ROLLING

, or Rotation, in Mechanics, a kind of circular motion, by which the moveable body turns round its own axis, or centre, and continually applies new parts of its surface to the body it moves upon. Such is that of a wheel, a sphere, a garden roller, or the like.

The motion of Rolling is opposed to that of sliding; in which latter motion the same surface is continually applied to the plane it moves along.

In a wheel, it is only the circumference that properly and simply rolls; the rest of the wheel proceeds in a compound angular kind of motion, and partly | rolls, partly slides. The want of distinguishing between which two motions, occasioned the difficulty of that celebrated problem of Aristotle's Wheel.

The friction of a body in rolling, is much less than the friction in sliding. And hence arises the great use of wheels, rolls, &c, in machines; as much of the action as possible being laid upon it, to make the resistance the less.

ROMAN Order, in Architecture, is the same as the composite. It was invented by the Romans, in the time of Augustus; and it is made up of the Ionic and Corinthian orders, being more ornamental than either.