A bearing is a machine element that constrains relative motion between moving parts to only the desired motion. The design of the bearing may, for
example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling
the vectors of normal forces that bear on the moving parts. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the
loads (forces) applied to the parts.