Question

what are the factors that maintain gravitational force ?

Answer 1

a gravitational force is a force of attraction , which attracts the all organisms and things , it also attracts the things in space [universe for where the gravitational field is there] for suppose our earth is a planet which have gravity , a sun[star] have more gravity in solar system.

Improved answer:
Gravitational force on a body brings the weight of the body. This is given by the expression W = mg. m-the mass of the body. g-the acceleration due to gravity. When this g gets affected then gravitational force varies. 
g is affected by so many factors. 
i) the altitu. de as we go away from the centre of the earth, g decreases 
ii) The depth. As we go towards the centre of the earth once again g decreases 
iii) Due to rotation of the earth the centrifugal acceleration would decrease the value of g, the most along the equator. 
iv) g could be proved to be GM/R2. G the universal gravitational constant M-mass of the earth R- radius of the earth. Hence due to non even spherical shape of the earth g value varies 
v) if a body gets immersed in a liquid then the weight is affected by the buoyant force. So the weight is reduced.

Answer 2

Masses of the product
Distance between them