The vertical motion of ocean water refers to tides. It is the rise and fall of water in the oceans and seas. Due to the attraction of the sun and the moon, the ocean water is raised up and falls down twice a day. The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational pull, are the major causes for the occurrence of tides. Another factor is centrifugal force, which is the force that acts to counterbalance gravity. Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth.