 Bearing (mechanical)

A mechanical bearing supports relative motion while transmitting constraint forces between machine components. A shaft support can permit rotation while constraining translation, with the permitted motions depending on its construction and arrangement. A ball bearing uses rolling contacts; a journal bearing supports a shaft through a sliding or fluid-film interface. The support reaction is distinct from resistance to the permitted motion: an ideal support can transmit a large transverse force with zero resisting shaft torque.^[ref]

For a simple ideal shaft supported at axial positions0 and $L$, an upward load $P$ applied at $a$ requires reactionsWith $P=200\mathrm{N}$, $L=100\mathrm{mm}$ and $a=40\mathrm{mm}$, the downward support loads are120N and80N. These reactions exist even if the shaft rotates without an applied resisting torque. In a real mechanical bearing, an illustrative frictional resisting moment $M_f=0.020\mathrm{N}\mathrm{m}$ at angular speed $100rad/s$ dissipates $M_f|\omega |=2\mathrm{W}$; force equilibrium alone does not determine that loss.

A locating bearing arrangement fixes the shaft's axial position relative to the housing, while a non-locating bearing support permits the required axial displacement, for example from thermal expansion. The manufacturer distinguishes this arrangement from adjusted and floating arrangements.^[ref] Radial support does not by itself establish which support carries axial thrust.

Selection must therefore consider permitted motion, combined loads, alignment and operating conditions. An idler support reaction determines a shaft-level load; it does not directly give each rolling contact's Hertzian contact pressure or a service-life prediction. Those require the bearing's internal geometry and a suitable load/life model.

In mechanical engineering, a bearing is a component that allows for controlled movement between two parts while reducing friction. Bearings are used to support rotating or moving shafts and other components, enabling smooth and efficient motion. They can handle radial and axial loads—radial loads are perpendicular to the shaft, while axial loads are parallel to the shaft.