Identify the subject of the formula. The subject of the formula is the unknown quantity you are trying to calculate. The subject will be one of the elements in the formula: F = (G) x (M1) x (M2) / (R)^2, where F is the force between two objects, M1 and M2 are the masses of objects 1 and 2, G is the universal gravitational constant with a value of 6.67 x 10^-11 Nm^2/kg^2, and R is the distance between the centers of the two objects. For example, if required to find the gravitational force between two objects, the subject of the formula is the force (F). If trying to find the mass (M1) of one of the objects exerting a known force on another object of mass M2, the subject of the formula would be M1.
Rearrange the formula so that the subject of the formula lies to the left of the equality sign, while the rest of the formula is gathered on the right side of the equality sign. For example, if trying to find the mass (M1) of one of the objects exerting a known force on another object of mass M2, move M1 to the left of the equality sign: M1 = {(F) x (R)^2}/{(G) x (M2)}.
Substitute all the known values into the right side of the equation. For example, if trying to find the mass (M1) of object 1 exerting a force of 800 N on another object 2 with mass 500 kg positioned 2,000 m from object 1, substitute into: M1 = {(F) x (R)^2}/{(G) x (M2)} = {(800) x (2,000)^2}/{(6.67 x10^-11) x (500)}.
Enter the equation into a calculator and solve for the unknown quantity. For example, the mass (M1) of object 1 exerting a force of 800 N on object 2 with mass 500 kg positioned 2,000 m from object 1 is given by: M1 = 9.6 x 10^16 = {(800) x (2,000)^2}/{(6.67 x10^-11) x (500)} = {(F) x (R)^2}/{(G) x (M2)}.