CBSE Class 11 — Notes, Chapters & Practice Quizzes

Chapter 13: Movements of Ocean Water

Summary

Ocean water is dynamic, moving horizontally as waves and currents and vertically as tides. Waves are energy, not water, moving across the surface; water particles travel in small circles while the wave train moves ahead, and waves break when the depth is less than half the wavelength. Waves get their energy from the wind, and their size depends on wind strength, duration and fetch. Tides are the periodical rise and fall of the sea level, mainly due to the gravitational attraction of the moon and, to a lesser extent, the sun, together with the centrifugal force, which create two tidal bulges. Tides are classified by frequency (semi-diurnal, diurnal, mixed) and by the sun-moon-earth positions: spring tides (higher, when sun, moon and earth are aligned, at full and new moon) and neap tides (lower, when sun and moon are at right angles). Tides aid navigation, fishing, desilting and tidal power generation. Ocean currents are continuous flows of water in a definite direction, driven by primary forces (solar heating, wind, gravity, the Coriolis force) and secondary forces (density differences). They are classified by depth (surface and deep-water) and by temperature (warm and cold). Currents influence climate, fog and the world's best fishing grounds where warm and cold currents mix.

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