Newton's law of universal gravitation is:

Here, *F* is the attractive force that particle 1 with mass, *m*_{1}, exerts on particle 2 with mass, *m*_{2}, is the direction vector from particle 1 to particle 2, and *G* is the universal gravitational constant that has the same value for all particles. Measurements show that *G* has the value 6.67 x 10^{-11} Nm^{2}/kg^{2}. This equation also embodies Newton's third law of motion. By switching the labels of the particles, the force that particle 2 exerts on 1 is equal in magnitude but opposite in direction because only changes sign.