When two surfaces are coated with a lubricant, then they:

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1. **Function of Lubricants:** Lubricants (like oil or grease) are applied between two surfaces to reduce friction. They fill the minute irregularities (depressions and elevations) on the surfaces.
2. **Mechanism:** The lubricant forms a thin layer separating the two solid surfaces. Consequently, the actual contact between the solid surfaces is replaced by the contact between liquid layers of the lubricant.
3. **Result:** Since the fluid friction (viscosity) is generally much lower than the dry sliding friction between solids, the surfaces move smoothly relative to one another. This relative motion is a 'sliding' motion, unlike ball bearings which convert sliding friction into rolling friction [Source 69].

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