Hunt's Impact Theorem was developed by physicist Kieran Hunt in the latter half of 2008. It is given by where ? is the impact coefficient, m is the mass of the impacting object, v is the impact velocity, and d is the depth of the crater formed. The impact coefficient, ?, is 13200 ± 1720 kg·s-2 in dry sand. It is different from Newton's impact depth formula in that Newton assumes the material is compressed through momentum (i.e. bullets) whereas Hunt uses Conservation of Energy and assumes the material is notcompressed (i.e. a crater).