The force of gravity between two objects is equal to the product of their masses divided by the square of the distance between them, multiplied by the gravitational constant:
F = G * m1 * m2 / r2
where
F is the force of gravity
G is the gravitational constant (6.67 x 10-11 Nm2/kg
m1 and m2 are the masses of the two objects
r is the distance between them.
