However, most often our consideration of friction stems from having to find ways to overcome it. Even the smoothest highly polished surface will not eliminate friction completely. The best alternative is lubrication. By separating the two surfaces with a thin layer of liquid the moving surfaces are no longer in contact with each other but with the liquid instead. Because the liquid is able to flow, it moves with the moving surfaces rather than providing resistance to the movement.
Oils make particularly good lubricants.
Structures Through their design, structures have to balance out the mass and consequent weight of the materials used in their construction, and also any additional load that the structures may have to support. Other forces, such as those exerted by moving air or water around a structure must also be taken into account. An overall assessment of the strength of a structure will, therefore, involve consideration of those pushing, pulling and turning forces that will deform it or render it unstable. The choice of material is clearly very important. Characteristics such as flexibility, hardness and density can have a significant bearing upon the suitability of a material for construction purposes.