The resistance to motion experienced by an object moving through the air caused by the flow of air over the surface of the object. It is a force that affects, for example, the speed of a drop of rain or of a parachutist falling towards the Earth’s surface. As well as depending on the nature of the object, air resistance depends on the speed of the object. Possible mathematical models assume that the magnitude of the air resistance is proportional to the speed (laminar flow) or to the square of the speed (turbulent flow). See terminal speed.