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 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",