In engineering machinery, such as engines, weaving looms, and pumps, the most vulnerable parts to failure are those in which loads are transmitted between solid parts that move over each other. Common examples are piston rings, gears, and, of course, bearings. Bearings are designed to transmit large loads normal to the surface while allowing free movement tangential to the surface, with the minimum of friction. Bearings are to an engine, what hip joints and knee joints are to the human body. If the pressures generated are high compared with the elastic properties of the solid surfaces, then significant elastic deformation or “squashing” of the solids can occur, which modifies the geometry of the lubricating film. Pendulum machines have been used considerably in the past to evaluate natural joints, but the interpretation of their results is by no means easy.