Cause of the tides

Cause of the tides

. The Moon's gravitational attraction causes two tidal bulges in the Earth's ocean water, one on the closest side to the Moon and one on the farthest side. The Earth's rotation twists the closest bulge ahead of the Earth-Moon line (dashed line), and this produces a lag in time between the time the Moon is directly overhead and the highest tide. The Moon pulls on the nearest tidal bulge, slowing the Earth's rotation down. At the same time, the tidal bulge nearest the Moon produces a force that tend to pull the Moon ahead in its orbit, causing the Moon to spiral slowly outward.

Copyright 2010, Professor Kenneth R. Lang, Tufts University