linguistic:paraphrasing, structural:scholar_edition, structural:expansion
Friction

Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

Combinations of these can even be employed within the same bearing. An example is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.