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Waves

Waves. Chap 10. The energy of the wind is transferred to the water. The wind blows over the water and piles it up into waves. The stronger ( faster ) the wind, the bigger the waves. The longer distance over which the wind can blow ( 'fetch' ), the bigger the waves.

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Waves

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  1. Waves Chap 10

  2. The energy of the wind is transferred to the water. • The wind blows over the water and piles it up into waves. • The stronger (faster) the wind, the bigger the waves. • The longer distance over which the wind can blow ('fetch'), the bigger the waves. • The more days a given wind blows (time), the bigger the waves.

  3. Waves have identifiable parts • crest (p.222, f.10.2-3) • trough • wavelength (L) • wave height (also called amplitude) (H) • period • celerity

  4. How water moves in a wave? • Waves don't actually move water from one place to another. • Water in a wave moves up and down. • The water moves up as a crest passes, and moves down as a trough passes. •  Each molecule of water draws a circle as one complete wave (crest to crest) passes.

  5. waves are moving from left to right (p.233, f.10-1,3) • As the wave crest approaches the seagull, the bird moves UP. • As the trough approaches, the bird moves DOWN. • There is a small amount of side-to-side motion (more with longer wavelengths), but mainly the water motion is up and down. • This is called orbital motion.

  6. The circle (=orbit) of water motion at the surface sets in motion another orbit of water beneath it. • However, some of the energy from the first orbit is lost, so the next orbit is somewhat smaller • Eventually the orbit of motion gets so small, it disappears altogether, and there is no motion.

  7. This water depth is called wave base and is usually ~1/2 the wavelength. • This means that waves in deep water do not touch bottom!!! They do not touch bottom unless the water depth is less than 1/2 the wave's wavelength. • Waves start out in the open ocean, and eventually move toward land, across the continental shelf and up onto the beach.

  8. As waves approach the beach, water depth decreases (it gets shallow!), and • waves start to touch bottom where water depth is around 1/2 the wavelength. • When waves begin to touch the seafloor, friction starts to distort the perfect circles of the orbits. • The orbits change from circles to ellipses (oval-shaped)

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