Gravity is a force that attracts objects toward the Earth. It is an approximation of the gravitational force that attracts objects of mass toward each other at great distances. Gravity applies to objects on or near the surface of the Earth.
The equation for the force of gravity is F = mg, where g is the acceleration due to gravity. Units can be designated in metric (SI) or English system. The equation also indicates the weight of an object.
The Weight w of an object is proportional to its mass m, also relation between W and m is given by,
where,g has a constant value in a particular place.
At the surface of the earth, if m is the mass in Kg then the value of g is 9.8 newton per kg, giving W in newtons.
The force acting on each and every kilogram is called the gravitational field strength and is given by the relation:
Gravitational field strength,
g = force*(weight)/mass
g = W/m
where g = 9.8N/kg.
The major feature of this force is that all objects fall at the same rate, regardless of their mass. Gravity on the Moon and on other planets have different values of the acceleration due to gravity. However, the effects of the force are similar.