The virial theorem is frequently applied in astrophysics, especially relating the gravitational potential energy of a system to its kinetic or thermal energy. Some common virial relations are 3 5 G M R = 3 2 k B T m p = 1 2 v 2 for a mass M, radius R, velocity v, and temperature T. The constants are Newton's constant G, the Boltzmann constant k B, and proton mass m p. Note that these relations are only approximate, and often the leading numerical factors (e.g. ⁠ 3 / 5 ⁠ or ⁠ 1 / 2 ⁠) are neglected entirely.