Aeronautics is the science of flight as well as the theory and practice of aircraft navigation. Any machine that flies through the air falls into the field of aeronautics. This includes helicopters, airplanes, as well as space vehicles such as the SpaceX Dragon and the retired NASA space shuttles. Aerodynamics is a branch of physical science which deals with the motion of air and the way that it interacts with objects in motion. By studying the way air flows, engineers can define the shape of a plane. The wings, tail, and the main body - or fuselage - all affect the way air will move around the plane. Students may find it interesting that engineers consider air to behave as a fluid, like water, but they should not confuse these two states of matter. They must take into account aerodynamics, propulsion, materials, structure, stability and control.