Gravities

Gravities, in a scientific sense, refer to the set of phenomena associated with gravitation, the attractive interaction that acts between masses. In Newtonian physics, gravity is described by the universal law of gravitation, F = G m1 m2 / r^2, which implies an inverse-square force that governs the orbits of planets, moons, and artificial satellites. In Einstein's general relativity, gravity is not a force but the curvature of spacetime produced by mass-energy, with objects moving along geodesics in curved geometry.

On Earth, gravity gives weight. The standard gravity, defined as g = 9.80665 m/s^2, is a conventional reference value at sea level and near the equator, but actual gravitational acceleration varies with altitude, latitude, and geology. These variations are measured with gravimeters and used in gravity models such as EGM2008 to understand Earth's shape and mass distribution.

Gravitational interactions also govern orbital mechanics. The gravitational parameter μ = GM determines orbital speeds and trajectories; gravity assists use the gravity of celestial bodies to change a spacecraft's path. In many real-world settings, objects in free fall experience microgravity, as in orbit, where apparent weightlessness arises from continuous acceleration toward a central body.

Related concepts include gravitational potential energy, gravitational fields, and gravitational waves—ripples in spacetime produced by accelerating masses, predicted by general relativity and detected experimentally in 2015 onward. Gravity remains the dominant interaction shaping astrophysical, planetary, and cosmological processes at large scales, while other forces prevail at atomic and subatomic scales.