Theory of tides

The physical account of ocean tides as the response of Earth’s oceans to lunar and solar gravity, Earth’s rotation, and the shape and motion of ocean basins.

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Tidal force: A differential gravitational force across an extended body, arising because gravity changes with distance. The Moon’s gravity varies across Earth, creating the force that drives tidal deformation.
Newton's law of universal gravitation: The law stating that any two masses attract with a force proportional to their masses and inversely proportional to distance squared. Its distance dependence makes the Moon’s near and far sides pull differently.
Tide prediction: The estimation of future sea levels and tidal currents from astronomical cycles and observations. Harmonic tide theory turns constituent amplitudes and phases into local forecasts.
Tidal locking: A state in which a rotating body’s rotation period matches its orbital period, keeping one side facing its companion. It concerns long-term rotational synchronization, not the daily ocean response to tidal forces.
Isaac Newton: The English mathematician and physicist who formulated classical mechanics and universal gravitation. Newton used gravitation to explain the Moon’s and Sun’s influence on tides.
Equilibrium tide: An idealized global ocean surface shaped instantaneously by lunar and solar gravity on a nonrotating Earth. It predicts two tidal bulges but omits basin dynamics and Earth’s rotation.
Moon: Earth’s natural satellite, whose gravity is the strongest astronomical influence on terrestrial tides. Its changing position supplies the dominant periodic tidal forcing.
Tidal current: A periodic horizontal movement of seawater driven chiefly by the rise and fall of tides. The same tidal forcing that changes sea level also drives currents.
Tidal acceleration: The gradual change in an orbiting body’s orbital motion caused by tidal interactions and transfer of angular momentum. It is a long-term orbital consequence of tides rather than a theory of ocean water levels.
Equilibrium theory of tides: The idealized theory that treats Earth’s ocean as a global fluid surface in gravitational equilibrium. It formalized the static-bulge approach that later dynamic accounts refined.