Mechanical energy swing because of the work done by the pendulum to oppose these non-conservative forces. That the loss of mechanical energy in a system always resulted in an increase of the system's temperature has been known for a long time, but it was the amateur physicist James Prescott Joule who first experimentally demonstrated how a certain amount of work done against friction resulted in a definite quantity of heat which should be conceived as the random motions of the particles that comprise matter. This equivalence between mechanical energy and heat is especially important when considering colliding objects. In an elastic collision,
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,