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Rolling
From Wikipedia, the free encyclopedia
Rolling is a combination of rotation (of a more or less cylindrically or spherically symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that the two are in contact with each other without sliding. This is achieved by a rotational speed at the cylinder or circle of contact which is equal to the translational speed. Rolling of a round object typically requires less energy than sliding, therefore such an object will more easily move, if it experiences a force with a component along the surface, for instance gravity on a tilted surface; wind; pushing; pulling; an engine. Objects with corners, such as dice, roll by successive rotations about the edge or corner which is in contact with the surface.
Two surfaces can "slide" more easily using rolling objects in between, see rolling-element bearing.
Apart from being easily transported itself (and if it is hollow, transporting things inside), a rolling object can be used as a tool for transportation. One of the most basic ways is placing an object on rolling objects. These can be taken from the backside and put at the front side repeatedly (see rolling-element bearing and history of bearings). More advanced is the wheel. These rolling techniques require a smoother surface/road than when people and animals walk and carry things.
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