Mechanical energy nonconservative forces, like frictional forces, will be present, but often they are of negligible values and the mechanical energy's being constant can therefore be a useful approximation. In elastic collisions, the mechanical energy is conserved but in inelastic collisions, some mechanical energy is converted into heat. The equivalence between lost mechanical energy (dissipation) and an increase in temperature was discovered by James Prescott Joule. Many devices are used to convert mechanical energy to or from other forms of energy, e.g. an electric motor converts electrical energy to mechanical energy, an electric generator converts mechanical energy into electrical energy and a
Feathers: The Evolution of a Natural Miracle "Archaeopteryx" fossil specimen and the resulting debate between English paleontologist Richard Owen, an opponent to evolution by natural selection, and Thomas Henry Huxley, an advocate for evolution. Hanson himself visits the Wyoming Dinosaur Center, a small museum in Thermopolis, Wyoming, which had acquired an "Archaeopteryx" specimen. Hanson interviews Richard Prum, the Coe Professor of Ornithology at Yale University, who proposed a developmental theory of feather evolution, which focuses "on how feathers grow and not worrying about what they're used for." Hanson also interviews Alan Feduccia, a professor at the University of North Carolina, who disagrees with the scientific consensus that