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 and how feather insulation has also been utilized by humans. "Flight" discusses how flight might have evolved in birds, interviewing Prum, Feduccia, Xu, and also ornithologist Ken Dial, who described wing-assisted incline running. In "Fancy", Hanson discusses the role of feathers in sexual selection, as well as how humans have utilized feathers for fashion, interviewing costume and fashion designers on the Las Vegas Strip and New York City. "Function" discusses how feathers have been adapted for other purposes, such as waterproofing, fly fishing, and quill pens. Hanson decided he would write "Feathers" after going on a run and noticing a