Answer : Mass and distance.
Explanation : The strength of the force between two objects mainly depends on two factors, one is mass and the other is distance.
The force of gravity that masses exert on each other is of great influencing factor. For example, if one of the masses is doubled, the force between the objects is doubled then the force between them increases.
When the distance between the objects is increased, then the force is found to decrease. For example, If the distance is doubled, then the force becomes one-fourth strong as it was before.
Force, it is often expressed as the product of mass and acceleration, and can be expressed as;
F = m x a;
where F - Force;
m - mass;
a - acceleration due to gravity.