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 feathered flight has influenced human aviation. Hanson describes the behavior of birds-of-paradise and the role of their elaborate feathers in sexual selection. Hanson also visits the Las Vegas Strip and observes how feathers play a role in pageant shows like "Jubilee!". Hanson interviews Marios Ignadiou, the head of "Jubilee!"'s costume shop, as well as fashion designer Pete Menefree. Hanson then describes the history of the feather trade in fashion. In the period before World War I, feathers were highly valuable commodities. Wanting to capitalize on the economic strength of feathers, the government of South Africa sponsored the Trans-Saharan Ostrich Expedition,