Friction

Friction is much reduced when ball bearings are used. Ball bearings make a wheel turn easily.
Friction is much reduced if the surfaces are lubricated with oil or water. Oil and water are examples of lubricants.
Friction is also reduced to rolling. People wearing rollar skates move quickly and soomthly over flat surfaces.
Friction can also be reduced by supporting the loving object on a layer of air. The hovercraft works on this principle.
Friction in liquids and gases can be reduced if an object is streamlined in shape. Boats, fishes and dolphins all have streamlined shapes.

2010-11-19 18:59:17 補充：
hope can help you~^^

I guess it should not related with surface are but I do not how it reduces.
Just feeling that the ball-bearings in wheels can do so.