The existence of two daily tides is explained by the Moon's gravitational pull, creating two opposite bulges in Mother Earth’s oceans, combined with her daily rotation, and the interaction of the Moon and the Sun's gravitational forces.

Oscillating currents produced by tides are known as tidal currents. The moment that the tidal current ceases is called slack water. The tide then changes direction and is said to be turning.

The Moon’s gravitational pull must contend with the water’s physical inertia, thus explaining the delay before the tide actually turns, or reverses.