= Bearing
{disambiguate=mechanical}
= Mechanical bearing
{synonym}
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>.<Shafts and Bearings by SDP-SI>[§4.0, “Bearing Loads”, shaft support reactions and gear-loading cases]{ref}
For a simple ideal shaft supported at axial positions0 and $L$, an upward load $P$ applied at $a$ requires reactions
$$
R_A=-P\left(1-\frac aL\right),\qquad R_B=-P\frac aL.
$$
With $P=200\,\mathrm N$, $L=100\,\mathrm{mm}$ 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 $M_f=0.020\,\mathrm{N\,m}$ at <angular speed> $100\,\mathrm{rad/s}$ 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.<Rolling bearings by SKF>[Section B.2, “Arrangements and their bearing types”, printed p.70, locating/non-locating supports]{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.
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