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 vultures and their feathers, and later that day, as he went on a run, he noticed four turkey vultures keeping watch over a roadkill deer. One of the vultures began flapping and dropped a feather at Hanson's feet. Moved by this coincidence, Hanson decided then to write a book about feathers. Basic Books first published "Feathers" in hardcover in 2011. In 2012, Basic Books published it in paperback as well, and the book has also been published as an ebook and audiobook. An essay-length adaptation titled "The Multiple Miracles of Bird Feathers" appeared in the January–February 2012 edition of "Audubon",