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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.


Fig. 6.1. (A) High tide at Ma‘ili Point on the island of O‘ahu, Hawai‘i

Image by Alyssa Gundersen

Fig. 6.1. (B) Low tide at Ma‘ili Point

Image by Alyssa Gundersen

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:



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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.