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Waves and Tides Chapter 16, Section 2 Waves • Ocean waves are energy traveling along the boundary between ocean and atmosphere • Waves transfer energy through the ocean, that’s why even on a calm day in the middle of the ocean there may still be waves from a far off storm Waves Wave Characteristics • Most ocean waves obtain their energy and motion from the wind • Crests – the tops of the waves • Troughs – the bottoms of the waves • Wave Height – the vertical displacement between crest and trough • Wavelength – the horizontal distance between two successive crests or two successive troughs • Wave Period – the time it takes one wavelength to pass a fixed position Wave Characteristics • The height, length, and period that are eventually achieved by a wave depend on three factors: (1) wind speed; (2) length of time the wind has blown; and (3) fetch • Fetch – distance that the wind has traveled across open water Wave Motion • Waves can travel great distances across ocean basins • As a wave travels, the water particles pass the energy along by moving in a circle; so the water doesn’t move, only the energy • Circular orbital motion allows energy to move forward through the water while the individual water particles that transmit the wave move around in a circle • The wind energy is not only transmitted along the surface, but also downward Anatomy of a Wave Breaking Waves • As long as a wave is in deep water, it is unaffected by water depth • When a wave approaches shore, the water becomes shallower and influences wave behavior • As a wave advances on the shore, the slightly faster waves further out will catch-up and decrease the wavelength, making the wave grow steadily higher • When a critical point is reached, the wave is too steep to support itself and the wave front collapses, or breaks, and the water advances up the shore Breaking Waves BREAK! Tides • Tides are regular changes in the elevation of the ocean surface • Other than waves, they are the easiest ocean movements to observe • Newton showed that there is a mutually attractive force between any two bodies, Earth and the moon • Ocean tides result from differences in the gravitational attraction exerted upon different parts of Earth’s surface by the moon and, to a lesser extent, by the sun The Cause of Tides • The primary body that influences the tides is the moon • The gravitational pull is greatest on the side of Earth closest to the moon, causing Earth to be stretched slightly • On the side of Earth closest to the moon, the pull of the moon’s gravity on the oceans is greater than it is on solid Earth • Water will flow towards this tidal “bulge”, creating a high tide • As Earth rotates, it will go “through” the tidal bulges, resulting in alternating high and low tides Cause of Tides Tidal Cycle • The sun also produces tidal bulges, slightly smaller than those produced by the moon • The influence is most noticeable during new and full moon phases (Earth-moon-sun are aligned), causing larger tidal bulges • Tidal Range – the difference in height between successive high and low tides • Spring Tides – have the greatest tidal range due to the alignment of the Earth-moon-sun system (new and full moons) • Neap Tides – daily tidal range is less due to the sun and moon acting against each other Spring Tides Neap Tides Tidal Patterns • Tides at various locations respond differently to the tide-producing forces • Three main tidal patterns exist worldwide: diurnal tides, semidiurnal tides, and mixed tides • Diurnal Tidal Pattern – characterized by a single high tide and a single low tide each tidal day • Semidiurnal Tidal Pattern – characterized by two high tides and two low tides each tidal day • Mixed Tidal Pattern – characterized by a large inequality in high water heights, low water heights, or both Tidal Patterns Assignment • Read Chapter 16, Section 2 (pg. 455-460) • Do Section 16.2 Assessment #1-7 (pg. 460)
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