A bearing is the machine element that realizes the constraints of motion as such that only the desired motion remains in the system while reducing friction between moving components. A set of bearings can realize a rotational degree of freedom along an axis of rotation, while preventing undesired motion in other degrees of freedom, such as tilt motion or radial and axial linear motion. Bearings are classified broadly according to the type of operation, the allowed motion, or to the directions of the loads the element can withstand. Well-known type of bearings are the rolling element bearing and the sliding bearings. In this paper we will highlight air bearings as a part of the fluid film bearings.

In an air bearing, a thin film of pressurized air is used to provide an interface layer between surfaces that can transfer loads in a frictionless way. Although called air bearings, the utilized gas is not solely limited to air, e.g., also pure nitrogen is often used. Since the two surfaces are properly separated and contact-free, no wear, particulate generation or excessive friction is present, as opposed to sliding or rolling contact bearings. Due to the low friction in the film, air bearings are excellent in high-speed applications, but also in high-precision applications, where the lack of friction facilitates more precise positioning and a smoother motion.