Aeronautics is the science  involved with the study, design, and manufacture of flight-capable machines, or the techniques of operating aircraft. While the term—literally meaning "sailing the air"—originally referred solely to the science of operating the aircraft, it has since been expanded to include technology, business and other aspects related to aircraft. One of the significant parts in aeronautics is a branch of physical science called aerodynamics, which deals with the motion of air and the way it interacts with objects in motion, such as an aircraft. Aviation is a term sometimes used interchangeably with aeronautics, although "aeronautics" includes lighter-than-air craft such as airships, while "aviation" does not.