  • As the speed and length of the wave decrease, the wave steadily grows higher as the crests of the wave move suddenly closer together.
  • Finally, a critical point is reached when the wave is too steep to support itself, and the wave front collapsesor breaks causing water to advance up the shoreline.
breaking waves2
Breaking waves
  • The turbulent water created by breaking surf is called surf.
  • On the landward side, the sheet of water from the collapsing waves is called swash.
  • When the energy from the swash is extended, the water than flows back down the beach toward the surf zone as backwash.