Introduction

The tide is a natural movement; in others words, it is not created by humans.  It is the reason why the beach is full of water and six hours later, it's empty.  It's the moon and sun that cause this big movement with their gravitational force.  The tide goes in and out regularly each day.  If the moon, the earth and the sun were immobile (don't move), there would be no tide because the tide wouldn't change!