Oil lubricates things. A lubricant is a film of liquid that prevents parts from touching, so they slide easily past one another. Lubricants generally work because their molecules bind more tightly to the parts that would otherwise rub together than they do to one another. The oil added to machines sticks to the metal parts, so it stays on the metal as a coating. But the coatings themselves do not stick to one another and instead just glide by.
Why does a machine work better with oil in it?
