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Fluid bearings generally have very low friction—far better than mechanical bearings. One source of friction in a fluid bearing is the viscosity of the fluid leading to dynamic friction that increases with speed, but static friction is typically negligible. Hydrostatic gas bearings are among the lowest friction bearings even at very high speeds.
A rolling element bearing's static load rating is defined to avoid this failure type. Increasing the number of elements can provide better distribution of the load, so bearings intended for a large load may have many balls, or use needles instead. This decreases the chances of brinelling, but increases friction and other factors.
Nikolai Pavlovich Petrov's method of lubrication analysis, which assumes a concentric shaft and bearing, was the first to explain the phenomenon of bearing friction.This method, which ultimately produces the equation known as Petrov's law (or Petroff's law), is useful because it defines groups of relevant dimensionless parameters, and predicts a fairly accurate coefficient of friction, even ...
An important difference compared with plain bearings is that the relative motion between the two connected parts is accommodated by strain in the rubber, rather than by shear or friction at the interface. Some rubber bushings, such as the D block for a sway bar, do allow sliding at the interface between one part and the rubber.
Therefore, the part of the shaft in contact with the bearing slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on [3] or the ways on the bed of a lathe.
A ball bearing. A bearing is a machine element that constrains relative motion to only the desired motion and reduces friction between moving parts.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.
In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as a spindle
Working principle for a ball bearing; red dots show direction of rotation. A four-point angular-contact ball bearing. A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It ...