☞ That part of mechanics which considers the action of forces in producing rest or equilibrium is called ; that which relates to such action in producing motion is called . The term mechanics includes the action of forces on all bodies, whether solid, liquid, or gaseous. It is sometimes, however, and formerly was often, used distinctively of solid bodies only: The mechanics of liquid bodies is called also , or , according as the laws of rest or of motion are considered. The mechanics of gaseous bodies is called also . The mechanics of fluids in motion, with special reference to the methods of obtaining from them useful results, constitutes .