Tides

Tides are recurring rises and falls in sea level caused mainly by the Moon’s and Sun’s gravity and Earth’s rotation. Their timing and range vary with coastline shape, ocean depth, and the alignment of these bodies.

Tidal force: A difference in gravitational force across an extended body, which can stretch or deform it. The Moon’s changing gravitational pull across Earth helps produce tidal bulges.
Lunar day: The time Earth takes to rotate once relative to the Moon, about 24 hours and 50 minutes. Its length helps explain why successive high tides occur later each day.
Tidal range: The vertical difference between high water and the following low water. It quantifies the water-level change relevant to coastal operations and structures.
Ocean surface wave: A surface disturbance that transfers energy through the ocean, commonly generated by wind. Waves oscillate over short periods, unlike the long-cycle rise and fall of tides.
Tidal locking: A state in which an orbiting body’s rotation period matches its orbital period around another body. Tidal dissipation helped synchronize the Moon’s rotation with its orbit around Earth.
Equilibrium tide: An idealized model of ocean tides as bulges aligned with the positions of the Moon and Sun. It explains the basic gravitational picture before real ocean dynamics are considered.
Spring tide: A tide with an unusually large range, occurring near new and full moons. Lunar and solar tidal effects reinforce one another during these alignments.
Tidal bore: A moving surge that travels upriver when an incoming tide is funneled into a narrowing estuary. It is a striking hazard and natural spectacle produced by particular tidal conditions.
Ocean current: A sustained movement of seawater in a particular direction. Tidal currents are one type of current, but currents also arise from wind and density differences.
Tidal acceleration: The gradual increase in the Moon’s orbital distance and period caused by angular-momentum transfer from Earth’s rotation. Ocean tides transfer rotational energy and angular momentum to the Moon’s orbit.

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