Universal law of gravity - It states that every object attract each other with the same ammount of force. This force is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between the objects.
F= (G×m1×m2)/ d2
Consider two objects of masses m1 and m2 having distance d between them. These objects will attract each other by a force. Now according to the law of gravitation
F∝ m1× m2
And
F∝1/d×d
When we combine these two equations we will get F∝ ( m1×m2)/d2
To make an equation we need to remove the sign of proportion, i.e.
F= (G× m1× m2)/d2
Here G is the constant and is called constant of proportionality.
The value of G is defind as 6.6×10-11