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 murres if they are not on water). He then explains how the structure of feathers is waterproofing, keeping birds dry in wet conditions. Hanson interviews John Sullivan, an experienced fly fisher who explains the role of feathers in fly fishing. Later, Hanson explains the history and use of feathers in quill pens, which he uses as an example of how feathers have been adapted for other purposes beyond their natural evolutionary purposes. Hanson also describes his experience observing the behavior of vultures in Kenya, in which he discusses the lack of feathers on the heads of vultures. Hanson interviews Kimberly