Moon - Cause of tides

The strong pull between Earth and Moon, together with the pull of the Sun, is responsible for the patterns of tides on Earth. The rise and fall of tides follow the pull of the Moon on the land as well as the sea. On the side of the Earth closest to the Moon, the sea bulges to produce a high tide. However, the Moon also exerts a pull on the land. In effect, this force pulls the land away from the sea on the far side of the Earth. Water moves to fill the gap, causing tidal bulges on opposite sides of the Earth simultaneously.

When the Sun and the Moon are in line with the Earth, their combined pull creates especially high and low tides. These 'spring tides' coincide with the time of full and new moons in the Moon's 29-day cycle. The friction of tidal waters against their beds is actually showing the Earth down. The time of Earth's rotation is being reduced by 0.001 seconds per day every century. Four hundred million years ago, the Earth's rotational day was 22 hours long.

The Earth's gravitational effect on the Moon is expressed in the flexing of rock, for there is no liquid on the Moon. This flexing has slowed down the Moon's rotation. It now rotates at exactly the same speed as its orbit, which means that the same face is always seen from Earth.