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Introduction to Tides

Tides are the periodic rise and fall of surface water caused by the gravitational force of the moon and the sun and by the rotation of the earth. The movements of the solar system that influence the tides are predictable; therefore changes in tide height and time are predictable. As tides change, large quantities of water move toward or away from shore causing tidal currents. The movement of tidal currents contributes to ocean circulation.

<p><strong>Fig. 6.1.</strong> (<strong>A</strong>) High tide at&nbsp;Ma‘ili Point on the island of O‘ahu, Hawai‘i</p><br />
<p><strong>Fig. 6.1.</strong> (<strong>B</strong>) Low tide at&nbsp;Ma‘ili Point</p><br />

Ocean Literacy Principles

Principle 1: The earth has one big ocean with many features.

Ocean Literacy Fundamental Concept: Throughout the ocean there is one interconnected circulation system powered by wind, tides, the force of the earth’s rotation (Coriolis effect), the sun, and water density differences. The shape of the ocean basins and adjacent landmasses influence the path of circulation. (OLP 1c)


To build an understanding of the periodic rise and fall of surface water, it is important to understand the predictable movements of the earth, the moon, and the sun, which produce tides due to a combination of gravitational forces.


These concepts will be explored in this unit through the following activities and investigations:


Activity: Kinesthetic Model of the Sun, the Moon, and the Earth

Model the movements of three objects in our solar system—the sun, the moon, and the earth—using your body.


Activity: Tide Formation—Gravitational Pull

Graph the combined effect of tidal changes caused by the sun and the moon during a spring tide and a neap tide.


Activity: Modeling Amphidromic Points

Model tidal movement and height within ocean basins.


Activity: Tide Prediction

Plot a tide graph from a tide table.


Activity: Tidal Patterns Across the Globe

Compare tide records in two parts of the world.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.