Tides

Note that tides on Earth are caused by a combination of Earth's rotation, the Moon's gravity, and the Sun's gravity (other planets contribute negligible forces as well). Water is by far the object most displaced by tidal forces on Earth, but Earth's atmosphere, liquid core, and surface are also effected to a less noticeable degree. Tides exist everywhere, even in small bodies of water and even on other planets (with or without liquid water). Ice-surfaced Europa may have a liquid water core due to heat from friction caused by the tidal forces of Jupiter and large neighboring moons plying the planet's shape. A long term effect of tidal forces is to cause speed and rotation of the objects to reach a mutual equilibrium, making the two objects tidally locked. Galactic level tides exist as well and have many long term effects, such as plying the shape of our local Ort Cloud and contributing to the phenomenon of long-period comets.

The science fiction genre may make use of extreme tidal effects; such as having relatively large solid objects levitating due to close proximity of a neighboring planet.