While friction is highly essential in some circumstances, It IS a great nuisance in others. In a car engine, for example, oil under pressure is supplied continuously to all bearing surfaces. Failure of the oil supply will allow metal-to-metal contact and the resultant friction often raises the temperature and causes the bearing and pistons to “seize up”.
Although liquid molecules attract one another they can interchange partners quite easily. The opposing force which one layer of liquid exerts on another is called viscosity. For liquid lubricants this is very much less than the frictional force most solids exert on one another. Some lubricating oils contain certain solid or liquid substances which attach themselves to the bearing surfaces to form a tenacious slippery coating. The possibility of metal-to-metal contact is thus greatly reduced accompanied by less wear and smoother running.