Tidal force

Tidal force is the difference in gravitational acceleration across an extended body. It can deform the body, drive tides, and disrupt objects whose self-gravity cannot resist it.

Gravitational gradient: The spatial rate of change of a gravitational field or acceleration. Tidal force is the gravitational gradient acting across an extended body.
Earth tide: The deformation of Earth’s solid body under the gravitational influence of the Moon and Sun. The same differential gravity that moves oceans also flexes the solid Earth.
Gravitational field: A physical field describing the gravitational acceleration experienced at each point in space. Tidal force compares field values at different locations within one body.
Uniform gravitational field: A gravitational field with the same acceleration and direction at every point in a region. It accelerates a body as a whole but produces no tidal force across it.
Newtonian gravity: A theory describing gravitational attraction between masses through an inverse-square force. Its inverse-square field makes gravitational acceleration differ across a body.
Ocean tide: The periodic rise and fall of sea level, driven mainly by lunar and solar gravity. It is the most familiar large-scale consequence of tidal forcing on Earth.
Inverse-square law: A relation in which a quantity decreases in proportion to the square of distance from its source. Newtonian gravity’s distance dependence creates stronger pull on the nearer side of a body.
Centrifugal force: An apparent outward force introduced when motion is described in a rotating reference frame. It can contribute to tidal deformation in rotating systems but is not differential gravity itself.
Geodesic deviation: The relative acceleration of neighboring freely falling paths in curved spacetime. It expresses relativistic tidal effects without treating gravity as an ordinary force.
Io (moon): Jupiter’s volcanic moon, whose interior is strongly heated by tidal flexing. Changing gravitational forces from Jupiter and orbital resonances power its volcanism.

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