Answer: Technically, a body is not in a situation of weightlessness in free fall if it is large enough, or if the gravitational field is sufficiently intense and non-uniform, for the body to be subject to non-negligible tidal forces.
The gravity field is the attractive field which is exerted on any body endowed with a mass on the Earth (or another star). It is about an acceleration field, often called more simply gravity or “g” 1. Most of the earth’s gravity is due to gravity, but differs from it because of the axifugal acceleration induced by the rotation of the Earth on itself.
Earth’s gravity stems from Newton’s universal law of gravity, according to which all massive bodies, including celestial bodies and the Earth, exert a gravitational field responsible for an attractive force on other massive bodies. In the terrestrial frame of reference, the rotational movement around the axis of the poles induces an axifugal drive acceleration which, combined with gravity, defines gravity. This definition can be generalized to other celestial bodies: we then speak, for example, of the gravity of Mars.
The force to which a body is subjected due to gravity is called the weight of this body and is directly related to gravity by its mass; its unit of measurement is the newton, as for any force. This force defines the vertical of the place, the direction in which all the free bodies fall towards the ground in a given place and which can be measured by a plumb line.
Earth’s gravity varies depending on the location. For practical purposes, the General Conference on Weights and Measures defined in 19012.3 a normal value of the acceleration of gravity, noted g0, equal to 9.806 65 m / s2, or approximately 9.81 ms − 2 ( or 9.81 N / kg). This value corresponds to the gravity on an ideal ellipsoid approaching sea level and at 45 ° latitude