Many equations in relativistic physics appear simpler when expressed in geometric units, because all occurrences of "G" and of "c" drop out. For example, the Schwarzschild radius of a nonrotating uncharged black hole with mass "m" becomes . For this reason, many books and papers on relativistic physics use geometric units. An alternative system of geometrized units is often used in particle physics and cosmology, in which instead. This introduces an additional factor of 8π into Newton's law of universal gravitation but simplifies Einstein's equations, the Einstein–Hilbert action, the Friedmann equations and the Newtonian Poisson equation by removing the corresponding factor.