In the history of science, Newton was the first who was able to recognize the gravitational force and gave a famous theory called Newton’s law of gravitation.
According to Newton’s law of gravitation
the gravitational force between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
The gravitational force between two objects of masses m_1 and m_2 separated by a distance r is given by the equation;
F_g = \dfrac{Gm_1m_2}{r^2}
where G = 6.67\times10^{ -11}\ \rm Nm^2/kg^2 is called Universal Gravitational Constant and r is the distance between center of mass of the objects.
Gravitational force is always attractive in nature.