Tidal Force Calculator

There is a bulge on the side of Earth facing the Moon (pulled toward the Moon) and another bulge on the opposite side (where water is left behind because that part of Earth is pulled more toward the Moon than the water is). Both bulges are caused by the differential force: the near side experiences stronger-than-average attraction, the far side experiences weaker-than-average attraction.

Tidal locking occurs when tidal forces slow a body's rotation until it rotates once per orbit — always showing the same face to its host. The Moon is tidally locked to Earth. Most large moons in the Solar System are tidally locked to their planets. Tidal locking occurs over timescales that depend on the mass of the host, the moon's distance, and its composition.

The Roche limit is the orbital distance within which a fluid (or weakly bound) secondary body will be disrupted by the tidal forces of the primary. Inside this distance, tidal forces exceed the secondary's self-gravity. The rigid body Roche limit is closer than the fluid limit. Saturn's rings lie within Saturn's Roche limit, explaining why ring material cannot coalesce into a moon.

Spaghettification is the extreme tidal stretching that occurs when an object falls toward a black hole (or neutron star). The tidal acceleration along the radial direction stretches the object into a long, thin strand while compressing it laterally. For a stellar-mass black hole, spaghettification occurs outside the event horizon. For a supermassive black hole, tidal forces at the event horizon are much weaker and an observer could survive crossing it.

When a moon's orbit is elliptical or influenced by other moons (orbital resonance), its distance from the parent planet varies. This causes the tidal force to change cyclically, constantly flexing the moon's interior. The mechanical energy of this flexing is converted to heat through friction within the moon's material. Jupiter's moon Io experiences such strong tidal heating that it loses as much heat as the entire terrestrial heat flux of Earth.

Yes. In close binary systems, tidal forces distort both stars into ellipsoidal shapes (the Roche lobe geometry). If a star expands (e.g., as it becomes a red giant) to fill its Roche lobe, mass transfers to the companion through the L1 Lagrange point. This mass transfer can trigger novae, form accretion disks around neutron stars or black holes, and eventually lead to Type Ia supernovae if the recipient white dwarf exceeds the Chandrasekhar limit.

The Moon's tidal bulge on Earth is slightly ahead of the Earth-Moon line due to Earth's rotation (Earth rotates faster than the Moon orbits). The Moon's gravity pulls back on this bulge, slowing Earth's rotation by about 1.4 milliseconds per century. This lost angular momentum is transferred to the Moon, which spirals outward by about 3.8 cm per year. Eventually Earth and Moon will be mutually tidally locked.

A tidal disruption event (TDE) occurs when a star passes close enough to a supermassive black hole to be disrupted by tidal forces. Part of the stellar debris falls onto the black hole, producing a luminous flare detectable across the universe. TDEs are observed in optical, UV, and X-ray surveys and provide unique information about otherwise quiescent supermassive black holes in galactic nuclei.

Earth's tidal force on the Moon was responsible for tidally locking the Moon billions of years ago. Today, Earth also raises tidal bulges on the Moon's solid body. The Moon's rock tides (deformation of the lunar crust and mantle) dissipate some energy as heat. The Moon's interior is thus warmer than it would be in the absence of tidal heating, though the effect is much weaker than Jupiter's effect on Io.