Summary: Lubrication

Friction can be useful. It prevents the screw-jack from running back and is the basis for the functioning of belt drives as well as brakes and vices. Nevertheless the 20-percent-loss of power in motor cars due to friction is a very serious disadvantage. Manufacturers try to compensate this with a good aerodynamic design, by using bearings with a low friction coefficient, and very often with lubrication. The background is that blocks of metal are never perfectly flat: Under the microscope little hills and valleys become visible. As a result, two blocks touch only at a few points, the hills. These points of contact often weld together. A greater force is required to start moving the blocks (static friction) than to keep the blocks moving (sliding friction). When sliding the hills scrape against each other breaking off some pieces. In order to reduce wear lubrication oil is used to fill up the valleys. That way one block can move over the other more easily. The power lost depends on the thickness of the lubricant used: Various lubricants offer different resistances. Therefore lubricants have to be selected depending on machine operating speeds and the temperature range worked at.